Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors
- Jack E. N. SwallowJack E. N. SwallowStephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, U.K.Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K.More by Jack E. N. Swallow
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- Robert G. PalgraveRobert G. PalgraveDepartment of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.More by Robert G. Palgrave
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- Philip A. E. MurgatroydPhilip A. E. MurgatroydStephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, U.K.More by Philip A. E. Murgatroyd
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- Anna RegoutzAnna RegoutzDepartment of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.More by Anna Regoutz
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- Michael LorenzMichael LorenzFelix Bloch Institute for Solid State Physics, Universität Leipzig, Leipzig, GermanyMore by Michael Lorenz
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- Anna HassaAnna HassaFelix Bloch Institute for Solid State Physics, Universität Leipzig, Leipzig, GermanyMore by Anna Hassa
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- Marius GrundmannMarius GrundmannFelix Bloch Institute for Solid State Physics, Universität Leipzig, Leipzig, GermanyMore by Marius Grundmann
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- Holger von WencksternHolger von WencksternFelix Bloch Institute for Solid State Physics, Universität Leipzig, Leipzig, GermanyMore by Holger von Wenckstern
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- Joel B. VarleyJoel B. VarleyLawrence Livermore National Laboratory, Livermore, California 94550, United StatesMore by Joel B. Varley
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- Tim D. Veal*Tim D. Veal*Email: [email protected]Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 7ZF, U.K.More by Tim D. Veal
Abstract
The electronic and optical properties of (InxGa1–x)2O3 alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ x ≤ 0.82) and three crystallographic phases (monoclinic, hexagonal, and bixbyite). The optical gaps over this composition range are determined, and only a weak optical gap bowing is found (b = 0.36 eV). The valence band edge evolution along with the change in the fundamental band gap over the composition gradient enables the surface space-charge properties to be probed. This is an important property when considering metal contact formation and heterojunctions for devices. A transition from surface electron accumulation to depletion occurs at x ∼ 0.35 as the film goes from the bixbyite In2O3 phase to the monoclinic β-Ga2O3 phase. The electronic structure of the different phases is investigated by using density functional theory calculations and compared to the valence band X-ray photoemission spectra. Finally, the properties of these alloys, such as the n-type dopability of In2O3 and use of Ga2O3 as a solar-blind UV detector, are understood with respect to other common-cation compound semiconductors in terms of simple chemical trends of the band edge positions and the hydrostatic volume deformation potential.
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License Summary*
You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
Creative Commons (CC): This is a Creative Commons license.
Attribution (BY): Credit must be given to the creator.
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1. Introduction
2. Methods
2.1. Experimental Details
2.2. Computational Details
3. Results and Discussion
3.1. Structure and Composition
3.2. Valence Band X-ray Photoelectron Spectroscopy (XPS)
3.3. Surface Space Charge
3.4. Electronic Structure
4. Chemical Trends in Common-Cation Materials
Ga2O3 | GaN | GaP | GaAs | GaSb | In2O3 | InN | InP | InAs | InSb | InGaO3 | |
---|---|---|---|---|---|---|---|---|---|---|---|
α (%) | 32 | 28 | 28 | 32 | 33 | 28 | 25 | 26 | 29 | 30 | 32 |
EBP (eV) | 4.06 | 2.38 | 0.68 | 0.42 | –0.11 | 3.39 | 1.65 | 0.75 | 0.47 | 0.04 | 3.79 |
EgΓ (eV) | 4.85 | 3.46 | 2.90 | 1.53 | 0.82 | 2.86 | 0.73 | 1.42 | 0.41 | 0.22 | 4.13 |
B0 (kbar) | 1844 | 2003 | 885 | 751 | 552 | 1715 | 1423 | 696 | 596 | 455 | 2026 |
volume (Å3) | 104.31 | 45.20 | 40.62 | 45.62 | 57.78 | 522.24 | 62.10 | 51.36 | 56.88 | 70.23 | 113.99 |
V/atom (Å3) | 10.43 | 11.30 | 20.31 | 22.81 | 28.89 | 13.06 | 15.52 | 25.68 | 28.44 | 35.11 | 11.40 |
aVΓ (eV) | –8.66 | –7.82 | –9.08 | –8.54 | –8.46 | –6.34 | –4.04 | –6.14 | –5.92 | –6.77 | –8.70 |
aVΓ,c (eV) | –4.96 | –6.48 | –9.86 | –8.86 | –9.27 | –3.70 | –3.23 | –6.33 | –6.66 | –7.79 | –5.43 |
aVΓ,v (eV) | 3.70 | 1.34 | –0.78 | –0.32 | –0.81 | 2.64 | 0.81 | –0.19 | –0.73 | –1.02 | 3.27 |
The band edge deformation potentials were determined by using the branch-point energy (EBP, defined relative to each material’s VBM) as a reference level, as described in the text. The α parameter represents the fraction of Hartree–Fock exact exchange incorporated into the HSE06 range-separated hybrid functional, which was tuned to reproduce the experimental band gaps.
5. Conclusion
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.0c16021.
XPS core levels and associated analysis, optical transmission and absorption spectra, XPS semicore levels, DFT of semicore levels accounting for SOC, DFT calculated band gap deformation potentials (PDF)
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Acknowledgments
J.E.N.S. acknowledges funding through the Engineering and Physical Sciences Research Council (EPSRC) Centre for Doctoral Training in New and Sustainable Photovoltaics (EP/L01551X/1). James Gibbon is acknowledged for preliminary analysis of the photoemission data. T.D.V. acknowledges funding from EPSRC Grant EP/N015800/1. P.A.E.M. acknowledges undergraduate vacation bursary funding from the EPSRC. This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. This work was also supported by the Air Force Office of Scientific Research under Award FA9550-18-1-0024.
References
This article references 73 other publications.
- 1Walsh, A.; Da Silva, J. L. F.; Wei, S.-H.; Korber, C.; Klein, A.; Piper, L. F. J.; DeMasi, A.; Smith, K. E.; Panaccione, G.; Torelli, P.; Payne, D. J.; Bourlange, A.; Egdell, R. G. Nature of the Band Gap of In2O3 Revealed by First-Principles Calculations and X-Ray Spectroscopy. Phys. Rev. Lett. 2008, 100, 167402, DOI: 10.1103/PhysRevLett.100.167402Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXltFOlurw%253D&md5=913b840052042078c7bf8442f03bddbbNature of the Band Gap of In2O3 Revealed by First-Principles Calculations and X-Ray SpectroscopyWalsh, Aron; Da Silva, Juarez L. F.; Wei, Su-Huai; Korber, C.; Klein, A.; Piper, L. F. J.; DeMasi, Alex; Smith, Kevin E.; Panaccione, G.; Torelli, P.; Payne, D. J.; Bourlange, A.; Egdell, R. G.Physical Review Letters (2008), 100 (16), 167402/1-167402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for In2O3 is found significantly closer to the bottom of the conduction band than expected from the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of In2O3 exhibit a small dispersion and the conduction band min. is positioned at Γ. However, direct optical transitions give a minimal dipole intensity until 0.8 eV below the valence band max. The results set an upper limit on the fundamental band gap of 2.9 eV.
- 2Ellmer, K. Past Achievements and Future Challenges in the Development of Optically Transparent Electrodes. Nat. Photonics 2012, 6, 809– 817, DOI: 10.1038/nphoton.2012.282Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCntLzF&md5=9387299074a07fd9aa9f35c7f70d9867Past achievements and future challenges in the development of optically transparent electrodesEllmer, KlausNature Photonics (2012), 6 (12), 809-817CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Transparent conductive electrodes play important roles in information and energy technologies. These materials, particularly transparent conductive oxides, are widely used as transparent electrodes across tech. fields such as low-emissivity coatings, flat-panel displays, thin-film solar cells and org. light-emitting diodes. This Review begins by summarizing the properties and applications of transparent conductive oxides such as In2O3, SnO2, ZnO and TiO2. Owing to the increasing demand for raw materials - esp. indium - scientists are currently searching for alternatives to indium tin oxide. Carbon nanotube and metal nanowire networks, as well as regular metal grids, have been investigated for use as transparent conductive electrodes. This Review compares these materials and the recently 'rediscovered' graphene with today's established transparent conductive oxides.
- 3Pearton, S. J.; Yang, J.; Cary, P. H.; Ren, F.; Kim, J.; Tadjer, M. J.; Mastro, M. A. A Review of Ga2O3 Materials, Processing, and Devices. Appl. Phys. Rev. 2018, 5, 011301, DOI: 10.1063/1.5006941Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotFSgsw%253D%253D&md5=145f298a1ae45c7ab9dcf874b84fc732A review of Ga2O3 materials, processing, and devicesPearton, S. J.; Yang, Jiancheng; Cary, Patrick H.; Ren, F.; Kim, Jihyun; Tadjer, Marko J.; Mastro, Michael A.Applied Physics Reviews (2018), 5 (1), 011301/1-011301/56CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)A review. Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (ε) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. The performance of technol. important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger crit. elec. field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielecs. for gate formation, and passivation are discussed. (c) 2018 American Institute of Physics.
- 4Lorenz, M. The 2016 Oxide Electronic Materials and Oxide Interfaces Roadmap. J. Phys. D: Appl. Phys. 2016, 49, 433001, DOI: 10.1088/0022-3727/49/43/433001Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1anu7Y%253D&md5=19f887f4fb5274766b5c1d20f992f000The 2016 oxide electronic materials and oxide interfaces roadmapLorenz, M.; Rao, M. S. Ramachandra; Venkatesan, T.; Fortunato, E.; Barquinha, P.; Branquinho, R.; Salgueiro, D.; Martins, R.; Carlos, E.; Liu, A.; Shan, F. K.; Grundmann, M.; Boschker, H.; Mukherjee, J.; Priyadarshini, M.; DasGupta, N.; Rogers, D. J.; Teherani, F. H.; Sandana, E. V.; Bove, P.; Rietwyk, K.; Zaban, A.; Veziridis, A.; Weidenkaff, A.; Muralidhar, M.; Murakami, M.; Abel, S.; Fompeyrine, J.; Zuniga-Perez, J.; Ramesh, R.; A. Spaldin, N.; Ostanin, S.; Borisov, V.; Mertig, I.; Lazenka, V.; Srinivasan, G.; Prellier, W.; Uchida, M.; Kawasaki, M.; Pentcheva, R.; Gegenwart, P.; Granozio, F. Miletto; Fontcuberta, J. PrydsJournal of Physics D: Applied Physics (2016), 49 (43), 433001/1-433001/53CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)A review. Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addn. to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-vol. ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelecs., piezoelecs., power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theor. considerations behind both present and future applications in many technol. important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topol. oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chem., which even after many years of very successful development shows in short intervals novel insights and achievements.
- 5Gonçalves, G.; Barquinha, P.; Pereira, L.; Franco, N.; Alves, E.; Martins, R.; Fortunato, E. High Mobility a-IGO Films Produced at Room Temperature and Their Application in TFTs. Electrochem. Solid-State Lett. 2010, 13, H20– H22, DOI: 10.1149/1.3257613Google ScholarThere is no corresponding record for this reference.
