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ReviewOctober 14, 2016

Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors
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Chemistry of Materials

Cite this: Chem. Mater. 2017, 29, 6, 2402–2413

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https://doi.org/10.1021/acs.chemmater.6b03306

Published October 14, 2016

Abstract

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The paucity of high performance transparent p-type semiconductors has been 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 have been 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. In this article, we extend this mixing concept further, by utilizing quantum chemistry techniques to investigate ternary copper phosphides as potential high mobility p-type materials. We use hybrid density 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 standard n-type transparent conducting oxides. As a proof of concept, we synthesized and characterized powders of CaCuP, showing that they display high levels of p-type conductivity, without any external acceptor dopant. Lastly, we discuss the role of Cu-coordination in promoting valence band dispersion and provide design principles for producing degenerate p-type materials.

Subjects

SPECIAL ISSUE

This article is part of the Computational Design of Functional Materials special issue.

Introduction

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Devices based on p–n junctions have revolutionized our lives, being ubiquitous in modern consumer electronics such as smartphones, tablets, laptops, and flat screen displays as well as pushing the boundaries of renewable energy. (1-5) Transparent p–n junctions represent a major area where the lack of a wide band gap degenerate p-type material has limited the progress of such devices, despite the huge successes seen with their n-type transparent conducting oxide (TCO) counterparts. The field of solar cells can also benefit from a highly conducting transparent p-type material as they provide good ohmic contact and band matching to the solar absorber, unlike their n-type counterparts. (6-8) Over half a century of research has failed to produce a high performance p-type TCO, meaning they are used as passive electrodes and as such limit the fulfilment of “transparent electronics”. (4)

Initial attempts at designing p-type TCOs focused on acceptor doping of the high performance n-type TCOs (e.g., In₂O₃, ZnO, SnO₂) (9-14) and is in fact still currently attempted. (15, 16) The thinking behind this procedure is that the fabrication of a p–n homojunction would be relatively facile if p-type SnO₂ was to be combined with n-type SnO₂, for example. Recent theoretical studies have pointed out that due to the large electron affinities and ionization potentials of these systems (17-20) there is a thermodynamic driving force for n-type defects (excess electrons) increasing the probability that even if holes could form they would result in immediate compensation by intrinsic donor defects under all growth conditions. (10, 11, 13)In addition to this, the localized O 2p states at the top of the valence band promote a tendency to form polaronic defects localized on oxygen sites. (11) These factors all indicate that it is extremely unlikely that these n-type TCOs can ever be turned into p-type.

Initial attempts at designing p-type TCOs came in the form of the “Chemical Modulation of the Valence Band” (denoted CMVB herein) as proposed by Hosono and co-workers in 1997. (21) The authors reported that CuAlO₂, which crystallizes in the delafossite structure possessed both native p-type conductivity and optical transparency. (21) It was noted that the Cu 3d–O 2p mixing in the valence band of Cu₂O mediated a smaller ionization potential than most binary oxides, promoted an increased valence band dispersion, and favored p-type conductivity. (22-24)

Hosono postulated that a ternary Cu-based oxide could provide a larger fundamental band gap while retaining the valence band features of Cu₂O. Other delafossite TCOs such as CuMO₂ (M = B, (25, 26) Sc, (27, 28) Cr, (29) Ga, (28, 30) Y, (28) In, (28) La (28)) and also SrCu₂O₂ (31, 32) were identified where, in each case, Cu is linearly coordinated to two oxygens in a O–Cu–O dumbell-like motif. (21, 33) It was also postulated that it was important to break the localization of electrons on the oxygen 2p states through a tetrahedral coordination reducing the nonbonding nature of the ions as all the electrons are distributed along the four σ bonds and thus no lone pairs are formed. (34)

Although these Cu-based oxides were transparent and displayed p-type conductivity, their conductivities were typically orders of magnitude smaller than that of their n-type counterparts. It has subsequently been demonstrated that the ionization levels of acceptor defects in these systems are quite deep in nature, (35-39) meaning that degenerate conductivity is virtually impossible. In addition, the indirect nature of the band gaps in these materials meant that they would be quite inefficient in optoelectronic devices. (40, 41) To date, the p-type TCO with the highest reported conductivity is CuCrO₂/Mg, with a conductivity of 220 S cm^–1, (29) two orders of magnitude smaller than that of the industry standard n-type TCO, In₂O₃/Sn (∼10⁴ S cm^–1). The reason that CuCrO₂ has increased undoped and doped conductivity over the other delafossites is due to the involvement of Cr(III) in the formation of the VB. As Cr has a greater covalency with O than Al in CuAlO₂, for instance, the increased presence of Cr 3d states across the VB means that there is a greater delocalization of the hole states in CuCrO₂. (42) The role of the second cation can be as important to the effectiveness of the material as the Cu. (43)

The concept of the CMVB was then extended further to include other chalcogenide anions. Cu₂S and Cu₂Se display much higher levels of p-type conductivity than Cu₂O due to increased Cu–Ch mixing; however, their band gaps are much lower. (44-46) Hosono and coworkers identified that layered Cu-based oxychalcogenides could possess large band gaps and efficient Cu–Ch (Ch = S, Se) mixing at the VBM leading to more disperse bands and lower effective masses. (47) LaCuOS was first discovered to be a p-type TCO possessing a band gap of 3.1 eV. The conductivity when acceptor doped with Sr, however, was low at 2.6 × 10^–1 S cm^–1. (47) LaCuOSe on the other hand displayed a larger conductivity, especially when doped with Mg producing a degenerate p-type material with a conductivity of 910 S cm^–1 (48, 49) arising from an increased hybridization of Cu 3d with Se 4p over S 3p, (48, 50) however at the expense of transparency with a fundamental band gap of ∼2.8 eV (51)

Arising from the CMVB, the metastable compound Cu₃N with the anti-ReO₃ structure has been identified for solar absorber applications due to its ability to be bipolar and defect tolerant, i.e., the ability to maintain semiconducting properties when defects are present. The experimental band gap reported is 1.4 eV (52) which is ideal for photovoltaic applications. (53) Cu₃N has a calculated indirect band gap of 1.0 eV (54) (using DFT + U) and conductivities of ∼10^–3 S cm^–1. (52) The defect tolerance of the material as identified by Zakutaev et al. (54) has been attributed to the nature of its band maxima and minima in that the top of the valence band is antibonding in character and contrariwise the bottom of the conduction band is bonding in its nature. This hybridization of the states at both the VBM and CBM is due to the N–Cu–N dumbbell motif in the structure, something that is seen in other compounds such as the delafossite CuTaN₂ which has a direct band gap of 1.5 eV and an indirect band gap of 1.4 eV. (55) The benefit of having these properties means that Cu₃N can accommodate both shallow p-type and n-type defects allowing for easy fabrication of compatible p–n junctions.

In this article, we extend the concept of CMVB further, by testing Cu–P mixing at the valence band maximum and examine the effects of Cu coordination on the valence band dispersion and therefore the effective masses. We have identified four compounds from the Inorganic Crystal Structure Database (ICSD), namely, MCuP (M = Mg, Ca, Sr, Ba), which possess group II cations that should not influence the makeup of the valence band maximum meaning that it should be dominated solely by Cu and P states. MgCuP, which was first reported by Mewis in 1979, (56) crystallizes in the Pnma crystal structure displaying tetrahedrally coordinated Cu with P, which itself is coordinated to four Cu atoms and five Mg atoms where Mg(II) displays square pyramidal coordination to P (shown in Figure 1a). CaCuP, (57) SrCuP, (57) and BaCuP (56) were also reported by Mewis in 1978–79, and all crystallize in the P6₃/mmc structure as shown in Figure 1b,c. It is clear that there are planar layers of M(II) atoms (Ca, Sr, or Ba) repeated along the c-axis at a distance of c/2 each sitting between the two voids in the planar hexagonal networks of Cu–P coordinated to 6 Cu (3 above and 3 below) and 6 P (3 above and 3 below) as shown in Figure 1c. These hexagonal networks lie within the ab plane with the stacking along the c-axis which means that above every Cu atom there is a P atom and vice versa where each Cu forms a trigonal planar complex with three P anions (and likewise for P). To date, only crystallographic data on these materials exist with no analysis of their electronic properties.

Figure 1. Crystal structure of (a) MgCuP (*Pnma*) displaying the tetrahedrally coordinated Cu. The crystal structure of MCuP (P6₃/*mmc*) is shown in (b) as viewed along the (100) direction and (c) shown down the c-axis displaying the hexagonal layered network of trigonally planar coordinated Cu–P and the M(II) cations in the void between the layers. M(II) is colored green, Cu is blue, and P is shown in orange. Bonds have been made between Cu and P, and the unitcell is represented with a dashed line.

Our hybrid density functional theory (hDFT) calculations, specifically using the PBE0 functional, (58, 59) have demonstrated that the Cu–P mixing at the valence band maximum (VBM) does produce excellent dispersion comparable to that seen for excellent n-type materials. We critically discuss the importance of coordination environment in creating degenerate p-type materials and provide guidance for the design of novel p-type systems.

Computational Methodology

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The hybrid PBE0 (58, 59) functional using 25% exact Fock exchange was used for the electronic structure and total energy calculations as implemented in the VASP code. (60-63) Structural optimizations were carried out using a plane wave cut off energy of 400 eV and a k-point sampling of Γ-centered 7 × 7 × 4 for CaCuP, SrCuP, and BaCuP and Γ-centered 8 × 5 × 4 for MgCuP. The projector-augmented wave method (PAW) (64, 65) was utilized to describe the interactions between the valence and the core electrons (Ca:[Ar], Sr:[Kr], Ba:[Xe], Mg:[Ne], Cu:[Ar], and P:[Ne]), and the structures were deemed to be converged when the forces on all the atoms were less than 0.01 eV Å^–1. The effective masses at the edges of the valence band and conduction band were calculated using the equation:

(1)where E(k) is the energy of the band as a function of the wave vector k.

The calculated density of states (DoS) for CaCuP was weighted using the atomic orbital photoionization cross sections formulated by Yeh and Lindau (66) simulating valence band X-ray photoelectron spectroscopy (XPS) that can be compared directly with the experiment. A Gaussian broadening of 0.47 eV was also applied to match experimental broadening. This approach has been shown to give an accurate account of the electronic states that give rise to the XPS data. (67-70)

The optical absorption spectrum and optical transition matrix elements were calculated within the PAW method and transversal approximation. (71) This approach sums the absorption spectrum over all the direct valence band to conduction band transitions and ignores indirect and intraband absorptions. (72) This method has been applied to a number of previous works and is in good agreement with regards to the experiment, despite the electron–hole correlation not being addressed. (2, 32, 73-77)

Experimental Methodology

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Ca (99.0%), Cu (99.9%), and P (99.9%) were obtained from SigmaAldrich. CaCuP was synthesized from the elements with an addition of 5% P over the required stoichiometry which was necessary due to evaporation. The starting materials were ground in an agate mortar and pestle in a nitrogen glovebox, sealed in a quartz tube under reduced pressure (c. 10^–3 mbar), and heated at 500 °C, with heating and cooling rates of 5 °C/min for a total of 24 h with one intermittent regrinding which was carried out in the glovebox. Powder X-ray diffraction (XRD) was carried out on a STOE diffractometer in transmission geometry using Mo Kα radiation over the 2θ range of 2–40° with a step size of 0.05°. X-ray photoelectron spectroscopy (XPS) was carried out using a Thermo K-alpha spectrometer utilizing Al Kα radiation and run in constant analyzer energy (CAE) mode. Survey and high resolution spectra were taken with a pass energy of 200 and 50 eV, respectively. For high resolution scans, a binding energy step size of 0.1 eV was used. The spectral resolution, measured as the full width at half-maximum (FWHM) of the Ag 3d_5/2 peak on a clean Ag surface, was 0.9 eV under these conditions. In situ Ar ion etching was carried out using a 2000 eV Ar ion beam in a background Ar pressure of 2 × 10^–7 mbar. The binding energy scale was corrected for charging by adjusting the adventitious C 1s peak to 284.6 eV. Optical measurements were taken using a PerkinElmer Fourier Transform Lambda 950 UV–vis spectrophotometer in diffuse reflectance geometry. Powder samples were packed into a holder presenting a surface area significantly larger than the incident beam and with sufficient thickness to ensure no transmission. Reflected light was measured using an integrating sphere, and reflectance values were converted using the Kubelka–Munk function to yield values proportional to absorption. (78) Conductivity measurements were carried out using an Ecopia HMS-3000 instrument and a van der Pauw electrode geometry.

Results

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The calculated structural parameters and Cu–P bond lengths for MgCuP, CaCuP, SrCuP, and BaCuP are presented in Table 1 and are in excellent agreement with the experimental values, (56, 57) the slight underestimation of the data is due to DFT being carried out at the athermal limit in comparison to the room temperature conditions of the experimental analysis. Trends can be seen in the P6₃/mmc structures as there is an increase in all lattice parameters and bond lengths down the group (Ca–Sr–Ba) which follows with the increase in ionic radii. The a/b and c lattice parameters stretch by around 5% and 14%, respectively, from CaCuP to BaCuP and the Cu–P bond lengths by ∼5%. The Cu–P bond lengths in MgCuP in the Pnma structure do not follow this trend and are in fact larger than those for CaCuP.

Table 1. Calculated (PBE0) Lattice Parameters and Bond Lengths^a

system	a/Å	b/Å	c/Å	Cu–P/Å	volume/Å³
MgCuP	3.82 (3.84)	6.50 (6.53)	7.15 (7.17)	2.40 (2.46)	177.48 (179.61)
CaCuP	4.05 (4.06)	4.05 (4.06)	7.83 (7.80)	2.34 (2.34)	111.34 (111.12)
SrCuP	4.14 (4.15)	4.14 (4.15)	8.42 (8.48)	2.39 (2.39)	125.14 (126.18)
BaCuP	4.25 (4.24)	4.25 (4.24)	9.10 (9.01)	2.46 (2.45)	142.59 (140.15)

Experimental values are shown in brackets. (56, 57)

The PBE0 calculated band structure for MgCuP is displayed in Figure 2a. The VBM is situated at the high symmetry point Γ, and the conduction band minimum (CBM) is located between the points Y and Γ. MgCuP has an indirect band gap of 1.14 eV (the direct fundamental band gap at Γ is 2.06 eV). The top valence band from Γ–Y shows a decreased dispersion over the Γ–Z direction indicating a heavier hole effective mass, as shown in Table 2. The dispersion along Γ–Y leads to a hole effective mass of ∼0.15 m_e whereas Γ–Z possesses a much higher value of ∼6.30 m_e corresponding to a flatter band curvature seen clearly in Figure 2a. The CBM possesses relatively high dispersion in both the CBM−Γ and CBM–Y directions with electron effective masses of ∼0.68 and ∼0.62 m_e, respectively.

Figure 2. Calculated band structure diagram (a) and the density of states (DoS) (b) for MgCuP in the *Pnma* space group. For (a), the filled valence band is colored in blue and the unfilled conduction band is colored in orange. The valence band maximum (VBM) is centered at 0 eV in both cases. In (b), an expanded view of the VBM and the CBM is shown.

Table 2. Effective Masses (m*) of Charge Carriers at the VBM and the CBM^a

system	VBM/m_e	CBM/m_e
MgCuP	6.30 (Γ–Z) 0.15 (Γ–Y)	0.68 (CBM−Γ) 0.62 (CBM–Y)
CaCuP	0.25, 0.11 (Γ–M) 0.25, 0.11 (Γ–K) 0.79 (Γ–A)	0.39 (CBM–L) 0.90 (CBM−Γ)
SrCuP	0.27, 0.11 (Γ–M) 0.28, 0.11 (Γ–K) 0.87 (Γ–A)	3.50 (M–L) 0.30 (M−Γ)
BaCuP	0.28, 0.11 (Γ–M) 0.29, 0.11 (Γ–K) 0.81 (Γ–A)	0.39 (M–L) 0.22 (M−Γ)

Italicized values refer to light hole effective masses.

The calculated total and partial density of states (DoS) for MgCuP are presented in Figure 2b, and a collation of the percentages of states at the VBM and the CBM are shown in Table 3. The width of the upper valence band (VB) is approximately 8 eV with P 3s states seen from −8 to −7 eV mixed with Cu 3d + 3p, P 3p, and Mg 3s states. From −6 to −4 eV, the Cu 3d states dominate as shown with a large peak at −4.5 eV mixed with some P 3p states. Toward the VBM (0 eV), an increased hybridization of Cu 3d with P 3p states in a 42:54 ratio is observed alongside some slight Cu 3p mixing (∼4%). The CBM is predominantly of Cu d and s states mixed with a similar magnitude of Mg s states and P s + p states. From the CBM to 6 eV, a fairly uniform mixing of the P s + p, Cu p + d, and Mg s states is observed.

Table 3. Approximate Percentages of States at the Valence Band Maximum (VBM) and the Conduction Band Minimum (CBM)

	VBM/%		CBM/%
system	Cu	P	M(II)	Cu	P
MgCuP	4(p) + 42(d)	54(p)	22(s) + 5(p)	15(s) + 3(p) + 30(d)	19(s) + 6(p)
CaCuP	14(p) + 38(d)	48(p)	5(s) + 4(p) + 50(d)	34(p) + 2(d)	2(s) + 3(p)
SrCuP	14(p) + 38(d)	48(p)	5(s) + 2(p) + 51(d)	35(p) + 1(d)	6(p)
BaCuP	13(p) + 38(d)	49(p)	4(s) + 1(p) + 62(d)	24(p) + 3(d)	6(p)

The band structures for CaCuP, SrCuP, and BaCuP are shown in Figure 3. The VBM is situated at Γ in all three compounds, and low hole effective masses are observed in the Γ–M and Γ–K directions. Two degenerate bands are present at the Γ point producing both extremely light and heavier effective masses. The lighter masses, being 0.11 m_e in all compounds, are insensitive to the group II cation whereas the heavier effective masses increase down the group (Ca–Sr–Ba) from ∼0.25 m_e (CaCuP) to ∼0.29 m_e (BaCuP). These values are competitive with and in some cases even surpass the industry standard n-type electron effective masses (∼0.22, ∼0.28, ∼0.28, and ∼0.22 m_e for In₂O₃, (79) ZnO, (80) SnO₂, (81) and BaSnO₃, (82) respectively) . From Γ–A however, the effective mass is limited to ∼0.79–0.81 m_e and shows no particular trend down the group, yet these effective masses are superior to some of the top performing p-type TCOs such as (Cu₂S₂)(Sr₃Sc₂O₅) and LaCuOSe/Mg (0.9 and 1.06 m_e, respectively). (49, 76)

Figure 3. Calculated band structures of (a) CaCuP, (b) SrCuP, and (c) BaCuP in the P6₃/*mmc* space group. The filled valence band is colored in blue, and the unfilled conduction band is colored in orange. The valence band maximum (VBM) is centered at 0 eV.

Similar to MgCuP, these materials also possess indirect band gaps, which decrease down group II; a maximum value of 1.23 eV is seen for CaCuP followed by 1.20 and 0.80 eV for SrCuP and BaCuP, respectively. The direct band gaps at Γ are 2.17, 1.86, and 1.48 eV, respectively. An increase in curvature at the CBM is seen from CaCuP to BaCuP resulting in an effective mass as low as ∼0.22 m_e for BaCuP in the M−Γ direction. The CBM also shifts from between the L and M high symmetry points toward M down the group.

The DoS for the P6₃/mmc structures are displayed in Figure 4. The valence band widths of CaCuP, SrCuP, and BaCuP are ∼7, ∼6.5, and ∼6 eV, respectively. The electronic states are very similar in all three compounds; therefore, CaCuP is taken as an example for this analysis. From −7 to −4 eV, Cu 3d states dominate mixing with some P 3p states similar to that with MgCuP. The difference in intensity between these states decreases substantially from −4 to −2 eV where there is almost 50:50 overlap of the Cu d states with the P p states; however, there is an increase in Cu 3p mixing. From −2 to 0 eV (the VBM), the Cu 3p states tail off leaving the Cu 3d and P 3p states in a consistent 38:48 ratio from CaCuP to BaCuP with a remainder of ∼14% Cu 3p states. The CBM consists of primarily unoccupied M(II) d states, the presence of which increase down the group (50–62%), alongside ∼35% Cu p states and some negligible P p states. From 2 to 4 eV, a net increase in M(II) d states is seen together with hybridization from the Cu p states which decline leaving the region between 4 and 6 eV as primarily M(II) d states.

Figure 4. Calculated density of states (DoS) for (a) CaCuP, (b) SrCuP, and (c) BaCuP. The valence band maximum (VBM) is set at 0 eV. Underneath each DoS is an expanded view of the VBM and CBM.

Experimental Results

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The powder XRD pattern from the sample of CaCuP was recorded, and the published structural model in the P6₃/mmc space group (57) was used as a basis for Rietveld refinement using the EXPGUI and GSAS software and is shown in Figure 5. (83, 84) The initial fitting was carried out using the CaCuP phase alone, which led to a satisfactory fit of all intense peaks but some small peaks remained unaccounted for. A two phase refinement containing CaCuP and CaCu_3.8P₂ yielded an improvement in fit and accounted for several of the unknown peaks. (85) The CaCuP unit cell was refined in the P6₃/mmc space group yielding lattice parameters of a = 4.070(1) Å and c = 7.826(2) Å which compare well with the reported structure. (57) The literature structure of CaCu_3.8P₂ was used without refinement of its unit cell. In the final refinement, an RWP value of 0.081 was obtained, and the impurity level of CaCu_3.8P₂ phase was 1.6(2) weight %.

Figure 5. Powder X-ray diffraction pattern from CaCuP synthesized here (black) and calculated from the standard structure (red) with the difference between the calculated and observed intensities shown underneath in gray. The phase ticks for CaCuP and CaCu_3.8P₄ are shown in blue and green, respectively.

Figure 6 displays the XPS spectra for the Cu 2p, Ca 2p, and P 2p regions alongside the valence band (VB) XPS. The surface of the as synthesized powder contained a significant amount of oxygen. Ar ion etching for 60 s using a 2000 eV Ar ion beam was able to reduce the level of oxygen suggesting that the oxidation was localized on the surface. High resolution spectra showed a symmetrical Cu 2p_3/2 peak at 933.2 eV, corresponding to Cu(I). This assignment is supported by the lack of strong, sharp satellite peaks that typically accompany Cu(II) spectra. (86) Such satellite peaks arise from a 3d⁹ initial state that results on photemission in a series of screened and unscreened final states (87) and are detectable even with low concentrations of Cu(II) within a predominantly Cu(I) matrix. (88) The spectral region between the Cu 2p spin orbit doublet that we measure in CaCuP does show a very broad feature centered on 949.4 eV with fwhm of 8 eV. The origin of this feature is unknown, but it is unlike previously reported Cu(II) satellites, which are typically much sharper. (86-88) The feature may, therefore, be due to an as yet unassigned loss process. Given its position, some 16 eV above the Cu 2p_3/2 peak, the feature may be due to valence band plasmon loss, which is typically seen in materials with similar valence band electron density at c. 20 eV to the high binding energy side of the main photoemission peak. (89) Unfortunately, the corresponding Cu 2p_1/2 loss peak (if it were present) would be obscured by the O Auger line which overlaps on the binding energy scale at this photon energy. Further study is needed to ascertain the nature of the loss feature present in the Cu 2p spectrum.

Figure 6. X-ray photoelectron spectra of CaCuP. (a) Cu 2p, (b) Ca 2p, and (c) P 2p regions are shown, with curve fitting as described in the text. The valence band region up to 35 eV binding energy is shown in (c) with the simulated VB XPS overlaid (red dashed line) taken from the PBE0 calculated DoS for CaCuP.

Ca 2p spectra showed two overlapping doublets. The lower binding energy component has Ca 2p_3/2 component at 346.3 eV (red trace, Figure 6b). We could find no reference of the XPS binding energy of Ca phosphide compounds. Ca₃P₂ itself is highly toxic and unstable, which may have precluded its measurement. However, CaS has been reported with a Ca 2p_3/2 binding energy of 346.5 eV, very similar to our observed value. (90) Therefore, we assign the Ca 2p_3/2 environment at 346.3 eV to Ca within the CaCuP structure. The other observed Ca 2p component, with Ca 2p_3/2 binding energy of 347.8 eV (blue trace, Figure 6b) corresponds well to Ca₃(PO₄)₂ or CaHPO₄. (91) This indicates a level of oxidation of the surface as discussed above. No crystalline Ca₃(PO₄)₂ or CaHPO₄ was observed in XRD, again suggesting this is surface limited oxidation.

The P 2p region again was composed of overlapping peaks. Deconvolution showed that the principal chemical component (representing 66% of the P signal) was associated with a P 2p_3/2 peak at 128.7 eV (red trace, Figure 6c), corresponding to phosphide compounds: for example, InP is reported with the same P 2p_3/2 binding energy. (92) A higher binding energy component (representing 18% of the P signal) is also observed with a P 2p_3/2 peak at 133.4 eV (blue trace, Figure 6c), corresponding to phosphate groups, (93) and consistent with the interpretation of the Ca 2p region given above. The remainder (c. 16% of the observed P signal) was fitted with a P 2p_3/2 component at 130.5 eV (purple trace, Figure 6c) and may originate from elemental P, which may be located at the sample surface due to evaporation during synthesis.

The valence band was recorded up to 30 eV binding energy. The main feature at low binding energy is a spectral maximum at 3.9 eV corresponding to Cu 3d electrons, which was confirmed by the excellent agreement with our simulated XPS (red dashed lines, Figure 6d). The onset of the valence band begins immediately at the Fermi level (BE = 0 eV), indicating a filled band immediately below the Fermi level, i.e., a p-type semiconductor or a metal. However, no Fermi edge was observed, meaning that if this is a metal the density of states at the Fermi level is low. This fits with our calculations of a very disperse valence band, with the Fermi level found near the VBM, most likely through Cu deficiency. The Ca 3p shallow core line appears at 25.5 eV.

Diffuse reflectance optical spectra were recorded in the interval of 1.5–3.5 eV. The Kubelka–Munk function, F(R), is taken to be proportional to absorption; this is valid if scattering is constant throughout the wavelength range used, which is a reasonable assumption. (78) There appears to be an absorption edge toward the higher energy range. Recently, Poeppelmeier and co-workers have proposed a method for accurate determination of the band gap in degenerately doped semiconductors. (94) This is similar to the well established Tauc method (95) but takes into account the presence of a large concentration of charge carriers. Using the Poeppelmeier method, plots of F(R) and F(R)² against energy were made and are displayed in Figure 7a alongside the simulated PBE0 optical absorption spectrum (b). The absorption edge of each plot was extrapolated to the x-axis (y = 0). For the F(R) plot, the extrapolated value E₁ = 2.66 eV. For the F(R)², the extrapolated value E₂ = 2.72 eV. According to the Poeppelmeier method, the band gap E_g = 2E₂ – E₁, which in this case gives 2.78 eV. Below the absorption edge, there are two strong absorption peaks located at 1.8 and 2.2 eV. The origin of these peaks is not clear. Cu(II) d–d transitions can occur in this energy range, (96) but XPS detects no Cu(II). While XPS detects calcium phosphate impurities at the surface, these are not expected to give rise to visible light absorption. The weight percentage of crystalline impurities (c. 1.7 wt %) is too low to effect strong absorption bands as seen here. The absorptions likely arise from as-yet unidentified defects within the CaCuP structure. Figure 7b displays the simulated PBE0 optical absorption in terms of the absorption coefficient α. A weak absorption onset is seen at ∼2.17 eV, and the stronger optical absorption occurs at ∼2.71 eV. These results are in excellent agreement with the experimental optical spectra in Figure 7a.

Figure 7. Diffuse reflectance optical spectra showing the Kubelka–Munk function F(R) and F(R)² is displayed in (a). The direct band gap calculated from the Poeppelmeier method is shown to be 2.78 eV. (b) Shows the calculated optical absorption spectrum using the PBE0 functional where a weak absorption onset at 2.17 eV and a strong absorption at 2.71 eV are seen.

Conductivity measurements were carried out by forming a 12 mm diameter pellet, which was prepared by biaxial pressing at 1 tonne pressure followed by annealing at 300 °C for 4 h under nitrogen to sinter the particles. This yielded a pellet approximately 3 mm thick with a density of approximately 70%. The surface was polished to remove surface oxidation, and gold electrodes were sputtered in a van der Pauw geometry. Conductivity was then measured using a four point probe. A resistivity of 2.0 × 10^–3 ± 0.2 × 10^–3 Ω cm was measured in this way. We were unable to record reliable Hall Effect data on the pellet.

Discussion

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Comparing the electronic structure of MgCuP to that of CaCuP, SrCuP, and BaCuP, it is clear that the electronic aspects differ due to the change in Cu coordination that occurs on going from the Pnma to P6₃/mmc structure. Unlike CaCuP, SrCuP, and BaCuP, overall MgCuP displays only average hole effective masses at the VBM (despite the favorable Γ–Y mass of ∼0.15 m_e) and moderately heavy electron masses at the CBM. The excellent dispersion seen for CaCuP, SrCuP, and BaCuP in the Γ–M and the Γ–K directions can be attributed to excellent orbital overlap in the hexagonal layers. The Γ–A direction spans the c direction and therefore shows far less dispersion as the Cu and P atoms are coordinated only in the xy plane. MgCuP on the other hand should not be as prone to this anisotropic behavior as the tetrahedrally coordinated Cu is connected in a three-dimensional array throughout the lattice. This raises the question of whether, for copper phosphides, a trigonal planar Cu coordination is preferable over a tetrahedral coordination in terms of orbital overlap for dispersion in the valence band.

Cu coordination in all Cu⁺-based systems is key to controlling the degree of overlap seen between the anion and cation states, which in turn controls the band dispersion at the VBM. For second row anions (O and N), Cu coordination is usually linear, as seen in Cu₂O (97, 98) and delafossite CuAlO₂ (40) structures as well as Cu₃N and CuTaN₂. (54, 99) This unusually low coordination preference has originally been described by Orgel in 1958 to be due to the closed shell metal cations such as Cu⁺, Ag⁺, and Hg²⁺ having a low energy difference between the first excited state d⁹s¹ and the ground state d¹⁰ energy level. (100) This hybridized Cu [3d_z² + 4s] state is able to stabilize a low coordination level and is therefore the preferred configuration. In contrast, other d¹⁰ cations such as Zn²⁺ display a much higher separation between the d⁹s¹ state and the d¹⁰ ground state meaning a higher coordination number is required for a lower energy configuration, as seen in, e.g., zinc blende or wurtzite ZnO where Zn is tetrahedrally coordinated to O.

Wurtzite-like β-CuGaO₂ was shown to yield a low band gap (∼1.5 eV) and was considered quite promising for solar cell absorber applications. (101) A recent computational analysis, however, has shown that the tetrahedral coordination of the Cu⁺ yields a very different valence band make up compared to that of the linear O–Cu–O coordination in the delafossite oxides. (102) For the delafossites, the Cu 3d and O 2p states overlap strongly, producing a relatively disperse VBM. (103-105) For β-CuGaO₂ and related systems, no mixing is observed at the VBM producing “flat” bands made soley of Cu 3d states. (102) Understanding the role of coordination in driving the valence band make up of a system is therefore vital.

