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ArticleOctober 25, 2023

Limits to Hole Mobility and Doping in Copper Iodide
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Joe Willis
Joe Willis
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.
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https://orcid.org/0000-0002-1900-2677
Romain Claes
Romain Claes
UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
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Qi Zhou
Qi Zhou
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.
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Matteo Giantomassi
Matteo Giantomassi
UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
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Gian-Marco Rignanese
Gian-Marco Rignanese
UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
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https://orcid.org/0000-0002-1422-1205
Geoffroy Hautier*
Geoffroy Hautier
UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, United States
*Email: [email protected]
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David O. Scanlon*
David O. Scanlon
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.
School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
*Email: [email protected]
More by David O. Scanlon
https://orcid.org/0000-0001-9174-8601

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Chemistry of Materials

Cite this: Chem. Mater. 2023, 35, 21, 8995–9006

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https://doi.org/10.1021/acs.chemmater.3c01628

Published October 25, 2023

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Abstract

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Over one hundred years have passed since the discovery of the p-type transparent conducting material copper iodide, predating the concept of the “electron–hole” itself. Supercentenarian status notwithstanding, little is understood about the charge transport mechanisms in CuI. Herein, a variety of modeling techniques are used to investigate the charge transport properties of CuI, and limitations to the hole mobility over experimentally achievable carrier concentrations are discussed. Poor dielectric response is responsible for extensive scattering from ionized impurities at degenerately doped carrier concentrations, while phonon scattering is found to dominate at lower carrier concentrations. A phonon-limited hole mobility of 162 cm² V^–1 s^–1 is predicted at room temperature. The simulated charge transport properties for CuI are compared to existing experimental data, and the implications for future device performance are discussed. In addition to charge transport calculations, the defect chemistry of CuI is investigated with hybrid functionals, revealing that reasonably localized holes from the copper vacancy are the predominant source of charge carriers. The chalcogens S and Se are investigated as extrinsic dopants, where it is found that despite relatively low defect formation energies, they are unlikely to act as efficient electron acceptors due to the strong localization of holes and subsequent deep transition levels.

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Introduction

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High mobility p-type transparent conducting materials (TCMs) have eluded researchers for decades. The unlikely bedfellows of good optical transparency (a wide band gap >3 eV and above 90% visible transmission), high valence band dispersion (typically requiring carrier effective mass < 0.5m_e), and correct point defect chemistry (facile and controllable generation of electron–holes up to 10²¹ cm^–3, depending on applications) prove difficult to unite. In fact, these strict requirements preclude the vast majority of materials from ever displaying transparent p-type conducting properties. Early efforts focused on the development of p-type oxides, such as CuAlO₂, (1) attempting to mimic the wide optical band gap of the n-type transparent conducting oxides. However, CuAlO₂ and other delafossite materials are plagued by low mobility and conductivity due to the polaronic nature of the holes generated in these systems, which are bound to Cu states at the valence band maximum. (2−13)

Several other oxides have been considered as p-type transparent conductors, with varying degrees of success: Li-doped NiO can reach hole concentrations on the order of 1 × 10²¹ cm^–3 and conductivity up to 11 S cm^–1, but mobility is less than 0.05 cm² V^–1 s^–1 and transmission drops to 50% upon doping; (14) SnO is a reasonably good p-type TCM, with mobility around 7 cm² V^–1 s^–1 at 1 × 10¹⁷ cm^–3 carriers, and can also be doped n-type, but incurs stability issues due to the presence of Sn(II) [a problem which pervades ternary Sn(II) materials also]; (15,16) quasi-closed shell d³ and d⁶ materials such as Sr-doped LaCrO₃ and the ZnM₂O₄ spinels (M = Co, Rh, Ir) have been investigated as TCMs, exploiting the large crystal field splitting between e_g and t_2g states to engineer transparency, but their mobilities and conductivities routinely fall short of requirements; (17,18) and Ba₂BiTaO₆, which shows excellent mobility (up to 30 cm² V^–1 s^–1) due to strong Bi 6s²–O 2p interaction at the valence band, but the carrier density is limited to 1 × 10¹⁴ cm^–3. (19,20) Therefore, research into nonoxides has taken center stage in recent years (21−26) in the hope that greater valence band delocalization and bond covalency can improve hole mobility while simultaneously generating enough carriers to enable degenerate conductivity.

One such material is copper iodide, CuI, first discovered in 1907 by the “father of transparent conductors” Bädeker, (27) and now enjoying somewhat of a renaissance. It crystallizes in the cubic zincblende structure below 643 K (Figure 1a), possesses an optical band gap of around 3 eV, displays native p-type conductivity, and consistently shows one of the highest figures of merit, Φ,^a for any p-type transparent conductor (over 60,000 MΩ^–1 for S-doped CuI). (28−30) It has a disperse, isotropic valence band maximum (Figure 1b), with an average light hole parabolic effective mass of around 0.21m_e, indicative of a reasonably high hole mobility. The valence band maximum is formed by the interaction of Cu 3d t₂ and I 5p orbitals, while the conduction band minimum is formed by the interaction of Cu 4s with I 5s orbitals, (31,32) as shown schematically in the molecular orbital (MO) diagram in Figure 1c.

Φ = \frac{σ}{α} = \frac{- 1}{R_{s} \ln (T_{v i s} + R)}

(1)

where T_vis is transmission and R_s is the sheet resistance, related to conductivity and thickness d by

R_{s} = \frac{1}{σ d}

(2)

Figure 1. Crystal and electronic structures of CuI. (a) Zincblende crystal structure of CuI, viewed along the face diagonal. Cu and I atoms in blue and green, respectively. Cu atoms have tetrahedral coordination, shown in gray. (b) Electronic band structure of CuI. Calculated using the PBE0 hybrid functional with the inclusion of spin–orbit coupling (SOC). (c) Schematic molecular orbital (MO) diagram of CuI. Upon the inclusion of SOC, further splitting occurs on the t₂─5p MOs into light and heavy hole channels and a spin–orbit split-off band, as seen in (b)

In addition to its rather attractive electronic structure, the simplicity of CuI is another strong factor in its revival in popularity. Good quality thin films can be deposited via relatively straightforward techniques such as vaporizing iodine onto thin films of copper (à la Bädeker), (33) solid- and solution-based iodization reactions, (34−36) and inkjet printing, (37) while more advanced techniques such as pulsed laser deposition (PLD), (38) molecular beam epitaxy (MBE), (39) and magnetron sputtering are beginning to gain traction. (29) Stability of films in air and to thermal cycling can be improved by encapsulation with amorphous Al₂O₃, (38,40) to prevent the oxidation of Cu(I) to Cu(II). Single crystal growth of CuI is reported more sporadically and over a much narrower range of charge carrier concentrations. (41,42) In terms of devices and applications, CuI has been successfully used in thin film transistors (TFTs) with high operational stability and efficiency, (43) while CuI nanoparticle inks have contributed to improvements in high resolution X-ray imaging technology. (44) This manufacturing simplicity is further enhanced by its strong compatibility with various n-type oxides (such as ZnO, AgI, BaSnO₃, and NiI₂), positioning CuI as an optimal contender for combined n- and p-type applications. (45−51)

Despite this fashionable return to the forefront of p-type TCM research, the charge transport behavior of CuI is poorly understood. Experimental reports show no clear trend between hole mobility and carrier concentration, while little computational work has been undertaken on this subject. In this work, the intrinsic limits of CuI as a high-mobility transparent conductor are investigated from first-principles calculations and state-of-the-art charge carrier transport modeling. The intrinsic defect chemistry and the effects of chalcogen doping are examined to estimate the window of achievable charge carrier concentrations in CuI. The different contributions to the overall scattering rate are analyzed using two separate approaches, where it is found that scattering from phonons and ionized impurities dominate at either end of the charge carrier concentration range, respectively.

Computational Methodology

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Electronic band structure, AMSET inputs, and defect calculations were performed within VASP, a periodic plane-wave code that uses the projector-augmented wave (PAW) method for describing the interaction between core and valence electrons. (52−58) The explicit electron configurations of the pseudopotentials used were as follows: Cu 3d¹⁰4s¹; I 5s²5p⁵; S 3s²3p⁴; and Se 4s²4p⁴. A plane-wave cutoff of 500 eV and a Γ-centered k-point mesh of 7 × 7 × 7 were found to converge the total energy to within 1 meV atom^–1. Structural relaxations were carried out with a plane-wave cutoff of 650 eV to avoid Pulay stress and with a convergence criteria of 0.1 meV atom^–1. The GGA PBEsol functional was used for all convergence testing and density functional perturbation theory (DFPT)-related inputs, (59) while the hybrid PBE0 functional was used for electronic structure, defect, and finite differences (FD) calculations. (60) For all electronic structure calculations, spin–orbit coupling (SOC) effects were explicitly considered due to the presence of heavy I atoms. Considering the size of the spin–orbit split-off in the electronic band structure, the addition of SOC effects via a single-shot electronic structure calculation after structural optimization is crucial to get the correct value of the band gap and relative band edge positions during defect calculations. SOC effects are negligible when computing structural properties, so they were not included during relaxations.

Charge transport properties were calculated by using both ABINIT and the AMSET package. ABINIT uses a fully first-principles approach to calculate phonon-limited mobilities based on an iterative solver to the Boltzmann transport equation (IBTE). (61−64) The approach used in ABINIT, which is detailed in refs (64) and (65), allow us to achieve a level of performance that is competitive with Wannier-based packages while bypassing the need for Wannier functions altogether. First, our approach takes advantage of the tetrahedron integration scheme to significantly reduce the number of e–ph matrix elements that need to be computed. In addition, we employ a Fourier interpolation of the scattering potentials in q space, which includes the accurate treatment of dipole and quadrupole contributions and the exact Kohn–Sham (KS) wave functions are computed only for the k-points lying inside a small energy window around the band edges. Here, a convergence is assumed to be reached when three consecutive grids lead to mobilities a maximum 5% away from each other. In CuI, the converged IBTE mobilities were obtained with k-meshes of 162 × 162 × 162 and interpolated DFPT scattering potentials and interatomic force constants obtained on a 9 × 9 × 9 coarse q-mesh. All the calculations needed to obtain the mobility within ABINIT were done with the GGA PBEsol functional including SOC. The dynamical quadrupoles (Q*) were also included for the scattering potentials and mobilities. However, as the DFPT computation of Q* is still limited to norm-conserving pseudopotentials without nonlinear core corrections (NLCC) and without SOC, a slight deviation of the mobility can be expected but by several orders of magnitude less than doing the calculations without taking the Q* into account.

On the other hand, AMSET solves the linearized Boltzmann transport equation using the relaxation time approximation (RTA). Individual scattering rates were explicitly calculated using material properties, going beyond the constant relaxation time approximation to give a more accurate description of carrier lifetimes. In this study, scattering from polar optical phonons (POP), acoustic deformation potentials (ADP), ionized impurities (IMP), and piezoelectric effects (PIE) were considered, which require deformation potentials, the elastic constant, low- and high-frequency dielectric constants, the polar optical phonon frequency, and the piezoelectric constant. Explicit values (and convergence of these parameters) can be found in the Supporting Information. A dense uniform Γ-centered k-point mesh of 14 × 14 × 14 was used to obtain the wave function overlaps for determining scattering rates, and the corresponding band structure was plotted using the SUMO package. (66) The deformation potentials were calculated from density of states calculations using the same convergence parameters as bulk calculations. The low-frequency dielectric constant, piezoelectric constant, and polar optical phonon frequency were calculated using both DFPT and FD implementations in VASP. The high-frequency dielectric constant was calculated with the PBE0 functional using the independent particle random phase approximation (IP-RPA) optics routine in VASP and converged against the number of empty bands and k-point density.

Phonon calculations on CuI were performed with DFPT and ABINIT using PBEsol + SOC and a 9 × 9 × 9 q-mesh following the methodology used by Petretto et al. (67) The structures were relaxed until all the forces on the atoms and the stresses were below 10^–6 Ha/bohr and 10^–4 Ha/bohr³, respectively, using a plane-wave cutoff of 46 Ha.

Defect calculations were performed with VASP on a 64 atom supercell and with a Γ-centered 2 × 2 × 2 k-point mesh. Each defect was fully relaxed using the PBE0 functional, followed by a spin–orbit coupling single-shot calculation to obtain accurate energies. This goes beyond the GGA relaxation plus hybrid single-shot calculations of Graužinytė et al., fully capturing structural distortions caused by charge localization that would otherwise be missed with a semilocal exchange–correlation functional. (68) The potential energy surface was explored using the ShakeNBreak method. (69,70) Defect formation energies were obtained in the usual fashion, within the Lany–Zunger formalism (71−74)

(3)

The transition level diagrams and self-consistent Fermi level were calculated using the PY-SC-FERMI package. (75,76)

The EFFMASS package was used to analyze the transport effective mass. (77,78)

Results

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Crystal and Electronic Structure

The structural properties (lattice parameter, lattice angle, and Cu–I bond length) of CuI are summarized in Table 1, where good agreement is found between the calculated values and both the experimental and computational literature. The PBEsol lattice parameters are slightly underestimated compared to room temperature neutron powder diffraction measurements by Keen and Hull, (79) while the PBE0 results show closer agreement. Low-temperature diffraction data are scarcely reported but are expected to yield lattice parameters closer to the PBEsol results. Thin film CuI often displays slightly larger lattice parameters (6.06 Å from Moditswe et al.) (80) owing to tensile strain between the film and substrate.

Table 1. Structural and Band Structure Properties of CuI

parameter	Exp (79)	PBE0	PBE0 lit (32)	PBEsol
a/Å	6.05	6.08	6.07	5.95
α/°	90.0	90.0	90.0	90.0
Cu–I/Å	2.57	2.63	2.62	2.58
band gap/eV	2.95 (81)	2.99	2.97	0.95
SOC splitting energy/eV	0.64 (82)	0.63		0.47
hole conductivity effective mass/m₀		0.61		0.72

As shown in Table 1, a direct band gap of 2.99 eV at Γ is calculated with the PBE0 functional including spin–orbit coupling effects (PBE0 + SOC, Figure 1b), which is in good agreement with experimental values obtained from a variety of measurements: pressure-dependent optical absorption from Ves et al., 2.95 eV; (81) transmission spectra from Storm et al., 3.11 eV. (38) This also matches well previous hybrid DFT calculations, with Yu et al. most recently reporting a value of 2.97 eV. (32) On the other hand, the direct band gap computed with PBEsol is severely underestimated, as is often the case in semilocal DFT. The hole conductivity effective mass (or the transport mass) determined from PBE0 calculations is slightly lower than that from PBEsol. Semilocal DFT functionals often struggle to accurately describe localized d states (regardless of electronic occupation) without the inclusion of the Hubbard U parameter, so a mismatch in the transport effective mass is not unexpected.

In CuI, the inclusion of SOC has a direct effect on the band edges. Figure 2a illustrates that without SOC, the valence band maximum (VBM) of CuI has three degenerate bands. The addition of SOC results in the lifting of the degeneracy, with one of the bands (the split-off band) dropping in energy, a common feature of zincblende semiconductors. As for the band gap, PBEsol tends to undervalue the spin–orbit splitting at the Γ-point of the VBM which is around 470 meV, whereas the value computed with PBE0 is around 630 meV, in excellent agreement with the value of 640 meV determined experimentally by Blacha et al. using hydrostatic pressure-dependent thin-film absorption. (82)

Figure 2. (a) Top of the valence bands of CuI around Γ with and without SOC as computed with the PBEsol functional. (b) The normalized function $- v_{VB}^{2} τ_{VB} \frac{\partial f}{\partial ε}$ , convoluted with δ(ε – ε_VB) in the valence band at different T. In this expression, v_VB and τ_VB stand for the carrier velocity and lifetime in the valence band (VB), $\frac{\partial f}{\partial ε}$ is the derivative of the Fermi–Dirac distribution function with respect to the energy and δ the Dirac delta function. By integration of this function, relaxation time approximation (RTA) hole mobility is obtained.

Charge Transport

Two methods are used to simulate charge transport in CuI: an iterative Boltzmann transport equation (IBTE) solution to calculate phonon-limited mobilities using the ABINIT code; (61−64) and a phenomenological model (AMSET) that calculates scattering rates for ADP, PIE, IMP, and POP scattering, utilizing low-cost inputs from first-principles calculations using the VASP code. (52,53,55−58,83) While IBTE provides a high-quality representation of transport properties, AMSET complements the analysis by evaluating the effects of impurities and also by providing an additional analysis of the phonon scattering mechanisms by decoupling the different contributions. AMSET also offers the advantage of using hybrid functionals, which are difficult to employ in fully first-principles IBTE calculations due to the computational cost and absence of implementations able to compute electron–phonon (e–ph) quantities within DFPT. The methodology for each approach is outlined in the Supporting Information.

Iterative Boltzmann Transport Equation

The lifting of degeneracy resulting from the addition of SOC has a clear impact on the hole transport. Indeed, for transport in semiconductors, only energies near the top of the VBM are relevant. (78) As depicted in Figure 2b, the function

- v_{VB}^{2} τ_{VB} \frac{\partial f}{\partial ε} δ (ε - ε_{VB})

, which once integrated provides direct access to the RTA hole mobility, quickly approaches zero for energies further from the Fermi level. This means that only the electronic states covered by this function participate in hole transport. As a result, the inclusion of SOC in CuI leads to the complete removal of a scattering channel as the split-off band is no longer included in the energy windows responsible for transport, even at higher temperatures. Using ABINIT, we obtain a converged IBTE mobility of 162 cm² V^–1 s^–1 at 300 K with SOC and dynamical quadrupoles (Q*) using 162 × 162 × 162 k- and q-point grids (refer to Figure S2). The inclusion of the SOC leads to an enhancement in mobility by removing a scattering channel. Note that, despite the increase in mobility due to the effect of SOC on the electronic bands, its effect on phonons remains negligible on both phonon band structure and mobility, as shown in Figures S1 and S2. The integration of Q*, the next order of correction to dynamical dipoles, in the computation is also necessary to obtain accurate results, (63,64) preventing an error of about 15% in the case of CuI.

The DFPT phonon dispersion of CuI is shown in Figure 3a and shows good agreement with the experimental frequencies reported in the literature. (84,85) The minor disparity, such as for the LO-TO splitting, may be attributed to the challenge of precisely capturing the dielectric constants in CuI, as discussed in the next section. This plot is accompanied by the corresponding spectral decomposition of the hole scattering rates at different T (Figure 3b), and shows that the high-frequency longitudinal optical mode T₂ (LO) is the main contributor to the e–ph scattering in CuI. Although the spectral decomposition encompasses both short- and long-range phonons, transport in CuI is mainly influenced by the latter ones (near Γ). This is due to the unique and curvy pocket present at the VBM of the electronic band structure of the material, allowing only transitions with a small momentum transfer q. Figure 3c represents the T₂ (LO) phonon mode of CuI at Γ (toward the X direction) with the Cu and I atoms moving in phase opposition with twice the displacement amplitude for Cu. The relative contribution to scattering increases with T due to the growing number of phonons that are thermally excited, as evidenced by the area under the curve of Figure 3b expanding from 100 to 400 K. This results in a decrease of the e–ph IBTE mobility with temperature, as shown in Figure S3.

Figure 3. (a) CuI phonon dispersion computed with SOC and the PBEsol functional with experimentally reported frequencies overlaid. (84,85) (b) Spectral decomposition of the hole scattering rates as a function of frequency at different temperatures. (c) Structure of CuI showing the atomic displacements corresponding to the longitudinal optical phonon mode at the Γ point (toward the X direction), viewed along the face diagonal; Cu and I atoms in blue and green, respectively.

AMSET

Figure 4 shows the hole mobility calculated with AMSET at low and high carrier concentrations. The mobility is split by scattering mechanism, and the total mobility is plotted as the reciprocal sum of each component (via Matthiessen’s rule). At a carrier concentration of 1 × 10¹⁶ cm^–3 (Figure 4a), scattering from POP is predicted to dominate the hole mobility, yielding a total room temperature hole mobility of 41.3 cm² V^–1 s^–1. Scattering from ADP, PIE, and IMP is essentially negligible at low concentrations compared to POP scattering. The piezoelectric constant calculated from DFPT is in excellent agreement with the experiment (0.10 C m^–2 against 0.13 C m^–2) (86) and confirms that PIE scattering does not compromise the mobility despite the noncentrosymmetric inversion native to the zincblende crystal structure.

Figure 4. CuI hole mobility as a function of the temperature at two carrier concentrations. Colored lines represent mobility contributions from each type of scattering: ADP is acoustic deformation potential scattering (orange); IMP is ionized impurity scattering (dark blue); PIE is piezoelectric scattering (light blue); POP is polar optical phonon scattering (pink); and total is the reciprocal sum of these contributions (black). (a) Low carrier concentration, 1 × 10¹⁶ cm^–3. (b) High carrier concentration, 1 × 10²⁰ cm^–3.

Moving to a higher carrier concentration of 1 × 10²⁰ cm^–3 (Figure 4b), the effects of both POP and PIE scattering are diminished further, while ionized impurities begin to control the charge transport behavior in CuI─a room-temperature hole mobility of 32.6 cm² V^–1 s^–1 is predicted. IMP (and indeed POP scattering in the AMSET implementation) scattering is largely determined by the value of the static dielectric response of a material, i.e., its ability to screen electric charge. For CuI, calculated dielectric constants range from 5.27 to 8.85, dependent on the flavor of DFT functional and the method used to calculate the high- and low-frequency responses, and are shown in Table 2. Meanwhile, an experimental dielectric response of 6.5 is reported by Hanson et al. (86) Accurate calculation of the dielectric response in tetrahedral semiconductors is benchmarked by Skelton et al., (87) who note that semilocal DFT nearly always overestimates the high-frequency dielectric response, while hybrid functionals nearly always underestimate the high-frequency dielectric response, with PBE0 performing worse than HSE06. Considering the tetrahedral zincblende structure of CuI, it is reasonable to assume that similar trends are followed here. Due to the fact that the dielectric constant is quite small for CuI, these quite large percentage errors in ϵ₀ have significant effects on the POP and IMP scattering rates, as shown in Figure S4 in the Supporting Information. To this end, the dielectric constant used in the AMSET calculations in Figures 4 and 5 is that determined from experiment (6.5, where ϵ_ionic is set as the calculated value of 1.1 from DFPT, and the remainder is assigned to ϵ_∞), with lower and upper limits (5.27 and 8.85) shown for context in the Supporting Information. More sophisticated methods for calculating the dielectric response that can accurately model excited state features, such as GW (Green’s function G with screened Coulomb interaction W) and BSE (Bethe–Salpeter equation) implementations, would provide a clearer picture, (88) but exceed the scope of the current work.

Table 2. Dielectric Constants Calculated Using a Variety of Methods^a

details	ϵ_ionic	ϵ_∞	ϵ₀
PBEsol DFPT; PBEsol IP-RPA*	1.10	7.75	8.85
PBEsol DFPT; PBE0 IP-RPA*	1.10	4.17	5.27
PBE0 FD; PBE0 IP-RPA*	1.65	4.17	5.82
materials project: PBE	0.87	6.82	7.69
Li et al. (89) PBE	1.53	4.77	6.30
Hanson et al. (exp.) (86)			6.5

^{^a}

* denotes calculations from this work; DFPT (density functional perturbation theory) or FD (finite differences method) calculations were used to determine the low-frequency, ϵ_ionic, response, while IP-RPA (independent particle random phase approximation) optical calculations were used to determine the high-frequency, ϵ_∞, response. Further details can be found in the methodology section.

Figure 5. Experimental hole mobility as a function of carrier concentration, broken down by the deposition method. Experimental data are reported in refs (29), (30), (33)– (35), (37)– (42), (95)– (96) (97) (98). IBTE and AMSET drift mobilities overlaid as dashed lines; IBTE + IMP mobility $(\frac{1}{μ_{IBTE + IMP}} = \frac{1}{μ_{IBTE}} + \frac{1}{μ_{IMP}})$ overlaid as a filled black line; gray shaded region denotes space between AMSET-estimated upper limit and IBTE + IMP-estimated upper limit.

Combined Approach

While AMSET correctly predicts the relative importance of the different scattering mechanisms, the low concentration regime phonon-limited mobility predicted by AMSET and the IBTE method varies by a factor of 4. As POP scattering is the primary mobility-limiting mechanism in this material at low carrier concentrations, this overestimation of the scattering rate results in mobility values that are lower than those reported in the experimental literature (notably the single crystal result from Chen et al.). (41) One way to explain this is the inelastic treatment of POP in AMSET. Indeed, AMSET approximates POP scattering using the self-energy relaxation time approximation (SERTA), which as part of its formalism considers scattering only in the forward direction relative to charge carrier motion. The omission of backward scattering can lead to an underestimation of phonon-limited mobility, the extent of which varies between materials depending on the complexity of the band edge (single band or multidegenerate), the effective mass, and spin–orbit effects. (65,90)

The comparison between phonon-limited mobility and experimental results can be challenging since most calculations do not consider impurities or defects. While SERTA serves as an approximation of IBTE, it is advisible to prioritize the latter due to its comprehensive nature, even if certain SERTA results appear closer to experimental data. For instance in Si, the computed electron mobility with the two methods fall within the range of experimentally reported mobilities, (64) although the hole mobility is overestimated by both approaches─only when performing simulations using the experimental lattice parameter and fitting the band structure to the experimental hole effective mass is agreement with experimental mobility recovered using the IBTE approach; (90) for SiC the IBTE performs better than the SERTA for electron mobility (SERTA underestimates by around 30%), while they straddle the upper and lower side of experimental results for the hole mobility, respectively; (91) and for GaAs both the implementations provide rather unreliable results, not helped by the large range of experimental mobilities reported. (92) Surveying over 50 materials, Claes et al. show that differences in computed mobility using IBTE and SERTA can reach up to 60%, (65) and that the differences are often particularly large for binary halides with low ω_POP such as NaI, CsI, and TlBr. The general trend is that SERTA will, if at all, underestimate phonon-limited mobilities compared with the exact IBTE results. Crucially, it is difficult to predict a priori the severity of the underestimation.

To this end, mobility values obtained using SERTA under ABINIT are compared with those acquired using AMSET, as illustrated in Figure S3. It is found that the agreement between the two SERTA results is close, and this indicates that POP scattering is potentially overestimated in AMSET for CuI due to the SERTA. Therefore, we propose that the mobility limit in CuI is determined in the low concentration regime by IBTE e–ph scattering and in the high concentration regime by ionized impurity scattering.

Figure 5 shows the hole mobility determined by summing the e–ph contribution from IBTE and the IMP contribution from AMSET assuming the validity of Matthiessen’s rule on mobility

(\frac{1}{μ_{IBTE + IMP}} = \frac{1}{μ_{IBTE}} + \frac{1}{μ_{IMP}})

. While this does not represent an exact solution to the BTE, it provides a reasonable upper limit to the mobility that is achievable in CuI. The e–ph IBTE and total AMSET drift mobilities (computed using the experimentally determined dielectric constant of 6.5) are also shown, as are experimental Hall mobility values from the literature. As the Hall factor (r_H) is close to 1 for CuI and CuBr, (93,94) it is reasonable to compare the simulated drift mobility with experimental Hall mobility (r_Hμ ∼ μ_H).

The combined mobility from IBTE and IMP acts as an upper limit to hole mobility in CuI, within which the presently available data from experiment falls. First, single crystal data are considered (orange stars in Figure 5), which should represent the highest achievable experimental mobility and truest comparison to simulation, as only the intrinsic, material-dependent scattering processes should be present. It is well-known however that single crystal size, cleanliness, and surface defects can all impact mobility measurements. Record single crystal mobility is reported by Chen et al., (41) achieving a value of 43.9 cm² V^–1 s^–1 at a carrier concentration of 4.3 × 10¹⁶ cm^–3 in a sample of dimensions 15 × 10 × 1 mm. This is in the electron–phonon scattering limit and suggests significant scope for improvement in mobility at low carrier concentrations. Other single crystals have been synthesized by Lv et al., (42) obtaining a sample of similar size and carrier concentration but with a reduced mobility of 12.8 cm² V^–1 s^–1, and Matsuzaki et al., (97) achieving mobility up to 29 cm² V^–1 s^–1 at low concentrations (2.0 × 10¹⁴ cm^–3) and 19 cm² V^–1 s^–1 at carrier concentrations approaching the degenerate conductivity limit. By considering the POP scattering rate from AMSET as the dominant low concentration scattering mechanism, Chen’s measurement exceeds the predicted mobility. It is reasonable to assume that this single crystal measurement is within the “low” carrier concentration regime, as a rough calculation of the Mott criterion using the parabolic (transport) band edge effective masses and the experimental dielectric constant indicates a carrier density of 8.5 × 10¹⁷ cm^–3 (1.65 × 10¹⁸ cm^–3). This failure of the SERTA to describe the low carrier density experimental data points was the first indication that a more sophisticated treatment of the e–ph scattering would be required for CuI.

Turning now to thin films, the record mobility measurement is more difficult to identify. Several papers report promising mobilities, even surpassing the 43.9 cm V^–2 s^–1 from Chen et al.: 35 cm² V^–1 s^–1 at 8.5 × 10¹⁸ cm^–3 via liquid iodization of metallic Cu from Wang et al.; (99) 35 to 50 cm² V^–1 s^–1 at concentrations in the region of 1 × 10¹⁸ cm^–3 via iodization of metallic Cu on crystalline Si substrates from Madkhali et al.; (100) and 110 cm² V^–1 s^–1 at 1.1 × 10¹⁸ cm^–3 via MBE on crystalline Si from Ahn et al. (101) However, these measurements are from extremely thin films that have XRD peaks that can be attributed to the Cu and c-Si substrates, which themselves are extremely good charge carriers, making it difficult to decouple the transport properties of the substrate from those of the film. These results are therefore omitted from Figure 5. Storm et al. report consistently high thin film mobility via pulsed laser deposition (PLD, purple triangles in Figure 5) over a wide range of carrier concentrations, (38,40) which comprises the most reliable thin film data available in the literature. At the higher end of the carrier concentrations reported, films deposited from sputtering and liquid iodization appear to approach the mobility limit arising from ionized impurity scattering, peaking around 10 cm² V^–1 s^–1. Across the entire carrier concentration range, the experimental results fall within the IBTE + IMP limit (and critically fall outside the SERTA + IMP, i.e., AMSET, limit), justifying our approach.

The final and perhaps most crucial point to consider is the electronic performance achievable via scalable synthesis methods. While PLD, MBE and sputtering offer reasonably high mobilities across the carrier concentration range, they are not commercially viable deposition techniques. Instead, inkjet printing, spin coating, and, potentially, iodination reactions are likely to be the most industrially relevant. The hole mobilities reported from these methods seldom exceed 10 cm² V^–1 s^–1 regardless of carrier concentration, owing to the lower crystallinity of the films and subsequent grain boundary and interface scattering. Such CuI films are roughly on par with SnO mobility, (15) but are beaten by Ba₂BiTaO₆ (30 cm² V^–1 s^–1) (19,20) and the layered oxychalcogenide (Cu₂S₂)(Sr₃Sc₂O₅) (150 cm² V^–1 s^–1), (102) and are still up to 2 orders of magnitude lower than the degenerately doped n-type transparent conductors (In₂O₃ 130 cm² V^–1 s^–1, Ga₂O₃ 75 cm² V^–1 s^–1, SnO₂ 130 cm² V^–1 s^–1, BaSnO₃ 320 cm² V^–1 s^–1, and ZnSb₂O₆ 49 cm² V^–1 s^–1). (103−107) Despite this, CuI has been successfully used to make thin film transistors via solution-based and inkjet deposition with competitive switching ratios and current densities, (37,43,108) and amorphous CuI thin-film transistors (TFTs) have been reported to outperform polycrystalline devices. (109) Such applications often require a carrier density lower than 10²⁰ cm^–3, where the mobility of CuI can be significantly improved. The prediction of such a large scope for improvement in CuI mobility indicates that other scattering processes may also be in play, such as surface and grain boundary scattering, which could be mitigated as deposition and device engineering process become more sophisticated. These results indicate that CuI will retain its position as the front-runner in the race for a marketable p-type TCM, and provide useful insights for quality control in CuI.

Defect Chemistry

Suitable point defect chemistry is crucial to the operation of transparent conducting materials. For a p-type system, it is necessary to have low formation energy acceptor defects at Fermi levels close to, or ideally within, the VBM. As the separation between the defect state and band edge decreases, more holes can be generated at the VBM through thermal excitation of an electron to the defect (with energy ∼ k_BT), increasing conductivity. It is also desirable that such p-type defects generate delocalized charge density, enabling a high charge carrier mobility with no energetic barrier─the formation of localized charge, or hole polarons, necessitates an activation energy E_A (with an Arrhenius-like temperature dependency) for charge transport, which significantly reduces optoelectronic performance (consider the polaron-limited mobility in CuAlO₂ of 3 cm² V^–1 s^–1). (7,110) To this end, both the intrinsic defect chemistry of CuI and the effects of chalcogen doping (S and Se) were studied using hybrid functionals. Transition level diagrams under a variety of Cu–I chemical potentials (Cu-rich, midpoint, and Cu-poor) are shown in Figure 6, while tabulated formation energies of defects and competing phases, along with extended methodology, can be found in the Supporting Information.

Figure 6. Transition level diagrams for CuI under three sets of chemical potentials. Fermi energy (eV) on the x-axis, formation energy (eV) on y-axis. The valence band maximum (VBM) is denoted by the shaded blue region. The gradient of each line represents the charge state, and filled circles denote transition levels where two charge states are in thermodynamic equilibrium. (a) Cu-rich, I-poor, chalcogen-poor. (b) Cu-mid, I-mid, chalcogen-rich. (c) Cu-poor, I-rich, chalcogen-rich.

Intrinsic Defects

The copper vacancy is the predominant defect in CuI, with a formation energy below 1 eV regardless of the growth conditions. It has a transition level from the 0/1─charge state approximately at 0.24 eV from the band edge, indicative of a deep defect. A significant disruption to the local crystal structure upon vacancy formation supports this behavior, with one nearby Cu atom relaxing toward the vacancy by 0.09 Å. The hole generated at the VBM by the formation of a copper vacancy is found to localize on this displaced atom, shown in Figure S6. However, analysis of the Fröhlich polaron constant for CuI (α = 0.44 for PBEsol and 1.55 for PBE0) indicates that such a polaron is likely to be spread over several unit cells (supported by observation of several metastable defect geometries within 1 meV of the ground state with less localized hole density, see Figures S5 and S6) so should still result in reasonable charge carrier mobility, and crucially indicates that the band carrier model assumed for the charge transport calculations is still valid. Under Cu-poor conditions, charge carrier concentrations of up to 2 × 10¹⁹ cm^–3 are predicted solely due to the increased concentration of copper vacancies, indicating that this species is the key factor in controlling p-type conductivity in CuI.

The remaining intrinsic defect species are the p-type iodine interstitial (I_int), the n-type iodine vacancy (V_I), and the n-type copper interstitial (Cu_int). The iodine interstitial is an ultradeep acceptor with prohibitively high formation energies under all growth conditions (2.5 eV in the best case), and is unlikely to play a major role in boosting p-type conductivity. The n-type defects are both deep donors and under Cu-rich conditions are predicted to charge compensate the holes generated by the copper vacancy (where the blue and orange lines intersect in Figure 6a). However, as growth conditions are modulated toward a Cu-poor environment, the formation energies of both the iodine vacancy and copper interstitial are sufficiently raised such that they can no longer charge compensate.

Extrinsic Defects─Post Hoc Ergo Propter Hoc?

Chalcogen (S, Se) doping has been explored as a route to further enhance hole conductivity both computationally and experimentally. (30,38,40,68) The formation energies of Cu_xS_y and Cu_xSe_y competing phases within the chemical potential limits of CuI control the chemical potentials of the dopant atoms, but it is observed that synthesis conditions have little effect on the formation energies of the substitutional species S_I and Se_I due to the concomitant changing chemical potential of iodine. Much larger changes in formation energy are observed for the interstitial defects S_int and Se_int, where the changing chemical potential of iodine has no impact on the formation energy of the chalcogen defect.

The substitutional defects themselves are higher in energy than the copper vacancy under p-type growth conditions (Figure 6b,c), at around 0.9 eV for S_I and 1.0 eV for Se_I, and have deeper transition levels. This suggests a greater degree of charge localization than for the copper vacancy, which is shown in Figure 7. The hole generated by the formation of both defects is strongly bound to the site of the substitution and causes a significant inward relaxation of the four surrounding copper atoms. This deep transition level is supported by the experimental work of Storm et al., who report a binding energy for the Se substitution of around 300 meV. (40) Graužinytė et al. predict shallower transition levels for both S_I and Se_I, but these are from defect relaxations performed with a semilocal exchange–correlation functional without SOC, leading to an overdelocalization of charge and an incorrect defect geometry. (68)

Figure 7. Partial hole density generated by various defects in CuI. Defect supercell is denoted by a dotted black line; blue regions are Cu, green regions are I, and lime green regions are dopants. (a) S_I⁰, 0.006 e Å^–3. (b) Se_I⁰, 0.006 e Å^–3.

Finally, the interstitial chalcogen species are much higher in formation energy and are predicted to act as ultradeep acceptors, with negative-U 0/2─transitions occurring at Fermi levels close to 2.0 eV. These characteristics preclude them from having any significant effect on the electronic properties of CuI.

Overall, the defect chemistry of CuI is rather straightforward. Native p-type conductivity is enabled by the formation of copper vacancies, the concentration of which can be fine-tuned by strict control of the copper chemical potential during synthesis, while the remaining intrinsic species have little to no effect on the defect landscape. Despite the small improvements in electronic properties after doping with S and Se reported in the literature, these dopants are predicted to be electronically inactive with deep transition levels that result in significant charge trapping. This is an example of the logical fallacy post hoc, ergo propter hoc, or “after this, therefore because of this”. A number of factors could contribute to the prediction of deeper transition levels in the current work compared to those from Graužinytė et al.: a more thorough exploration of the potential energy surface for each defect state via use of the ShakeNBreak method; full geometric optimization with hybrid functionals, rather than relaxation with semi-local functionals plus a hybrid functional single-shot on a volume-scaled structure; and the explicit inclusion of SOC during defect calculations to accurately model the position of the band edges. With these new insights on the electronic role of chalcogen dopants, it is instead proposed that indirect changes in host chemical potentials as a result of chalcogen doping have a greater impact on overall hole concentration. Furthermore, effects on crystallinity and morphology should be considered during experimental investigation of chalcogen doping, as this can be a further source of indirect improvements to optoelectronic performance.