- 6Huang, W.-L.; Hsu, M.-H.; Chang, S.-P.; Chang, S.-J.; Chiou, Y.-Z. Indium Gallium Oxide Thin Film Transistor for Two-Stage UV Sensor Application. ECS J. Solid State Sci. Technol. 2019, 8, Q3140– Q3143, DOI: 10.1149/2.0251907jssGoogle Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVymtL7P&md5=acfd81d9893fb64c7bdba196d02753bcIndium gallium oxide thin film transistor for two-stage UV sensor applicationHuang, Wei-Lun; Hsu, Ming-Hung; Chang, Sheng-Po; Chang, Shoou-Jinn; Chiou, Yu-ZungECS Journal of Solid State Science and Technology (2019), 8 (7), Q3140-Q3143CODEN: EJSSBG; ISSN:2162-8769. (Electrochemical Society)In this work, indium gallium oxide (IGO) thin film transistor (TFT) was fabricated by radio-frequency (RF) sputtering. The transmittance of the TFT shows larger than 80% cross the visible light region. As a wide bandgap and high transparency semiconducting material, IGO is a potential candidate for UV-detection applications.Measured in the dark, the IGO TFT exhibits a threshold voltage of 0.9 V, mobility of 2.66 cm2/Vs, on-off ratio of 1.21×106, subthreshold swing of 0.41 V/dec. The TFT was then employed to detect UV light and the sensing properties are investigated. The IGO phototransistor has a high responsivity of 5.012 A/W and a rejection ratio of 1.65×105. The above results reveal that IGO phototransistor is a brilliant multi-functional device, which can serve as either a switch component or a UV sensor.
- 7Kim, Y. G.; Kim, T.; Avis, C.; Lee, S.-H.; Jang, J. Stable and High-Performance Indium Oxide Thin-Film Transistor by Ga Doping. IEEE Trans. Electron Devices 2016, 63, 1078– 1084, DOI: 10.1109/TED.2016.2518703Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFerurnE&md5=5ce5baba01d5548be4d5da1f36b7593aStable and high-performance indium oxide thin-film transistor by Ga dopingKim, Youn Goo; Kim, Taehun; Avis, Christophe; Lee, Seung-Hun; Jang, JinIEEE Transactions on Electron Devices (2016), 63 (3), 1078-1084CODEN: IETDAI; ISSN:0018-9383. (Institute of Electrical and Electronics Engineers)Research on a replacement of amorphous silicon for a thin-film transistor (TFT) and large area electronics has been driven by costly vacuum processed indium-gallium-zinc oxide (IGZO). Even though widely studied, the performances still require improvement, and a wide no. of other materials have been tested. While indium-zinc oxide, IGZO, indium-zinc-tin oxide (ZTO), and ZTO have been widely investigated, gallium-doped indium oxide (IGO) has not been under highlight. Here, we report the use of simple and cost effective spin-coated IGO TFT using spin-coated AlOx gate dielec. We achieved high mobility over 50 cm2/Vs and high stability. The thin films are studied by transmission electron microscopy, X-ray diffraction, XPS, Raman spectra, at. force microscopy, and field-effect measurements. Analyses reveal the strong dependence between crystallinity, mobility, and stability. All TFTs show excellent operation, with champion characteristics for the 10% Ga-doped InOx, revealing a mobility of 52.6 cm2/Vs, on/off ratios of 108, and VTH variation of <0.1 V during 1 h of stress measurement.
- 8von Wenckstern, H.; Splith, D.; Werner, A.; Müller, S.; Lorenz, M.; Grundmann, M. Properties of Schottky Barrier Diodes on (InxGa1-x)2O3 for 0.01 ≤ x ≤ 0.85 Determined by a Combinatorial Approach. ACS Comb. Sci. 2015, 17, 710– 715, DOI: 10.1021/acscombsci.5b00084Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs12qurrL&md5=a25f1c78c7e6baa196aab19a87c779acProperties of Schottky Barrier Diodes on (InxGa1-x)2O3 for 0.01 ≤ x ≤ 0.85 Determined by a Combinatorial Approachvon Wenckstern, H.; Splith, D.; Werner, A.; Mueller, S.; Lorenz, M.; Grundmann, M.ACS Combinatorial Science (2015), 17 (12), 710-715CODEN: ACSCCC; ISSN:2156-8944. (American Chemical Society)We investigated properties of an (InxGa1-x)2O3 thin film with laterally varying cation compn. that was realized by a large-area offset pulsed laser deposition approach. Within a two inch diam. thin film, the compn. varies between 0.01 ≤ x ≤ 0.85, and three crystallog. phases (cubic, hexagonal, and monoclinic) were identified. We obsd. a correlation between characteristic parameters of Schottky barrier diodes fabricated on the thin film and its chem. and structural material properties. The highest Schottky barriers and rectification of the diodes were found for low indium contents. The thermal stability of the diodes is also best for Ga-rich parts of the sample. Conversely, the series resistance is lowest for large In content. Overall, the (InxGa1-x)2O3 alloy is well-suited for potential applications such as solar-blind photodetectors with a tunable absorption edge.
- 9Kranert, C.; Lenzner, J.; Jenderka, M.; Lorenz, M.; von Wenckstern, H.; Schmidt-Grund, R.; Grundmann, M. Lattice Parameters and Raman-active Phonon Modes of (InxGa1-x)2O3 for x < 0.4. J. Appl. Phys. 2014, 116, 013505, DOI: 10.1063/1.4886895Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSlsr%252FM&md5=75ddadbd64a9e62b9589aa3465d77273Lattice parameters and Raman-active phonon modes of (InxGa1-x)2O3 for x < 0.4Kranert, Christian; Lenzner, Joerg; Jenderka, Marcus; Lorenz, Michael; von Wenckstern, Holger; Schmidt-Grund, Ruediger; Grundmann, MariusJournal of Applied Physics (Melville, NY, United States) (2014), 116 (1), 013505/1-013505/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We present X-ray diffraction and Raman spectroscopy investigations of (InxGa1-x)2O3 thin films and bulk-like ceramics in dependence of their compn. The thin films grown by pulsed laser deposition have a continuous lateral compn. spread allowing the detn. of phonon mode properties and lattice parameters with high sensitivity to the compn. from a single 2-in. wafer. In the regime of low indium concn., the phonon energies depend linearly on the compn. and show a good agreement between both sample types. We detd. the slopes of these dependencies for eight different Raman modes. While the lattice parameters of the ceramics follow Vegard's rule, deviations are obsd. for the thin films. Further, we found indications of the high-pressure phase InGaO3 II in the thin films above a crit. indium concn., its value depending on the type of substrate. (c) 2014 American Institute of Physics.
- 10Shannon, R. D.; Prewitt, C. T. Synthesis and Structure of Phases in the In2O3-Ga2O3 System. J. Inorg. Nucl. Chem. 1968, 30, 1389– 1398, DOI: 10.1016/0022-1902(68)80277-5Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXks1agtro%253D&md5=4f9b48da0fbf8c5517190b3f66e79b56Synthesis and structure of phases in the indium sesquioxide-gallium sesquioxide systemShannon, R. D.; Prewitt, C. T.Journal of Inorganic and Nuclear Chemistry (1968), 30 (6), 1389-98CODEN: JINCAO; ISSN:0022-1902.Compns. Ga2-xInxO3 (x = 0.0-1.0) having the β-Ga2O3 structure were prepd. in the powder form and as single crystals by several techniques and characterized by x-ray and resistivity measurements. The compn. InGaO3 transforms at high pressures to a new phase, InGaO3 II. InGaO3 II has a simple hexagonal oxide structure which is the 1st structure reported contg. Ga3+ in 5-fold coordination. The cell parameters are: a 3.310 ± 0.002, c 12.039 ± 0.002 A.; Z = 2; ρ(calcd.) = 6.756; and the space group is P63/mmc. Interat. distances obtained from least-sqs. refinement results are In-O(1)[×2], 3.010 A.; In-O(2)[×6], 2.174 A.; Ga-O(1)[×3], 1.911 A.; and Ga-O(2)[×2], 1.973 A. InGaO3 II is isotypic with hexagonal YAlO3, and its structure is related to that of YMnO3, which contains 5 coordinated Mn3+. 20 references.
- 11Kneiß, M.; Hassa, A.; Splith, D.; Sturm, C.; von Wenckstern, H.; Lorenz, M.; Grundmann, M. Epitaxial Stabilization of Single Phase κ-(InxGa1-x)2O3 Thin Films up to x = 0.28 on c-Sapphire and κ-Ga2O3(001) Templates by Tin-Assisted VCCS-PLD. APL Mater. 2019, 7, 101102, DOI: 10.1063/1.5120578Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFaksr7J&md5=8ae376374581a0b013f39056fe5f9cc7Epitaxial stabilization of single phase κ (InxGa1-x)2O3 thin films up to x = 0.28 on c-sapphire and κ -Ga2O3(001) templates by tin-assisted VCCS-PLDKneiss, M.; Hassa, A.; Splith, D.; Sturm, C.; von Wenckstern, H.; Lorenz, M.; Grundmann, M.APL Materials (2019), 7 (10), 101102/1-101102/10CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)High-quality (InxGa1-x)2O3 thin films in the orthorhombic κ -phase were grown by pulsed-laser deposition (PLD) on c-sapphire substrates as well as PLD-grown κ -Ga2O3 thin film templates. We varied the In-content 0 = x = 0.38 of the layers using a single, elliptically segmented, and tin-doped (In0.4Ga0.6)2O3/Ga2O3 target, employing the vertical continuous compn. spread (VCCS) PLD-technique. A stoichiometric transfer of In and Ga from the target to the thin films has been confirmed, suggesting that the formation of volatile Ga2O and In2O suboxides is not a limiting factor in the tin-assisted growth mode. For all x, the thin films crystd. predominantly in the κ -modification as demonstrated by XRD 2θ -ω scans. However, for x > 0.28, phase sepn. of the cubic bixbyite and the κ -phase occurred. The κ -Ga2O3 template increased the cryst. quality of the κ -(InxGa1-x)2O3 thin film layers remarkably. Epitaxial, but relaxed growth with three in-plane rotational domains has been found for all thin films by XRD κ -scans or reciprocal space map measurements. Smooth surface morphologies (Rq < 3 nm) for all phase pure thin films were evidenced by at. force microscopy measurements, making them suitable for multilayer heterostructures. The compn.-dependent in- and out-of plane lattice consts. follow a linear behavior according to Vegard's law. A linear relationship can also be confirmed for the optical bandgaps that demonstrate the feasibility of bandgap engineering in the energy range of 4.1-4.9 eV. The results suggest κ -(InxGa1-x)2O3 as a promising material for heterostructure device applications or photodetectors. (c) 2019 American Institute of Physics.
- 12Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118, 8207– 8215, DOI: 10.1063/1.1564060Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjtlSisLw%253D&md5=05a44dc5890abc3dfa8e1ef5338a4781Hybrid functionals based on a screened Coulomb potentialHeyd, Jochen; Scuseria, Gustavo E.; Ernzerhof, MatthiasJournal of Chemical Physics (2003), 118 (18), 8207-8215CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Hybrid d. functionals are very successful in describing a wide range of mol. properties accurately. In large mols. and solids, however, calcg. the exact (Hartree-Fock) exchange is computationally expensive, esp. for systems with metallic characteristics. In the present work, we develop a new hybrid d. functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodn. properties of mols. are comparable in quality to the most widely used hybrid functionals. In addn., we present results of periodic boundary condition calcns. for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree-Fock exchange enables fast and accurate hybrid calcns., even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential hybrid, combined with its computational advantages, makes it widely applicable to large mols. and periodic systems.
- 13Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.17953Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfjslSntA%253D%253D&md5=1853d67af808af2edab58beaab5d3051Projector augmented-wave methodBlochlPhysical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.There is no expanded citation for this reference.
- 14Kresse, 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.54.11169Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xms1Whu7Y%253D&md5=9c8f6f298fe5ffe37c2589d3f970a697Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis setKresse, 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.