Despite describing cuprous oxides and nitrides well, the Orgel’s theory fails to give an understanding of why higher coordination numbers for Cu⁺ are seen for chalcogenides such as the tetrahedrally coordinated CuAlS₂ (99) and Cu₂S (which shows 3-fold coordination (106)). Instead, a push toward a more ionic model down the chalcogenides is necessary. (107) Tossel and Vaughan (106) provided another possibility taking into account the ligand interactions. In this model, the M d–L p (where M = Cu and L = anion such as O, S, Se, etc.) energy separation determines the coordination. The coordination should aim to reduce the spacing between the M d and the L p levels, in which, taking Cu₂O as an example where the spacing is large, a low coordination number would be favored.

An overview by Gaudin et al. (107) determined that the Cu 3d–O 2p interaction is in fact important in lowering the energy of the main Cu 4s–O 2p interaction thereby incorporating Orgel’s theory. The authors also described another factor: the polarizing influence of the anion over the Cu⁺ ion (Cu 3d electrons are poorly screened, making the ion quite polarizable), in which, for less polarizing anions (down the group and from right to left on the periodic table), this effect is lower and therefore the lower coordination number is less stable. It can then be said that higher coordination numbers are preferred for Se and Te copper compounds, as in KCuSe and KCuTe. (108) The presence of a third ion could also affect the polarization of the Cu cation by the anion, such as in the difference between Cu₂S and KCuS where coordination nos. of 3 and 2 are seen, respectively. A noticeable depletion in the electron density of the d electron cloud was observed for KCuS over Cu₂S indicating that the potassium cation contributes to the polarizability. (107)

The above explanations could help describe why for group II copper phosphides higher coordination numbers are preferred over copper oxides but also why a trigonal planar configuration is stabilized. Due to the polarizability argument described, P should adopt a higher coordination due to the low polarizability of P, as well as prefer a higher coordination down group II due to the decrease in polarizing power seen from Ca to Sr to Ba. However, from our calculations, CaCuP, SrCuP, and BaCuP all prefer the trigonal planar configuration, failing to adopt the same Pnma structure as MgCuP. Steric effects most likely play a role here as both phosphorus and the increasing M(II) cation down the group are relatively large. The tetrahedral coordination in these examples show a poorer orbital overlap than the trigonal planar configuration which can be seen in an increase in the Cu–P bond lengths. MgCuP in the P6₃mmc space group (i.e., trigonal planar Cu–P) displays shorter Cu–P bond lengths over those in the Pnma structure (2.28 Å versus 2.40 Å) alongside lower overall effective masses.

What is seen in the P6₃mmc structures is the increase in Cu–P bond length down the group and a detrimental effect on the hole effective masses and a concomitant lowering of the band gaps. An increase in the electron effective masses at the CBM is seen, however, as well as a decrease in the difference between the indirect and direct band gap. CaCuP, SrCuP, and BaCuP all possess a significant contribution from Cu 3p states at the VBM, from the p_x and p_y orbitals which add to the bonding, and hence the dispersion of the VBM. Taking into account the description by Tossel and Vaughan, (106) the P 3p and Cu 3d levels are closer in energy and hence a tetrahedral or trigonal planar is preferred over a linear configuration, as the Cu d–P p energy spacing is already minimal. Moving from a tetrahedral to a trigonal planar configuration also increases the crystal field splitting of Cu making the VBM more disperse pushing the antibonding states higher in energy and therefore reducing the ionization potential, which should favor hole formation. (109, 110)

The experimental analysis on CaCuP supports our computational analysis and indicates that the material is a degenerate semiconductor with a relatively high p-type conductivity. What is most promising is that this high level of conductivity is for a nominally undoped pressed powder pellet and most likely originates from Cu deficiency. The nature of a pressed pellet means that this conductivity and mobility is limited by surface and interface effects. It is likely that this conductivity would be significantly boosted for a single crystal, making it competitive with the conductivities of the best n-type TCOs. The hole concentration could also be increased further with a suitable 1+ cation dopant for the divalent cation site.

The quest to find high performance p-type semiconductors for a range of applications is still ongoing. (8, 111-115)Although CaCuP possesses a large optical band gap, this material is not transparent to visible light (E_g > 3.1 eV). However, the insights gained from this analysis of M(II)CuP and the interplay between structure and electronic properties provide design principles for the production of more effective p-type ability in semiconductor materials. As more and more technological breakthroughs occur for growth of materials, particularly designer layered compounds, increasingly complex systems can be fabricated. (116-118) To successfully create materials with trigonal Cu–P layers in this way could generate materials with tailored VBMs and band gaps, i.e., larger band gaps for transparent conducting applications. (119-121)

Conclusions

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In order to gain insights into how to design excellent p-type transparent semiconductors, we have analyzed four ternary copper phosphide materials using hybrid density functional theory, finding low effective masses comparable to that of the highest performing n-type TCO. Synthesized powders of CaCuP have been created showing competitively high p-type conductivity in line with these results. We demonstrate that by extending the chemical modulation of the valence band method to include Cu–P interactions, a stronger hybridization with copper is observed which, together with a trigonal planar coordination, produces highly favorable dispersion at the VBM. The design principles proposed herein can further the field of p-type semiconductors, opening up a pathway to the holy grail of degenerate p-type transparent conducting materials.

Author Information

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Corresponding Author
- David O. Scanlon - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom; Email: [email protected]
Authors
- Benjamin A. D. Williamson - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- John Buckeridge - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom
- Jennilee Brown - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; University College London, Department of Chemistry, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
- Simon Ansbro - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; University College London, Department of Chemistry, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
- Robert G. Palgrave - University College London, Kathleen Lonsdale Materials Chemistry, Department of Chemistry, 20 Gordon Street, London WC1H 0AJ, United Kingdom; University College London, Department of Chemistry, Christopher Ingold Building, London WC1H 0AJ, United Kingdom
Notes
The authors declare no competing financial interest.

Acknowledgment

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D.O.S. and R.G.P. acknowledge support from the SUPERSOLAR Solar Energy Hub (EP/J017361/1) for the provision of a flexible funding call award and membership of the Materials Design Network. D.O.S. also acknowledges EPSRC (EP/N01572X/1). J.B. acknowledges EPSRC (EP/K016288/1). This work made use of the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk), via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202). The UCL Legion and Grace HPC Facilities (Legion@UCL and Grace@UCL) were also used in completion of this work. B.A.D.W. would like to acknowledge D.P. Howard and A.M. Ganose for useful discussions.