Conclusions

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This article examined the suitability of CuI as a high performance p-type transparent conductor. Using sophisticated charge transport modeling, an upper limit to hole mobility as a function of carrier concentration was predicted, ranging from 162 cm² V^–1 s^–1 in the phonon-limited range to 32.6 cm² V^–1 s^–1 in the degenerately doped, ionized impurity-limited range. These results suggest a significant scope for improvement in experimental mobility, particularly in the low to mid concentration range, which could be achieved by mitigating surface and grain boundary scattering processes and by further optimization of synthesis conditions. The prospect of achieving samples with mobilities that closely align with our theoretical projections holds significant promise. Such progress has the capacity to yield a noteworthy 2- to 3-fold enhancement in the existing experimental FoM, Φ, for CuI, thereby propelling it to a competitive stance alongside the finest n-type materials currently prevalent on the market. An examination of the defect chemistry revealed that the copper vacancy is the predominant source of charge carriers in CuI and that modulation of the copper chemical potential during synthesis is key to controlling the hole concentration. The chalcogens S and Se are predicted to be electronically inactive dopants but can result in increased conductivity and hole concentration via indirect effects such as improved sample crystallinity. Revisiting nondoped CuI and exercising greater control over the copper vacancy could lead to enhanced mobility at lower carrier concentrations, which would improve the performance of CuI in thin film electronics. This work will act as a useful benchmark to experimental studies on CuI and related p-type transparent conductors and indicates that there is still scope for enhanced optoelectronic performance.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.chemmater.3c01628.

Phonon dispersion, charge transport constants, further AMSET plots, and convergence testing (PDF)

cm3c01628_si_001.pdf (1.11 MB)

Terms & Conditions

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Author Information

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Corresponding Authors
- Geoffroy Hautier - UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium; Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, United States; Email: [email protected]
- David O. Scanlon - Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.; Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.; School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.; https://orcid.org/0000-0001-9174-8601; Email: [email protected]
Authors
- Joe Willis - Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.; Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.; https://orcid.org/0000-0002-1900-2677
- Romain Claes - UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
- Qi Zhou - Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.; Thomas Young Centre, University College London, Gower Street, London WC1E 6BT, U.K.
- Matteo Giantomassi - UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium
- Gian-Marco Rignanese - UCLouvain, Institute of Condensed Matter and Nanosciences (IMCN), Chemin des Étoiles 8, Louvain-la-Neuve B-1348, Belgium; https://orcid.org/0000-0002-1422-1205
Author Contributions
J.W. and R.C. contributed equally to this work.
Notes
The authors declare no competing financial interest.
Online repository which can be found at DOI: https://doi.org/10.5281/zenodo.8318329 contains charge transport and defect formation energy data.

Acknowledgments

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J.W. and R.C. acknowledge fruitful discussions with Dr Andrea Crovetto, Dr Alex Squires, Dr Alex Ganose, Dr Chris Savory, and Dr Guillaume Brunin. J.W. and D.O.S. acknowledge Diamond Light Source Ltd for cosponsorship of an EngD studentship on the EPSRC Centre for Doctoral Training in Molecular Modelling and Materials Science (EP/L015862/1), support for EPSRC Grant number EP/N01572X/1, and from the European Research Council, ERC (grant no. 758345). This work used the ARCHER and ARCHER2 UK National Supercomputing Service (https://www.archer2.ac.uk), via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202, EP/R029431, and EP/T022213). We are grateful to the UK Materials and Molecular Modelling Hub for computational resources (Thomas and Young), which is partially funded by EPSRC (EP/P020194/1 and EP/T022213/1). The authors acknowledge the use of the UCL Myriad, Kathleen, and Thomas High Performance Computing Facilities (Myriad@UCL, Kathleen@UCL, and Thomas@UCL), and associated support services, in the completion of this work. R.C. acknowledges financial support from the Communauté Française de Belgique, grant ARC 18/23-093. G.M.R. acknowledges financial support from the Fonds de la Recherche Scientifique de Belgique (F.R.S.-FNRS). Computational resources were provided by the Consortium des Équipements de Calcul Intensif, funded by the F.R.S.- FNRS under grant no. 2.5020.11 and by the Walloon Region. The present research benefited from computational resources made available on the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under grant no. 1117545. G.H. acknowledges funding by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-05-CH11231: Materials Project program KC23MP. The work has received partial support from the European Union’s Horizon 2020 research and innovation program, grant no. 951786 through the Center of Excellence NOMAD.

Additional Note

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^a Generally, the figure of merit is calculated as the ratio between electrical conductivity σ and the visible absorption coefficient α, where T_vis is transmission and R_s is the sheet resistance, related to conductivity and thickness d.

References

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This article references 110 other publications.