- 15Blöchl, P. E.; Jepsen, O.; Andersen, O. K. Improved Tetrahedron Method for Brillouin-zone Integrations. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 16223– 16233, DOI: 10.1103/PhysRevB.49.16223Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXks1Gqtb0%253D&md5=d1aa48b406bfccde3e58d26cbf21a809Improved tetrahedron method for Brillouin-zone integrationsBlochl, Peter E.; Jepsen, O.; Andersen, O. K.Physical Review B: Condensed Matter and Materials Physics (1994), 49 (23), 16223-33CODEN: PRBMDO; ISSN:0163-1829.Several improvements of the tetrahedron method for Brillouin-zone integrations are presented. (1) A translational grid of k points and tetrahedra is suggested that renders the results for insulators identical to those obtained with special-point methods with the same no. of k points. (2) A simple correction formula goes beyond the linear approxn. of matrix elements within the tetrahedra and also improves the results for metals significantly. For a required accuracy this reduces the no. of k points by orders of magnitude. (3) Irreducible k points and tetrahedra are selected by a fully automated procedure, requiring as input only the space-group operations. (4) The integration is formulated as a weighted sum over irreducible k points with integration wts. calcd. using the tetrahedron method once for a given band structure. This allows an efficient use of the tetrahedron method also in plane-wave-based electronic-structure methods.
- 16Onuma, T.; Saito, S.; Sasaki, K.; Goto, K.; Masui, T.; Yamaguchi, T.; Honda, T.; Kuramata, A.; Higashiwaki, M. Temperature-Dependent Exciton Resonance Energies and their Correlation with IR-active Optical Phonon Modes in β-Ga2O3 Single Crystals. Appl. Phys. Lett. 2016, 108, 101904, DOI: 10.1063/1.4943175Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVWqs74%253D&md5=517b6df3b9978d3e7e81446b2eea1893Temperature-dependent exciton resonance energies and their correlation with IR-active optical phonon modes in β-Ga2O3 single crystalsOnuma, T.; Saito, S.; Sasaki, K.; Goto, K.; Masui, T.; Yamaguchi, T.; Honda, T.; Kuramata, A.; Higashiwaki, M.Applied Physics Letters (2016), 108 (10), 101904/1-101904/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Temp.-dependent exciton resonance energies Eexciton in β-Ga2O3 single crystals are studied by using polarized reflectance measurement. The Eexciton values exhibit large energy changes at 179-268 meV from 5 to 300 K. The IR-active Au and Bu optical phonon modes are selectively obsd. in the IR ellipsometry spectra by reflecting the polarization selection rules. The LO phonon energies can be divided into 3 ranges: ℏωLO = 35-48, 70-73, and 88-99 meV. The broadening parameters, which are obtained from the reflectance measurements, correspond to the lower 2 ranges of ℏωLO at low temp. and 75 meV >150 K. The large Eexciton changes with temp. in β-Ga2O3 are originated from the exciton-LO-phonon interaction. (c) 2016 American Institute of Physics.
- 17Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Y.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstübner, U.; Vines, L. Iron and Intrinsic Deep Level States in Ga2O3. Appl. Phys. Lett. 2018, 112, 042104, DOI: 10.1063/1.5020134Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsl2iu74%253D&md5=67c0fa08a94280c035424b2f4553a0ffIron and intrinsic deep level states in Ga2O3Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Yu.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstubner, U.; Vines, L.Applied Physics Letters (2018), 112 (4), 042104/1-042104/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradn., and hybrid functional calcns., we identify two similar deep levels that are assocd. with Fe impurities and intrinsic defects in bulk crystals and mol. beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ∼0.78 eV below the conduction band min. Second, by provoking addnl. intrinsic defect generation via proton irradn., we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different exptl. conditions. (c) 2018 American Institute of Physics.
- 18Geller, S. Crystal Structure of β-Ga2O3. J. Chem. Phys. 1960, 33, 676– 684, DOI: 10.1063/1.1731237Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF3MXisF2gsg%253D%253D&md5=a1369607c308a8592f2a30ffa0f7e6bcCrystal structure of β-Ga2O3Geller, S.Journal of Chemical Physics (1960), 33 (), 676-84CODEN: JCPSA6; ISSN:0021-9606.The monoclinic crystal has cell dimensions a = 12.23, b = 3.04, c = 5.80 A., β = 103.7°. There are 4 mols. per unit cell. The most probable space group is C32h-C2/m; the atoms are in 5 sets of special positions 4i: (000, 1/2 1/2 0) ± (x0z). There are 2 kinds of co.ovrddot.ordination for Ga+++ in this structure, tetrahedral and octahedral. Av. interionic distances are: tetrahedral Ga-O; 1.83 A.; octahedral Ga-O, 2.00 A.; tetrahedron edge O-O, 3.02 A.; and octahedron edge O-O, 2.84 A. Because of the reduced co.ovrddot.ordination of half of the metal ions, the d. of β-Ga2O3 is lower than that of α-Ga2O3. The av. Ga-O distances in the structure account for the fact that although the Ga+++ is substantially larger than the Al+++, its quant. preference for tetrahedrally co.ovrddot.ordinated sites when substituted for Fe+++ in the Fe garnets is nearly the same as that of the Al+++ ion. The magnetic aspects of the β-Ga2O3 structure are discussed, and a possible Fe2O3 isomorph may be expected to be at least antiferromagnetic with a Neel temp. of about 700°K.
- 19Prozheeva, V.; Hölldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F. Effects of Alloy Composition and Si-doping on Vacancy Defect Formation in (InxGa1-x)2O3 Thin Films. J. Appl. Phys. 2018, 123, 125705, DOI: 10.1063/1.5022245Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXms1Ggtb8%253D&md5=3675ad4d0b4012ffd8cce25e97fb83cbEffects of alloy composition and Si-doping on vacancy defect formation in (InxGa1-x)2O3 thin filmsProzheeva, V.; Holldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F.Journal of Applied Physics (Melville, NY, United States) (2018), 123 (12), 125705/1-125705/6CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Various nominally undoped and Si-doped (InxGa1-x)2O3 thin films were grown by pulsed laser deposition in a continuous compn. spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterization technique in order to investigate the effect of alloy compn. and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concns. changing to In2O3-like behavior along with the increase in the indium fraction. Increasing indium concn. is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron satn. trapping in VIn-like defects, suggesting a vacancy concn. of at least mid-1018 cm-3 independent of the indium content. This is a solid soln. study. (c) 2018 American Institute of Physics.
- 20Schmidt-Grund, R.; Kranert, C.; Bontgen, T.; von Wenckstern, H.; Krauß, H.; Grundmann, M. Dielectric Function in the NIR-VUV Spectral Range of (InxGa1-x)2O3 Thin Films. J. Appl. Phys. 2014, 116, 053510, DOI: 10.1063/1.4891521Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1KksrvN&md5=0cf97c8d4b0ab35cffe159bb8f56ed50Dielectric function in the NIR-VUV spectral range of (InxGa1-x)2O3 thin filmsSchmidt-Grund, R.; Kranert, C.; Boentgen, T.; von Wenckstern, H.; Krauss, H.; Grundmann, M.Journal of Applied Physics (Melville, NY, United States) (2014), 116 (5), 053510/1-053510/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We detd. the dielec. function of the alloy system (InxGa1-x)2O3 by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for In contents ranging from x = 0.02 to x = 0.61. The predicted optical transitions for binary, monoclinic β-Ga2O3, and cubic bcc-In2O3 are well reflected by the change of the dielec. functions' lineshape as a function of the In content. In an intermediate compn. range with phase-sepd. material (x ≈ 0.3...0.4), the lineshape differs considerably, which we assign to the presence of the high-pressure rhombohedral InGaO3-II phase, which we also observe in Raman expts. in this range. By model anal. of the dielec. function, we derived spectra of the refractive index and the absorption coeff. and energy parameters of electronic band-band transitions. We discuss the sub-band gap absorption tail in relation to the influence of the In 4d orbitals on the valence bands. The data presented here provide a basis for a deeper understanding of the electronic properties of this technol. important material system and may be useful for device engineering. (c) 2014 American Institute of Physics.
- 21von Wenckstern, H.; Kneiß, M.; Hassa, A.; Storm, P.; Splith, D.; Grundmann, M. A Review of the Segmented-Target Approach to Combinatorial Material Synthesis by Pulsed-Laser Deposition. Phys. Status Solidi B 2020, 257, 1900626, DOI: 10.1002/pssb.201900626Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlyms7nF&md5=1e12c15dcdda939efdb6df2c11a3a372A Review of the Segmented-Target Approach to Combinatorial Material Synthesis by Pulsed-Laser Depositionvon Wenckstern, Holger; Kneiss, Max; Hassa, Anna; Storm, Philipp; Splith, Daniel; Grundmann, MariusPhysica Status Solidi B: Basic Solid State Physics (2020), 257 (7), 1900626CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)Combinatorial material synthesis has led to a significant acceleration in the optimization of multinary compds. and a more efficient usage of source and substrate materials. Various growth methods, including phys. vapor deposition, can be adopted to realize material libraries. Herein, two approaches to combinatorial material synthesis based on ablation of segmented targets during pulsed-laser deposition are reviewed. For these two processes, either laterally or radially segmented targets are utilized and allow the creation of lateral and vertical compn. spreads, resp. Radially segmented targets can addnl. be used to synthesize a discrete binary material library. Both approaches are introduced by calcg. the expected material distribution with a simple geometric plasma expansion model. Then, exptl. detd. elemental distributions and growth rates are compared to predictions and it is demonstrated that differences between calcd. and exptl. data contain vital information on the influence of, for example, thermodn. processes on the growth mechanism.
- 22Vines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M. Electrical Conductivity of In2O3 and Ga2O3 after Low Temperature Ion Irradiation; Implications for Intrinsic Defect Formation and Charge Neutrality Level. J. Phys.: Condens. Matter 2018, 30, 025502, DOI: 10.1088/1361-648X/aa9e2aGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFygurjO&md5=fd0cd7d4c51f1e50f1e7560f0274adcbElectrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality levelVines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M.Journal of Physics: Condensed Matter (2018), 30 (2), 025502/1-025502/6CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)The evolution of sheet resistance of n-type In2O3 and Ga2O3 exposed to bombardment with MeV 12C and 28Si ions at 35 K is studied in situ. While the sheet resistance of Ga2O3 increased by more than 8-fold as a result of ion irradn., In2O3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temp. reduced the sheet resistivity somewhat, but Ga2O3 remained highly resistive, while In2O3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradn. up to 2 × 1012 cm-2. A model where larger defect complexes preferentially produce donor like defects in In2O3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.
- 23King, P. D. C.; Veal, T. D.; Fuchs, F.; Wang, C. Y.; Payne, D. J.; Bourlange, A.; Zhang, H.; Bell, G. R.; Cimalla, V.; Ambacher, O.; Egdell, R. G.; Bechstedt, F.; McConville, C. F. Band Gap, Electronic Structure, and Surface Electron Accumulation of Cubic and Rhombohedral In2O3. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 205211, DOI: 10.1103/PhysRevB.79.205211Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvFyhtbc%253D&md5=eb6fd198231cbef4b3383cb1c844cf11Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3King, P. D. C.; Veal, T. D.; Fuchs, F.; Wang, Ch. Y.; Payne, D. J.; Bourlange, A.; Zhang, H.; Bell, G. R.; Cimalla, V.; Ambacher, O.; Egdell, R. G.; Bechstedt, F.; McConville, C. F.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (20), 205211/1-205211/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The bulk and surface electronic structure of In2O3 has proved controversial, prompting the current combined exptl. and theor. investigation. The band gap of single-cryst. In2O3 is detd. as 2.93±0.15 and 3.02±0.15 eV for the cubic bixbyite and rhombohedral polymorphs, resp. The valence-band d. of states is investigated from x-ray photoemission spectroscopy measurements and d.-functional theory calcns. These show excellent agreement, supporting the absence of any significant indirect nature of the In2O3 band gap. Clear exptl. evidence for an s-d coupling between In 4d and O 2s derived states is also obsd. Electron accumulation, recently reported at the (001) surface of bixbyite material, is also shown to be present at the bixbyite (111) surface and the (0001) surface of rhombohedral In2O3.