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Optical Properties and Boron Doping-Induced Conduction-Type Change in SnO2 Thin Films
Tran, Quang-Phu; Fang, Jau-Shiung; Chin, Tsung-Shune
Journal of Electronic Materials (2016), 45 (1), 349-356CODEN: JECMA5; ISSN:0361-5235. (Springer)
Boron-doped tin oxide (BTO) films, 0-5 at.% B, were prepd. by sol-gel dip coating on a glass substrate. Dried precursor films were post-annealed at a temp. between 400°C and 750°C for 2 h. The obtained BTO thin films were characterized by x-ray diffraction (XRD), SEM (SEM), UV-visible light (UV-Vis) spectrometry, a four-point probe, and Hall-effect and Seebeck-effect measurements. Optimal optical transmittance was achieved for post-annealed BTO thin film at 700°C. XRD results show a rutile SnO2 structure with a preferred (110) orientation for all the films. The grain size is 47-21 nm, which reduces with increasing B contents. The optical transmittance is 84.6-88.5% at a wavelength of 550 nm and optical band gap of 3.52-3.75 eV. Elec. resistivity is (3.4-8.2) × 10-3 Ω cm, and figure of merit (0.9-4.3) × 10-3 Ω-1. Carrier concn. is (0.97-7.4) × 1020 cm-3 and mobility (2.5-7.8) cm2 V-1 s-1. BTO film with 4 at.% B shows an optimal combination of properties. Conduction type changes from n- (undoped) to p- (1-4 at.% B), then to n-types (5 at.% B), as evidenced from Hall-effect and Seebeck-effect measurements. This is explained by doping-generated defects and phase sepns. of Sn3O4 and B2O3.
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Pathak, T. K.; Kumar, V.; Swart, H.; Purohit, L. Effect of Doping Concentration on the Conductivity and Optical Properties of p-Type ZnO Thin Films Phys. B 2016, 480, 31– 35 DOI: 10.1016/j.physb.2015.09.033
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Effect of doping concentration on the conductivity and optical properties of p-type ZnO thin films
Pathak, Trilok Kumar; Kumar, Vinod; Swart, H. C.; Purohit, L. P.
Physica B: Condensed Matter (Amsterdam, Netherlands) (2016), 480 (), 31-35CODEN: PHYBE3; ISSN:0921-4526. (Elsevier B.V.)
Nitrogen doped ZnO (NZO) thin films were synthesized on glass substrates by the sol-gel and spin coating method. Zinc acetate dihydrates and ammonium acetate were used as precursors for zinc and nitrogen, resp. X-ray diffraction study showed that the thin films have a hexagonal wurtzite structure corresponding (002) peak for undoped and doped ZnO thin films. The transmittance of the films was above 80% and the band gap of the film varies from 3.21±0.03 eV for undoped and doped ZnO. The min. resistivity of NZO thin films was obtained as 0.473 Ω cm for the 4 at% of nitrogen (N) doping with a mobility of 1.995 cm2/V s. The NZO thin films showed p-type cond. at 2 and 3 at% of N doping. The AC cond. measurements that were carried out in the frequency range 10 kHz to 0.1 MHz showed localized conduction in the NZO thin films. These highly transparent ZnO films can be used as a possible window layer in solar cells.
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Zhang, S. B.; Wei, S.-H. H.; Zunger, A. A Phenomenological Model for Systematization and Prediction of Doping Limits in II–VI and I–III–VI₂ Compounds J. Appl. Phys. 1998, 83, 3192 DOI: 10.1063/1.367120
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A phenomenological model for systematization and prediction of doping limits in II-VI and I-III-VI2 compounds
Zhang, S. B.; Wei, Su-Huai; Zunger, Alex
Journal of Applied Physics (1998), 83 (6), 3192-3196CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Semiconductors differ widely in their ability to be doped. As their band gap increases, it is usually possible to dope them either n or p type, but not both. This asymmetry is documented here, and explained phenomenol. in terms of the "doping pinning rule.".
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Zhang, S. B.; Wei, S. H.; Zunger, A. Overcoming Doping Bottlenecks in Semiconductors and Wide-Gap Materials Phys. B 1999, 273–274, 976– 980 DOI: 10.1016/S0921-4526(99)00605-5
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Overcoming doping bottlenecks in semiconductors and wide-gap materials
Zhang, S. B.; Wei, S.-H.; Zunger, A.
Physica B: Condensed Matter (Amsterdam) (1999), 273-274 (), 976-980CODEN: PHYBE3; ISSN:0921-4526. (Elsevier Science B.V.)
A review with 33 refs. There often exist strong doping bottlenecks that may severely restrict potential applications of semiconductors, esp. in wide-band-gap materials where bipolar doping is impossible. Recent rapid progress in semiconductor research has reached a point where these doping limitations must be overcome to tune semiconductors for precisely required properties. Here, the authors discuss how to find out what causes the doping bottlenecks. The authors based the discussion on a set of recent, novel developments regarding the doping limitations: the doping limit rule distd. from both phenomenol. studies and from 1st-principles calcns. The thermodn. doping bottlenecks are identified as due mainly to the formation of intrinsic defects whose formation enthalpies depend on the Fermi energy, and always act to negate the effect of doping.
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Zhang, S. B. The Microscopic Origin of the Doping Limits in Semiconductors and Wide-Gap Materials and Recent Developments in Overcoming These Limits: a Review J. Phys.: Condens. Matter 2002, 14, R881– R903 DOI: 10.1088/0953-8984/14/34/201
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The microscopic origin of the doping limits in semiconductors and wide-gap materials and recent developments in overcoming these limits: a review
Zhang, S. B.
Journal of Physics: Condensed Matter (2002), 14 (34), R881-R903CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
A review of the recent developments in first-principles total energy studies of the phenomenol. equil. "doping limit rule" that governs the max. elec. cond. of semiconductors via extrinsic or intrinsic doping.
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Walsh, A.; Buckeridge, J.; Catlow, C. R. a.; Jackson, A. J.; Keal, T. W.; Miskufova, M.; Sherwood, P.; Shevlin, S. a.; Watkins, M. B.; Woodley, S. M.; Sokol, A. a. Limits to Doping of Wide Band Gap Semiconductors Chem. Mater. 2013, 25, 2924– 2926 DOI: 10.1021/cm402237s
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Kawazoe, H.; Yasukawa, M.; Hyodo, H.; Kurita, M.; Yanagi, H.; Hosono, H. P-Type Electrical Conduction in Transparent Thin Films of CuAlO₂ Nature 1997, 389, 939– 942 DOI: 10.1038/40087
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P-type electrical conduction in transparent thin films of CuAlO2
Kawazoe, Hiroshi; Yasukawa, Masahiro; Kyodo, Hiroyuki; Kurita, Masaaki; Yanagi, Hiroshi; Hosono, Hideo
Nature (London) (1997), 389 (6654), 939-942CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
Optically transparent oxides tend to be elec. insulators, by virtue of their large electronic band gap (≥3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO-all n-type (electron) conductors-which are widely used as the transparent electrodes in flat-panel displays. However, no transparent oxide exhibiting high p-type (hole) cond. is known to exist, whereas such materials could open the way to range of novel applications. For example, a combination of the 2 types of transparent conductor as a pn junction could lead to a functional window that transmits visible light yet generates elec. in response to the absorption of UV photons. Here the authors describe a strategy for identifying oxide materials that should combine p-type cond. with good optical transparency. The authors illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temp. p-type cond. up to 1 S cm-1. Although the cond. of the candidate material is significantly lower than that obsd. for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.
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Scanlon, D. O.; Morgan, B. J.; Watson, G. W. Modeling the Polaronic Nature of p-Type Defects in Cu₂O: the Failure of GGA and GGA+U J. Chem. Phys. 2009, 131, 124703 DOI: 10.1063/1.3231869
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Modeling the polaronic nature of p-type defects in Cu2O: The failure of GGA and GGA+U
Scanlon, David O.; Morgan, Benjamin J.; Watson, Graeme W.
Journal of Chemical Physics (2009), 131 (12), 124703/1-124703/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
The exact nature of the hole traps reported deep in the band gap of Cu2O has been a topic of vigorous debate, with copper vacancies and oxygen interstitials both having been proposed as the relevant defects. In this article, the electronic structure of acceptor-forming defects in Cu2O, namely, copper vacancies and oxygen interstitials, is investigated using generalized gradient approxn. (GGA) and GGA cor. for on-site Coulombic interactions (GGA+U). GGA produces notionally semimetallic defect complexes, which is not consistent with the exptl. known polaronic nature of conduction in Cu2O. GGA+U also predicts a semimetallic defect complex for the "simple" copper vacancy but predicts the "split" vacancy and both oxygen interstitials are characterized by localized polarons, with distinct single particle levels found in the band gap. For both methods, however, the positions of calcd. transition levels are inconsistent with exptl. ionization levels. Hence neither GGA nor GGA+U are successful in modeling p-type defects in Cu2O. (c) 2009 American Institute of Physics.
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Scanlon, D. O.; Watson, G. W. Uncovering the Complex Behavior of Hydrogen in Cu₂O Phys. Rev. Lett. 2011, 106, 1– 4 DOI: 10.1103/PhysRevLett.106.186403
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Miao, M.-S.; Yarbro, S.; Barton, P. T.; Seshadri, R. Electron Affinities and Ionization Energies of Cu and Ag Delafossite Compounds: A Hybrid Functional Study Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 045306 DOI: 10.1103/PhysRevB.89.045306
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Electron affinities and ionization energies of Cu and Ag delafossite compounds: a hybrid functional study
Miao, Mao-Sheng; Yarbro, Sam; Barton, Phillip T.; Seshadri, Ram
Physical Review B: Condensed Matter and Materials Physics (2014), 89 (4), 045306/1-045306/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
Using d. functional theory with a hybrid functional, we calc. the ionization energies and electron affinities of a series of delafossite compds. (AMO2: A = Cu, Ag; M = B, Al, Ga, In, Sc). The alignments of the valence band max. and the conduction band min., which directly relate to the ionization energies and electron affinities, were obtained by calcns. of supercell slab models constructed in a nonpolar orientation. Our calcns. reveal that the ionization energy decreases with an increasing at. no. of group-III elements, and thus suggest an improved p-type doping propensity for heavier compds. For keeping both a low ionization energy and a band gap of sufficient size, CuScO2 is superior to the Cu-based group-III delafossites. By analyzing the electronic structures, we demonstrate that the compositional trend of the ionization energies and electron affinities is the result of a combined effect of d-band broadening due to Cu(Ag)-Cu(Ag) coupling and a repositioning of the d-band center.
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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
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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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Snure, M.; Tiwari, A. CuBO₂: A p-Type Transparent Oxide Appl. Phys. Lett. 2007, 91, 092123 DOI: 10.1063/1.2778755
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CuBO2. A p-type transparent oxide
Snure, Michael; Tiwari, Ashutosh
Applied Physics Letters (2007), 91 (9), 092123/1-092123/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
The authors report the synthesis of CuBO2, a p-type transparent oxide belonging to Cu-delafossite family. High quality thin films of CuBO2 were deposited on c-plane sapphire substrates by pulsed laser deposition technique. Detailed structural, optical, and elec. characterizations on these films were performed. Optical transmission measurement showed the films to be highly transparent in the visible range and having indirect and direct band gaps of 2.2 and 4.5 eV, resp. Room-temp. elec. cond. of CuBO2 films was 1.65 S cm-1 and exhibited semiconductor-like temp. dependence. The Hall and Seebeck coeffs. of the film were pos., indicating the p-type nature of the material.
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Shi, L.-J.; Fang, Z.-J.; Li, J. First-Principles Study of p-Type Transparent Conductive Oxides CuXO₂ (X = Y, Sc, and Al) J. Appl. Phys. 2008, 104, 073527 DOI: 10.1063/1.2991157
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Marquardt, M. a.; Ashmore, N. a.; Cann, D. P. Crystal Chemistry and Electrical Properties of the Delafossite Structure Thin Solid Films 2006, 496, 146– 156 DOI: 10.1016/j.tsf.2005.08.316
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Crystal chemistry and electrical properties of the delafossite structure
Marquardt, Meagen A.; Ashmore, Nathan A.; Cann, David P.
Thin Solid Films (2005), 496 (1), 146-156CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
A review. Over the past few decades, the field of transparent conducting oxides has undergone tremendous advances. With the rapid growth of optoelectronic applications related to display technologies, traditional materials such as Sn-doped indium oxide (ITO) are now widely used as transparent electrodes. In addn., with the advent of p-type transparent conductors, through the transparent pn-junction building block, a wide range of functional transparent optoelectronic devices were demonstrated including UV-emitting diodes, UV-detectors, and transparent thin film transistors. This paper will highlight the unique characteristics of oxide materials based on the delafossite structure with a focus on the interrelationship between the chem., crystal structure, process conditions, and elec. and optical properties. The delafossite structure (ABO2) is characterized by a layer of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). The A-site cation is comprised of Pt, Pd, Ag, or Cu ions nominally in a monovalent state. The B-site cation can consist of most trivalent transition metals, group III elements, rare earths, or charge compensated pairs (e.g. B2+/B4+). This layered structure leads to highly anisotropic phys. properties. The crystal chem. of the delafossite structure will be discussed in ref. to phase stability, the stability of dopants, and the important phys. properties such as the cond. and optical transparency.
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Nagarajan, R.; Draeseke, a. D.; Sleight, a. W.; Tate, J. p-Type Conductivity in CuCr_1–xMg_xO₂ Films and Powders J. Appl. Phys. 2001, 89, 8022 DOI: 10.1063/1.1372636
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p-type conductivity in CuCr1-xMgxO2 films and powders
Nagarajan, R.; Draeseke, A. D.; Sleight, A. W.; Tate, J.
Journal of Applied Physics (2001), 89 (12), 8022-8025CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
CuCr1-xMgxO2, a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped CuCrO2 is almost black and has moderate cond. with p-type carriers. Upon doping with 5[percent] Mg, the cond. increases by a factor of 1000. In films, the best p-type cond. is 220 S cm-1 in CuCr0.95Mg0.05O2, a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a cond. of order 1 S cm-1. Films are usually polycryst. on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650°. Optical and UV transmission data indicate a direct band gap of 3.1 eV.
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Ueda, K.; Hase, T.; Yanagi, H.; Kawazoe, H.; Hosono, H.; Ohta, H.; Orita, M.; Hirano, M. Epitaxial Growth of Transparent p-Type Conducting CuGaO₂ Thin Films on Sapphire (001) Substrates by Pulsed Laser Deposition J. Appl. Phys. 2001, 89, 1790 DOI: 10.1063/1.1337587
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Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) substrates by pulsed laser deposition
Ueda, K.; Hase, T.; Yanagi, H.; Kawazoe, H.; Hosono, H.; Ohta, H.; Orita, M.; Hirano, M.
Journal of Applied Physics (2001), 89 (3), 1790-1793CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Transparent p-type conducting CuGaO2 thin films were prepd. on α-Al2O3 (001) single-crystal substrates by pulsed laser deposition. The films were grown epitaxially on the substrates in an as-deposited state. X-ray pole figure anal. revealed that the films were composed of two types of epitaxial grains, both with c axes oriented perpendicular to the surface and a axes rotated 60° with respect to each other around the c axis. Observation of the CuGaO2 thin films by at. force microscopy and high-resoln. transmission electron microscopy substantiated this conclusion. The films have high optical transparency (∼80[percent]) in the visible region, and the energy gap of CuGaO2 for direct allowed transition was estd. to be 3.6 eV. p-type cond. was confirmed by Seebeck and Hall measurements. The elec. cond., carrier (pos. hole) d., and Hall mobility of the films at room temp. were detd.
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Kudo, A.; Yanagi, H.; Hosono, H.; Kawazoe, H. SrCu₂O₂: A p-Type Conductive Oxide with Wide Band Gap Appl. Phys. Lett. 1998, 73, 220 DOI: 10.1063/1.121761
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SrCu2O2: A p-type conductive oxide with wide band gap
Kudo, Atsushi; Yanagi, Hiroshi; Hosono, Hideo; Kawazoe, Hiroshi
Applied Physics Letters (1998), 73 (2), 220-222CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
SrCu2O2 thin films were prepd. on SiO2 glass substrates by pulsed laser deposition. The film deposited in O2 atmosphere of 7×10-4 Pa at 573 K showed high optical transmission in visible and near-IR regions. Potassium was doped at Sr site for substitutional doping. The optical band gap of the K-doped film was estd. to be ∼3.3 eV. The dc elec. cond. of the K-doped film at 300 K was 4.8×10-2 S cm-1 and the activation energy was 0.10 eV. Pos. sign of Seebeck and Hall coeffs. demonstrated the p-type conduction of the film. Hole concn. and mobility at 300 K were 6.1×1017 cm-3 and 0.46 cm2 V-1 s-1, resp.
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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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Kandpal, H. C.; Seshadri, R. First-Principles Electronic Structure of the Delafossites ABO₂ (A = Cu, Ag, Au; B = Al, Ga, Sc, In, Y): Evolution of d¹⁰-d¹⁰ Interactions Solid State Sci. 2002, 4, 1045– 1052 DOI: 10.1016/S1293-2558(02)01363-8
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First-principles electronic structure of the delafossites ABO2 (A = Cu, Ag, Au; B = Al, Ga, Sc, In, Y): evolution of d10-d10 interactions
Kandpal, Hem Chandra; Seshadri, Ram
Solid State Sciences (2002), 4 (8), 1045-1052CODEN: SSSCFJ; ISSN:1293-2558. (Editions Scientifiques et Medicales Elsevier)
While bonding between d10 atoms and ions in mol. systems has been well studied, less attention has been paid to interactions between such seemingly closed shell species in extended inorg. solids. We present visualizations of the electronic structures of the delafossites ABO2 with particular emphasis on the nature of d10-d10 interactions in the close packed plane of the coinage metal ion. LDA-GGA-DFT and LMTO-ASA methods were used. On going from Cu to Ag to Au, the extent of bonding between A and A increases. However, the structures (in terms of distances) of these compds. are largely detd. by the strongly ionic BIII-O interaction and for the larger B ions Sc, In and Y, the A atoms are sufficiently well-sepd. that A-A bonding is almost negligible. We also analyze some interesting differences between Ag and Au, including the larger A-O covalency of the Au. The trends in electronic structure suggest that the Ag and Au compds. are not good candidate transparent conducting oxides.
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Kawazoe, H.; Yanagi, H.; Ueda, K.; Hosono, H. Transparent p-Type Conducting Oxides: Design and Fabrication of p-n Heterojunctions MRS Bull. 2000, 25, 28– 36 DOI: 10.1557/mrs2000.148
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Transparent p-type conducting oxides. Design and fabrication of p-n heterojunctions
Kawazoe, Hiroshi; Yanagi, Hiroshi; Ueda, Kazushige; Hosono, Hideo
MRS Bulletin (2000), 25 (8), 28-36CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)
A review with 23 refs. is given on results of investigations into chem. design, fabrication of thin films, the optical and elec. properties of the thin films, and a trial to fabricate p-n heterojunctions based on transparent conducting oxides. The following topics and materials are considered: design of p-type conducting wide-gap oxides (selection of cationic species, preferred crystal structure), p-type cond. in CuAlO2 and CuGaO2 delafossites, p-type cond. in SrCu2O2 (SCO), semiquant. estn. of valence-bond edge structure in CuAlO2, n-type cond. in AgInO2 delafossite, fabrication of transparent heterojunction thin-film diodes, UV light emission from a p-SCO/n-ZnO p-n heterojunction by current injection, chem. modulation of the valence bond, and codoping.
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Benko, F.; Koffyberg, F. Opto-Electronic Properties of p and n-Type Delafossite, CuFeO₂ J. Phys. Chem. Solids 1987, 48, 431– 434 DOI: 10.1016/0022-3697(87)90103-X
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Optoelectronic properties of p- and n-type delafossite, CuFeO2
Benko, F. A.; Koffyberg, F. P.
Journal of Physics and Chemistry of Solids (1987), 48 (5), 431-4CODEN: JPCSAW; ISSN:0022-3697.
CuFeO2 doped with Mg is a p-type semiconductor with a hole mobility of 10-5 m2/V-s; the electron mobility in n-type CuFeO2 doped with Sn is 10-10 m2/v-s. From photo-electrochem. measurements, the valence band edge is 4.9 eV below the vacuum level. The valence band is made up of mainly Cu-3d wave functions; a deeper lying O-2p band has its edge at 7.1 eV. The indirect allowed bandgap is 1.15 eV; further optical transitions occur at 2.03 and 3.35 eV. The results are compared with similar data for the delafossites CuMO2 with M = Al, Cr, ga and Y.
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Ingram, B.; Mason, T.; Asahi, R.; Park, K.; Freeman, A. Electronic Structure and Small Polaron Hole Transport of Copper Aluminate Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 1– 7 DOI: 10.1103/PhysRevB.64.155114
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Ingram, B. J.; Harder, B. J.; Hrabe, N. W.; Mason, T. O.; Poeppelmeier, K. R. Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO₂ and CuYO₂ Chem. Mater. 2004, 16, 5623– 5629 DOI: 10.1021/cm048982k
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Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO2 and CuYO2
Ingram, Brian J.; Harder, Bryan J.; Hrabe, Nikolas W.; Mason, Thomas O.; Poeppelmeier, Kenneth R.
Chemistry of Materials (2004), 16 (26), 5623-5629CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The delafossite structure (ABO2) accommodates a wide range of transition and rare-earth cations on the B-site in combination with a short list of A-site cations. This paper reports the effects on defect chem. and transport as a function of the B-site cation in copper-based delafossite materials, with CuScO2 and CuYO2 as examples. Large B-site cation delafossites exhibit small polaron conduction, a diffusion-limited conduction mechanism, with an activation energy approx. twice that of CuAlO2 (0.22 eV vs. 0.14 eV, resp.). The mobility for these materials is found to be <1 cm2 V-1 s-1, further evidence of small polaron conduction. The majority defect species is highly dependent on the B-site cation, such that CuScO2 and CuYO2 are dominated by extrinsic defects (acceptor doping) and free oxygen interstitials, whereas off-stoichiometry dominates CuAlO2. Dopant soly. is shown to be 1% for bulk CuScO2 samples and lower in CuYO2.
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Ingram, B. J.; Gonzàlez, G. B.; Mason, T. O.; Shahriari, D. Y.; Barnabè, A.; Ko, D.; Poeppelmeier, K. R. Transport and Defect Mechanisms in Cuprous Delafossites. 1. Comparison of Hydrothermal and Standard Solid-State Synthesis in CuAlO₂ Chem. Mater. 2004, 16, 5616– 5622 DOI: 10.1021/cm048983c
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Transport and Defect Mechanisms in Cuprous Delafossites. 1. Comparison of Hydrothermal and Standard Solid-State Synthesis in CuAlO2
Ingram, Brian J.; Gonzalez, Gabriela B.; Mason, Thomas O.; Shahriari, Dean Y.; Barnabe, Antoine; Ko, Donggeun; Poeppelmeier, Kenneth R.
Chemistry of Materials (2004), 16 (26), 5616-5622CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
CuAlO2 exhibits a unique defect structure that is dependent on the synthesis route. High-temp. solid-state and low-temp. hydrothermal techniques are compared to illustrate how cation off-stoichiometry affects the elec. properties of CuAlO2. A defect complex of Al on a Cu-site stabilized by two bound oxygen interstitials (AlCu••2Oi'')'' is proposed which serves as an acceptor dopant to set the hole concn. Trapping of holes (small polarons) by such complexes with decreasing temp. is proposed to account for the decreasing carrier content with temp. Hydrothermal samples exhibit approx. an order of magnitude increase in hole concn. relative to the solid-state synthesized samples; this is reflected in the elec. cond. and may explain the variations in elec. properties reported for CuAlO2.
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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: Condens. Matter Mater. Phys. 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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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
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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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Brander, R. A Review of the Merits of Direct and Indirect Gap Semiconductors for Electroluminescence Devices Rev. Phys. Technol. 1972, 3, 145– 194 DOI: 10.1088/0034-6683/3/3/I01
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Review of the merits of direct- and indirect-gap semiconductors for electroluminescence devices
Brander, R. W.
Review of Physics in Technology (1972), 3 (3), 145-94CODEN: RPTCAL; ISSN:0034-6683.
A review with many refs.
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Scanlon, D. O.; Godinho, K. G.; Morgan, B. J.; Watson, G. W. Understanding Conductivity Anomalies in Cu-Based Delafossite Transparent Conducting Oxides: Theoretical Insights J. Chem. Phys. 2010, 132, 024707 DOI: 10.1063/1.3290815
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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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Nakano, Y.; Saeki, S.; Morikawa, T. Optical Bandgap Widening of p-Type Cu₂O Films by Nitrogen Doping Appl. Phys. Lett. 2009, 94, 022111 DOI: 10.1063/1.3072804
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Optical bandgap widening of p-type Cu2O films by nitrogen doping
Nakano, Yoshitaka; Saeki, Shu; Morikawa, Takeshi
Applied Physics Letters (2009), 94 (2), 022111/1-022111/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
The authors have studied the effect of N doping into Cu2O films deposited by reactive magnetron sputtering. With increasing N-doping concn. up to 3%, the optical bandgap energy is enlarged from ∼2.1 to ∼2.5 eV with retaining p-type cond. as detd. by optical absorption and Hall effect measurements. Addnl., photoelectron spectroscopy in air measurements shows an increase in the valence and conduction band shifts with N doping. These exptl. results demonstrate possible optical bandgap widening of p-type N-doped Cu2O films, which is a phenomenon that is probably assocd. with significant structural changes induced by N doping, as suggested from x-ray diffraction measurements. (c) 2009 American Institute of Physics.
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Liu, G.; Schulmeyer, T.; BrÖtz, J.; Klein, A.; Jaegermann, W. Interface Properties and Band Alignment of Cu₂/CdS Thin Film Solar Cells Thin Solid Films 2003, 431–432, 477– 482 DOI: 10.1016/S0040-6090(03)00190-1
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Riha, S. C.; Johnson, D. C.; Prieto, A. L. Cu₂Se Nanoparticles with Tunable Electronic Properties due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction J. Am. Chem. Soc. 2011, 133, 1383– 1390 DOI: 10.1021/ja106254h
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Cu2Se Nanoparticles with Tunable Electronic Properties Due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction
Riha, Shannon C.; Johnson, Derek C.; Prieto, Amy L.
Journal of the American Chemical Society (2011), 133 (5), 1383-1390CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Stoichiometric copper(I) selenide nanoparticles were synthesized using the hot injection method. The effects of air exposure on the surface compn., crystal structure, and electronic properties were monitored using XPS, x-ray diffraction, and cond. measurements. The current-voltage response changes from semiconducting to ohmic, and within a week a 3000-fold increase in cond. is obsd. under ambient conditions. The enhanced electronic properties can be explained by the oxidn. of Cu+ and Se2- on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu2Se to cubic Cu1.8Se. This behavior is a result of the facile solid-state ionic cond. of cationic Cu within the crystal and the high susceptibility of the nanoparticle surface to oxidn. This regulated transformation is appealing as one could envision using layers of Cu2Se nanoparticles as both semiconducting and conducting domains in optoelectronic devices simply by tuning the electronic properties for each layer through controlled oxidn.
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Ueda, K.; Inoue, S.; Hirose, S.; Kawazoe, H.; Hosono, H. Transparent p-Type Semiconductor: LaCuOS Layered Oxysulfide Appl. Phys. Lett. 2000, 77, 2701 DOI: 10.1063/1.1319507
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Transparent p-type semiconductor: LaCuOS layered oxysulfide
Ueda, K.; Inoue, S.; Hirose, S.; Kawazoe, H.; Hosono, H.
Applied Physics Letters (2000), 77 (17), 2701-2703CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
La1-xSrxCuOS (x = 0, 0.05) thin films prepd. by radiofrequency sputtering have high optical transmission (≥70%) at the visible and near-IR wavelengths and an energy gap of ∼3.1 eV. The d.c. elec. conductivities of x = 0 and 0.05 films at room temp. were 1.2 × 10-2 and 2.6 × 10-1 S cm-1, resp. The Seebeck coeffs. of these samples were pos., indicating that p-type elec. conduction is dominant in these materials. A sharp luminescence peak, probably originating from an interband transition, was obsd. at the optical absorption edge. The present study demonstrates that LaCuOS is a promising transparent p-type semiconductor for optoelectronic applications. The material design, based on chem. modulation of the valence band, was extended to oxysulfide systems.
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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 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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Hiramatsu, H.; Ueda, K.; Ohta, H.; Hirano, M.; Kikuchi, M.; Yanagi, H.; Kamiya, T.; Hosono, H. Heavy Hole Doping of Epitaxial Thin Films of a Wide Gap p-Type Semiconductor, LaCuOSe, and Analysis of the Effective Mass Appl. Phys. Lett. 2007, 91, 012104 DOI: 10.1063/1.2753546
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Heavy hole doping of epitaxial thin films of a wide gap p-type semiconductor, LaCuOSe, and analysis of the effective mass
Hiramatsu, Hidenori; Ueda, Kazushige; Ohta, Hiromichi; Hirano, Masahiro; Kikuchi, Maiko; Yanagi, Hiroshi; Kamiya, Toshio; Hosono, Hideo
Applied Physics Letters (2007), 91 (1), 012104/1-012104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
The high d. hole doping (1.7×1021 cm-3) for a wide gap (Eg=∼2.8 eV) p-type semiconductor was achieved on 40 nm thick Mg-doped LaCuOSe epitaxial films. These films exhibited distinct free carrier absorption, and the effective mass and momentum relaxation time were analyzed. Its small hole mobility [∼3.5 cm2/(V s)] compared to the electron mobilities of wide gap n-type semiconductors is attributed to a heavy effective mass of 1.6 ± 0.2me. Regardless of the heavy hole doping, a band filling effect was not obsd. These results are discussed with a rigid band model and an acceptor band model.
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Liu, M. L.; Wu, L. B.; Huang, F. Q.; Chen, L. D.; Ibers, J. A. Syntheses, Crystal and Electronic Structure, and Some Optical and Transport Properties of LnCuOTe (Ln = La, Ce, Nd) J. Solid State Chem. 2007, 180, 62– 69 DOI: 10.1016/j.jssc.2006.09.014
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Syntheses, crystal and electronic structure, and some optical and transport properties of LnCuOTe (Ln = La, Ce, Nd)
Liu, Min Ling; Wu, Li Bin; Huang, Fu Qiang; Chen, Li Dong; Ibers, James A.
Journal of Solid State Chemistry (2007), 180 (1), 62-69CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)
Three new compds., LaCuOTe, CeCuOTe, and NdCuOTe, were synthesized from the resp. rare-earth elements, CuO, Te, and a KI flux at 1023 K. The compds., which have the ZrSiCuAs structure type, are isostructural to LaCuOS, and crystallize in space group P4/nmm of the tetragonal system with two formula units in cells of dimensions at 153 K of a 4.1775(5), c 9.3260(16) Å for LaCuOTe; a 4.1497(3), c 9.3090(10) Å for CeCuOTe; and a 4.1056(9), c 9.332(4) Å for NdCuOTe. The structure of LnCuOTe (Ln = La, Ce, Nd) is composed of alternating PbO-like [Ln2O2] and anti-PbO-like [Cu2Te2] layers stacked perpendicular to [0 0 1]. The exptl. optical band gaps of LaCuOTe and NdCuOTe are 2.31 and 2.26 eV, resp. At 298 K the elec. cond. of LaCuOTe is 1.65 S/cm and the Hall mobility is +80.6 cm2 V-1 s-1. The pos. values of the Seebeck and Hall coeffs. indicate p-type elec. conduction. First-principle theor. calcns. were performed on LaCuOQ (Q = S, Se, Te). In LaCuOTe, Cu 3d and Te 5p orbitals dominate the states near the valence band max.; the states near the conduction band min. are composed of Cu 4s, Te 5p, and La 5d orbitals. The larger dispersion of Cu 3d orbitals and the presence of Te 5p orbitals near the valence band max. are responsible for the larger hole mobility of LaCuOTe compared to LaCuOS and LaCuOSe.
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Ueda, K.; Hosono, H.; Hamada, N. Energy Band Structure of LaCuOCh (Ch = S, Se and Te) Calculated by the Full-Potential Linearized Augmented Plane-Wave Method J. Phys.: Condens. Matter 2004, 16, 5179– 5186 DOI: 10.1088/0953-8984/16/28/036