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CuAlO2 is a prototypical delafossite p-type transparent conducting oxide (TCO). Despite this, many fundamental questions about its band structure and cond. remain unanswered. We utilize the screened hybrid exchange functional (HSE06) to investigate defects in CuAlO2 and find that Cu vacancies and Cu on Al antisites will dominate under Cu-poor/Al-poor conditions. Our calcd. transitions levels are deep in the band gap, consistent with exptl. findings, and we identify the likely defect levels that are often mistaken as indirect band gaps. Finally, we critically discuss delafossite oxides as TCO materials.
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Scanlon, D. O.; Watson, G. W. Undoped n-type Cu₂O: Fact or Fiction?. J. Phys. Chem. Lett. 2010, 1, 2582– 2585, DOI: 10.1021/jz100962n
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Undoped n-Type Cu2O: Fact or Fiction?
Scanlon, David O.; Watson, Graeme W.
Journal of Physical Chemistry Letters (2010), 1 (17), 2582-2585CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Cuprous oxide is widely known to be a native p-type semiconductor. Despite this, reports of electrodeposited films of n-type Cu2O continue to appear in the literature, with oxygen vacancies commonly implicated as the electron-donating defect. Through first-principles calcns., we demonstrate conclusively that intrinsic n-type defects or defect complexes in Cu2O cannot be the source of any n-type behavior displayed by electrodeposited samples. In light of these results, we discuss the exptl. findings.
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Scanlon, D. O.; Godinho, K. G.; Morgan, B. J.; Watson, G. W. Understanding conductivity anomalies in Cu(I)-based delafossite transparent conducting oxides: Theoretical insights. J. Chem. Phys. 2010, 132, 024707, DOI: 10.1063/1.3290815
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Understanding conductivity anomalies in CuI-based delafossite transparent conducting oxides: Theoretical insights
Scanlon, David O.; Godinho, Kate G.; Morgan, Benjamin J.; Watson, Graeme W.
Journal of Chemical Physics (2010), 132 (2), 024707/1-024707/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
The Cu(I)-based delafossite structure, Cu(I)M(III)O2, can accommodate a wide range of rare earth and transition metal cations on the M(III) site. Substitutional doping of divalent ions for these trivalent metals is known to produce higher p-type cond. than that occurring in the undoped materials. However, an explanation of the cond. anomalies obsd. in these p-type materials, as the trivalent metal is varied, is still lacking. We examine the electronic structure of Cu(I)M(III)O2 (M(III) = Al, Cr, Sc, Y) using d. functional theory cor. for on-site Coulomb interactions in strongly correlated systems (GGA + U) and discuss the unusual exptl. trends. The importance of covalent interactions between the M(III) cation and O for improving cond. in the delafossite structure is highlighted, with the covalency trends found to perfectly match the cond. trends. We also show that calcg. the natural band offsets and the effective masses of the valence band maxima is not an ideal method to classify the conduction properties of these ternary materials. (c) 2010 American Institute of Physics.
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Godinho, K. G.; Carey, J. J.; Morgan, B. J.; Scanlon, D. O.; Watson, G. W. Understanding conductivity in SrCu₂O₂: stability, geometry and electronic structure of intrinsic defects from first principles. J. Mater. Chem. 2010, 20, 1086– 1096, DOI: 10.1039/B921061J
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Understanding conductivity in SrCu2O2: stability, geometry and electronic structure of intrinsic defects from first principles
Godinho, Kate G.; Carey, John J.; Morgan, Benjamin J.; Scanlon, David O.; Watson, Graeme W.
Journal of Materials Chemistry (2010), 20 (6), 1086-1096CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
D. functional theory calcns. were performed on stoichiometric and intrinsically defective p-type transparent conducting oxide SrCu2O2, using GGA cor. for on-site Coulombic interactions (GGA + U). Anal. of the absorption spectrum of SrCu2O2 indicates that the fundamental direct band gap could be as much as ∼0.5 eV smaller than the optical band gap. Our results indicate that the defects that cause p-type cond. are favored under all conditions, with defects that cause n-type cond. having significantly higher formation energies. We show conclusively that the most stable defects are copper and strontium vacancies. Copper vacancies introduce a distinct acceptor single particle level above the valence band max., consistent with the exptl. known activated hopping mechanism.
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Scanlon, D. O.; Watson, G. W. Understanding the p-type defect chemistry of CuCrO₂. J. Mater. Chem. 2011, 21, 3655, DOI: 10.1039/c0jm03852k
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Understanding the p-type defect chemistry of CuCrO2
Scanlon, David O.; Watson, Graeme W.
Journal of Materials Chemistry (2011), 21 (11), 3655-3663CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
CuCrO2 is the most promising Cu-based delafossite for p-type optoelectronic devices. Despite this, little is known about the p-type conduction mechanism of this material, with both CuI/CuII and CrIII/CrIV hole mechanisms being proposed. In this article we examine the electronic structure, thermodn. stability and the p-type defect chem. of this ternary compd. using d. functional theory with three different approaches to the exchange and correlation; the generalized-gradient-approxn. of Perdew, Burke and Ernzerhof (PBE), PBE with an addnl. correction for on-site Coulombic interactions (PBE + U) and the nonlocal, screened-exchange hybrid functional HSE06. The fundamental band gap of CuCrO2 is demonstrated to be indirect in nature. Under all growth conditions, the dominant intrinsic p-type defect will be the Cu vacancy, with hole formation centered solely on the Cu sublattice. Mg doping is found to be significantly lower in energy than intrinsic defect formation, explaining the large increases in cond. seen exptl. Cu-rich/Cr-poor growth conditions are found to be optimal for both intrinsic and extrinsic (Mg doping) defect formation, and should be adopted to maximize performance.
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Godinho, K. G.; Morgan, B. J.; Allen, J. P.; Scanlon, D. O.; Watson, G. W. Chemical bonding in copper-based transparent conducting oxides: CuMO₂ (M = In, Ga, Sc). J. Phys.: Condens. Matter 2011, 23, 334201, DOI: 10.1088/0953-8984/23/33/334201
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Chemical bonding in copper-based transparent conducting oxides: CuMO2 (M = In, Ga, Sc)
Godinho, K. G.; Morgan, B. J.; Allen, J. P.; Scanlon, D. O.; Watson, G. W.
Journal of Physics: Condensed Matter (2011), 23 (33), 334201/1-334201/10CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
The geometry and electronic structure of copper-based p-type delafossite transparent conducting oxides, CuMO2 (M = In, Ga, Sc), are studied using the generalized gradient approxn. (GGA) cor. for on-site Coulomb interactions (GGA + U). The bonding and valence band compns. of these materials are investigated, and the origins of changes in the valence band features between group 3 and group 13 cations are discussed. Anal. of the effective masses at the valence and conduction band edge explains the exptl. reported cond. trends.
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Scanlon, D. O.; Buckeridge, J.; Catlow, C. R. A.; Watson, G. W. Understanding doping anomalies in degenerate p-type semiconductor LaCuOSe. J. Mater. Chem. C 2014, 2, 3429– 3438, DOI: 10.1039/C4TC00096J
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Understanding doping anomalies in degenerate p-type semiconductor LaCuOSe
Scanlon, David O.; Buckeridge, John; Catlow, C. Richard A.; Watson, Graeme W.
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2014), 2 (17), 3429-3438CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
The failure to develop a degenerate, wide band gap, p-type oxide material has been a stumbling block for the optoelectronics industry for decades. Mg-doped LaCuOSe has recently emerged as a very promising p-type anode layer for optoelectronic devices, displaying high conductivities and low hole injection barriers. Despite these promising results, many questions regarding the defect chem. of this system remain unanswered, namely (i) why does this degenerate semiconductor not display a Moss-Burnstein shift, (ii) what is the origin of cond. in doped and un-doped samples, and (iii) why is Mg reported to be the best dopant, despite the large cation size mismatch between Mg and La In this article we use screened hybrid d. functional theory to study both intrinsic and extrinsic defects in LaCuOSe, and identify for the first time the source of charge carriers in this system. We successfully explain why LaCuOSe does not exhibit a Moss-Burstein shift, and we identify the source of the subgap optical absorption reported in expts. Lastly we demonstrate that Mg doping is not the most efficient mechanism for p-type doping LaCuOSe, and propose an exptl. reinvestigation of this system.
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Zhang, J. Y.; Li, W. W.; Hoye, R. L. Z.; MacManus-Driscoll, J. L.; Budde, M.; Bierwagen, O.; Wang, L.; Du, Y.; Wahila, M. J.; Piper, L. F. J.; Lee, T.-L.; Edwards, H. J.; Dhanak, V. R.; Zhang, K. H. L. Electronic and transport properties of Li-doped NiO epitaxial thin films. J. Mater. Chem. C 2018, 6, 2275– 2282, DOI: 10.1039/C7TC05331B
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Electronic and transport properties of Li-doped NiO epitaxial thin films
Zhang, J. Y.; Li, W. W.; Hoye, R. L. Z.; MacManus-Driscoll, J. L.; Budde, M.; Bierwagen, O.; Wang, L.; Du, Y.; Wahila, M. J.; Piper, L. F. J.; Lee, T.-L.; Edwards, H. J.; Dhanak, V. R.; Zhang, K. H. L.
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2018), 6 (9), 2275-2282CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type cond. of NiO, but all the films have relatively low room-temp. mobilities (<0.05 cm2 V-1 s-1). The conduction mechanism is better described by small-polaron hoping model in the temp. range of 200 K < T < 330 K, and variable range hopping at T < 200 K. A combination of X-ray photoemission and O K-edge X-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band max. (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.
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Quackenbush, N. F.; Allen, J. P.; Scanlon, D. O.; Sallis, S.; Hewlett, J. A.; Nandur, A. S.; Chen, B.; Smith, K. E.; Weiland, C.; Fischer, D. A.; Woicik, J. C.; White, B. E.; Watson, G. W.; Piper, L. F. J. Origin of the Bipolar Doping Behavior of SnO from X-ray Spectroscopy and Density Functional Theory. Chem. Mater. 2013, 25, 3114– 3123, DOI: 10.1021/cm401343a
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Origin of the Bipolar Doping Behavior of SnO from X-ray Spectroscopy and Density Functional Theory
Quackenbush, N. F.; Allen, J. P.; Scanlon, D. O.; Sallis, S.; Hewlett, J. A.; Nandur, A. S.; Chen, B.; Smith, K. E.; Weiland, C.; Fischer, D. A.; Woicik, J. C.; White, B. E.; Watson, G. W.; Piper, L. F. J.
Chemistry of Materials (2013), 25 (15), 3114-3123CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The origin of the almost unique combination of optical transparency and the ability to bipolar dope Sn monoxide is explained using a combination of soft and hard x-ray photoemission spectroscopy, O K-edge X-ray emission and absorption spectroscopy, and d. functional theory calcns. incorporating van der Waals corrections. The authors reveal that the origin of the high hole mobility, bipolar ability, and transparency is a result of (i) significant Sn 5s character at the valence band max. (due to O 2p-Sn 5s antibonding character assocd. with the lone pair distortion), (ii) the combination of a small indirect band gap of ∼0.7 eV (Γ-M) and a much larger direct band gap of 2.6 - 2.7 eV, and (iii) the location of both band edges with respect to the vacuum level. This work supports Sn2+-based oxides as a paradigm for next-generation transparent semiconducting oxides.
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Li, Y.; Singh, D. J.; Du, M.-H.; Xu, Q.; Zhang, L.; Zheng, W.; Ma, Y. Design of ternary alkaline-earth metal Sn(II) oxides with potential good p-type conductivity. J. Mater. Chem. C 2016, 4, 4592– 4599, DOI: 10.1039/C6TC00996D
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Design of ternary alkaline-earth metal Sn oxides with potential good p-type conductivity
Li, Yuwei; Singh, David J.; Du, Mao-Hua; Xu, Qiaoling; Zhang, Lijun; Zheng, Weitao; Ma, Yanming
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (20), 4592-4599CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
Oxides with good p-type cond. have been long sought after to achieve high performance all-oxide optoelectronic devices. Divalent Sn based oxides are promising candidates because of their rather dispersive upper valence bands caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known Sn oxides being p-type conductive suitable for device applications. Here, we present via first-principles global optimization structure searches a material design study for a hitherto unexplored Sn-based system, ternary alk.-earth metal Sn oxides in the stoichiometry of MSn2O3 (M = Mg, Ca, Sr, Ba). We identify two stable compds. of SrSn2O3 and BaSn2O3, which can be stabilized by Sn-rich conditions in phase stability diagrams. Their structures follow the Zintl behavior and consist of basic structural motifs of SnO3 tetrahedra. Unexpectedly they show distinct electronic properties with band gaps ranging from 1.90 (BaSn2O3) to 3.15 (SrSn2O3) eV, and hole effective masses ranging from 0.87 (BaSn2O3) to above 6.0 (SrSn2O3) m0. Further exploration of metastable phases indicates a wide tunability of electronic properties controlled by the details of the bonding between the basic structural motifs. This suggests further exploration of alk.-earth metal Sn oxides for potential applications requiring good p-type cond. such as transparent conductors and photovoltaic absorbers.
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Zhang, K. H. L.; Du, Y.; Papadogianni, A.; Bierwagen, O.; Sallis, S.; Piper, L. F. J.; Bowden, M. E.; Shutthanandan, V.; Sushko, P. V.; Chambers, S. A. Perovskite Sr-Doped LaCrO₃ as a New p-Type Transparent Conducting Oxide. Adv. Mater. 2015, 27, 5191– 5195, DOI: 10.1002/adma.201501959
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Perovskite Sr-Doped LaCrO3 as a New p-Type Transparent Conducting Oxide
Zhang, Kelvin H. L.; Du, Yingge; Papadogianni, Alexandra; Bierwagen, Oliver; Sallis, Shawn; Piper, Louis F. J.; Bowden, Mark E.; Shutthanandan, Vaithiyalingam; Sushko, Peter V.; Chambers, Scott A.
Advanced Materials (Weinheim, Germany) (2015), 27 (35), 5191-5195CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
A new p-type transparent conductive oxide (TCO) based on LaCrO3 (LCO), which shows competitive performance within a structure that can be readily integrated with other oxide electronic materials, is reported. Substituting Sr2+ for La3+ in LCO effectively dopes holes into the top of the valence band (VB) and results in p-type cond., which is the motivation used to explore La1-xSrxCrO3 (LSCO) as a candidate p-type TCO. LSCO epitaxial films were grown on (001)-oriented SrTiO3 (STO) substrates by mol. beam epitaxy and their cond. and elec. properties studied.
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Amini, M. N.; Dixit, H.; Saniz, R.; Lamoen, D.; Partoens, B. The origin of p-type conductivity in ZnM₂O₄ (M = Co, Rh, Ir) spinels. Phys. Chem. Chem. Phys. 2014, 16, 2588, DOI: 10.1039/c3cp53926a
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The origin of p-type conductivity in ZnM2O4 (M = Co, Rh, Ir) spinels
Amini, M. N.; Dixit, H.; Saniz, R.; Lamoen, D.; Partoens, B.
Physical Chemistry Chemical Physics (2014), 16 (6), 2588-2596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
ZnM2O4 (M = Co, Rh, Ir) spinels are considered as a class of potential p-type transparent conducting oxides (TCOs). We report the formation energy of acceptor-like defects using 1st principles calcns. with an advanced hybrid exchange-correlation functional (HSE06) within d. functional theory (DFT). Due to the discrepancies between the theor. obtained band gaps with this hybrid functional and the - scattered - exptl. results, we also perform GW calcns. to support the validity of the description of these spinels with the HSE06 functional. The considered defects are the cation vacancy and antisite defects, which are supposed to be the leading source of disorder in the spinel structures. We also discuss the band alignments in these spinels. The calcd. formation energies indicate that the antisite defects ZnM (Zn replacing M, M = Co, Rh, Ir) and VZn act as shallow acceptors in ZnCo2O4, ZnRh2O4 and ZnIr2O4, which explains the exptl. obsd. p-type cond. in those systems. Moreover, our systematic study indicates that the ZnIr antisite defect has the lowest formation energy in the group and it corroborates the highest p-type cond. reported for ZnIr2O4 among the group of ZnM2O4 spinels. To gain further insight into factors affecting the p-type cond., we have also investigated the formation of localized small polarons by calcg. the self-trapping energy of the holes.
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Bhatia, A.; Hautier, G.; Nilgianskul, T.; Miglio, A.; Sun, J.; Kim, H. J.; Kim, K. H.; Chen, S.; Rignanese, G.-M.; Gonze, X.; Suntivich, J. High-Mobility Bismuth-based Transparent p-Type Oxide from High-Throughput Material Screening. Chem. Mater. 2016, 28, 30– 34, DOI: 10.1021/acs.chemmater.5b03794
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High-Mobility Bismuth-based Transparent p-Type Oxide from High-Throughput Material Screening
Bhatia, Amit; Hautier, Geoffroy; Nilgianskul, Tan; Miglio, Anna; Sun, Jingying; Kim, Hyung Joon; Kim, Kee Hoon; Chen, Shuo; Rignanese, Gian-Marco; Gonze, Xavier; Suntivich, Jin
Chemistry of Materials (2016), 28 (1), 30-34CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
Transparent semiconducting oxides are essential building blocks to many technologies, ranging from components in transparent electronics, transparent conductors, to absorbers and protection layers in photovoltaics and photoelectrochem. devices. However, thus far, it has been difficult to develop p-type oxides with wide band gap and high hole mobility. For example, current state-of-art transparent p-type oxides have hole mobility in the range of < 10 cm2/V·s, much lower than their n-type counterpart. Using high-throughput computational screening to guide the discovery of new materials with wide band gap and high hole mobility, we report the computational identification and the exptl. verification of a bismuth-based double-perovskite oxide that can meet these requirements. Our identified candidate, Ba2BiTaO6, has an optical band gap larger than 4 eV and a Hall hole mobility above 30 cm2/V·s. We rationalize this finding with the following MO explanation: Bi3+ with filled s-orbitals strongly overlaps with the oxygen p, increasing the extent of the metal-oxygen covalency and effectively reducing the valence band effective mass, while Ta5+ electronic states form a conduction band, leading to a high band gap beyond the visible range. Our concerted theory-expt. effort points to the growing utility of a data-driven materials discovery and the combination of both informatics and expt. as an approach to discover future technol. materials.
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Shi, J.; Rubinstein, E. A.; Li, W.; Zhang, J.; Yang, Y.; Lee, T.-L.; Qin, C.; Yan, P.; MacManus-Driscoll, J. L.; Scanlon, D. O.; Zhang, K. H. Modulation of the Bi³⁺ 6s² Lone Pair State in Perovskites for High-Mobility p-Type Oxide Semiconductors. Advanced Science 2022, 9, 2104141, DOI: 10.1002/advs.202104141
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Modulation of the Bi3+ 6s2 Lone Pair State in Perovskites for High-Mobility p-Type Oxide Semiconductors
Shi, Jueli; Rubinstein, Ethan A.; Li, Weiwei; Zhang, Jiaye; Yang, Ye; Lee, Tien-Lin; Qin, Changdong; Yan, Pengfei; MacManus-Driscoll, Judith L.; Scanlon, David O.; Zhang, Kelvin H. L.
Advanced Science (Weinheim, Germany) (2022), 9 (6), 2104141CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
Oxide semiconductors are key materials in many technologies from flat-panel displays, solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p-type oxide semiconductors due to the localized O-2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba2BiMO6 (M = Bi, Nb, Ta) via the Bi 6s2 lone pair state to achieve p-type oxide semiconductors with high hole mobility up to 21 cm2 V-1 s-1, and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x-ray photoemission, x-ray absorption spectroscopies, and d. functional theory calcns. are used to gain insight into the electronic structure of Ba2BiMO6. The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4-0.7 me). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P-N junction diode constructed with p-type Ba2BiTaO6 and n-type Nb doped SrTiO3 exhibits high rectifying ratio of 1.3 x 104 at ±3 V, showing great potential in fabricating high-quality devices. This work provides deep insight into the electronic structure of Bi3+ based perovskites and guides the development of new p-type oxide semiconductors.
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Williamson, B. A. D.; Buckeridge, J.; Brown, J.; Ansbro, S.; Palgrave, R. G.; Scanlon, D. O. Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors. Chem. Mater. 2017, 29, 2402– 2413, DOI: 10.1021/acs.chemmater.6b03306
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Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors
Williamson, Benjamin A. D.; Buckeridge, John; Brown, Jennilee; Ansbro, Simon; Palgrave, Robert G.; Scanlon, David O.
Chemistry of Materials (2017), 29 (6), 2402-2413CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The paucity of high performance transparent p-type semiconductors was a stumbling block for the electronics industry for decades, effectively hindering the route to efficient transparent devices based on p-n junctions. Cu-based oxides and subsequently Cu-based oxychalcogenides were heavily studied as affordable, earth-abundant p-type transparent semiconductors, where the mixing of the Cu 3d states with the chalcogenide 2p states at the top of the valence band encourages increased valence band dispersion. The authors extend this mixing concept further, by using quantum chem. techniques to study ternary copper phosphides as potential high mobility p-type materials. The authors use hybrid d. functional theory to examine a family of phosphides, namely, MCuP (M = Mg, Ca, Sr, Ba) which all possess extremely disperse valence band maxima, comparable to the dispersion of excellent industry std. n-type transparent conducting oxides. As a proof of concept, the authors synthesized and characterized powders of CaCuP, showing that they display high levels of p-type cond., without any external acceptor dopant. Lastly, the role of Cu-coordination in promoting valence band dispersion and provide design principles for producing degenerate p-type materials are discussed.
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Varley, J. B.; Miglio, A.; Ha, V.-A.; van Setten, M. J.; Rignanese, G.-M.; Hautier, G. High-Throughput Design of Non-oxide p-Type Transparent Conducting Materials: Data Mining, Search Strategy, and Identification of Boron Phosphide. Chem. Mater. 2017, 29, 2568– 2573, DOI: 10.1021/acs.chemmater.6b04663
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High-Throughput Design of Non-oxide p-Type Transparent Conducting Materials: Data Mining, Search Strategy, and Identification of Boron Phosphide
Varley, Joel B.; Miglio, Anna; Ha, Viet-Anh; van Setten, Michiel J.; Rignanese, Gian-Marco; Hautier, Geoffroy
Chemistry of Materials (2017), 29 (6), 2568-2573CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
High-performance p-type transparent conducting materials (TCMs) are needed in a wide range of applications ranging from solar cells to transparent electronics. p-type TCMs require a large band gap (for transparency), low hole effective mass (for high mobility), and hole dopability. Oxides have inherent limitations in terms of hole effective masses making them difficult to use as a high-performance p-type TCM. The authors use a high-throughput computational approach to identify novel, nonoxide, p-type TCMs. By data mining a large computational data set (more than 30,000 compds.), nonoxide materials can lead to much lower hole effective masses but to the detriment of smaller gaps and lower transparencies. The authors propose a strategy to overcome this fundamental correlation between low effective mass and small band gap by exploiting the weak absorption for indirect optical transitions. The authors apply this strategy to phosphides and identify zinc blende boron phosphide (BP) as a very promising candidate. Follow-up computational studies on defects formation indicate that BP can also be doped p-type and potentially n-type as well. The authors' work demonstrates how high-throughput computational design can lead to identification of materials with exceptional properties, and the authors propose a strategy to open the design of TCMs to nonoxide materials.
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Williamson, B. A. D.; Limburn, G. J.; Watson, G. W.; Hyett, G.; Scanlon, D. O. Computationally Driven Discovery of Layered Quinary Oxychalcogenides: Potential p-Type Transparent Conductors?. Matter 2020, 3, 759– 781, DOI: 10.1016/j.matt.2020.05.020
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Computationally Driven Discovery of Layered Quinary Oxychalcogenides: Potential p-Type Transparent Conductors?
Williamson Benjamin A D; Scanlon David O; Williamson Benjamin A D; Scanlon David O; Limburn Gregory J; Hyett Geoffrey; Watson Graeme W; Scanlon David O
Matter (2020), 3 (3), 759-781 ISSN:.
n-type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high-performance p-type TC has lagged far behind that of its n-type counterparts, delaying the advent of "transparent electronics"-based p-n junctions. Here, we propose the layered oxysulfide [Cu2S2][Sr3Sc2O5] as a structural motif for discovering p-type TCs. We have used density functional theory to screen 24 compositions based on this motif in terms of their thermodynamic and dynamic stability and their electronic structure, thus predicting two p-type TCs and eight other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu2S2][Ba3Sc2O5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC.
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Willis, J.; Scanlon, D. O. Latest directions in p-type transparent conductor design. J. Mater. Chem. C 2021, 9, 11995– 12009, DOI: 10.1039/D1TC02547C
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Latest directions in p-type transparent conductor design
Willis, Joe; Scanlon, David O.
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2021), 9 (36), 11995-12009CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
A review. Transparent conducting materials (TCMs) are crucial in the operation of modern opto-electronic devices, combining the lucrative properties of optical transparency and electronic cond. More than ever we rely on display and touch screens, energy efficient windows and solar cells in our day to day lives. The market for transparent electronics is projected to surpass $3.8 billion by 2026 as the automotive industry seek to incorporate pop-up displays into driver windshields, and the prospect of touch-enabled transparent displays challenges the traditional mouse and keyboard mode of computer operation. However, these new technologies rely heavily on the development of high performance p-type TCMs, a task that has posed a significant challenge to researchers for decades. This review will cover the basic theory and design principles of transparent conductors, followed by an overview of early p-type TCMs and their shortcomings. We discuss the impact of high-throughput screening studies on materials discovery and critically assess the family of p-type halide perovskites that emerged from these, ruling them as unsuitable candidates for high-performance applications. We find that phosphides, selenides, tellurides and halides are the most promising emerging materials, capable of achieving greater valence band dispersion than traditional oxides, and we discuss the challenges facing these more exotic systems. The smorgasbord of materials presented in this review should guide exptl. and computational scientists alike in the next phase of p-type transparent conductor research.
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Willis, J.; Bravić, I.; Schnepf, R. R.; Heinselman, K. N.; Monserrat, B.; Unold, T.; Zakutayev, A.; Scanlon, D. O.; Crovetto, A. Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films. Chem. Sci. 2022, 13, 5872– 5883, DOI: 10.1039/D2SC01538B
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Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films
Willis, Joe; Bravic, Ivona; Schnepf, Rekha R.; Heinselman, Karen N.; Monserrat, Bartomeu; Unold, Thomas; Zakutayev, Andriy; Scanlon, David O.; Crovetto, Andrea
Chemical Science (2022), 13 (20), 5872-5883CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concn. and hole mobility exceed 1 x 1020 cm-3 and 35 cm2 V-1 s-1 at room temp., resp. Transport calcns. indicate potential for even higher mobilities. Copper vacancies are identified as the main source of cond., displaying markedly different behavior compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calcns. of phonon-mediated indirect transitions. This discrepancy could be partly attributed to cryst. imperfections within the films, increasing the strength of indirect transitions. We det. the transparent conductor figure of merit of CaCuP films as a function of compn., revealing links between stoichiometry, cryst. quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.
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Crovetto, A.; Adamczyk, J. M.; Schnepf, R. R.; Perkins, C. L.; Hempel, H.; Bauers, S. R.; Toberer, E. S.; Tamboli, A. C.; Unold, T.; Zakutayev, A. Boron Phosphide Films by Reactive Sputtering: Searching for a P-Type Transparent Conductor. Adv. Mater. Interfaces 2022, 9, 2200031, DOI: 10.1002/admi.202200031
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Boron Phosphide Films by Reactive Sputtering: Searching for a P-Type Transparent Conductor
Crovetto, Andrea; Adamczyk, Jesse M.; Schnepf, Rekha R.; Perkins, Craig L.; Hempel, Hannes; Bauers, Sage R.; Toberer, Eric S.; Tamboli, Adele C.; Unold, Thomas; Zakutayev, Andriy
Advanced Materials Interfaces (2022), 9 (12), 2200031CODEN: AMIDD2; ISSN:2196-7350. (Wiley-VCH Verlag GmbH & Co. KGaA)
With an indirect band gap in the visible and a direct band gap at a much higher energy, boron phosphide (BP) holds promise as an unconventional p-type transparent conductor. This work reports on reactive sputtering of amorphous BP films, their partial crystn. in a P-contg. annealing atm., and extrinsic doping by C and Si. The highest hole concn. to date for p-type BP (5 x 1020 cm-3) is achieved using C doping under B-rich conditions. Furthermore, bipolar doping is confirmed to be feasible in BP. An anneal temp. of at least 1000°C is necessary for crystn. and dopant activation. Hole mobilities are low and indirect optical transitions are stronger than that predicted by theory. Low cryst. quality probably plays a role in both cases. High figures of merit for transparent conductors might be achievable in extrinsically doped BP films with improved cryst. quality.
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Bädeker, K. Über die elektrische Leitfähigkeit und die thermoelektrische Kraft einiger Schwermetallverbindungen. Ann. Phys. 1907, 327, 749– 766, DOI: 10.1002/andp.19073270409
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There is no corresponding record for this reference.
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Grundmann, M.; Schein, F.-L.; Lorenz, M.; Böntgen, T.; Lenzner, J.; von Wenckstern, H. Cuprous iodide - a p-type transparent semiconductor: history and novel applications. Phys. Status Solidi A 2013, 210, 1671– 1703, DOI: 10.1002/pssa.201329349
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Cuprous iodide: A p-type transparent semiconductor, history, and novel applications
Grundmann, Marius; Schein, Friedrich-Leonhard; Lorenz, Michael; Boentgen, Tammo; Lenzner, Joerg; von Wenckstern, Holger
Physica Status Solidi A: Applications and Materials Science (2013), 210 (9), 1671-1703CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Halide semiconductors stand at the very beginning of semiconductor science and technol. CuI was reported as the first transparent conductor, and the first field effect transistor was made from KBr. Although halogens are frequently used in semiconductor prepn., little use is currently made from halide semiconductors in electronics and photonics. We review past reports on the metal halide semiconductor CuI and related alloys and discuss recent progress with regard to this material including its use in org. electronics and solar cells as well as our own work on fully transparent bipolar heterostructure diodes (p-CuI/n-ZnO) with high rectification of several 107 and ideality factors down to 1.5. γ-CuI(111) thin film on glass (1 × 1 cm2) and IV-characteristics of p-CuI/n-ZnO/a-Al2O3 bipolar heterojunction diode.
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Yang, C.; Kneiβ, M.; Lorenz, M.; Grundmann, M. Room-temperature synthesized copper iodide thin film as degenerate p-type transparent conductor with a boosted figure of merit. Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 12929– 12933, DOI: 10.1073/pnas.1613643113
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Room-temperature synthesized copper iodide thin film as degenerate p-type transparent conductor with a boosted figure of merit
Yang, Chang; Kneiβ, Max; Lorenz, Michael; Grundmann, Marius
Proceedings of the National Academy of Sciences of the United States of America (2016), 113 (46), 12929-12933CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
A degenerate p-type conduction of cuprous iodide (CuI) thin films is achieved at the iodine-rich growth condition, allowing for the record high room-temp. cond. of ∼156 S/cm for as-deposited CuI and ∼283 S/cm for I-doped CuI. At the same time, the films appear clear and exhibit a high transmission of 60-85% in the visible spectral range. The realization of such simultaneously high cond. and transparency boosts the figure of merit of a p-type TC: its value jumps from ∼200 to ∼17,000 MΩ-1. Polycryst. CuI thin films were deposited at room temp. by reactive sputtering. Their elec. and optical properties are examd. relative to other p-type transparent conductors. The transport properties of CuI thin films were investigated by temp.-dependent cond. measurements, which reveal a semiconductor-metal transition depending on the iodine/argon ratio in the sputtering gas.
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Ahn, K.; Kim, G. H.; Kim, S.-J.; Kim, J.; Ryu, G.-S.; Lee, P.; Ryu, B.; Cho, J. Y.; Kim, Y.-H.; Kang, J.; Kim, H.; Noh, Y.-Y.; Kim, M.-G. Highly Conductive p-Type Transparent Conducting Electrode with Sulfur-Doped Copper Iodide. Chem. Mater. 2022, 34, 10517– 10527, DOI: 10.1021/acs.chemmater.2c02603
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Highly Conductive p-Type Transparent Conducting Electrode with Sulfur-Doped Copper Iodide
Ahn, Kyunghan; Kim, Ga Hye; Kim, Se-Jun; Kim, Jihyun; Ryu, Gi-Seong; Lee, Paul; Ryu, Byungki; Cho, Jung Young; Kim, Yong-Hoon; Kang, Joohoon; Kim, Hyungjun; Noh, Yong-Young; Kim, Myung-Gil
Chemistry of Materials (2022), 34 (23), 10517-10527CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
Although n-type transparent conductors have been commercialized with high optical transmittance and elec. cond., the realization of their p-type counterparts has been a challenging problem. Here, we report the synthesis of a highly conductive transparent p-type sulfur-doped CuI (CuI:S) thin film using a liq.-iodination method with a thiol additive. The CuI:S film shows a remarkably high elec. cond. of 511 S cm-1 with an optical transmittance of greater than 80%. Furthermore, addnl. hole doping of CuI:S with H2O2 treatment improves the elec. cond. to 596 S cm-1. Consequently, CuI:S exhibits a record-high figure of merit (FOM) value of 63,000 M Ω-1 (73,000 M Ω-1 with H2O2 treatment), which is ~ 370% (~ 430% with H2O2 treatment) higher than the previously reported record-high FOM value. The highly conducting CuI:S electrode is successfully applied as transparent conducting electrodes of the org. light-emitting diode and transparent p-type thin-film transistor. The liq.-iodination chem. method with unconventional control of the reaction parameters can be generalized to produce high-quality metal halide thin films, allowing them to be applicable for transparent electronics and optoelectronics.
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Ferhat, M.; Zaoui, A.; Certier, M.; Dufour, J.; Khelifa, B. Electronic structure of the copper halides CuCl, CuBr and Cul. Mater. Sci. Eng. B 1996, 39, 95– 100, DOI: 10.1016/0921-5107(95)01518-3
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Electronic structure of the copper halides CuCl, CuBr and CuI
Ferhat, M.; Zaoui, A.; Certier, M.; Dufour, J. P.; Khelifa, B.
Materials Science & Engineering, B: Solid-State Materials for Advanced Technology (1996), B39 (2), 95-100CODEN: MSBTEK; ISSN:0921-5107. (Elsevier)
The electronic band structures and densities of states of zinc-blende CuCl, CuBr, and CuI have been computed using the tight-binding method. These band structures have been used to calc. the valence and conduction band effective masses. The results are compared with other calcd. and exptl. values.
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Yu, H.; Cai, X.; Yang, Y.; Wang, Z.-H.; Wei, S.-H. Band gap anomaly in cuprous halides. Comput. Mater. Sci. 2022, 203, 111157, DOI: 10.1016/j.commatsci.2021.111157
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Band gap anomaly in cuprous halides
Yu, Haoyang; Cai, Xuefen; Yang, Yang; Wang, Zhi-Hao; Wei, Su-Huai
Computational Materials Science (2022), 203 (), 111157CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
Unlike the conventional zinc-blende II-VI and III-V common-cation systems, which exhibit a general trend of decreasing band gap with increasing anion at. no., the zinc-blende I-VII cuprous halides CuX (X = Cl, Br, and I) all have an approx. equal direct band gap. Here, using first-principles calcns., we demonstrate that this band gap anomaly in Cu halides is attributed to the unique energy level order of Cu 3d well above X p, making the valence band max. (VBM) an antibonding state derived mostly from the Cu 3d orbital, thus, a relatively small variation of the band gap with respect to the anion at. no.
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Crovetto, A.; Hempel, H.; Rusu, M.; Choubrac, L.; Kojda, D.; Habicht, K.; Unold, T. Water Adsorption Enhances Electrical Conductivity in Transparent P-Type CuI. ACS Appl. Mater. Interfaces 2020, 12, 48741– 48747, DOI: 10.1021/acsami.0c11040
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Water Adsorption Enhances Electrical Conductivity in Transparent P-Type CuI
Crovetto, Andrea; Hempel, Hannes; Rusu, Marin; Choubrac, Leo; Kojda, Danny; Habicht, Klaus; Unold, Thomas
ACS Applied Materials & Interfaces (2020), 12 (43), 48741-48747CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
CuI has been recently rediscovered as a p-type transparent conductor with a high figure of merit. Even though many metal iodides are hygroscopic, the effect of moisture on the elec. properties of CuI has not been clarified. In this work, we observe a 2-fold increase in the cond. of CuI after exposure to ambient humidity for 5 h, followed by slight long-term degrdn. Simultaneously, the work function of CuI decreases by almost 1 eV, which can explain the large spread in the previously reported work function values. The cond. increase is partially reversible and is maximized at intermediate humidity levels. On the basis of the large intragrain mobility measured by THz spectroscopy, we suggest that hydration of grain boundaries may be beneficial for the overall hole mobility.
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Yamada, N.; Ino, R.; Ninomiya, Y. Truly Transparent p-Type CuI Thin Films with High Hole Mobility. Chem. Mater. 2016, 28, 4971– 4981, DOI: 10.1021/acs.chemmater.6b01358
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Truly Transparent p-Type γ-CuI Thin Films with High Hole Mobility
Yamada, Naoomi; Ino, Ryuichiro; Ninomiya, Yoshihiko
Chemistry of Materials (2016), 28 (14), 4971-4981CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The γ-phase of copper(I) iodide (γ-CuI) is a p-type semiconductor with a wide bandgap (Eg ≈ 3.1 eV). Conventionally, γ-CuI thin films were synthesized by the iodination of Cu thin layers with iodine vapor. However, γ-CuI films fabricated by this method have a rough surface and thus a frosted-glass-like appearance, which make it difficult to apply this material to transparent electronics. A simple new method is proposed for the synthesis of truly transparent p-type γ-CuI films. The chem. reaction between Cu3N thin films and solid-phase iodine at 25° yields highly transparent polycryst. γ-CuI films with shiny appearance. The γ-CuI films fabricated by this method had root-mean-square roughness values of 8-12 nm, which are <1/3 of those for γ-CuI films synthesized by the conventional method. As a result, specular transmittance of >75% in the visible region was attained. An as-prepd. film had a resistivity (ρ) of 3.1 × 10-2 Ω cm, hole d. (nh) of 8.9 × 1019 cm-3, and mobility (μ) of 2.4 cm2 V-1 s-1. Mild heat treatment at 100-150° under an inert atm. was found to suppress nh and enhance μ. The heat-treated films had μ values of 9-10 cm2 V-1 s-1, which are comparable to those of other wide-bandgap p-type semiconductors grown epitaxially at high temps. >400°. These findings would assist studies on applications of γ-CuI thin films in transparent electronics.
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Peng, W.; Li, L.; Yu, S.; Yang, P.; Xu, K.; Luo, W. High-performance flexible transparent p-CuI film by optimized solid iodization. Vacuum 2021, 183, 109862, DOI: 10.1016/j.vacuum.2020.109862
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High-performance flexible transparent p-CuI film by optimized solid iodization
Peng, Wei; Li, Lingxia; Yu, Shihui; Yang, Pan; Xu, Kangli; Luo, Weijia
Vacuum (2021), 183 (), 109862CODEN: VACUAV; ISSN:0042-207X. (Elsevier Ltd.)
High-performance flexible transparent p-CuI films were prepd. on polycarbonate substrates at room temp. by combining solid iodization and vacuum thermal evapn. The structural anal. shows that as-prepd. CuI films are polycryst. with zinc blende structure, exhibiting highly preferred oriented (1 1 1) plane. Atomic force microscope shows homogeneous surface morphol. with no fissure or exfoliation. X-ray photoelectron spectra indicate that the valence state of copper is Cu+ after being completely iodinated and the calcd. value of [I]/[Cu] increases as iodination time increase. The improvement of elec. performance is inseparable from the relative content of excess iodine. Moreover, the flexible p-CuI films exhibit a high av. transmittance of 87.1% in the visible region with excellent cond. of 31.7 S/cm, which shows superior performance than the other rigid p-type transparent conductors prepd. at high temps. In particular, flexible p-CuI films also display excellent durability and flexibility in the tests of the radius of curvature and bending cycle. These results prove that the as-prepd. p-CuI films have great potential in flexible and wearable electronics.
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Vora-ud, A.; Chaarmart, K.; Kasemsin, W.; Boonkirdram, S.; Seetawan, T. Transparent thermoelectric properties of copper iodide thin films. Phys. B 2022, 625, 413527, DOI: 10.1016/j.physb.2021.413527
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Transparent thermoelectric properties of copper iodide thin films
Vora-ud, Athorn; Chaarmart, Kongphope; Kasemsin, Wassana; Boonkirdram, Sarawoot; Seetawan, Tosawat
Physica B: Condensed Matter (Amsterdam, Netherlands) (2022), 625 (), 413527CODEN: PHYBE3; ISSN:0921-4526. (Elsevier B.V.)
Copper Iodide (CuI) transparent thin films were synthesized by using the as-deposited Cu thin film dip in the Iodine (I2) soln. (1% per 100 cc.) for 15s, 30s, and 60s within the liq. iodination method. The as-deposited Cu thin films on glass slide substrates as used were prepd. by a dc magnetron sputtering method from the Cu target. The microstructure, morphol., and thermoelec. properties were studied by using X-ray diffraction (XRD) techniques, SEM (SEM), and the ZEM-3 method, resp. The optical property of the film samples was detd. from measured transmittance using a UV-visible spectrophotometer. The optical bandgap energy is 3.0 eV and the transmittance is around 80-95% for the thin film as dipped 30s. At room temp., the power factor of Cul thin films were 14.71, 17.49, and 17.48μW m-1 K-2 for as dipped 15s, 30s, and 60s, resp.
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Choi, C.-H.; Gorecki, J. Y.; Fang, Z.; Allen, M.; Li, S.; Lin, L.-Y.; Cheng, C.-C.; Chang, C.-H. Low-temperature, inkjet printed p-type copper(I) iodide thin film transistors. J. Mater. Chem. C 2016, 4, 10309– 10314, DOI: 10.1039/C6TC03234F
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Low-temperature, inkjet printed p-type copper(I) iodide thin film transistors
Choi, Chang-Ho; Gorecki, Jenna Y.; Fang, Zhen; Allen, Marshall; Li, Shujie; Lin, Liang-Yu; Cheng, Chun-Cheng; Chang, Chih-Hung
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (43), 10309-10314CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
Low temp. fabrication of printed p-type CuI TFTs was reported for the first time. The printed CuI film was fabricated by printing mol. CuI ink directly onto the device substrate followed by immediate crystn. of CuI nanoparticles as the solvent evapd. The substrate temp. during inkjet printing was varied in order to obtain continuous CuI films with large grain size for improved device performance. The CuI TFTs printed at 60 °C exhibited an av. field-effect mobility of 1.86 ± 1.6 cm2 V-1 s-1, with the max. value of 4.4 cm2 V-1 s-1 and an av. On/Off ratio of 101-102. This study demonstrates potential low temp., directly printed p-type TFTs for constructing transparent, complementary inorg. TFT circuits.
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Storm, P.; Bar, M. S.; Benndorf, G.; Selle, S.; Yang, C.; von Wenckstern, H.; Grundmann, M.; Lorenz, M. High mobility, highly transparent, smooth, p-type CuI thin films grown by pulsed laser deposition. APL Mater. 2020, 8, 091115, DOI: 10.1063/5.0021781
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High mobility, highly transparent, smooth, p-type CuI thin films grown by pulsed laser deposition
Storm, P.; Bar, M. S.; Benndorf, G.; Selle, S.; Yang, C.; von Wenckstern, H.; Grundmann, M.; Lorenz, M.
APL Materials (2020), 8 (9), 091115CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
We report pulsed laser deposition being a quite suitable growth method for smooth and transparent p-type copper iodide (CuI) thin films with tailored elec. properties. The film characteristics are strongly influenced by the temp. during growth. Increasing substrate temps. result in significant improvements in crystallinity compared to deposition at room temp. In contrast to other growth techniques, the hole carrier d. p can be varied systematically between 5 x 1016 cm-3 and 1 x 1019 cm-3 with hole mobilities up to 20 cm2/V s for lowest p. The surfaces exhibit irregularly shaped grains, and the roughness can be decreased down to 1 nm. Furthermore, the samples exhibit high transmittance up to 90% in the visible spectrum. (c) 2020 American Institute of Physics.