- 24Swallow, J. E. N.; Varley, J. B.; Jones, L. A. H.; Gibbon, J. T.; Piper, L. F. J.; Dhanak, V. R.; Veal, T. D. Transition from Electron Accumulation to Depletion at β-Ga2O3 Surfaces: The Role of Hydrogen and the Charge Neutrality Level. APL Mater. 2019, 7, 022528, DOI: 10.1063/1.5054091Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjtVGru7w%253D&md5=fe7b421ae053736c23e30989e6c1d53bTransition from electron accumulation to depletion at β-Ga2O3 surfaces: The role of hydrogen and the charge neutrality levelSwallow, J. E. N.; Varley, J. B.; Jones, L. A. H.; Gibbon, J. T.; Piper, L. F. J.; Dhanak, V. R.; Veal, T. D.APL Materials (2019), 7 (2), 022528/1-022528/8CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)The surface electronic properties of bulk-grown β-Ga2O3 (201) single crystals are investigated. The band gap is found using optical transmission to be 4.68 eV. High-resoln. x-ray photoemission coupled with hybrid d. functional theory calcn. of the valence band d. of states provides insights into the surface band bending. Importantly, the std. linear extrapolation method for detg. the surface valence band max. (VBM) binding energy is found to underestimate the sepn. from the Fermi level by ∼0.5 eV. According to our interpretation, most reports of surface electron depletion and upward band bending based on photoemission spectroscopy actually provide evidence of surface electron accumulation. For uncleaned surfaces, the surface VBM to Fermi level sepn. is found to be 4.95 ± 0.10 eV, corresponding to downward band bending of ∼0.24 eV and an electron accumulation layer with a sheet d. of ∼5 × 1012 cm-2. Uncleaned surfaces possess hydrogen termination which acts as surface donors, creating electron accumulation and downward band bending at the surface. In situ cleaning by thermal annealing removes H from the surface, resulting in a ∼0.5 eV shift of the surface VBM and formation of a surface electron depletion layer with upward band bending of ∼0.26 eV due to native acceptor surface states. These results are discussed in the context of the charge neutrality level, calcd. bulk interstitial hydrogen transition levels, and related previous exptl. findings. (c) 2019 American Institute of Physics.
- 25Nagata, T.; Hoga, T.; Yamashita, A.; Asahi, T.; Yagyu, S.; Chikyow, T. Valence Band Modification of a (GaxIn1-x)2O3 Solid Solution System Fabricated by Combinatorial Synthesis. ACS Comb. Sci. 2020, 22, 433439, DOI: 10.1021/acscombsci.0c00033Google ScholarThere is no corresponding record for this reference.
- 26King, P. D. C.; Veal, T. D.; Payne, D. J.; Bourlange, A.; Egdell, R. G.; McConville, C. F. Surface Electron Accumulation and the Charge Neutrality Level in In2O3. Phys. Rev. Lett. 2008, 101, 116808, DOI: 10.1103/PhysRevLett.101.116808Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtFWltrrK&md5=e15c564b1e0560b21cb9aa23a3f474b1Surface electron accumulation and the charge neutrality level in In2O3King, P. D. C.; Veal, T. D.; Payne, D. J.; Bourlange, A.; Egdell, R. G.; McConville, C. F.Physical Review Letters (2008), 101 (11), 116808/1-116808/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)High-resoln. x-ray photoemission spectroscopy, IR reflectivity and Hall effect measurements, combined with surface space-charge calcns., are used to show that electron accumulation occurs at the surface of undoped single-cryst. In2O3. From a combination of measurements performed on undoped and heavily Sn-doped samples, the charge neutrality level is shown to lie ∼0.4 eV above the conduction band min. in In2O3, explaining the electron accumulation at the surface of undoped material, the propensity for n-type cond., and the ease of n-type doping in In2O3, and hence its use as a transparent conducting oxide material.
- 27Lovejoy, T. C.; Chen, R.; Zheng, X.; Villora, E. G.; Shimamura, K.; Yoshikawa, H.; Yamashita, Y.; Ueda, S.; Kobayashi, K.; Dunham, S. T.; Ohuchi, F. S.; Olmstead, M. A. Band Bending and Surface Defects in β-Ga2O3. Appl. Phys. Lett. 2012, 100, 181602, DOI: 10.1063/1.4711014Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmtlGqs7s%253D&md5=48382782a6c5523dba943133949f216bBand bending and surface defects in β-Ga2O3Lovejoy, T. C.; Chen, Renyu; Zheng, X.; Villora, E. G.; Shimamura, K.; Yoshikawa, H.; Yamashita, Y.; Ueda, S.; Kobayashi, K.; Dunham, S. T.; Ohuchi, F. S.; Olmstead, M. A.Applied Physics Letters (2012), 100 (18), 181602/1-181602/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Surface band bending and surface defects on the UV-transparent conducting oxide β-Ga2O3 (100) are studied with hard x-ray photoemission spectroscopy and scanning tunneling microscopy. Highly doped β-Ga2O3 shows flat bands near the surface, while the bands on nominally undoped (but still n-type), air-cleaved β-Ga2O3 are bent upwards by > 0.5 eV. Neg. charged surface defects are obsd. on vacuum annealed β-Ga2O3, which also shows upward band bending. D. functional calcns. show O vacancies are not likely to be ionized in the bulk, but could be activated by surface band bending. The large band bending may also hinder formation of ohmic contacts. (c) 2012 American Institute of Physics.
- 28Navarro-Quezada, A.; Alamé, S.; Esser, N.; Furthmüller, J.; Bechstedt, F.; Galazka, Z.; Skuridina, D.; Vogt, P. Near Valence-band Electronic Properties of Semiconducting β-Ga2O3 (100) Single Crystals. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 195306, DOI: 10.1103/PhysRevB.92.195306Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtF2lurvM&md5=87c0a49c3be11c955027cd184f299d63Near valence-band electronic properties of semiconducting β-Ga2O3 (100) single crystalsNavarro-Quezada, A.; Alame, S.; Esser, N.; Furthmueller, J.; Bechstedt, F.; Galazka, Z.; Skuridina, D.; Vogt, P.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (19), 195306/1-195306/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)β-Ga2O3 is a transparent wide-band-gap semiconductor that has attracted considerable interest in recent years due to its suitable elec. cond. and transparency in the UV spectral region. In this work we investigate the electronic properties of the near valence-band-edge region for semiconducting β-Ga2O3 (100) bulk single crystals using core-level photoelectron spectroscopy and ab initio theory within the framework of d. functional theory and the GW approach. We find good agreement between the exptl. results and the theor. calcns. This is explained by the hybridization of the Ga 3d and O 2s states, similar as for In2O3.
- 29King, P. D. C.; Veal, T. D.; Schleife, A.; Zúñiga-Pérez, J.; Martel, B.; Jefferson, P. H.; Fuchs, F.; Muñoz-Sanjosé, V.; Bechstedt, F.; McConville, C. F. Valence-band Electronic Structure of CdO, ZnO, and MgO from X-ray Photoemission Spectroscopy and Quasi-particle-corrected Density-functional Theory Calculations. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 205205, DOI: 10.1103/PhysRevB.79.205205Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvFyiurY%253D&md5=4366fa00f414c9f91a0b17dd25666ae6Valence-band electronic structure of CdO, ZnO, and MgO from x-ray photoemission spectroscopy and quasi-particle-corrected density-functional theory calculationsKing, P. D. C.; Veal, T. D.; Schleife, A.; Zuniga-Perez, J.; Martel, B.; Jefferson, P. H.; Fuchs, F.; Munoz-Sanjose, V.; Bechstedt, F.; McConville, C. F.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (20), 205205/1-205205/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The valence-band d. of states of single-cryst. rock-salt CdO(001), wurtzite c-plane ZnO, and rock- salt MgO(001) are investigated by high-resoln. x-ray photoemission spectroscopy. A classic two-peak structure is obsd. in the VB-DOS due to the anion 2p-dominated valence bands. Good agreement is found between the exptl. results and quasi-particle-cor. d.-functional theory calcns. Occupied shallow semicore d levels are obsd. in CdO and ZnO. While these exhibit similar spectral features to the calcns., they occur at slightly higher binding energies, detd. as 8.8 eV and 7.3 eV below the valence band max. in CdO and ZnO, resp. The implications of these on the electronic structure are discussed.
- 30Moses, P. G.; Van de Walle, C. G. Band Bowing and Band Alignment in InGaN Alloys. Appl. Phys. Lett. 2010, 96, 021908, DOI: 10.1063/1.3291055Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXnsValtg%253D%253D&md5=1338c895900ffcf26637e7830b9da0e3Band bowing and band alignment in InGaN alloysMoses, Poul Georg; Van de Walle, Chris G.Applied Physics Letters (2010), 96 (2), 021908/1-021908/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)We use d. functional theory calcns. with the HSE06 hybrid exchange-correlation functional to investigate InGaN alloys and accurately det. band gaps and band alignments. We find a strong band-gap bowing at low In content. Band positions on an abs. energy scale are detd. from surface calcns. The resulting GaN/InN valence-band offset is 0.62 eV. The dependence of InGaN valence-band alignment on In content is found to be almost linear. Based on the values of band gaps and band alignments, we conclude that InGaN fulfills the requirements for a photoelectrochem. electrode for In contents up to 50%. (c) 2010 American Institute of Physics.
- 31Peelaers, H.; Steiauf, D.; Varley, J. B.; Janotti, A.; Van de Walle, C. G. (InxGa1-x)2O3 Alloys for Transparent Electronics. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 085206, DOI: 10.1103/PhysRevB.92.085206Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XivVOnurs%253D&md5=7e6c49c8687400f2b1b306eeee680c26(InxGa1-x)2O3 alloys for transparent electronicsPeelaers, Hartwin; Steiauf, Daniel; Varley, Joel B.; Janotti, Anderson; Van de Walle, Chris G.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (8), 085206/1-085206/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)(InxGa1-x)2O3 alloys show promise as transparent conducting oxides. Using hybrid d. functional calcns., band gaps, formation enthalpies, and structural parameters are detd. for monoclinic and bixbyite crystal structures. In the monoclinic phase the band gap exhibits a linear dependence on alloy concn., whereas in the bixbyite phase a large band-gap bowing occurs. The calcd. formation enthalpies show that the monoclinic structure is favorable for In compns. up to 50% and bixbyite for larger compns. This is caused by In strongly preferring sixfold oxygen coordination. The formation enthalpy of the 50:50 monoclinic alloy is much lower than the formation enthalpy of the 50:50 bixbyite alloy and also lower than most monoclinic alloys with lower In concn.; these trends are explained in terms of local strain. Consequences for expt. and applications are discussed.