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Energy band structure of LaCuOCh (Ch = S, Se and Te) calculated by the full-potential linearized augmented plane-wave method
Ueda, Kazushige; Hosono, Hideo; Hamada, Noriaki
Journal of Physics: Condensed Matter (2004), 16 (28), 5179-5186CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
Energy band diagrams of LaCuOCh (Ch = S, Se and Te) were calcd. by a full-potential linearized augmented plane-wave method. The calcns., based on the local d. approxn. with/without an on-site Coulomb repulsion parameter, were to examine the energy levels of La 4f states. The results of the calcns. showed that the on-site correlation parameter is necessary for evaluating the energy levels of La 4f states appropriately. The calcns. for LaCuOCh with the on-site correlation parameter revealed that LaCuOS and LaCuOSe have almost the same energy band structure with a direct allowed-type band gap, while LaCuOTe has significantly different conduction band structure that exhibits an indirect-type band gap. This difference in electronic structure between LaCuOCh (Ch = S, Se and Te) is consistent with the obsd. optical properties of these materials.
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Caskey, C. M.; Richards, R. M.; Ginley, D. S.; Zakutayev, A. Thin Film Synthesis and Properties of Copper Nitride, a Metastable Semiconductor Mater. Horiz. 2014, 1, 424 DOI: 10.1039/c4mh00049h
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Thin film synthesis and properties of copper nitride, a metastable semiconductor
Caskey, Christopher M.; Richards, Ryan M.; Ginley, David S.; Zakutayev, Andriy
Materials Horizons (2014), 1 (4), 424-430CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
Copper nitride (Cu3N) thin films were grown by reactive sputtering using a high-throughput combinatorial approach with orthogonal gradients of substrate temp. and target-substrate distance. This technique enables high-throughput modulation of the anion activity, and is broadly applicable to the combinatorial synthesis of other materials. Stable, phase pure Cu3N thin films were grown on glass substrates at temps. between 150 and 200°C, depending on the target-substrate distance. These 00L oriented thin films have 10-3 S cm-1 cond. and 1.5 eV optical absorption onset, making Cu3N interesting for future studies in the context of solar energy conversion applications. The anal. of the synthetic results provides insights into the thermodn. origins of the growth of metastable Cu3N, and sets a nitrogen chem. potential of +1 eV per atom as a lower limit of the anion activity that can be achieved in non-equil. thin film growth of metastable materials. The first step towards testing the transferability of this result to other materials was made by reactive sputtering of tin, antimony, and bismuth in nitrogen.
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Walsh, A.; Chen, S.; Wei, S.-H.; Gong, X.-G. Kesterite Thin-Film Solar Cells: Advances in Materials Modelling of Cu₂ZnSnS₄ Adv. Energy Mater. 2012, 2, 400– 409 DOI: 10.1002/aenm.201100630
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Kesterite thin-film solar cells: advances in materials modelling of Cu2ZnSnS4
Walsh, Aron; Chen, Shiyou; Wei, Su-Huai; Gong, Xin-Gao
Advanced Energy Materials (2012), 2 (4), 400-409CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
A review. Quaternary semiconducting materials based on the kesterite (A2BCX4) mineral structure are the most promising candidates to overtake the current generation of light-absorbing materials for thin-film solar cells. Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and their alloy Cu2ZnSn(Se,S)4 consist of abundant, low-cost and non-toxic elements, unlike current CdTe and Cu(In,Ga)Se2 based technologies. Zinc-blende related structures are formed by quaternary compds., but the complexity assocd. with the multi-component system introduces difficulties in material growth, characterization, and application. First-principles electronic structure simulations, performed over the past five years, that address the structural, electronic, and defect properties of this family of compds. are reviewed. Initial predictions of the bandgaps and crystal structures have recently been verified exptl. The calcns. highlight the role of at. disorder on the cation sub-lattice, as well as phase sepn. of Cu2ZnSnS4 into ZnS and CuSnS3, on the material performance for light-to-electricity conversion in photovoltaic devices. Finally, the current grand challenges for materials modeling of thin-film solar cells are highlighted.
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Zakutayev, A.; Caskey, C. M.; Fioretti, A. N.; Ginley, D. S.; Vidal, J.; Stevanovic, V.; Tea, E.; Lany, S. Defect Tolerant Semiconductors for Solar Energy Conversion J. Phys. Chem. Lett. 2014, 5, 1117– 1125 DOI: 10.1021/jz5001787
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Defect tolerant semiconductors for solar energy conversion
Zakutayev, Andriy; Caskey, Christopher M.; Fioretti, Angela N.; Ginley, David S.; Vidal, Julien; Stevanovic, Vladan; Tea, Eric; Lany, Stephan
Journal of Physical Chemistry Letters (2014), 5 (7), 1117-1125CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Defect tolerance is the tendency of a semiconductor to keep its properties despite the presence of crystallog. defects. Scientific understanding of the origin of defect tolerance is currently missing. Here we show that semiconductors with antibonding states at the top of the valence band are likely to be tolerant to defects. Theor. calcns. demonstrate that Cu3N with antibonding valence band max. has shallow intrinsic defects and no surface states, in contrast to GaN with bonding valence band max. Exptl. measurements indicate shallow native donors and acceptors in Cu3N thin films, leading to 1016-1017 cm-3 doping with either electrons or holes depending on the growth conditions. The exptl. measured bipolar doping and the solar-matched optical absorption onset (1.4 eV) make Cu3N a promising candidate absorber for photovoltaic and photoelectrochem. solar cells, despite the calcd. indirect fundamental band gap (1.0 eV). These conclusions can be extended to other materials with antibonding character of the valence band, defining a class of defect-tolerant semiconductors for solar energy conversion applications.
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Yang, M.; Zakutayev, A.; Vidal, J.; Zhang, X.; Ginley, D. S.; DiSalvo, F. J. Strong Optical Absorption in CuTaN₂ Nitride Delafossite Energy Environ. Sci. 2013, 6, 2994 DOI: 10.1039/c3ee40621k
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Strong optical absorption in CuTaN2 nitride delafossite
Yang, Minghui; Zakutayev, Andriy; Vidal, Julien; Zhang, Xiuwen; Ginley, David S.; DiSalvo, Francis J.
Energy & Environmental Science (2013), 6 (10), 2994-2999CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
We report on synthesis, stability, electronic structure and optical properties of CuTaN2 with the delafossite crystal structure and its potential use as an absorber for solar energy conversion applications. According to theor. first-principles calcns., the formation enthalpy of CuTaN2 is neg. (-0.66 eV per atom), but this material is metastable with respect to decompn. into Cu, Ta3N5 and N2. Nevertheless, the exptl. thermal stability limit of single phase CuTaN2 powders synthesized using an ion exchange method is 250 °C in ambient atm., according to combined temp.-dependent X-ray diffraction and thermo-gravimetric analyses. Electronic structure of the CuTaN2 is different compared to that of CuAlO2, in particular the band gap of this nitride delafossite (1.3 eV) calcd. using HSE06+G0W0 is much smaller than the band gap of the oxide delafossite. The onset of optical absorption onset of CuTaN2 at 1.5 eV detd. from exptl. diffuse reflectance measurements is consistent with the theor. 1.4 eV optical band gap and large calcd. absorption coeff. (>105 cm-1 above 1.5 eV) detd. from time-dependent HSE06 calcns. cor. by a scissors operator. The significance of our findings is that optical properties of CuTaN2 are nearly optimal for photovoltaic energy conversion.
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Mewis, A. Darstellung und Struktur der Verbindungen MgCuP, BaCuP(As) und BaAgP(As) Z. Naturforsch., B: J. Chem. Sci. 1979, 34, 1373– 1376 DOI: 10.1515/znb-1979-1006
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Preparation and crystal structure of magnesium-copper-phosphide, barium-copper-phosphide(arsenide), and barium-silver-phosphide(arsenide
Mewis, Albrecht
Zeitschrift fuer Naturforschung, Teil B: Anorganische Chemie, Organische Chemie (1979), 34B (10), 1373-6CODEN: ZNBAD2; ISSN:0340-5087.
MgCuP, BaCuP(As), and BaAgP(As) were prepd. and their structures detd. MgCuP crystd. orthorhombically in an anti-PbCl2 structure (space group Pnma, a 653.2(1), b 383.5(1), c 717.0(1) pm). BaCuP(As) and BaAgP(As) are isotypic and crystd. in a modified Ni2In-structure (space group P63/mmc with a 423.9(1) and c 900.6(2) pm for BaCuP, a 437.2(1) and c 907.3(2) pm for BaCuAs, a 449.61(1) and c 882.8(2) pm for BaAgP, and a 461.3(1) and c 889.6(1) pm for BaAgAs.
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Mewis, A. ABX Verbindungen mit Ni₂ In-Struktur. Darstellung und Struktur der Verbindungen CaCuP(As), SrCuP(As), SrAgP(As) und EuCuAs Z. Naturforsch., B: J. Chem. Sci. 1978, 33, 983– 986 DOI: 10.1515/znb-1978-0906
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There is no corresponding record for this reference.
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Adamo, C.; Barone, V. Toward Reliable Density Functional Methods Without Adjustable Parameters: The PBE0Model J. Chem. Phys. 1999, 110, 6158 DOI: 10.1063/1.478522
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Toward reliable density functional methods without adjustable parameters: the PBE0 model
Adamo, Carlo; Barone, Vincenzo
Journal of Chemical Physics (1999), 110 (13), 6158-6170CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
We present an anal. of the performances of a parameter free d. functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amt. of exact exchange. The results obtained for structural, thermodn., kinetic and spectroscopic (magnetic, IR and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chem. and condensed matter physics.
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Paier, J.; Hirschl, R.; Marsman, M.; Kresse, G. The Perdew-Burke-Ernzerhof Exchange-Correlation Functional Applied to the G2–1 Test Set Using a Plane-Wave Basis Set J. Chem. Phys. 2005, 122, 234102 DOI: 10.1063/1.1926272
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The Perdew-Burke-Ernzerhof exchange-correlation functional applied to the G2-1 test set using a plane-wave basis set
Paier, Joachim; Hirschl, Robin; Marsman, Martijn; Kresse, Georg
Journal of Chemical Physics (2005), 122 (23), 234102/1-234102/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
Present local and semilocal functionals show significant errors, for instance, in the energetics of small mols. and in the description of band gaps. One possible soln. to these problems is the introduction of exact exchange and hybrid functionals. A plane-wave-based algorithm was implemented in VASP (Vienna ab-initio simulation package) to allow for the calcn. of the exact exchange. To systematically assess the precision of the present implementation, calcns. for the 55 mols. of the G2-1 quantum chem. test set were performed applying the PBE and PBE0 functionals. Excellent agreement for both atomization energies and geometries compared with the results obtained by GAUSSIAN 03 calcns. using large basis sets (augmented correlation consistent polarized valence quadruple zeta for the geometry optimization and augmented correlation-consistent polarized valence quintuple zeta for the energy calcns.) was found. The mean abs. error for atomization energies between VASP and the expt. is 8.6 and 3.7 kcal/mol, as calcd. with the PBE and PBE0 functionals, resp. The mean deviations between VASP and GAUSSIAN are 0.46 and 0.49 kcal/mol for the PBE and PBE0 functionals, resp.
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Kresse, G.; Hafner, J. Ab-initio Molecular Dynamics for Liquid Metals Phys. Rev. B: Condens. Matter Mater. Phys. 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: Condens. Matter Mater. Phys. 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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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-Initio Total-Energy Calculations Using a Plane-Wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 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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Blöchl, P. E. Projector Augmented-Wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 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.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 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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Yeh, J.; Lindau, I. Atomic Subshell Photoionization Cross Sections and Asymmetry Parameters: 1 ⩽ Z ⩽ 103 At. Data Nucl. Data Tables 1985, 32, 1– 155 DOI: 10.1016/0092-640X(85)90016-6
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Atomic subshell photoionization cross sections and asymmetry parameters: 1 ≤ Z ≤ 103
Yeh, J. J.; Lindau, I.
Atomic Data and Nuclear Data Tables (1985), 32 (1), 1-155CODEN: ADNDAT; ISSN:0092-640X.
At. subshell photoionization cross sections and asymmetry parameters are calcd. with the Hartree-Fock-Slater one-electron central potential model (dipole approxn.) for all elements Z = 1-103. The cross-section results are plotted for all subshells in the energy region 0-1500 eV, and cross sections and asymmetry parameters are tabulated for selected energies in the region 10.2-8047.8 eV. In addn., more detailed graphs are given for the 4d (Z = 39-71) and 5d (Z = 64-100) subshell cross sections in the vicinity of the Cooper min. These data should be particularly useful for work based on spectroscopic investigations of at. subshells using synchrotron radiation and/or discrete line sources.
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Savory, C. N.; Ganose, A. M.; Travis, W.; Atri, R. S.; Palgrave, R. G.; Scanlon, D. O. An Assessment of Silver Copper Sulfides for Photovoltaic Applications: Theoretical and Experimental Insights J. Mater. Chem. A 2016, 4, 12648 DOI: 10.1039/C6TA03376H
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An assessment of silver copper sulfides for photovoltaic applications: theoretical and experimental insights
Savory, Christopher N.; Ganose, Alex M.; Travis, Will; Atri, Ria S.; Palgrave, Robert G.; Scanlon, David O.
Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (32), 12648-12657CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
As the worldwide demand for energy increases, low-cost solar cells are being looked to as a soln. for the future. To attain this, non-toxic earth-abundant materials are crucial, however cell efficiencies for current materials are limited in many cases. In this article, we examine the two silver copper sulfides AgCuS and Ag3CuS2 as possible solar absorbers using hybrid d. functional theory, diffuse reflectance spectroscopy, XPS and Hall effect measurements. We show that both compds. demonstrate promising electronic structures and band gaps for high theor. efficiency solar cells, based on Shockley-Queisser limits. Detailed anal. of their optical properties, however, indicates that only AgCuS should be of interest for PV applications, with a high theor. efficiency. From this, we also calc. the band alignment of AgCuS against various buffer layers to aid in future device construction.
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Bhachu, D. S.; Moniz, S. J. A.; Sathasivam, S.; Scanlon, D. O.; Walsh, A.; Bawaked, S. M.; Mokhtar, M.; Obaid, A. Y.; Parkin, I. P.; Tang, J.; Carmalt, C. J. Bismuth Oxyhalides: Synthesis, Structure and Photoelectrochemical Activity Chem. Sci. 2016, 7, 4832– 4841 DOI: 10.1039/C6SC00389C
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Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity
Bhachu, Davinder S.; Moniz, Savio J. A.; Sathasivam, Sanjayan; Scanlon, David O.; Walsh, Aron; Bawaked, Salem M.; Mokhtar, Mohamed; Obaid, Abdullah Y.; Parkin, Ivan P.; Tang, Junwang; Carmalt, Claire J.
Chemical Science (2016), 7 (8), 4832-4841CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
The authors report the synthesis and photoelectrochem. assessment of phase pure tetragonal matlockite structured BiOX (X = Cl, Br, I) films. The materials were deposited using aerosol-assisted CVD. The measured optical bandgaps of the oxyhalides, supported by d. functional theory calcns., showed a red shift with the increasing size of halide following the binding energy of the anion p-orbitals that form the valence band. Stability and photoelectrochem. studies carried out without a sacrificial electron donor showed the n-type BiOBr film to have the highest photocurrent reported for BiOBr in the literature to date (0.3 mA cm-2 at 1.23 V vs. RHE), indicating it is an excellent candidate for solar fuel prodn. with a very low onset potential of 0.2 V vs. RHE. The high performance was attributed to the preferred growth of the film in the [011] direction, as shown by x-ray diffraction, leading to internal elec. fields that minimize charge carrier recombination.
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Marchand, P.; Sathasivam, S.; Williamson, B. A. D.; Pugh, D.; Bawaked, S. M.; Basahel, S. N.; Obaid, A. Y.; Scanlon, D. O.; Parkin, I. P.; Carmalt, C. J. A Single-Source Precursor Approach to Solution Processed Indium Arsenide Thin Films J. Mater. Chem. C 2016, 4, 6761– 6768 DOI: 10.1039/C6TC02293F
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A single-source precursor approach to solution processed indium arsenide thin films
Marchand, Peter; Sathasivam, Sanjayan; Williamson, Benjamin A. D.; Pugh, David; Bawaked, Salem M.; Basahel, Sulaiman N.; Obaid, Abdullah Y.; Scanlon, David O.; Parkin, Ivan P.; Carmalt, Claire J.
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (28), 6761-6768CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
This paper reports the synthesis of the novel single-source precursor, [{(MeInAstBu)3}2(Me2InAs(tBu)H)2] and the subsequent first report of aerosol-assisted chem. vapor deposition of InAs thin films. Owing to the use of the single-source precursor, highly cryst. and stoichiometric films were grown at a relatively low deposition temp. of 450 °C. Core level XPS depth profiling studies showed some partial oxidn. of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS anal. matched well with the simulated d. of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10-3 Ω cm) and carrier mobility (410 cm2 V-1 s-1) values despite growth on amorphous glass substrates.
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Sathasivam, S.; Arnepalli, R. R.; Bhachu, D. S.; Lu, Y.; Buckeridge, J.; Scanlon, D. O.; Kumar, B.; Singh, K. K.; Visser, R. J.; Blackman, C. S.; Carmalt, C. J. Single Step Solution Processed GaAs Thin Films from GaMe₃ and tBuAsH₂ under Ambient Pressure J. Phys. Chem. C 2016, 120, 7013– 7019 DOI: 10.1021/acs.jpcc.6b00850
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Single Step Solution Processed GaAs Thin Films from GaMe3 and tBuAsH2 under Ambient Pressure
Sathasivam, Sanjayan; Arnepalli, Ranga R.; Bhachu, Davinder S.; Lu, Yao; Buckeridge, John; Scanlon, David O.; Kumar, Bhaskar; Singh, Kaushal K.; Visser, Robert J.; Blackman, Christopher S.; Carmalt, Claire J.
Journal of Physical Chemistry C (2016), 120 (13), 7013-7019CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
This article reports on the possibility of low-cost GaAs formed under ambient pressure via a single step soln. processed route from only readily available precursors, tBuAsH2 and GaMe3. The thin films of GaAs on glass substrates have good crystallinity with crystallites as large as 150 nm and low contamination with exptl. results matching well with theor. d. of states calcns. These results open up a route to efficient and cost-effective scale up of GaAs thin films with high material properties for widespread industrial use. Confirmation of film quality was detd. using XRD, Raman, EDX mapping, SEM, HRTEM, XPS, and SIMS.
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Gajdoš, M.; Hummer, K.; Kresse, G.; Furthmüller, J.; Bechstedt, F. Linear Optical Properties in the Projector-Augmented Wave Methodology Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 045112 DOI: 10.1103/PhysRevB.73.045112
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Linear optical properties in the projector-augmented wave methodology
Gajdos, M.; Hummer, K.; Kresse, G.; Furthmuller, J.; Bechstedt, F.
Physical Review B: Condensed Matter and Materials Physics (2006), 73 (4), 045112/1-045112/9CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
In this work we derive closed expressions for the head of the frequency-dependent microscopic polarizability matrix in the projector-augmented wave (PAW) methodol. Contrary to previous applications, the longitudinal expression is utilized, resulting in dielec. properties that are largely independent of the applied potentials. The improved accuracy of the present approach is demonstrated by comparing the longitudinal and transversal expressions of the polarizability matrix for a no. of cubic semiconductors and one insulator, i.e., Si, SiC, AlP, GaAs, and diamond (C), resp. The methodol. is readily extendable to more complicated nonlocal Hamiltonians or to the calcn. of the macroscopic dielec. matrix including local field effects in the random phase or d. functional approxn., which is demonstrated for the previously mentioned model systems. Furthermore, d. functional perturbation theory is extended to the PAW method, and the resp. results are compared to those obtained by summation over the conduction band states.
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Adolph, B.; Furthmüller, J.; Bechstedt, F. Optical Properties of Semiconductors Using Projector-Augmented Waves Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63, 125108 DOI: 10.1103/PhysRevB.63.125108
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Optical properties of semiconductors using projector-augmented waves
Adolph, B.; Furthmuller, J.; Bechstedt, F.
Physical Review B: Condensed Matter and Materials Physics (2001), 63 (12), 125108/1-125108/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
The frozen-core projector-augmented wave (PAW) method is applied to construct all-electron valence wave functions from nonnorm-conserving pseudo wave functions and at. functions. The use of all-electron wave functions possesses the advantage that no nonlocal contributions to the optical transition operator have to be taken into account. In addn., the more accurate description of the wave functions in the core region improves the quality of the calcd. spectra compared to those obtained from a pseudopotential approach. The authors demonstrate the accuracy of the PAW approach by comparing optical spectra of several semiconductors with those obtained employing a full all-electron method or norm-conserving pseudopotentials.
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Nie, X.; Wei, S.-H.; Zhang, S. B. Bipolar Doping and Band-Gap Anomalies in Delafossite Transparent Conductive Oxides Phys. Rev. Lett. 2002, 88, 066405 DOI: 10.1103/PhysRevLett.88.066405
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Bipolar doping and band-gap anomalies in delafossite transparent conductive oxides
Nie, Xiliang; Wei, Su-Huai; Zhang, S. B.
Physical Review Letters (2002), 88 (6), 066405/1-066405/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
Doping wide-gap materials p type is highly desirable but often difficult. This makes the recent discovery of p-type delafossite oxides, CuMIIIO2, very attractive. The CuMIIIO2 also show unique and unexplained phys. properties: Increasing band gap from MIII=Al, Ga, to In, not seen in conventional semiconductors. The largest gap CuInO2 can be mysteriously doped both n and p type but not the smaller gaps CuAlO2 and CuGaO2. Here, both properties are results of a large disparity between the fundamental gap and the apparent optical gap, a finding that could lead to a breakthrough in the study of bipolarly dopable wide-gap semiconductor oxides.
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Walsh, A.; Da Silva, J. L. F.; Yan, Y.; Al-Jassim, M. M.; Wei, S.-H. Origin of Electronic and Optical Trends in Ternary In₂O₃ (ZnO)_n Transparent Conducting Oxides (n = 1.3,5): Hybrid Density Functional Theory Calculations Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 073105 DOI: 10.1103/PhysRevB.79.073105
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Walsh, A.; Yan, Y.; Huda, M. N.; Al-Jassim, M. M.; Wei, S.-H. Band Edge Electronic Structure of BiVO₄: Elucidating the Role of the Bi s and V d Orbitals Chem. Mater. 2009, 21, 547– 551 DOI: 10.1021/cm802894z
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Band Edge Electronic Structure of BiVO4: Elucidating the Role of the Bi s and V d Orbitals
Walsh, Aron; Yan, Yanfa; Huda, Muhammad N.; Al-Jassim, Mowafak M.; Wei, Su-Huai
Chemistry of Materials (2009), 21 (3), 547-551CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The authors report the 1st-principles electronic structure of BiVO4, a promising photocatalyst for H generation. BiVO4 is a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center. Coupling between Bi 6s and O 2p forces an upward dispersion of the valence band at the zone boundary; however, a direct gap is maintained via coupling between V 3d, O 2p, and Bi 6p, which lowers the conduction band min. These interactions result in sym. hole and electron masses. Implications for the design of ambipolar metal oxides are discussed.
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Scanlon, D. O.; Watson, G. W. (Cu₂S₂) (Sr₃Sc₂O₅)-A Layered, Direct Band Gap, p-Type Transparent Conducting Oxychalcogenide: A Theoretical Analysis Chem. Mater. 2009, 21, 5435– 5442 DOI: 10.1021/cm902260b
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Allen, J. P.; Nilsson, M. K.; Scanlon, D. O.; Watson, G. W. Comparison of the Defective Pyrochlore and Ilmenite Polymorphs of AgSbO₃ using GGA and hybrid DFT Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 035207 DOI: 10.1103/PhysRevB.83.035207
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Kubelka, P. New Contributions to the Optics of Intensely Light-Scattering Materials Part I J. Opt. Soc. Am. 1948, 38, 448 DOI: 10.1364/JOSA.38.000448
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New contributions to the optics of intensely light-scattering materials
KUBELKA P
Journal of the Optical Society of America (1948), 38 (5), 448-57 ISSN:0030-3941.
There is no expanded citation for this reference.
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Preissler, N.; Bierwagen, O.; Ramu, A. T.; Speck, J. S. Electrical Transport, Electrothermal Transport, and Effective Electron Mass in Single-Crystalline In₂O₃ films Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 085305 DOI: 10.1103/PhysRevB.88.085305
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Electrical transport, electrothermal transport, and effective electron mass in single-crystalline In2O3 films
Preissler, Natalie; Bierwagen, Oliver; Ramu, Ashok T.; Speck, James S.
Physical Review B: Condensed Matter and Materials Physics (2013), 88 (8), 085305/1-085305/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
A comprehensive study of the room-temp. elec. and electrothermal transport of single-cryst. indium oxide (In2O3) and indium tin oxide (ITO) films over a wide range of electron concns. is reported. We measured the room-temp. Hall mobility μH and Seebeck coeff. S of unintentionally doped and Sn-doped high-quality, plasma-assisted mol.-beam-epitaxy-grown In2O3 for vol. Hall electron concns. nH from 7 × 1016 cm-3 (unintentionally doped) to 1 × 1021 cm-3 (highly Sn-doped, ITO). The resulting empirical S(nH) relation can be directly used in other In2O3 samples to est. the vol. electron concn. from simple Seebeck coeff. measurements. The mobility and Seebeck coeff. were modeled by a numerical soln. of the Boltzmann transport equation. Ionized impurity scattering and polar optical phonon scattering were found to be the dominant scattering mechanisms. Acoustic phonon scattering was found to be negligible. Fitting the temp.-dependent mobility above room temp. of an In2O3 film with high mobility allowed us to find the effective Debye temp. (ΘD = 700 K) and no. of phonon modes (NOPML = 1.33) that best describe the polar optical phonon scattering. The modeling also yielded the Hall scattering factor rH as a function of electron concn., which is not negligible (rH ≈ 1.4) at nondegenerate electron concns. Fitting the Hall-scattering-factor cor. concn.-dependent Seebeck coeff. S(n) for nondegenerate samples to the numerical soln. of the Boltzmann transport equation and to widely used, simplified equations allowed us to ext. an effective electron mass of m* = (0.30 ± 0.03)me (with free electron mass me). The modeled mobility and Seebeck coeff. based on polar optical phonon and ionized impurity scattering describes the exptl. results very accurately up to electron concns. of 1019 cm-3, and qual. explains a mobility plateau or local max. around 1020 cm-3. Ionized impurity scattering with doubly charged donors best describes the mobility in our unintentionally doped films, consistent with oxygen vacancies as unintentional shallow donors, whereas singly charged donors best describe our Sn-doped films. Our modeling yields a (phonon-limited) max. theor. drift mobility and Hall mobility of μ = 190 cm2/Vs and μH = 270 cm2/V s, resp. Simplified equations for the Seebeck coeff. describe the measured values in the nondegenerate regime using a Seebeck scattering parameter of r = -0.55 (which is consistent with the detd. Debye temp.), and provide an est. of the Seebeck coeff. to lower electron concns. The simplified equations fail to describe the Seebeck coeff. around the Mott transition (nMott = 5.5 × 1018 cm-3) from nondegenerate to degenerate electron concns., whereas the numerical modeling accurately describes this region.
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Button, K. J.; Cohn, D. R.; Von Ortenbert, M.; Lax, B.; Mollwo, E.; Helbig, R. Zeeman Splitting of Anomalous Shallow Bound States in ZnO Phys. Rev. Lett. 1972, 28, 1637– 1639 DOI: 10.1103/PhysRevLett.28.1637
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Button, K. J.; Fonstad, C. G.; Dreybrodt, W. Determination of the Electron Masses in Stannic Oxide by Submillimeter Cyclotron Resonance 1971, 4, 4539– 4541 DOI: 10.1103/PhysRevB.4.4539
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Scanlon, D. O. Defect Engineering of BaSnO₃ for High-Performance Transparent Conducting Oxide Applications Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 161201 DOI: 10.1103/PhysRevB.87.161201
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Defect engineering of BaSnO3 for high-performance transparent conducting oxide applications
Scanlon, David O.
Physical Review B: Condensed Matter and Materials Physics (2013), 87 (16), 161201/1-161201/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
The high cost and low abundance of indium has driven research to find In-free n-type transparent conducting oxides (TCOs). La-doped cubic perovskite BaSnO3 has been reported to possess electron mobilities as high as 320 cm2 V-1 s-1 for carrier concns. of 8 × 1019 cm-3, comparable to the very best TCOs. To date, however, the origins of cond. in this material have remained unclear. Here we study the defect chem. of BaSnO3 using a hybrid d. functional theory approach, in order to understand how to control the n-type cond. We show that in undoped samples, native defects cannot cause high levels of n-type cond.; however, adventitious H present in samples can act as shallow donors. By studying the effect of a range of donor dopants, we pinpoint ideal growth conditions and donor dopants for high-performance n-type BaSnO3 samples.
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Toby, B. H. EXPGUI, a Graphical User Interface for GSAS J. Appl. Crystallogr. 2001, 34, 210– 213 DOI: 10.1107/S0021889801002242
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EXPGUI, a graphical user interface for GSAS
Toby, Brian H.
Journal of Applied Crystallography (2001), 34 (2), 210-213CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
A description and justification of the EXPGUI program is presented. This program implements a graphical user interface and shell for the GSAS (Generalized Structure and Anal. Software) single-crystal and Rietveld package. Use of the Tcl/Tk scripting language allows EXPGUI to be platform independent. Also included is a synopsis of how the program is implemented.
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Larson, A.; Dreele, R. V. General Structure Analysis System (GSAS); Los Alamos National Laboratory Report LAUR 86-748; Los Alamos National Laboratory: Los Alamos, NM, 2004.
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Mewis, A. Darstellung und Struktur der Verbindung CaCu₄P₂ Z. Naturforsch., B: J. Chem. Sci. 1980, 35, 942– 945 DOI: 10.1515/znb-1980-0802
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Ghijsen, J.; Tjeng, L. H.; van Elp, J.; Eskes, H.; Westerink, J.; Sawatzky, G. A.; Czyzyk, M. T. Electronic Structure of Cu₂O and CuO Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 38, 11322– 11330 DOI: 10.1103/PhysRevB.38.11322
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Electronic structure of cuprous and cupric oxides
Ghijsen, J.; Tjeng, L. H.; Van Elp, J.; Eskes, H.; Westerink, J.; Sawatzky, G. A.; Czyzyk, M. T.
Physical Review B: Condensed Matter and Materials Physics (1988), 38 (16-A), 11322-30CODEN: PRBMDO; ISSN:0163-1829.
The electronic structure of Cu oxides has been investigated by photoelectron (x-ray photoemission, UV photoemission), Auger electron, and bremsstrahlung isochromat spectroscopies. The exptl. results are compared with one-electron band-structure calcns. as well as with a cluster CI model. It is demonstrated that the results for Cu2O agree well with band theory, whereas those for CuO clearly show strong deviations which we argue are due to electron-correlation effects in the open-shell d bands. From the comparison to cluster calcns., we ext. values for the Cu d-d and O p-p Coulomb interactions, the O to Cu charge transfer energy, and the degree of Cu d-O 2p hybridization. From this we demonstrate that CuO is a charge-transfer gap insulator.