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Inagaki, S.; Nakamura, M.; Aizawa, N.; Peng, L. C.; Yu, X. Z.; Tokura, Y.; Kawasaki, M. Molecular beam epitaxy of high-quality CuI thin films on a low temperature grown buffer layer. Appl. Phys. Lett. 2020, 116, 192105, DOI: 10.1063/5.0007389
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Molecular beam epitaxy of high-quality CuI thin films on a low temperature grown buffer layer
Inagaki, S.; Nakamura, M.; Aizawa, N.; Peng, L. C.; Yu, X. Z.; Tokura, Y.; Kawasaki, M.
Applied Physics Letters (2020), 116 (19), 192105CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
The authors show a growth of high-quality thin films of a wide band gap semiconductor copper iodide (CuI) on Al2O3 substrates by mol. beam epitaxy. Employing a thin buffer layer deposited at a lower temp. (160°C) prior to the main growth, the max. growth temp. is elevated up to 240°C, resulting in a significant improvement in the crystallinity as verified by sharp x-ray diffraction peaks as well as a step-and-terrace structure obsd. by at. force microscopy. Optimum films show more intense free exciton emission in photoluminescence spectra than others, implying the suppression of defects. These results indicate that the fabrication process developed in this study is quite effective at realizing high-quality CuI thin films. (c) 2020 American Institute of Physics.
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Storm, P.; Bar, M. S.; Selle, S.; von Wenckstern, H.; Grundmann, M.; Lorenz, M. p-Type Doping and Alloying of CuI Thin Films with Selenium. Phys. Status Solidi RRL 2021, 15, 2100214, DOI: 10.1002/pssr.202100214
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p-Type Doping and Alloying of CuI Thin Films with Selenium
Storm, Philipp; Bar, Michael Sebastian; Selle, Susanne; von Wenckstern, Holger; Grundmann, Marius; Lorenz, Michael
Physica Status Solidi RRL: Rapid Research Letters (2021), 15 (8), 2100214CODEN: PSSRCS; ISSN:1862-6254. (Wiley-VCH Verlag GmbH & Co. KGaA)
The impact of the intentional selenium doping of CuI thin films is investigated concerning crucial cryst., elec. and optical properties. For selenium contents in between x(Se)= 0.1 at.% and x(Se)= 1 at.%, the carrier d. can be systematically adjusted by the selenium supply during growth between p=1015 cm-3 and p=8x1017 cm-3 while transparency and crystallinity remain unaffected. By temp.-dependent Hall-effect measurements, a carrier freeze out is obsd. and the binding energy of the selenium dopant is detd. The long-term elec. stability in combination with Al2O3 cappings is significantly improved compared to undoped or oxygen doped CuI. However, for selenium contents exceeding x(Se)= 1 at.%, major cryst. changes are obsd. that are presumably correlated to a phase transformation. Transmission and elec. measurements suggest that the soly. limit of Se in CuI is about 1 at.% since a degrdn. of the transparency and decreasing free hole densities are obsd. for Se contents exceeding 1 at.%. Hence, the doping limit for Se in CuI corresponds to ≈1 at.%.
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Chen, D.; Wang, Y.; Lin, Z.; Huang, J.; Chen, X.; Pan, D.; Huang, F. Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal. Cryst. Growth Des. 2010, 10, 2057– 2060, DOI: 10.1021/cg100270d
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Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal
Chen, Dagui; Wang, Yongjing; Lin, Zhang; Huang, Jiakui; Chen, Xian Zhi; Pan, Danmei; Huang, Feng
Crystal Growth & Design (2010), 10 (5), 2057-2060CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
Acquiring stable binary wide band-gap semiconductor (WBS) materials with high p-type mobility is essential for the development of WBS optoelectronic devices. CuI is a p-type WBS material with a large band gap (3.1 eV) and high exciton binding energy (62 meV). However, the semiconductor characteristics of the CuI single crystal are unknown due to the lack of a large sized and high quality crystal. Our approach focuses on the design of the mineralizer for the hydrothermal method to effectively control the growth habit and the impurity concn. in the crystal. A large size (15 mm × 10 mm × 1 mm) and high quality CuI single crystal is obtained by using a new mineralizer (NH4I + KI). The crystal shows high p-type mobility (43.9 cm2·V-1·S1-). The strong and sharp band-edge emission at 410 nm indicates that the interband excitonic transition dominates the optical response in the spectrum. Such a binary cryst. material may open the way to new applications in optoelectronic devices.
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Lv, Y.; Xu, Z.; Ye, L.; Zhang, Z.; Su, G.; Zhuang, X. Large CuI semiconductor single crystal growth by a temperature reduction method from an NH₄I aqueous solution. CrystEngComm 2015, 17, 862– 867, DOI: 10.1039/C4CE02045F
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Large γ-CuI semiconductor single crystal growth by a temperature reduction method from an NH4I aqueous solution
Lv, Yangyang; Xu, Zhihuang; Ye, Liwang; Zhang, Zhaojun; Su, Genbo; Zhuang, Xinxin
CrystEngComm (2015), 17 (4), 862-867CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
NH4I has been proven to be a promising cosolvent for cuprous iodide (CuI) single crystal growth from aq. solns. by the temp. redn. method. In our work, as compared with NH4Cl and NH4Br, NH4I offers more advantages for single crystal growth, such as by remarkably increasing the soly. and growth rate of CuI crystals, effectively reducing the impurity concn., and enhancing the crystal quality and crystallinity. A regular, centimeter-sized, high optical quality single crystal was successfully obtained using NH4I as a cosolvent. The electronic and optical properties of the as-grown crystal were characterized by Hall-effect measurements and optical transmission and photoluminescence spectra, resp. The results demonstrated that the CuI crystal is conductive (high p-type mobility of 12.81 cm2 V-1 s-1) and transparent (great transmittance over 80%).
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Liu, A.; Zhu, H.; Park, W.-T.; Kim, S.-J.; Kim, H.; Kim, M.-G.; Noh, Y.-Y. High-performance p-channel transistors with transparent Zn doped-CuI. Nat. Commun. 2020, 11, 4309, DOI: 10.1038/s41467-020-18006-6
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High-performance p-channel transistors with transparent Zn doped-CuI
Liu, Ao; Zhu, Huihui; Park, Won-Tae; Kim, Se-Jun; Kim, Hyungjun; Kim, Myung-Gil; Noh, Yong-Young
Nature Communications (2020), 11 (1), 4309CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
'Ideal' transparent p-type semiconductors are required for the integration of high-performance thin-film transistors (TFTs) and circuits. Although CuI has recently attracted attention owing to its excellent opto-elec. properties, soln. processability, and low-temp. synthesis, the uncontrolled copper vacancy generation and subsequent excessive hole doping hinder its use as a semiconductor material in TFT devices. In this study, we propose a doping approach through soft chem. soln. process and transparent p-type Zn-doped CuI semiconductor for high-performance TFTs and circuits. The optimized TFTs annealed at 80°C exhibit a high hole mobility of over 5 cm2 V-1 s-1 and high on/off current ratio of ~ 10-7 with good operational stability and reproducibility. The CuI:Zn semiconductors show intrinsic advantages for next-generation TFT applications and wider applications in optoelectronics and energy conversion/storage devices. This study paves the way for the realization of transparent, flexible, and large-area integrated circuits combined with n-type metal-oxide semiconductor.
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He, T.; Zhou, Y.; Yuan, P.; Yin, J.; Gutiérrez-Arzaluz, L.; Chen, S.; Wang, J.-X.; Thomas, S.; Alshareef, H. N.; Bakr, O. M.; Mohammed, O. F. Copper Iodide Inks for High-Resolution X-ray Imaging Screens. ACS Energy Lett. 2023, 8, 1362– 1370, DOI: 10.1021/acsenergylett.3c00097
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Copper Iodide Inks for High-Resolution X-ray Imaging Screens
He, Tengyue; Zhou, Yang; Yuan, Peng; Yin, Jun; Gutierrez-Arzaluz, Luis; Chen, Shulin; Wang, Jian-Xin; Thomas, Simil; Alshareef, Husam N.; Bakr, Osman M.; Mohammed, Omar F.
ACS Energy Letters (2023), 8 (3), 1362-1370CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
Cu-based halide scintillators have attracted considerable interest because of their high light yields, low detection limits, low toxicity, and moderate fabrication conditions. Here, the authors synthesized two Cu(I) iodide inks, comprising zero-dimensional Cu4I6(L1)2 nanoparticles (L1 = 1-propyl-1,4-diazabicyclo[2.2.2]octan-1-ium) and 1-dimensional Cu4I6(L2)2 nanorods (L2 = 4-dimethylamino-1-ethylpyridinium) for x-ray imaging application. The Cu4I6(L1)2 nanoparticles and Cu4I6(L2)2 nanorods exhibited broadband green and yellow emission with an ultrahigh photoluminescence quantum yield of 95.3% and 92.2%, resp. Consequently, the two Cu(I) iodide ink-based x-ray screens exhibited low detection limits of 96.4 and 102.1 nGy s-1, resp., which are ∼55 times lower than the dose required for std. medical diagnosis (5.5 μGy s-1). Importantly, both the scintillation screens exhibited extraordinary x-ray imaging resolns. exceeding 30 lp mm-1, more than double those of the conventional CsI:Tl and Ga2O2S:Tb scintillators. This study provides a new avenue for exploring high-resoln. x-ray imaging screens from Cu-based halide ink for medical radiog. and nondestructive detection.
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Schein, F.-L.; von Wenckstern, H.; Grundmann, M. Transparent p-CuI/n-ZnO heterojunction diodes. Appl. Phys. Lett. 2013, 102, 092109, DOI: 10.1063/1.4794532
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Transparent p-CuI/n-ZnO heterojunction diodes
Schein, Friedrich-Leonhard; von Wenckstern, Holger; Grundmann, Marius
Applied Physics Letters (2013), 102 (9), 092109/1-092109/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
Transparent and elec. conducting p-type CuI thin-films form highly rectifying p-CuI/n-ZnO diodes. Sputtered Cu thin films on glass were transformed into polycryst. γ-CuI by exposing them to I vapor. The elec. parameters extd. from Hall effect are p = 5 × 1018 cm-3, μh,Hall = 6 cm2/Vs, and ρ = 0.2 Ω cm for hole concn., mobility, and elec. resistivity, resp. Heterostructures consisting of p-CuI and pulsed-laser deposited n-ZnO were fabricated on a-plane sapphire substrates. The p-CuI/n-ZnO diode exhibits a current rectification ratio of 6 × 106 at ±2 V and an ideality factor of η = 2.14. (c) 2013 American Institute of Physics.
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Annadi, A.; Zhang, N.; Boon Kiang Lim, D.; Gong, H. New Transparent Magnetic Semiconductor Ni_xCu_1–xI which Can Perform as Either P-type or N-type and Success in the P–N Homojunction Diode. ACS Appl. Mater. Interfaces 2020, 12, 6048– 6055, DOI: 10.1021/acsami.9b19550
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New Transparent Magnetic Semiconductor NixCu1-xI which Can Perform as Either P-type or N-type and Success in the P-N Homojunction Diode
Annadi, Anil; Zhang, Nengduo; Boon Kiang Lim, David; Gong, Hao
ACS Applied Materials & Interfaces (2020), 12 (5), 6048-6055CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
A semiconductor that can be doped to be either p-type or n-type is of great importance, as p-n homojunctions are desirable for realizing various electronic devices and processes. However, because of pervasive doping asymmetry for wide band gap semiconductors, the achievement of both p-type and n-type in a single wide gap material is very difficult. Here, the authors report the success in developing a new transparent magnetic NixCu1-xI halide semiconductor that can be either p-type or n-type depending on Ni fraction in NixCu1-xI. For 0 ≤ x ≤ 0.10, NixCu1-xI films show p-type cond. For the range 0.15 ≤ x ≤ 0.35, NixCu1-xI films show an n-type character. The NixCu1-xI films are elec. conducting and optically transparent and show soft ferromagnetic behavior with an optimum cond. of 42 S cm-1 (x = 0.03) and visible light transmission of 80%. UPS studies on NixCu1-xI films reveal the systematic Fermi level shift toward the conduction band with respect to the valence band as a function Ni concn. XPS anal. on Ni and I peak positions reveals Ni+2 valence for Ni in NixCu1-xI films, with signatures of Ni-I bonding. The obsd. p-type behavior originates from Cu vacancy, while the n-type character is identified to originate from the electron donor states generated by Ni incorporation in NixCu1-xI. The constructed homojunction with p-Ni0.0Cu1.0I/n-Ni0.16Cu0.84I shows a characteristic p-n junction behavior with a good rectification ratio of 2 × 102. This new type of NixCu1-xI transparent semiconductor with a tunable carrier type and magnetism may be a candidate for halide-based optoelectronic as well as spintronics development.
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Lee, J. H.; Lee, W.-J.; Kim, T. H.; Lee, T.; Hong, S.; Kim, K. H. Transparent p-CuI/n-BaSnO₃- δ heterojunctions with a high rectification ratio. J. Phys.: Condens. Matter 2017, 29, 384004, DOI: 10.1088/1361-648X/aa7cbf
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Transparent p-CuI/n-BaSnO3-δ heterojunctions with a high rectification ratio
Lee, Jeong Hyuk; Lee, Woong-Jhae; Kim, Tai Hoon; Lee, Takhee; Hong, Seunghun; Kim, Kee Hoon
Journal of Physics: Condensed Matter (2017), 29 (38), 384004/1-384004/8CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
Transparent p-CuI/n-BaSnO3-δ heterojunction diodes were successfully fabricated by the thermal evapn. of a (1 1 1) oriented γ-phase CuI film on top of an epitaxial BaSnO3-δ(0 0 1) film grown by the pulsed laser deposition. Upon the thickness of the CuI film being increased from 30 to 400 nm, the hole carrier d. was systematically reduced from 6.0 × 1019 to 1.0 × 1019 cm-3 and the corresponding rectification ratio of the pn diode was proportionally enhanced from ∼10 to ∼106. An energy band diagram exhibiting the type-II band alignment is proposed to describe the behavior of the heterojunction diode. A shift of a built-in potential caused by the hole carrier d. change in the CuI film is attributed to the thickness-dependent rectification ratio. The best performing p-CuI/n-BaSnO3-δ diode exhibited a high current rectification ratio of 6.75 × 105 at ±2 V and an ideality factor of ∼1.5.
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Ding, K.; Hu, Q.; Chen, D.; Zheng, Q.; Xue, X.; Huang, F. Fabrication and energy band alignment of n-ZnO/p-CuI heterojunction. IEEE Electron Device Lett. 2012, 33, 1750– 1752, DOI: 10.1109/LED.2012.2218274
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Fabrication and energy band alignment of n-ZnO/p-CuI heterojunction
Ding, K.; Hu, Q. C.; Chen, D. G.; Zheng, Q. H.; Xue, X. G.; Huang, F.
IEEE Electron Device Letters (2012), 33 (12), 1750-1752CODEN: EDLEDZ; ISSN:0741-3106. (Institute of Electrical and Electronics Engineers)
N-ZnO/P-CuI heterojunctions are fabricated by growing undoped n-type ZnO thin films on p-type γ-CuI (111) single-crystal substrates using radio-frequency magnetron sputtering. The ZnO films are identified to be columnar structured with c-axis-preferred orientation by using X-ray diffraction and scanning electron microscope. Measurements of the energy band alignment of ZnO/CuI interface by using XPS result in a valence band offset of 1.74 eV and a conduction band offset of -1.37 eV, meaning a type-II band alignment at the interface. A typical diodelike behavior of the current-voltage curve indicates its possible applications in optoelectronics with further development.
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Cha, J.-H.; Jung, D.-Y. Air-stable transparent silver iodide–copper iodide heterojunction diode. ACS Appl. Mater. Interfaces 2017, 9, 43807– 43813, DOI: 10.1021/acsami.7b14378
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Air-Stable Transparent Silver Iodide-Copper Iodide Heterojunction Diode
Cha, Ji-Hyun; Jung, Duk-Young
ACS Applied Materials & Interfaces (2017), 9 (50), 43807-43813CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
Transparent AgI-CuI heterojunctions with high rectifying diode behavior were prepd. via vapor-phase iodization of metal thin films on transparent conducting oxide substrates. At room temp., Ag and Cu metal thin films were quickly transformed into the transparent and well-crystd. β-phase of AgI and the γ-phase of CuI, resp. The AgI and CuI films exhibited n-type and p-type semiconductor properties, resp., with wide band gaps. The heterojunctions were obtained by applying the CuI film to the AgI film in a sequential iodization process. AgI compds. generally have poor air-stability under light, making them suboptimal for use in electronic applications. Here, we used a CuI top layer to inhibit the photodecompn. of the AgI bottom layer, resulting in an air-stable and smooth AgI-CuI film. We also propose a simple patterning method for the AgI-CuI layer using selective decompn. of AgI without the need for lithog. equipment or toxic chems. Although there is metal ion exchange between the two layers, each layer has a different chem. compn. and crystal structure; therefore, the AgI-CuI heterojunction exhibits pn-diode behavior with a rectifying ratio of 9.4 × 104, which is comparable to that of other transparent pn-diodes. These findings open a new path for electronic application of AgI materials.
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Yang, C.; Kneiß, M.; Schein, F.-L.; Lorenz, M.; Grundmann, M. Room-temperature domain-epitaxy of copper iodide thin films for transparent CuI/ZnO heterojunctions with high rectification ratios larger than 109. Sci. Rep. 2016, 6, 21937, DOI: 10.1038/srep21937
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Room-temperature Domain-epitaxy of Copper Iodide Thin Films for Transparent CuI/ZnO Heterojunctions with High Rectification Ratios Larger than 109
Yang, Chang; Kneiss, Max; Schein, Friedrich-Leonhard; Lorenz, Michael; Grundmann, Marius
Scientific Reports (2016), 6 (), 21937CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
CuI is a p-type transparent conductive semiconductor with unique optoelectronic properties, including wide band gap (3.1 eV), high hole mobility (>40 cm2 V-1 s-1 in bulk), and large room-temp. exciton binding energy (62 meV). The difficulty in epitaxy of CuI is the main obstacle for its application in advanced solid-state electronic devices. Herein, room-temp. heteroepitaxial growth of CuI on various substrates with well-defined in-plane epitaxial relations is realized by reactive sputtering technique. In such heteroepitaxial growth the formation of rotation domains is obsd. and hereby systematically investigated in accordance with existing theor. study of domain-epitaxy. The controllable epitaxy of CuI thin films allows for the combination of p-type CuI with suitable n-type semiconductors with the purpose to fabricate epitaxial thin film heterojunctions. Such heterostructures have superior properties to structures without or with weakly ordered in-plane orientation. The obtained epitaxial thin film heterojunction of p-CuI(111)/n-ZnO(00.1) exhibits a high rectification up to 2 × 109 (±2 V), a 100-fold improvement compared to diodes with disordered interfaces. Also a low satn. c.d. down to 5 × 10-9 Acm-2 is formed. These results prove the great potential of epitaxial CuI as a promising p-type optoelectronic material.
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Liu, A.; Zhu, H.; Kim, M.-G.; Kim, J.; Noh, Y.-Y. Engineering copper iodide (CuI) for multifunctional p-type transparent semiconductors and conductors. Advanced Science 2021, 8, 2100546, DOI: 10.1002/advs.202100546
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Engineering Copper Iodide (CuI) for Multifunctional p-Type Transparent Semiconductors and Conductors
Liu, Ao; Zhu, Huihui; Kim, Myung-Gil; Kim, Junghwan; Noh, Yong-Young
Advanced Science (Weinheim, Germany) (2021), 8 (14), 2100546CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Developing transparent p-type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n-type characteristics at room temp. Among the different candidates, copper iodide (CuI) is one of the most promising p-type materials because of its widely adjustable cond. from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region using various low-temp. deposition techniques. This progress report aims to provide a basic understanding of CuI-based materials and recent progress in the development of various devices. The first section provides a brief introduction to CuI with respect to electronic structure, defect states, charge transport physics, and overviews the CuI film deposition methods. The material design concepts through doping/alloying approaches to adjust the optoelec. properties are also discussed in the first section. The following section presents recent advances in state-of-the-art CuI-based devices, including transparent electrodes, thermoelec. devices, p-n diodes, p-channel transistors, light emitting diodes, and solar cells. In conclusion, current challenges and perspective opportunities are highlighted.
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Kresse, G.; Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B 1993, 47, 558– 561, DOI: 10.1103/PhysRevB.47.558
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Ab initio molecular dynamics of liquid metals
Kresse, G.; Hafner, J.
Physical Review B: Condensed Matter and Materials Physics (1993), 47 (1), 558-61CODEN: PRBMDO; ISSN:0163-1829.
The authors present ab initio quantum-mech. mol.-dynamics calcns. based on the calcn. of the electronic ground state and of the Hellmann-Feynman forces in the local-d. approxn. at each mol.-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using sub-space alignment. This approach avoids the instabilities inherent in quantum-mech. mol.-dynamics calcns. for metals based on the use of a factitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows one to perform simulations over several picoseconds.
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Kresse, G.; Hafner, J. Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Phys. Rev. B 1994, 49, 14251– 14269, DOI: 10.1103/PhysRevB.49.14251
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Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium
Kresse, G.; Hafner, J.
Physical Review B: Condensed Matter and Materials Physics (1994), 49 (20), 14251-69CODEN: PRBMDO; ISSN:0163-1829.
The authors present ab initio quantum-mech. mol.-dynamics simulations of the liq.-metal-amorphous-semiconductor transition in Ge. The simulations are based on (a) finite-temp. d.-functional theory of the 1-electron states, (b) exact energy minimization and hence calcn. of the exact Hellmann-Feynman forces after each mol.-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nose' dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows the authors to perform simulations over >30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liq. and amorphous Ge in very good agreement with expt.. The simulation allows the authors to study in detail the changes in the structure-property relation through the metal-semiconductor transition. The authors report a detailed anal. of the local structural properties and their changes induced by an annealing process. The geometrical, bounding, and spectral properties of defects in the disordered tetrahedral network are studied and compared with expt.
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Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.17953
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Projector augmented-wave method
Blochl
Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
There is no expanded citation for this reference.
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Kresse, G.; Hafner, J. Norm-conserving and ultrasoft pseudopotentials for first-row and transition elements. J. Phys.: Condens. Matter 1994, 6, 8245– 8257, DOI: 10.1088/0953-8984/6/40/015
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Norm-conserving and ultrasoft pseudopotentials for first-row and transition elements
Kresse, G.; Hafner, J.
Journal of Physics: Condensed Matter (1994), 6 (40), 8245-57CODEN: JCOMEL; ISSN:0953-8984.
The construction of accurate pseudopotentials with good convergence properties for the first-row and transition elements is discussed. By combining an improved description of the pseudo-wavefunction inside the cut-off radius with the concept of ultrasoft pseudopotentials introduced by Vanderbilt optimal compromise between transferability and plane-wave convergence can be achieved. With the new pseudopotentials, basis sets with no more than 75-100 plane waves per atom are sufficient to reproduce the results obtained with the most accurate norm-conserving pseudopotentials.
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Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 15– 50, DOI: 10.1016/0927-0256(96)00008-0
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Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
Kresse, G.; Furthmuller, J.
Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)
The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
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Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab inition total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169– 11186, DOI: 10.1103/PhysRevB.54.11169
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Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
Kresse, G.; Furthmueller, J.
Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
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Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 1758– 1775, DOI: 10.1103/PhysRevB.59.1758
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From ultrasoft pseudopotentials to the projector augmented-wave method
Kresse, G.; Joubert, D.
Physical Review B: Condensed Matter and Materials Physics (1999), 59 (3), 1758-1775CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived. The total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addn., crit. tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed-core all-electron methods. These tests include small mols. (H2, H2O, Li2, N2, F2, BF3, SiF4) and several bulk systems (diamond, Si, V, Li, Ca, CaF2, Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
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Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.; Constantin, L. A.; Zhou, X.; Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Phys. Rev. Lett. 2008, 100, 136406, DOI: 10.1103/PhysRevLett.100.136406
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Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces
Perdew, John P.; Ruzsinszky, Adrienn; Csonka, Gabor I.; Vydrov, Oleg A.; Scuseria, Gustavo E.; Constantin, Lucian A.; Zhou, Xiaolan; Burke, Kieron
Physical Review Letters (2008), 100 (13), 136406/1-136406/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
Popular modern generalized gradient approxns. are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of d. gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approxn. that improves equil. properties of densely packed solids and their surfaces.
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Perdew, J. P.; Ernzerhof, M.; Burke, K. Rationale for mixing exact exchange with density functional approximations. J. Chem. Phys. 1996, 105, 9982– 9985, DOI: 10.1063/1.472933
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Rationale for mixing exact exchange with density functional approximations
Perdew, John P.; Ernzerhof, Matthias; Burke, Kieron
Journal of Chemical Physics (1996), 105 (22), 9982-9985CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
D. functional approxns. for the exchange-correlation energy ExcDFA of an electronic system are often improved by admixing some exact exchange Ex: Exc ≈ ExcDFA + (1/n)(Ex - ExDFA). This procedure is justified when the error in ExcDFA arises from the λ = 0 or exchange end of the coupling-const. integral ∫01dλ Exc,λDFA. We argue that the optimum integer n is approx. the lowest order of Goerling-Levy perturbation theory which provides a realistic description of the coupling-const. dependence Exc,λ in the range 0 ≤ λ ≤ 1, whence n ≈ 4 for atomization energies of typical mols. We also propose a continuous generalization of n as an index of correlation strength, and a possible mixing of second-order perturbation theory with the generalized gradient approxn.
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Gonze, X.; Amadon, B.; Antonius, G.; Arnardi, F.; Baguet, L.; Beuken, J.-M.; Bieder, J.; Bottin, F.; Bouchet, J.; Bousquet, E. The ABINIT project: Impact, environment and recent developments. Comput. Phys. Commun. 2020, 248, 107042, DOI: 10.1016/j.cpc.2019.107042
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The ABINIT project: Impact, environment and recent developments
Gonze, Xavier; Amadon, Bernard; Antonius, Gabriel; Arnardi, Frederic; Baguet, Lucas; Beuken, Jean-Michel; Bieder, Jordan; Bottin, Francois; Bouchet, Johann; Bousquet, Eric; Brouwer, Nils; Bruneval, Fabien; Brunin, Guillaume; Cavignac, Theo; Charraud, Jean-Baptiste; Chen, Wei; Cote, Michel; Cottenier, Stefaan; Denier, Jules; Geneste, Gregory; Ghosez, Philippe; Giantomassi, Matteo; Gillet, Yannick; Gingras, Olivier; Hamann, Donald R.; Hautier, Geoffroy; He, Xu; Helbig, Nicole; Holzwarth, Natalie; Jia, Yongchao; Jollet, Francois; Lafargue-Dit-Hauret, William; Lejaeghere, Kurt; Marques, Miguel A. L.; Martin, Alexandre; Martins, Cyril; Miranda, Henrique P. C.; Naccarato, Francesco; Persson, Kristin; Petretto, Guido; Planes, Valentin; Pouillon, Yann; Prokhorenko, Sergei; Ricci, Fabio; Rignanese, Gian-Marco; Romero, Aldo H.; Schmitt, Michael Marcus; Torrent, Marc; van Setten, Michiel J.; Van Troeye, Benoit; Verstraete, Matthieu J.; Zerah, Gilles; Zwanziger, Josef W.
Computer Physics Communications (2020), 248 (), 107042CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
A review. ABINIT is a material- and nanostructure-oriented package that implements d.-functional theory (DFT) and many-body perturbation theory (MBPT) to find, from first principles, numerous properties including total energy, electronic structure, vibrational and thermodn. properties, different dielec. and non-linear optical properties, and related spectra. In the special issue to celebrate the 40th anniversary of CPC, published in 2009, a detailed account of ABINIT was included, and has been amply cited. The present article comes as a follow-up to this 2009 publication. It includes an anal. of the impact that ABINIT has had, through for example the bibliometric indicators of the 2009 publication. Links with several other computational materials science projects are described. This article also covers the new capabilities of ABINIT that have been implemented during the last three years, complementing a recent update of the 2009 article published in 2016. Phys. and tech. developments inside the abinit application are covered, as well as developments provided with the ABINIT package, such as the MULTIBINIT and A-TDEP projects, and related ABINIT organization developments such as ABIPY. The new developments are described with relevant refs., input variables, tests, and tutorials.
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Romero, A. H.; Allan, D. C.; Amadon, B.; Antonius, G.; Applencourt, T.; Baguet, L.; Bieder, J.; Bottin, F.; Bouchet, J.; Bousquet, E. ABINIT: Overview and focus on selected capabilities. J. Chem. Phys. 2020, 152, 124102, DOI: 10.1063/1.5144261
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ABINIT: Overview and focus on selected capabilities
Romero, Aldo H.; Allan, Douglas C.; Amadon, Bernard; Antonius, Gabriel; Applencourt, Thomas; Baguet, Lucas; Bieder, Jordan; Bottin, Francois; Bouchet, Johann; Bousquet, Eric; Bruneval, Fabien; Brunin, Guillaume; Caliste, Damien; Cote, Michel; Denier, Jules; Dreyer, Cyrus; Ghosez, Philippe; Giantomassi, Matteo; Gillet, Yannick; Gingras, Olivier; Hamann, Donald R.; Hautier, Geoffroy; Jollet, Francois; Jomard, Gerald; Martin, Alexandre; Miranda, Henrique P. C.; Naccarato, Francesco; Petretto, Guido; Pike, Nicholas A.; Planes, Valentin; Prokhorenko, Sergei; Rangel, Tonatiuh; Ricci, Fabio; Rignanese, Gian-Marco; Royo, Miquel; Stengel, Massimiliano; Torrent, Marc; van Setten, Michiel J.; Van Troeye, Benoit; Verstraete, Matthieu J.; Wiktor, Julia; Zwanziger, Josef W.; Gonze, Xavier
Journal of Chemical Physics (2020), 152 (12), 124102CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
ABINIT Is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements d. functional theory, d.-functional perturbation theory (DFPT), many-body perturbation theory (GW approxn. and Bethe-Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the "temp.-dependent effective potential" approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, d., and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and mols. can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the assocd. capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite elec. fields; properties at nuclei (elec. field gradient, Mossbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calcns. of response to strain perturbation (elastic consts. and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temp. dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calcns. (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library LIBPAW. ABINIT has strong links with many other software projects that are briefly mentioned. (c) 2020 American Institute of Physics.
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Brunin, G.; Miranda, H. P. C.; Giantomassi, M.; Royo, M.; Stengel, M.; Verstraete, M. J.; Gonze, X.; Rignanese, G.-M.; Hautier, G. Electron-phonon beyond Fröhlich: dynamical quadrupoles in polar and covalent solids. Phys. Rev. Lett. 2020, 125, 136601, DOI: 10.1103/PhysRevLett.125.136601
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Electron-Phonon beyond Frohlich: Dynamical Quadrupoles in Polar and Covalent Solids
Brunin, Guillaume; Miranda, Henrique Pereira Coutada; Giantomassi, Matteo; Royo, Miquel; Stengel, Massimiliano; Verstraete, Matthieu J.; Gonze, Xavier; Rignanese, Gian-Marco; Hautier, Geoffroy
Physical Review Letters (2020), 125 (13), 136601CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
We include the treatment of quadrupolar fields beyond the Frohlich interaction in the first-principles electron-phonon vertex in semiconductors. Such quadrupolar fields induce long-range interactions that have to be taken into account for accurate phys. results. We apply our formalism to Si (nonpolar), GaAs, and GaP (polar) and demonstrate that electron mobilities show large errors if dynamical quadrupoles are not properly treated.
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Brunin, G.; Miranda, H. P. C.; Giantomassi, M.; Royo, M.; Stengel, M.; Verstraete, M. J.; Gonze, X.; Rignanese, G.-M.; Hautier, G. Phonon-limited electron mobility in Si, GaAs, and GaP with exact treatment of dynamical quadrupoles. Phys. Rev. B 2020, 102, 094308, DOI: 10.1103/PhysRevB.102.094308
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Phonon-limited electron mobility in Si, GaAs, and GaP with exact treatment of dynamical quadrupoles
Brunin, Guillaume; Miranda, Henrique Pereira Coutada; Giantomassi, Matteo; Royo, Miquel; Stengel, Massimiliano; Verstraete, Matthieu J.; Gonze, Xavier; Rignanese, Gian-Marco; Hautier, Geoffroy
Physical Review B (2020), 102 (9), 094308CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
We describe a new approach to compute the electron-phonon self-energy and carrier mobilities in semiconductors. Our implementation does not require a localized basis set to interpolate the electron-phonon matrix elements, with the advantage that computations can be easily automated. Scattering potentials are interpolated on dense q meshes using Fourier transforms and ab initio models to describe the long-range potentials generated by dipoles and quadrupoles. To reduce significantly the computational cost, we take advantage of crystal symmetries and employ the linear tetrahedron method and double-grid integration schemes, in conjunction with filtering techniques in the Brillouin zone. We report results for the electron mobility in Si, GaAs, and GaP obtained with this new methodol.
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Claes, R.; Brunin, G.; Giantomassi, M.; Rignanese, G.-M.; Hautier, G. Assessing the quality of relaxation-time approximations with fully automated computations of phonon-limited mobilities. Phys. Rev. B 2022, 106, 094302, DOI: 10.1103/PhysRevB.106.094302
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Assessing the quality of relaxation-time approximations with fully automated computations of phonon-limited mobilities
Claes, Romain; Brunin, Guillaume; Giantomassi, Matteo; Rignanese, Gian-Marco; Hautier, Geoffroy
Physical Review B (2022), 106 (9), 094302CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
The mobility of carriers, as limited by their scattering with phonons, can now routinely be obtained from first-principles electron-phonon coupling calcns. However, so far, most computations have relied on some form of simplification of the linearized Boltzmann transport equation based on either the self-energy or the momentum relaxation-time or const. relaxation-time approxns. Here, we develop a high-throughput infrastructure and an automatic workflow and we compute 67 phonon-limited mobilities in semiconductors. We compare the results resorting to the approxns. with the exact iterative soln. We conclude that the approx. values may deviate significantly from the exact ones and are thus not reliable. Given the minimal computational overhead, our paper encourages reliance on this exact iterative soln.
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M Ganose, A.; J Jackson, A.; O Scanlon, D. sumo: Command-line tools for plotting and analysis of periodic ab initio calculations. J. Open Source Softw. 2018, 3, 717, DOI: 10.21105/joss.00717
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Petretto, G.; Dwaraknath, S.; Miranda, H. P.; Winston, D.; Giantomassi, M.; Van Setten, M. J.; Gonze, X.; Persson, K. A.; Hautier, G.; Rignanese, G.-M. High-throughput density-functional perturbation theory phonons for inorganic materials. Sci. Data 2018, 5, 180065, DOI: 10.1038/sdata.2018.65
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High-throughput density-functional perturbation theory phonons for inorganic materials
Petretto, Guido; Dwaraknath, Shyam; Miranda, Henrique P. C.; Winston, Donald; Giantomassi, Matteo; van Setten, Michiel J.; Gonze, Xavier; Persson, Kristin A.; Hautier, Geoffroy; Rignanese, Gian-Marco
Scientific Data (2018), 5 (), 180065CODEN: SDCABS; ISSN:2052-4463. (Nature Research)
A review. The knowledge of the vibrational properties of a material is of key importance to understand phys. phenomena such as thermal cond., supercond., and ferroelectricity among others. However, detailed exptl. phonon spectra are available only for a limited no. of materials, which hinders the large-scale anal. of vibrational properties and their derived quantities. In this work, we perform ab initio calcns. of the full phonon dispersion and vibrational d. of states for 1521 semiconductor compds. in the harmonic approxn. based on d. functional perturbation theory. The data is collected along with derived dielec. and thermodn. properties. We present the procedure used to obtain the results, the details of the provided database and a validation based on the comparison with exptl. data.
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Graužinytė, M.; Botti, S.; Marques, M. A. L.; Goedecker, S.; Flores-Livas, J. A. Computational acceleration of prospective dopant discovery in cuprous iodide. Phys. Chem. Chem. Phys. 2019, 21, 18839– 18849, DOI: 10.1039/C9CP02711D
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Computational acceleration of prospective dopant discovery in cuprous iodide
Grauzinyte, Migle; Botti, Silvana; Marques, Miguel A. L.; Goedecker, Stefan; Flores-Livas, Jose A.
Physical Chemistry Chemical Physics (2019), 21 (35), 18839-18849CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
The zinc blende (γ) phase of copper iodide holds the record hole cond. for intrinsic transparent p-type semiconductors. In this work, we employ a high-throughput approach to systematically explore strategies for enhancing γ-CuI further by impurity incorporation. Our objectives are not only to find a practical approach to increase the hole cond. in CuI thin films, but also to explore the possibility for ambivalent doping. In total 64 chem. elements were investigated as possible substitutionals on either the copper or the iodine site. All chalcogen elements were found to display acceptor character when substituting iodine, with sulfur and selenium significantly enhancing carrier concns. produced by the native VCu defects under conditions most favorable for impurity incorporation. Furthermore, eight impurities suitable for n-type doping were discovered. Unfortunately, our work also reveals that donor doping is hindered by compensating native defects, making ambipolar doping unlikely. Finally, we investigated how the presence of impurities influences the optical properties. In the majority of the interesting cases, we found no deep states in the band-gap, showing that CuI remains transparent upon doping.
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Mosquera-Lois, I.; Kavanagh, S. R.; Walsh, A.; Scanlon, D. O. ShakeNBreak: Navigating the defect configurational landscape. J. Open Source Softw. 2022, 7, 4817, DOI: 10.21105/joss.04817
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Mosquera-Lois, I.; Kavanagh, S. R.; Walsh, A.; Scanlon, D. O. Identifying the ground state structures of point defects in solids. npj Comput. Mater. 2023, 9, 25, DOI: 10.1038/s41524-023-00973-1
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Identifying the ground state structures of point defects in solids
Mosquera-Lois, Irea; Kavanagh, Sean R.; Walsh, Aron; Scanlon, David O.
npj Computational Materials (2023), 9 (1), 25CODEN: NCMPCS; ISSN:2057-3960. (Nature Portfolio)
Point defects are a universal feature of crystals. Their identification is addressed by combining exptl. measurements with theor. models. The std. modeling approach is, however, prone to missing the ground state at. configurations assocd. with energy-lowering reconstructions from the idealised crystallog. environment. Missed ground states compromise the accuracy of calcd. properties. To address this issue, we report an approach to navigate the defect configurational landscape using targeted bond distortions and rattling. Application of our workflow to eight materials (CdTe, GaAs, Sb2S3, Sb2Se3, CeO2, In2O3, ZnO, anatase-TiO2) reveals symmetry breaking in each host crystal that is not found via conventional local minimisation techniques. The point defect distortions are classified by the assocd. physico-chem. factors. We demonstrate the impact of these defect distortions on derived properties, including formation energies, concns. and charge transition levels. Our work presents a step forward for quant. modeling of imperfect solids.
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Persson, C.; Zhao, Y.-J.; Lany, S.; Zunger, A. n-type doping of CuInSe₂ and CuGaSe₂. Phys. Rev. B 2005, 72, 035211, DOI: 10.1103/PhysRevB.72.035211
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n-type doping of CuInSe2 and CuGaSe2
Persson, Clas; Zhao, Yu-Jun; Lany, Stephan; Zunger, Alex
Physical Review B: Condensed Matter and Materials Physics (2005), 72 (3), 035211/1-035211/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
The efficiency of CuInSe2 based solar cell devices could improve significantly if CuGaSe2, a wider band gap chalcopyrite semiconductor, could be added to the CuInSe2 absorber layer. This is, however, limited by the difficulty of doping n-type CuGaSe2 and, hence, in its alloys with CuInSe2. Indeed, wider-gap members of semiconductor series are often more difficult to dope than lower-gap members of the same series. In chalcopyrites, there are 3 crit. values of the Fermi energy EF that control n-type doping: (i) EFn,pin is the value of EF where the energy to form Cu vacancies is zero. At this point, the spontaneously formed vacancies (=acceptors) kill all electrons. (ii) EFn,comp is the value of EF where the energy to form a Cu vacancy equals the energy to form an n-type dopant, e.g., CdCu. (iii) EFn,site is the value of EF where the formation of Cd-on-In is equal to the formation of Cd-on-Cu. For good n-type doping, EFn,pin, EFn,comp, and EFn,site need to be as high as possible in the gap. These quantities are higher in the gap in CuInSe2 than in CuGaSe2, so the latter is difficult to dope n-type. We calc. all 3 crit. Fermi energies and study theor. the best growth condition for n-type CuInSe2 and CuGaSe2 with possible cation and anion doping. We find that the intrinsic defects such as VCu and InCu or GaCu play significant roles in doping in both chalcopyrites. For group-II cation (Cd, Zn, or Mg) doping, the best n-type growth condition is In/Ga-rich, and maximal Se-poor, which is also the optimal condition for stabilizing the intrinsic InCu/GaCu donors. Bulk CuInSe2 can be doped at equil. n-type, but bulk CuGaSe2 cannot be due to the low formation energy of intrinsic Cu-vacancy. For halogen anion doping, the best n-type materials growth is still under In/Ga-rich, and maximal Se-poor conditions. These conditions are not best for halogen substitutional defects, but are optimal for intrinsic InCu/GaCu donors. Again, CuGaSe2 cannot be doped n-type by halogen doping, while CuInSe2 can.
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Lany, S.; Zunger, A. Assessment of correction methods for the band-gap problem and for finite-size effects in supercell defect calculations: Case studies for ZnO and GaAs. Phys. Rev. B 2008, 78, 235104, DOI: 10.1103/PhysRevB.78.235104
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Assessment of correction methods for the band-gap problem and for finite-size effects in supercell defect calculations: Case studies for ZnO and GaAs
Lany, Stephan; Zunger, Alex
Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 235104/1-235104/25CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
Contemporary theories of defects and impurities in semiconductors rely to a large extent on supercell calcns. within d.-functional theory using the approx. local-d. approxn. (LDA) or generalized gradient approxn. (GGA) functionals. Such calcns. are, however, affected by considerable uncertainties assocd. with: (i) the "band-gap problem," which occurs not only in the Kohn-Sham single-particle energies but also in the quasiparticle gap (LDA or GGA) calcd. from total-energy differences, and (ii) supercell finite-size effects. In the case of the oxygen vacancy in ZnO, uncertainties (i) and (ii) have led to a large spread in the theor. predictions, with some calcns. suggesting negligible vacancy concns., even under Zn-rich conditions, and others predicting high concns. Here, we critically assess (i) the different methodologies to correct the band-gap problem. We discuss approaches based on the extrapolation of perturbations which open the band gap, and the self-consistent band-gap correction employing the LDA + U method for d and s states simultaneously. From the comparison of the results of different gap-correction, including also recent results from other literature, we conclude that to date there is no universal scheme for band gap correction in general defect systems. Therefore, we turn instead to classification of different types of defect behavior to provide guidelines on how the phys. correct situation in an LDA defect calcn. can be recovered. (ii) Supercell finite-size effects: We performed test calcns. in large supercells of up to 1728 atoms, resolving a long-standing debate pertaining to image charge corrections for charged defects. We show that once finite-size effects not related to electrostatic interactions are eliminated, the analytic form of the image charge correction as proposed by Makov and Payne leads to size-independent defect formation energies, thus allowing the calcn. of well-converged energies in fairly small supercells. We find that the delocalized contribution to the defect charge (i.e., the defect-induced change of the charge distribution) is dominated by the dielec. screening response of the host, which leads to an unexpected effective 1/L scaling of the image charge energy, despite the nominal 1/L3 scaling of the third-order term. Based on this anal., we suggest that a simple scaling of the first order term by a const. factor (approx. 2/3) yields a simple but accurate image-charge correction for common supercell geometries. Finally, we discuss the theor. controversy pertaining to the formation energy of the O vacancy in ZnO in light of the assessment of different methodologies in the present work, and we review the present exptl. situation on the topic.