- 32Oshima, T.; Fujita, S. Properties of Ga2O3-based (InxGa1-x)2O3 Alloy Thin Films Grown by Molecular Beam Epitaxy. Phys. Status Solidi C 2008, 5, 3113– 3115, DOI: 10.1002/pssc.200779297Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXpsVyhuro%253D&md5=7925c1ca2221aa78c120015fb02729bbProperties of Ga2O3-based (InxGa1-x)2O3 alloy thin films grown by molecular beam epitaxyOshima, Takayoshi; Fujita, ShizuoPhysica Status Solidi C: Current Topics in Solid State Physics (2008), 5 (9), 3113-3115CODEN: PSSCGL; ISSN:1862-6351. (Wiley-VCH Verlag GmbH & Co. KGaA)A series of Ga2O3-based (InxGa1-x)2O3 alloy thin films were grown on c-plane Al2O3 substrates with a thin Ga2O3 buffer layer by plasma-assisted MBE. At growth temps. of 700° and higher, even with a slight inclusion of In2O3 to Ga2O3, for example, the film of (In0.08Ga0.92)2O3, exhibited a rough surface and degraded transmission spectrum resulting from phase sepn. of In2O3. Due to low temp. growth at 600°, however, the phase sepn. was suppressed for the In compn. ≤35%, which was confirmed by x-ray diffraction measurement, and the films exhibited high transmittance over 85% with sharp absorption edges. The bandgap could be tuned from 5.0-4.0 eV. The results encourage the application of (InxGa1-x)2O3 thin films in short-wavelength optical devices.
- 33Regoutz, A.; Egdell, R.; Morgan, D.; Palgrave, R.; Téllez, H.; Skinner, S.; Payne, D.; Watson, G.; Scanlon, D. Electronic and Surface Properties of Ga-doped In2O3 Ceramics. Appl. Surf. Sci. 2015, 349, 970– 982, DOI: 10.1016/j.apsusc.2015.04.106Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXntlGgsLw%253D&md5=e9497081343790fc4db705e9ad92596cElectronic and surface properties of Ga-doped In2O3 ceramicsRegoutz, A.; Egdell, R. G.; Morgan, D. J.; Palgrave, R. G.; Tellez, H.; Skinner, S. J.; Payne, D. J.; Watson, G. W.; Scanlon, D. O.Applied Surface Science (2015), 349 (), 970-982CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)The limit of soly. of Ga2O3 in the cubic bixbyite In2O3 phase was established by x-ray diffraction and Raman spectroscopy to correspond to replacement of around 6% of In cations by Ga for samples prepd. at 1250°. D. functional theory calcns. suggest that Ga substitution should lead to widening of the bulk bandgap, as expected from the much larger gap of Ga2O3 as compared to In2O3. However both diffuse reflectance spectroscopy and valence band x-ray photoemission reveal an apparent narrowing of the gap with Ga doping. It is tentatively concluded that this anomaly arises from introduction of Ga+ surface lone pair states at the top of the valence band and structure at the top of the valence band in Ga-segregated samples is assigned to these lone pair states. In addn. photoemission reveals a broadening of the valence band edge. Core x-ray photoemission spectra and low energy ion scattering spectroscopy both reveal pronounced segregation of Ga to the ceramic surface, which may be linked to both relief of strain in the bulk and the preferential occupation of surface sites by lone pair cations. Surprisingly Ga segregation is not accompanied by the development of chem. shifted structure in Ga 2p core XPS assocd. with Ga+. However expts. on ion bombarded Ga2O3, where a shoulder at the top edge of the valence band spectra provide a clear signature of Ga+ at the surface, show that the chem. shift between Ga+ and Ga3+ is too small to be resolved in Ga 2p core level spectra. Thus the failure to observe chem. shifted structure assocd. with Ga+ is not inconsistent with the proposal that band gap narrowing is assocd. with lone pair states at surfaces and interfaces.
- 34von Wenckstern, H.; Splith, D.; Purfürst, M.; Zhang, Z.; Kranert, C.; Müller, S.; Lorenz, M.; Grundmann, M. Structural and Optical Properties of (In,Ga)2O3 Thin Films and Characteristics of Schottky Contacts Thereon. Semicond. Sci. Technol. 2015, 30, 024005, DOI: 10.1088/0268-1242/30/2/024005Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXit1ygsr0%253D&md5=99f3012eb139364fea9f0e4bfa2c9469Structural and optical properties of (In, Ga)2O3 thin films and characteristics of Schottky contacts thereonvon Wenckstern, H.; Splith, D.; Purfuerst, M.; Zhang, Z.; Kranert, Ch.; Mueller, S.; Lorenz, M.; Grundmann, M.Semiconductor Science and Technology (2015), 30 (2), 24005/1-24005/7, 7 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)We report on structural and optical properties of a (InxGa1-x)2O3 thin film having a monotonic lateral variation of the indium content x (0 ≤ x ≤ 0.9). The growth condition for each In content is similar allowing precise detn. of the dependence of material properties on x. For low In content (x < 0.15) the thin film has monoclinic crystal structure; for highest In contents (x > 0.8) the cubic bixbyite phase is predominant. For intermediate alloying we observe addnl. the rhombohedral InGaO3(II) crystallog. phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (InxGa1-x)2O3 and photo response measurements for x < 0.1.
- 35Yang, F.; Ma, J.; Luan, C.; Kong, L. Structural and Optical Properties of Ga2(1-x)In2xO3 films Prepared on α-Al2O3 (0001) by MOCVD. Appl. Surf. Sci. 2009, 255, 4401– 4404, DOI: 10.1016/j.apsusc.2008.10.129Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpvFSitw%253D%253D&md5=147cc7a7f8cc0019b9ce061e6b323a12Structural and optical properties of Ga2(1-x)In2xO3 films prepared on α-Al2O3 (0001) by MOCVDYang, Fan; Ma, Jin; Luan, Caina; Kong, LingyiApplied Surface Science (2009), 255 (8), 4401-4404CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Ga2(1-x)In2xO3 thin films with different indium content x [In/(Ga + In) at. ratio] were prepd. on α-Al2O3 (0 0 0 1) substrates by the metal org. chem. vapor deposition (MOCVD). The structural and optical properties of the Ga2(1-x)In2xO3 films were investigated in detail. Microstructure anal. revealed that the film deposited with compn. x = 0.2 was polycryst. structure and the sample prepd. with x up to 0.8 exhibited single cryst. structure of In2O3. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The av. transmittance for the films in the visible range was over 90%.
- 36Zhang, Z.; von Wenckstern, H.; Lenzner, J.; Lorenz, M.; Grundmann, M. Visible-blind and Solar-blind Ultraviolet Photodiodes Based on (InxGa1-x)2O3. Appl. Phys. Lett. 2016, 108, 123503, DOI: 10.1063/1.4944860Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVCltL4%253D&md5=233d1f6efa45ed6b1195cf33b394e67cVisible-blind and solar-blind ultraviolet photodiodes based on (InxGa1-x)2O3Zhang, Zhipeng; von Wenckstern, Holger; Lenzner, Joerg; Lorenz, Michael; Grundmann, MariusApplied Physics Letters (2016), 108 (12), 123503/1-123503/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)UV and deep-UV selective photodiodes from visible-blind to solar-blind were realized based on a Si-doped (InxGa1-x)2O3 thin film with a monotonic lateral variation of 0.0035 < x < 0.83. Such layer was deposited by employing a continuous compn. spread approach relying on the ablation of a single segmented target in pulsed-laser deposition. The photo response signal is provided from a metal-semiconductor-metal structure upon backside illumination. The absorption onset was tuned from 4.83 to 3.22 eV for increasing x. Higher responsivities were obsd. for photodiodes fabricated from indium-rich part of the sample, for which an internal gain mechanism could be identified. (c) 2016 American Institute of Physics.
- 37Michel, J.; Splith, D.; Rombach, J.; Papadogianni, A.; Berthold, T.; Krischok, S.; Grundmann, M.; Bierwagen, O.; von Wenckstern, H.; Himmerlich, M. Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from In2O3. ACS Appl. Mater. Interfaces 2019, 11, 27073– 27087, DOI: 10.1021/acsami.9b06455Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlSntbnN&md5=e32c825ad1d3131c600b3c557c8cae7cProcessing strategies for high-performance Schottky contacts on n-type oxide semiconductors: insights from In2O3Michel, Jonas; Splith, Daniel; Rombach, Julius; Papadogianni, Alexandra; Berthold, Theresa; Krischok, Stefan; Grundmann, Marius; Bierwagen, Oliver; von Wenckstern, Holger; Himmerlich, MarcelACS Applied Materials & Interfaces (2019), 11 (30), 27073-27087CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Prepn. of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In2O3), is often challenged by the presence of a distinct surface electron accumulation layer. Here, the authors investigated the material properties and elec. transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the prepn. of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evapn. and (reactive) sputtering in an (O and) Ar atm., with oxygen plasma interface treatments, the authors identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chem. properties of the contact layers and the interface region toward In2O3, to analyze charge transfer and plasma oxidn. processes as well as to evaluate the precision and limits of different methodologies to det. heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissoln. of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In2O3 electron concn. of ∼1018 cm-3. A reactive sputter process in an Ar and O atm. is required to fabricate rectifying contacts that are composed of platinum oxide (PtOx). Combining oxygen plasma interface oxidn. of the semiconductor surface with reactive sputtering of PtOx layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 106. An addnl. oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.
- 38Rombach, J.; Papadogianni, A.; Mischo, M.; Cimalla, V.; Kirste, L.; Ambacher, O.; Berthold, T.; Krischok, S.; Himmerlich, M.; Selve, S.; Bierwagen, O. The Role of Surface Electron Accumulation and Bulk Doping for Gas-Sensing Explored with Single-Crystalline In2O3 Thin Films. Sens. Actuators, B 2016, 236, 909– 916, DOI: 10.1016/j.snb.2016.03.079Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvFOnu7c%253D&md5=e8e979d3bfdf3f57b5b6920697b467f3The role of surface electron accumulation and bulk doping for gas-sensing explored with single-crystalline In2O3 thin filmsRombach, Julius; Papadogianni, Alexandra; Mischo, Markus; Cimalla, Volker; Kirste, Lutz; Ambacher, Oliver; Berthold, Theresa; Krischok, Stefan; Himmerlich, Marcel; Selve, Soeren; Bierwagen, OliverSensors and Actuators, B: Chemical (2016), 236 (), 909-916CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Single cryst. and textured In2O3 thin films with (1 1 1) surface orientation, grown by plasma-assisted mol. beam epitaxy, were used as a model system to study the role of bulk and surface electron accumulation layer conductance for ozone sensing. Both conductance contributions, which add to the total film conductance, were systematically varied. The resulting ozone sensitivity was detd. by total conductance measurements in synthetic air with defined ozone concn. using UV irradn. instead of heating to regenerate the In2O3 surface. Depletion of the surface electron accumulation by an oxygen plasma treatment, confirmed by XPS, rendered the films ozone insensitive. The ozone response of films with an accumulation layer was increased by thickness redn. or by designing the bulk of the film semi-insulating using deep acceptor doping by Mg. Our results of using electron accumulation layers for gas sensing and bulk doping by deep acceptors to increase sensitivity can be generalized to other gas sensing materials. The use of single cryst. films allows selecting the most sensitive crystallog. surface orientation and may have further advantages over polycryst. films, such as increased stability and sensing speed.
- 39Veal, T. D.; Jefferson, P. H.; Piper, L. F. J.; McConville, C. F.; Joyce, T. B.; Chalker, P. R.; Considine, L.; Lu, H.; Schaff, W. J. Transition from Electron Accumulation to Depletion at InGaN Surfaces. Appl. Phys. Lett. 2006, 89, 202110, DOI: 10.1063/1.2387976Google Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktlak&md5=b14fb532a9578efd68907d2f3b43d496Transition from electron accumulation to depletion at InGaN surfacesVeal, T. D.; Jefferson, P. H.; Piper, L. F. J.; McConville, C. F.; Joyce, T. B.; Chalker, P. R.; Considine, L.; Lu, Hai; Schaff, W. J.Applied Physics Letters (2006), 89 (20), 202110/1-202110/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)The compn. dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1-xN films (0 ≤ x ≤ 1) was studied using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band min. (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approx. x = 0.3. The results are consistent with the compn. dependence of the band edges with respect to the charge neutrality level.