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Shin, D.; Foord, J. S.; Egdell, R. G.; Walsh, A. Electronic Structure of CuCrO₂ Thin Films Grown on Al₂O₃(001) by Oxygen Plasma Assisted Molecular Beam Epitaxy J. Appl. Phys. 2012, 112, 113718 DOI: 10.1063/1.4768726
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Electronic structure of CuCrO2 thin films grown on Al2O3(001) by oxygen plasma assisted molecular beam epitaxy
Shin, D.; Foord, J. S.; Egdell, R. G.; Walsh, A.
Journal of Applied Physics (2012), 112 (11), 113718/1-113718/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Thin films of CuCrO2 were grown on Al2O3(001) substrates by O plasma assisted mol. beam epitaxy. With a substrate temp. of 700° or 750°, the films showed an unanticipated (015) orientation but at a higher substrate temp. of 800° the expected basal (001) orientation predominates. The optical absorption spectrum of CuCrO2 shows a direct allowed absorption onset at 3.18 eV together with a weak peak at 2.0 eV which is suppressed by Sn doping. The low energy peak should be attributed to 3d→3d excitations assocd. with Cu2+ defect states rather than excitations localized on Cr3+. Valence band X-ray photoemission spectra of (001) and (015) oriented CuCrO2 are compared with those obtained from polycryst. samples. (c) 2012 American Institute of Physics.
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Deuermeier, J.; Gassmann, J.; Brötz, J.; Klein, A. Reactive Magnetron Sputtering of Cu₂O: Dependence on Oxygen Pressure and Interface Formation with Indium Tin Oxide J. Appl. Phys. 2011, 109, 113704 DOI: 10.1063/1.3592981
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Reactive magnetron sputtering of Cu2O. Dependence on oxygen pressure and interface formation with indium tin oxide
Deuermeier, Jonas; Gassmann, Juergen; Broetz, Joachim; Klein, Andreas
Journal of Applied Physics (2011), 109 (11), 113704/1-113704/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Thin films of Cu oxides were prepd. by reactive magnetron sputtering and structural, morphol., chem., and electronic properties were analyzed using x-ray diffraction, AFM, in situ photoelectron spectroscopy, and elec. resistance measurements. The deposition conditions for prepn. of Cu(I)-oxide (Cu2O) are identified. In addn., the interface formation between Cu2O and Sn-doped In2O3 (ITO) was studied by stepwise deposition of Cu2O onto ITO and vice versa. A type II (staggered) band alignment with a valence band offset ΔEVB = 2.1-2.6 eV depending on interface prepn. is obsd. The band alignment explains the nonrectifying behavior of p-Cu2O/n-ITO junctions, which were investigated for thin film solar cells. (c) 2011 American Institute of Physics.
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Egdell, R. G.; Henrich, V. E.; Bowdler, R.; Sekine, T. On the Difference in Valence Electron Plasmon Energy and Density of States Between Beta- and Cubic-Si₃N₄ J. Appl. Phys. 2003, 94, 6611 DOI: 10.1063/1.1619568
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On the difference in valence electron plasmon energy and density of states between beta- and cubic-Si3N4
Egdell, R. G.; Henrich, V. E.; Bowdler, R.; Sekine, T.
Journal of Applied Physics (2003), 94 (10), 6611-6615CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
Core and valence level photoemission spectra of β- and cubic-Si3N4 were measured under monochromatic Al Kα excitation. Strong satellites to high binding energy of the core lines arise from excitation of valence electron plasmons during the photoemission process. An increase in the plasmon energy from 23.45 eV for β-Si3N4 to 26.10 eV for cubic-Si3N4 is of the magnitude expected from the 26% increase in the valence electron d. assocd. with the shock-induced β-to-cubic phase transition. The measured valence band d. of states for cubic-Si3N4 is in agreement with theor. calcns.
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Franzen, H.; Merrick, J.; Umaña, M.; Khan, A.; Peterson, D.; McCreary, J.; Thorn, R. XPS Spectra and Crystalline Potentials in Alkaline-Earth Chalcogenides and Hydrides J. Electron Spectrosc. Relat. Phenom. 1977, 11, 439– 443 DOI: 10.1016/0368-2048(77)80019-4
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XPS spectra and crystalline potentials in alkaline-earth chalcogenides and hydrides
Franzen, H. F.; Merrick, Jean; Umana, Mirtha; Khan, A. S.; Peterson, D. T.; McCreary, J. R.; Thorn, R. J.
Journal of Electron Spectroscopy and Related Phenomena (1977), 11 (4), 439-43CODEN: JESRAW; ISSN:0368-2048.
X-ray photoelectron spectral measurements were carried out on BaH2, CaH2, and SrH2 for the 1st time and on the corresponding chalcogenide (for Ca and Sr) for comparison; information was obtained on the nature of the distribution of electron d. in the hydrides relation to the elements. Electron binding energies are given for Ca, Sr, and Ba in the compds. studied. The calcd. cryst. potentials at the cation site for CaO and CaSe differ by 4 eV, whereas the exptl. binding energies differ by only 0.75 eV. The calcd. cryst. potentials differ by 3.5 eV for the Sr compds., whereas the exptl. binding energies differ by only 0.35 eV. Thus the simple assumption that the alk. earth element is +2 in all of the compds. results in a significant difference between calcd. and obsd. shifts. The results clearly indicate that CaH2 is a strongly ionic solid.
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Demri, B.; Muster, D. XPS Study of Some Calcium Compounds J. Mater. Process. Technol. 1995, 55, 311– 314 DOI: 10.1016/0924-0136(95)02023-3
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Clark, D.; Fok, T.; Roberts, G.; Sykes, R. An Investigation by Electron Spectroscopy for Chemical Analysis of Chemical Treatments of the (100) Surface of n-type InP Epitaxial Layers for Langmuir Film Deposition Thin Solid Films 1980, 70, 261– 283 DOI: 10.1016/0040-6090(80)90367-3
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Streubel, P.; Franke, R.; Chassé, T.; Fellenberg, R.; Szargan, R. Chemical State Information from Photoelectron and Auger Electron Lines - Investigation of Potential and Relaxation Effects of Solid Silicon and Phosphorus Compounds J. Electron Spectrosc. Relat. Phenom. 1991, 57, 1– 13 DOI: 10.1016/0368-2048(91)85010-Q
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Chemical state information from photoelectron and Auger electron lines - investigation of potential and relaxation effects of solid silicon and phosphorus compounds
Streubel, P.; Franke, R.; Chasse, T.; Fellenberg, R.; Szargan, R.
Journal of Electron Spectroscopy and Related Phenomena (1991), 57 (1), 1-13CODEN: JESRAW; ISSN:0368-2048.
Measured chem. shifts of photoelectron and Auger electron energies of solid silicon and phosphorus compds. are used for detn. of potential energy and relaxation energy shifts. The trends of these shifts and their dependences on parameters characterizing the chem. bond and on the at. no. are discussed. The trends of relaxation energy shifts for both silicon and phosphorus compds. are the same. However, the trends of potential shifts of these two elements in their compds. are different depending on the at. contribution to the potential effect. The obsd. larger relaxation energy values of the solids in comparison with volatile mols. are caused by the Madelung contribution of higher coordination spheres. Theor. ests. of relaxation energies using an extended version of the Fenske-Hall method and taking into account the charge of the mol. potential term give an excellent correlation with exptl. values. The Shirley approach for detn. of potential energy and relaxation energy shifts proves to be a sensitive method for describing electronic changes when atoms combine to form mols. or solids. It is able to distinguish between the at. term and the surroundings term (Madelung term) of the chem. shift.
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Dolgonos, A.; Mason, T. O.; Poeppelmeier, K. R. Direct Optical Band Gap Measurement in Polycrystalline Semiconductors: A Critical Look at the Tauc Method J. Solid State Chem. 2016, 240, 43– 48 DOI: 10.1016/j.jssc.2016.05.010
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Direct optical band gap measurement in polycrystalline semiconductors: A critical look at the Tauc method
Dolgonos, Alex; Mason, Thomas O.; Poeppelmeier, Kenneth R.
Journal of Solid State Chemistry (2016), 240 (), 43-48CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
The direct optical band gap of semiconductors is traditionally measured by extrapolating the linear region of the square of the absorption curve to the x-axis, and a variation of this method, developed by Tauc, has also been widely used. The application of the Tauc method to cryst. materials is rooted in misconception-and traditional linear extrapolation methods are inappropriate for use on degenerate semiconductors, where the occupation of conduction band energy states cannot be ignored. A new method is proposed for extg. a direct optical band gap from absorption spectra of degenerately-doped bulk semiconductors. This method was applied to pseudo-absorption spectra of Sn-doped In2O3 (ITO)-converted from diffuse-reflectance measurements on bulk specimens. The results of this anal. were corroborated by room-temp. photoluminescence excitation measurements, which yielded values of optical band gap and Burstein-Moss shift that are consistent with previous studies on In2O3 single crystals and thin films.
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Tauc, J.; Grigorovici, R.; Vancu, A. Optical Properties and Electronic Structure of Amorphous Germanium Phys. Status Solidi B 1966, 15, 627– 637 DOI: 10.1002/pssb.19660150224
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Optical properties and electronic structure of amorphous germanium
Tauc, J.; Grigorovici, R.; Vancu, A.
Physica Status Solidi (1966), 15 (2), 627-37CODEN: PHSSAK; ISSN:0031-8957.
The optical consts. of amorphous Ge are detd. for photon energies 0.08-1.6 ev. From 0.08 to 0.5 ev., the absorption is due to k-conserving transitions of holes between the valence bands as in p-type crystals; the spin-orbit splitting is 0.20 and 0.21 ev. in nonannealed and annealed samples, resp. The effective masses of the holes in the 3 bands are 0.49 m (0.43 m), 0.04 m, and 0.08 m. An absorption band is observed below the main absorption edge (at 300°K. the max. of this band is at 0.86 ev.); the absorption in this band increases with increasing temp. This band is due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties, which are considered to be assocd. with vacancies. The absorption edge has the form ω2ε2 ∼ (ℏω - Eg)2 (Eg = 0.88 ev. at 300°K.). This suggests that the optical transitions conserve energy but not k vector, and that the ds. of states near the band extrema have the same energy dependence as in cryst. Ge. A simple theory describing this situation is proposed, and comparison of it with the exptl. results leads to an estimate of the localization of the conduction-band wave functions. 24 references.
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Jianmin, L.; Yugeng, Z. The d-d Transition Spectra of Copper (II) Complexes in Different Coordination Environment. Study on Cu(TTA)₂ and Cu₂(sacch)₄(Im)₄ Cryst. Res. Technol. 1991, 26, 331– 337 DOI: 10.1002/crat.2170260316
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Zuo, J. M.; Kim, M.; O’Keeffe, M.; Spence, J. C. H. Direct Observation of d-Orbital Holes and Cu-Cu Bonding in Cu₂O Nature 1999, 401, 49– 52 DOI: 10.1038/43403
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Direct observation of d-orbital holes and Cu-Cu bonding in Cu2O
Zuo, J. M.; Kim, M.; O'Keeffe, M.; Spence, J. C. H.
Nature (London) (1999), 401 (6748), 49-52CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
A striking feature of metal oxide chem. is the unusual electronic and chem. behavior of Cu(I) and Ag(I): a case in point is that detailed understanding of Cu-O bonding is essential to the theory of high-temp. copper oxide superconductors. Both cations are usually coordinated in a linear fashion to two oxygens, particularly for Cu(I). In many compds., the Cu(I) and Ag(I) cations also adopt close-packed (and related) configurations with short metal-metal distances that are strongly suggestive of the occurrence of metal-metal bonding despite their formal nd configuration. Such observations have been explained by invoking the participation in bonding of electronic orbitals of higher principal quantum no. - i.e., (n + 1)s and (n + 1)p-accompanied by the creation of d-orbital holes on the metal ion. To test this hypothesis, we have used a recently developed method of quant. convergent-beam electron diffraction combined with X-ray diffraction to map the charge-d. distribution in the simple oxide Cu2O, the results of which we then compare with electronic-structure calcn. We are able to image directly the d holes on the copper atoms, and also demonstrate the existence of Cu-Cu bonding in this compd.
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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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Hahn, U.; Weber, W. Electronic Structure and Chemical-Bonding Mechanism of Cu₃N, Cui₃NPd, and Related Cu(I) Compounds Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 53, 12684 DOI: 10.1103/PhysRevB.53.12684
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Orgel, L. Stereochemistry of Metals of the B Sub-Groups. Part I. Ions with Filled & Electron Shells J. Chem. Soc. 1958, 4186– 4190 DOI: 10.1039/jr9580004186
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Omata, T.; Nagatani, H.; Suzuki, I.; Kita, M.; Yanagi, H.; Ohashi, N. Wurtzite CuGaO₂: A New Direct and Narrow Band Gap Oxide Semiconductor Applicable as a Solar Cell Absorber J. Am. Chem. Soc. 2014, 136, 3378– 3381 DOI: 10.1021/ja501614n
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Wurtzite CuGaO2: a new direct and narrow band gap oxide semiconductor applicable as a solar cell absorber
Omata, Takahisa; Nagatani, Hiraku; Suzuki, Issei; Kita, Masao; Yanagi, Hiroshi; Ohashi, Naoki
Journal of the American Chemical Society (2014), 136 (9), 3378-3381CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
An oxide semiconductor β-CuGaO2 with a wurtzite-derived β-NaFeO2 structure has been synthesized. Structural characterization has been carried out by Rietveld anal. using XRD and SAED, and it was shown that the lattice size is very close to that of zinc oxide. The optical absorption spectrum indicated that the band gap is 1.47 eV, which matches the band gap required to achieve the theor. max. conversion efficiency for a single-junction solar cell. The thermoelectromotive force indicated p-type conduction in its intrinsic state. D. functional theory calcns. were performed to understand the electronic structure and optical properties of the semiconductor. These calcns. indicated that β-CuGaO2 is a direct semiconductor and intense absorption of light occurs near the band edge. These properties render this new material promising as an absorber in solar cells.
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Scanlon, D. O.; Walsh, A. Polymorph Engineering of CuMO₂ (M = Al, Ga, Sc, Y) Semiconductors for Solar Energy Applications: From Delafossite to Wurtzite Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2015, 71, 702– 706 DOI: 10.1107/S2052520615018387
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Polymorph engineering of CuMO2 (M = Al, Ga, Sc, Y) semiconductors for solar energy applications: from delafossite to wurtzite
Scanlon, David O.; Walsh, Aron
Acta Crystallographica, Section B: Structural Science, Crystal Engineering and Materials (2015), 71 (6), 702-706CODEN: ACSBDA; ISSN:2052-5206. (International Union of Crystallography)
The cuprous oxide based ternary delafossite semiconductors have been well studied in the context of p-type transparent conducting oxides. CuAlO2, CuGaO2 and CuInO2 represent a homologous series where the electronic properties can be tuned over a large range. The optical transparency of these materials has been assocd. with dipole forbidden transitions, which are related to the linear O-Cu-O coordination motif. The recent demonstration that these materials can be synthesized in tetrahedral structures (wurtzite analogs of the chalcopyrite lattice) opens up a new vista of applications. We investigate the underlying structure-property relationships (for Group 3 and 13 metals), from the perspective of first-principles materials modeling, towards developing earth-abundant photoactive metal oxides. All materials studied possess indirect fundamental band gaps ranging from 1 to 2 eV, which are smaller than their delafossite counterparts, although in all cases the difference between direct and indirect band gaps is less than 0.03 eV.
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Arnold, T. X-ray Spectroscopic Study of the Electronic Structure of CuCrO 2 Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 075102 DOI: 10.1103/PhysRevB.79.075102
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Shin, D. Comparative Study of Bandwidths in Copper Delafossites from X-ray Emission Spectroscopy Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 233105 DOI: 10.1103/PhysRevB.80.233105
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Scanlon, D. O.; Walsh, A.; Morgan, B. J.; Watson, G. W.; Payne, D. J.; Egdell, R. G. Effect of Cr Substitution on the Electronic Structure of CuAl_1–xCr_xO₂ Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 035101 DOI: 10.1103/PhysRevB.79.035101
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Effect of Cr substitution on the electronic structure of CuAl1-xCrxO2
Scanlon, David O.; Walsh, Aron; Morgan, Benjamin J.; Watson, Graeme W.; Payne, David J.; Egdell, Russell G.
Physical Review B: Condensed Matter and Materials Physics (2009), 79 (3), 035101/1-035101/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
The geometries and electronic structures of CuAl1-xCrxO2 have been investigated using d.-functional theory with on-site corrections for strongly correlated systems (GGA + U) for x = 0, 0.5, and 1. Al is found to be well described within the ionic model, with a valence charge corresponding to a +3 oxidn. state. Substituting Cr for Al is predicted to increase the d. of states at the top of the valence band, in agreement with exptl. x-ray photoemission spectroscopy data. Anal. of atom-projected densities of states and valence charges suggests that this is due to increased covalency between Cr and O; the valence charge for O in the Cu-O-(Al,Cr) subunits changes from -1.74 to ∼-1.25 when Cr replaces Al. This produces an indirect oxygen-mediated change to the Cu d states.
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Tossell, J. A.; Vaughan, D. J. Relationships Between Valence Orbital Binding Energies and Crystal Structures in Compounds of Copper, Silver, Gold, Zinc, Cadmium, and Mercury Inorg. Chem. 1981, 20, 3333– 3340 DOI: 10.1021/ic50224a038
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Gaudin, E. Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments J. Solid State Chem. 2001, 160, 212– 221 DOI: 10.1006/jssc.2001.9225
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Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments
Gaudin, Etienne; Boucher, Florent; Evain, Michel
Journal of Solid State Chemistry (2001), 160 (1), 212-221CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)
The factors influencing the low coordination of Cu+ and Ag+ d10 cations in chalcogenides were analyzed by means of FLAPW band structure calcns. The metal s/d orbital mixing is the predominant factor, in agreement with most previous research reports. The d10 cation polarization is reduced when the chalcogen electronegativity decreases, thus the coordination increases when going from the oxides to the tellurides. The calcn. results make clear the fact that the d10 element low coordination can be raised for a given chalcogen by enhancing the polarization influence of the chalcogen through a charge transfer from an alkali metal. The shift in behavior from Cu+ to Ag+ is shown to be related to their different polarizabilities. (c) 2001 Academic Press.
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Savelsberg, G.; Schäfer, H. Ternäre Pnictide und Chalkogenide von Alkalimetallen und IB-bzw Z. Naturforsch., B: J. Chem. Sci. 1978, 33, 370– 373 DOI: 10.1515/znb-1978-0705
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Ternary pnictides and chalcogenides of alkali metals and Group IB and IIB elements
Savelsberg, Gerhard; Schaefer, Herbert
Zeitschrift fuer Naturforschung, Teil B: Anorganische Chemie, Organische Chemie (1978), 33B (4), 370-3CODEN: ZNBAD2; ISSN:0340-5087.
NaCuSe, NaCuTe, KCuSe, KCuTe, and KZnP were prepd. and their structures - together with those of KZnSb, NaCdSb, and NaZnSb - detd. NaCuSe, NaCuTe, and NaZnSb crystallize in a PbFCl type, while NaCdSb forms the anti-PbCl2-structure, KCuSe, KCuTe, KZnP, and KZnSb have the Ni2In-structure. The lattice parameters of the 8 compds. are given. The structures were refined to final R's = 0.061-0.085.
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Buckeridge, J.; Butler, K. T.; Catlow, C. R. A.; Logsdail, A. J.; Scanlon, D. O.; Shevlin, S. A.; Woodley, S. M.; Sokol, A. A.; Walsh, A. Polymorph Engineering of TiO₂: Demonstrating how Absolute Reference Potentials are Determined by Local Coordination Chem. Mater. 2015, 27, 3844– 3851 DOI: 10.1021/acs.chemmater.5b00230
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Polymorph Engineering of TiO2: Demonstrating How Absolute Reference Potentials Are Determined by Local Coordination
Buckeridge, John; Butler, Keith T.; Catlow, C. Richard A.; Logsdail, Andrew J.; Scanlon, David O.; Shevlin, Stephen A.; Woodley, Scott M.; Sokol, Alexey A.; Walsh, Aron
Chemistry of Materials (2015), 27 (11), 3844-3851CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
We report that the valence and conduction band energies of TiO2 can be tuned over a 4 eV range by varying the local coordination environments of Ti and O. We examine the electronic structure of eight known polymorphs and align their ionization potential and electron affinity relative to an abs. energy ref., using an accurate multiscale quantum-chem. approach. For applications in photocatalysis, we identify the optimal combination of phases to enhance activity in the visible spectrum. The results provide a coherent explanation for a wide range of phenomena, including the performance of TiO2 as an anode material for Li-ion batteries, allow us to pinpoint hollandite TiO2 as a new candidate transparent conducting oxide, and serve as a guide to improving the efficiency of photo-electrochem. water splitting through polymorph engineering of TiO2.
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Burbano, M.; Scanlon, D. O.; Watson, G. W. Sources of Conductivity and Doping Limits in CdO from Hybrid Density Functional Theory J. Am. Chem. Soc. 2011, 133, 15065– 15072 DOI: 10.1021/ja204639y
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Sources of Conductivity and Doping Limits in CdO from Hybrid Density Functional Theory
Burbano, Mario; Scanlon, David O.; Watson, Graeme W.
Journal of the American Chemical Society (2011), 133 (38), 15065-15072CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
CdO has been studied for decades as a prototypical wide band gap transparent conducting oxide with excellent n-type ability. Despite this, uncertainty remains over the source of cond. in CdO and over the lack of p-type CdO, despite its valence band max. (VBM) being high with respect to other wide band gap oxides. In this article, we use screened hybrid DFT to study intrinsic defects and hydrogen impurities in CdO and identify for the first time the source of charge carriers in this system. We explain why the oxygen vacancy in CdO acts as a shallow donor and does not display neg.-U behavior similar to all other wide band gap n-type oxides. We also demonstrate that p-type CdO is not achievable, as n-type defects dominate under all growth conditions. Lastly, we est. theor. doping limits and explain why CdO can be made transparent by a large Moss-Burstein shift caused by suitable n-type doping.
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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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Aksit, M.; Kolli, S. K.; Slauch, I. M.; Robinson, R. D. Misfit Layered Ca₃Co₄O₉ as a High Figure of Merit p-Type Transparent Conducting Oxide Film Through Solution Processing Appl. Phys. Lett. 2014, 104, 161901 DOI: 10.1063/1.4871506
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Misfit layered Ca3Co4O9 as a high figure of merit p-type transparent conducting oxide film through solution processing
Aksit, M.; Kolli, S. K.; Slauch, I. M.; Robinson, R. D.
Applied Physics Letters (2014), 104 (16), 161901/1-161901/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
Ca3Co4O9 thin films synthesized through soln. processing are shown to be high-performing, p-type transparent conducting oxides (TCOs). The synthesis method is a cost-effective and scalable process that consists of sol-gel chem., spin coating, and heat treatments. The process parameters can be varied to produce TCO thin films with sheet resistance as low as 5.7 kΩ/sq (ρ ≈ 57 mΩ cm) or with av. visible range transparency as high as 67%. The most conductive Ca3Co4O9 TCO thin film has near IR region optical transmission as high as 85%. The figure of merit (FOM) for the top-performing Ca3Co4O9 thin film (151 MΩ-1) is higher than FOM values reported in the literature for all other soln. processed, p-type TCO thin films and higher than most others prepd. by phys. vapor deposition and chem. vapor deposition. Transparent cond. in misfit layered oxides presents new opportunities for TCO compns. (c) 2014 American Institute of Physics.
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Arca, E.; Fleischer, K.; Shvets, I. V. Magnesium, Nitrogen Codoped Cr₂O₃: A p-Type Transparent Conducting Oxide Appl. Phys. Lett. 2011, 99, 111910 DOI: 10.1063/1.3638461
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Magnesium, nitrogen codoped Cr2O3: A p-type transparent conducting oxide
Arca, E.; Fleischer, K.; Shvets, I. V.
Applied Physics Letters (2011), 99 (11), 111910/1-111910/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
A p-type transparent conductive oxide (TCO) was synthesized by codoping of poorly conducting chromium oxide (Cr2O3) with magnesium and nitrogen. The codoping produced a TCO with good figure of merit despite using spray pyrolysis for deposition. The nitrogen enhances the specular transparency of the films in the visible range (400-700 nm), and Mg improves the cond. while retaining the p-type character of the material. Co-doping with both elements produces a p-type oxide with a low resistivity of 3 Ω cm and transmission up to 65% for a 150. nm thick film. A comparison with other known p-type materials is given. (c) 2011 American Institute of Physics.
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Wei, R.; Tang, X.; Hu, L.; Hui, Z.; Yang, J.; Luo, H.; Luo, X.; Dai, J.; Song, W.; Yang, Z.; Zhu, X.; Sun, Y. Transparent Conducting p-Type Thin Films of c-Axis Self-Oriented Bi₂Sr₂Co₂O_y with High Figure of Merit Chem. Commun. 2014, 50, 9697 DOI: 10.1039/C4CC03800B
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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 a New p-Type Transparent Conducting Oxide Adv. Mater. 2015, 27, 5191– 5195 DOI: 10.1002/adma.201501959
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Palgrave, R. G.; Borisov, P.; Dyer, M. S.; McMitchell, S. R. C.; Darling, G. R.; Claridge, J. B.; Batuk, M.; Tan, H.; Tian, H.; Verbeeck, J.; Hadermann, J.; Rosseinsky, M. J. Artificial Construction of the Layered Ruddlesden–Popper Manganite La₂Sr₂Mn₃O₁₀ Reflection High Energy Electron Diffraction Monitored Pulsed Laser Deposition J. Am. Chem. Soc. 2012, 134, 7700– 7714 DOI: 10.1021/ja211138x
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Haeni, J. H.; Theis, C. D.; Schlom, D. G.; Tian, W.; Pan, X. Q.; Chang, H.; Takeuchi, I.; Xiang, X.-D. Epitaxial Growth of the First Five Members of the Sr_n+1Ti_nO_3n+1 Ruddlesden-Popper Homologous Series Appl. Phys. Lett. 2001, 78, 3292 DOI: 10.1063/1.1371788
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Epitaxial growth of the first five members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series
Haeni, J. H.; Theis, C. D.; Schlom, D. G.; Tian, W.; Pan, X. Q.; Chang, H.; Takeuchi, I.; Xiang, X.-D.
Applied Physics Letters (2001), 78 (21), 3292-3294CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
The 1st five members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series, i.e., Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, Sr5Ti4O13, and Sr6Ti5O16, were grown by reactive MBE. A combination of at. absorption spectroscopy and RHEED intensity oscillations were used for the strict compn. control necessary for the synthesis of these phases. X-ray diffraction and high-resoln. transmission electron microscope images confirm that these films are epitaxially oriented and nearly free of intergrowths. Dielec. measurements indicate that the dielec. const. tensor coeff. ε33 increases from a min. of 44 ± 4 in the n = 1(Sr2TiO4) film to a max. of 263 ± 2 in the n = ∞(SrTiO3) film.
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Tian, W.; Pan, X. Q.; Haeni, J. H.; Schlom, D. G. Transmission Electron Microscopy Study of n = 1–5 Sr_n+1Ti_nO_3n+1 Epitaxial Thin Films J. Mater. Res. 2001, 16, 2013– 2026 DOI: 10.1557/JMR.2001.0276
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Transmission electron microscopy study of n = 1-5 Srn+1TinO3n+1 epitaxial thin films
Tian, W.; Pan, X. Q.; Haeni, J. H.; Schlom, D. G.
Journal of Materials Research (2001), 16 (7), 2013-2026CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)
Epitaxial Srn+1TinO3n+1 thin films with n = 1-5 were synthesized on (001) SrTiO3 substrates by reactive MBE. The structure and microstructure of the films were studied by x-ray diffraction, transmission electron microbeam diffraction, and high-resoln. TEM (HRTEM) in combination with computer image simulations. Both diffraction and HRTEM studies revealed that all the films are epitaxially oriented with their c axis perpendicular to the (001) SrTiO3 plane of the substrate. Detailed studies using quant. HRTEM methods indicated that the films have the expected n = 1-5 structures of the Ruddlesden-Popper Srn+1TinO3n+1 homologous series. Among these films, Sr2TiO4, Sr3Ti2O7, and Sr4Ti3O10 thin films are nearly free of intergrowths, while Sr5Ti4O13 and Sr6Ti5O16 thin films contain noticeably more antiphase boundaries in their perovskite sheets and intergrowth defects. The authors show that these results are consistent with what is known about the thermodn. of Srn+1TinO3n+1 phases.
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Johnson, R. W.; Hultqvist, A.; Bent, S. F. A Brief Review of Atomic Layer Deposition: from Fundamentals to Applications Mater. Today 2014, 17, 236– 246 DOI: 10.1016/j.mattod.2014.04.026
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A brief review of atomic layer deposition: from fundamentals to applications
Johnson, Richard W.; Hultqvist, Adam; Bent, Stacey F.
Materials Today (Oxford, United Kingdom) (2014), 17 (5), 236-246CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
A review. Atomic layer deposition (ALD) is a vapor phase technique capable of producing thin films of a variety of materials. Based on sequential, self-limiting reactions, ALD offers exceptional conformality on high-aspect ratio structures, thickness control at the Angstrom level, and tunable film compn. With these advantages, ALD has emerged as a powerful tool for many industrial and research applications. In this review, we provide a brief introduction to ALD and highlight select applications, including Cu(In,Ga)Se2 solar cell devices, high-k transistors, and solid oxide fuel cells. These examples are chosen to illustrate the variety of technologies that are impacted by ALD, the range of materials that ALD can deposit - from metal oxides such as Zn1-xSnxOy, ZrO2, Y2O3, to noble metals such as Pt - and the way in which the unique features of ALD can enable new levels of performance and deeper fundamental understanding to be achieved.
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Hiramatsu, H.; Ueda, K.; Ohta, H.; Orita, M.; Hirano, M.; Hosono, H. Heteroepitaxial Growth of a Wide-Gap p-Type Semiconductor, LaCuOS Appl. Phys. Lett. 2002, 81, 598 DOI: 10.1063/1.1494853
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Heteroepitaxial growth of a wide-gap p-type semiconductor, LaCuOS
Hiramatsu, Hidenori; Ueda, Kazushige; Ohta, Hiromichi; Orita, Masahiro; Hirano, Masahiro; Hosono, Hideo
Applied Physics Letters (2002), 81 (4), 598-600CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
High-quality epitaxial films of LaCuOS, a wide-gap p-type semiconductor, are grown on yittria-stabilized-zirconia (001) or MgO (001) single-crystal substrates by a unique method. Postannealing of a bilayer film composed of an extremely thin metallic copper layer and an amorphous LaCuOS layer at 1000° results in an epitaxially grown LaCuOS thin film. This thin copper layer with high orientation, which likely acts as an epitaxial initiator, is essential for epitaxial growth. The resulting epitaxial films exhibit relatively intense UV emission assocd. with excitons at room temp., confirming the high crystal quality of the films.
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Su, G.; Hadjiev, V. G.; Loya, P. E.; Zhang, J.; Lei, S.; Maharjan, S.; Dong, P.; Ajayan, P. M.; Lou, J.; Peng, H. Chemical Vapor Deposition of Thin Crystals of Layered Semiconductor SnS₂ for Fast Photodetection Application Nano Lett. 2015, 15, 506– 513 DOI: 10.1021/nl503857r
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Chemical Vapor Deposition of Thin Crystals of Layered Semiconductor SnS2 for Fast Photodetection Application
Su, Guoxiong; Hadjiev, Viktor G.; Loya, Phillip E.; Zhang, Jing; Lei, Sidong; Maharjan, Surendra; Dong, Pei; M. Ajayan, Pulickel; Lou, Jun; Peng, Haibing
Nano Letters (2015), 15 (1), 506-513CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
Layered two-dimensional (2D) semiconductors, such as MoS2 and SnS2, have been receiving intensive attention due to their technol. importance for the next-generation electronic/photonic applications. We report a novel approach to the controlled synthesis of thin crystal arrays of SnS2 at predefined locations on chip by chem. vapor deposition with seed engineering and have demonstrated their application as fast photodetectors with photocurrent response time ∼5 μs. This opens a pathway for the large-scale prodn. of layered 2D semiconductor devices, important for applications in integrated nanoelectronic/photonic systems.