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Lany, S.; Zunger, A. Accurate prediction of defect properties in density functional supercell calculations. Modell. Simul. Mater. Sci. Eng. 2009, 17, 084002, DOI: 10.1088/0965-0393/17/8/084002
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Accurate prediction of defect properties in density functional supercell calculations
Lany, Stephan; Zunger, Alex
Modelling and Simulation in Materials Science and Engineering (2009), 17 (8), 084002/1-084002/14CODEN: MSMEEU; ISSN:1361-651X. (Institute of Physics Publishing)
The theor. description of defects and impurities in semiconductors is largely based on d. functional theory (DFT) employing supercell models. The literature discussion of uncertainties that limit the predictivity of this approach has focused mostly on two issues: (1) finite-size effects, in particular for charged defects; (2) the band-gap problem in local or semi-local DFT approxns. We here describe how finite-size effects (1) in the formation energy of charged defects can be accurately cor. in a simple way, i.e. by potential alignment in conjunction with a scaling of the Madelung-like screened first order correction term. The factor involved with this scaling depends only on the dielec. const. and the shape of the supercell, and quite accurately accounts for the full third order correction according to Makov and Payne. We further discuss in some detail the background and justification for this correction method, and also address the effect of the ionic screening on the magnitude of the image charge energy. In regard to (2) the band-gap problem, we discuss the merits of non-local external potentials that are added to the DFT Hamiltonian and allow for an empirical band-gap correction without significantly increasing the computational demand over that of std. DFT calcns. In combination with LDA + U, these potentials are further instrumental for the prediction of polaronic defects with localized holes in anion-p orbitals, such as the metal-site acceptors in wide-gap oxide semiconductors.
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Murphy, S. T.; Hine, N. D. M. Anisotropic charge screening and supercell size convergence of defect formation energies. Phys. Rev. B 2013, 87, 094111, DOI: 10.1103/PhysRevB.87.094111
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Anisotropic charge screening and supercell size convergence of defect formation energies
Murphy, Samuel T.; Hine, Nicholas D. M.
Physical Review B: Condensed Matter and Materials Physics (2013), 87 (9), 094111/1-094111/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
One of the main sources of error assocd. with the calcn. of defect formation energies using plane-wave d. functional theory (DFT) is finite size error resulting from the use of relatively small simulation cells and periodic boundary conditions. Most widely used methods for correcting this error, such as that of Makov and Payne, assume that the dielec. response of the material is isotropic and can be described using a scalar dielec. const. ε. However, this is strictly only valid for cubic crystals, and cannot work in highly anisotropic cases. Here we introduce a variation of the technique of extrapolation based on the Madelung potential that allows the calcn. of well-converged dil. limit defect formation energies in noncubic systems with highly anisotropic dielec. properties. As an example of the implementation of this technique we study a selection of defects in the ceramic oxide Li2TiO3 which is currently being considered as a lithium battery material and a breeder material for fusion reactors.
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Buckeridge, J. Equilibrium point defect and charge carrier concentrations in a material determined through calculation of the self-consistent Fermi energy. Comput. Phys. Commun. 2019, 244, 329– 342, DOI: 10.1016/j.cpc.2019.06.017
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Equilibrium point defect and charge carrier concentrations in a material determined through calculation of the self-consistent Fermi energy
Buckeridge, J.
Computer Physics Communications (2019), 244 (), 329-342CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
A concise procedure to det. the self-consistent Fermi energy and defect and carrier concns. in an extended cryst. system is presented. It is assumed that the formation enthalpies of a set of variously charged point defects in thermodn. equil. are known, as well as the d. of electronic states in the defect-free system. By applying the constraint of overall charge neutrality, the self-consistent Fermi energy is detd. using an iterative searching routine. The procedure is incorporated within a Fortran code 'SC-FERMI': the input consists of the defect formation energies, d. of sites where they can form, and the degeneracy of each charge state; the material band gap; and the calcd. d. of states of the pristine system. The output is the self-consistent Fermi energy, the total concns. of each defect as well as the concn. of its individual charge states, and the free carrier concns. Furthermore, the procedure facilitates fixing the concn. of one or more defects and detg. the resulting self-consistent Fermi energy and concns. of other defects (performed using the related code 'FROZEN-SC-FERMI'), thus modeling 'frozen-in' defects which may form by kinetic, rather than thermodn., processes. One can fix the total concn. or the concn. of a particular charge state; it is also possible to introduce new defects with a fixed concn., but here the charge state must be specified. The background theory is discussed in some detail, and the operation of the program is demonstrated by some examples.Program Title:SC-FERMIProgram Files doi:http://dx.doi.org/10.17632/dh3hjdf4fc.1Licensing provisions: MIT license-Programming language:FORTRAN 90. Nature of problem: To det. the self-consistent Fermi energy and equil. defect and carrier concns. given a set of point defect formation energies in a cryst. system, assuming the constraint of charge neutrality. Soln. method: The concns. of each defect in each charge state are calcd., as are the free carrier concns. These concns. are functions of the Fermi energy. The code, using an iterative search algorithm, dets. the Fermi energy that satisfies the charge neutrality constraint (the self-consistent Fermi energy). The defect and carrier concns. at that Fermi energy are then reported, as well as the Fermi energy itself. Restrictions: Thermodn. equil. is assumed. The defect formation enthalpies and electronic d. of states of the pristine system must be known. Addnl. comments: The concns. of defects can be fixed to a particular value, thus modeling 'frozen-in' defects formed by e.g. kinetic processes. This procedure is facilitated by the related program, FROZEN-SC-FERMI, which is identical to SC-FERMI apart from the addnl. defect concn. fixing routine.
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Squires, A. G.; Scanlon, D. O.; Morgan, B. J. py-sc-fermi: self-consistent Fermi energies and defect concentrations from electronic structure calculations. J. Open Source Softw. 2023, 8, 4962, DOI: 10.21105/joss.04962
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D Whalley, L. effmass: An effective mass package. J. Open Source Softw. 2018, 3, 797, DOI: 10.21105/joss.00797
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Whalley, L. D.; Frost, J. M.; Morgan, B. J.; Walsh, A. Impact of nonparabolic electronic band structure on the optical and transport properties of photovoltaic materials. Phys. Rev. B 2019, 99, 085207, DOI: 10.1103/PhysRevB.99.085207
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Impact of nonparabolic electronic band structure on the optical and transport properties of photovoltaic materials
Whalley, Lucy D.; Frost, Jarvist M.; Morgan, Benjamin J.; Walsh, Aron
Physical Review B (2019), 99 (8), 085207CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
The effective mass approxn. (EMA) models the response to an external perturbation of an electron in a periodic potential as the response of a free electron with a renormalized mass. For semiconductors used in photovoltaic devices, the EMA allows calcn. of important material properties from first-principles calcns., including optical properties (e.g., exciton binding energies), defect properties (e.g., donor and acceptor levels), and transport properties (e.g., polaron radii and carrier mobilities). The conduction and valence bands of semiconductors are commonly approximated as parabolic around their extrema, which gives a simple theor. description but ignores the complexity of real materials. In this work, we use d. functional theory to assess the impact of band nonparabolicity on four common thin-film photovoltaic materials-GaAs, CdTe, Cu2ZnSnS4 and CH3NH3PbI3-at temps. and carrier densities relevant for real-world applications. First, we calc. the effective mass at the band edges. We compare finite-difference, unweighted least-squares and thermally weighted least-squares approaches. We find that the thermally weighted least-squares method reduces sensitivity to the choice of sampling d. Second, we employ a Kane quasilinear dispersion to quantify the extent of nonparabolicity and compare results from different electronic structure theories to consider the effect of spin-orbit coupling and electron exchange. Finally, we focus on the halide perovskite CH3NH3PbI3 as a model system to assess the impact of nonparabolicity on calcd. electron transport and optical properties at high carrier concns. We find that at a concn. of 1020cm-3 the optical effective mass increases by a factor of two relative to the low carrier-concn. value, and the polaron mobility decreases by a factor of three. Our work suggests that similar adjustments should be made to the predicted optical and transport properties of other semiconductors with significant band nonparabolicity.
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Keen, D. A.; Hull, S. The high-temperature structural behaviour of copper(I) iodide. J. Phys.: Condens. Matter 1995, 7, 5793– 5804, DOI: 10.1088/0953-8984/7/29/007
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The high-temperature structural behavior of copper(I) iodide
Keen, D. A.; Hull, S.
Journal of Physics: Condensed Matter (1995), 7 (29), 5793-804CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics)
The structural behavior of CuI was studied between room temp. and its m.p. (TM = 878 K) using neutron powder diffraction. Detailed measurements were made in the vicinity of the two known structural phase transitions γ → β and β → α, which are obsd. at 643 ± 2 K and 673 ± 8 K. Within the Zn-blende structured γ-phase (space group F‾43m) increasing disorder of the Cu+ ion sublattice is obsd. as temp. approaches the γ → β transition, in addn. to a nonlinear thermal expansion. The hexagonal β-phase (space group P‾3m1) is obsd. as a single phase in the temp. range 645-668 K, but on 1st heating it is found to coexist with a rhombohedral phase. This transient phase was obsd. in isolation for only a short time but this was sufficient to show that its structure was that of CuI-IV (space group R‾3m), which had only been obsd. previously at elevated pressures. The high-temp. phase α-CuI has Fm‾3m symmetry with Cu+ ions distributed randomly over all the tetrahedral sites within the cubic close-packed I- sublattice.
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Moditswe, C.; Muiva, C. M.; Luhanga, P.; Juma, A. Effect of annealing temperature on structural and optoelectronic properties of CuI thin films prepared by the thermal evaporation method. Ceram. Int. 2017, 43, 5121– 5126, DOI: 10.1016/j.ceramint.2017.01.026
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Effect of annealing temperature on structural and optoelectronic properties of γ-CuI thin films prepared by the thermal evaporation method
Moditswe, Charles; Muiva, Cosmas M.; Luhanga, Pearson; Juma, Albert
Ceramics International (2017), 43 (6), 5121-5126CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
High quality transparent conducting CuI thin films were deposited at room temp. via thermal evapn. technique followed by post deposition annealing at different temps. The samples were characterised by X-ray diffraction (XRD), UV-Vis spectrophotometry, SEM and I-V measurements. The structural, morphol. and optical properties were studied as a function of the annealing temp. from room temp. (RT) to 200°C. XRD results revealed that the films were polycryst. with zinc blende structure of cubic phase. Increasing the annealing temp. increased the crystallite size from 33 to 49 nm while the dislocation d. and lattice strain shifted to lower values. High transmittance of about 70-80% was exhibited by all films in the entire visible spectral range. The as deposited film possesed the lowest resistivity of 3.0×10-3 Ω cm.
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Ves, S.; Glötzel, D.; Cardona, M.; Overhof, H. Pressure dependence of the optical properties and the band structure of the copper and silver halides. Phys. Rev. B 1981, 24, 3073– 3085, DOI: 10.1103/PhysRevB.24.3073
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81
Pressure dependence of the optical properties and the band structure of the copper and silver halides
Ves, S.; Gloetzel, D.; Cardona, M.; Overhof, H.
Physical Review B: Condensed Matter and Materials Physics (1981), 24 (6), 3073-85CODEN: PRBMDO; ISSN:0163-1829.
The absorption edge of CuCl, CuBr, CuI, and AgI was investigated with a diamond anvil cell as a function of pressure up to 16 GPa. The measurements, which reflect the various phase transitions undergone by these materials, yield the pressure coeffs. of the lowest gaps. Particular attention was paid to the high-pressure rock salt modifications, which have an indirect absorption edge in contrast to the direct edge of the sphalerite phases. This results from the influence of the different lattice symmetries on the halogen-p-metal-d hybridization in the valence bands. To interpret the data quant., self-consistent local-d. calcns. were performed with the linear combination of muffin-tin-orbitals-at.-sphere approxn. method and non-self-consistent Korringa-Kohn-Rostoker calcns. with the std. muffin-tin potential. The pressure-coeffs. so obtained agree reasonably with the exptl. ones. The gaps obtained by the self-consistent potential (with no adjustable parameter) are ∼2 eV smaller than the exptl. ones, thus reflecting shortcomings of the local-d. method for excitation properties.
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Blacha, A.; Cardona, M.; Christensen, N.; Ves, S.; Overhof, H. Volume dependence of the spin-orbit splitting in the copper halides. Physica B+C 1983, 117–118, 63– 65, DOI: 10.1016/0378-4363(83)90441-2
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83
Ganose, A. M.; Park, J.; Faghaninia, A.; Woods-Robinson, R.; Persson, K. A.; Jain, A. Efficient calculation of carrier scattering rates from first principles. Nat. Commun. 2021, 12, 2222, DOI: 10.1038/s41467-021-22440-5
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Efficient calculation of carrier scattering rates from first principles
Ganose, Alex M.; Park, Junsoo; Faghaninia, Alireza; Woods-Robinson, Rachel; Persson, Kristin A.; Jain, Anubhav
Nature Communications (2021), 12 (1), 2222CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
The electronic transport behavior of materials dets. their suitability for technol. applications. We develop a computationally efficient method for calcg. carrier scattering rates of solid-state semiconductors and insulators from first principles inputs. The present method extends existing polar and non-polar electron-phonon coupling, ionized impurity, and piezoelec. scattering mechanisms formulated for isotropic band structures to support highly anisotropic materials. We test the formalism by calcg. the electronic transport properties of 23 semiconductors, including the large 48 atom CH3NH3PbI3 hybrid perovskite, and comparing the results against exptl. measurements and more detailed scattering simulations. The Spearman rank coeff. of mobility against expt. (rs = 0.93) improves significantly on results obtained using a const. relaxation time approxn. (rs = 0.52). We find our approach offers similar accuracy to state-of-the art methods at approx. 1/500th the computational cost, thus enabling its use in high-throughput computational workflows for the accurate screening of carrier mobilities, lifetimes, and thermoelec. power.
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84
Hennion, B.; Moussa, F.; Prevot, B.; Carabatos, C.; Schawb, C. Normal Modes of Vibrations in CuI. Phys. Rev. Lett. 1972, 28, 964– 966, DOI: 10.1103/PhysRevLett.28.964
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84
Normal modes of vibrations in copper(I) iodide
Hennion, B.; Moussa, F.; Prevot, B.; Carabatos, C.; Schwab, C.
Physical Review Letters (1972), 28 (15), 964-6CODEN: PRLTAO; ISSN:0031-9007.
Phonon dispersion curves for CuI were measured at room temp. for the [100], [110], and [111] symmetry directions by using inelastic neutron scattering. The results are interpreted in terms of a rigid-ion model. Estns. are given for elastic consts.
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Fukumoto, T.; Nakashima, S.; Tabuchi, K.; Mitsuishi, A. Temperature Dependence of Raman Spectra of Cuprous Halides. Phys. Status Solidi B 1976, 73, 341– 351, DOI: 10.1002/pssb.2220730134
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85
Temperature dependence of Raman spectra of cuprous halides
Fukumoto, T.; Nakashima, S.; Tabuchi, K.; Mitsuishi, A.
Physica Status Solidi B: Basic Research (1976), 73 (1), 341-51CODEN: PSSBBD; ISSN:0370-1972.
The temp. dependence of the half linewidth and frequency shift of Raman lines in cuprous halides were investigated at 4.2-300°K. As for the LO and TO mode of CuI and CuBr, and the LO mode of CuCl, the exptl. linewidth and frequency shift are in good agreement with the theor. ones which were calcd. in terms of 3-phonon interaction. In order to explain the temp. dependence of a strong combination mode in conjunction with the TO phonons of CuCl, the hybridization theory proposed by J. Ruvalds and A. Zawadowski (1971) was employed in which hybridization between a 2-phonon and a single phonon state is postulated. A numerical anal. was made assuming that the acoustic combination mode (TA + LA) hybridizes with the TO mode. The anomalous frequency shift and line broadening of the strong combination line were explained by the temp. dependence of the coupling const. of 2 acoustic phonons (between TA and LA mode). The linewidth and frequency shift of the TO mode can be explained in some degree by this hybridization theory.
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Hanson, R.; Hallberg, J.; Schwab, C. Elastic and piezoelectric constants of the cuprous halides. Appl. Phys. Lett. 1972, 21, 490– 492, DOI: 10.1063/1.1654230
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86
Elastic and piezoelectric constants of the cuprous halides
Hanson, R. C.; Hallberg, J. R.; Schwab, C.
Applied Physics Letters (1972), 21 (10), 490-2CODEN: APPLAB; ISSN:0003-6951.
Elastic and piezoelec. consts. of CuCl, CuBr, and CuI were measured. The elastic consts. of zinc-blende-structure materials when plotted on a reduced scale indicate a striking instability as the Phillips crit. ionicity (0.785) is approached. CuCl is the most piezoelec. of these materials, with a piezoelec. const. e14 = 0.41 coulomb/m2 at 80°K.
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87
Skelton, J. M.; Gunn, D. S. D.; Metz, S.; Parker, S. C. Accuracy of Hybrid Functionals with Non-Self-Consistent Kohn–Sham Orbitals for Predicting the Properties of Semiconductors. J. Chem. Theory Comput. 2020, 16, 3543– 3557, DOI: 10.1021/acs.jctc.9b01218
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87
Accuracy of Hybrid Functionals with Non-Self-Consistent Kohn-Sham Orbitals for Predicting the Properties of Semiconductors
Skelton, Jonathan M.; Gunn, David S. D.; Metz, Sebastian; Parker, Stephen C.
Journal of Chemical Theory and Computation (2020), 16 (6), 3543-3557CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
Accurately modeling the electronic structure of materials is a persistent challenge to high-throughput screening. A promising means of balancing accuracy against computational cost is non-self-consistent calcns. with hybrid d.-functional theory, where the electronic band energies are evaluated using a hybrid functional from orbitals obtained with a less demanding (semi)local functional. We have quantified the performance of this technique for predicting the phys. properties of 16 tetrahedral semiconductors with bandgaps from 0.2 to 5.5 eV. Provided the base functional predicts a nonmetallic electronic structure, bandgaps within 5% of the PBE0 and HSE06 gaps can be obtained with an order of magnitude redn. in computing time. The positions of the valence and conduction band extrema and the Fermi level are well reproduced, enabling calcn. of the band dispersion, d. of states, and dielec. properties using Fermi's Golden Rule. While the error in the non-self-consistent total energies is ~ 50 meV atom-1, the energy-vol. curves are reproduced accurately enough to obtain the equil. vol. and bulk modulus with minimal error. We also test the dielec.-dependent scPBE0 functional and obtain bandgaps and dielec. consts. to within 2.5% of the self-consistent results, which amts. to a significant improvement over self-consistent PBE0 for a similar computational cost. We identify cases where the non-self-consistent approach is expected to perform poorly and demonstrate that partial self-consistency provides a practical and efficient workaround. Finally, we perform proof-of-concept calcns. on CoO and NiO to demonstrate the applicability of the technique to strongly correlated open-shell transition-metal oxides.
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Onida, G.; Reining, L.; Rubio, A. Electronic excitations: density-functional versus many-body Green’s-function approaches. Rev. Mod. Phys. 2002, 74, 601– 659, DOI: 10.1103/RevModPhys.74.601
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Electronic excitations: density-functional versus many-body Green's-function approaches
Onida, Giovanni; Reining, Lucia; Rubio, Angel
Reviews of Modern Physics (2002), 74 (2), 601-659CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)
A review. Electronic excitations lie at the origin of most of the commonly measured spectra. However, the 1st-principles computation of excited states requires a larger effort than ground-state calcns., which can be very efficiently carried out within d.-functional theory. However, two theor. and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a 1-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy Σ and the electron-hole interaction. A good approxn. for Σ was obtained with Hedin's GW approach, using d.-functional theory as a zero-order soln. First-principles GW calcns. for real systems were successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional deriv. of Σ. An alternative approach to calcg. electronic excitations is the time-dependent d.-functional theory (TDDFT), which offers the important practical advantage of a dependence on d. rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-d. approxn. gave promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theor. and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress.
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Li, Y.; Sun, J.; Singh, D. J. Optical and electronic properties of doped p -type CuI: Explanation of transparent conductivity from first principles. Phys. Rev. Mater. 2018, 2, 035003, DOI: 10.1103/PhysRevMaterials.2.035003
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89
Optical and electronic properties of doped p-type CuI: Explanation of transparent conductivity from first principles
Li, Yuwei; Sun, Jifeng; Singh, David J.
Physical Review Materials (2018), 2 (3), 035003CODEN: PRMHBS; ISSN:2475-9953. (American Physical Society)
We report the properties of the reported transparent conductor CuI, including the effect of heavy p-type doping. The results, based on first-principles calcns., include an anal. of the electronic structure and calcns. of optical and dielec. properties. We find that the origin of the favorable transparent conducting behavior lies in the absence in the visible of strong interband transitions between deeper valence bands and states at the valence-band max. that become empty with p-type doping. Instead, strong interband transitions to the valence-band max. are concd. in the IR with energies below 1.3 eV. This is contrast to the valence bands of many wide-band-gap materials. Turning to the mobility, we find that the states at the valence-band max. are relatively dispersive. This originates from their antibonding Cu d-I p character. We find a modest enhancement of the Born effective charges relative to nominal values, leading to a dielec. const. ε(0)=6.3. This is sufficiently large to reduce ionized impurity scattering, leading to the expectation that the properties of CuI can still be significantly improved through sample quality.
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Poncé, S.; Margine, E. R.; Giustino, F. Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors. Phys. Rev. B 2018, 97, 121201, DOI: 10.1103/PhysRevB.97.121201
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Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors
Ponce, Samuel; Margine, Elena R.; Giustino, Feliciano
Physical Review B (2018), 97 (12), 121201CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
We probe the accuracy limit of ab initio calcns. of carrier mobilities in semiconductors, within the framework of the Boltzmann transport equation. By focusing on the paradigmatic case of silicon, we show that fully predictive calcns. of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space. By considering all these factors we obtain excellent agreement with expt., and we identify the band effective masses as the most crit. parameters to achieve predictive accuracy. Our findings set a blueprint for future calcns. of carrier mobilities, and pave the way to engineering transport properties in semiconductors by design.
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Meng, F.; Ma, J.; He, J.; Li, W. Phonon-limited carrier mobility and temperature-dependent scattering mechanism of 3C-SiC from first principles. Phys. Rev. B 2019, 99, 045201, DOI: 10.1103/PhysRevB.99.045201
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Phonon-limited carrier mobility and temperature-dependent scattering mechanism of 3C-SiC from first principles
Meng, Fanchen; Ma, Jinlong; He, Jian; Li, Wu
Physical Review B (2019), 99 (4), 045201CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
A review. Electron-phonon coupling is at the core of various regimes of material-based science and technol. Taking 3C-silicon carbide (3C-SiC) as an example, despite its very wide application in high-temp. and high-power devices, the transport properties of 3C-SiC are not yet fully understood at the microscopic level because of inadequate knowledge in electron-phonon coupling. In this paper, with electron-phonon coupling matrix elements calcd. from first principles, the phonon limited carrier mobility of 3C-SiC is quantified by solving the Boltzmann transport equation. The calcd. mobilities for both holes and electrons are in reasonable agreement with the exptl. data. Unlike other polar semiconductors such as GaAs, where the polar-longitudinal-optical (LO)-phonon interactions are the dominant scattering mechanism, the mobilities of electrons and holes are dominated by the intravalley longitudinal acoustic phonon scattering at 300 K due to the low occupation no. of high-frequency polar LO phonons in 3C-SiC. The dominant scattering mechanism in 3C-SiC varies with temp. At high temp. (800 K), LO phonons govern the scattering instead. The max. mean-free paths of electrons and holes at room temp. are found to be 40 nm and 15 nm, resp.
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Ma, J.; Nissimagoudar, A. S.; Li, W. First-principles study of electron and hole mobilities of Si and GaAs. Phys. Rev. B 2018, 97, 045201, DOI: 10.1103/PhysRevB.97.045201
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First-principles study of electron and hole mobilities of Si and GaAs
Ma, Jinlong; Nissimagoudar, Arun S.; Li, Wu
Physical Review B (2018), 97 (4), 045201CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
With first-principles calcd. electron-phonon coupling matrix elements, the phonon-limited electron and hole mobilities of Si and GaAs are studied using the Boltzmann transport equation. The calcd. mobilities agree well with the exptl. measurements. For electrons in GaAs, the calcd. mobility is very sensitive to the band structure characterized by the effective mass and the energy gap between Γ and L valleys, which clarifies the discrepancies between recent literature findings [J.-J. Zhou and M. Bernardi, Phys. Rev. B94, 201201(R) (2016)2469-995010.1103/PhysRevB.94.201201; T.-H. Liu, Phys. Rev. B95, 075206 (2017)2469-995010.1103/PhysRevB.95.075206]. Unlike electrons in GaAs, where the longitudinal optical phonon dominates the scattering, the other phonon branches have a comparable influence on the mobility of holes in GaAs. In Si and GaAs, the spin-orbit coupling interaction has a significant effect on the valence bands and, further, on the hole mobilities, without which the calcd. mobility is underestimated, esp. at relatively low temps., while it has almost no effect on the electrons.
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Prasad, M.; Gupta, S. Hall effect measurement of a CuI_1.0046 pellet. Phys. Status Solidi A 1986, 94, K65– K68, DOI: 10.1002/pssa.2210940173
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Hall effect measurement of a copper iodide (CuI1.0046) pellet
Prasad, M.; Gupta, S. K.
Physica Status Solidi A: Applied Research (1986), 94 (1), K65-K68CODEN: PSSABA; ISSN:0031-8965.
The Hall effect of CuI1.0046 was measured at room temp. with a magnetic field of 4.3 × 10-2 T. The mean value of the Hall coeff., the concn. of pos. holes, and the hole mobility are reported. The results are compared with those of B. H. Vine and R. J. Maurer (1951).
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Knauth, P.; Massiani, Y.; Pasquinelli, M. Semiconductor properties of polycrystalline CuBr by Hall effect and capacitive measurements. Phys. Status Solidi A 1998, 165, 461– 465, DOI: 10.1002/(SICI)1521-396X(199802)165:2<461::AID-PSSA461>3.0.CO;2-W
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Semiconductor properties of polycrystalline CuBr by Hall effect and capacitive measurements
Knauth, P.; Massiani, Y.; Pasquinelli, M.
Physica Status Solidi A: Applied Research (1998), 165 (2), 461-465CODEN: PSSABA; ISSN:0031-8965. (Wiley-VCH Verlag Berlin GmbH)
Polycryst. CuBr was investigated by Hall effect expts. and capacitive measurements on semiconductor-electrolyte contacts. A p-type semicond. of CuBr samples was found; the flat-band potential and the d. and mobility of holes were detd. The results were discussed in view of semiconductor theory. We conclude that the O impurities are the origin for the high acceptor concn. in the Hall samples and that the charge carrier d. calcd. from semiconductor-electrolyte contact expts is more reliable.
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Yang, C.; Souchay, D.; Kneiß, M.; Bogner, M.; Wei, H. M.; Lorenz, M.; Oeckler, O.; Benstetter, G.; Fu, Y. Q.; Grundmann, M. Transparent flexible thermoelectric material based on non-toxic earth-abundant p-type copper iodide thin film. Nat. Commun. 2017, 8, 16076, DOI: 10.1038/ncomms16076
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Transparent flexible thermoelectric material based on non-toxic earth-abundant p-type copper iodide thin film
Yang, C.; Souchay, D.; Kneiss, M.; Bogner, M.; Wei, H. M.; Lorenz, M.; Oeckler, O.; Benstetter, G.; Fu, Y. Q.; Grundmann, M.
Nature Communications (2017), 8 (), 16076CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
Thermoelec. devices that are flexible and optically transparent hold unique promise for future electronics. However, development of invisible thermoelec. elements is hindered by the lack of p-type transparent thermoelec. materials. Here we present the superior room-temp. thermoelec. performance of p-type transparent copper iodide (CuI) thin films. Large Seebeck coeffs. and power factors of the obtained CuI thin films are analyzed based on a single-band model. The low-thermal cond. of the CuI films is attributed to a combined effect of the heavy element iodine and strong phonon scattering. Accordingly, we achieve a large thermoelec. figure of merit of ZT=0.21 at 300 K for the CuI films, which is three orders of magnitude higher compared with state-of-the-art p-type transparent materials. A transparent and flexible CuI-based thermoelec. element is demonstrated. Our findings open a path for multifunctional technologies combing transparent electronics, flexible electronics and thermoelectricity.
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Li, Z. H.; He, J. X.; Lv, X. H.; Chi, L. F.; Egbo, K. O.; Li, M.-D.; Tanaka, T.; Guo, Q. X.; Yu, K. M.; Liu, C. P. Optoelectronic properties and ultrafast carrier dynamics of copper iodide thin films. Nat. Commun. 2022, 13, 6346, DOI: 10.1038/s41467-022-34117-8
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Optoelectronic properties and ultrafast carrier dynamics of copper iodide thin films
Li, Zhan Hua; He, Jia Xing; Lv, Xiao Hu; Chi, Ling Fei; Egbo, Kingsley O.; Li, Ming-De; Tanaka, Tooru; Guo, Qi Xin; Yu, Kin Man; Liu, Chao Ping
Nature Communications (2022), 13 (1), 6346CODEN: NCAOBW; ISSN:2041-1723. (Nature Portfolio)
As a promising high mobility p-type wide bandgap semiconductor, copper iodide has received increasing attention in recent years. However, the defect physics/evolution are still controversial, and particularly the ultrafast carrier and exciton dynamics in copper iodide has rarely been investigated. Here, we study these fundamental properties for copper iodide thin films by a synergistic approach employing a combination of anal. techniques. Steady-state photoluminescence spectra reveal that the emission at ∼420 nm arises from the recombination of electrons with neutral copper vacancies. The photogenerated carrier d. dependent ultrafast phys. processes are elucidated with using the femtosecond transient absorption spectroscopy. Both the effects of hot-phonon bottleneck and the Auger heating significantly slow down the cooling rate of hot-carriers in the case of high excitation d. The effect of defects on the carrier recombination and the two-photon induced ultrafast carrier dynamics are also investigated. These findings are crucial to the optoelectronic applications of copper iodide.
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Matsuzaki, K.; Tsunoda, N.; Kumagai, Y.; Tang, Y.; Nomura, K.; Oba, F.; Hosono, H. Hole-Doping to a Cu(I)-Based Semiconductor with an Isovalent Cation: Utilizing a Complex Defect as a Shallow Acceptor. J. Am. Chem. Soc. 2022, 144, 16572– 16578, DOI: 10.1021/jacs.2c06283
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Hole-Doping to a Cu(I)-Based Semiconductor with an Isovalent Cation: Utilizing a Complex Defect as a Shallow Acceptor
Matsuzaki, Kosuke; Tsunoda, Naoki; Kumagai, Yu; Tang, Yalun; Nomura, Kenji; Oba, Fumiyasu; Hosono, Hideo
Journal of the American Chemical Society (2022), 144 (36), 16572-16578CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
P-Type doping in Cu(I)-based semiconductors is pivotal for solar cell photoabsorbers and hole transport materials to improve the device performance. Impurity doping is a fundamental technol. to overcome the intrinsic limits of hole concn. controlled by native defects. Here, we report that alkali metal impurities are prominent p-type dopants for the Cu(I)-based cation-deficient hole conductors. When the size mismatch with Cu+ in the host lattice is increased, these isovalent impurities are preferentially located at interstitial positions to interact with the constituent Cu cations, forming stable impurity-defect complexes. We demonstrate that the Cs impurity in γ-CuI semiconductors enhances hole concn. controllability for single crystals and thin films in the range of 1013-1019 cm-3. First-principles calcns. indicate that the Cs impurity forms impurity-defect complexes that act as shallow acceptors leading to the increased p-type cond. This isovalent doping provides an approach for controlled doping into cation-deficient semiconductors through an interaction of impurities with native defects.
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Almasoudi, M.; Saeed, A.; Salah, N.; Alshahrie, A.; Hasan, P. M. Z.; Melaibari, A.; Koumoto, K. CuI. CuI: A Promising Halide for Thermoelectric Applications below 373 K. ACS Appl. Energy Mater. 2022, 5, 10177– 10186, DOI: 10.1021/acsaem.2c01929
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CuI: A Promising Halide for Thermoelectric Applications below 373 K
Almasoudi, M.; Saeed, Abdu; Salah, Numan; Alshahrie, Ahmed; Hasan, P. M. Z.; Melaibari, A.; Koumoto, Kunihito
ACS Applied Energy Materials (2022), 5 (8), 10177-10186CODEN: AAEMCQ; ISSN:2574-0962. (American Chemical Society)
Highly transparent p-type γ-CuI thin films with enhanced thermoelec. (TE) properties were produced by the pulsed laser deposition (PLD) technique. The film composed of fine nanoparticles was found to show transparency close to 90% and excellent TE performance at 300-360 K. Postannealing at three different temps. in the range of 373-573 K in a vacuum was found to diminish the deviation from the stoichiometric compn., namely, δ in Cu1-δI, possibly due to iodine evapn. The carrier (hole) concn. decreased and the Hall mobility increased on increasing the postannealing temp., i.e., by decreasing δ. The film postannealed at 373 K showed the best TE performance with a high elec. cond. of ~ 14 000 S/m, a large Seebeck coeff. of ~ 350μV/K, and a high power factor of ~ 1600μW/(m K2) at 300 K. The degeneracy of the heavy- and light-hole bands of γ-CuI could enhance the Seebeck coeff. through enhancing the effective mass of holes and decreasing the carrier concn., while elec. cond. was only slightly decreased. Thermal cond. of the γ-CuI thin films was verified to be as low as 0.77-0.83 W/(m K) at 300 K. The present study firmly demonstrates the high potential of the γ-CuI thin film as a p-type TE material to be paired with an n-type material for flexible TE devices and self-powered electronic systems operating at 300-360 K.
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Wang, M.; Wei, H.; Wu, Y.; Yang, C.; Han, P.; Juan, F.; Chen, Y.; Xu, F.; Cao, B. Highly transparent and conductive γ-CuI films grown by simply dipping copper films into iodine solution. Phys. B 2019, 573, 45– 48, DOI: 10.1016/j.physb.2019.08.021
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Highly transparent and conductive γ-CuI films grown by simply dipping copper films into iodine solution
Wang, Mingxu; Wei, Haoming; Wu, Yangqing; Yang, Chao; Han, Peigao; Juan, Fangying; Chen, Yang; Xu, Fan; Cao, Bingqiang
Physica B: Condensed Matter (Amsterdam, Netherlands) (2019), 573 (), 45-48CODEN: PHYBE3; ISSN:0921-4526. (Elsevier B.V.)
In this Letter, we demonstrate a simple and environmentally friendly method to grow large-area p-type conductive CuI films by dipping copper films into ethanol soln. of iodine at room temp. The effects of iodine concn. and film thickness on the morphologies, cryst. phases, optical and elec. properties of CuI films were investigated. All the films are γ-CuI with preferential (111) orientation. At the optimized growth condition, the CuI films exhibit a high transmission which exceeds 73% in the visible spectral range and low resistivity of 0.02 Ω cm. These results pave the way for the growth and further application of large-area CuI films in optoelectronic devices.
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Madkhali, O.; Jullien, M.; Giba, A. E.; Ghanbaja, J.; Mathieu, S.; Gendarme, C.; Migot, S.; Alajlani, Y.; Can, N.; Alnjiman, F.; Horwat, D.; Redjaimia, A.; Pierson, J. Blue emission and twin structure of p-type copper iodide thin films. Surf. Interfaces 2021, 27, 101500, DOI: 10.1016/j.surfin.2021.101500
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Blue emission and twin structure of p-type copper iodide thin films
Madkhali, O.; Jullien, M.; Giba, Alaa E.; Ghanbaja, J.; Mathieu, S.; Gendarme, C.; Migot, S.; Alajlani, Y.; Can, N.; Alnjiman, F.; Horwat, D.; Redjaimia, A.; Pierson, J. F.
Surfaces and Interfaces (2021), 27 (), 101500CODEN: SIUNCN; ISSN:2468-0230. (Elsevier B.V.)
Copper iodide is an attractive p-type transparent material suitable for optoelectronic applications. This work reports on the synthesis of copper iodide (CuI) by iodination of sputtered Cu films previously deposited on glass and silicon substrates. The cryst. phase and surface morphol. were studied by X-ray diffraction (XRD) and SEM (SEM), resp. The prepd. CuI films crystallize in the zinc blende structure (γ-phase) at different amts. of iodine and exhibit preferential orientation along the <111> direction. Moreover, detailed investigation of the microstructure via high-resoln. transmission electron microscopy (HR-TEM) revealed the presence and details of alternating twin crystallog. domains between adjacent grains. The elec. properties of the CuI films were characterized by Hall effect measurements and revealed a p-type carrier behavior for all films. The elec. behavior was discussed and attributed to the change in intrinsic point defects. In addn., the electronic bandgap and luminescence properties were investigated using optical transmission and photoluminescence (PL). The CuI films showed a wide band gap (about 3.05 eV) with an av. transmittance of about (66%) in the visible region. Moreover, the PL showed a blue emission ranging from 400 to 440 nm originating from the excitonic recombination and radiative point defects.
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Ahn, D.; Song, J. D.; Kang, S. S.; Lim, J. Y.; Yang, S. H.; Ko, S.; Park, S. H.; Park, S. J.; Kim, D. S.; Chang, H. J.; Chang, J. Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes. Sci. Rep. 2020, 10, 3995, DOI: 10.1038/s41598-020-61021-2
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Intrinsically p-type cuprous iodide semiconductor for hybrid light-emitting diodes
Ahn, D.; Song, J. D.; Kang, S. S.; Lim, J. Y.; Yang, S. H.; Ko, S.; Park, S. H.; Park, S. J.; Kim, D. S.; Chang, H. J.; Chang, Joonyeon
Scientific Reports (2020), 10 (1), 3995CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
Abstr.: Cuprous halides, characterized by a direct wide band-gap and a good lattice matching with Si, is an intrinsic p-type I-VII compd. semiconductor. It shows remarkable optoelectronic properties, including a large exciton binding energy at room temp. and a very small piezoelec. coeff. The major obstacle to its application is the difficulty in growing a single-crystal epitaxial film of cuprous halides. We first demonstrate the single crystal epitaxy of high quality cuprous iodide (CuI) film grown on Si and sapphire substrates by mol. beam epitaxy. Enhanced photoluminescence on the order of magnitude larger than that of GaN and continuous-wave optically pumped lasing were found in MBE grown CuI film. The intrinsic p-type characteristics of CuI were confirmed using an n-AlGaN/p-CuI junction that emits blue light. The discovery will provide an alternative way towards highly efficient optoelectronic devices compatible with both Si and III-nitride technologies.
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Liu, M.-L.; Wu, L.-B.; Huang, F.-Q.; Chen, L.-D.; Chen, I.-W. A promising p-type transparent conducting material: Layered oxysulfide [Cu₂S₂] [Sr₃Sc₂O₅]. J. Appl. Phys. 2007, 102, 116108, DOI: 10.1063/1.2817643
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A promising p-type transparent conducting material. Layered oxysulfide [Cu2S2][Sr3Sc2O5]
Liu, Min-Ling; Wu, Li-Bin; Huang, Fu-Qiang; Chen, Li-Dong; Chen, I.-Wei
Journal of Applied Physics (2007), 102 (11), 116108/1-116108/3CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Sr3Cu2Sc2O5S2, a layered oxysulfide, composed of anti-PbO-like [Cu2S2] slabs alternating with perovskite-like [Sr3Sc2O5] slabs, was systematically studied as a p-type transparent conducting material. The material has a wide energy gap of 3.1 eV and a p-type elec. cond. of 2.8 S cm-1 at room temp. The hole mobility of +150 cm2 V-1 S-1 at room temp., which is much higher than the typical value of ∼10-1-10 cm2 V-1 S-1 found in other copper compds. The performances of bulk undoped Sr3Cu2Sc2O5S2 show the promise of copper oxysulfides as a class of p-type transparent conductive materials that is essential for optoelectronic applications.
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Swallow, J. E. N.; Williamson, B. A. D.; Sathasivam, S.; Birkett, M.; Featherstone, T. J.; Murgatroyd, P. A. E.; Edwards, H. J.; Lebens-Higgins, Z. W.; Duncan, D. A.; Farnworth, M. Resonant doping for high mobility transparent conductors: the case of Mo-doped In₂O₃. Mater. Horiz. 2020, 7, 236– 243, DOI: 10.1039/C9MH01014A
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Resonant doping for high mobility transparent conductors: the case of Mo-doped In2O3
Swallow, Jack E. N.; Williamson, Benjamin A. D.; Sathasivam, Sanjayan; Birkett, Max; Featherstone, Thomas J.; Murgatroyd, Philip A. E.; Edwards, Holly J.; Lebens-Higgins, Zachary W.; Duncan, David A.; Farnworth, Mark; Warren, Paul; Peng, Nianhua; Lee, Tien-Lin; Piper, Louis F. J.; Regoutz, Anna; Carmalt, Claire J.; Parkin, Ivan P.; Dhanak, Vin R.; Scanlon, David O.; Veal, Tim D.
Materials Horizons (2020), 7 (1), 236-243CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
Transparent conductors are a vital component of smartphones, touch-enabled displays, low emissivity windows and thin film photovoltaics. Tin-doped In2O3 (ITO) dominates the transparent conductive films market, accounting for the majority of the current multi-billion dollar annual global sales. Due to the high cost of indium, however, alternatives to ITO have been sought but have inferior properties. Here we demonstrate that molybdenum-doped In2O3 (IMO) has higher mobility and therefore higher cond. than ITO with the same carrier d. This also results in IMO having increased IR transparency compared to ITO of the same cond. These properties enable current performance to be achieved using thinner films, reducing the amt. of indium required and raw material costs by half. The enhanced doping behavior arises from Mo 4d donor states being resonant high in the conduction band and negligibly perturbing the host conduction band min., in contrast to the adverse perturbation caused by Sn 5s dopant states. This new understanding will enable better and cheaper TCOs based on both In2O3 and other metal oxides.