- 40Kajiyama, K.; Mizushima, Y.; Sakata, S. Schottky Barrier Height of n-InxGa1-xAs Diodes. Appl. Phys. Lett. 1973, 23, 458, DOI: 10.1063/1.1654957Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXjtFOitg%253D%253D&md5=36c14898e87f403b143525b8a0b70f17Schottky barrier height of n-indium gallium arsenide (n-InxGa1-xAs) diodesKajiyama, K.; Mizushima, Y.; Sakata, S.Applied Physics Letters (1973), 23 (8), 458-9CODEN: APPLAB; ISSN:0003-6951.The barrier heights, ΦB, of Au/n-InxGa1-xAs diodes were measured by the capacitance-voltage and satn. current methods. The compn. dependence of the barrier height is ΦB (eV) = 0.95 - 1.90x + 0.90x2. A low barrier height with a relatively wide band gap is obtained in this system.
- 41Lüth, H. Research on III-V Semiconductor Interfaces: Its Impact on Technology and Devices. Physica Status Solidi (a) 2001, 187, 33– 44, DOI: 10.1002/1521-396X(200109)187:1<33::AID-PSSA33>3.0.CO;2-9Google ScholarThere is no corresponding record for this reference.
- 42Wei, S.-H.; Zunger, A. Role of Metal d States in II-VI Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 8958, DOI: 10.1103/PhysRevB.37.8958Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXkvVSjsrk%253D&md5=4a52c17c7dabbdc3b5fe4eb181336e72Role of metal d states in II-VI semiconductorsWei, S. H.; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1988), 37 (15), 8958-81CODEN: PRBMDO; ISSN:0163-1829.All-electron band-structure calcns. and photoemission expts. on II-VI semiconductors both exhibit a metal d subband inside the main valence band. It has nevertheless been customary in pseudopotential and tight-binding approaches to neglect the metal d band by choosing Hamiltonian parameters which place this band inside the chem. inert at. cores. By using all-electron self-consistent electronic-structure techniques (which treat the outermost d electrons in the same way as other valence electrons) and by comparing the results to those obtained by methods which remove the d band from the valence spectrum, the effects on valence properties were studied. For II-VI semiconductors p-d repulsion and hybridization (1) lower the band gaps, (2) reduce the cohesive energy, (3) increase the equil. lattice parameters, (4) reduce the spin-orbit splitting, (5) alter the sign of the crystal-field splitting, (6) increase the valence-band offset between common-anion II-VI semiconductors, and (7) modify the charge distributions of various II-VI systems and their alloys. P-d repulsion is also responsible for the occurrence of deep Cu acceptor levels in II-VI semiconductors (compared with shallow acceptors of Zn in III-V), for the anomalously small band gaps in chalcopyrites, and for the neg. exchange splitting in ferromagnetic MnTe.
- 43Varley, J. B.; Weber, J. R.; Janotti, A.; Van de Walle, C. G. Oxygen Vacancies and Donor Impurities in β-Ga2O3. Appl. Phys. Lett. 2010, 97, 142106, DOI: 10.1063/1.3499306Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Gns7bJ&md5=73782eef178ad7fa1e75df78e496b428Oxygen vacancies and donor impurities in β-Ga2O3Varley, J. B.; Weber, J. R.; Janotti, A.; Van de Walle, C. G.Applied Physics Letters (2010), 97 (14), 142106/1-142106/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using hybrid functionals we have investigated the role of O vacancies and various impurities in the elec. and optical properties of the transparent conducting oxide β-Ga2O3. We find that O vacancies are deep donors, and thus cannot explain the unintentional n-type cond. Instead, we attribute the cond. to common background impurities such as Si and H. Monoat. H has low formation energies and acts as a shallow donor in both interstitial and substitutional configurations. We also explore other dopants, where substitutional forms of Si, Ge, Sn, F, and Cl are shown to behave as shallow donors. (c) 2010 American Institute of Physics.
- 44Karazhanov, S. Z.; Ravindran, P.; Vajeeston, P.; Ulyashin, A.; Finstad, T. G.; Fjellvag, H. Phase Stability, Electronic Structure, and Optical Properties of Indium Oxide Polytypes. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 075129, DOI: 10.1103/PhysRevB.76.075129Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtVWqsbbE&md5=5cc91051bdbb67b7a3a92d3f6b9fe4ccPhase stability, electronic structure, and optical properties of indium oxide polytypesKarazhanov, S. Zh.; Ravindran, P.; Vajeeston, P.; Ulyashin, A.; Finstad, T. G.; Fjellvag, H.Physical Review B: Condensed Matter and Materials Physics (2007), 76 (7), 075129/1-075129/13CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Structural phase stability, electronic structure, optical properties, and high-pressure behavior of polytypes of In2O3 in three space group symmetries I213, Ia3, and R3 were studied by 1st-principles d.-functional calcns. From structural optimization based on total energy calcns., lattice and positional parameters were established, which are in good agreement with the corresponding exptl. data except for I213, where the symmetry anal. for optimized structure indicates that it arrived at the Ia3 phase. In2O3 of space group symmetry Ia3 is found to undergo a pressure-induced phase transition to the R3 phase at pressures around 3.8 GPa. From the anal. of band structure coming out from the calcns. within the local d. and generalized gradient approxns., In2O3 of space group symmetry I213 and R3 are indirect band gap semiconductors, while the other phase of space group Ia3 is having direct band gap. The calcd. carrier effective masses for all these three phases are compared with available exptl. and theor. values. From charge-d. and electron localization function anal., these phases have dominant ionic bonding with noticeable covalent interaction between In and O. The magnitudes of the absorption and reflection coeffs. for In2O3 with space groups Ia3 and R3 are small in the energy range 0-5 eV, indicating that these phases can be regarded and classified as transparent.
- 45Mryasov, O. N.; Freeman, A. J. Electronic Band Structure of Indium Tin Oxide and Criteria for Transparent Conducting Behavior. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 233111, DOI: 10.1103/PhysRevB.64.233111Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXovV2qsro%253D&md5=6df82de30ad4bd7eb3b010f0725253a6Electronic band structure of indium tin oxide and criteria for transparent conducting behaviorMryasov, O. N.; Freeman, A. J.Physical Review B: Condensed Matter and Materials Physics (2001), 64 (23), 233111/1-233111/3CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Indium-based transparent conductors, notably indium tin oxide (ITO), have a wide range of applications due to a unique combination of visible light transparency and modest cond. A fundamental understanding of such an unusual combination of properties is strongly motivated by the great demand for materials with improved transparent conducting properties. Here we formulate conditions for transparent conducting behavior on the basis of the local d. full-potential linear muffin-tin orbital electronic band structure calcns. for Sn-doped In2O3 and available exptl. data. We conclude that the position, dispersion, and character of the lowest conduction band are the key characteristics of the band structure responsible for its electro-optical properties. Further, we find that this lowest band is split with Sn doping due to the strong hybridization with dopant s-type states and this splitting contributes to both the decrease of the plasma frequency and the mobility of the carriers.
- 46Furthmüller, J.; Bechstedt, F. Quasiparticle Bands and Spectra of Ga2O3 Polymorphs. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 115204, DOI: 10.1103/PhysRevB.93.115204Google ScholarThere is no corresponding record for this reference.
- 47Hajnal, Z.; Miró, J.; Kiss, G.; Réti, F.; Deák, P.; Herndon, R. C.; Kuperberg, J. M. Role of Oxygen Vacancy Defect States in the n-type Conduction of β-Ga2O3. J. Appl. Phys. 1999, 86, 3792, DOI: 10.1063/1.371289Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvFWht7g%253D&md5=18fc2c6c7448d58d7642c51e52040171Role of oxygen vacancy defect states in the n-type conduction of β-Ga2O3Hajnal, Zoltan; Miro, Jozsef; Kiss, Gabor; Reti, Ferenc; Deak, Peter; Herndon, Roy C.; Kuperberg, J. MichaelJournal of Applied Physics (1999), 86 (7), 3792-3796CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Based on semiempirical quantum-chem. calcns., the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equil. geometries and formation energies of neutral and doubly ionized vacancies were calcd. Using the calcd. donor level positions of the vacancies, the high temp. n-type conduction is explained. The vacancy concn. is obtained by fitting to the exptl. resistivity and electron mobility.
- 48Swallow, J. E. N. Influence of Polymorphism on the Electronic Structure of Ga2O3. Chem. Mater. 2020, 32, 8460– 8470, DOI: 10.1021/acs.chemmater.0c02465Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVeju7bM&md5=a15f97f6d4857fec636c475c0fd61889Influence of Polymorphism on the Electronic Structure of Ga2O3Swallow, Jack E. N.; Vorwerk, Christian; Mazzolini, Piero; Vogt, Patrick; Bierwagen, Oliver; Karg, Alexander; Eickhoff, Martin; Schormann, Jorg; Wagner, Markus R.; Roberts, Joseph W.; Chalker, Paul R.; Smiles, Matthew J.; Murgatroyd, Philip; Razek, Sara A.; Lebens-Higgins, Zachary W.; Piper, Louis F. J.; Jones, Leanne A. H.; Thakur, Pardeep K.; Lee, Tien-Lin; Varley, Joel B.; Furthmuller, Jurgen; Draxl, Claudia; Veal, Tim D.; Regoutz, AnnaChemistry of Materials (2020), 32 (19), 8460-8470CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The search for new wide-band-gap materials is intensifying to satisfy the need for more advanced and energy-efficient power electronic devices. Ga2O3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theor. approaches to gain insights into their structure-electronic structure relationships. Valence and conduction electronic structure as well as semicore and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron d. functional theory and many-body perturbation theory, provides detailed understanding of the spectroscopic results. The calcd. spectra provide very accurate descriptions of all exptl. spectra and addnl. illuminate the origin of obsd. spectral features. This work provides a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device generations.
- 49Scofield, J. Theoretical photoionization cross sections from 1 to 1500 keV, 1973.Google ScholarThere is no corresponding record for this reference.
- 50Persson, C.; Zunger, A. s-d Coupling in Zinc-blende Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 68, 073205, DOI: 10.1103/PhysRevB.68.073205Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXntV2gu7k%253D&md5=2ee875f84bc050ffbd0ce2324fb7870as-d coupling in zinc-blende semiconductorsPersson, Clas; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (2003), 68 (7), 073205/1-073205/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Most zinc blende semiconductors have a single anion-like s state near the bottom of the valence band, found in d.-of-states (DOS) calcns., and seen in photoemission. Here, we discuss the case where two s-like peaks appear, due to strong s-d coupling. Indeed, away from the k = 0 Brillouin zone center, cation d states and anion s states can couple in zinc blende symmetry. Depending on the energy difference ΔEsd = Esanion - Edcation, this interaction can lead to either a single or two s-like peaks in the DOS and photoemission. We find four types of behaviors: (i) in GaP, GaAs, InP, and InAs, ΔEsd is large, giving rise to a single cation d peak well below the single anion s peak; (ii) similarly, in CdS, CdSe, ZnS, ZnSe, and ZnTe, we see also a single s peak, but now the cation d is above the anion s. In both (i) and (ii) the s-d coupling is very weak. For (iii) in GaN and InN, the local d. approxn. (LDA) predicts two s-like peaks bracketing below and above the cation d-like state. Correcting the too low binding energies of LDA by LDA + SIC (self-interaction correction) still leaves the two s-like peaks. The occurrence of two s-like peaks represents the fingerprint of strong s-d coupling. And (iv) in CdTe, LDA predicts a single s-like peak just as in case (ii) above. However, LDA + SIC correction shifts down the cation d state closer to the anion s band, enhancing the s-d coupling, and leading to the appearance of two s-like peaks. Case (iv) is a remarkable situation where LDA errors cause not only quant. energetic errors, but actually leads to a qual. effect of a DOS peak that exists in LDA + SIC but is missing in LDA. We predict that the double-s peak should be obsd. in photoemission for GaN, InN, and CdTe.