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Cite this: Chem. Mater. 2017, 29, 6, 2402–2413

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https://doi.org/10.1021/acs.chemmater.6b03306

Published October 14, 2016

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Abstract
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Figure 1
Figure 1. Crystal structure of (a) MgCuP (Pnma) displaying the tetrahedrally coordinated Cu. The crystal structure of MCuP (P6₃/mmc) is shown in (b) as viewed along the (100) direction and (c) shown down the c-axis displaying the hexagonal layered network of trigonally planar coordinated Cu–P and the M(II) cations in the void between the layers. M(II) is colored green, Cu is blue, and P is shown in orange. Bonds have been made between Cu and P, and the unitcell is represented with a dashed line.
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Figure 2
Figure 2. Calculated band structure diagram (a) and the density of states (DoS) (b) for MgCuP in the Pnma space group. For (a), the filled valence band is colored in blue and the unfilled conduction band is colored in orange. The valence band maximum (VBM) is centered at 0 eV in both cases. In (b), an expanded view of the VBM and the CBM is shown.
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Figure 3
Figure 3. Calculated band structures of (a) CaCuP, (b) SrCuP, and (c) BaCuP in the P6₃/mmc space group. The filled valence band is colored in blue, and the unfilled conduction band is colored in orange. The valence band maximum (VBM) is centered at 0 eV.
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Figure 4
Figure 4. Calculated density of states (DoS) for (a) CaCuP, (b) SrCuP, and (c) BaCuP. The valence band maximum (VBM) is set at 0 eV. Underneath each DoS is an expanded view of the VBM and CBM.
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Figure 5
Figure 5. Powder X-ray diffraction pattern from CaCuP synthesized here (black) and calculated from the standard structure (red) with the difference between the calculated and observed intensities shown underneath in gray. The phase ticks for CaCuP and CaCu_3.8P₄ are shown in blue and green, respectively.
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Figure 6
Figure 6. X-ray photoelectron spectra of CaCuP. (a) Cu 2p, (b) Ca 2p, and (c) P 2p regions are shown, with curve fitting as described in the text. The valence band region up to 35 eV binding energy is shown in (c) with the simulated VB XPS overlaid (red dashed line) taken from the PBE0 calculated DoS for CaCuP.
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Figure 7
Figure 7. Diffuse reflectance optical spectra showing the Kubelka–Munk function F(R) and F(R)² is displayed in (a). The direct band gap calculated from the Poeppelmeier method is shown to be 2.78 eV. (b) Shows the calculated optical absorption spectrum using the PBE0 functional where a weak absorption onset at 2.17 eV and a strong absorption at 2.71 eV are seen.
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References
This article references 121 other publications.
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  A review. Dye-sensitized solar cells provide a promising low-cost technol. for harnessing this energy source. Until recently, much of the research surrounding dye-sensitized solar cells had been focused on the sensitization of n-type semiconductors, such as titanium dioxide (Gratzel cells). In an n-type dye-sensitized solar cell, an electron is injected into the conduction band of an n-type semiconductor from the excited state of the sensitizer. Comparatively few studies have examd. the sensitization of wide bandgap p-type semiconductors. In a p-type dye-sensitized solar cell, the photoexcited sensitizer is reductively quenched by hole injection into the valence band of a p-type semiconductor. The study of p-type dye-sensitized solar cells is important both to understand the factors that control the rate of hole photoinjection and to aid the rational design of efficient p-type dye-sensitized solar cells. In theory, p-type dye-sensitized solar cells should be able to work as efficiently as n-type dye-sensitized solar cells. In addn., this research provides a method for prepg. tandem dye-sensitized solar cells consisting of a TiO2-photosensitized anode and a photosensitized p-type semiconductor as a cathode. Tandem dye-sensitized solar cells are particularly important because they represent low-cost photovoltaic devices whose photoconversion efficiencies could exceed 15%. This paper describes recent research results on p-type dye-sensitized solar cells. Because these photoelectrochem. devices are the mirror images of conventional n-type dye-sensitized solar cells, they share some structural similarities, but they use different materials and have different charge transfer kinetics. In this technol., nickel oxide is the predominant p-type semiconductor material used, but much higher photoconversion efficiencies could be achieved with new p-type semiconductors materials with deeper valence band potential. Currently, iodide/triiodide is the main redox mediator of electron transport within these devices, but we expect that this material could be advantageously replaced with more efficient redox couples. We also discuss valuable information obtained by ultrafast transient absorption spectroscopy, which sheds some light on the factors that govern the efficiency of the cell. Notably, we demonstrate that ultrafast hole injection generally occurs between the sensitizer and the semiconductor, but the resulting charge-sepd. state (e.g. electron on the sensitizer and hole in the valence band) is short-lived and recombines quickly. So far, the only effective strategy for slowing the back recombination reaction relies on a bimol. system consisting of the sensitizer linked to an electron acceptor, which increases the sepn. distance between the charges. A photoconversion efficiency of 0.41% under air-mass 1.5 was recently measured with a p-type dye-sensitized solar cell using this strategy.
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  Tin monoxide is a technol. important p-type material which has a layered structure dictated by nonbonded dispersion forces. As std. d. functional theory (DFT) approaches are unable to account for dispersion forces properly, they routinely give rise to a poor description of the unit cell structure. This study therefore applies two forms of empirical dispersion corrections, using either at.- or ionic-based parameters for the dispersion coeffs., to assess their ability to correctly model the at. structure and the formation energies of the important p-type defects. Although both approaches show an improvement in the predicted unit cell structure over that with no dispersion corrections, the ionic-based parameter set shows significantly better results, with lattice vectors reproduced within 0.2% of expt. The at.-based parameters still predict a distorted cell though, which is carried through to the defective system. On the introduction of defects, a similar degree of structural relaxation is obsd. regardless of the approach. The defect formation energies, however, are seen to differ more substantially, with the at.-based set giving an overestimation of the energies due to excessive Sn-Sn interactions. Overall, this study shows that empirical van der Waals corrections utilizing an ionic-based parameter set can be used to model SnO.
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  A review. High-performance gas sensors prepd. using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 are reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concn. through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. P-type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.
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  Oxide Semiconductor Thin-Film Transistors: A Review of Recent Advances
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  Advanced Materials (Weinheim, Germany) (2012), 24 (22), 2945-2986CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is obsd. in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. The recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on soln.-processed and p-type, and the major milestones already achieved with this emerging and very promising technol. are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by phys. vapor deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: soln.-processed oxide TFTs. Also, a more detailed focus anal. will be given concerning p-type oxide TFTs, mainly centered on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the prodn. of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMATI3N during the last six years is included in more detail, which led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.
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  Gordon, R. G. Criteria for Choosing Transparent Conductors MRS Bull. 2000, 25, 52– 57 DOI: 10.1557/mrs2000.151
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  Criteria for choosing transparent conductors
  Gordon, Roy G.
  MRS Bulletin (2000), 25 (8), 52-57CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)
  A review with 38 refs. is given on phys. properties (optical and elec. performance, figure of merit, cond., work function, electron concn., resistivity, thermal stability, deposition temp., and diffusion barriers between TC and Na-contg. glass substrates), etchants, and chem. durability of transparent conductive films. Some applications of TCs are outlined and criteria to select appropriate TC materials for new use are stated.
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  Beyer, W.; Hüpkes, J.; Stiebig, H. Transparent conducting oxide films for thin film silicon photovoltaics Thin Solid Films 2007, 516, 147– 154 DOI: 10.1016/j.tsf.2007.08.110
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  Beyer, W.; Huepkes, J.; Stiebig, H.
  Thin Solid Films (2007), 516 (2-4), 147-154CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
  A review. The requirements for applications of transparent conducting oxide (TCO) films in thin-film silicon solar cells are summarized with a focus on sputtered Al-doped zinc oxide and fluorine-doped tin oxide films. TCO films are employed as a front contact and as part of a highly reflective back contact so that the silicon absorber layer is embedded by TCO films. The optoelectronic properties of TCO layers and their influence on the solar cell performance are discussed. In addn., recent results on the stability of such films in solar cells and solar modules are presented. While zinc and tin oxides have similar optical and elec. properties, the chem. is quite different. SnO2 is highly stable against environmental substances as well as acids and bases but rather unstable against hydrogen plasma. ZnO is little affected by hydrogen plasma but quite unstable in acids. This latter property bears the advantage that an easy post-deposition texturing is possible by wet chem. etching. For solar cells, damp heat tests for >1000 h revealed the high stability of even non-encapsulated solar modules consisting of an aluminum-doped ZnO front contact, microcryst. silicon cell and ZnO/Ag back reflector.
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  Liu, H.; Avrutin, V.; Izyumskaya, N.; Özgür, U.; Morkoç, H. Transparent conducting oxides for electrode applications in light emitting and absorbing devices Superlattices Microstruct. 2010, 48, 458– 484 DOI: 10.1016/j.spmi.2010.08.011
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  Liu, Hui-Yong; Avrutin, V.; Izyumskaya, N.; Ozgur, U.; Morkoc, H.
  Superlattices and Microstructures (2010), 48 (5), 458-484CODEN: SUMIEK; ISSN:0749-6036. (Elsevier Ltd.)
  A review. In both light emitting devices such as light emitting diodes (LEDs), and light absorbing devices such as solar cells (also photodetectors), which are gaining considerable interest for their energy saving and energy prodn. capability, resp., a compromise must be struck between the need to increase the light emitting/absorbing area/potential and the need for low series resistance of the metal contact grid. This undesirable compromise can be mitigated by using transparent conducting oxides (TCOs), which heretofore have been dominated by ITO (indium tin oxide-an In-rich alloy of indium oxide and tin oxide). Due to the expected scarcity of Indium used in ITO, efforts are underway to develop indium-free TCOs for the above-mentioned devices as well as flat panel displays. ZnO heavily doped with Ga or Al (GZO or AZO) is becoming a very attractive candidate for future generation TCOs. GZO and AZO as well as multilayer TCOs consisting of two TCO layers with a thin metal layer in between have been widely investigated for LEDs and solar cells to enhance device performance. This article succinctly reviews the latest developments in and properties of TCOs, particularly in relation to thin film transparent electrode applications for LEDs and solar cells. Pertinent crit. issues and possible solns. are provided as well.
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  Hautier, G.; Miglio, A.; Ceder, G.; Rignanese, G.-M.; Gonze, X. Identification and Design Principles of Low Hole Effective Mass p-Type Transparent Conducting Oxides Nat. Commun. 2013, 4, 2292 DOI: 10.1038/ncomms3292
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  Identification and design principles of low hole effective mass p-type transparent conducting oxides
  Hautier Geoffroy; Miglio Anna; Ceder Gerbrand; Rignanese Gian-Marco; Gonze Xavier
  Nature communications (2013), 4 (), 2292 ISSN:.
  The development of high-performance transparent conducting oxides is critical to many technologies from transparent electronics to solar cells. Whereas n-type transparent conducting oxides are present in many devices, their p-type counterparts are not largely commercialized, as they exhibit much lower carrier mobilities due to the large hole effective masses of most oxides. Here we conduct a high-throughput computational search on thousands of binary and ternary oxides and identify several highly promising compounds displaying exceptionally low hole effective masses (up to an order of magnitude lower than state-of-the-art p-type transparent conducting oxides), as well as wide band gaps. In addition to the discovery of specific compounds, the chemical rationalization of our findings opens new directions, beyond current Cu-based chemistries, for the design and development of future p-type transparent conducting oxides.
9. 9
  Scanlon, D. O.; Watson, G. W. On the Possibility of p-Type SnO₂ J. Mater. Chem. 2012, 22, 25236 DOI: 10.1039/c2jm34352e
  9
  On the possibility of p-type SnO2
  Scanlon, David O.; Watson, Graeme W.
  Journal of Materials Chemistry (2012), 22 (48), 25236-25245CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
  SnO2 is an abundant, low cost, natively n-type, wide band gap oxide, which can achieve high conductivities due to facile donor doping. Realization of a p-type SnO2 would, however, open up many new avenues in device applications, and has become a major research goal. Previous exptl. and theor. studies have proved inconclusive, with the p-type ability of SnO2 being both supported and questioned in equal measure. We use state of the art hybrid d. functional theory to investigate the nature of intrinsic and extrinsic p-type defects in SnO2. All the p-type defects considered in SnO2 produce localized hole polarons centered on anion sites. We calc. the thermodn. ionization energies of these defects, and demonstrate that an efficient p-type SnO2 is not achievable.
10. 10
  Look, D. C. Electrical and Optical Properties of p-Type ZnO Semicond. Sci. Technol. 2005, 20, S55– S61 DOI: 10.1088/0268-1242/20/4/007
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11. 11
  Lany, S.; Zunger, A. Polaronic Hole Localization and Multiple Hole Binding of Acceptors in Oxide Wide-Gap Semiconductors Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 1– 5 DOI: 10.1103/PhysRevB.80.085202
  There is no corresponding record for this reference.
12. 12
  Lany, S.; Zunger, A. Generalized Koopmans Density Functional Calculations Reveal the Deep Acceptor State of NO in ZnO Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81, 1– 5 DOI: 10.1103/PhysRevB.81.205209
  There is no corresponding record for this reference.
13. 13
  Lyons, J. L.; Janotti, A.; Van De Walle, C. G. Why Nitrogen Cannot Lead to p-Type Conductivity in ZnO Appl. Phys. Lett. 2009, 95, 252105 DOI: 10.1063/1.3274043
  13
  Why nitrogen cannot lead to p-type conductivity in ZnO
  Lyons, J. L.; Janotti, A.; Van de Walle, C. G.
  Applied Physics Letters (2009), 95 (25), 252105/1-252105/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  Based on electronic structure and at. size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous exptl. efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calcns. we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole cond. in ZnO. In light of this result, we reexamine prior expts. on nitrogen doping of ZnO. (c) 2009 American Institute of Physics.
14. 14
  Catlow, C. R. a.; Sokol, A. a.; Walsh, A. Microscopic Origins of Electron and Hole Stability in ZnO Chem. Commun. 2011, 47, 3386 DOI: 10.1039/c1cc10314h
  14
  Microscopic origins of electron and hole stability in ZnO
  Catlow, C. Richard A.; Sokol, Alexey A.; Walsh, Aron
  Chemical Communications (Cambridge, United Kingdom) (2011), 47 (12), 3386-3388CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  We present a fundamental method to assess the doping limits of hetero-polar materials; applied to the case of ZnO, we show clearly that electrons are stable and holes are unstable under the limits of thermodn. control.
15. 15
  Tran, Q.-P.; Fang, J.-S.; Chin, T.-S. Optical Properties and Boron Doping-Induced Conduction-Type Change in SnO₂ Thin Films J. Electron. Mater. 2016, 45, 349– 356 DOI: 10.1007/s11664-015-4081-1
  15
  Optical Properties and Boron Doping-Induced Conduction-Type Change in SnO2 Thin Films
  Tran, Quang-Phu; Fang, Jau-Shiung; Chin, Tsung-Shune
  Journal of Electronic Materials (2016), 45 (1), 349-356CODEN: JECMA5; ISSN:0361-5235. (Springer)
  Boron-doped tin oxide (BTO) films, 0-5 at.% B, were prepd. by sol-gel dip coating on a glass substrate. Dried precursor films were post-annealed at a temp. between 400°C and 750°C for 2 h. The obtained BTO thin films were characterized by x-ray diffraction (XRD), SEM (SEM), UV-visible light (UV-Vis) spectrometry, a four-point probe, and Hall-effect and Seebeck-effect measurements. Optimal optical transmittance was achieved for post-annealed BTO thin film at 700°C. XRD results show a rutile SnO2 structure with a preferred (110) orientation for all the films. The grain size is 47-21 nm, which reduces with increasing B contents. The optical transmittance is 84.6-88.5% at a wavelength of 550 nm and optical band gap of 3.52-3.75 eV. Elec. resistivity is (3.4-8.2) × 10-3 Ω cm, and figure of merit (0.9-4.3) × 10-3 Ω-1. Carrier concn. is (0.97-7.4) × 1020 cm-3 and mobility (2.5-7.8) cm2 V-1 s-1. BTO film with 4 at.% B shows an optimal combination of properties. Conduction type changes from n- (undoped) to p- (1-4 at.% B), then to n-types (5 at.% B), as evidenced from Hall-effect and Seebeck-effect measurements. This is explained by doping-generated defects and phase sepns. of Sn3O4 and B2O3.
16. 16
  Pathak, T. K.; Kumar, V.; Swart, H.; Purohit, L. Effect of Doping Concentration on the Conductivity and Optical Properties of p-Type ZnO Thin Films Phys. B 2016, 480, 31– 35 DOI: 10.1016/j.physb.2015.09.033
  16
  Effect of doping concentration on the conductivity and optical properties of p-type ZnO thin films
  Pathak, Trilok Kumar; Kumar, Vinod; Swart, H. C.; Purohit, L. P.
  Physica B: Condensed Matter (Amsterdam, Netherlands) (2016), 480 (), 31-35CODEN: PHYBE3; ISSN:0921-4526. (Elsevier B.V.)
  Nitrogen doped ZnO (NZO) thin films were synthesized on glass substrates by the sol-gel and spin coating method. Zinc acetate dihydrates and ammonium acetate were used as precursors for zinc and nitrogen, resp. X-ray diffraction study showed that the thin films have a hexagonal wurtzite structure corresponding (002) peak for undoped and doped ZnO thin films. The transmittance of the films was above 80% and the band gap of the film varies from 3.21±0.03 eV for undoped and doped ZnO. The min. resistivity of NZO thin films was obtained as 0.473 Ω cm for the 4 at% of nitrogen (N) doping with a mobility of 1.995 cm2/V s. The NZO thin films showed p-type cond. at 2 and 3 at% of N doping. The AC cond. measurements that were carried out in the frequency range 10 kHz to 0.1 MHz showed localized conduction in the NZO thin films. These highly transparent ZnO films can be used as a possible window layer in solar cells.
17. 17
  Zhang, S. B.; Wei, S.-H. H.; Zunger, A. A Phenomenological Model for Systematization and Prediction of Doping Limits in II–VI and I–III–VI₂ Compounds J. Appl. Phys. 1998, 83, 3192 DOI: 10.1063/1.367120
  17
  A phenomenological model for systematization and prediction of doping limits in II-VI and I-III-VI2 compounds
  Zhang, S. B.; Wei, Su-Huai; Zunger, Alex
  Journal of Applied Physics (1998), 83 (6), 3192-3196CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  Semiconductors differ widely in their ability to be doped. As their band gap increases, it is usually possible to dope them either n or p type, but not both. This asymmetry is documented here, and explained phenomenol. in terms of the "doping pinning rule.".
18. 18
  Zhang, S. B.; Wei, S. H.; Zunger, A. Overcoming Doping Bottlenecks in Semiconductors and Wide-Gap Materials Phys. B 1999, 273–274, 976– 980 DOI: 10.1016/S0921-4526(99)00605-5
  18
  Overcoming doping bottlenecks in semiconductors and wide-gap materials
  Zhang, S. B.; Wei, S.-H.; Zunger, A.
  Physica B: Condensed Matter (Amsterdam) (1999), 273-274 (), 976-980CODEN: PHYBE3; ISSN:0921-4526. (Elsevier Science B.V.)
  A review with 33 refs. There often exist strong doping bottlenecks that may severely restrict potential applications of semiconductors, esp. in wide-band-gap materials where bipolar doping is impossible. Recent rapid progress in semiconductor research has reached a point where these doping limitations must be overcome to tune semiconductors for precisely required properties. Here, the authors discuss how to find out what causes the doping bottlenecks. The authors based the discussion on a set of recent, novel developments regarding the doping limitations: the doping limit rule distd. from both phenomenol. studies and from 1st-principles calcns. The thermodn. doping bottlenecks are identified as due mainly to the formation of intrinsic defects whose formation enthalpies depend on the Fermi energy, and always act to negate the effect of doping.
19. 19
  Zhang, S. B. The Microscopic Origin of the Doping Limits in Semiconductors and Wide-Gap Materials and Recent Developments in Overcoming These Limits: a Review J. Phys.: Condens. Matter 2002, 14, R881– R903 DOI: 10.1088/0953-8984/14/34/201
  19
  The microscopic origin of the doping limits in semiconductors and wide-gap materials and recent developments in overcoming these limits: a review
  Zhang, S. B.
  Journal of Physics: Condensed Matter (2002), 14 (34), R881-R903CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
  A review of the recent developments in first-principles total energy studies of the phenomenol. equil. "doping limit rule" that governs the max. elec. cond. of semiconductors via extrinsic or intrinsic doping.
20. 20
  Walsh, A.; Buckeridge, J.; Catlow, C. R. a.; Jackson, A. J.; Keal, T. W.; Miskufova, M.; Sherwood, P.; Shevlin, S. a.; Watkins, M. B.; Woodley, S. M.; Sokol, A. a. Limits to Doping of Wide Band Gap Semiconductors Chem. Mater. 2013, 25, 2924– 2926 DOI: 10.1021/cm402237s
  There is no corresponding record for this reference.
21. 21
  Kawazoe, H.; Yasukawa, M.; Hyodo, H.; Kurita, M.; Yanagi, H.; Hosono, H. P-Type Electrical Conduction in Transparent Thin Films of CuAlO₂ Nature 1997, 389, 939– 942 DOI: 10.1038/40087
  21
  P-type electrical conduction in transparent thin films of CuAlO2
  Kawazoe, Hiroshi; Yasukawa, Masahiro; Kyodo, Hiroyuki; Kurita, Masaaki; Yanagi, Hiroshi; Hosono, Hideo
  Nature (London) (1997), 389 (6654), 939-942CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
  Optically transparent oxides tend to be elec. insulators, by virtue of their large electronic band gap (≥3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO-all n-type (electron) conductors-which are widely used as the transparent electrodes in flat-panel displays. However, no transparent oxide exhibiting high p-type (hole) cond. is known to exist, whereas such materials could open the way to range of novel applications. For example, a combination of the 2 types of transparent conductor as a pn junction could lead to a functional window that transmits visible light yet generates elec. in response to the absorption of UV photons. Here the authors describe a strategy for identifying oxide materials that should combine p-type cond. with good optical transparency. The authors illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temp. p-type cond. up to 1 S cm-1. Although the cond. of the candidate material is significantly lower than that obsd. for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.
22. 22
  Scanlon, D. O.; Morgan, B. J.; Watson, G. W. Modeling the Polaronic Nature of p-Type Defects in Cu₂O: the Failure of GGA and GGA+U J. Chem. Phys. 2009, 131, 124703 DOI: 10.1063/1.3231869
  22
  Modeling the polaronic nature of p-type defects in Cu2O: The failure of GGA and GGA+U
  Scanlon, David O.; Morgan, Benjamin J.; Watson, Graeme W.
  Journal of Chemical Physics (2009), 131 (12), 124703/1-124703/8CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  The exact nature of the hole traps reported deep in the band gap of Cu2O has been a topic of vigorous debate, with copper vacancies and oxygen interstitials both having been proposed as the relevant defects. In this article, the electronic structure of acceptor-forming defects in Cu2O, namely, copper vacancies and oxygen interstitials, is investigated using generalized gradient approxn. (GGA) and GGA cor. for on-site Coulombic interactions (GGA+U). GGA produces notionally semimetallic defect complexes, which is not consistent with the exptl. known polaronic nature of conduction in Cu2O. GGA+U also predicts a semimetallic defect complex for the "simple" copper vacancy but predicts the "split" vacancy and both oxygen interstitials are characterized by localized polarons, with distinct single particle levels found in the band gap. For both methods, however, the positions of calcd. transition levels are inconsistent with exptl. ionization levels. Hence neither GGA nor GGA+U are successful in modeling p-type defects in Cu2O. (c) 2009 American Institute of Physics.
23. 23
  Scanlon, D. O.; Watson, G. W. Uncovering the Complex Behavior of Hydrogen in Cu₂O Phys. Rev. Lett. 2011, 106, 1– 4 DOI: 10.1103/PhysRevLett.106.186403
  There is no corresponding record for this reference.
24. 24
  Miao, M.-S.; Yarbro, S.; Barton, P. T.; Seshadri, R. Electron Affinities and Ionization Energies of Cu and Ag Delafossite Compounds: A Hybrid Functional Study Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 045306 DOI: 10.1103/PhysRevB.89.045306
  24
  Electron affinities and ionization energies of Cu and Ag delafossite compounds: a hybrid functional study
  Miao, Mao-Sheng; Yarbro, Sam; Barton, Phillip T.; Seshadri, Ram
  Physical Review B: Condensed Matter and Materials Physics (2014), 89 (4), 045306/1-045306/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  Using d. functional theory with a hybrid functional, we calc. the ionization energies and electron affinities of a series of delafossite compds. (AMO2: A = Cu, Ag; M = B, Al, Ga, In, Sc). The alignments of the valence band max. and the conduction band min., which directly relate to the ionization energies and electron affinities, were obtained by calcns. of supercell slab models constructed in a nonpolar orientation. Our calcns. reveal that the ionization energy decreases with an increasing at. no. of group-III elements, and thus suggest an improved p-type doping propensity for heavier compds. For keeping both a low ionization energy and a band gap of sufficient size, CuScO2 is superior to the Cu-based group-III delafossites. By analyzing the electronic structures, we demonstrate that the compositional trend of the ionization energies and electron affinities is the result of a combined effect of d-band broadening due to Cu(Ag)-Cu(Ag) coupling and a repositioning of the d-band center.
25. 25
  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
  25
  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.
26. 26
  Snure, M.; Tiwari, A. CuBO₂: A p-Type Transparent Oxide Appl. Phys. Lett. 2007, 91, 092123 DOI: 10.1063/1.2778755
  26
  CuBO2. A p-type transparent oxide
  Snure, Michael; Tiwari, Ashutosh
  Applied Physics Letters (2007), 91 (9), 092123/1-092123/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  The authors report the synthesis of CuBO2, a p-type transparent oxide belonging to Cu-delafossite family. High quality thin films of CuBO2 were deposited on c-plane sapphire substrates by pulsed laser deposition technique. Detailed structural, optical, and elec. characterizations on these films were performed. Optical transmission measurement showed the films to be highly transparent in the visible range and having indirect and direct band gaps of 2.2 and 4.5 eV, resp. Room-temp. elec. cond. of CuBO2 films was 1.65 S cm-1 and exhibited semiconductor-like temp. dependence. The Hall and Seebeck coeffs. of the film were pos., indicating the p-type nature of the material.
27. 27
  Shi, L.-J.; Fang, Z.-J.; Li, J. First-Principles Study of p-Type Transparent Conductive Oxides CuXO₂ (X = Y, Sc, and Al) J. Appl. Phys. 2008, 104, 073527 DOI: 10.1063/1.2991157
  There is no corresponding record for this reference.
28. 28
  Marquardt, M. a.; Ashmore, N. a.; Cann, D. P. Crystal Chemistry and Electrical Properties of the Delafossite Structure Thin Solid Films 2006, 496, 146– 156 DOI: 10.1016/j.tsf.2005.08.316
  28
  Crystal chemistry and electrical properties of the delafossite structure
  Marquardt, Meagen A.; Ashmore, Nathan A.; Cann, David P.
  Thin Solid Films (2005), 496 (1), 146-156CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
  A review. Over the past few decades, the field of transparent conducting oxides has undergone tremendous advances. With the rapid growth of optoelectronic applications related to display technologies, traditional materials such as Sn-doped indium oxide (ITO) are now widely used as transparent electrodes. In addn., with the advent of p-type transparent conductors, through the transparent pn-junction building block, a wide range of functional transparent optoelectronic devices were demonstrated including UV-emitting diodes, UV-detectors, and transparent thin film transistors. This paper will highlight the unique characteristics of oxide materials based on the delafossite structure with a focus on the interrelationship between the chem., crystal structure, process conditions, and elec. and optical properties. The delafossite structure (ABO2) is characterized by a layer of linearly coordinated A cations stacked between edge-shared octahedral layers (BO6). The A-site cation is comprised of Pt, Pd, Ag, or Cu ions nominally in a monovalent state. The B-site cation can consist of most trivalent transition metals, group III elements, rare earths, or charge compensated pairs (e.g. B2+/B4+). This layered structure leads to highly anisotropic phys. properties. The crystal chem. of the delafossite structure will be discussed in ref. to phase stability, the stability of dopants, and the important phys. properties such as the cond. and optical transparency.
29. 29
  Nagarajan, R.; Draeseke, a. D.; Sleight, a. W.; Tate, J. p-Type Conductivity in CuCr_1–xMg_xO₂ Films and Powders J. Appl. Phys. 2001, 89, 8022 DOI: 10.1063/1.1372636
  29
  p-type conductivity in CuCr1-xMgxO2 films and powders
  Nagarajan, R.; Draeseke, A. D.; Sleight, A. W.; Tate, J.
  Journal of Applied Physics (2001), 89 (12), 8022-8025CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  CuCr1-xMgxO2, a wide band gap semiconductor with the delafossite structure, has been synthesized in bulk and thin-film form. Bulk undoped CuCrO2 is almost black and has moderate cond. with p-type carriers. Upon doping with 5[percent] Mg, the cond. increases by a factor of 1000. In films, the best p-type cond. is 220 S cm-1 in CuCr0.95Mg0.05O2, a factor of 7 higher than previously reported for Cu-based p-type delafossites. Undoped films have a cond. of order 1 S cm-1. Films are usually polycryst. on amorphous substrates, but undoped films can be c-axis oriented if deposited at or above 650°. Optical and UV transmission data indicate a direct band gap of 3.1 eV.
30. 30
  Ueda, K.; Hase, T.; Yanagi, H.; Kawazoe, H.; Hosono, H.; Ohta, H.; Orita, M.; Hirano, M. Epitaxial Growth of Transparent p-Type Conducting CuGaO₂ Thin Films on Sapphire (001) Substrates by Pulsed Laser Deposition J. Appl. Phys. 2001, 89, 1790 DOI: 10.1063/1.1337587
  30
  Epitaxial growth of transparent p-type conducting CuGaO2 thin films on sapphire (001) substrates by pulsed laser deposition
  Ueda, K.; Hase, T.; Yanagi, H.; Kawazoe, H.; Hosono, H.; Ohta, H.; Orita, M.; Hirano, M.
  Journal of Applied Physics (2001), 89 (3), 1790-1793CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  Transparent p-type conducting CuGaO2 thin films were prepd. on α-Al2O3 (001) single-crystal substrates by pulsed laser deposition. The films were grown epitaxially on the substrates in an as-deposited state. X-ray pole figure anal. revealed that the films were composed of two types of epitaxial grains, both with c axes oriented perpendicular to the surface and a axes rotated 60° with respect to each other around the c axis. Observation of the CuGaO2 thin films by at. force microscopy and high-resoln. transmission electron microscopy substantiated this conclusion. The films have high optical transparency (∼80[percent]) in the visible region, and the energy gap of CuGaO2 for direct allowed transition was estd. to be 3.6 eV. p-type cond. was confirmed by Seebeck and Hall measurements. The elec. cond., carrier (pos. hole) d., and Hall mobility of the films at room temp. were detd.
31. 31
  Kudo, A.; Yanagi, H.; Hosono, H.; Kawazoe, H. SrCu₂O₂: A p-Type Conductive Oxide with Wide Band Gap Appl. Phys. Lett. 1998, 73, 220 DOI: 10.1063/1.121761
  31
  SrCu2O2: A p-type conductive oxide with wide band gap
  Kudo, Atsushi; Yanagi, Hiroshi; Hosono, Hideo; Kawazoe, Hiroshi
  Applied Physics Letters (1998), 73 (2), 220-222CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  SrCu2O2 thin films were prepd. on SiO2 glass substrates by pulsed laser deposition. The film deposited in O2 atmosphere of 7×10-4 Pa at 573 K showed high optical transmission in visible and near-IR regions. Potassium was doped at Sr site for substitutional doping. The optical band gap of the K-doped film was estd. to be ∼3.3 eV. The dc elec. cond. of the K-doped film at 300 K was 4.8×10-2 S cm-1 and the activation energy was 0.10 eV. Pos. sign of Seebeck and Hall coeffs. demonstrated the p-type conduction of the film. Hole concn. and mobility at 300 K were 6.1×1017 cm-3 and 0.46 cm2 V-1 s-1, resp.
32. 32
  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
  32
  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.
33. 33
  Kandpal, H. C.; Seshadri, R. First-Principles Electronic Structure of the Delafossites ABO₂ (A = Cu, Ag, Au; B = Al, Ga, Sc, In, Y): Evolution of d¹⁰-d¹⁰ Interactions Solid State Sci. 2002, 4, 1045– 1052 DOI: 10.1016/S1293-2558(02)01363-8
  33
  First-principles electronic structure of the delafossites ABO2 (A = Cu, Ag, Au; B = Al, Ga, Sc, In, Y): evolution of d10-d10 interactions
  Kandpal, Hem Chandra; Seshadri, Ram
  Solid State Sciences (2002), 4 (8), 1045-1052CODEN: SSSCFJ; ISSN:1293-2558. (Editions Scientifiques et Medicales Elsevier)
  While bonding between d10 atoms and ions in mol. systems has been well studied, less attention has been paid to interactions between such seemingly closed shell species in extended inorg. solids. We present visualizations of the electronic structures of the delafossites ABO2 with particular emphasis on the nature of d10-d10 interactions in the close packed plane of the coinage metal ion. LDA-GGA-DFT and LMTO-ASA methods were used. On going from Cu to Ag to Au, the extent of bonding between A and A increases. However, the structures (in terms of distances) of these compds. are largely detd. by the strongly ionic BIII-O interaction and for the larger B ions Sc, In and Y, the A atoms are sufficiently well-sepd. that A-A bonding is almost negligible. We also analyze some interesting differences between Ag and Au, including the larger A-O covalency of the Au. The trends in electronic structure suggest that the Ag and Au compds. are not good candidate transparent conducting oxides.
34. 34
  Kawazoe, H.; Yanagi, H.; Ueda, K.; Hosono, H. Transparent p-Type Conducting Oxides: Design and Fabrication of p-n Heterojunctions MRS Bull. 2000, 25, 28– 36 DOI: 10.1557/mrs2000.148
  34
  Transparent p-type conducting oxides. Design and fabrication of p-n heterojunctions
  Kawazoe, Hiroshi; Yanagi, Hiroshi; Ueda, Kazushige; Hosono, Hideo
  MRS Bulletin (2000), 25 (8), 28-36CODEN: MRSBEA; ISSN:0883-7694. (Materials Research Society)
  A review with 23 refs. is given on results of investigations into chem. design, fabrication of thin films, the optical and elec. properties of the thin films, and a trial to fabricate p-n heterojunctions based on transparent conducting oxides. The following topics and materials are considered: design of p-type conducting wide-gap oxides (selection of cationic species, preferred crystal structure), p-type cond. in CuAlO2 and CuGaO2 delafossites, p-type cond. in SrCu2O2 (SCO), semiquant. estn. of valence-bond edge structure in CuAlO2, n-type cond. in AgInO2 delafossite, fabrication of transparent heterojunction thin-film diodes, UV light emission from a p-SCO/n-ZnO p-n heterojunction by current injection, chem. modulation of the valence bond, and codoping.
35. 35
  Benko, F.; Koffyberg, F. Opto-Electronic Properties of p and n-Type Delafossite, CuFeO₂ J. Phys. Chem. Solids 1987, 48, 431– 434 DOI: 10.1016/0022-3697(87)90103-X
  35
  Optoelectronic properties of p- and n-type delafossite, CuFeO2
  Benko, F. A.; Koffyberg, F. P.
  Journal of Physics and Chemistry of Solids (1987), 48 (5), 431-4CODEN: JPCSAW; ISSN:0022-3697.
  CuFeO2 doped with Mg is a p-type semiconductor with a hole mobility of 10-5 m2/V-s; the electron mobility in n-type CuFeO2 doped with Sn is 10-10 m2/v-s. From photo-electrochem. measurements, the valence band edge is 4.9 eV below the vacuum level. The valence band is made up of mainly Cu-3d wave functions; a deeper lying O-2p band has its edge at 7.1 eV. The indirect allowed bandgap is 1.15 eV; further optical transitions occur at 2.03 and 3.35 eV. The results are compared with similar data for the delafossites CuMO2 with M = Al, Cr, ga and Y.
36. 36
  Ingram, B.; Mason, T.; Asahi, R.; Park, K.; Freeman, A. Electronic Structure and Small Polaron Hole Transport of Copper Aluminate Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 1– 7 DOI: 10.1103/PhysRevB.64.155114
  There is no corresponding record for this reference.
37. 37
  Ingram, B. J.; Harder, B. J.; Hrabe, N. W.; Mason, T. O.; Poeppelmeier, K. R. Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO₂ and CuYO₂ Chem. Mater. 2004, 16, 5623– 5629 DOI: 10.1021/cm048982k
  37
  Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO2 and CuYO2