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Zhang, J.; Willis, J.; Yang, Z.; Lian, X.; Chen, W.; Wang, L.-S.; Xu, X.; Lee, T.-L.; Chen, L.; Scanlon, D. O.; Zhang, K. H. Deep UV transparent conductive oxide thin films realized through degenerately doped wide-bandgap gallium oxide. Cell Rep. Phys. Sci. 2022, 3, 100801, DOI: 10.1016/j.xcrp.2022.100801
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Deep ultraviolet transparent conductive oxide thin films released through degenerately doped wide-bandgap gallium oxide
Zhang, Jiaye; Willis, Joe; Yang, Zhenni; Lian, Xu; Chen, Wei; Wang, Lai-Sen; Xu, Xiangyu; Lee, Tien-Lin; Chen, Lang; Scanlon, David O.; Zhang, Kelvin H. L.
Cell Reports Physical Science (2022), 3 (3), 100801CODEN: CRPSF5; ISSN:2666-3864. (Elsevier Inc.)
Deep UV transparent thin films have recently attracted considerable attention owing to their potential in UV and org.-based optoelectronics. Here, we report the achievement of a deep UV transparent and highly conductive thin film based on Si-doped Ga2O3 (SGO) with high cond. of 2500 S/cm. The SGO thin films exhibit high transparency over a wide spectrum ranging from visible light to deep UV wavelength and, meanwhile, have a very low work-function of approx. 3.2 eV. A combination of photoemission spectroscopy and theor. studies reveals that the delocalized conduction band derived from Ga 4s orbitals is responsible for the Ga2O3 films' high cond. Furthermore, Si is shown to act as an efficient shallow donor, yielding high mobility up to approx. 60 cm2/Vs. The superior optoelectronic properties of SGO films make it a promising material for use as electrodes in high-power electronics and deep UV and org.-based optoelectronic devices.
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High mobility approaching the intrinsic limit in Ta-doped SnO2 films epitaxially grown on TiO2 (001) substrates
Fukumoto, Michitaka; Nakao, Shoichiro; Shigematsu, Kei; Ogawa, Daisuke; Morikawa, Kazuo; Hirose, Yasushi; Hasegawa, Tetsuya
Scientific Reports (2020), 10 (1), 6844CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
Achieving high mobility in SnO2, which is a typical wide gap oxide semiconductor, has been pursued extensively for device applications such as field effect transistors, gas sensors, and transparent electrodes. In this study, we investigated the transport properties of lightly Ta-doped SnO2 (Sn1-xTaxO2, TTO) thin films epitaxially grown on TiO2 (001) substrates by pulsed laser deposition. The carrier d. (ne) of the TTO films was systematically controlled by x. Optimized TTO (x = 3 x 10-3) films with ne ∼ 1 x 1020 cm-3 exhibited a very high Hall mobility (μH) of 130 cm2V-1s-1 at room temp., which is the highest among SnO2 films thus far reported. The μH value coincided well with the intrinsic limit of μH calcd. on the assumption that only phonon and ionized impurities contribute to the carrier scattering. The suppressed grain-boundary scattering might be explained by the reduced d. of the {101} crystallog. shear planes.
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Kim, H. J.; Kim, U.; Kim, H. M.; Kim, T. H.; Mun, H. S.; Jeon, B.-G.; Hong, K. T.; Lee, W.-J.; Ju, C.; Kim, K. H.; Char, K. High Mobility in a Stable Transparent Perovskite Oxide. Appl. Phys. Express 2012, 5, 061102, DOI: 10.1143/APEX.5.061102
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High mobility in a stable transparent perovskite oxide
Kim, Hyung Joon; Kim, Useong; Kim, Hoon Min; Kim, Tai Hoon; Mun, Hyo Sik; Jeon, Byung-Gu; Hong, Kwang Taek; Lee, Woong-Jhae; Ju, Chanjong; Kim, Kee Hoon; Char, Kookrin
Applied Physics Express (2012), 5 (6), 061102/1-061102/3CODEN: APEPC4; ISSN:1882-0778. (Japan Society of Applied Physics)
La-doped BaSnO3 with the perovskite structure has an unprecedentedly high mobility at room temp. while retaining its optical transparency. In single crystals, the mobility reached 320 cm2 V-1 s-1 at a doping level of 8 × 1019 cm-3, constituting the highest value among wide-band-gap semiconductors. In epitaxial films, the max. mobility was 70 cm2 V-1 s-1 at a doping level of 4.4 × 1020 cm-3. Resistance of (Ba,La)SnO3 changes little even after a thermal cycle to 530° in air, pointing to an unusual stability of O atoms and great potential for realizing transparent high-frequency, high-power functional devices.
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Jackson, A. J.; Parrett, B. J.; Willis, J.; Ganose, A. M.; Leung, W. W. W.; Liu, Y.; Williamson, B. A. D.; Kim, T. K.; Hoesch, M.; Veiga, L. S. I. Computational Prediction and Experimental Realization of Earth-Abundant Transparent Conducting Oxide Ga-Doped ZnSb₂O₆. ACS Energy Lett. 2022, 7, 3807– 3816, DOI: 10.1021/acsenergylett.2c01961
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Computational Prediction and Experimental Realization of Earth-Abundant Transparent Conducting Oxide Ga-Doped ZnSb2O6
Jackson, Adam J.; Parrett, Benjamin J.; Willis, Joe; Ganose, Alex M.; Leung, W. W. Winnie; Liu, Yuhan; Williamson, Benjamin A. D.; Kim, Timur K.; Hoesch, Moritz; Veiga, Larissa S. I.; Kalra, Raman; Neu, Jens; Schmuttenmaer, Charles A.; Lee, Tien-Lin; Regoutz, Anna; Lee, Tung-Chun; Veal, Tim D.; Palgrave, Robert G.; Perry, Robin; Scanlon, David O.
ACS Energy Letters (2022), 7 (11), 3807-3816CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the no. of oxides that are transparent to visible light and have the metallic-like cond. necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid d. functional theory and defect chem. anal. to demonstrate that tri-rutile zinc antimonate, ZnSb2O6, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high cond. and transparency. To validate our computational predictions, we have synthesized both powder samples and single crystals of Ga-doped ZnSb2O6 which conclusively show behavior consistent with a degenerate transparent conducting oxide. This study demonstrates the possibility of a family of Sb(V)-contg. oxides for transparent conducting oxide and power electronics applications.
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Lee, H.-A.; Yatsu, K.; Kim, T. I.; Kwon, H.-I.; Park, I.-J. Synthesis of Vacancy-Controlled Copper Iodide Semiconductor for High-Performance p-Type Thin-Film Transistors. ACS Appl. Mater. Interfaces 2022, 14, 56416– 56426, DOI: 10.1021/acsami.2c18865
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Synthesis of Vacancy-Controlled Copper Iodide Semiconductor for High-Performance p-Type Thin-Film Transistors
Lee, Hyun-Ah; Yatsu, Kie; Kim, Tae In; Kwon, Hyuck-In; Park, Ick-Joon
ACS Applied Materials & Interfaces (2022), 14 (50), 56416-56426CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
Copper iodide (CuI) has emerged as a promising p-type semiconductor material owing to its excellent carrier mobility, high transparency, and soln. processability. Although CuI has potential for numerous applications, including perovskite solar cells, photovoltaic devices, and thin-film transistors (TFTs), the close relationship between the anion vacancy generation and the charge transport mechanism in CuI-based devices is underexplored. In this study, we propose soln.-processed p-type CuI TFTs which were subject to the thermal annealing process in air and vacuum atmospheres at temps. of 100, 200, and 300°C. The chem. states and surface morphologies of the CuI thin films were systematically investigated, revealing the generation of iodine vacancy states and the redn. of carrier concn., as well as increased film d. and grain size according to the annealing condition. Further, the effective role of the Al2O3 passivation layer on the elec. characteristics of the soln.-processed CuI TFTs is demonstrated for the first time, where the Al2O3 precursor greatly enhanced the elec. performance of the CuI TFTs, exhibiting a field-effect mobility of 4.02 cm2/V·s, a subthreshold swing of 0.61 V/decade, and an on/off current ratio of 1.12 x 104, which exceed the values of CuI TFTs reported so far. Based on the synergistic effects of the annealing process and the passivation layer that engineered the iodine vacancy state and morphol. of CuI, the proposed CuI TFTs with the Al2O3 passivation layer showed excellent reliability under 100 times repeated operation and long-term stability over 216 h, where the transfer curves slightly shifted in the pos. direction of 1.36 and 1.88 V measured at a current level of 10-6 A for the reliability and stability tests, resp. Thus, this work opens a new window for soln.-processed p-type CuI TFTs with excellent stability for developing next-generation complementary logic circuits.
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Lee, H. J.; Lee, S.; Lee, K. H.; Hong, K. Amorphous copper iodide: a p-type semiconductor for solution processed p-channel thin-film transistors and inverters. J. Mater. Chem. C 2022, 10, 7815– 7821, DOI: 10.1039/D2TC00410K
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Amorphous copper iodide: a p-type semiconductor for solution processed p-channel thin-film transistors and inverters
Lee, Han Ju; Lee, Seonjeong; Lee, Keun Hyung; Hong, Kihyon
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2022), 10 (20), 7815-7821CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
Until now, inorg. p-channel thin-film transistors (TFTs) have shown relatively low performance in terms of mobility, ON-current level, and on/off ratio compared to their n-channel counterparts. For inorg. p-channel TFTs, high-temp. annealed single- or poly-cryst. materials such as CuO, SnO, or 2D dichalcogenides have been the typical materials of choice. Development of amorphous semiconductor materials can provide a wide range of promising semiconductors for the TFT industry owing to their unique advantages, such as large area applicability, high device-to-device uniformity, and low temp. processing; however, the poor TFT performance using the conventional amorphous p-type semiconductors limits the use of materials in practical applications. In the present work, we demonstrate the 1st high-performance soln.-processed p-channel TFT using an amorphous copper iodide (a-CuI) semiconductor, which outperforms its polycryst. counterpart. Amorphous CuI films were formed by spin coating of precursor solns. based on co-solvents. By using a-CuI semiconductors as the channel layer, electrolyte-gated p-channel TFTs were fabricated with a vertical device structure. Measurement of the TFT characteristics reveals that the amorphous CuI channel layer leads to better device performance than devices with a polycryst. CuI. The optimized vertical TFTs showed high current densities above 1000 mA cm-2, ON/OFF current ratios of > 104, and large normalized transconductances of about 6 S m-1, which are the highest among soln.-processed vertical TFTs. These results pave the way for application of amorphous p-type inorgs. in high-performance complementary circuits and represent a breakthrough for p-type semiconductor materials.
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Tate, J.; Ju, H. L.; Moon, J. C.; Zakutayev, A.; Richard, A. P.; Russell, J.; McIntyre, D. H. Origin of p-type conduction in single-crystal CuAlO₂. Phys. Rev. B 2009, 80, 165206, DOI: 10.1103/PhysRevB.80.165206
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Origin of p-type conduction in single-crystal CuAlO2
Tate, J.; Ju, H. L.; Moon, J. C.; Zakutayev, A.; Richard, A. P.; Russell, J.; McIntyre, D. H.
Physical Review B: Condensed Matter and Materials Physics (2009), 80 (16), 165206/1-165206/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
We report measurements of the structural, optical, transport, and magnetic properties of single crystals of the anisotropic p-type transparent semiconductor CuAlO2. The indirect and direct band gaps are 2.97 and 3.47 eV, resp. Temp.-dependent Hall measurements yield a pos. Hall coeff. in the measured range and an activated carrier temp. dependence. The resistivity is anisotropic, with the ab-plane resistivity about 25 times smaller than the c-axis resistivity at room temp. Both are activated with similar activation energies. The room-temp. ab-plane mobility is relatively large at 3 cm2 V-1 s-1, and we infer a c-axis mobility of 0.12 cm2 V-1 s-1. The Seebeck coeff. is pos. at all measured temps., and has a T-1 dependence over most of the measured range. The low-temp. paramagnetic moment is consistent with a spin-1/2 defect with a d. of 3.4×1020 cm-3. These results suggest that the conduction mechanism for p-type carriers in CuAlO2 is charge transport in the valence band and that the holes are thermally activated from copper-vacancy acceptor states located about 700 meV above the valence-band max.
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Abstract
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Figure 1
Figure 1. Crystal and electronic structures of CuI. (a) Zincblende crystal structure of CuI, viewed along the face diagonal. Cu and I atoms in blue and green, respectively. Cu atoms have tetrahedral coordination, shown in gray. (b) Electronic band structure of CuI. Calculated using the PBE0 hybrid functional with the inclusion of spin–orbit coupling (SOC). (c) Schematic molecular orbital (MO) diagram of CuI. Upon the inclusion of SOC, further splitting occurs on the t₂─5p MOs into light and heavy hole channels and a spin–orbit split-off band, as seen in (b)
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Figure 2
Figure 2. (a) Top of the valence bands of CuI around Γ with and without SOC as computed with the PBEsol functional. (b) The normalized function $- v_{VB}^{2} τ_{VB} \frac{\partial f}{\partial ε}$ , convoluted with δ(ε – ε_VB) in the valence band at different T. In this expression, v_VB and τ_VB stand for the carrier velocity and lifetime in the valence band (VB), $\frac{\partial f}{\partial ε}$ is the derivative of the Fermi–Dirac distribution function with respect to the energy and δ the Dirac delta function. By integration of this function, relaxation time approximation (RTA) hole mobility is obtained.
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Figure 3
Figure 3. (a) CuI phonon dispersion computed with SOC and the PBEsol functional with experimentally reported frequencies overlaid. (84,85) (b) Spectral decomposition of the hole scattering rates as a function of frequency at different temperatures. (c) Structure of CuI showing the atomic displacements corresponding to the longitudinal optical phonon mode at the Γ point (toward the X direction), viewed along the face diagonal; Cu and I atoms in blue and green, respectively.
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Figure 4
Figure 4. CuI hole mobility as a function of the temperature at two carrier concentrations. Colored lines represent mobility contributions from each type of scattering: ADP is acoustic deformation potential scattering (orange); IMP is ionized impurity scattering (dark blue); PIE is piezoelectric scattering (light blue); POP is polar optical phonon scattering (pink); and total is the reciprocal sum of these contributions (black). (a) Low carrier concentration, 1 × 10¹⁶ cm^–3. (b) High carrier concentration, 1 × 10²⁰ cm^–3.
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Figure 5
Figure 5. Experimental hole mobility as a function of carrier concentration, broken down by the deposition method. Experimental data are reported in refs (29), (30), (33)– (35), (37)– (42), (95)– (96) (97) (98). IBTE and AMSET drift mobilities overlaid as dashed lines; IBTE + IMP mobility $(\frac{1}{μ_{IBTE + IMP}} = \frac{1}{μ_{IBTE}} + \frac{1}{μ_{IMP}})$ overlaid as a filled black line; gray shaded region denotes space between AMSET-estimated upper limit and IBTE + IMP-estimated upper limit.
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Figure 6
Figure 6. Transition level diagrams for CuI under three sets of chemical potentials. Fermi energy (eV) on the x-axis, formation energy (eV) on y-axis. The valence band maximum (VBM) is denoted by the shaded blue region. The gradient of each line represents the charge state, and filled circles denote transition levels where two charge states are in thermodynamic equilibrium. (a) Cu-rich, I-poor, chalcogen-poor. (b) Cu-mid, I-mid, chalcogen-rich. (c) Cu-poor, I-rich, chalcogen-rich.
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Figure 7
Figure 7. Partial hole density generated by various defects in CuI. Defect supercell is denoted by a dotted black line; blue regions are Cu, green regions are I, and lime green regions are dopants. (a) S_I⁰, 0.006 e Å^–3. (b) Se_I⁰, 0.006 e Å^–3.
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References
This article references 110 other publications.
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  The electronic structure of the p-type transparent conducting oxide CuCrO2 has been studied by x-ray photoemission, x-ray absorption, and x-ray emission spectroscopies. The upper part of the valence band derives mainly from Cu 3d and Cr 3d states while the lower valence-band states are of dominant O 2p at. character, but with pronounced mutual hybridization among Cu 3d, Cr 3d, and O 2p states. Site specific electronic excitations have been studied by resonant inelastic x-ray scattering at the Cu L and Cr L edges. Inelastic loss at the Cu L edge is dominated by on-site interband excitations similar to those found in Cu2O, while at the Cr L edge localized excitations arising from ligand field splitting of the Cr 3d levels are obsd. Mg doping on the Cr sites in CuCrO2 is shown to lead to a pronounced shift in the Fermi level toward the edge of the valence band. The exptl. data are compared to electronic structure calcns. on CuCrO2 carried out using d.-functional methods cor. for onsite Coulomb repulsion.
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4. 4
  Shin, D.; Foord, J. S.; Payne, D. J.; Arnold, T.; Aston, D. J.; Egdell, R. G.; Godinho, K. G.; Scanlon, D. O.; Morgan, B. J.; Watson, G. W. Comparative study of bandwidths in copper delafossites from x-ray emission spectroscopy. Phys. Rev. B 2009, 80, 233105, DOI: 10.1103/PhysRevB.80.233105
  4
  Comparative study of bandwidths in copper delafossites from x-ray emission spectroscopy
  Shin, D.; Foord, J. S.; Payne, D. J.; Arnold, T.; Aston, D. J.; Egdell, R. G.; Godinho, K. G.; Scanlon, D. O.; Morgan, B. J.; Watson, G. W.; Mugnier, E.; Yaicle, C.; Rougier, A.; Colakerol, L.; Glans, P. A.; Piper, L. F. J.; Smith, K. E.
  Physical Review B: Condensed Matter and Materials Physics (2009), 80 (23), 233105/1-233105/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  The widths of the valence bands in the Cu(I) delafossites CuGaO2, CuInO2, and CuScO2 were measured by O K-shell x-ray emission spectroscopy and are compared with previous exptl. work on CuAlO2 and CuCrO2. In agreement with recent d.-functional theory calcns. the bandwidth decreases in the series CuAlO2°CuGaO2°CuInO2°CuScO2. States at the top of the valence band are of dominant Cu 3dz2 at. character but with significant mixing with O 2p states.
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5. 5
  Scanlon, D. O.; Morgan, B. J.; Watson, G. W.; Walsh, A. Acceptor Levels in p-type Cu₂O: Rationalizing Theory and Experiment. Phys. Rev. Lett. 2009, 103, 096405, DOI: 10.1103/PhysRevLett.103.096405
  5
  Acceptor levels in p-type Cu2O. Rationalizing theory and experiment
  Scanlon, David O.; Morgan, Benjamin J.; Watson, Graeme W.; Walsh, Aron
  Physical Review Letters (2009), 103 (9), 096405/1-096405/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  Understanding conduction in Cu2O is vital to the optimization of Cu-based p-type transparent conducting oxides. Using a screened hybrid-d.-functional approach we have investigated the formation of p-type defects in Cu2O giving rise to single-particle levels that are deep in the band gap, consistent with exptl. obsd. activated, polaronic conduction. Our calcd. transition levels for simple and split Cu vacancies explain the source of the 2 distinct hole states seen in DLTS expts. The necessity of techniques that go beyond the present generalized-gradient- and local-d.-approxn. techniques for accurately describing p-type defects in Cu(I)-based oxides is discussed.
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6. 6
  Scanlon, D. O.; Walsh, A.; Watson, G. W. Understanding the p-Type Conduction Properties of the Transparent Conducting Oxide CuBO₂: A Density Functional Theory Analysis. Chem. Mater. 2009, 21, 4568– 4576, DOI: 10.1021/cm9015113
  6
  Understanding the p-type conduction properties of the transparent conducting oxide CuBO2. A density functional theory analysis
  Scanlon, David O.; Walsh, Aron; Watson, Graeme W.
  Chemistry of Materials (2009), 21 (19), 4568-4576CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  Discovering new candidate p-type transparent conducting oxides has become a major goal for material scientists. Recently delafossite CuBO2 was proposed as a promising candidate, showing good room temp. elec. cond. and excellent transparency. We report a d. functional theory investigation of CuBO2, examg. the geometry and electronic structure using GGA cor. for on-site Coulomb interactions (GGA + U) and a hybrid d. functional (HSE06). From anal. of the calcd. band structure, d. of states, and optical absorption, we predict an indirect fundamental band gap of ∼3.1 eV and a direct optical band gap of ∼3.6 eV. The hole effective mass at the valence band max. indicates the potential for good p-type cond., consistent with the reported exptl. results. These results are discussed in relation to other delafossite oxides.
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7. 7
  Scanlon, D. O.; Watson, G. W. Conductivity Limits in CuAlO₂ from Screened-Hybrid Density Functional Theory. J. Phys. Chem. Lett. 2010, 1, 3195– 3199, DOI: 10.1021/jz1011725
  7
  Conductivity limits in CuAlO2 from screened-hybrid density functional theory
  Scanlon, David O.; Watson, Graeme W.
  Journal of Physical Chemistry Letters (2010), 1 (21), 3195-3199CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  CuAlO2 is a prototypical delafossite p-type transparent conducting oxide (TCO). Despite this, many fundamental questions about its band structure and cond. remain unanswered. We utilize the screened hybrid exchange functional (HSE06) to investigate defects in CuAlO2 and find that Cu vacancies and Cu on Al antisites will dominate under Cu-poor/Al-poor conditions. Our calcd. transitions levels are deep in the band gap, consistent with exptl. findings, and we identify the likely defect levels that are often mistaken as indirect band gaps. Finally, we critically discuss delafossite oxides as TCO materials.
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8. 8
  Scanlon, D. O.; Watson, G. W. Undoped n-type Cu₂O: Fact or Fiction?. J. Phys. Chem. Lett. 2010, 1, 2582– 2585, DOI: 10.1021/jz100962n
  8
  Undoped n-Type Cu2O: Fact or Fiction?
  Scanlon, David O.; Watson, Graeme W.
  Journal of Physical Chemistry Letters (2010), 1 (17), 2582-2585CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Cuprous oxide is widely known to be a native p-type semiconductor. Despite this, reports of electrodeposited films of n-type Cu2O continue to appear in the literature, with oxygen vacancies commonly implicated as the electron-donating defect. Through first-principles calcns., we demonstrate conclusively that intrinsic n-type defects or defect complexes in Cu2O cannot be the source of any n-type behavior displayed by electrodeposited samples. In light of these results, we discuss the exptl. findings.
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9. 9
  Scanlon, D. O.; Godinho, K. G.; Morgan, B. J.; Watson, G. W. Understanding conductivity anomalies in Cu(I)-based delafossite transparent conducting oxides: Theoretical insights. J. Chem. Phys. 2010, 132, 024707, DOI: 10.1063/1.3290815
  9
  Understanding conductivity anomalies in CuI-based delafossite transparent conducting oxides: Theoretical insights
  Scanlon, David O.; Godinho, Kate G.; Morgan, Benjamin J.; Watson, Graeme W.
  Journal of Chemical Physics (2010), 132 (2), 024707/1-024707/10CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  The Cu(I)-based delafossite structure, Cu(I)M(III)O2, can accommodate a wide range of rare earth and transition metal cations on the M(III) site. Substitutional doping of divalent ions for these trivalent metals is known to produce higher p-type cond. than that occurring in the undoped materials. However, an explanation of the cond. anomalies obsd. in these p-type materials, as the trivalent metal is varied, is still lacking. We examine the electronic structure of Cu(I)M(III)O2 (M(III) = Al, Cr, Sc, Y) using d. functional theory cor. for on-site Coulomb interactions in strongly correlated systems (GGA + U) and discuss the unusual exptl. trends. The importance of covalent interactions between the M(III) cation and O for improving cond. in the delafossite structure is highlighted, with the covalency trends found to perfectly match the cond. trends. We also show that calcg. the natural band offsets and the effective masses of the valence band maxima is not an ideal method to classify the conduction properties of these ternary materials. (c) 2010 American Institute of Physics.
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10. 10
  Godinho, K. G.; Carey, J. J.; Morgan, B. J.; Scanlon, D. O.; Watson, G. W. Understanding conductivity in SrCu₂O₂: stability, geometry and electronic structure of intrinsic defects from first principles. J. Mater. Chem. 2010, 20, 1086– 1096, DOI: 10.1039/B921061J
  10
  Understanding conductivity in SrCu2O2: stability, geometry and electronic structure of intrinsic defects from first principles
  Godinho, Kate G.; Carey, John J.; Morgan, Benjamin J.; Scanlon, David O.; Watson, Graeme W.
  Journal of Materials Chemistry (2010), 20 (6), 1086-1096CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
  D. functional theory calcns. were performed on stoichiometric and intrinsically defective p-type transparent conducting oxide SrCu2O2, using GGA cor. for on-site Coulombic interactions (GGA + U). Anal. of the absorption spectrum of SrCu2O2 indicates that the fundamental direct band gap could be as much as ∼0.5 eV smaller than the optical band gap. Our results indicate that the defects that cause p-type cond. are favored under all conditions, with defects that cause n-type cond. having significantly higher formation energies. We show conclusively that the most stable defects are copper and strontium vacancies. Copper vacancies introduce a distinct acceptor single particle level above the valence band max., consistent with the exptl. known activated hopping mechanism.
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11. 11
  Scanlon, D. O.; Watson, G. W. Understanding the p-type defect chemistry of CuCrO₂. J. Mater. Chem. 2011, 21, 3655, DOI: 10.1039/c0jm03852k
  11
  Understanding the p-type defect chemistry of CuCrO2
  Scanlon, David O.; Watson, Graeme W.
  Journal of Materials Chemistry (2011), 21 (11), 3655-3663CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
  CuCrO2 is the most promising Cu-based delafossite for p-type optoelectronic devices. Despite this, little is known about the p-type conduction mechanism of this material, with both CuI/CuII and CrIII/CrIV hole mechanisms being proposed. In this article we examine the electronic structure, thermodn. stability and the p-type defect chem. of this ternary compd. using d. functional theory with three different approaches to the exchange and correlation; the generalized-gradient-approxn. of Perdew, Burke and Ernzerhof (PBE), PBE with an addnl. correction for on-site Coulombic interactions (PBE + U) and the nonlocal, screened-exchange hybrid functional HSE06. The fundamental band gap of CuCrO2 is demonstrated to be indirect in nature. Under all growth conditions, the dominant intrinsic p-type defect will be the Cu vacancy, with hole formation centered solely on the Cu sublattice. Mg doping is found to be significantly lower in energy than intrinsic defect formation, explaining the large increases in cond. seen exptl. Cu-rich/Cr-poor growth conditions are found to be optimal for both intrinsic and extrinsic (Mg doping) defect formation, and should be adopted to maximize performance.
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12. 12
  Godinho, K. G.; Morgan, B. J.; Allen, J. P.; Scanlon, D. O.; Watson, G. W. Chemical bonding in copper-based transparent conducting oxides: CuMO₂ (M = In, Ga, Sc). J. Phys.: Condens. Matter 2011, 23, 334201, DOI: 10.1088/0953-8984/23/33/334201
  12
  Chemical bonding in copper-based transparent conducting oxides: CuMO2 (M = In, Ga, Sc)
  Godinho, K. G.; Morgan, B. J.; Allen, J. P.; Scanlon, D. O.; Watson, G. W.
  Journal of Physics: Condensed Matter (2011), 23 (33), 334201/1-334201/10CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
  The geometry and electronic structure of copper-based p-type delafossite transparent conducting oxides, CuMO2 (M = In, Ga, Sc), are studied using the generalized gradient approxn. (GGA) cor. for on-site Coulomb interactions (GGA + U). The bonding and valence band compns. of these materials are investigated, and the origins of changes in the valence band features between group 3 and group 13 cations are discussed. Anal. of the effective masses at the valence and conduction band edge explains the exptl. reported cond. trends.
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13. 13
  Scanlon, D. O.; Buckeridge, J.; Catlow, C. R. A.; Watson, G. W. Understanding doping anomalies in degenerate p-type semiconductor LaCuOSe. J. Mater. Chem. C 2014, 2, 3429– 3438, DOI: 10.1039/C4TC00096J
  13
  Understanding doping anomalies in degenerate p-type semiconductor LaCuOSe
  Scanlon, David O.; Buckeridge, John; Catlow, C. Richard A.; Watson, Graeme W.
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2014), 2 (17), 3429-3438CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  The failure to develop a degenerate, wide band gap, p-type oxide material has been a stumbling block for the optoelectronics industry for decades. Mg-doped LaCuOSe has recently emerged as a very promising p-type anode layer for optoelectronic devices, displaying high conductivities and low hole injection barriers. Despite these promising results, many questions regarding the defect chem. of this system remain unanswered, namely (i) why does this degenerate semiconductor not display a Moss-Burnstein shift, (ii) what is the origin of cond. in doped and un-doped samples, and (iii) why is Mg reported to be the best dopant, despite the large cation size mismatch between Mg and La In this article we use screened hybrid d. functional theory to study both intrinsic and extrinsic defects in LaCuOSe, and identify for the first time the source of charge carriers in this system. We successfully explain why LaCuOSe does not exhibit a Moss-Burstein shift, and we identify the source of the subgap optical absorption reported in expts. Lastly we demonstrate that Mg doping is not the most efficient mechanism for p-type doping LaCuOSe, and propose an exptl. reinvestigation of this system.
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14. 14
  Zhang, J. Y.; Li, W. W.; Hoye, R. L. Z.; MacManus-Driscoll, J. L.; Budde, M.; Bierwagen, O.; Wang, L.; Du, Y.; Wahila, M. J.; Piper, L. F. J.; Lee, T.-L.; Edwards, H. J.; Dhanak, V. R.; Zhang, K. H. L. Electronic and transport properties of Li-doped NiO epitaxial thin films. J. Mater. Chem. C 2018, 6, 2275– 2282, DOI: 10.1039/C7TC05331B
  14
  Electronic and transport properties of Li-doped NiO epitaxial thin films
  Zhang, J. Y.; Li, W. W.; Hoye, R. L. Z.; MacManus-Driscoll, J. L.; Budde, M.; Bierwagen, O.; Wang, L.; Du, Y.; Wahila, M. J.; Piper, L. F. J.; Lee, T.-L.; Edwards, H. J.; Dhanak, V. R.; Zhang, K. H. L.
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2018), 6 (9), 2275-2282CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type cond. of NiO, but all the films have relatively low room-temp. mobilities (<0.05 cm2 V-1 s-1). The conduction mechanism is better described by small-polaron hoping model in the temp. range of 200 K < T < 330 K, and variable range hopping at T < 200 K. A combination of X-ray photoemission and O K-edge X-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band max. (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.
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15. 15
  Quackenbush, N. F.; Allen, J. P.; Scanlon, D. O.; Sallis, S.; Hewlett, J. A.; Nandur, A. S.; Chen, B.; Smith, K. E.; Weiland, C.; Fischer, D. A.; Woicik, J. C.; White, B. E.; Watson, G. W.; Piper, L. F. J. Origin of the Bipolar Doping Behavior of SnO from X-ray Spectroscopy and Density Functional Theory. Chem. Mater. 2013, 25, 3114– 3123, DOI: 10.1021/cm401343a
  15
  Origin of the Bipolar Doping Behavior of SnO from X-ray Spectroscopy and Density Functional Theory
  Quackenbush, N. F.; Allen, J. P.; Scanlon, D. O.; Sallis, S.; Hewlett, J. A.; Nandur, A. S.; Chen, B.; Smith, K. E.; Weiland, C.; Fischer, D. A.; Woicik, J. C.; White, B. E.; Watson, G. W.; Piper, L. F. J.
  Chemistry of Materials (2013), 25 (15), 3114-3123CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The origin of the almost unique combination of optical transparency and the ability to bipolar dope Sn monoxide is explained using a combination of soft and hard x-ray photoemission spectroscopy, O K-edge X-ray emission and absorption spectroscopy, and d. functional theory calcns. incorporating van der Waals corrections. The authors reveal that the origin of the high hole mobility, bipolar ability, and transparency is a result of (i) significant Sn 5s character at the valence band max. (due to O 2p-Sn 5s antibonding character assocd. with the lone pair distortion), (ii) the combination of a small indirect band gap of ∼0.7 eV (Γ-M) and a much larger direct band gap of 2.6 - 2.7 eV, and (iii) the location of both band edges with respect to the vacuum level. This work supports Sn2+-based oxides as a paradigm for next-generation transparent semiconducting oxides.
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16. 16
  Li, Y.; Singh, D. J.; Du, M.-H.; Xu, Q.; Zhang, L.; Zheng, W.; Ma, Y. Design of ternary alkaline-earth metal Sn(II) oxides with potential good p-type conductivity. J. Mater. Chem. C 2016, 4, 4592– 4599, DOI: 10.1039/C6TC00996D
  16
  Design of ternary alkaline-earth metal Sn oxides with potential good p-type conductivity
  Li, Yuwei; Singh, David J.; Du, Mao-Hua; Xu, Qiaoling; Zhang, Lijun; Zheng, Weitao; Ma, Yanming
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (20), 4592-4599CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  Oxides with good p-type cond. have been long sought after to achieve high performance all-oxide optoelectronic devices. Divalent Sn based oxides are promising candidates because of their rather dispersive upper valence bands caused by the Sn-5s/O-2p anti-bonding hybridization. There are so far few known Sn oxides being p-type conductive suitable for device applications. Here, we present via first-principles global optimization structure searches a material design study for a hitherto unexplored Sn-based system, ternary alk.-earth metal Sn oxides in the stoichiometry of MSn2O3 (M = Mg, Ca, Sr, Ba). We identify two stable compds. of SrSn2O3 and BaSn2O3, which can be stabilized by Sn-rich conditions in phase stability diagrams. Their structures follow the Zintl behavior and consist of basic structural motifs of SnO3 tetrahedra. Unexpectedly they show distinct electronic properties with band gaps ranging from 1.90 (BaSn2O3) to 3.15 (SrSn2O3) eV, and hole effective masses ranging from 0.87 (BaSn2O3) to above 6.0 (SrSn2O3) m0. Further exploration of metastable phases indicates a wide tunability of electronic properties controlled by the details of the bonding between the basic structural motifs. This suggests further exploration of alk.-earth metal Sn oxides for potential applications requiring good p-type cond. such as transparent conductors and photovoltaic absorbers.
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17. 17
  Zhang, K. H. L.; Du, Y.; Papadogianni, A.; Bierwagen, O.; Sallis, S.; Piper, L. F. J.; Bowden, M. E.; Shutthanandan, V.; Sushko, P. V.; Chambers, S. A. Perovskite Sr-Doped LaCrO₃ as a New p-Type Transparent Conducting Oxide. Adv. Mater. 2015, 27, 5191– 5195, DOI: 10.1002/adma.201501959
  17
  Perovskite Sr-Doped LaCrO3 as a New p-Type Transparent Conducting Oxide
  Zhang, Kelvin H. L.; Du, Yingge; Papadogianni, Alexandra; Bierwagen, Oliver; Sallis, Shawn; Piper, Louis F. J.; Bowden, Mark E.; Shutthanandan, Vaithiyalingam; Sushko, Peter V.; Chambers, Scott A.
  Advanced Materials (Weinheim, Germany) (2015), 27 (35), 5191-5195CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A new p-type transparent conductive oxide (TCO) based on LaCrO3 (LCO), which shows competitive performance within a structure that can be readily integrated with other oxide electronic materials, is reported. Substituting Sr2+ for La3+ in LCO effectively dopes holes into the top of the valence band (VB) and results in p-type cond., which is the motivation used to explore La1-xSrxCrO3 (LSCO) as a candidate p-type TCO. LSCO epitaxial films were grown on (001)-oriented SrTiO3 (STO) substrates by mol. beam epitaxy and their cond. and elec. properties studied.
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18. 18
  Amini, M. N.; Dixit, H.; Saniz, R.; Lamoen, D.; Partoens, B. The origin of p-type conductivity in ZnM₂O₄ (M = Co, Rh, Ir) spinels. Phys. Chem. Chem. Phys. 2014, 16, 2588, DOI: 10.1039/c3cp53926a
  18
  The origin of p-type conductivity in ZnM2O4 (M = Co, Rh, Ir) spinels
  Amini, M. N.; Dixit, H.; Saniz, R.; Lamoen, D.; Partoens, B.
  Physical Chemistry Chemical Physics (2014), 16 (6), 2588-2596CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  ZnM2O4 (M = Co, Rh, Ir) spinels are considered as a class of potential p-type transparent conducting oxides (TCOs). We report the formation energy of acceptor-like defects using 1st principles calcns. with an advanced hybrid exchange-correlation functional (HSE06) within d. functional theory (DFT). Due to the discrepancies between the theor. obtained band gaps with this hybrid functional and the - scattered - exptl. results, we also perform GW calcns. to support the validity of the description of these spinels with the HSE06 functional. The considered defects are the cation vacancy and antisite defects, which are supposed to be the leading source of disorder in the spinel structures. We also discuss the band alignments in these spinels. The calcd. formation energies indicate that the antisite defects ZnM (Zn replacing M, M = Co, Rh, Ir) and VZn act as shallow acceptors in ZnCo2O4, ZnRh2O4 and ZnIr2O4, which explains the exptl. obsd. p-type cond. in those systems. Moreover, our systematic study indicates that the ZnIr antisite defect has the lowest formation energy in the group and it corroborates the highest p-type cond. reported for ZnIr2O4 among the group of ZnM2O4 spinels. To gain further insight into factors affecting the p-type cond., we have also investigated the formation of localized small polarons by calcg. the self-trapping energy of the holes.
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19. 19
  Bhatia, A.; Hautier, G.; Nilgianskul, T.; Miglio, A.; Sun, J.; Kim, H. J.; Kim, K. H.; Chen, S.; Rignanese, G.-M.; Gonze, X.; Suntivich, J. High-Mobility Bismuth-based Transparent p-Type Oxide from High-Throughput Material Screening. Chem. Mater. 2016, 28, 30– 34, DOI: 10.1021/acs.chemmater.5b03794
  19
  High-Mobility Bismuth-based Transparent p-Type Oxide from High-Throughput Material Screening
  Bhatia, Amit; Hautier, Geoffroy; Nilgianskul, Tan; Miglio, Anna; Sun, Jingying; Kim, Hyung Joon; Kim, Kee Hoon; Chen, Shuo; Rignanese, Gian-Marco; Gonze, Xavier; Suntivich, Jin
  Chemistry of Materials (2016), 28 (1), 30-34CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  Transparent semiconducting oxides are essential building blocks to many technologies, ranging from components in transparent electronics, transparent conductors, to absorbers and protection layers in photovoltaics and photoelectrochem. devices. However, thus far, it has been difficult to develop p-type oxides with wide band gap and high hole mobility. For example, current state-of-art transparent p-type oxides have hole mobility in the range of < 10 cm2/V·s, much lower than their n-type counterpart. Using high-throughput computational screening to guide the discovery of new materials with wide band gap and high hole mobility, we report the computational identification and the exptl. verification of a bismuth-based double-perovskite oxide that can meet these requirements. Our identified candidate, Ba2BiTaO6, has an optical band gap larger than 4 eV and a Hall hole mobility above 30 cm2/V·s. We rationalize this finding with the following MO explanation: Bi3+ with filled s-orbitals strongly overlaps with the oxygen p, increasing the extent of the metal-oxygen covalency and effectively reducing the valence band effective mass, while Ta5+ electronic states form a conduction band, leading to a high band gap beyond the visible range. Our concerted theory-expt. effort points to the growing utility of a data-driven materials discovery and the combination of both informatics and expt. as an approach to discover future technol. materials.
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20. 20
  Shi, J.; Rubinstein, E. A.; Li, W.; Zhang, J.; Yang, Y.; Lee, T.-L.; Qin, C.; Yan, P.; MacManus-Driscoll, J. L.; Scanlon, D. O.; Zhang, K. H. Modulation of the Bi³⁺ 6s² Lone Pair State in Perovskites for High-Mobility p-Type Oxide Semiconductors. Advanced Science 2022, 9, 2104141, DOI: 10.1002/advs.202104141
  20
  Modulation of the Bi3+ 6s2 Lone Pair State in Perovskites for High-Mobility p-Type Oxide Semiconductors
  Shi, Jueli; Rubinstein, Ethan A.; Li, Weiwei; Zhang, Jiaye; Yang, Ye; Lee, Tien-Lin; Qin, Changdong; Yan, Pengfei; MacManus-Driscoll, Judith L.; Scanlon, David O.; Zhang, Kelvin H. L.
  Advanced Science (Weinheim, Germany) (2022), 9 (6), 2104141CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Oxide semiconductors are key materials in many technologies from flat-panel displays, solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p-type oxide semiconductors due to the localized O-2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba2BiMO6 (M = Bi, Nb, Ta) via the Bi 6s2 lone pair state to achieve p-type oxide semiconductors with high hole mobility up to 21 cm2 V-1 s-1, and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x-ray photoemission, x-ray absorption spectroscopies, and d. functional theory calcns. are used to gain insight into the electronic structure of Ba2BiMO6. The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4-0.7 me). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P-N junction diode constructed with p-type Ba2BiTaO6 and n-type Nb doped SrTiO3 exhibits high rectifying ratio of 1.3 x 104 at ±3 V, showing great potential in fabricating high-quality devices. This work provides deep insight into the electronic structure of Bi3+ based perovskites and guides the development of new p-type oxide semiconductors.
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21. 21
  Williamson, B. A. D.; Buckeridge, J.; Brown, J.; Ansbro, S.; Palgrave, R. G.; Scanlon, D. O. Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors. Chem. Mater. 2017, 29, 2402– 2413, DOI: 10.1021/acs.chemmater.6b03306
  21
  Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors
  Williamson, Benjamin A. D.; Buckeridge, John; Brown, Jennilee; Ansbro, Simon; Palgrave, Robert G.; Scanlon, David O.
  Chemistry of Materials (2017), 29 (6), 2402-2413CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The paucity of high performance transparent p-type semiconductors was a stumbling block for the electronics industry for decades, effectively hindering the route to efficient transparent devices based on p-n junctions. Cu-based oxides and subsequently Cu-based oxychalcogenides were heavily studied as affordable, earth-abundant p-type transparent semiconductors, where the mixing of the Cu 3d states with the chalcogenide 2p states at the top of the valence band encourages increased valence band dispersion. The authors extend this mixing concept further, by using quantum chem. techniques to study ternary copper phosphides as potential high mobility p-type materials. The authors use hybrid d. functional theory to examine a family of phosphides, namely, MCuP (M = Mg, Ca, Sr, Ba) which all possess extremely disperse valence band maxima, comparable to the dispersion of excellent industry std. n-type transparent conducting oxides. As a proof of concept, the authors synthesized and characterized powders of CaCuP, showing that they display high levels of p-type cond., without any external acceptor dopant. Lastly, the role of Cu-coordination in promoting valence band dispersion and provide design principles for producing degenerate p-type materials are discussed.
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22. 22
  Varley, J. B.; Miglio, A.; Ha, V.-A.; van Setten, M. J.; Rignanese, G.-M.; Hautier, G. High-Throughput Design of Non-oxide p-Type Transparent Conducting Materials: Data Mining, Search Strategy, and Identification of Boron Phosphide. Chem. Mater. 2017, 29, 2568– 2573, DOI: 10.1021/acs.chemmater.6b04663
  22
  High-Throughput Design of Non-oxide p-Type Transparent Conducting Materials: Data Mining, Search Strategy, and Identification of Boron Phosphide
  Varley, Joel B.; Miglio, Anna; Ha, Viet-Anh; van Setten, Michiel J.; Rignanese, Gian-Marco; Hautier, Geoffroy
  Chemistry of Materials (2017), 29 (6), 2568-2573CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  High-performance p-type transparent conducting materials (TCMs) are needed in a wide range of applications ranging from solar cells to transparent electronics. p-type TCMs require a large band gap (for transparency), low hole effective mass (for high mobility), and hole dopability. Oxides have inherent limitations in terms of hole effective masses making them difficult to use as a high-performance p-type TCM. The authors use a high-throughput computational approach to identify novel, nonoxide, p-type TCMs. By data mining a large computational data set (more than 30,000 compds.), nonoxide materials can lead to much lower hole effective masses but to the detriment of smaller gaps and lower transparencies. The authors propose a strategy to overcome this fundamental correlation between low effective mass and small band gap by exploiting the weak absorption for indirect optical transitions. The authors apply this strategy to phosphides and identify zinc blende boron phosphide (BP) as a very promising candidate. Follow-up computational studies on defects formation indicate that BP can also be doped p-type and potentially n-type as well. The authors' work demonstrates how high-throughput computational design can lead to identification of materials with exceptional properties, and the authors propose a strategy to open the design of TCMs to nonoxide materials.
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23. 23
  Williamson, B. A. D.; Limburn, G. J.; Watson, G. W.; Hyett, G.; Scanlon, D. O. Computationally Driven Discovery of Layered Quinary Oxychalcogenides: Potential p-Type Transparent Conductors?. Matter 2020, 3, 759– 781, DOI: 10.1016/j.matt.2020.05.020
  23
  Computationally Driven Discovery of Layered Quinary Oxychalcogenides: Potential p-Type Transparent Conductors?
  Williamson Benjamin A D; Scanlon David O; Williamson Benjamin A D; Scanlon David O; Limburn Gregory J; Hyett Geoffrey; Watson Graeme W; Scanlon David O
  Matter (2020), 3 (3), 759-781 ISSN:.
  n-type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high-performance p-type TC has lagged far behind that of its n-type counterparts, delaying the advent of "transparent electronics"-based p-n junctions. Here, we propose the layered oxysulfide [Cu2S2][Sr3Sc2O5] as a structural motif for discovering p-type TCs. We have used density functional theory to screen 24 compositions based on this motif in terms of their thermodynamic and dynamic stability and their electronic structure, thus predicting two p-type TCs and eight other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu2S2][Ba3Sc2O5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC.