- 51Fuchs, F.; Bechstedt, F. Indium-oxide Polymorphs from First Principles: Quasiparticle Electronic States. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 155107, DOI: 10.1103/PhysRevB.77.155107Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsVGktbw%253D&md5=7c9918c14851840394558fc5e4b4fc9dIndium-oxide polymorphs from first principles: Quasiparticle electronic statesFuchs, F.; Bechstedt, F.Physical Review B: Condensed Matter and Materials Physics (2008), 77 (15), 155107/1-155107/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The electronic structure of In2O3 polymorphs is calcd. from first principles using d. functional theory (DFT) and many-body perturbation theory (MBPT). DFT calcns. with a local exchange-correlation (XC) functional give the relaxed at. coordinates of the two stable polymorphs. Their electronic structure, i.e., the band structure and d. of states, is studied within MBPT. The quasiparticle equation is solved in two steps. As the zeroth approxn. for the XC self-energy the nonlocal potential resulting from a HSE03 hybrid functional is used. In the sense of a self-consistent procedure G0W0 quasiparticle corrections are computed on top. The calcd. direct quasiparticle gaps at Γ amt. to 3.3 eV (rhombohedral) and 3.1 eV (cubic). The rhombohedral polymorph is found to exhibit a near degeneracy of the valence-band maxima at the Γ point and on the Γ-L line, while the valence-band max. of the cubic polymorph occurs near Γ. Interconduction band transitions are identified as possible origin of conflicting exptl. reports, claiming a much larger difference between the direct and indirect gap. The results for gaps, d-band positions, and d. of states are compared with available exptl. data.
- 52Fuchs, F.; Furthmüller, J.; Bechstedt, F.; Shishkin, M.; Kresse, G. Quasiparticle Band Structure based on a Generalized Kohn-Sham Scheme. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 115109, DOI: 10.1103/PhysRevB.76.115109Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFeqt7fI&md5=ef0914feed4c7203ad821c666df823c4Quasiparticle band structure based on a generalized Kohn-Sham schemeFuchs, F.; Furthmuller, J.; Bechstedt, F.; Shishkin, M.; Kresse, G.Physical Review B: Condensed Matter and Materials Physics (2007), 76 (11), 115109/1-115109/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We present a comparative full-potential study of generalized Kohn-Sham (gKS) schemes with explicit focus on their suitability as starting point for the soln. of the quasiparticle equation. We compare G0W0 quasiparticle band structures calcd. upon local-d. approxn. (LDA), screened-exchange, HSE03, PBE0, and Hartree-Fock functionals for exchange and correlation (XC) for Si, InN, and ZnO. Furthermore, the HSE03 functional is studied and compared to the generalized gradient approxn. (GGA) for 15 nonmetallic materials for its use as a starting point in the calcn. of quasiparticle excitation energies. For this case, the effects of self-consistency in the GW self-energy are also analyzed. It is shown that the use of a gKS scheme as a starting point for a perturbative quasiparticle correction can improve upon the deficiencies found for LDA or GGA starting points for compds. with shallow d bands. For these solids, the order of the valence and conduction bands is often inverted using local or semilocal approxns. for XC, which makes perturbative G0W0 calcns. unreliable. The use of a gKS starting point allows for the calcn. of fairly accurate band gaps even in these difficult cases, and generally single-shot G0W0 calcns. following calcns. using the HSE03 functional are very close to expt.
- 53Ley, L.; Pollak, R. A.; McFeely, F. R.; Kowalczyk, S. P.; Shirley, D. A. Total Valence-band Densities of States of III-V and II-VI Compounds from X-ray Photoemission Spectroscopy. Phys. Rev. B 1974, 9, 600– 621, DOI: 10.1103/PhysRevB.9.600Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXhtFClsbY%253D&md5=d78a05cbcbffbc1ff9e665a1a4bc6743Total valence-band densities of states of [Groups] III-V and II-VI compounds from x-ray photoemission spectroscopyLey, L.; Pollak, R. A.; McFeely, F. R.; Kowalczyk, S. P.; Shirley, D. A.Physical Review B: Solid State (1974), 9 (2), 600-21CODEN: PLRBAQ; ISSN:0556-2805.A comprehensive survey of the total valence-band x-ray-photoemission spectra of 14 semiconductors is reported. The x-ray photoelectron spectra of cubic GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdTe, and HgTe, and of hexagonal ZnO, CdS, and CdSe were obtained from freshly cleaved single crystals, in the 0-50-eV binding-energy range, by using monochromatized Al Kα (1486.6 eV) radiation. The binding energies of the outermost d shells are reported. They were detd. relative both to the top of the valence bands (EBV) and to the Fermi level of a thin layer of Au that was vapor deposited after each run (EBF). These data also yielded accurate measures of sample charging. The Fermi level fell near the center of the gap for 6 samples, near the top for 2, and near the bottom for 3. Evidence for an apparent increase in core d-level spin-orbit splitting over free-atom values was interpreted as a possible spreading of a Γ7 and a Γ8 level from the upper (d3/2) Γ8 level by a tetrahedral crystal field. The s, p valence-band spectra showed 3 main peaks, with considerable structure on the least-bound peak. A discussion is given of the validity of comparing the valence-band (VB) spectrum I'(E) with VB d. of states, including cross-section modulation, final-state modulation, and relaxation effects. Characteristic binding energies of spectra features in I'(E) are tabulated. In addn., the energies of the characteristic symmetry points L3, X5, W2, Σ1min., W1, X3(L1), X1, L1, and Γ1 are given for the 11 cubic compds. These are compared with uv photoemission spectroscopy results where available and with theor. band-structure results where available. The energies calcd. by using the relativistic-orthogonalized-plane-wave approach with Xαβ exchange agree very well with expt., on the whole. In particular, they predict the important ionicity gap X3-X1 quite accurately. The ds. of states calcd. by using the empirical-pseudopotential method provided a useful basis for relating features in I'(E) to energies of the characteristic symmetry points. Band-structure calcns. in combination with x-ray-photoemission spectra appears to provide a very powerful approach to establishing the total valence-band structure of semiconductors.
- 54Erhart, P.; Klein, A.; Egdell, R. G.; Albe, K. Band Structure of Indium Oxide: Indirect Versus Direct Band Gap. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 153205, DOI: 10.1103/PhysRevB.75.153205Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXltVSgsLg%253D&md5=9bfb8b973344fb98a131cb2b8c3bd9e0Band structure of indium oxide: Indirect versus direct band gapErhart, Paul; Klein, Andreas; Egdell, Russell G.; Albe, KarstenPhysical Review B: Condensed Matter and Materials Physics (2007), 75 (15), 153205/1-153205/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The nature of the band gap of In oxide is still a matter of debate. Based on optical measurements the presence of an indirect band gap was suggested, which is 0.9 to 1.1 eV smaller than the direct band gap at the Γ point. This could be caused by strong mixing of O 2p and In 4d orbitals off Γ. The authors have performed extensive d. functional theory calcns. using the LDA+U and the GGA+U methods to elucidate the contribution of the In 4d states and the effect of spin-orbit coupling on the valence band structure. Although an indirect band gap is obtained, the energy difference between the overall valence band max. and the highest occupied level at the Γ point is <50 meV. The exptl. observation cannot be related to the electronic structure of the defect free bulk material.
- 55Wei, S.-H.; Nie, X.; Batyrev, I. G.; Zhang, S. B. Breakdown of the Band-gap-common-cation Rule: The Origin of the Small Band Gap of InN. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 67, 165209, DOI: 10.1103/PhysRevB.67.165209Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjvVKnsbk%253D&md5=c98fd287274834b31befd3c84871662eBreakdown of the band-gap-common-cation rule: the origin of the small band gap of InNWei, Su-Huai; Nie, Xiliang; Batyrev, Iskander G.; Zhang, S. B.Physical Review B: Condensed Matter and Materials Physics (2003), 67 (16), 165209/1-165209/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)It is well accepted that the band gap of a semiconductor compd. increases as the at. no. decreases. However, recent measurements of the small band gap of InN (Eg ∼ 0.9 eV) suggest that this rule may not hold for the common-cation In compds. Using a band-structure method that includes band-gap correction, we systematically study the chem. trends of the band-gap variation in III-V semiconductors. The calcd. InN band gap is 0.85 ± 0.1 eV, much smaller than previous exptl. value of ∼1.9 eV. The InN band-gap anomaly is explained in terms of at.-orbital energies and the band-gap deformation potentials.
- 56Wei, S.-H.; Zunger, A. Predicted Band-gap Pressure Coefficients of all Diamond and Zinc-blende Semiconductors: Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 60, 5404, DOI: 10.1103/PhysRevB.60.5404Google Scholar56https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlt1yjs70%253D&md5=e5fd953bf853520618f5819ee277e8f6Predicted band-gap pressure coefficients of all diamond and zinc-blende semiconductors: Chemical trendsWei, Su-Huai; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1999), 60 (8), 5404-5411CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)We have studied systematically the chem. trends of the band-gap pressure coeffs. of all Group IVA, IIIA-VA, and IIB-VIA semiconductors using first-principles band-structure method. We have also calcd. the individual "abs." deformation potentials of the valence-band max. (VBM) and conduction-band min. (CBM). We find that (1) the vol. deformation potentials of the Γ6c CBM are usually large and always neg., while (2) the vol. deformation potentials of the Γ8v VBM state are usually small and neg. for compds. contg. occupied valence d state but pos. for compds. without occupied valence d orbitals. Regarding the chem. trends of the band-gap pressure coeffs., we find that (3) apΓ-Γ decreases as the ionicity increases (e.g., from Ge → GaAs → ZnSe), (4) apΓ-Γ increases significantly as anion at. no. increases (e.g., from GaN → GaP → GaAs → GaSb), (5) apΓ-Γ decreases slightly as cation at. no. increases (e.g., from AlAs → GaAs → InAs), (6) the variation of apΓ-L are relatively small and follow similar trends as apΓ-Γ, and (7) the magnitude of apΓ-X are small and usually neg., but are sometimes slightly pos. for compds. contg. first-row elements. Our calcd. chem. trends are explained in terms of the energy levels of the at. valence orbitals and coupling between these orbital. In light of the above, we suggest that "empirical rule" of the pressure coeffs. should be modified.
- 57Li, Y.-H.; Gong, X. G.; Wei, S.-H. Ab Initio All-Electron Calculation of Absolute Volume Deformation Potentials of IV-IV, III-V, and II-VI Semiconductors: The Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 245206, DOI: 10.1103/PhysRevB.73.245206Google Scholar57https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvFCgtb0%253D&md5=885f504cdae67febdf534bab954e9433Ab initio all-electron calculation of absolute volume deformation potentials of IV-IV, III-V, and II-VI semiconductors: The chemical trendsLi, Yong-Hua; Gong, X. G.; Wei, Su-HuaiPhysical Review B: Condensed Matter and Materials Physics (2006), 73 (24), 245206/1-245206/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We calc. systematically the abs. vol. deformation potential (AVDP) of the Γ8v valence band max. (VBM) and the Γ6c conduction band min. (CBM) states for all group IV, III-V, and II-VI semiconductors. Unlike previous calcns. that involve various assumptions, the AVDPs are calcd. using a recently developed approach that is independent of the selection of the ref. energy levels. We find that although the vol. deformation potentials of the CBM state are usually large and always neg., those of the VBM state are usually small and always pos. The AVDP of the VBM state decreases as the p-d coupling increases, e.g., in the II-VI compds. The AVDP of CBM decreases as the ionicity increases. Our calcd. chem. trends of the AVDPs are explained in terms of the AO energy levels and coupling between these orbitals.