  Ingram, Brian J.; Harder, Bryan J.; Hrabe, Nikolas W.; Mason, Thomas O.; Poeppelmeier, Kenneth R.
  Chemistry of Materials (2004), 16 (26), 5623-5629CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The delafossite structure (ABO2) accommodates a wide range of transition and rare-earth cations on the B-site in combination with a short list of A-site cations. This paper reports the effects on defect chem. and transport as a function of the B-site cation in copper-based delafossite materials, with CuScO2 and CuYO2 as examples. Large B-site cation delafossites exhibit small polaron conduction, a diffusion-limited conduction mechanism, with an activation energy approx. twice that of CuAlO2 (0.22 eV vs. 0.14 eV, resp.). The mobility for these materials is found to be <1 cm2 V-1 s-1, further evidence of small polaron conduction. The majority defect species is highly dependent on the B-site cation, such that CuScO2 and CuYO2 are dominated by extrinsic defects (acceptor doping) and free oxygen interstitials, whereas off-stoichiometry dominates CuAlO2. Dopant soly. is shown to be 1% for bulk CuScO2 samples and lower in CuYO2.
38. 38
  Ingram, B. J.; Gonzàlez, G. B.; Mason, T. O.; Shahriari, D. Y.; Barnabè, A.; Ko, D.; Poeppelmeier, K. R. Transport and Defect Mechanisms in Cuprous Delafossites. 1. Comparison of Hydrothermal and Standard Solid-State Synthesis in CuAlO₂ Chem. Mater. 2004, 16, 5616– 5622 DOI: 10.1021/cm048983c
  38
  Transport and Defect Mechanisms in Cuprous Delafossites. 1. Comparison of Hydrothermal and Standard Solid-State Synthesis in CuAlO2
  Ingram, Brian J.; Gonzalez, Gabriela B.; Mason, Thomas O.; Shahriari, Dean Y.; Barnabe, Antoine; Ko, Donggeun; Poeppelmeier, Kenneth R.
  Chemistry of Materials (2004), 16 (26), 5616-5622CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  CuAlO2 exhibits a unique defect structure that is dependent on the synthesis route. High-temp. solid-state and low-temp. hydrothermal techniques are compared to illustrate how cation off-stoichiometry affects the elec. properties of CuAlO2. A defect complex of Al on a Cu-site stabilized by two bound oxygen interstitials (AlCu••2Oi'')'' is proposed which serves as an acceptor dopant to set the hole concn. Trapping of holes (small polarons) by such complexes with decreasing temp. is proposed to account for the decreasing carrier content with temp. Hydrothermal samples exhibit approx. an order of magnitude increase in hole concn. relative to the solid-state synthesized samples; this is reflected in the elec. cond. and may explain the variations in elec. properties reported for CuAlO2.
39. 39
  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: Condens. Matter Mater. Phys. 2009, 80, 165206 DOI: 10.1103/PhysRevB.80.165206
  39
  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.
40. 40
  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
  40
  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.
41. 41
  Brander, R. A Review of the Merits of Direct and Indirect Gap Semiconductors for Electroluminescence Devices Rev. Phys. Technol. 1972, 3, 145– 194 DOI: 10.1088/0034-6683/3/3/I01
  41
  Review of the merits of direct- and indirect-gap semiconductors for electroluminescence devices
  Brander, R. W.
  Review of Physics in Technology (1972), 3 (3), 145-94CODEN: RPTCAL; ISSN:0034-6683.
  A review with many refs.
42. 42
  Scanlon, D. O.; Godinho, K. G.; Morgan, B. J.; Watson, G. W. Understanding Conductivity Anomalies in Cu-Based Delafossite Transparent Conducting Oxides: Theoretical Insights J. Chem. Phys. 2010, 132, 024707 DOI: 10.1063/1.3290815
  There is no corresponding record for this reference.
43. 43
  Scanlon, D. O.; Watson, G. W. Understanding the p-Type Defect Chemistry of CuCrO₂ J. Mater. Chem. 2011, 21, 3655 DOI: 10.1039/c0jm03852k
  43
  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.
44. 44
  Nakano, Y.; Saeki, S.; Morikawa, T. Optical Bandgap Widening of p-Type Cu₂O Films by Nitrogen Doping Appl. Phys. Lett. 2009, 94, 022111 DOI: 10.1063/1.3072804
  44
  Optical bandgap widening of p-type Cu2O films by nitrogen doping
  Nakano, Yoshitaka; Saeki, Shu; Morikawa, Takeshi
  Applied Physics Letters (2009), 94 (2), 022111/1-022111/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  The authors have studied the effect of N doping into Cu2O films deposited by reactive magnetron sputtering. With increasing N-doping concn. up to 3%, the optical bandgap energy is enlarged from ∼2.1 to ∼2.5 eV with retaining p-type cond. as detd. by optical absorption and Hall effect measurements. Addnl., photoelectron spectroscopy in air measurements shows an increase in the valence and conduction band shifts with N doping. These exptl. results demonstrate possible optical bandgap widening of p-type N-doped Cu2O films, which is a phenomenon that is probably assocd. with significant structural changes induced by N doping, as suggested from x-ray diffraction measurements. (c) 2009 American Institute of Physics.
45. 45
  Liu, G.; Schulmeyer, T.; BrÖtz, J.; Klein, A.; Jaegermann, W. Interface Properties and Band Alignment of Cu₂/CdS Thin Film Solar Cells Thin Solid Films 2003, 431–432, 477– 482 DOI: 10.1016/S0040-6090(03)00190-1
  There is no corresponding record for this reference.
46. 46
  Riha, S. C.; Johnson, D. C.; Prieto, A. L. Cu₂Se Nanoparticles with Tunable Electronic Properties due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction J. Am. Chem. Soc. 2011, 133, 1383– 1390 DOI: 10.1021/ja106254h
  46
  Cu2Se Nanoparticles with Tunable Electronic Properties Due to a Controlled Solid-State Phase Transition Driven by Copper Oxidation and Cationic Conduction
  Riha, Shannon C.; Johnson, Derek C.; Prieto, Amy L.
  Journal of the American Chemical Society (2011), 133 (5), 1383-1390CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Stoichiometric copper(I) selenide nanoparticles were synthesized using the hot injection method. The effects of air exposure on the surface compn., crystal structure, and electronic properties were monitored using XPS, x-ray diffraction, and cond. measurements. The current-voltage response changes from semiconducting to ohmic, and within a week a 3000-fold increase in cond. is obsd. under ambient conditions. The enhanced electronic properties can be explained by the oxidn. of Cu+ and Se2- on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu2Se to cubic Cu1.8Se. This behavior is a result of the facile solid-state ionic cond. of cationic Cu within the crystal and the high susceptibility of the nanoparticle surface to oxidn. This regulated transformation is appealing as one could envision using layers of Cu2Se nanoparticles as both semiconducting and conducting domains in optoelectronic devices simply by tuning the electronic properties for each layer through controlled oxidn.
47. 47
  Ueda, K.; Inoue, S.; Hirose, S.; Kawazoe, H.; Hosono, H. Transparent p-Type Semiconductor: LaCuOS Layered Oxysulfide Appl. Phys. Lett. 2000, 77, 2701 DOI: 10.1063/1.1319507
  47
  Transparent p-type semiconductor: LaCuOS layered oxysulfide
  Ueda, K.; Inoue, S.; Hirose, S.; Kawazoe, H.; Hosono, H.
  Applied Physics Letters (2000), 77 (17), 2701-2703CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  La1-xSrxCuOS (x = 0, 0.05) thin films prepd. by radiofrequency sputtering have high optical transmission (≥70%) at the visible and near-IR wavelengths and an energy gap of ∼3.1 eV. The d.c. elec. conductivities of x = 0 and 0.05 films at room temp. were 1.2 × 10-2 and 2.6 × 10-1 S cm-1, resp. The Seebeck coeffs. of these samples were pos., indicating that p-type elec. conduction is dominant in these materials. A sharp luminescence peak, probably originating from an interband transition, was obsd. at the optical absorption edge. The present study demonstrates that LaCuOS is a promising transparent p-type semiconductor for optoelectronic applications. The material design, based on chem. modulation of the valence band, was extended to oxysulfide systems.
48. 48
  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 DOI: 10.1039/c4tc00096j
  48
  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.
49. 49
  Hiramatsu, H.; Ueda, K.; Ohta, H.; Hirano, M.; Kikuchi, M.; Yanagi, H.; Kamiya, T.; Hosono, H. Heavy Hole Doping of Epitaxial Thin Films of a Wide Gap p-Type Semiconductor, LaCuOSe, and Analysis of the Effective Mass Appl. Phys. Lett. 2007, 91, 012104 DOI: 10.1063/1.2753546
  49
  Heavy hole doping of epitaxial thin films of a wide gap p-type semiconductor, LaCuOSe, and analysis of the effective mass
  Hiramatsu, Hidenori; Ueda, Kazushige; Ohta, Hiromichi; Hirano, Masahiro; Kikuchi, Maiko; Yanagi, Hiroshi; Kamiya, Toshio; Hosono, Hideo
  Applied Physics Letters (2007), 91 (1), 012104/1-012104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  The high d. hole doping (1.7×1021 cm-3) for a wide gap (Eg=∼2.8 eV) p-type semiconductor was achieved on 40 nm thick Mg-doped LaCuOSe epitaxial films. These films exhibited distinct free carrier absorption, and the effective mass and momentum relaxation time were analyzed. Its small hole mobility [∼3.5 cm2/(V s)] compared to the electron mobilities of wide gap n-type semiconductors is attributed to a heavy effective mass of 1.6 ± 0.2me. Regardless of the heavy hole doping, a band filling effect was not obsd. These results are discussed with a rigid band model and an acceptor band model.
50. 50
  Liu, M. L.; Wu, L. B.; Huang, F. Q.; Chen, L. D.; Ibers, J. A. Syntheses, Crystal and Electronic Structure, and Some Optical and Transport Properties of LnCuOTe (Ln = La, Ce, Nd) J. Solid State Chem. 2007, 180, 62– 69 DOI: 10.1016/j.jssc.2006.09.014
  50
  Syntheses, crystal and electronic structure, and some optical and transport properties of LnCuOTe (Ln = La, Ce, Nd)
  Liu, Min Ling; Wu, Li Bin; Huang, Fu Qiang; Chen, Li Dong; Ibers, James A.
  Journal of Solid State Chemistry (2007), 180 (1), 62-69CODEN: JSSCBI; ISSN:0022-4596. (Elsevier)
  Three new compds., LaCuOTe, CeCuOTe, and NdCuOTe, were synthesized from the resp. rare-earth elements, CuO, Te, and a KI flux at 1023 K. The compds., which have the ZrSiCuAs structure type, are isostructural to LaCuOS, and crystallize in space group P4/nmm of the tetragonal system with two formula units in cells of dimensions at 153 K of a 4.1775(5), c 9.3260(16) Å for LaCuOTe; a 4.1497(3), c 9.3090(10) Å for CeCuOTe; and a 4.1056(9), c 9.332(4) Å for NdCuOTe. The structure of LnCuOTe (Ln = La, Ce, Nd) is composed of alternating PbO-like [Ln2O2] and anti-PbO-like [Cu2Te2] layers stacked perpendicular to [0 0 1]. The exptl. optical band gaps of LaCuOTe and NdCuOTe are 2.31 and 2.26 eV, resp. At 298 K the elec. cond. of LaCuOTe is 1.65 S/cm and the Hall mobility is +80.6 cm2 V-1 s-1. The pos. values of the Seebeck and Hall coeffs. indicate p-type elec. conduction. First-principle theor. calcns. were performed on LaCuOQ (Q = S, Se, Te). In LaCuOTe, Cu 3d and Te 5p orbitals dominate the states near the valence band max.; the states near the conduction band min. are composed of Cu 4s, Te 5p, and La 5d orbitals. The larger dispersion of Cu 3d orbitals and the presence of Te 5p orbitals near the valence band max. are responsible for the larger hole mobility of LaCuOTe compared to LaCuOS and LaCuOSe.
51. 51
  Ueda, K.; Hosono, H.; Hamada, N. Energy Band Structure of LaCuOCh (Ch = S, Se and Te) Calculated by the Full-Potential Linearized Augmented Plane-Wave Method J. Phys.: Condens. Matter 2004, 16, 5179– 5186 DOI: 10.1088/0953-8984/16/28/036
  51
  Energy band structure of LaCuOCh (Ch = S, Se and Te) calculated by the full-potential linearized augmented plane-wave method
  Ueda, Kazushige; Hosono, Hideo; Hamada, Noriaki
  Journal of Physics: Condensed Matter (2004), 16 (28), 5179-5186CODEN: JCOMEL; ISSN:0953-8984. (Institute of Physics Publishing)
  Energy band diagrams of LaCuOCh (Ch = S, Se and Te) were calcd. by a full-potential linearized augmented plane-wave method. The calcns., based on the local d. approxn. with/without an on-site Coulomb repulsion parameter, were to examine the energy levels of La 4f states. The results of the calcns. showed that the on-site correlation parameter is necessary for evaluating the energy levels of La 4f states appropriately. The calcns. for LaCuOCh with the on-site correlation parameter revealed that LaCuOS and LaCuOSe have almost the same energy band structure with a direct allowed-type band gap, while LaCuOTe has significantly different conduction band structure that exhibits an indirect-type band gap. This difference in electronic structure between LaCuOCh (Ch = S, Se and Te) is consistent with the obsd. optical properties of these materials.
52. 52
  Caskey, C. M.; Richards, R. M.; Ginley, D. S.; Zakutayev, A. Thin Film Synthesis and Properties of Copper Nitride, a Metastable Semiconductor Mater. Horiz. 2014, 1, 424 DOI: 10.1039/c4mh00049h
  52
  Thin film synthesis and properties of copper nitride, a metastable semiconductor
  Caskey, Christopher M.; Richards, Ryan M.; Ginley, David S.; Zakutayev, Andriy
  Materials Horizons (2014), 1 (4), 424-430CODEN: MHAOBM; ISSN:2051-6355. (Royal Society of Chemistry)
  Copper nitride (Cu3N) thin films were grown by reactive sputtering using a high-throughput combinatorial approach with orthogonal gradients of substrate temp. and target-substrate distance. This technique enables high-throughput modulation of the anion activity, and is broadly applicable to the combinatorial synthesis of other materials. Stable, phase pure Cu3N thin films were grown on glass substrates at temps. between 150 and 200°C, depending on the target-substrate distance. These 00L oriented thin films have 10-3 S cm-1 cond. and 1.5 eV optical absorption onset, making Cu3N interesting for future studies in the context of solar energy conversion applications. The anal. of the synthetic results provides insights into the thermodn. origins of the growth of metastable Cu3N, and sets a nitrogen chem. potential of +1 eV per atom as a lower limit of the anion activity that can be achieved in non-equil. thin film growth of metastable materials. The first step towards testing the transferability of this result to other materials was made by reactive sputtering of tin, antimony, and bismuth in nitrogen.
53. 53
  Walsh, A.; Chen, S.; Wei, S.-H.; Gong, X.-G. Kesterite Thin-Film Solar Cells: Advances in Materials Modelling of Cu₂ZnSnS₄ Adv. Energy Mater. 2012, 2, 400– 409 DOI: 10.1002/aenm.201100630
  53
  Kesterite thin-film solar cells: advances in materials modelling of Cu2ZnSnS4
  Walsh, Aron; Chen, Shiyou; Wei, Su-Huai; Gong, Xin-Gao
  Advanced Energy Materials (2012), 2 (4), 400-409CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)
  A review. Quaternary semiconducting materials based on the kesterite (A2BCX4) mineral structure are the most promising candidates to overtake the current generation of light-absorbing materials for thin-film solar cells. Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and their alloy Cu2ZnSn(Se,S)4 consist of abundant, low-cost and non-toxic elements, unlike current CdTe and Cu(In,Ga)Se2 based technologies. Zinc-blende related structures are formed by quaternary compds., but the complexity assocd. with the multi-component system introduces difficulties in material growth, characterization, and application. First-principles electronic structure simulations, performed over the past five years, that address the structural, electronic, and defect properties of this family of compds. are reviewed. Initial predictions of the bandgaps and crystal structures have recently been verified exptl. The calcns. highlight the role of at. disorder on the cation sub-lattice, as well as phase sepn. of Cu2ZnSnS4 into ZnS and CuSnS3, on the material performance for light-to-electricity conversion in photovoltaic devices. Finally, the current grand challenges for materials modeling of thin-film solar cells are highlighted.
54. 54
  Zakutayev, A.; Caskey, C. M.; Fioretti, A. N.; Ginley, D. S.; Vidal, J.; Stevanovic, V.; Tea, E.; Lany, S. Defect Tolerant Semiconductors for Solar Energy Conversion J. Phys. Chem. Lett. 2014, 5, 1117– 1125 DOI: 10.1021/jz5001787
  54
  Defect tolerant semiconductors for solar energy conversion
  Zakutayev, Andriy; Caskey, Christopher M.; Fioretti, Angela N.; Ginley, David S.; Vidal, Julien; Stevanovic, Vladan; Tea, Eric; Lany, Stephan
  Journal of Physical Chemistry Letters (2014), 5 (7), 1117-1125CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Defect tolerance is the tendency of a semiconductor to keep its properties despite the presence of crystallog. defects. Scientific understanding of the origin of defect tolerance is currently missing. Here we show that semiconductors with antibonding states at the top of the valence band are likely to be tolerant to defects. Theor. calcns. demonstrate that Cu3N with antibonding valence band max. has shallow intrinsic defects and no surface states, in contrast to GaN with bonding valence band max. Exptl. measurements indicate shallow native donors and acceptors in Cu3N thin films, leading to 1016-1017 cm-3 doping with either electrons or holes depending on the growth conditions. The exptl. measured bipolar doping and the solar-matched optical absorption onset (1.4 eV) make Cu3N a promising candidate absorber for photovoltaic and photoelectrochem. solar cells, despite the calcd. indirect fundamental band gap (1.0 eV). These conclusions can be extended to other materials with antibonding character of the valence band, defining a class of defect-tolerant semiconductors for solar energy conversion applications.
55. 55
  Yang, M.; Zakutayev, A.; Vidal, J.; Zhang, X.; Ginley, D. S.; DiSalvo, F. J. Strong Optical Absorption in CuTaN₂ Nitride Delafossite Energy Environ. Sci. 2013, 6, 2994 DOI: 10.1039/c3ee40621k
  55
  Strong optical absorption in CuTaN2 nitride delafossite
  Yang, Minghui; Zakutayev, Andriy; Vidal, Julien; Zhang, Xiuwen; Ginley, David S.; DiSalvo, Francis J.
  Energy & Environmental Science (2013), 6 (10), 2994-2999CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
  We report on synthesis, stability, electronic structure and optical properties of CuTaN2 with the delafossite crystal structure and its potential use as an absorber for solar energy conversion applications. According to theor. first-principles calcns., the formation enthalpy of CuTaN2 is neg. (-0.66 eV per atom), but this material is metastable with respect to decompn. into Cu, Ta3N5 and N2. Nevertheless, the exptl. thermal stability limit of single phase CuTaN2 powders synthesized using an ion exchange method is 250 °C in ambient atm., according to combined temp.-dependent X-ray diffraction and thermo-gravimetric analyses. Electronic structure of the CuTaN2 is different compared to that of CuAlO2, in particular the band gap of this nitride delafossite (1.3 eV) calcd. using HSE06+G0W0 is much smaller than the band gap of the oxide delafossite. The onset of optical absorption onset of CuTaN2 at 1.5 eV detd. from exptl. diffuse reflectance measurements is consistent with the theor. 1.4 eV optical band gap and large calcd. absorption coeff. (>105 cm-1 above 1.5 eV) detd. from time-dependent HSE06 calcns. cor. by a scissors operator. The significance of our findings is that optical properties of CuTaN2 are nearly optimal for photovoltaic energy conversion.
56. 56
  Mewis, A. Darstellung und Struktur der Verbindungen MgCuP, BaCuP(As) und BaAgP(As) Z. Naturforsch., B: J. Chem. Sci. 1979, 34, 1373– 1376 DOI: 10.1515/znb-1979-1006
  56
  Preparation and crystal structure of magnesium-copper-phosphide, barium-copper-phosphide(arsenide), and barium-silver-phosphide(arsenide
  Mewis, Albrecht
  Zeitschrift fuer Naturforschung, Teil B: Anorganische Chemie, Organische Chemie (1979), 34B (10), 1373-6CODEN: ZNBAD2; ISSN:0340-5087.
  MgCuP, BaCuP(As), and BaAgP(As) were prepd. and their structures detd. MgCuP crystd. orthorhombically in an anti-PbCl2 structure (space group Pnma, a 653.2(1), b 383.5(1), c 717.0(1) pm). BaCuP(As) and BaAgP(As) are isotypic and crystd. in a modified Ni2In-structure (space group P63/mmc with a 423.9(1) and c 900.6(2) pm for BaCuP, a 437.2(1) and c 907.3(2) pm for BaCuAs, a 449.61(1) and c 882.8(2) pm for BaAgP, and a 461.3(1) and c 889.6(1) pm for BaAgAs.
57. 57
  Mewis, A. ABX Verbindungen mit Ni₂ In-Struktur. Darstellung und Struktur der Verbindungen CaCuP(As), SrCuP(As), SrAgP(As) und EuCuAs Z. Naturforsch., B: J. Chem. Sci. 1978, 33, 983– 986 DOI: 10.1515/znb-1978-0906
  There is no corresponding record for this reference.
58. 58
  Adamo, C.; Barone, V. Toward Reliable Density Functional Methods Without Adjustable Parameters: The PBE0Model J. Chem. Phys. 1999, 110, 6158 DOI: 10.1063/1.478522
  58
  Toward reliable density functional methods without adjustable parameters: the PBE0 model
  Adamo, Carlo; Barone, Vincenzo
  Journal of Chemical Physics (1999), 110 (13), 6158-6170CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  We present an anal. of the performances of a parameter free d. functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amt. of exact exchange. The results obtained for structural, thermodn., kinetic and spectroscopic (magnetic, IR and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chem. and condensed matter physics.
59. 59
  Paier, J.; Hirschl, R.; Marsman, M.; Kresse, G. The Perdew-Burke-Ernzerhof Exchange-Correlation Functional Applied to the G2–1 Test Set Using a Plane-Wave Basis Set J. Chem. Phys. 2005, 122, 234102 DOI: 10.1063/1.1926272
  59
  The Perdew-Burke-Ernzerhof exchange-correlation functional applied to the G2-1 test set using a plane-wave basis set
  Paier, Joachim; Hirschl, Robin; Marsman, Martijn; Kresse, Georg
  Journal of Chemical Physics (2005), 122 (23), 234102/1-234102/13CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
  Present local and semilocal functionals show significant errors, for instance, in the energetics of small mols. and in the description of band gaps. One possible soln. to these problems is the introduction of exact exchange and hybrid functionals. A plane-wave-based algorithm was implemented in VASP (Vienna ab-initio simulation package) to allow for the calcn. of the exact exchange. To systematically assess the precision of the present implementation, calcns. for the 55 mols. of the G2-1 quantum chem. test set were performed applying the PBE and PBE0 functionals. Excellent agreement for both atomization energies and geometries compared with the results obtained by GAUSSIAN 03 calcns. using large basis sets (augmented correlation consistent polarized valence quadruple zeta for the geometry optimization and augmented correlation-consistent polarized valence quintuple zeta for the energy calcns.) was found. The mean abs. error for atomization energies between VASP and the expt. is 8.6 and 3.7 kcal/mol, as calcd. with the PBE and PBE0 functionals, resp. The mean deviations between VASP and GAUSSIAN are 0.46 and 0.49 kcal/mol for the PBE and PBE0 functionals, resp.
60. 60
  Kresse, G.; Hafner, J. Ab-initio Molecular Dynamics for Liquid Metals Phys. Rev. B: Condens. Matter Mater. Phys. 1993, 47, 558– 561 DOI: 10.1103/PhysRevB.47.558
  60
  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.
61. 61
  Kresse, G.; Hafner, J. Ab-initio Molecular-Dynamics Simulation of the Liquid-Metal-Amorphous-Semiconductor Transition in Germanium Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 14251– 14269 DOI: 10.1103/PhysRevB.49.14251
  61
  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.
62. 62
  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
  62
  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.
63. 63
  Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab-Initio Total-Energy Calculations Using a Plane-Wave Basis Set Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169– 11186 DOI: 10.1103/PhysRevB.54.11169
  63
  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.
64. 64
  Blöchl, P. E. Projector Augmented-Wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953– 17979 DOI: 10.1103/PhysRevB.50.17953
  64
  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.
65. 65
  Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 1758– 1775 DOI: 10.1103/PhysRevB.59.1758
  65
  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.
66. 66
  Yeh, J.; Lindau, I. Atomic Subshell Photoionization Cross Sections and Asymmetry Parameters: 1 ⩽ Z ⩽ 103 At. Data Nucl. Data Tables 1985, 32, 1– 155 DOI: 10.1016/0092-640X(85)90016-6
  66
  Atomic subshell photoionization cross sections and asymmetry parameters: 1 ≤ Z ≤ 103
  Yeh, J. J.; Lindau, I.
  Atomic Data and Nuclear Data Tables (1985), 32 (1), 1-155CODEN: ADNDAT; ISSN:0092-640X.
  At. subshell photoionization cross sections and asymmetry parameters are calcd. with the Hartree-Fock-Slater one-electron central potential model (dipole approxn.) for all elements Z = 1-103. The cross-section results are plotted for all subshells in the energy region 0-1500 eV, and cross sections and asymmetry parameters are tabulated for selected energies in the region 10.2-8047.8 eV. In addn., more detailed graphs are given for the 4d (Z = 39-71) and 5d (Z = 64-100) subshell cross sections in the vicinity of the Cooper min. These data should be particularly useful for work based on spectroscopic investigations of at. subshells using synchrotron radiation and/or discrete line sources.
67. 67
  Savory, C. N.; Ganose, A. M.; Travis, W.; Atri, R. S.; Palgrave, R. G.; Scanlon, D. O. An Assessment of Silver Copper Sulfides for Photovoltaic Applications: Theoretical and Experimental Insights J. Mater. Chem. A 2016, 4, 12648 DOI: 10.1039/C6TA03376H
  67
  An assessment of silver copper sulfides for photovoltaic applications: theoretical and experimental insights
  Savory, Christopher N.; Ganose, Alex M.; Travis, Will; Atri, Ria S.; Palgrave, Robert G.; Scanlon, David O.
  Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (32), 12648-12657CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)
  As the worldwide demand for energy increases, low-cost solar cells are being looked to as a soln. for the future. To attain this, non-toxic earth-abundant materials are crucial, however cell efficiencies for current materials are limited in many cases. In this article, we examine the two silver copper sulfides AgCuS and Ag3CuS2 as possible solar absorbers using hybrid d. functional theory, diffuse reflectance spectroscopy, XPS and Hall effect measurements. We show that both compds. demonstrate promising electronic structures and band gaps for high theor. efficiency solar cells, based on Shockley-Queisser limits. Detailed anal. of their optical properties, however, indicates that only AgCuS should be of interest for PV applications, with a high theor. efficiency. From this, we also calc. the band alignment of AgCuS against various buffer layers to aid in future device construction.
68. 68
  Bhachu, D. S.; Moniz, S. J. A.; Sathasivam, S.; Scanlon, D. O.; Walsh, A.; Bawaked, S. M.; Mokhtar, M.; Obaid, A. Y.; Parkin, I. P.; Tang, J.; Carmalt, C. J. Bismuth Oxyhalides: Synthesis, Structure and Photoelectrochemical Activity Chem. Sci. 2016, 7, 4832– 4841 DOI: 10.1039/C6SC00389C
  68
  Bismuth oxyhalides: synthesis, structure and photoelectrochemical activity
  Bhachu, Davinder S.; Moniz, Savio J. A.; Sathasivam, Sanjayan; Scanlon, David O.; Walsh, Aron; Bawaked, Salem M.; Mokhtar, Mohamed; Obaid, Abdullah Y.; Parkin, Ivan P.; Tang, Junwang; Carmalt, Claire J.
  Chemical Science (2016), 7 (8), 4832-4841CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  The authors report the synthesis and photoelectrochem. assessment of phase pure tetragonal matlockite structured BiOX (X = Cl, Br, I) films. The materials were deposited using aerosol-assisted CVD. The measured optical bandgaps of the oxyhalides, supported by d. functional theory calcns., showed a red shift with the increasing size of halide following the binding energy of the anion p-orbitals that form the valence band. Stability and photoelectrochem. studies carried out without a sacrificial electron donor showed the n-type BiOBr film to have the highest photocurrent reported for BiOBr in the literature to date (0.3 mA cm-2 at 1.23 V vs. RHE), indicating it is an excellent candidate for solar fuel prodn. with a very low onset potential of 0.2 V vs. RHE. The high performance was attributed to the preferred growth of the film in the [011] direction, as shown by x-ray diffraction, leading to internal elec. fields that minimize charge carrier recombination.
69. 69
  Marchand, P.; Sathasivam, S.; Williamson, B. A. D.; Pugh, D.; Bawaked, S. M.; Basahel, S. N.; Obaid, A. Y.; Scanlon, D. O.; Parkin, I. P.; Carmalt, C. J. A Single-Source Precursor Approach to Solution Processed Indium Arsenide Thin Films J. Mater. Chem. C 2016, 4, 6761– 6768 DOI: 10.1039/C6TC02293F
  69
  A single-source precursor approach to solution processed indium arsenide thin films
  Marchand, Peter; Sathasivam, Sanjayan; Williamson, Benjamin A. D.; Pugh, David; Bawaked, Salem M.; Basahel, Sulaiman N.; Obaid, Abdullah Y.; Scanlon, David O.; Parkin, Ivan P.; Carmalt, Claire J.
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2016), 4 (28), 6761-6768CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  This paper reports the synthesis of the novel single-source precursor, [{(MeInAstBu)3}2(Me2InAs(tBu)H)2] and the subsequent first report of aerosol-assisted chem. vapor deposition of InAs thin films. Owing to the use of the single-source precursor, highly cryst. and stoichiometric films were grown at a relatively low deposition temp. of 450 °C. Core level XPS depth profiling studies showed some partial oxidn. of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS anal. matched well with the simulated d. of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10-3 Ω cm) and carrier mobility (410 cm2 V-1 s-1) values despite growth on amorphous glass substrates.
70. 70
  Sathasivam, S.; Arnepalli, R. R.; Bhachu, D. S.; Lu, Y.; Buckeridge, J.; Scanlon, D. O.; Kumar, B.; Singh, K. K.; Visser, R. J.; Blackman, C. S.; Carmalt, C. J. Single Step Solution Processed GaAs Thin Films from GaMe₃ and tBuAsH₂ under Ambient Pressure J. Phys. Chem. C 2016, 120, 7013– 7019 DOI: 10.1021/acs.jpcc.6b00850
  70
  Single Step Solution Processed GaAs Thin Films from GaMe3 and tBuAsH2 under Ambient Pressure
  Sathasivam, Sanjayan; Arnepalli, Ranga R.; Bhachu, Davinder S.; Lu, Yao; Buckeridge, John; Scanlon, David O.; Kumar, Bhaskar; Singh, Kaushal K.; Visser, Robert J.; Blackman, Christopher S.; Carmalt, Claire J.
  Journal of Physical Chemistry C (2016), 120 (13), 7013-7019CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  This article reports on the possibility of low-cost GaAs formed under ambient pressure via a single step soln. processed route from only readily available precursors, tBuAsH2 and GaMe3. The thin films of GaAs on glass substrates have good crystallinity with crystallites as large as 150 nm and low contamination with exptl. results matching well with theor. d. of states calcns. These results open up a route to efficient and cost-effective scale up of GaAs thin films with high material properties for widespread industrial use. Confirmation of film quality was detd. using XRD, Raman, EDX mapping, SEM, HRTEM, XPS, and SIMS.
71. 71
  Gajdoš, M.; Hummer, K.; Kresse, G.; Furthmüller, J.; Bechstedt, F. Linear Optical Properties in the Projector-Augmented Wave Methodology Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 045112 DOI: 10.1103/PhysRevB.73.045112
  71
  Linear optical properties in the projector-augmented wave methodology
  Gajdos, M.; Hummer, K.; Kresse, G.; Furthmuller, J.; Bechstedt, F.
  Physical Review B: Condensed Matter and Materials Physics (2006), 73 (4), 045112/1-045112/9CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  In this work we derive closed expressions for the head of the frequency-dependent microscopic polarizability matrix in the projector-augmented wave (PAW) methodol. Contrary to previous applications, the longitudinal expression is utilized, resulting in dielec. properties that are largely independent of the applied potentials. The improved accuracy of the present approach is demonstrated by comparing the longitudinal and transversal expressions of the polarizability matrix for a no. of cubic semiconductors and one insulator, i.e., Si, SiC, AlP, GaAs, and diamond (C), resp. The methodol. is readily extendable to more complicated nonlocal Hamiltonians or to the calcn. of the macroscopic dielec. matrix including local field effects in the random phase or d. functional approxn., which is demonstrated for the previously mentioned model systems. Furthermore, d. functional perturbation theory is extended to the PAW method, and the resp. results are compared to those obtained by summation over the conduction band states.
72. 72
  Adolph, B.; Furthmüller, J.; Bechstedt, F. Optical Properties of Semiconductors Using Projector-Augmented Waves Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63, 125108 DOI: 10.1103/PhysRevB.63.125108
  72
  Optical properties of semiconductors using projector-augmented waves
  Adolph, B.; Furthmuller, J.; Bechstedt, F.
  Physical Review B: Condensed Matter and Materials Physics (2001), 63 (12), 125108/1-125108/8CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
  The frozen-core projector-augmented wave (PAW) method is applied to construct all-electron valence wave functions from nonnorm-conserving pseudo wave functions and at. functions. The use of all-electron wave functions possesses the advantage that no nonlocal contributions to the optical transition operator have to be taken into account. In addn., the more accurate description of the wave functions in the core region improves the quality of the calcd. spectra compared to those obtained from a pseudopotential approach. The authors demonstrate the accuracy of the PAW approach by comparing optical spectra of several semiconductors with those obtained employing a full all-electron method or norm-conserving pseudopotentials.
73. 73
  Nie, X.; Wei, S.-H.; Zhang, S. B. Bipolar Doping and Band-Gap Anomalies in Delafossite Transparent Conductive Oxides Phys. Rev. Lett. 2002, 88, 066405 DOI: 10.1103/PhysRevLett.88.066405
  73
  Bipolar doping and band-gap anomalies in delafossite transparent conductive oxides
  Nie, Xiliang; Wei, Su-Huai; Zhang, S. B.
  Physical Review Letters (2002), 88 (6), 066405/1-066405/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
  Doping wide-gap materials p type is highly desirable but often difficult. This makes the recent discovery of p-type delafossite oxides, CuMIIIO2, very attractive. The CuMIIIO2 also show unique and unexplained phys. properties: Increasing band gap from MIII=Al, Ga, to In, not seen in conventional semiconductors. The largest gap CuInO2 can be mysteriously doped both n and p type but not the smaller gaps CuAlO2 and CuGaO2. Here, both properties are results of a large disparity between the fundamental gap and the apparent optical gap, a finding that could lead to a breakthrough in the study of bipolarly dopable wide-gap semiconductor oxides.
74. 74
  Walsh, A.; Da Silva, J. L. F.; Yan, Y.; Al-Jassim, M. M.; Wei, S.-H. Origin of Electronic and Optical Trends in Ternary In₂O₃ (ZnO)_n Transparent Conducting Oxides (n = 1.3,5): Hybrid Density Functional Theory Calculations Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 073105 DOI: 10.1103/PhysRevB.79.073105
  There is no corresponding record for this reference.
75. 75
  Walsh, A.; Yan, Y.; Huda, M. N.; Al-Jassim, M. M.; Wei, S.-H. Band Edge Electronic Structure of BiVO₄: Elucidating the Role of the Bi s and V d Orbitals Chem. Mater. 2009, 21, 547– 551 DOI: 10.1021/cm802894z
  75
  Band Edge Electronic Structure of BiVO4: Elucidating the Role of the Bi s and V d Orbitals
  Walsh, Aron; Yan, Yanfa; Huda, Muhammad N.; Al-Jassim, Mowafak M.; Wei, Su-Huai
  Chemistry of Materials (2009), 21 (3), 547-551CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The authors report the 1st-principles electronic structure of BiVO4, a promising photocatalyst for H generation. BiVO4 is a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center. Coupling between Bi 6s and O 2p forces an upward dispersion of the valence band at the zone boundary; however, a direct gap is maintained via coupling between V 3d, O 2p, and Bi 6p, which lowers the conduction band min. These interactions result in sym. hole and electron masses. Implications for the design of ambipolar metal oxides are discussed.
76. 76
  Scanlon, D. O.; Watson, G. W. (Cu₂S₂) (Sr₃Sc₂O₅)-A Layered, Direct Band Gap, p-Type Transparent Conducting Oxychalcogenide: A Theoretical Analysis Chem. Mater. 2009, 21, 5435– 5442 DOI: 10.1021/cm902260b
  There is no corresponding record for this reference.
77. 77
  Allen, J. P.; Nilsson, M. K.; Scanlon, D. O.; Watson, G. W. Comparison of the Defective Pyrochlore and Ilmenite Polymorphs of AgSbO₃ using GGA and hybrid DFT Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 035207 DOI: 10.1103/PhysRevB.83.035207
  There is no corresponding record for this reference.
78. 78
  Kubelka, P. New Contributions to the Optics of Intensely Light-Scattering Materials Part I J. Opt. Soc. Am. 1948, 38, 448 DOI: 10.1364/JOSA.38.000448
  78
  New contributions to the optics of intensely light-scattering materials
  KUBELKA P
  Journal of the Optical Society of America (1948), 38 (5), 448-57 ISSN:0030-3941.
  There is no expanded citation for this reference.
79. 79
  Preissler, N.; Bierwagen, O.; Ramu, A. T.; Speck, J. S. Electrical Transport, Electrothermal Transport, and Effective Electron Mass in Single-Crystalline In₂O₃ films Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 085305 DOI: 10.1103/PhysRevB.88.085305
  79
  Electrical transport, electrothermal transport, and effective electron mass in single-crystalline In2O3 films
  Preissler, Natalie; Bierwagen, Oliver; Ramu, Ashok T.; Speck, James S.
  Physical Review B: Condensed Matter and Materials Physics (2013), 88 (8), 085305/1-085305/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  A comprehensive study of the room-temp. elec. and electrothermal transport of single-cryst. indium oxide (In2O3) and indium tin oxide (ITO) films over a wide range of electron concns. is reported. We measured the room-temp. Hall mobility μH and Seebeck coeff. S of unintentionally doped and Sn-doped high-quality, plasma-assisted mol.-beam-epitaxy-grown In2O3 for vol. Hall electron concns. nH from 7 × 1016 cm-3 (unintentionally doped) to 1 × 1021 cm-3 (highly Sn-doped, ITO). The resulting empirical S(nH) relation can be directly used in other In2O3 samples to est. the vol. electron concn. from simple Seebeck coeff. measurements. The mobility and Seebeck coeff. were modeled by a numerical soln. of the Boltzmann transport equation. Ionized impurity scattering and polar optical phonon scattering were found to be the dominant scattering mechanisms. Acoustic phonon scattering was found to be negligible. Fitting the temp.-dependent mobility above room temp. of an In2O3 film with high mobility allowed us to find the effective Debye temp. (ΘD = 700 K) and no. of phonon modes (NOPML = 1.33) that best describe the polar optical phonon scattering. The modeling also yielded the Hall scattering factor rH as a function of electron concn., which is not negligible (rH ≈ 1.4) at nondegenerate electron concns. Fitting the Hall-scattering-factor cor. concn.-dependent Seebeck coeff. S(n) for nondegenerate samples to the numerical soln. of the Boltzmann transport equation and to widely used, simplified equations allowed us to ext. an effective electron mass of m* = (0.30 ± 0.03)me (with free electron mass me). The modeled mobility and Seebeck coeff. based on polar optical phonon and ionized impurity scattering describes the exptl. results very accurately up to electron concns. of 1019 cm-3, and qual. explains a mobility plateau or local max. around 1020 cm-3. Ionized impurity scattering with doubly charged donors best describes the mobility in our unintentionally doped films, consistent with oxygen vacancies as unintentional shallow donors, whereas singly charged donors best describe our Sn-doped films. Our modeling yields a (phonon-limited) max. theor. drift mobility and Hall mobility of μ = 190 cm2/Vs and μH = 270 cm2/V s, resp. Simplified equations for the Seebeck coeff. describe the measured values in the nondegenerate regime using a Seebeck scattering parameter of r = -0.55 (which is consistent with the detd. Debye temp.), and provide an est. of the Seebeck coeff. to lower electron concns. The simplified equations fail to describe the Seebeck coeff. around the Mott transition (nMott = 5.5 × 1018 cm-3) from nondegenerate to degenerate electron concns., whereas the numerical modeling accurately describes this region.