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24. 24
  Willis, J.; Scanlon, D. O. Latest directions in p-type transparent conductor design. J. Mater. Chem. C 2021, 9, 11995– 12009, DOI: 10.1039/D1TC02547C
  24
  Latest directions in p-type transparent conductor design
  Willis, Joe; Scanlon, David O.
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2021), 9 (36), 11995-12009CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  A review. Transparent conducting materials (TCMs) are crucial in the operation of modern opto-electronic devices, combining the lucrative properties of optical transparency and electronic cond. More than ever we rely on display and touch screens, energy efficient windows and solar cells in our day to day lives. The market for transparent electronics is projected to surpass $3.8 billion by 2026 as the automotive industry seek to incorporate pop-up displays into driver windshields, and the prospect of touch-enabled transparent displays challenges the traditional mouse and keyboard mode of computer operation. However, these new technologies rely heavily on the development of high performance p-type TCMs, a task that has posed a significant challenge to researchers for decades. This review will cover the basic theory and design principles of transparent conductors, followed by an overview of early p-type TCMs and their shortcomings. We discuss the impact of high-throughput screening studies on materials discovery and critically assess the family of p-type halide perovskites that emerged from these, ruling them as unsuitable candidates for high-performance applications. We find that phosphides, selenides, tellurides and halides are the most promising emerging materials, capable of achieving greater valence band dispersion than traditional oxides, and we discuss the challenges facing these more exotic systems. The smorgasbord of materials presented in this review should guide exptl. and computational scientists alike in the next phase of p-type transparent conductor research.
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25. 25
  Willis, J.; Bravić, I.; Schnepf, R. R.; Heinselman, K. N.; Monserrat, B.; Unold, T.; Zakutayev, A.; Scanlon, D. O.; Crovetto, A. Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films. Chem. Sci. 2022, 13, 5872– 5883, DOI: 10.1039/D2SC01538B
  25
  Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films
  Willis, Joe; Bravic, Ivona; Schnepf, Rekha R.; Heinselman, Karen N.; Monserrat, Bartomeu; Unold, Thomas; Zakutayev, Andriy; Scanlon, David O.; Crovetto, Andrea
  Chemical Science (2022), 13 (20), 5872-5883CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concn. and hole mobility exceed 1 x 1020 cm-3 and 35 cm2 V-1 s-1 at room temp., resp. Transport calcns. indicate potential for even higher mobilities. Copper vacancies are identified as the main source of cond., displaying markedly different behavior compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calcns. of phonon-mediated indirect transitions. This discrepancy could be partly attributed to cryst. imperfections within the films, increasing the strength of indirect transitions. We det. the transparent conductor figure of merit of CaCuP films as a function of compn., revealing links between stoichiometry, cryst. quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.
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26. 26
  Crovetto, A.; Adamczyk, J. M.; Schnepf, R. R.; Perkins, C. L.; Hempel, H.; Bauers, S. R.; Toberer, E. S.; Tamboli, A. C.; Unold, T.; Zakutayev, A. Boron Phosphide Films by Reactive Sputtering: Searching for a P-Type Transparent Conductor. Adv. Mater. Interfaces 2022, 9, 2200031, DOI: 10.1002/admi.202200031
  26
  Boron Phosphide Films by Reactive Sputtering: Searching for a P-Type Transparent Conductor
  Crovetto, Andrea; Adamczyk, Jesse M.; Schnepf, Rekha R.; Perkins, Craig L.; Hempel, Hannes; Bauers, Sage R.; Toberer, Eric S.; Tamboli, Adele C.; Unold, Thomas; Zakutayev, Andriy
  Advanced Materials Interfaces (2022), 9 (12), 2200031CODEN: AMIDD2; ISSN:2196-7350. (Wiley-VCH Verlag GmbH & Co. KGaA)
  With an indirect band gap in the visible and a direct band gap at a much higher energy, boron phosphide (BP) holds promise as an unconventional p-type transparent conductor. This work reports on reactive sputtering of amorphous BP films, their partial crystn. in a P-contg. annealing atm., and extrinsic doping by C and Si. The highest hole concn. to date for p-type BP (5 x 1020 cm-3) is achieved using C doping under B-rich conditions. Furthermore, bipolar doping is confirmed to be feasible in BP. An anneal temp. of at least 1000°C is necessary for crystn. and dopant activation. Hole mobilities are low and indirect optical transitions are stronger than that predicted by theory. Low cryst. quality probably plays a role in both cases. High figures of merit for transparent conductors might be achievable in extrinsically doped BP films with improved cryst. quality.
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27. 27
  Bädeker, K. Über die elektrische Leitfähigkeit und die thermoelektrische Kraft einiger Schwermetallverbindungen. Ann. Phys. 1907, 327, 749– 766, DOI: 10.1002/andp.19073270409
  There is no corresponding record for this reference.
28. 28
  Grundmann, M.; Schein, F.-L.; Lorenz, M.; Böntgen, T.; Lenzner, J.; von Wenckstern, H. Cuprous iodide - a p-type transparent semiconductor: history and novel applications. Phys. Status Solidi A 2013, 210, 1671– 1703, DOI: 10.1002/pssa.201329349
  28
  Cuprous iodide: A p-type transparent semiconductor, history, and novel applications
  Grundmann, Marius; Schein, Friedrich-Leonhard; Lorenz, Michael; Boentgen, Tammo; Lenzner, Joerg; von Wenckstern, Holger
  Physica Status Solidi A: Applications and Materials Science (2013), 210 (9), 1671-1703CODEN: PSSABA; ISSN:1862-6300. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Halide semiconductors stand at the very beginning of semiconductor science and technol. CuI was reported as the first transparent conductor, and the first field effect transistor was made from KBr. Although halogens are frequently used in semiconductor prepn., little use is currently made from halide semiconductors in electronics and photonics. We review past reports on the metal halide semiconductor CuI and related alloys and discuss recent progress with regard to this material including its use in org. electronics and solar cells as well as our own work on fully transparent bipolar heterostructure diodes (p-CuI/n-ZnO) with high rectification of several 107 and ideality factors down to 1.5. γ-CuI(111) thin film on glass (1 × 1 cm2) and IV-characteristics of p-CuI/n-ZnO/a-Al2O3 bipolar heterojunction diode.
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29. 29
  Yang, C.; Kneiβ, M.; Lorenz, M.; Grundmann, M. Room-temperature synthesized copper iodide thin film as degenerate p-type transparent conductor with a boosted figure of merit. Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 12929– 12933, DOI: 10.1073/pnas.1613643113
  29
  Room-temperature synthesized copper iodide thin film as degenerate p-type transparent conductor with a boosted figure of merit
  Yang, Chang; Kneiβ, Max; Lorenz, Michael; Grundmann, Marius
  Proceedings of the National Academy of Sciences of the United States of America (2016), 113 (46), 12929-12933CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
  A degenerate p-type conduction of cuprous iodide (CuI) thin films is achieved at the iodine-rich growth condition, allowing for the record high room-temp. cond. of ∼156 S/cm for as-deposited CuI and ∼283 S/cm for I-doped CuI. At the same time, the films appear clear and exhibit a high transmission of 60-85% in the visible spectral range. The realization of such simultaneously high cond. and transparency boosts the figure of merit of a p-type TC: its value jumps from ∼200 to ∼17,000 MΩ-1. Polycryst. CuI thin films were deposited at room temp. by reactive sputtering. Their elec. and optical properties are examd. relative to other p-type transparent conductors. The transport properties of CuI thin films were investigated by temp.-dependent cond. measurements, which reveal a semiconductor-metal transition depending on the iodine/argon ratio in the sputtering gas.
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30. 30
  Ahn, K.; Kim, G. H.; Kim, S.-J.; Kim, J.; Ryu, G.-S.; Lee, P.; Ryu, B.; Cho, J. Y.; Kim, Y.-H.; Kang, J.; Kim, H.; Noh, Y.-Y.; Kim, M.-G. Highly Conductive p-Type Transparent Conducting Electrode with Sulfur-Doped Copper Iodide. Chem. Mater. 2022, 34, 10517– 10527, DOI: 10.1021/acs.chemmater.2c02603
  30
  Highly Conductive p-Type Transparent Conducting Electrode with Sulfur-Doped Copper Iodide
  Ahn, Kyunghan; Kim, Ga Hye; Kim, Se-Jun; Kim, Jihyun; Ryu, Gi-Seong; Lee, Paul; Ryu, Byungki; Cho, Jung Young; Kim, Yong-Hoon; Kang, Joohoon; Kim, Hyungjun; Noh, Yong-Young; Kim, Myung-Gil
  Chemistry of Materials (2022), 34 (23), 10517-10527CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  Although n-type transparent conductors have been commercialized with high optical transmittance and elec. cond., the realization of their p-type counterparts has been a challenging problem. Here, we report the synthesis of a highly conductive transparent p-type sulfur-doped CuI (CuI:S) thin film using a liq.-iodination method with a thiol additive. The CuI:S film shows a remarkably high elec. cond. of 511 S cm-1 with an optical transmittance of greater than 80%. Furthermore, addnl. hole doping of CuI:S with H2O2 treatment improves the elec. cond. to 596 S cm-1. Consequently, CuI:S exhibits a record-high figure of merit (FOM) value of 63,000 M Ω-1 (73,000 M Ω-1 with H2O2 treatment), which is ~ 370% (~ 430% with H2O2 treatment) higher than the previously reported record-high FOM value. The highly conducting CuI:S electrode is successfully applied as transparent conducting electrodes of the org. light-emitting diode and transparent p-type thin-film transistor. The liq.-iodination chem. method with unconventional control of the reaction parameters can be generalized to produce high-quality metal halide thin films, allowing them to be applicable for transparent electronics and optoelectronics.
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31. 31
  Ferhat, M.; Zaoui, A.; Certier, M.; Dufour, J.; Khelifa, B. Electronic structure of the copper halides CuCl, CuBr and Cul. Mater. Sci. Eng. B 1996, 39, 95– 100, DOI: 10.1016/0921-5107(95)01518-3
  31
  Electronic structure of the copper halides CuCl, CuBr and CuI
  Ferhat, M.; Zaoui, A.; Certier, M.; Dufour, J. P.; Khelifa, B.
  Materials Science & Engineering, B: Solid-State Materials for Advanced Technology (1996), B39 (2), 95-100CODEN: MSBTEK; ISSN:0921-5107. (Elsevier)
  The electronic band structures and densities of states of zinc-blende CuCl, CuBr, and CuI have been computed using the tight-binding method. These band structures have been used to calc. the valence and conduction band effective masses. The results are compared with other calcd. and exptl. values.
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32. 32
  Yu, H.; Cai, X.; Yang, Y.; Wang, Z.-H.; Wei, S.-H. Band gap anomaly in cuprous halides. Comput. Mater. Sci. 2022, 203, 111157, DOI: 10.1016/j.commatsci.2021.111157
  32
  Band gap anomaly in cuprous halides
  Yu, Haoyang; Cai, Xuefen; Yang, Yang; Wang, Zhi-Hao; Wei, Su-Huai
  Computational Materials Science (2022), 203 (), 111157CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
  Unlike the conventional zinc-blende II-VI and III-V common-cation systems, which exhibit a general trend of decreasing band gap with increasing anion at. no., the zinc-blende I-VII cuprous halides CuX (X = Cl, Br, and I) all have an approx. equal direct band gap. Here, using first-principles calcns., we demonstrate that this band gap anomaly in Cu halides is attributed to the unique energy level order of Cu 3d well above X p, making the valence band max. (VBM) an antibonding state derived mostly from the Cu 3d orbital, thus, a relatively small variation of the band gap with respect to the anion at. no.
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33. 33
  Crovetto, A.; Hempel, H.; Rusu, M.; Choubrac, L.; Kojda, D.; Habicht, K.; Unold, T. Water Adsorption Enhances Electrical Conductivity in Transparent P-Type CuI. ACS Appl. Mater. Interfaces 2020, 12, 48741– 48747, DOI: 10.1021/acsami.0c11040
  33
  Water Adsorption Enhances Electrical Conductivity in Transparent P-Type CuI
  Crovetto, Andrea; Hempel, Hannes; Rusu, Marin; Choubrac, Leo; Kojda, Danny; Habicht, Klaus; Unold, Thomas
  ACS Applied Materials & Interfaces (2020), 12 (43), 48741-48747CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
  CuI has been recently rediscovered as a p-type transparent conductor with a high figure of merit. Even though many metal iodides are hygroscopic, the effect of moisture on the elec. properties of CuI has not been clarified. In this work, we observe a 2-fold increase in the cond. of CuI after exposure to ambient humidity for 5 h, followed by slight long-term degrdn. Simultaneously, the work function of CuI decreases by almost 1 eV, which can explain the large spread in the previously reported work function values. The cond. increase is partially reversible and is maximized at intermediate humidity levels. On the basis of the large intragrain mobility measured by THz spectroscopy, we suggest that hydration of grain boundaries may be beneficial for the overall hole mobility.
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34. 34
  Yamada, N.; Ino, R.; Ninomiya, Y. Truly Transparent p-Type CuI Thin Films with High Hole Mobility. Chem. Mater. 2016, 28, 4971– 4981, DOI: 10.1021/acs.chemmater.6b01358
  34
  Truly Transparent p-Type γ-CuI Thin Films with High Hole Mobility
  Yamada, Naoomi; Ino, Ryuichiro; Ninomiya, Yoshihiko
  Chemistry of Materials (2016), 28 (14), 4971-4981CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The γ-phase of copper(I) iodide (γ-CuI) is a p-type semiconductor with a wide bandgap (Eg ≈ 3.1 eV). Conventionally, γ-CuI thin films were synthesized by the iodination of Cu thin layers with iodine vapor. However, γ-CuI films fabricated by this method have a rough surface and thus a frosted-glass-like appearance, which make it difficult to apply this material to transparent electronics. A simple new method is proposed for the synthesis of truly transparent p-type γ-CuI films. The chem. reaction between Cu3N thin films and solid-phase iodine at 25° yields highly transparent polycryst. γ-CuI films with shiny appearance. The γ-CuI films fabricated by this method had root-mean-square roughness values of 8-12 nm, which are <1/3 of those for γ-CuI films synthesized by the conventional method. As a result, specular transmittance of >75% in the visible region was attained. An as-prepd. film had a resistivity (ρ) of 3.1 × 10-2 Ω cm, hole d. (nh) of 8.9 × 1019 cm-3, and mobility (μ) of 2.4 cm2 V-1 s-1. Mild heat treatment at 100-150° under an inert atm. was found to suppress nh and enhance μ. The heat-treated films had μ values of 9-10 cm2 V-1 s-1, which are comparable to those of other wide-bandgap p-type semiconductors grown epitaxially at high temps. >400°. These findings would assist studies on applications of γ-CuI thin films in transparent electronics.
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35. 35
  Peng, W.; Li, L.; Yu, S.; Yang, P.; Xu, K.; Luo, W. High-performance flexible transparent p-CuI film by optimized solid iodization. Vacuum 2021, 183, 109862, DOI: 10.1016/j.vacuum.2020.109862
  35
  High-performance flexible transparent p-CuI film by optimized solid iodization
  Peng, Wei; Li, Lingxia; Yu, Shihui; Yang, Pan; Xu, Kangli; Luo, Weijia
  Vacuum (2021), 183 (), 109862CODEN: VACUAV; ISSN:0042-207X. (Elsevier Ltd.)
  High-performance flexible transparent p-CuI films were prepd. on polycarbonate substrates at room temp. by combining solid iodization and vacuum thermal evapn. The structural anal. shows that as-prepd. CuI films are polycryst. with zinc blende structure, exhibiting highly preferred oriented (1 1 1) plane. Atomic force microscope shows homogeneous surface morphol. with no fissure or exfoliation. X-ray photoelectron spectra indicate that the valence state of copper is Cu+ after being completely iodinated and the calcd. value of [I]/[Cu] increases as iodination time increase. The improvement of elec. performance is inseparable from the relative content of excess iodine. Moreover, the flexible p-CuI films exhibit a high av. transmittance of 87.1% in the visible region with excellent cond. of 31.7 S/cm, which shows superior performance than the other rigid p-type transparent conductors prepd. at high temps. In particular, flexible p-CuI films also display excellent durability and flexibility in the tests of the radius of curvature and bending cycle. These results prove that the as-prepd. p-CuI films have great potential in flexible and wearable electronics.
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36. 36
  Vora-ud, A.; Chaarmart, K.; Kasemsin, W.; Boonkirdram, S.; Seetawan, T. Transparent thermoelectric properties of copper iodide thin films. Phys. B 2022, 625, 413527, DOI: 10.1016/j.physb.2021.413527
  36
  Transparent thermoelectric properties of copper iodide thin films
  Vora-ud, Athorn; Chaarmart, Kongphope; Kasemsin, Wassana; Boonkirdram, Sarawoot; Seetawan, Tosawat
  Physica B: Condensed Matter (Amsterdam, Netherlands) (2022), 625 (), 413527CODEN: PHYBE3; ISSN:0921-4526. (Elsevier B.V.)
  Copper Iodide (CuI) transparent thin films were synthesized by using the as-deposited Cu thin film dip in the Iodine (I2) soln. (1% per 100 cc.) for 15s, 30s, and 60s within the liq. iodination method. The as-deposited Cu thin films on glass slide substrates as used were prepd. by a dc magnetron sputtering method from the Cu target. The microstructure, morphol., and thermoelec. properties were studied by using X-ray diffraction (XRD) techniques, SEM (SEM), and the ZEM-3 method, resp. The optical property of the film samples was detd. from measured transmittance using a UV-visible spectrophotometer. The optical bandgap energy is 3.0 eV and the transmittance is around 80-95% for the thin film as dipped 30s. At room temp., the power factor of Cul thin films were 14.71, 17.49, and 17.48μW m-1 K-2 for as dipped 15s, 30s, and 60s, resp.
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37. 37
  Choi, C.-H.; Gorecki, J. Y.; Fang, Z.; Allen, M.; Li, S.; Lin, L.-Y.; Cheng, C.-C.; Chang, C.-H. Low-temperature, inkjet printed p-type copper(I) iodide thin film transistors. J. Mater. Chem. C 2016, 4, 10309– 10314, DOI: 10.1039/C6TC03234F
  37
  Low-temperature, inkjet printed p-type copper(I) iodide thin film transistors
  Choi, Chang-Ho; Gorecki, Jenna Y.; Fang, Zhen; Allen, Marshall; Li, Shujie; Lin, Liang-Yu; Cheng, Chun-Cheng; Chang, Chih-Hung
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (43), 10309-10314CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  Low temp. fabrication of printed p-type CuI TFTs was reported for the first time. The printed CuI film was fabricated by printing mol. CuI ink directly onto the device substrate followed by immediate crystn. of CuI nanoparticles as the solvent evapd. The substrate temp. during inkjet printing was varied in order to obtain continuous CuI films with large grain size for improved device performance. The CuI TFTs printed at 60 °C exhibited an av. field-effect mobility of 1.86 ± 1.6 cm2 V-1 s-1, with the max. value of 4.4 cm2 V-1 s-1 and an av. On/Off ratio of 101-102. This study demonstrates potential low temp., directly printed p-type TFTs for constructing transparent, complementary inorg. TFT circuits.
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38. 38
  Storm, P.; Bar, M. S.; Benndorf, G.; Selle, S.; Yang, C.; von Wenckstern, H.; Grundmann, M.; Lorenz, M. High mobility, highly transparent, smooth, p-type CuI thin films grown by pulsed laser deposition. APL Mater. 2020, 8, 091115, DOI: 10.1063/5.0021781
  38
  High mobility, highly transparent, smooth, p-type CuI thin films grown by pulsed laser deposition
  Storm, P.; Bar, M. S.; Benndorf, G.; Selle, S.; Yang, C.; von Wenckstern, H.; Grundmann, M.; Lorenz, M.
  APL Materials (2020), 8 (9), 091115CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)
  We report pulsed laser deposition being a quite suitable growth method for smooth and transparent p-type copper iodide (CuI) thin films with tailored elec. properties. The film characteristics are strongly influenced by the temp. during growth. Increasing substrate temps. result in significant improvements in crystallinity compared to deposition at room temp. In contrast to other growth techniques, the hole carrier d. p can be varied systematically between 5 x 1016 cm-3 and 1 x 1019 cm-3 with hole mobilities up to 20 cm2/V s for lowest p. The surfaces exhibit irregularly shaped grains, and the roughness can be decreased down to 1 nm. Furthermore, the samples exhibit high transmittance up to 90% in the visible spectrum. (c) 2020 American Institute of Physics.
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39. 39
  Inagaki, S.; Nakamura, M.; Aizawa, N.; Peng, L. C.; Yu, X. Z.; Tokura, Y.; Kawasaki, M. Molecular beam epitaxy of high-quality CuI thin films on a low temperature grown buffer layer. Appl. Phys. Lett. 2020, 116, 192105, DOI: 10.1063/5.0007389
  39
  Molecular beam epitaxy of high-quality CuI thin films on a low temperature grown buffer layer
  Inagaki, S.; Nakamura, M.; Aizawa, N.; Peng, L. C.; Yu, X. Z.; Tokura, Y.; Kawasaki, M.
  Applied Physics Letters (2020), 116 (19), 192105CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  The authors show a growth of high-quality thin films of a wide band gap semiconductor copper iodide (CuI) on Al2O3 substrates by mol. beam epitaxy. Employing a thin buffer layer deposited at a lower temp. (160°C) prior to the main growth, the max. growth temp. is elevated up to 240°C, resulting in a significant improvement in the crystallinity as verified by sharp x-ray diffraction peaks as well as a step-and-terrace structure obsd. by at. force microscopy. Optimum films show more intense free exciton emission in photoluminescence spectra than others, implying the suppression of defects. These results indicate that the fabrication process developed in this study is quite effective at realizing high-quality CuI thin films. (c) 2020 American Institute of Physics.
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40. 40
  Storm, P.; Bar, M. S.; Selle, S.; von Wenckstern, H.; Grundmann, M.; Lorenz, M. p-Type Doping and Alloying of CuI Thin Films with Selenium. Phys. Status Solidi RRL 2021, 15, 2100214, DOI: 10.1002/pssr.202100214
  40
  p-Type Doping and Alloying of CuI Thin Films with Selenium
  Storm, Philipp; Bar, Michael Sebastian; Selle, Susanne; von Wenckstern, Holger; Grundmann, Marius; Lorenz, Michael
  Physica Status Solidi RRL: Rapid Research Letters (2021), 15 (8), 2100214CODEN: PSSRCS; ISSN:1862-6254. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The impact of the intentional selenium doping of CuI thin films is investigated concerning crucial cryst., elec. and optical properties. For selenium contents in between x(Se)= 0.1 at.% and x(Se)= 1 at.%, the carrier d. can be systematically adjusted by the selenium supply during growth between p=1015 cm-3 and p=8x1017 cm-3 while transparency and crystallinity remain unaffected. By temp.-dependent Hall-effect measurements, a carrier freeze out is obsd. and the binding energy of the selenium dopant is detd. The long-term elec. stability in combination with Al2O3 cappings is significantly improved compared to undoped or oxygen doped CuI. However, for selenium contents exceeding x(Se)= 1 at.%, major cryst. changes are obsd. that are presumably correlated to a phase transformation. Transmission and elec. measurements suggest that the soly. limit of Se in CuI is about 1 at.% since a degrdn. of the transparency and decreasing free hole densities are obsd. for Se contents exceeding 1 at.%. Hence, the doping limit for Se in CuI corresponds to ≈1 at.%.
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41. 41
  Chen, D.; Wang, Y.; Lin, Z.; Huang, J.; Chen, X.; Pan, D.; Huang, F. Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal. Cryst. Growth Des. 2010, 10, 2057– 2060, DOI: 10.1021/cg100270d
  41
  Growth Strategy and Physical Properties of the High Mobility P-Type CuI Crystal
  Chen, Dagui; Wang, Yongjing; Lin, Zhang; Huang, Jiakui; Chen, Xian Zhi; Pan, Danmei; Huang, Feng
  Crystal Growth & Design (2010), 10 (5), 2057-2060CODEN: CGDEFU; ISSN:1528-7483. (American Chemical Society)
  Acquiring stable binary wide band-gap semiconductor (WBS) materials with high p-type mobility is essential for the development of WBS optoelectronic devices. CuI is a p-type WBS material with a large band gap (3.1 eV) and high exciton binding energy (62 meV). However, the semiconductor characteristics of the CuI single crystal are unknown due to the lack of a large sized and high quality crystal. Our approach focuses on the design of the mineralizer for the hydrothermal method to effectively control the growth habit and the impurity concn. in the crystal. A large size (15 mm × 10 mm × 1 mm) and high quality CuI single crystal is obtained by using a new mineralizer (NH4I + KI). The crystal shows high p-type mobility (43.9 cm2·V-1·S1-). The strong and sharp band-edge emission at 410 nm indicates that the interband excitonic transition dominates the optical response in the spectrum. Such a binary cryst. material may open the way to new applications in optoelectronic devices.
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42. 42
  Lv, Y.; Xu, Z.; Ye, L.; Zhang, Z.; Su, G.; Zhuang, X. Large CuI semiconductor single crystal growth by a temperature reduction method from an NH₄I aqueous solution. CrystEngComm 2015, 17, 862– 867, DOI: 10.1039/C4CE02045F
  42
  Large γ-CuI semiconductor single crystal growth by a temperature reduction method from an NH4I aqueous solution
  Lv, Yangyang; Xu, Zhihuang; Ye, Liwang; Zhang, Zhaojun; Su, Genbo; Zhuang, Xinxin
  CrystEngComm (2015), 17 (4), 862-867CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
  NH4I has been proven to be a promising cosolvent for cuprous iodide (CuI) single crystal growth from aq. solns. by the temp. redn. method. In our work, as compared with NH4Cl and NH4Br, NH4I offers more advantages for single crystal growth, such as by remarkably increasing the soly. and growth rate of CuI crystals, effectively reducing the impurity concn., and enhancing the crystal quality and crystallinity. A regular, centimeter-sized, high optical quality single crystal was successfully obtained using NH4I as a cosolvent. The electronic and optical properties of the as-grown crystal were characterized by Hall-effect measurements and optical transmission and photoluminescence spectra, resp. The results demonstrated that the CuI crystal is conductive (high p-type mobility of 12.81 cm2 V-1 s-1) and transparent (great transmittance over 80%).
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43. 43
  Liu, A.; Zhu, H.; Park, W.-T.; Kim, S.-J.; Kim, H.; Kim, M.-G.; Noh, Y.-Y. High-performance p-channel transistors with transparent Zn doped-CuI. Nat. Commun. 2020, 11, 4309, DOI: 10.1038/s41467-020-18006-6
  43
  High-performance p-channel transistors with transparent Zn doped-CuI
  Liu, Ao; Zhu, Huihui; Park, Won-Tae; Kim, Se-Jun; Kim, Hyungjun; Kim, Myung-Gil; Noh, Yong-Young
  Nature Communications (2020), 11 (1), 4309CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
  'Ideal' transparent p-type semiconductors are required for the integration of high-performance thin-film transistors (TFTs) and circuits. Although CuI has recently attracted attention owing to its excellent opto-elec. properties, soln. processability, and low-temp. synthesis, the uncontrolled copper vacancy generation and subsequent excessive hole doping hinder its use as a semiconductor material in TFT devices. In this study, we propose a doping approach through soft chem. soln. process and transparent p-type Zn-doped CuI semiconductor for high-performance TFTs and circuits. The optimized TFTs annealed at 80°C exhibit a high hole mobility of over 5 cm2 V-1 s-1 and high on/off current ratio of ~ 10-7 with good operational stability and reproducibility. The CuI:Zn semiconductors show intrinsic advantages for next-generation TFT applications and wider applications in optoelectronics and energy conversion/storage devices. This study paves the way for the realization of transparent, flexible, and large-area integrated circuits combined with n-type metal-oxide semiconductor.
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44. 44
  He, T.; Zhou, Y.; Yuan, P.; Yin, J.; Gutiérrez-Arzaluz, L.; Chen, S.; Wang, J.-X.; Thomas, S.; Alshareef, H. N.; Bakr, O. M.; Mohammed, O. F. Copper Iodide Inks for High-Resolution X-ray Imaging Screens. ACS Energy Lett. 2023, 8, 1362– 1370, DOI: 10.1021/acsenergylett.3c00097
  44
  Copper Iodide Inks for High-Resolution X-ray Imaging Screens
  He, Tengyue; Zhou, Yang; Yuan, Peng; Yin, Jun; Gutierrez-Arzaluz, Luis; Chen, Shulin; Wang, Jian-Xin; Thomas, Simil; Alshareef, Husam N.; Bakr, Osman M.; Mohammed, Omar F.
  ACS Energy Letters (2023), 8 (3), 1362-1370CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)
  Cu-based halide scintillators have attracted considerable interest because of their high light yields, low detection limits, low toxicity, and moderate fabrication conditions. Here, the authors synthesized two Cu(I) iodide inks, comprising zero-dimensional Cu4I6(L1)2 nanoparticles (L1 = 1-propyl-1,4-diazabicyclo[2.2.2]octan-1-ium) and 1-dimensional Cu4I6(L2)2 nanorods (L2 = 4-dimethylamino-1-ethylpyridinium) for x-ray imaging application. The Cu4I6(L1)2 nanoparticles and Cu4I6(L2)2 nanorods exhibited broadband green and yellow emission with an ultrahigh photoluminescence quantum yield of 95.3% and 92.2%, resp. Consequently, the two Cu(I) iodide ink-based x-ray screens exhibited low detection limits of 96.4 and 102.1 nGy s-1, resp., which are ∼55 times lower than the dose required for std. medical diagnosis (5.5 μGy s-1). Importantly, both the scintillation screens exhibited extraordinary x-ray imaging resolns. exceeding 30 lp mm-1, more than double those of the conventional CsI:Tl and Ga2O2S:Tb scintillators. This study provides a new avenue for exploring high-resoln. x-ray imaging screens from Cu-based halide ink for medical radiog. and nondestructive detection.
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45. 45
  Schein, F.-L.; von Wenckstern, H.; Grundmann, M. Transparent p-CuI/n-ZnO heterojunction diodes. Appl. Phys. Lett. 2013, 102, 092109, DOI: 10.1063/1.4794532
  45
  Transparent p-CuI/n-ZnO heterojunction diodes
  Schein, Friedrich-Leonhard; von Wenckstern, Holger; Grundmann, Marius
  Applied Physics Letters (2013), 102 (9), 092109/1-092109/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  Transparent and elec. conducting p-type CuI thin-films form highly rectifying p-CuI/n-ZnO diodes. Sputtered Cu thin films on glass were transformed into polycryst. γ-CuI by exposing them to I vapor. The elec. parameters extd. from Hall effect are p = 5 × 1018 cm-3, μh,Hall = 6 cm2/Vs, and ρ = 0.2 Ω cm for hole concn., mobility, and elec. resistivity, resp. Heterostructures consisting of p-CuI and pulsed-laser deposited n-ZnO were fabricated on a-plane sapphire substrates. The p-CuI/n-ZnO diode exhibits a current rectification ratio of 6 × 106 at ±2 V and an ideality factor of η = 2.14. (c) 2013 American Institute of Physics.
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46. 46
  Annadi, A.; Zhang, N.; Boon Kiang Lim, D.; Gong, H. New Transparent Magnetic Semiconductor Ni_xCu_1–xI which Can Perform as Either P-type or N-type and Success in the P–N Homojunction Diode. ACS Appl. Mater. Interfaces 2020, 12, 6048– 6055, DOI: 10.1021/acsami.9b19550
  46
  New Transparent Magnetic Semiconductor NixCu1-xI which Can Perform as Either P-type or N-type and Success in the P-N Homojunction Diode
  Annadi, Anil; Zhang, Nengduo; Boon Kiang Lim, David; Gong, Hao
  ACS Applied Materials & Interfaces (2020), 12 (5), 6048-6055CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
  A semiconductor that can be doped to be either p-type or n-type is of great importance, as p-n homojunctions are desirable for realizing various electronic devices and processes. However, because of pervasive doping asymmetry for wide band gap semiconductors, the achievement of both p-type and n-type in a single wide gap material is very difficult. Here, the authors report the success in developing a new transparent magnetic NixCu1-xI halide semiconductor that can be either p-type or n-type depending on Ni fraction in NixCu1-xI. For 0 ≤ x ≤ 0.10, NixCu1-xI films show p-type cond. For the range 0.15 ≤ x ≤ 0.35, NixCu1-xI films show an n-type character. The NixCu1-xI films are elec. conducting and optically transparent and show soft ferromagnetic behavior with an optimum cond. of 42 S cm-1 (x = 0.03) and visible light transmission of 80%. UPS studies on NixCu1-xI films reveal the systematic Fermi level shift toward the conduction band with respect to the valence band as a function Ni concn. XPS anal. on Ni and I peak positions reveals Ni+2 valence for Ni in NixCu1-xI films, with signatures of Ni-I bonding. The obsd. p-type behavior originates from Cu vacancy, while the n-type character is identified to originate from the electron donor states generated by Ni incorporation in NixCu1-xI. The constructed homojunction with p-Ni0.0Cu1.0I/n-Ni0.16Cu0.84I shows a characteristic p-n junction behavior with a good rectification ratio of 2 × 102. This new type of NixCu1-xI transparent semiconductor with a tunable carrier type and magnetism may be a candidate for halide-based optoelectronic as well as spintronics development.
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47. 47
  Lee, J. H.; Lee, W.-J.; Kim, T. H.; Lee, T.; Hong, S.; Kim, K. H. Transparent p-CuI/n-BaSnO₃- δ heterojunctions with a high rectification ratio. J. Phys.: Condens. Matter 2017, 29, 384004, DOI: 10.1088/1361-648X/aa7cbf
  47
  Transparent p-CuI/n-BaSnO3-δ heterojunctions with a high rectification ratio
  Lee, Jeong Hyuk; Lee, Woong-Jhae; Kim, Tai Hoon; Lee, Takhee; Hong, Seunghun; Kim, Kee Hoon
  Journal of Physics: Condensed Matter (2017), 29 (38), 384004/1-384004/8CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)
  Transparent p-CuI/n-BaSnO3-δ heterojunction diodes were successfully fabricated by the thermal evapn. of a (1 1 1) oriented γ-phase CuI film on top of an epitaxial BaSnO3-δ(0 0 1) film grown by the pulsed laser deposition. Upon the thickness of the CuI film being increased from 30 to 400 nm, the hole carrier d. was systematically reduced from 6.0 × 1019 to 1.0 × 1019 cm-3 and the corresponding rectification ratio of the pn diode was proportionally enhanced from ∼10 to ∼106. An energy band diagram exhibiting the type-II band alignment is proposed to describe the behavior of the heterojunction diode. A shift of a built-in potential caused by the hole carrier d. change in the CuI film is attributed to the thickness-dependent rectification ratio. The best performing p-CuI/n-BaSnO3-δ diode exhibited a high current rectification ratio of 6.75 × 105 at ±2 V and an ideality factor of ∼1.5.
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48. 48
  Ding, K.; Hu, Q.; Chen, D.; Zheng, Q.; Xue, X.; Huang, F. Fabrication and energy band alignment of n-ZnO/p-CuI heterojunction. IEEE Electron Device Lett. 2012, 33, 1750– 1752, DOI: 10.1109/LED.2012.2218274
  48
  Fabrication and energy band alignment of n-ZnO/p-CuI heterojunction
  Ding, K.; Hu, Q. C.; Chen, D. G.; Zheng, Q. H.; Xue, X. G.; Huang, F.
  IEEE Electron Device Letters (2012), 33 (12), 1750-1752CODEN: EDLEDZ; ISSN:0741-3106. (Institute of Electrical and Electronics Engineers)
  N-ZnO/P-CuI heterojunctions are fabricated by growing undoped n-type ZnO thin films on p-type γ-CuI (111) single-crystal substrates using radio-frequency magnetron sputtering. The ZnO films are identified to be columnar structured with c-axis-preferred orientation by using X-ray diffraction and scanning electron microscope. Measurements of the energy band alignment of ZnO/CuI interface by using XPS result in a valence band offset of 1.74 eV and a conduction band offset of -1.37 eV, meaning a type-II band alignment at the interface. A typical diodelike behavior of the current-voltage curve indicates its possible applications in optoelectronics with further development.
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49. 49
  Cha, J.-H.; Jung, D.-Y. Air-stable transparent silver iodide–copper iodide heterojunction diode. ACS Appl. Mater. Interfaces 2017, 9, 43807– 43813, DOI: 10.1021/acsami.7b14378
  49
  Air-Stable Transparent Silver Iodide-Copper Iodide Heterojunction Diode
  Cha, Ji-Hyun; Jung, Duk-Young
  ACS Applied Materials & Interfaces (2017), 9 (50), 43807-43813CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
  Transparent AgI-CuI heterojunctions with high rectifying diode behavior were prepd. via vapor-phase iodization of metal thin films on transparent conducting oxide substrates. At room temp., Ag and Cu metal thin films were quickly transformed into the transparent and well-crystd. β-phase of AgI and the γ-phase of CuI, resp. The AgI and CuI films exhibited n-type and p-type semiconductor properties, resp., with wide band gaps. The heterojunctions were obtained by applying the CuI film to the AgI film in a sequential iodization process. AgI compds. generally have poor air-stability under light, making them suboptimal for use in electronic applications. Here, we used a CuI top layer to inhibit the photodecompn. of the AgI bottom layer, resulting in an air-stable and smooth AgI-CuI film. We also propose a simple patterning method for the AgI-CuI layer using selective decompn. of AgI without the need for lithog. equipment or toxic chems. Although there is metal ion exchange between the two layers, each layer has a different chem. compn. and crystal structure; therefore, the AgI-CuI heterojunction exhibits pn-diode behavior with a rectifying ratio of 9.4 × 104, which is comparable to that of other transparent pn-diodes. These findings open a new path for electronic application of AgI materials.
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50. 50
  Yang, C.; Kneiß, M.; Schein, F.-L.; Lorenz, M.; Grundmann, M. Room-temperature domain-epitaxy of copper iodide thin films for transparent CuI/ZnO heterojunctions with high rectification ratios larger than 109. Sci. Rep. 2016, 6, 21937, DOI: 10.1038/srep21937
  50
  Room-temperature Domain-epitaxy of Copper Iodide Thin Films for Transparent CuI/ZnO Heterojunctions with High Rectification Ratios Larger than 109
  Yang, Chang; Kneiss, Max; Schein, Friedrich-Leonhard; Lorenz, Michael; Grundmann, Marius
  Scientific Reports (2016), 6 (), 21937CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
  CuI is a p-type transparent conductive semiconductor with unique optoelectronic properties, including wide band gap (3.1 eV), high hole mobility (>40 cm2 V-1 s-1 in bulk), and large room-temp. exciton binding energy (62 meV). The difficulty in epitaxy of CuI is the main obstacle for its application in advanced solid-state electronic devices. Herein, room-temp. heteroepitaxial growth of CuI on various substrates with well-defined in-plane epitaxial relations is realized by reactive sputtering technique. In such heteroepitaxial growth the formation of rotation domains is obsd. and hereby systematically investigated in accordance with existing theor. study of domain-epitaxy. The controllable epitaxy of CuI thin films allows for the combination of p-type CuI with suitable n-type semiconductors with the purpose to fabricate epitaxial thin film heterojunctions. Such heterostructures have superior properties to structures without or with weakly ordered in-plane orientation. The obtained epitaxial thin film heterojunction of p-CuI(111)/n-ZnO(00.1) exhibits a high rectification up to 2 × 109 (±2 V), a 100-fold improvement compared to diodes with disordered interfaces. Also a low satn. c.d. down to 5 × 10-9 Acm-2 is formed. These results prove the great potential of epitaxial CuI as a promising p-type optoelectronic material.
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51. 51
  Liu, A.; Zhu, H.; Kim, M.-G.; Kim, J.; Noh, Y.-Y. Engineering copper iodide (CuI) for multifunctional p-type transparent semiconductors and conductors. Advanced Science 2021, 8, 2100546, DOI: 10.1002/advs.202100546
  51
  Engineering Copper Iodide (CuI) for Multifunctional p-Type Transparent Semiconductors and Conductors
  Liu, Ao; Zhu, Huihui; Kim, Myung-Gil; Kim, Junghwan; Noh, Yong-Young
  Advanced Science (Weinheim, Germany) (2021), 8 (14), 2100546CODEN: ASDCCF; ISSN:2198-3844. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Developing transparent p-type semiconductors and conductors has attracted significant interest in both academia and industry because metal oxides only show efficient n-type characteristics at room temp. Among the different candidates, copper iodide (CuI) is one of the most promising p-type materials because of its widely adjustable cond. from transparent electrodes to semiconducting layers in transistors. CuI can form thin films with high transparency in the visible light region using various low-temp. deposition techniques. This progress report aims to provide a basic understanding of CuI-based materials and recent progress in the development of various devices. The first section provides a brief introduction to CuI with respect to electronic structure, defect states, charge transport physics, and overviews the CuI film deposition methods. The material design concepts through doping/alloying approaches to adjust the optoelec. properties are also discussed in the first section. The following section presents recent advances in state-of-the-art CuI-based devices, including transparent electrodes, thermoelec. devices, p-n diodes, p-channel transistors, light emitting diodes, and solar cells. In conclusion, current challenges and perspective opportunities are highlighted.
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52. 52
  Kresse, G.; Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B 1993, 47, 558– 561, DOI: 10.1103/PhysRevB.47.558
  52
  Ab initio molecular dynamics of liquid metals
  Kresse, G.; Hafner, J.
  Physical Review B: Condensed Matter and Materials Physics (1993), 47 (1), 558-61CODEN: PRBMDO; ISSN:0163-1829.
  The authors present ab initio quantum-mech. mol.-dynamics calcns. based on the calcn. of the electronic ground state and of the Hellmann-Feynman forces in the local-d. approxn. at each mol.-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using sub-space alignment. This approach avoids the instabilities inherent in quantum-mech. mol.-dynamics calcns. for metals based on the use of a factitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows one to perform simulations over several picoseconds.
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53. 53
  Kresse, G.; Hafner, J. Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Phys. Rev. B 1994, 49, 14251– 14269, DOI: 10.1103/PhysRevB.49.14251
  53
  Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium
  Kresse, G.; Hafner, J.
  Physical Review B: Condensed Matter and Materials Physics (1994), 49 (20), 14251-69CODEN: PRBMDO; ISSN:0163-1829.
  The authors present ab initio quantum-mech. mol.-dynamics simulations of the liq.-metal-amorphous-semiconductor transition in Ge. The simulations are based on (a) finite-temp. d.-functional theory of the 1-electron states, (b) exact energy minimization and hence calcn. of the exact Hellmann-Feynman forces after each mol.-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nose' dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows the authors to perform simulations over >30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liq. and amorphous Ge in very good agreement with expt.. The simulation allows the authors to study in detail the changes in the structure-property relation through the metal-semiconductor transition. The authors report a detailed anal. of the local structural properties and their changes induced by an annealing process. The geometrical, bounding, and spectral properties of defects in the disordered tetrahedral network are studied and compared with expt.
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54. 54
  Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.17953
  54
  Projector augmented-wave method
  Blochl
  Physical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.
  There is no expanded citation for this reference.
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55. 55
  Kresse, G.; Hafner, J. Norm-conserving and ultrasoft pseudopotentials for first-row and transition elements. J. Phys.: Condens. Matter 1994, 6, 8245– 8257, DOI: 10.1088/0953-8984/6/40/015
  55
  Norm-conserving and ultrasoft pseudopotentials for first-row and transition elements
  Kresse, G.; Hafner, J.
  Journal of Physics: Condensed Matter (1994), 6 (40), 8245-57CODEN: JCOMEL; ISSN:0953-8984.
  The construction of accurate pseudopotentials with good convergence properties for the first-row and transition elements is discussed. By combining an improved description of the pseudo-wavefunction inside the cut-off radius with the concept of ultrasoft pseudopotentials introduced by Vanderbilt optimal compromise between transferability and plane-wave convergence can be achieved. With the new pseudopotentials, basis sets with no more than 75-100 plane waves per atom are sufficient to reproduce the results obtained with the most accurate norm-conserving pseudopotentials.
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56. 56
  Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 15– 50, DOI: 10.1016/0927-0256(96)00008-0
  56
  Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
  Kresse, G.; Furthmuller, J.
  Computational Materials Science (1996), 6 (1), 15-50CODEN: CMMSEM; ISSN:0927-0256. (Elsevier)
  The authors present a detailed description and comparison of algorithms for performing ab-initio quantum-mech. calcns. using pseudopotentials and a plane-wave basis set. The authors will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temp. d.-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order N2atoms scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge d. including a new special preconditioning optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. The authors have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio mol.-dynamics package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.
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57. 57
  Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab inition total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169– 11186, DOI: 10.1103/PhysRevB.54.11169
  57
  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set
  Kresse, G.; Furthmueller, J.
  Physical Review B: Condensed Matter (1996), 54 (16), 11169-11186CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  The authors present an efficient scheme for calcg. the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrixes will be discussed. This approach is stable, reliable, and minimizes the no. of order Natoms3 operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special "metric" and a special "preconditioning" optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calcns. It will be shown that the no. of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order Natoms2 scaling is found for systems contg. up to 1000 electrons. If we take into account that the no. of k points can be decreased linearly with the system size, the overall scaling can approach Natoms. They have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large no. of different systems (liq. and amorphous semiconductors, liq. simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable.
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58. 58
  Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 1999, 59, 1758– 1775, DOI: 10.1103/PhysRevB.59.1758
  58
  From ultrasoft pseudopotentials to the projector augmented-wave method
  Kresse, G.; Joubert, D.
  Physical Review B: Condensed Matter and Materials Physics (1999), 59 (3), 1758-1775CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived. The total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addn., crit. tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed-core all-electron methods. These tests include small mols. (H2, H2O, Li2, N2, F2, BF3, SiF4) and several bulk systems (diamond, Si, V, Li, Ca, CaF2, Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
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59. 59
  Perdew, J. P.; Ruzsinszky, A.; Csonka, G. I.; Vydrov, O. A.; Scuseria, G. E.; Constantin, L. A.; Zhou, X.; Burke, K. Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Phys. Rev. Lett. 2008, 100, 136406, DOI: 10.1103/PhysRevLett.100.136406
  59
  Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces
  Perdew, John P.; Ruzsinszky, Adrienn; Csonka, Gabor I.; Vydrov, Oleg A.; Scuseria, Gustavo E.; Constantin, Lucian A.; Zhou, Xiaolan; Burke, Kieron
  Physical Review Letters (2008), 100 (13), 136406/1-136406/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  Popular modern generalized gradient approxns. are biased toward the description of free-atom energies. Restoration of the first-principles gradient expansion for exchange over a wide range of d. gradients eliminates this bias. We introduce a revised Perdew-Burke-Ernzerhof generalized gradient approxn. that improves equil. properties of densely packed solids and their surfaces.
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60. 60
  Perdew, J. P.; Ernzerhof, M.; Burke, K. Rationale for mixing exact exchange with density functional approximations. J. Chem. Phys. 1996, 105, 9982– 9985, DOI: 10.1063/1.472933
  60
  Rationale for mixing exact exchange with density functional approximations
  Perdew, John P.; Ernzerhof, Matthias; Burke, Kieron
  Journal of Chemical Physics (1996), 105 (22), 9982-9985CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  D. functional approxns. for the exchange-correlation energy ExcDFA of an electronic system are often improved by admixing some exact exchange Ex: Exc ≈ ExcDFA + (1/n)(Ex - ExDFA). This procedure is justified when the error in ExcDFA arises from the λ = 0 or exchange end of the coupling-const. integral ∫01dλ Exc,λDFA. We argue that the optimum integer n is approx. the lowest order of Goerling-Levy perturbation theory which provides a realistic description of the coupling-const. dependence Exc,λ in the range 0 ≤ λ ≤ 1, whence n ≈ 4 for atomization energies of typical mols. We also propose a continuous generalization of n as an index of correlation strength, and a possible mixing of second-order perturbation theory with the generalized gradient approxn.
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61. 61
  Gonze, X.; Amadon, B.; Antonius, G.; Arnardi, F.; Baguet, L.; Beuken, J.-M.; Bieder, J.; Bottin, F.; Bouchet, J.; Bousquet, E. The ABINIT project: Impact, environment and recent developments. Comput. Phys. Commun. 2020, 248, 107042, DOI: 10.1016/j.cpc.2019.107042
  61
  The ABINIT project: Impact, environment and recent developments
  Gonze, Xavier; Amadon, Bernard; Antonius, Gabriel; Arnardi, Frederic; Baguet, Lucas; Beuken, Jean-Michel; Bieder, Jordan; Bottin, Francois; Bouchet, Johann; Bousquet, Eric; Brouwer, Nils; Bruneval, Fabien; Brunin, Guillaume; Cavignac, Theo; Charraud, Jean-Baptiste; Chen, Wei; Cote, Michel; Cottenier, Stefaan; Denier, Jules; Geneste, Gregory; Ghosez, Philippe; Giantomassi, Matteo; Gillet, Yannick; Gingras, Olivier; Hamann, Donald R.; Hautier, Geoffroy; He, Xu; Helbig, Nicole; Holzwarth, Natalie; Jia, Yongchao; Jollet, Francois; Lafargue-Dit-Hauret, William; Lejaeghere, Kurt; Marques, Miguel A. L.; Martin, Alexandre; Martins, Cyril; Miranda, Henrique P. C.; Naccarato, Francesco; Persson, Kristin; Petretto, Guido; Planes, Valentin; Pouillon, Yann; Prokhorenko, Sergei; Ricci, Fabio; Rignanese, Gian-Marco; Romero, Aldo H.; Schmitt, Michael Marcus; Torrent, Marc; van Setten, Michiel J.; Van Troeye, Benoit; Verstraete, Matthieu J.; Zerah, Gilles; Zwanziger, Josef W.
  Computer Physics Communications (2020), 248 (), 107042CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
  A review. ABINIT is a material- and nanostructure-oriented package that implements d.-functional theory (DFT) and many-body perturbation theory (MBPT) to find, from first principles, numerous properties including total energy, electronic structure, vibrational and thermodn. properties, different dielec. and non-linear optical properties, and related spectra. In the special issue to celebrate the 40th anniversary of CPC, published in 2009, a detailed account of ABINIT was included, and has been amply cited. The present article comes as a follow-up to this 2009 publication. It includes an anal. of the impact that ABINIT has had, through for example the bibliometric indicators of the 2009 publication. Links with several other computational materials science projects are described. This article also covers the new capabilities of ABINIT that have been implemented during the last three years, complementing a recent update of the 2009 article published in 2016. Phys. and tech. developments inside the abinit application are covered, as well as developments provided with the ABINIT package, such as the MULTIBINIT and A-TDEP projects, and related ABINIT organization developments such as ABIPY. The new developments are described with relevant refs., input variables, tests, and tutorials.
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62. 62
  Romero, A. H.; Allan, D. C.; Amadon, B.; Antonius, G.; Applencourt, T.; Baguet, L.; Bieder, J.; Bottin, F.; Bouchet, J.; Bousquet, E. ABINIT: Overview and focus on selected capabilities. J. Chem. Phys. 2020, 152, 124102, DOI: 10.1063/1.5144261
  62
  ABINIT: Overview and focus on selected capabilities
  Romero, Aldo H.; Allan, Douglas C.; Amadon, Bernard; Antonius, Gabriel; Applencourt, Thomas; Baguet, Lucas; Bieder, Jordan; Bottin, Francois; Bouchet, Johann; Bousquet, Eric; Bruneval, Fabien; Brunin, Guillaume; Caliste, Damien; Cote, Michel; Denier, Jules; Dreyer, Cyrus; Ghosez, Philippe; Giantomassi, Matteo; Gillet, Yannick; Gingras, Olivier; Hamann, Donald R.; Hautier, Geoffroy; Jollet, Francois; Jomard, Gerald; Martin, Alexandre; Miranda, Henrique P. C.; Naccarato, Francesco; Petretto, Guido; Pike, Nicholas A.; Planes, Valentin; Prokhorenko, Sergei; Rangel, Tonatiuh; Ricci, Fabio; Rignanese, Gian-Marco; Royo, Miquel; Stengel, Massimiliano; Torrent, Marc; van Setten, Michiel J.; Van Troeye, Benoit; Verstraete, Matthieu J.; Wiktor, Julia; Zwanziger, Josef W.; Gonze, Xavier
  Journal of Chemical Physics (2020), 152 (12), 124102CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  ABINIT Is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements d. functional theory, d.-functional perturbation theory (DFPT), many-body perturbation theory (GW approxn. and Bethe-Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the "temp.-dependent effective potential" approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, d., and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and mols. can be treated with the supercell technique. The present article starts with a brief description of the project, a summary of the theories upon which ABINIT relies, and a list of the assocd. capabilities. It then focuses on selected capabilities that might not be present in the majority of electronic structure packages either among planewave codes or, in general, treatment of strongly correlated materials using DMFT; materials under finite elec. fields; properties at nuclei (elec. field gradient, Mossbauer shifts, and orbital magnetization); positron annihilation; Raman intensities and electro-optic effect; and DFPT calcns. of response to strain perturbation (elastic consts. and piezoelectricity), spatial dispersion (flexoelectricity), electronic mobility, temp. dependence of the gap, and spin-magnetic-field perturbation. The ABINIT DFPT implementation is very general, including systems with van der Waals interaction or with noncollinear magnetism. Community projects are also described: generation of pseudopotential and PAW datasets, high-throughput calcns. (databases of phonon band structure, second-harmonic generation, and GW computations of bandgaps), and the library LIBPAW. ABINIT has strong links with many other software projects that are briefly mentioned. (c) 2020 American Institute of Physics.
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63. 63
  Brunin, G.; Miranda, H. P. C.; Giantomassi, M.; Royo, M.; Stengel, M.; Verstraete, M. J.; Gonze, X.; Rignanese, G.-M.; Hautier, G. Electron-phonon beyond Fröhlich: dynamical quadrupoles in polar and covalent solids. Phys. Rev. Lett. 2020, 125, 136601, DOI: 10.1103/PhysRevLett.125.136601
  63
  Electron-Phonon beyond Frohlich: Dynamical Quadrupoles in Polar and Covalent Solids
  Brunin, Guillaume; Miranda, Henrique Pereira Coutada; Giantomassi, Matteo; Royo, Miquel; Stengel, Massimiliano; Verstraete, Matthieu J.; Gonze, Xavier; Rignanese, Gian-Marco; Hautier, Geoffroy
  Physical Review Letters (2020), 125 (13), 136601CODEN: PRLTAO; ISSN:1079-7114. (American Physical Society)
  We include the treatment of quadrupolar fields beyond the Frohlich interaction in the first-principles electron-phonon vertex in semiconductors. Such quadrupolar fields induce long-range interactions that have to be taken into account for accurate phys. results. We apply our formalism to Si (nonpolar), GaAs, and GaP (polar) and demonstrate that electron mobilities show large errors if dynamical quadrupoles are not properly treated.
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64. 64
  Brunin, G.; Miranda, H. P. C.; Giantomassi, M.; Royo, M.; Stengel, M.; Verstraete, M. J.; Gonze, X.; Rignanese, G.-M.; Hautier, G. Phonon-limited electron mobility in Si, GaAs, and GaP with exact treatment of dynamical quadrupoles. Phys. Rev. B 2020, 102, 094308, DOI: 10.1103/PhysRevB.102.094308
  64
  Phonon-limited electron mobility in Si, GaAs, and GaP with exact treatment of dynamical quadrupoles
  Brunin, Guillaume; Miranda, Henrique Pereira Coutada; Giantomassi, Matteo; Royo, Miquel; Stengel, Massimiliano; Verstraete, Matthieu J.; Gonze, Xavier; Rignanese, Gian-Marco; Hautier, Geoffroy
  Physical Review B (2020), 102 (9), 094308CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
  We describe a new approach to compute the electron-phonon self-energy and carrier mobilities in semiconductors. Our implementation does not require a localized basis set to interpolate the electron-phonon matrix elements, with the advantage that computations can be easily automated. Scattering potentials are interpolated on dense q meshes using Fourier transforms and ab initio models to describe the long-range potentials generated by dipoles and quadrupoles. To reduce significantly the computational cost, we take advantage of crystal symmetries and employ the linear tetrahedron method and double-grid integration schemes, in conjunction with filtering techniques in the Brillouin zone. We report results for the electron mobility in Si, GaAs, and GaP obtained with this new methodol.
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65. 65
  Claes, R.; Brunin, G.; Giantomassi, M.; Rignanese, G.-M.; Hautier, G. Assessing the quality of relaxation-time approximations with fully automated computations of phonon-limited mobilities. Phys. Rev. B 2022, 106, 094302, DOI: 10.1103/PhysRevB.106.094302
  65
  Assessing the quality of relaxation-time approximations with fully automated computations of phonon-limited mobilities
  Claes, Romain; Brunin, Guillaume; Giantomassi, Matteo; Rignanese, Gian-Marco; Hautier, Geoffroy
  Physical Review B (2022), 106 (9), 094302CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
  The mobility of carriers, as limited by their scattering with phonons, can now routinely be obtained from first-principles electron-phonon coupling calcns. However, so far, most computations have relied on some form of simplification of the linearized Boltzmann transport equation based on either the self-energy or the momentum relaxation-time or const. relaxation-time approxns. Here, we develop a high-throughput infrastructure and an automatic workflow and we compute 67 phonon-limited mobilities in semiconductors. We compare the results resorting to the approxns. with the exact iterative soln. We conclude that the approx. values may deviate significantly from the exact ones and are thus not reliable. Given the minimal computational overhead, our paper encourages reliance on this exact iterative soln.
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66. 66
  M Ganose, A.; J Jackson, A.; O Scanlon, D. sumo: Command-line tools for plotting and analysis of periodic ab initio calculations. J. Open Source Softw. 2018, 3, 717, DOI: 10.21105/joss.00717
  There is no corresponding record for this reference.
67. 67
  Petretto, G.; Dwaraknath, S.; Miranda, H. P.; Winston, D.; Giantomassi, M.; Van Setten, M. J.; Gonze, X.; Persson, K. A.; Hautier, G.; Rignanese, G.-M. High-throughput density-functional perturbation theory phonons for inorganic materials. Sci. Data 2018, 5, 180065, DOI: 10.1038/sdata.2018.65
  67
  High-throughput density-functional perturbation theory phonons for inorganic materials
  Petretto, Guido; Dwaraknath, Shyam; Miranda, Henrique P. C.; Winston, Donald; Giantomassi, Matteo; van Setten, Michiel J.; Gonze, Xavier; Persson, Kristin A.; Hautier, Geoffroy; Rignanese, Gian-Marco
  Scientific Data (2018), 5 (), 180065CODEN: SDCABS; ISSN:2052-4463. (Nature Research)
  A review. The knowledge of the vibrational properties of a material is of key importance to understand phys. phenomena such as thermal cond., supercond., and ferroelectricity among others. However, detailed exptl. phonon spectra are available only for a limited no. of materials, which hinders the large-scale anal. of vibrational properties and their derived quantities. In this work, we perform ab initio calcns. of the full phonon dispersion and vibrational d. of states for 1521 semiconductor compds. in the harmonic approxn. based on d. functional perturbation theory. The data is collected along with derived dielec. and thermodn. properties. We present the procedure used to obtain the results, the details of the provided database and a validation based on the comparison with exptl. data.
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68. 68
  Graužinytė, M.; Botti, S.; Marques, M. A. L.; Goedecker, S.; Flores-Livas, J. A. Computational acceleration of prospective dopant discovery in cuprous iodide. Phys. Chem. Chem. Phys. 2019, 21, 18839– 18849, DOI: 10.1039/C9CP02711D
  68
  Computational acceleration of prospective dopant discovery in cuprous iodide
  Grauzinyte, Migle; Botti, Silvana; Marques, Miguel A. L.; Goedecker, Stefan; Flores-Livas, Jose A.
  Physical Chemistry Chemical Physics (2019), 21 (35), 18839-18849CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  The zinc blende (γ) phase of copper iodide holds the record hole cond. for intrinsic transparent p-type semiconductors. In this work, we employ a high-throughput approach to systematically explore strategies for enhancing γ-CuI further by impurity incorporation. Our objectives are not only to find a practical approach to increase the hole cond. in CuI thin films, but also to explore the possibility for ambivalent doping. In total 64 chem. elements were investigated as possible substitutionals on either the copper or the iodine site. All chalcogen elements were found to display acceptor character when substituting iodine, with sulfur and selenium significantly enhancing carrier concns. produced by the native VCu defects under conditions most favorable for impurity incorporation. Furthermore, eight impurities suitable for n-type doping were discovered. Unfortunately, our work also reveals that donor doping is hindered by compensating native defects, making ambipolar doping unlikely. Finally, we investigated how the presence of impurities influences the optical properties. In the majority of the interesting cases, we found no deep states in the band-gap, showing that CuI remains transparent upon doping.
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69. 69
  Mosquera-Lois, I.; Kavanagh, S. R.; Walsh, A.; Scanlon, D. O. ShakeNBreak: Navigating the defect configurational landscape. J. Open Source Softw. 2022, 7, 4817, DOI: 10.21105/joss.04817
  There is no corresponding record for this reference.
70. 70
  Mosquera-Lois, I.; Kavanagh, S. R.; Walsh, A.; Scanlon, D. O. Identifying the ground state structures of point defects in solids. npj Comput. Mater. 2023, 9, 25, DOI: 10.1038/s41524-023-00973-1
  70
  Identifying the ground state structures of point defects in solids
  Mosquera-Lois, Irea; Kavanagh, Sean R.; Walsh, Aron; Scanlon, David O.
  npj Computational Materials (2023), 9 (1), 25CODEN: NCMPCS; ISSN:2057-3960. (Nature Portfolio)
  Point defects are a universal feature of crystals. Their identification is addressed by combining exptl. measurements with theor. models. The std. modeling approach is, however, prone to missing the ground state at. configurations assocd. with energy-lowering reconstructions from the idealised crystallog. environment. Missed ground states compromise the accuracy of calcd. properties. To address this issue, we report an approach to navigate the defect configurational landscape using targeted bond distortions and rattling. Application of our workflow to eight materials (CdTe, GaAs, Sb2S3, Sb2Se3, CeO2, In2O3, ZnO, anatase-TiO2) reveals symmetry breaking in each host crystal that is not found via conventional local minimisation techniques. The point defect distortions are classified by the assocd. physico-chem. factors. We demonstrate the impact of these defect distortions on derived properties, including formation energies, concns. and charge transition levels. Our work presents a step forward for quant. modeling of imperfect solids.
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71. 71
  Persson, C.; Zhao, Y.-J.; Lany, S.; Zunger, A. n-type doping of CuInSe₂ and CuGaSe₂. Phys. Rev. B 2005, 72, 035211, DOI: 10.1103/PhysRevB.72.035211
  71
  n-type doping of CuInSe2 and CuGaSe2
  Persson, Clas; Zhao, Yu-Jun; Lany, Stephan; Zunger, Alex
  Physical Review B: Condensed Matter and Materials Physics (2005), 72 (3), 035211/1-035211/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  The efficiency of CuInSe2 based solar cell devices could improve significantly if CuGaSe2, a wider band gap chalcopyrite semiconductor, could be added to the CuInSe2 absorber layer. This is, however, limited by the difficulty of doping n-type CuGaSe2 and, hence, in its alloys with CuInSe2. Indeed, wider-gap members of semiconductor series are often more difficult to dope than lower-gap members of the same series. In chalcopyrites, there are 3 crit. values of the Fermi energy EF that control n-type doping: (i) EFn,pin is the value of EF where the energy to form Cu vacancies is zero. At this point, the spontaneously formed vacancies (=acceptors) kill all electrons. (ii) EFn,comp is the value of EF where the energy to form a Cu vacancy equals the energy to form an n-type dopant, e.g., CdCu. (iii) EFn,site is the value of EF where the formation of Cd-on-In is equal to the formation of Cd-on-Cu. For good n-type doping, EFn,pin, EFn,comp, and EFn,site need to be as high as possible in the gap. These quantities are higher in the gap in CuInSe2 than in CuGaSe2, so the latter is difficult to dope n-type. We calc. all 3 crit. Fermi energies and study theor. the best growth condition for n-type CuInSe2 and CuGaSe2 with possible cation and anion doping. We find that the intrinsic defects such as VCu and InCu or GaCu play significant roles in doping in both chalcopyrites. For group-II cation (Cd, Zn, or Mg) doping, the best n-type growth condition is In/Ga-rich, and maximal Se-poor, which is also the optimal condition for stabilizing the intrinsic InCu/GaCu donors. Bulk CuInSe2 can be doped at equil. n-type, but bulk CuGaSe2 cannot be due to the low formation energy of intrinsic Cu-vacancy. For halogen anion doping, the best n-type materials growth is still under In/Ga-rich, and maximal Se-poor conditions. These conditions are not best for halogen substitutional defects, but are optimal for intrinsic InCu/GaCu donors. Again, CuGaSe2 cannot be doped n-type by halogen doping, while CuInSe2 can.
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72. 72
  Lany, S.; Zunger, A. Assessment of correction methods for the band-gap problem and for finite-size effects in supercell defect calculations: Case studies for ZnO and GaAs. Phys. Rev. B 2008, 78, 235104, DOI: 10.1103/PhysRevB.78.235104
  72
  Assessment of correction methods for the band-gap problem and for finite-size effects in supercell defect calculations: Case studies for ZnO and GaAs
  Lany, Stephan; Zunger, Alex
  Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 235104/1-235104/25CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  Contemporary theories of defects and impurities in semiconductors rely to a large extent on supercell calcns. within d.-functional theory using the approx. local-d. approxn. (LDA) or generalized gradient approxn. (GGA) functionals. Such calcns. are, however, affected by considerable uncertainties assocd. with: (i) the "band-gap problem," which occurs not only in the Kohn-Sham single-particle energies but also in the quasiparticle gap (LDA or GGA) calcd. from total-energy differences, and (ii) supercell finite-size effects. In the case of the oxygen vacancy in ZnO, uncertainties (i) and (ii) have led to a large spread in the theor. predictions, with some calcns. suggesting negligible vacancy concns., even under Zn-rich conditions, and others predicting high concns. Here, we critically assess (i) the different methodologies to correct the band-gap problem. We discuss approaches based on the extrapolation of perturbations which open the band gap, and the self-consistent band-gap correction employing the LDA + U method for d and s states simultaneously. From the comparison of the results of different gap-correction, including also recent results from other literature, we conclude that to date there is no universal scheme for band gap correction in general defect systems. Therefore, we turn instead to classification of different types of defect behavior to provide guidelines on how the phys. correct situation in an LDA defect calcn. can be recovered. (ii) Supercell finite-size effects: We performed test calcns. in large supercells of up to 1728 atoms, resolving a long-standing debate pertaining to image charge corrections for charged defects. We show that once finite-size effects not related to electrostatic interactions are eliminated, the analytic form of the image charge correction as proposed by Makov and Payne leads to size-independent defect formation energies, thus allowing the calcn. of well-converged energies in fairly small supercells. We find that the delocalized contribution to the defect charge (i.e., the defect-induced change of the charge distribution) is dominated by the dielec. screening response of the host, which leads to an unexpected effective 1/L scaling of the image charge energy, despite the nominal 1/L3 scaling of the third-order term. Based on this anal., we suggest that a simple scaling of the first order term by a const. factor (approx. 2/3) yields a simple but accurate image-charge correction for common supercell geometries. Finally, we discuss the theor. controversy pertaining to the formation energy of the O vacancy in ZnO in light of the assessment of different methodologies in the present work, and we review the present exptl. situation on the topic.
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73. 73
  Lany, S.; Zunger, A. Accurate prediction of defect properties in density functional supercell calculations. Modell. Simul. Mater. Sci. Eng. 2009, 17, 084002, DOI: 10.1088/0965-0393/17/8/084002
  73
  Accurate prediction of defect properties in density functional supercell calculations
  Lany, Stephan; Zunger, Alex
  Modelling and Simulation in Materials Science and Engineering (2009), 17 (8), 084002/1-084002/14CODEN: MSMEEU; ISSN:1361-651X. (Institute of Physics Publishing)
  The theor. description of defects and impurities in semiconductors is largely based on d. functional theory (DFT) employing supercell models. The literature discussion of uncertainties that limit the predictivity of this approach has focused mostly on two issues: (1) finite-size effects, in particular for charged defects; (2) the band-gap problem in local or semi-local DFT approxns. We here describe how finite-size effects (1) in the formation energy of charged defects can be accurately cor. in a simple way, i.e. by potential alignment in conjunction with a scaling of the Madelung-like screened first order correction term. The factor involved with this scaling depends only on the dielec. const. and the shape of the supercell, and quite accurately accounts for the full third order correction according to Makov and Payne. We further discuss in some detail the background and justification for this correction method, and also address the effect of the ionic screening on the magnitude of the image charge energy. In regard to (2) the band-gap problem, we discuss the merits of non-local external potentials that are added to the DFT Hamiltonian and allow for an empirical band-gap correction without significantly increasing the computational demand over that of std. DFT calcns. In combination with LDA + U, these potentials are further instrumental for the prediction of polaronic defects with localized holes in anion-p orbitals, such as the metal-site acceptors in wide-gap oxide semiconductors.
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74. 74
  Murphy, S. T.; Hine, N. D. M. Anisotropic charge screening and supercell size convergence of defect formation energies. Phys. Rev. B 2013, 87, 094111, DOI: 10.1103/PhysRevB.87.094111
  74
  Anisotropic charge screening and supercell size convergence of defect formation energies
  Murphy, Samuel T.; Hine, Nicholas D. M.
  Physical Review B: Condensed Matter and Materials Physics (2013), 87 (9), 094111/1-094111/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  One of the main sources of error assocd. with the calcn. of defect formation energies using plane-wave d. functional theory (DFT) is finite size error resulting from the use of relatively small simulation cells and periodic boundary conditions. Most widely used methods for correcting this error, such as that of Makov and Payne, assume that the dielec. response of the material is isotropic and can be described using a scalar dielec. const. ε. However, this is strictly only valid for cubic crystals, and cannot work in highly anisotropic cases. Here we introduce a variation of the technique of extrapolation based on the Madelung potential that allows the calcn. of well-converged dil. limit defect formation energies in noncubic systems with highly anisotropic dielec. properties. As an example of the implementation of this technique we study a selection of defects in the ceramic oxide Li2TiO3 which is currently being considered as a lithium battery material and a breeder material for fusion reactors.
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75. 75
  Buckeridge, J. Equilibrium point defect and charge carrier concentrations in a material determined through calculation of the self-consistent Fermi energy. Comput. Phys. Commun. 2019, 244, 329– 342, DOI: 10.1016/j.cpc.2019.06.017
  75
  Equilibrium point defect and charge carrier concentrations in a material determined through calculation of the self-consistent Fermi energy
  Buckeridge, J.
  Computer Physics Communications (2019), 244 (), 329-342CODEN: CPHCBZ; ISSN:0010-4655. (Elsevier B.V.)
  A concise procedure to det. the self-consistent Fermi energy and defect and carrier concns. in an extended cryst. system is presented. It is assumed that the formation enthalpies of a set of variously charged point defects in thermodn. equil. are known, as well as the d. of electronic states in the defect-free system. By applying the constraint of overall charge neutrality, the self-consistent Fermi energy is detd. using an iterative searching routine. The procedure is incorporated within a Fortran code 'SC-FERMI': the input consists of the defect formation energies, d. of sites where they can form, and the degeneracy of each charge state; the material band gap; and the calcd. d. of states of the pristine system. The output is the self-consistent Fermi energy, the total concns. of each defect as well as the concn. of its individual charge states, and the free carrier concns. Furthermore, the procedure facilitates fixing the concn. of one or more defects and detg. the resulting self-consistent Fermi energy and concns. of other defects (performed using the related code 'FROZEN-SC-FERMI'), thus modeling 'frozen-in' defects which may form by kinetic, rather than thermodn., processes. One can fix the total concn. or the concn. of a particular charge state; it is also possible to introduce new defects with a fixed concn., but here the charge state must be specified. The background theory is discussed in some detail, and the operation of the program is demonstrated by some examples.Program Title:SC-FERMIProgram Files doi:http://dx.doi.org/10.17632/dh3hjdf4fc.1Licensing provisions: MIT license-Programming language:FORTRAN 90. Nature of problem: To det. the self-consistent Fermi energy and equil. defect and carrier concns. given a set of point defect formation energies in a cryst. system, assuming the constraint of charge neutrality. Soln. method: The concns. of each defect in each charge state are calcd., as are the free carrier concns. These concns. are functions of the Fermi energy. The code, using an iterative search algorithm, dets. the Fermi energy that satisfies the charge neutrality constraint (the self-consistent Fermi energy). The defect and carrier concns. at that Fermi energy are then reported, as well as the Fermi energy itself. Restrictions: Thermodn. equil. is assumed. The defect formation enthalpies and electronic d. of states of the pristine system must be known. Addnl. comments: The concns. of defects can be fixed to a particular value, thus modeling 'frozen-in' defects formed by e.g. kinetic processes. This procedure is facilitated by the related program, FROZEN-SC-FERMI, which is identical to SC-FERMI apart from the addnl. defect concn. fixing routine.
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76. 76
  Squires, A. G.; Scanlon, D. O.; Morgan, B. J. py-sc-fermi: self-consistent Fermi energies and defect concentrations from electronic structure calculations. J. Open Source Softw. 2023, 8, 4962, DOI: 10.21105/joss.04962
  There is no corresponding record for this reference.
77. 77
  D Whalley, L. effmass: An effective mass package. J. Open Source Softw. 2018, 3, 797, DOI: 10.21105/joss.00797
  There is no corresponding record for this reference.
78. 78
  Whalley, L. D.; Frost, J. M.; Morgan, B. J.; Walsh, A. Impact of nonparabolic electronic band structure on the optical and transport properties of photovoltaic materials. Phys. Rev. B 2019, 99, 085207, DOI: 10.1103/PhysRevB.99.085207
  78
  Impact of nonparabolic electronic band structure on the optical and transport properties of photovoltaic materials
  Whalley, Lucy D.; Frost, Jarvist M.; Morgan, Benjamin J.; Walsh, Aron
  Physical Review B (2019), 99 (8), 085207CODEN: PRBHB7; ISSN:2469-9969. (American Physical Society)
  The effective mass approxn. (EMA) models the response to an external perturbation of an electron in a periodic potential as the response of a free electron with a renormalized mass. For semiconductors used in photovoltaic devices, the EMA allows calcn. of important material properties from first-principles calcns., including optical properties (e.g., exciton binding energies), defect properties (e.g., donor and acceptor levels), and transport properties (e.g., polaron radii and carrier mobilities). The conduction and valence bands of semiconductors are commonly approximated as parabolic around their extrema, which gives a simple theor. description but ignores the complexity of real materials. In this work, we use d. functional theory to assess the impact of band nonparabolicity on four common thin-film photovoltaic materials-GaAs, CdTe, Cu2ZnSnS4 and CH3NH3PbI3-at temps. and carrier densities relevant for real-world applications. First, we calc. the effective mass at the band edges. We compare finite-difference, unweighted least-squares and thermally weighted least-squares approaches. We find that the thermally weighted least-squares method reduces sensitivity to the choice of sampling d. Second, we employ a Kane quasilinear dispersion to quantify the extent of nonparabolicity and compare results from different electronic structure theories to consider the effect of spin-orbit coupling and electron exchange. Finally, we focus on the halide perovskite CH3NH3PbI3 as a model system to assess the impact of nonparabolicity on calcd. electron transport and optical properties at high carrier concns. We find that at a concn. of 1020cm-3 the optical effective mass increases by a factor of two relative to the low carrier-concn. value, and the polaron mobility decreases by a factor of three. Our work suggests that similar adjustments should be made to the predicted optical and transport properties of other semiconductors with significant band nonparabolicity.
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79. 79
  Keen, D. A.; Hull, S. The high-temperature structural behaviour of copper(I) iodide. J. Phys.: Condens. Matter 1995, 7, 5793– 5804, DOI: 10.1088/0953-8984/7/29/007
  79
  The high-temperature structural behavior of copper(I) iodide
  Keen, D. A.; Hull, S.
  Journal of Physics: Condensed Matter (1995), 7 (29), 5793-804CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics)
  The structural behavior of CuI was studied between room temp. and its m.p. (TM = 878 K) using neutron powder diffraction. Detailed measurements were made in the vicinity of the two known structural phase transitions γ → β and β → α, which are obsd. at 643 ± 2 K and 673 ± 8 K. Within the Zn-blende structured γ-phase (space group F‾43m) increasing disorder of the Cu+ ion sublattice is obsd. as temp. approaches the γ → β transition, in addn. to a nonlinear thermal expansion. The hexagonal β-phase (space group P‾3m1) is obsd. as a single phase in the temp. range 645-668 K, but on 1st heating it is found to coexist with a rhombohedral phase. This transient phase was obsd. in isolation for only a short time but this was sufficient to show that its structure was that of CuI-IV (space group R‾3m), which had only been obsd. previously at elevated pressures. The high-temp. phase α-CuI has Fm‾3m symmetry with Cu+ ions distributed randomly over all the tetrahedral sites within the cubic close-packed I- sublattice.
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80. 80
  Moditswe, C.; Muiva, C. M.; Luhanga, P.; Juma, A. Effect of annealing temperature on structural and optoelectronic properties of CuI thin films prepared by the thermal evaporation method. Ceram. Int. 2017, 43, 5121– 5126, DOI: 10.1016/j.ceramint.2017.01.026
  80
  Effect of annealing temperature on structural and optoelectronic properties of γ-CuI thin films prepared by the thermal evaporation method
  Moditswe, Charles; Muiva, Cosmas M.; Luhanga, Pearson; Juma, Albert
  Ceramics International (2017), 43 (6), 5121-5126CODEN: CINNDH; ISSN:0272-8842. (Elsevier Ltd.)
  High quality transparent conducting CuI thin films were deposited at room temp. via thermal evapn. technique followed by post deposition annealing at different temps. The samples were characterised by X-ray diffraction (XRD), UV-Vis spectrophotometry, SEM and I-V measurements. The structural, morphol. and optical properties were studied as a function of the annealing temp. from room temp. (RT) to 200°C. XRD results revealed that the films were polycryst. with zinc blende structure of cubic phase. Increasing the annealing temp. increased the crystallite size from 33 to 49 nm while the dislocation d. and lattice strain shifted to lower values. High transmittance of about 70-80% was exhibited by all films in the entire visible spectral range. The as deposited film possesed the lowest resistivity of 3.0×10-3 Ω cm.
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81. 81
  Ves, S.; Glötzel, D.; Cardona, M.; Overhof, H. Pressure dependence of the optical properties and the band structure of the copper and silver halides. Phys. Rev. B 1981, 24, 3073– 3085, DOI: 10.1103/PhysRevB.24.3073
  81
  Pressure dependence of the optical properties and the band structure of the copper and silver halides
  Ves, S.; Gloetzel, D.; Cardona, M.; Overhof, H.
  Physical Review B: Condensed Matter and Materials Physics (1981), 24 (6), 3073-85CODEN: PRBMDO; ISSN:0163-1829.
  The absorption edge of CuCl, CuBr, CuI, and AgI was investigated with a diamond anvil cell as a function of pressure up to 16 GPa. The measurements, which reflect the various phase transitions undergone by these materials, yield the pressure coeffs. of the lowest gaps. Particular attention was paid to the high-pressure rock salt modifications, which have an indirect absorption edge in contrast to the direct edge of the sphalerite phases. This results from the influence of the different lattice symmetries on the halogen-p-metal-d hybridization in the valence bands. To interpret the data quant., self-consistent local-d. calcns. were performed with the linear combination of muffin-tin-orbitals-at.-sphere approxn. method and non-self-consistent Korringa-Kohn-Rostoker calcns. with the std. muffin-tin potential. The pressure-coeffs. so obtained agree reasonably with the exptl. ones. The gaps obtained by the self-consistent potential (with no adjustable parameter) are ∼2 eV smaller than the exptl. ones, thus reflecting shortcomings of the local-d. method for excitation properties.
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82. 82
  Blacha, A.; Cardona, M.; Christensen, N.; Ves, S.; Overhof, H. Volume dependence of the spin-orbit splitting in the copper halides. Physica B+C 1983, 117–118, 63– 65, DOI: 10.1016/0378-4363(83)90441-2
  There is no corresponding record for this reference.
83. 83
  Ganose, A. M.; Park, J.; Faghaninia, A.; Woods-Robinson, R.; Persson, K. A.; Jain, A. Efficient calculation of carrier scattering rates from first principles. Nat. Commun. 2021, 12, 2222, DOI: 10.1038/s41467-021-22440-5
  83
  Efficient calculation of carrier scattering rates from first principles
  Ganose, Alex M.; Park, Junsoo; Faghaninia, Alireza; Woods-Robinson, Rachel; Persson, Kristin A.; Jain, Anubhav
  Nature Communications (2021), 12 (1), 2222CODEN: NCAOBW; ISSN:2041-1723. (Nature Research)
  The electronic transport behavior of materials dets. their suitability for technol. applications. We develop a computationally efficient method for calcg. carrier scattering rates of solid-state semiconductors and insulators from first principles inputs. The present method extends existing polar and non-polar electron-phonon coupling, ionized impurity, and piezoelec. scattering mechanisms formulated for isotropic band structures to support highly anisotropic materials. We test the formalism by calcg. the electronic transport properties of 23 semiconductors, including the large 48 atom CH3NH3PbI3 hybrid perovskite, and comparing the results against exptl. measurements and more detailed scattering simulations. The Spearman rank coeff. of mobility against expt. (rs = 0.93) improves significantly on results obtained using a const. relaxation time approxn. (rs = 0.52). We find our approach offers similar accuracy to state-of-the art methods at approx. 1/500th the computational cost, thus enabling its use in high-throughput computational workflows for the accurate screening of carrier mobilities, lifetimes, and thermoelec. power.
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84. 84
  Hennion, B.; Moussa, F.; Prevot, B.; Carabatos, C.; Schawb, C. Normal Modes of Vibrations in CuI. Phys. Rev. Lett. 1972, 28, 964– 966, DOI: 10.1103/PhysRevLett.28.964
  84
  Normal modes of vibrations in copper(I) iodide
  Hennion, B.; Moussa, F.; Prevot, B.; Carabatos, C.; Schwab, C.
  Physical Review Letters (1972), 28 (15), 964-6CODEN: PRLTAO; ISSN:0031-9007.
  Phonon dispersion curves for CuI were measured at room temp. for the [100], [110], and [111] symmetry directions by using inelastic neutron scattering. The results are interpreted in terms of a rigid-ion model. Estns. are given for elastic consts.
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85. 85
  Fukumoto, T.; Nakashima, S.; Tabuchi, K.; Mitsuishi, A. Temperature Dependence of Raman Spectra of Cuprous Halides. Phys. Status Solidi B 1976, 73, 341– 351, DOI: 10.1002/pssb.2220730134
  85
  Temperature dependence of Raman spectra of cuprous halides
  Fukumoto, T.; Nakashima, S.; Tabuchi, K.; Mitsuishi, A.
  Physica Status Solidi B: Basic Research (1976), 73 (1), 341-51CODEN: PSSBBD; ISSN:0370-1972.
  The temp. dependence of the half linewidth and frequency shift of Raman lines in cuprous halides were investigated at 4.2-300°K. As for the LO and TO mode of CuI and CuBr, and the LO mode of CuCl, the exptl. linewidth and frequency shift are in good agreement with the theor. ones which were calcd. in terms of 3-phonon interaction. In order to explain the temp. dependence of a strong combination mode in conjunction with the TO phonons of CuCl, the hybridization theory proposed by J. Ruvalds and A. Zawadowski (1971) was employed in which hybridization between a 2-phonon and a single phonon state is postulated. A numerical anal. was made assuming that the acoustic combination mode (TA + LA) hybridizes with the TO mode. The anomalous frequency shift and line broadening of the strong combination line were explained by the temp. dependence of the coupling const. of 2 acoustic phonons (between TA and LA mode). The linewidth and frequency shift of the TO mode can be explained in some degree by this hybridization theory.
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86. 86
  Hanson, R.; Hallberg, J.; Schwab, C. Elastic and piezoelectric constants of the cuprous halides. Appl. Phys. Lett. 1972, 21, 490– 492, DOI: 10.1063/1.1654230
  86
  Elastic and piezoelectric constants of the cuprous halides
  Hanson, R. C.; Hallberg, J. R.; Schwab, C.
  Applied Physics Letters (1972), 21 (10), 490-2CODEN: APPLAB; ISSN:0003-6951.
  Elastic and piezoelec. consts. of CuCl, CuBr, and CuI were measured. The elastic consts. of zinc-blende-structure materials when plotted on a reduced scale indicate a striking instability as the Phillips crit. ionicity (0.785) is approached. CuCl is the most piezoelec. of these materials, with a piezoelec. const. e14 = 0.41 coulomb/m2 at 80°K.
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87. 87
  Skelton, J. M.; Gunn, D. S. D.; Metz, S.; Parker, S. C. Accuracy of Hybrid Functionals with Non-Self-Consistent Kohn–Sham Orbitals for Predicting the Properties of Semiconductors. J. Chem. Theory Comput. 2020, 16, 3543– 3557, DOI: 10.1021/acs.jctc.9b01218
  87
  Accuracy of Hybrid Functionals with Non-Self-Consistent Kohn-Sham Orbitals for Predicting the Properties of Semiconductors
  Skelton, Jonathan M.; Gunn, David S. D.; Metz, Sebastian; Parker, Stephen C.
  Journal of Chemical Theory and Computation (2020), 16 (6), 3543-3557CODEN: JCTCCE; ISSN:1549-9618. (American Chemical Society)
  Accurately modeling the electronic structure of materials is a persistent challenge to high-throughput screening. A promising means of balancing accuracy against computational cost is non-self-consistent calcns. with hybrid d.-functional theory, where the electronic band energies are evaluated using a hybrid functional from orbitals obtained with a less demanding (semi)local functional. We have quantified the performance of this technique for predicting the phys. properties of 16 tetrahedral semiconductors with bandgaps from 0.2 to 5.5 eV. Provided the base functional predicts a nonmetallic electronic structure, bandgaps within 5% of the PBE0 and HSE06 gaps can be obtained with an order of magnitude redn. in computing time. The positions of the valence and conduction band extrema and the Fermi level are well reproduced, enabling calcn. of the band dispersion, d. of states, and dielec. properties using Fermi's Golden Rule. While the error in the non-self-consistent total energies is ~ 50 meV atom-1, the energy-vol. curves are reproduced accurately enough to obtain the equil. vol. and bulk modulus with minimal error. We also test the dielec.-dependent scPBE0 functional and obtain bandgaps and dielec. consts. to within 2.5% of the self-consistent results, which amts. to a significant improvement over self-consistent PBE0 for a similar computational cost. We identify cases where the non-self-consistent approach is expected to perform poorly and demonstrate that partial self-consistency provides a practical and efficient workaround. Finally, we perform proof-of-concept calcns. on CoO and NiO to demonstrate the applicability of the technique to strongly correlated open-shell transition-metal oxides.
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88. 88
  Onida, G.; Reining, L.; Rubio, A. Electronic excitations: density-functional versus many-body Green’s-function approaches. Rev. Mod. Phys. 2002, 74, 601– 659, DOI: 10.1103/RevModPhys.74.601
  88
  Electronic excitations: density-functional versus many-body Green's-function approaches
  Onida, Giovanni; Reining, Lucia; Rubio, Angel
  Reviews of Modern Physics (2002), 74 (2), 601-659CODEN: RMPHAT; ISSN:0034-6861. (American Physical Society)
  A review. Electronic excitations lie at the origin of most of the commonly measured spectra. However, the 1st-principles computation of excited states requires a larger effort than ground-state calcns., which can be very efficiently carried out within d.-functional theory. However, two theor. and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a 1-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy Σ and the electron-hole interaction. A good approxn. for Σ was obtained with Hedin's GW approach, using d.-functional theory as a zero-order soln. First-principles GW calcns. for real systems were successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional deriv. of Σ. An alternative approach to calcg. electronic excitations is the time-dependent d.-functional theory (TDDFT), which offers the important practical advantage of a dependence on d. rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-d. approxn. gave promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theor. and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress.
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89. 89
  Li, Y.; Sun, J.; Singh, D. J. Optical and electronic properties of doped p -type CuI: Explanation of transparent conductivity from first principles. Phys. Rev. Mate

Limits to Hole Mobility and Doping in Copper IodideClick to copy article linkArticle link copied!

Chemistry of Materials

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Introduction

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Computational Methodology

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Crystal and Electronic Structure

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Charge Transport

Iterative Boltzmann Transport Equation

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AMSET

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Combined Approach

Defect Chemistry

Figure 6

Intrinsic Defects

Extrinsic Defects─Post Hoc Ergo Propter Hoc?

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Limits to Hole Mobility and Doping in Copper Iodide
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