80. 80
  Button, K. J.; Cohn, D. R.; Von Ortenbert, M.; Lax, B.; Mollwo, E.; Helbig, R. Zeeman Splitting of Anomalous Shallow Bound States in ZnO Phys. Rev. Lett. 1972, 28, 1637– 1639 DOI: 10.1103/PhysRevLett.28.1637
  There is no corresponding record for this reference.
81. 81
  Button, K. J.; Fonstad, C. G.; Dreybrodt, W. Determination of the Electron Masses in Stannic Oxide by Submillimeter Cyclotron Resonance 1971, 4, 4539– 4541 DOI: 10.1103/PhysRevB.4.4539
  There is no corresponding record for this reference.
82. 82
  Scanlon, D. O. Defect Engineering of BaSnO₃ for High-Performance Transparent Conducting Oxide Applications Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 87, 161201 DOI: 10.1103/PhysRevB.87.161201
  82
  Defect engineering of BaSnO3 for high-performance transparent conducting oxide applications
  Scanlon, David O.
  Physical Review B: Condensed Matter and Materials Physics (2013), 87 (16), 161201/1-161201/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  The high cost and low abundance of indium has driven research to find In-free n-type transparent conducting oxides (TCOs). La-doped cubic perovskite BaSnO3 has been reported to possess electron mobilities as high as 320 cm2 V-1 s-1 for carrier concns. of 8 × 1019 cm-3, comparable to the very best TCOs. To date, however, the origins of cond. in this material have remained unclear. Here we study the defect chem. of BaSnO3 using a hybrid d. functional theory approach, in order to understand how to control the n-type cond. We show that in undoped samples, native defects cannot cause high levels of n-type cond.; however, adventitious H present in samples can act as shallow donors. By studying the effect of a range of donor dopants, we pinpoint ideal growth conditions and donor dopants for high-performance n-type BaSnO3 samples.
83. 83
  Toby, B. H. EXPGUI, a Graphical User Interface for GSAS J. Appl. Crystallogr. 2001, 34, 210– 213 DOI: 10.1107/S0021889801002242
  83
  EXPGUI, a graphical user interface for GSAS
  Toby, Brian H.
  Journal of Applied Crystallography (2001), 34 (2), 210-213CODEN: JACGAR; ISSN:0021-8898. (Munksgaard International Publishers Ltd.)
  A description and justification of the EXPGUI program is presented. This program implements a graphical user interface and shell for the GSAS (Generalized Structure and Anal. Software) single-crystal and Rietveld package. Use of the Tcl/Tk scripting language allows EXPGUI to be platform independent. Also included is a synopsis of how the program is implemented.
84. 84
  Larson, A.; Dreele, R. V. General Structure Analysis System (GSAS); Los Alamos National Laboratory Report LAUR 86-748; Los Alamos National Laboratory: Los Alamos, NM, 2004.
  There is no corresponding record for this reference.
85. 85
  Mewis, A. Darstellung und Struktur der Verbindung CaCu₄P₂ Z. Naturforsch., B: J. Chem. Sci. 1980, 35, 942– 945 DOI: 10.1515/znb-1980-0802
  There is no corresponding record for this reference.
86. 86
  Ghijsen, J.; Tjeng, L. H.; van Elp, J.; Eskes, H.; Westerink, J.; Sawatzky, G. A.; Czyzyk, M. T. Electronic Structure of Cu₂O and CuO Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 38, 11322– 11330 DOI: 10.1103/PhysRevB.38.11322
  86
  Electronic structure of cuprous and cupric oxides
  Ghijsen, J.; Tjeng, L. H.; Van Elp, J.; Eskes, H.; Westerink, J.; Sawatzky, G. A.; Czyzyk, M. T.
  Physical Review B: Condensed Matter and Materials Physics (1988), 38 (16-A), 11322-30CODEN: PRBMDO; ISSN:0163-1829.
  The electronic structure of Cu oxides has been investigated by photoelectron (x-ray photoemission, UV photoemission), Auger electron, and bremsstrahlung isochromat spectroscopies. The exptl. results are compared with one-electron band-structure calcns. as well as with a cluster CI model. It is demonstrated that the results for Cu2O agree well with band theory, whereas those for CuO clearly show strong deviations which we argue are due to electron-correlation effects in the open-shell d bands. From the comparison to cluster calcns., we ext. values for the Cu d-d and O p-p Coulomb interactions, the O to Cu charge transfer energy, and the degree of Cu d-O 2p hybridization. From this we demonstrate that CuO is a charge-transfer gap insulator.
87. 87
  Shin, D.; Foord, J. S.; Egdell, R. G.; Walsh, A. Electronic Structure of CuCrO₂ Thin Films Grown on Al₂O₃(001) by Oxygen Plasma Assisted Molecular Beam Epitaxy J. Appl. Phys. 2012, 112, 113718 DOI: 10.1063/1.4768726
  87
  Electronic structure of CuCrO2 thin films grown on Al2O3(001) by oxygen plasma assisted molecular beam epitaxy
  Shin, D.; Foord, J. S.; Egdell, R. G.; Walsh, A.
  Journal of Applied Physics (2012), 112 (11), 113718/1-113718/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  Thin films of CuCrO2 were grown on Al2O3(001) substrates by O plasma assisted mol. beam epitaxy. With a substrate temp. of 700° or 750°, the films showed an unanticipated (015) orientation but at a higher substrate temp. of 800° the expected basal (001) orientation predominates. The optical absorption spectrum of CuCrO2 shows a direct allowed absorption onset at 3.18 eV together with a weak peak at 2.0 eV which is suppressed by Sn doping. The low energy peak should be attributed to 3d→3d excitations assocd. with Cu2+ defect states rather than excitations localized on Cr3+. Valence band X-ray photoemission spectra of (001) and (015) oriented CuCrO2 are compared with those obtained from polycryst. samples. (c) 2012 American Institute of Physics.
88. 88
  Deuermeier, J.; Gassmann, J.; Brötz, J.; Klein, A. Reactive Magnetron Sputtering of Cu₂O: Dependence on Oxygen Pressure and Interface Formation with Indium Tin Oxide J. Appl. Phys. 2011, 109, 113704 DOI: 10.1063/1.3592981
  88
  Reactive magnetron sputtering of Cu2O. Dependence on oxygen pressure and interface formation with indium tin oxide
  Deuermeier, Jonas; Gassmann, Juergen; Broetz, Joachim; Klein, Andreas
  Journal of Applied Physics (2011), 109 (11), 113704/1-113704/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  Thin films of Cu oxides were prepd. by reactive magnetron sputtering and structural, morphol., chem., and electronic properties were analyzed using x-ray diffraction, AFM, in situ photoelectron spectroscopy, and elec. resistance measurements. The deposition conditions for prepn. of Cu(I)-oxide (Cu2O) are identified. In addn., the interface formation between Cu2O and Sn-doped In2O3 (ITO) was studied by stepwise deposition of Cu2O onto ITO and vice versa. A type II (staggered) band alignment with a valence band offset ΔEVB = 2.1-2.6 eV depending on interface prepn. is obsd. The band alignment explains the nonrectifying behavior of p-Cu2O/n-ITO junctions, which were investigated for thin film solar cells. (c) 2011 American Institute of Physics.
89. 89
  Egdell, R. G.; Henrich, V. E.; Bowdler, R.; Sekine, T. On the Difference in Valence Electron Plasmon Energy and Density of States Between Beta- and Cubic-Si₃N₄ J. Appl. Phys. 2003, 94, 6611 DOI: 10.1063/1.1619568
  89
  On the difference in valence electron plasmon energy and density of states between beta- and cubic-Si3N4
  Egdell, R. G.; Henrich, V. E.; Bowdler, R.; Sekine, T.
  Journal of Applied Physics (2003), 94 (10), 6611-6615CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
  Core and valence level photoemission spectra of β- and cubic-Si3N4 were measured under monochromatic Al Kα excitation. Strong satellites to high binding energy of the core lines arise from excitation of valence electron plasmons during the photoemission process. An increase in the plasmon energy from 23.45 eV for β-Si3N4 to 26.10 eV for cubic-Si3N4 is of the magnitude expected from the 26% increase in the valence electron d. assocd. with the shock-induced β-to-cubic phase transition. The measured valence band d. of states for cubic-Si3N4 is in agreement with theor. calcns.
90. 90
  Franzen, H.; Merrick, J.; Umaña, M.; Khan, A.; Peterson, D.; McCreary, J.; Thorn, R. XPS Spectra and Crystalline Potentials in Alkaline-Earth Chalcogenides and Hydrides J. Electron Spectrosc. Relat. Phenom. 1977, 11, 439– 443 DOI: 10.1016/0368-2048(77)80019-4
  90
  XPS spectra and crystalline potentials in alkaline-earth chalcogenides and hydrides
  Franzen, H. F.; Merrick, Jean; Umana, Mirtha; Khan, A. S.; Peterson, D. T.; McCreary, J. R.; Thorn, R. J.
  Journal of Electron Spectroscopy and Related Phenomena (1977), 11 (4), 439-43CODEN: JESRAW; ISSN:0368-2048.
  X-ray photoelectron spectral measurements were carried out on BaH2, CaH2, and SrH2 for the 1st time and on the corresponding chalcogenide (for Ca and Sr) for comparison; information was obtained on the nature of the distribution of electron d. in the hydrides relation to the elements. Electron binding energies are given for Ca, Sr, and Ba in the compds. studied. The calcd. cryst. potentials at the cation site for CaO and CaSe differ by 4 eV, whereas the exptl. binding energies differ by only 0.75 eV. The calcd. cryst. potentials differ by 3.5 eV for the Sr compds., whereas the exptl. binding energies differ by only 0.35 eV. Thus the simple assumption that the alk. earth element is +2 in all of the compds. results in a significant difference between calcd. and obsd. shifts. The results clearly indicate that CaH2 is a strongly ionic solid.
91. 91
  Demri, B.; Muster, D. XPS Study of Some Calcium Compounds J. Mater. Process. Technol. 1995, 55, 311– 314 DOI: 10.1016/0924-0136(95)02023-3
  There is no corresponding record for this reference.
92. 92
  Clark, D.; Fok, T.; Roberts, G.; Sykes, R. An Investigation by Electron Spectroscopy for Chemical Analysis of Chemical Treatments of the (100) Surface of n-type InP Epitaxial Layers for Langmuir Film Deposition Thin Solid Films 1980, 70, 261– 283 DOI: 10.1016/0040-6090(80)90367-3
  There is no corresponding record for this reference.
93. 93
  Streubel, P.; Franke, R.; Chassé, T.; Fellenberg, R.; Szargan, R. Chemical State Information from Photoelectron and Auger Electron Lines - Investigation of Potential and Relaxation Effects of Solid Silicon and Phosphorus Compounds J. Electron Spectrosc. Relat. Phenom. 1991, 57, 1– 13 DOI: 10.1016/0368-2048(91)85010-Q
  93
  Chemical state information from photoelectron and Auger electron lines - investigation of potential and relaxation effects of solid silicon and phosphorus compounds
  Streubel, P.; Franke, R.; Chasse, T.; Fellenberg, R.; Szargan, R.
  Journal of Electron Spectroscopy and Related Phenomena (1991), 57 (1), 1-13CODEN: JESRAW; ISSN:0368-2048.
  Measured chem. shifts of photoelectron and Auger electron energies of solid silicon and phosphorus compds. are used for detn. of potential energy and relaxation energy shifts. The trends of these shifts and their dependences on parameters characterizing the chem. bond and on the at. no. are discussed. The trends of relaxation energy shifts for both silicon and phosphorus compds. are the same. However, the trends of potential shifts of these two elements in their compds. are different depending on the at. contribution to the potential effect. The obsd. larger relaxation energy values of the solids in comparison with volatile mols. are caused by the Madelung contribution of higher coordination spheres. Theor. ests. of relaxation energies using an extended version of the Fenske-Hall method and taking into account the charge of the mol. potential term give an excellent correlation with exptl. values. The Shirley approach for detn. of potential energy and relaxation energy shifts proves to be a sensitive method for describing electronic changes when atoms combine to form mols. or solids. It is able to distinguish between the at. term and the surroundings term (Madelung term) of the chem. shift.
94. 94
  Dolgonos, A.; Mason, T. O.; Poeppelmeier, K. R. Direct Optical Band Gap Measurement in Polycrystalline Semiconductors: A Critical Look at the Tauc Method J. Solid State Chem. 2016, 240, 43– 48 DOI: 10.1016/j.jssc.2016.05.010
  94
  Direct optical band gap measurement in polycrystalline semiconductors: A critical look at the Tauc method
  Dolgonos, Alex; Mason, Thomas O.; Poeppelmeier, Kenneth R.
  Journal of Solid State Chemistry (2016), 240 (), 43-48CODEN: JSSCBI; ISSN:0022-4596. (Elsevier B.V.)
  The direct optical band gap of semiconductors is traditionally measured by extrapolating the linear region of the square of the absorption curve to the x-axis, and a variation of this method, developed by Tauc, has also been widely used. The application of the Tauc method to cryst. materials is rooted in misconception-and traditional linear extrapolation methods are inappropriate for use on degenerate semiconductors, where the occupation of conduction band energy states cannot be ignored. A new method is proposed for extg. a direct optical band gap from absorption spectra of degenerately-doped bulk semiconductors. This method was applied to pseudo-absorption spectra of Sn-doped In2O3 (ITO)-converted from diffuse-reflectance measurements on bulk specimens. The results of this anal. were corroborated by room-temp. photoluminescence excitation measurements, which yielded values of optical band gap and Burstein-Moss shift that are consistent with previous studies on In2O3 single crystals and thin films.
95. 95
  Tauc, J.; Grigorovici, R.; Vancu, A. Optical Properties and Electronic Structure of Amorphous Germanium Phys. Status Solidi B 1966, 15, 627– 637 DOI: 10.1002/pssb.19660150224
  95
  Optical properties and electronic structure of amorphous germanium
  Tauc, J.; Grigorovici, R.; Vancu, A.
  Physica Status Solidi (1966), 15 (2), 627-37CODEN: PHSSAK; ISSN:0031-8957.
  The optical consts. of amorphous Ge are detd. for photon energies 0.08-1.6 ev. From 0.08 to 0.5 ev., the absorption is due to k-conserving transitions of holes between the valence bands as in p-type crystals; the spin-orbit splitting is 0.20 and 0.21 ev. in nonannealed and annealed samples, resp. The effective masses of the holes in the 3 bands are 0.49 m (0.43 m), 0.04 m, and 0.08 m. An absorption band is observed below the main absorption edge (at 300°K. the max. of this band is at 0.86 ev.); the absorption in this band increases with increasing temp. This band is due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties, which are considered to be assocd. with vacancies. The absorption edge has the form ω2ε2 ∼ (ℏω - Eg)2 (Eg = 0.88 ev. at 300°K.). This suggests that the optical transitions conserve energy but not k vector, and that the ds. of states near the band extrema have the same energy dependence as in cryst. Ge. A simple theory describing this situation is proposed, and comparison of it with the exptl. results leads to an estimate of the localization of the conduction-band wave functions. 24 references.
96. 96
  Jianmin, L.; Yugeng, Z. The d-d Transition Spectra of Copper (II) Complexes in Different Coordination Environment. Study on Cu(TTA)₂ and Cu₂(sacch)₄(Im)₄ Cryst. Res. Technol. 1991, 26, 331– 337 DOI: 10.1002/crat.2170260316
  There is no corresponding record for this reference.
97. 97
  Zuo, J. M.; Kim, M.; O’Keeffe, M.; Spence, J. C. H. Direct Observation of d-Orbital Holes and Cu-Cu Bonding in Cu₂O Nature 1999, 401, 49– 52 DOI: 10.1038/43403
  97
  Direct observation of d-orbital holes and Cu-Cu bonding in Cu2O
  Zuo, J. M.; Kim, M.; O'Keeffe, M.; Spence, J. C. H.
  Nature (London) (1999), 401 (6748), 49-52CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
  A striking feature of metal oxide chem. is the unusual electronic and chem. behavior of Cu(I) and Ag(I): a case in point is that detailed understanding of Cu-O bonding is essential to the theory of high-temp. copper oxide superconductors. Both cations are usually coordinated in a linear fashion to two oxygens, particularly for Cu(I). In many compds., the Cu(I) and Ag(I) cations also adopt close-packed (and related) configurations with short metal-metal distances that are strongly suggestive of the occurrence of metal-metal bonding despite their formal nd configuration. Such observations have been explained by invoking the participation in bonding of electronic orbitals of higher principal quantum no. - i.e., (n + 1)s and (n + 1)p-accompanied by the creation of d-orbital holes on the metal ion. To test this hypothesis, we have used a recently developed method of quant. convergent-beam electron diffraction combined with X-ray diffraction to map the charge-d. distribution in the simple oxide Cu2O, the results of which we then compare with electronic-structure calcn. We are able to image directly the d holes on the copper atoms, and also demonstrate the existence of Cu-Cu bonding in this compd.
98. 98
  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
  98
  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.
99. 99
  Hahn, U.; Weber, W. Electronic Structure and Chemical-Bonding Mechanism of Cu₃N, Cui₃NPd, and Related Cu(I) Compounds Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 53, 12684 DOI: 10.1103/PhysRevB.53.12684
  There is no corresponding record for this reference.
100. 100
  Orgel, L. Stereochemistry of Metals of the B Sub-Groups. Part I. Ions with Filled & Electron Shells J. Chem. Soc. 1958, 4186– 4190 DOI: 10.1039/jr9580004186
  There is no corresponding record for this reference.
101. 101
  Omata, T.; Nagatani, H.; Suzuki, I.; Kita, M.; Yanagi, H.; Ohashi, N. Wurtzite CuGaO₂: A New Direct and Narrow Band Gap Oxide Semiconductor Applicable as a Solar Cell Absorber J. Am. Chem. Soc. 2014, 136, 3378– 3381 DOI: 10.1021/ja501614n
  101
  Wurtzite CuGaO2: a new direct and narrow band gap oxide semiconductor applicable as a solar cell absorber
  Omata, Takahisa; Nagatani, Hiraku; Suzuki, Issei; Kita, Masao; Yanagi, Hiroshi; Ohashi, Naoki
  Journal of the American Chemical Society (2014), 136 (9), 3378-3381CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  An oxide semiconductor β-CuGaO2 with a wurtzite-derived β-NaFeO2 structure has been synthesized. Structural characterization has been carried out by Rietveld anal. using XRD and SAED, and it was shown that the lattice size is very close to that of zinc oxide. The optical absorption spectrum indicated that the band gap is 1.47 eV, which matches the band gap required to achieve the theor. max. conversion efficiency for a single-junction solar cell. The thermoelectromotive force indicated p-type conduction in its intrinsic state. D. functional theory calcns. were performed to understand the electronic structure and optical properties of the semiconductor. These calcns. indicated that β-CuGaO2 is a direct semiconductor and intense absorption of light occurs near the band edge. These properties render this new material promising as an absorber in solar cells.
102. 102
  Scanlon, D. O.; Walsh, A. Polymorph Engineering of CuMO₂ (M = Al, Ga, Sc, Y) Semiconductors for Solar Energy Applications: From Delafossite to Wurtzite Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2015, 71, 702– 706 DOI: 10.1107/S2052520615018387
  102
  Polymorph engineering of CuMO2 (M = Al, Ga, Sc, Y) semiconductors for solar energy applications: from delafossite to wurtzite
  Scanlon, David O.; Walsh, Aron
  Acta Crystallographica, Section B: Structural Science, Crystal Engineering and Materials (2015), 71 (6), 702-706CODEN: ACSBDA; ISSN:2052-5206. (International Union of Crystallography)
  The cuprous oxide based ternary delafossite semiconductors have been well studied in the context of p-type transparent conducting oxides. CuAlO2, CuGaO2 and CuInO2 represent a homologous series where the electronic properties can be tuned over a large range. The optical transparency of these materials has been assocd. with dipole forbidden transitions, which are related to the linear O-Cu-O coordination motif. The recent demonstration that these materials can be synthesized in tetrahedral structures (wurtzite analogs of the chalcopyrite lattice) opens up a new vista of applications. We investigate the underlying structure-property relationships (for Group 3 and 13 metals), from the perspective of first-principles materials modeling, towards developing earth-abundant photoactive metal oxides. All materials studied possess indirect fundamental band gaps ranging from 1 to 2 eV, which are smaller than their delafossite counterparts, although in all cases the difference between direct and indirect band gaps is less than 0.03 eV.
103. 103
  Arnold, T. X-ray Spectroscopic Study of the Electronic Structure of CuCrO 2 Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 075102 DOI: 10.1103/PhysRevB.79.075102
  There is no corresponding record for this reference.
104. 104
  Shin, D. Comparative Study of Bandwidths in Copper Delafossites from X-ray Emission Spectroscopy Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 233105 DOI: 10.1103/PhysRevB.80.233105
  There is no corresponding record for this reference.
105. 105
  Scanlon, D. O.; Walsh, A.; Morgan, B. J.; Watson, G. W.; Payne, D. J.; Egdell, R. G. Effect of Cr Substitution on the Electronic Structure of CuAl_1–xCr_xO₂ Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 035101 DOI: 10.1103/PhysRevB.79.035101
  105
  Effect of Cr substitution on the electronic structure of CuAl1-xCrxO2
  Scanlon, David O.; Walsh, Aron; Morgan, Benjamin J.; Watson, Graeme W.; Payne, David J.; Egdell, Russell G.
  Physical Review B: Condensed Matter and Materials Physics (2009), 79 (3), 035101/1-035101/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
  The geometries and electronic structures of CuAl1-xCrxO2 have been investigated using d.-functional theory with on-site corrections for strongly correlated systems (GGA + U) for x = 0, 0.5, and 1. Al is found to be well described within the ionic model, with a valence charge corresponding to a +3 oxidn. state. Substituting Cr for Al is predicted to increase the d. of states at the top of the valence band, in agreement with exptl. x-ray photoemission spectroscopy data. Anal. of atom-projected densities of states and valence charges suggests that this is due to increased covalency between Cr and O; the valence charge for O in the Cu-O-(Al,Cr) subunits changes from -1.74 to ∼-1.25 when Cr replaces Al. This produces an indirect oxygen-mediated change to the Cu d states.
106. 106
  Tossell, J. A.; Vaughan, D. J. Relationships Between Valence Orbital Binding Energies and Crystal Structures in Compounds of Copper, Silver, Gold, Zinc, Cadmium, and Mercury Inorg. Chem. 1981, 20, 3333– 3340 DOI: 10.1021/ic50224a038
  There is no corresponding record for this reference.
107. 107
  Gaudin, E. Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments J. Solid State Chem. 2001, 160, 212– 221 DOI: 10.1006/jssc.2001.9225
  107
  Some Factors Governing Ag+ and Cu+ Low Coordination in Chalcogenide Environments
  Gaudin, Etienne; Boucher, Florent; Evain, Michel
  Journal of Solid State Chemistry (2001), 160 (1), 212-221CODEN: JSSCBI; ISSN:0022-4596. (Academic Press)
  The factors influencing the low coordination of Cu+ and Ag+ d10 cations in chalcogenides were analyzed by means of FLAPW band structure calcns. The metal s/d orbital mixing is the predominant factor, in agreement with most previous research reports. The d10 cation polarization is reduced when the chalcogen electronegativity decreases, thus the coordination increases when going from the oxides to the tellurides. The calcn. results make clear the fact that the d10 element low coordination can be raised for a given chalcogen by enhancing the polarization influence of the chalcogen through a charge transfer from an alkali metal. The shift in behavior from Cu+ to Ag+ is shown to be related to their different polarizabilities. (c) 2001 Academic Press.
108. 108
  Savelsberg, G.; Schäfer, H. Ternäre Pnictide und Chalkogenide von Alkalimetallen und IB-bzw Z. Naturforsch., B: J. Chem. Sci. 1978, 33, 370– 373 DOI: 10.1515/znb-1978-0705
  108
  Ternary pnictides and chalcogenides of alkali metals and Group IB and IIB elements
  Savelsberg, Gerhard; Schaefer, Herbert
  Zeitschrift fuer Naturforschung, Teil B: Anorganische Chemie, Organische Chemie (1978), 33B (4), 370-3CODEN: ZNBAD2; ISSN:0340-5087.
  NaCuSe, NaCuTe, KCuSe, KCuTe, and KZnP were prepd. and their structures - together with those of KZnSb, NaCdSb, and NaZnSb - detd. NaCuSe, NaCuTe, and NaZnSb crystallize in a PbFCl type, while NaCdSb forms the anti-PbCl2-structure, KCuSe, KCuTe, KZnP, and KZnSb have the Ni2In-structure. The lattice parameters of the 8 compds. are given. The structures were refined to final R's = 0.061-0.085.
109. 109
  Buckeridge, J.; Butler, K. T.; Catlow, C. R. A.; Logsdail, A. J.; Scanlon, D. O.; Shevlin, S. A.; Woodley, S. M.; Sokol, A. A.; Walsh, A. Polymorph Engineering of TiO₂: Demonstrating how Absolute Reference Potentials are Determined by Local Coordination Chem. Mater. 2015, 27, 3844– 3851 DOI: 10.1021/acs.chemmater.5b00230
  109
  Polymorph Engineering of TiO2: Demonstrating How Absolute Reference Potentials Are Determined by Local Coordination
  Buckeridge, John; Butler, Keith T.; Catlow, C. Richard A.; Logsdail, Andrew J.; Scanlon, David O.; Shevlin, Stephen A.; Woodley, Scott M.; Sokol, Alexey A.; Walsh, Aron
  Chemistry of Materials (2015), 27 (11), 3844-3851CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  We report that the valence and conduction band energies of TiO2 can be tuned over a 4 eV range by varying the local coordination environments of Ti and O. We examine the electronic structure of eight known polymorphs and align their ionization potential and electron affinity relative to an abs. energy ref., using an accurate multiscale quantum-chem. approach. For applications in photocatalysis, we identify the optimal combination of phases to enhance activity in the visible spectrum. The results provide a coherent explanation for a wide range of phenomena, including the performance of TiO2 as an anode material for Li-ion batteries, allow us to pinpoint hollandite TiO2 as a new candidate transparent conducting oxide, and serve as a guide to improving the efficiency of photo-electrochem. water splitting through polymorph engineering of TiO2.
110. 110
  Burbano, M.; Scanlon, D. O.; Watson, G. W. Sources of Conductivity and Doping Limits in CdO from Hybrid Density Functional Theory J. Am. Chem. Soc. 2011, 133, 15065– 15072 DOI: 10.1021/ja204639y
  110
  Sources of Conductivity and Doping Limits in CdO from Hybrid Density Functional Theory
  Burbano, Mario; Scanlon, David O.; Watson, Graeme W.
  Journal of the American Chemical Society (2011), 133 (38), 15065-15072CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  CdO has been studied for decades as a prototypical wide band gap transparent conducting oxide with excellent n-type ability. Despite this, uncertainty remains over the source of cond. in CdO and over the lack of p-type CdO, despite its valence band max. (VBM) being high with respect to other wide band gap oxides. In this article, we use screened hybrid DFT to study intrinsic defects and hydrogen impurities in CdO and identify for the first time the source of charge carriers in this system. We explain why the oxygen vacancy in CdO acts as a shallow donor and does not display neg.-U behavior similar to all other wide band gap n-type oxides. We also demonstrate that p-type CdO is not achievable, as n-type defects dominate under all growth conditions. Lastly, we est. theor. doping limits and explain why CdO can be made transparent by a large Moss-Burstein shift caused by suitable n-type doping.
111. 111
  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
  111
  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.
112. 112
  Aksit, M.; Kolli, S. K.; Slauch, I. M.; Robinson, R. D. Misfit Layered Ca₃Co₄O₉ as a High Figure of Merit p-Type Transparent Conducting Oxide Film Through Solution Processing Appl. Phys. Lett. 2014, 104, 161901 DOI: 10.1063/1.4871506
  112
  Misfit layered Ca3Co4O9 as a high figure of merit p-type transparent conducting oxide film through solution processing
  Aksit, M.; Kolli, S. K.; Slauch, I. M.; Robinson, R. D.
  Applied Physics Letters (2014), 104 (16), 161901/1-161901/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  Ca3Co4O9 thin films synthesized through soln. processing are shown to be high-performing, p-type transparent conducting oxides (TCOs). The synthesis method is a cost-effective and scalable process that consists of sol-gel chem., spin coating, and heat treatments. The process parameters can be varied to produce TCO thin films with sheet resistance as low as 5.7 kΩ/sq (ρ ≈ 57 mΩ cm) or with av. visible range transparency as high as 67%. The most conductive Ca3Co4O9 TCO thin film has near IR region optical transmission as high as 85%. The figure of merit (FOM) for the top-performing Ca3Co4O9 thin film (151 MΩ-1) is higher than FOM values reported in the literature for all other soln. processed, p-type TCO thin films and higher than most others prepd. by phys. vapor deposition and chem. vapor deposition. Transparent cond. in misfit layered oxides presents new opportunities for TCO compns. (c) 2014 American Institute of Physics.
113. 113
  Arca, E.; Fleischer, K.; Shvets, I. V. Magnesium, Nitrogen Codoped Cr₂O₃: A p-Type Transparent Conducting Oxide Appl. Phys. Lett. 2011, 99, 111910 DOI: 10.1063/1.3638461
  113
  Magnesium, nitrogen codoped Cr2O3: A p-type transparent conducting oxide
  Arca, E.; Fleischer, K.; Shvets, I. V.
  Applied Physics Letters (2011), 99 (11), 111910/1-111910/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  A p-type transparent conductive oxide (TCO) was synthesized by codoping of poorly conducting chromium oxide (Cr2O3) with magnesium and nitrogen. The codoping produced a TCO with good figure of merit despite using spray pyrolysis for deposition. The nitrogen enhances the specular transparency of the films in the visible range (400-700 nm), and Mg improves the cond. while retaining the p-type character of the material. Co-doping with both elements produces a p-type oxide with a low resistivity of 3 Ω cm and transmission up to 65% for a 150. nm thick film. A comparison with other known p-type materials is given. (c) 2011 American Institute of Physics.
114. 114
  Wei, R.; Tang, X.; Hu, L.; Hui, Z.; Yang, J.; Luo, H.; Luo, X.; Dai, J.; Song, W.; Yang, Z.; Zhu, X.; Sun, Y. Transparent Conducting p-Type Thin Films of c-Axis Self-Oriented Bi₂Sr₂Co₂O_y with High Figure of Merit Chem. Commun. 2014, 50, 9697 DOI: 10.1039/C4CC03800B
  There is no corresponding record for this reference.
115. 115
  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 a New p-Type Transparent Conducting Oxide Adv. Mater. 2015, 27, 5191– 5195 DOI: 10.1002/adma.201501959
  There is no corresponding record for this reference.
116. 116
  Palgrave, R. G.; Borisov, P.; Dyer, M. S.; McMitchell, S. R. C.; Darling, G. R.; Claridge, J. B.; Batuk, M.; Tan, H.; Tian, H.; Verbeeck, J.; Hadermann, J.; Rosseinsky, M. J. Artificial Construction of the Layered Ruddlesden–Popper Manganite La₂Sr₂Mn₃O₁₀ Reflection High Energy Electron Diffraction Monitored Pulsed Laser Deposition J. Am. Chem. Soc. 2012, 134, 7700– 7714 DOI: 10.1021/ja211138x
  There is no corresponding record for this reference.
117. 117
  Haeni, J. H.; Theis, C. D.; Schlom, D. G.; Tian, W.; Pan, X. Q.; Chang, H.; Takeuchi, I.; Xiang, X.-D. Epitaxial Growth of the First Five Members of the Sr_n+1Ti_nO_3n+1 Ruddlesden-Popper Homologous Series Appl. Phys. Lett. 2001, 78, 3292 DOI: 10.1063/1.1371788
  117
  Epitaxial growth of the first five members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series
  Haeni, J. H.; Theis, C. D.; Schlom, D. G.; Tian, W.; Pan, X. Q.; Chang, H.; Takeuchi, I.; Xiang, X.-D.
  Applied Physics Letters (2001), 78 (21), 3292-3294CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  The 1st five members of the Srn+1TinO3n+1 Ruddlesden-Popper homologous series, i.e., Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, Sr5Ti4O13, and Sr6Ti5O16, were grown by reactive MBE. A combination of at. absorption spectroscopy and RHEED intensity oscillations were used for the strict compn. control necessary for the synthesis of these phases. X-ray diffraction and high-resoln. transmission electron microscope images confirm that these films are epitaxially oriented and nearly free of intergrowths. Dielec. measurements indicate that the dielec. const. tensor coeff. ε33 increases from a min. of 44 ± 4 in the n = 1(Sr2TiO4) film to a max. of 263 ± 2 in the n = ∞(SrTiO3) film.
118. 118
  Tian, W.; Pan, X. Q.; Haeni, J. H.; Schlom, D. G. Transmission Electron Microscopy Study of n = 1–5 Sr_n+1Ti_nO_3n+1 Epitaxial Thin Films J. Mater. Res. 2001, 16, 2013– 2026 DOI: 10.1557/JMR.2001.0276
  118
  Transmission electron microscopy study of n = 1-5 Srn+1TinO3n+1 epitaxial thin films
  Tian, W.; Pan, X. Q.; Haeni, J. H.; Schlom, D. G.
  Journal of Materials Research (2001), 16 (7), 2013-2026CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)
  Epitaxial Srn+1TinO3n+1 thin films with n = 1-5 were synthesized on (001) SrTiO3 substrates by reactive MBE. The structure and microstructure of the films were studied by x-ray diffraction, transmission electron microbeam diffraction, and high-resoln. TEM (HRTEM) in combination with computer image simulations. Both diffraction and HRTEM studies revealed that all the films are epitaxially oriented with their c axis perpendicular to the (001) SrTiO3 plane of the substrate. Detailed studies using quant. HRTEM methods indicated that the films have the expected n = 1-5 structures of the Ruddlesden-Popper Srn+1TinO3n+1 homologous series. Among these films, Sr2TiO4, Sr3Ti2O7, and Sr4Ti3O10 thin films are nearly free of intergrowths, while Sr5Ti4O13 and Sr6Ti5O16 thin films contain noticeably more antiphase boundaries in their perovskite sheets and intergrowth defects. The authors show that these results are consistent with what is known about the thermodn. of Srn+1TinO3n+1 phases.
119. 119
  Johnson, R. W.; Hultqvist, A.; Bent, S. F. A Brief Review of Atomic Layer Deposition: from Fundamentals to Applications Mater. Today 2014, 17, 236– 246 DOI: 10.1016/j.mattod.2014.04.026
  119
  A brief review of atomic layer deposition: from fundamentals to applications
  Johnson, Richard W.; Hultqvist, Adam; Bent, Stacey F.
  Materials Today (Oxford, United Kingdom) (2014), 17 (5), 236-246CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
  A review. Atomic layer deposition (ALD) is a vapor phase technique capable of producing thin films of a variety of materials. Based on sequential, self-limiting reactions, ALD offers exceptional conformality on high-aspect ratio structures, thickness control at the Angstrom level, and tunable film compn. With these advantages, ALD has emerged as a powerful tool for many industrial and research applications. In this review, we provide a brief introduction to ALD and highlight select applications, including Cu(In,Ga)Se2 solar cell devices, high-k transistors, and solid oxide fuel cells. These examples are chosen to illustrate the variety of technologies that are impacted by ALD, the range of materials that ALD can deposit - from metal oxides such as Zn1-xSnxOy, ZrO2, Y2O3, to noble metals such as Pt - and the way in which the unique features of ALD can enable new levels of performance and deeper fundamental understanding to be achieved.
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  Hiramatsu, H.; Ueda, K.; Ohta, H.; Orita, M.; Hirano, M.; Hosono, H. Heteroepitaxial Growth of a Wide-Gap p-Type Semiconductor, LaCuOS Appl. Phys. Lett. 2002, 81, 598 DOI: 10.1063/1.1494853
  120
  Heteroepitaxial growth of a wide-gap p-type semiconductor, LaCuOS
  Hiramatsu, Hidenori; Ueda, Kazushige; Ohta, Hiromichi; Orita, Masahiro; Hirano, Masahiro; Hosono, Hideo
  Applied Physics Letters (2002), 81 (4), 598-600CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
  High-quality epitaxial films of LaCuOS, a wide-gap p-type semiconductor, are grown on yittria-stabilized-zirconia (001) or MgO (001) single-crystal substrates by a unique method. Postannealing of a bilayer film composed of an extremely thin metallic copper layer and an amorphous LaCuOS layer at 1000° results in an epitaxially grown LaCuOS thin film. This thin copper layer with high orientation, which likely acts as an epitaxial initiator, is essential for epitaxial growth. The resulting epitaxial films exhibit relatively intense UV emission assocd. with excitons at room temp., confirming the high crystal quality of the films.
121. 121
  Su, G.; Hadjiev, V. G.; Loya, P. E.; Zhang, J.; Lei, S.; Maharjan, S.; Dong, P.; Ajayan, P. M.; Lou, J.; Peng, H. Chemical Vapor Deposition of Thin Crystals of Layered Semiconductor SnS₂ for Fast Photodetection Application Nano Lett. 2015, 15, 506– 513 DOI: 10.1021/nl503857r
  121
  Chemical Vapor Deposition of Thin Crystals of Layered Semiconductor SnS2 for Fast Photodetection Application
  Su, Guoxiong; Hadjiev, Viktor G.; Loya, Phillip E.; Zhang, Jing; Lei, Sidong; Maharjan, Surendra; Dong, Pei; M. Ajayan, Pulickel; Lou, Jun; Peng, Haibing
  Nano Letters (2015), 15 (1), 506-513CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
  Layered two-dimensional (2D) semiconductors, such as MoS2 and SnS2, have been receiving intensive attention due to their technol. importance for the next-generation electronic/photonic applications. We report a novel approach to the controlled synthesis of thin crystal arrays of SnS2 at predefined locations on chip by chem. vapor deposition with seed engineering and have demonstrated their application as fast photodetectors with photocurrent response time ∼5 μs. This opens a pathway for the large-scale prodn. of layered 2D semiconductor devices, important for applications in integrated nanoelectronic/photonic systems.

Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors
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Chemistry of Materials

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Abstract

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SPECIAL ISSUE

Introduction

Figure 1

Computational Methodology

Experimental Methodology

Results

Figure 2

Figure 3

Figure 4

Experimental Results

Figure 5

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Figure 7

Discussion

Conclusions

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Acknowledgment

References

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Abstract

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Engineering Valence Band Dispersion for High Mobility p-Type SemiconductorsClick to copy article linkArticle link copied!

Chemistry of Materials

Abstract

SPECIAL ISSUE

Introduction

Figure 1

Computational Methodology

Experimental Methodology

Results

Figure 2

Figure 3

Figure 4

Experimental Results

Figure 5

Figure 6

Figure 7

Discussion

Conclusions

Author Information

Acknowledgment

References

Cited By

Chemistry of Materials

Article Views

Altmetric

Citations

Recommended Articles

Abstract

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

References

Engineering Valence Band Dispersion for High Mobility p-Type Semiconductors
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