- 58Mann, J. B.; Meek, T. L.; Allen, L. C. Configuration Energies of the Main Group Elements. J. Am. Chem. Soc. 2000, 122, 2780– 2783, DOI: 10.1021/ja992866eGoogle Scholar58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhs1Wktb8%253D&md5=dab049932dd3ad097093f524650cb1a5Configuration Energies of the Main Group ElementsMann, Joseph B.; Meek, Terry L.; Allen, Leland C.Journal of the American Chemical Society (2000), 122 (12), 2780-2783CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Configuration energies (CEs), formerly called spectroscopic electronegativities, are an attempt to quantum mech. define, and extend, the important chem. concept of electronegativity. In a previous paper (J. Am. Chem. Soc. 1989, 111, 9003) we reported high-resoln. exptl. values obtained from the National Institutes of Science and Technol. spectroscopic energy level tables using the formula CE = (nεs + mεp)/(n + m); n and m are the no. of s and p electrons and εs and εp are their multiplet-averaged one-electron energies, for the 34 s and p-block atoms H→Xe. This CE definition is a direct extension of N. Bohr's introduction of electron configurations to quantum mech. rationalize the periodic table (hence its designation as configuration energy). Here we give exptl. nos. for the remaining 8 sixth row representative atoms plus Zn, Cd, and Hg. In addn., we have carried out high accuracy numerical Dirac-Hartree-Fock solns. for all 45 atoms. Results from these calcns. closely parallel the exptl. values and enable us to est. some of the at. multiplet levels for which no exptl. data exist. CE leads to nos. which are interpretable as an "electron attracting power" in the same manner as the traditional scales of Pauling and Allred & Rochow. They are also strongly correlated with at. energy level spacings, therefore providing an addnl. interpretability compatible with energy level data and the MO diagrams that dominate much of contemporary chem. Likewise, CEs are able to rationalize the origin of the metalloid band (diagonal line sepg. metals from nonmetals) in the periodic table and the new detn. of sixth row CEs permit designation of bismuth and polonium as metalloids, clarifying their previous uncertain classification between metal and metalloid.
- 59Fischer, C. F. Average-energy-of-configuration Hartree-Fock Results for the Atoms Helium to Radon. At. Data Nucl. Data Tables 1973, 12, 87– 99, DOI: 10.1016/0092-640X(73)90014-4Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXjtVOrsw%253D%253D&md5=c7b272a39353aa4c72c5eed8b5af2af3Average-energy-of-configuration Hartree-Fock results for the atoms helium to radonFischer, Charlotte FroeseAtomic Data and Nuclear Data Tables (1973), 12 (1), 87-99CODEN: ADNDAT; ISSN:0092-640X.Table I of the paper [Atomic Data, 1972, 4, 301] is actually for the lowest term of the configuration rather than for the av.-energy-of-the-configuration, as the paper implies. For configurations contg. 4f electrons the results of that paper correspond to an incorrect energy expression. When the energy of the lowest term is also the av. energy as for complete groups or complete groups plus (or minus) one electron, all atomic parameters are correct except for the total energy which is too high by the amt. q(q - 1) [2/95 - 2/195]F2(4f,4f), where q is the no. of 4f electrons. In all other cases, the radial functions were detd. from an energy expression too low by the same amt. The at. properties are reasonably accurate but the energy is too low. Table I for the av.-energy-of-the-configuration is given.
- 60Herman, F.; Skillman, S. Atomic Structure Calculations; Prentice-Hall: Englewood Cliffs, NJ, 1963.Google ScholarThere is no corresponding record for this reference.
- 61Vurgaftman, I.; Meyer, J. R.; Ram-Mohan, L. R. Band Parameters for III-V Compound Semiconductors and their Alloys. J. Appl. Phys. 2001, 89, 5815– 5875, DOI: 10.1063/1.1368156Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXkt1Wrt74%253D&md5=cf8f5276c819c0a694a621e86c3d827bBand parameters for III-V compound semiconductors and their alloysVurgaftman, I.; Meyer, J. R.; Ram-Mohan, L. R.Journal of Applied Physics (2001), 89 (11, Pt. 1), 5815-5875CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)A review with 1001 refs. We present a comprehensive, up-to-date compilation of band parameters for the technol. important III-V zinc blende and wurtzite compd. semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calcns., we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temp. and alloy-compn. dependences where available. Heterostructure band offsets are also given, on an abs. scale that allows any material to be aligned relative to any other.
- 62Wu, J.; Walukiewicz, W.; Shan, W.; Yu, K. M.; Ager, J. W.; Li, S. X.; Haller, E. E.; Lu, H.; Schaff, W. J. Temperature Dependence of the Fundamental Band Gap of InN. J. Appl. Phys. 2003, 94, 4457– 4460, DOI: 10.1063/1.1605815Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsVWhur0%253D&md5=ecc91761222248b13d7a4706692ed570Temperature dependence of the fundamental band gap of InNWu, J.; Walukiewicz, W.; Shan, W.; Yu, K. M.; Ager, J. W.; Li, S. X.; Haller, E. E.; Lu, Hai; Schaff, William J.Journal of Applied Physics (2003), 94 (7), 4457-4460CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The fundamental band gap of InN films grown by MBE were measured by transmission and photoluminescence spectroscopy as a function of temp. The band edge absorption energy and its temp. dependence depend on the doping level. The band gap variation and Varshni parameters of InN are compared with other Group III nitrides. The energy of the photoluminescence peak is affected by the emission from localized states and cannot be used to det. the band gap energy. Based on the results obtained on two samples with distinctly different electron concns., the effect of degenerate doping on the optical properties of InN is discussed.
- 63Tippins, H. H. Optical Absorption and Photoconductivity in the Band Edge of β-Ga2O3. Phys. Rev. 1965, 140, A316– A319, DOI: 10.1103/PhysRev.140.A316Google Scholar63https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXks1Oqs7g%253D&md5=01581b3d252ce2533abeaea3b50246daOptical absorption and photoconductivity in the band edge of β-Ga2O3Tippins, H. H.Physical Review (1965), 140 (1A), 316-19CODEN: PHRVAO; ISSN:0031-899X.Optical absorption and photocond. were observed in the uv in single crystals of nominally pure β-Ga2O3. At room temp. a steep absorption edge, characteristic of a band-to-band transition, is observed at 2700 A. The edge is shifted approx. 100 A. toward shorter wavelengths when the temp. is reduced to 77°K. Photocond. begins coincident with the absorption edge at 77°K., but could not be detected at room temp. A model is proposed in which the absorption arises as a result of excitation of an electron from the O 2p band to the Ga 4s band. Calcns. using this model and the Born-Haber cycle are in good agreement with the observed band gap of 4.7 ev. The much smaller band gap of β-Ga2O3 as compared with sapphire is due to the reduced coordination no. of the ions involved in the transition.
- 64Varley, J. B.; Schleife, A. Bethe-Salpeter Calculation of Optical-absorption Spectra of In2O3 and Ga2O3. Semicond. Sci. Technol. 2015, 30, 024010, DOI: 10.1088/0268-1242/30/2/024010Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXit1ygs74%253D&md5=d2b3cafee0b2749f35fd4b24b9c2f3b4Bethe-Salpeter calculation of optical-absorption spectra of In2O3 and Ga2O3Varley, Joel B.; Schleife, AndreSemiconductor Science and Technology (2015), 30 (2), 24010/1-24010/5, 5 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)Transparent conducting oxides keep attracting strong scientific interest not only due to their promising potential for 'transparent electronics' applications but also due to their intriguing optical absorption characteristics. Materials such as In2O3 and Ga2O3 have complicated unit cells and, consequently, are interesting systems for studying the physics of excitons and anisotropy of optical absorption. Since currently no exptl. data is available, for instance, for their dielec. functions across a large photon-energy range, we employ modern first-principles computational approaches based on many-body perturbation theory to provide theor.-spectroscopy results. Using the Bethe-Salpeter framework, we compute dielec. functions and we compare to spectra computed without excitonic effects. We find that the electron-hole interaction strongly modifies the spectra and we discuss the anisotropy of optical absorption that we find for Ga2O3 in relation to existing theor. and exptl. data.
- 65Wei, S.-H.; Zunger, A. Calculated Natural Band Offsets of all II-VI and III-V Semiconductors: Chemical Trends and the Role of Cation d Orbitals. Appl. Phys. Lett. 1998, 72, 2011, DOI: 10.1063/1.121249Google Scholar65https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXisValtLk%253D&md5=748c0289622ef2e2d806e9ae6e83b510Calculated natural band offsets of all II-VI and III-V semiconductors: Chemical trends and the role of cation d orbitalsWei, Su-Huai; Zunger, AlexApplied Physics Letters (1998), 72 (16), 2011-2013CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using first-principles all-electron band structure method, we have systematically calcd. the natural band offsets ΔEv between all II-VI and sep. between III-V semiconductor compds. Fundamental regularities are uncovered: for common-cation systems ΔEv decreases when the cation at. no. increases, while for common-anion systems ΔEv decreases when the anion at. no. increases. We find that coupling between anion p and cation d states plays a decisive role in detg. the abs. position of the valence band max. and thus the obsd. chem. trends.
- 66Wei, S.-H.; Zunger, A. Role of d Orbitals in Valence-Band Offsets of Common-Anion Semiconductors. Phys. Rev. Lett. 1987, 59, 144, DOI: 10.1103/PhysRevLett.59.144Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsVWmtr8%253D&md5=6e378e78e911e4dd3859f08c2579982fRole of d orbitals in valence-band offsets of common-anion semiconductorsWei, Su Huai; Zunger, AlexPhysical Review Letters (1987), 59 (1), 144-7CODEN: PRLTAO; ISSN:0031-9007.All-electron first-principles electronic structure calcns. of core levels were made on common-anion semiconductors AlAs-GaAs and CdTe-HgTe and contrary to previous expectations, the valence-band offsets are decided primarily by intrinsic bulk effects and the interface charge transfer has but a small effect on these quantities. The failure of previous models results primarily from the omission of cation d orbitals.
- 67Van de Walle, C. G.; Martin, R. M. Absolute Deformation Potentials: Formulation and Ab initio Calculations for Semiconductors. Phys. Rev. Lett. 1989, 62, 2028– 2031, DOI: 10.1103/PhysRevLett.62.2028Google Scholar67https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXksVGmsrk%253D&md5=0a862095ddf2e99fab3c0424985451ec"Absolute" deformation potentials: formulation and ab initio calculations for semiconductorsVan de Walle, Chris G.; Martin, Richard M.Physical Review Letters (1989), 62 (17), 2028-31CODEN: PRLTAO; ISSN:0031-9007.The subjects of this paper are the proper inclusion of long-range electrostatic terms in the theory of electronic deformation potentials, a way to include these terms by using supercells in ab initio d.-functional methods, and calcns. for selected semiconductors. The connection with the heterojunction problem is described. The results are compared with previous model theories and with expt.
- 68Cardona, M.; Christensen, N. E. Acoustic Deformation Potentials and Heterostructure Band Offsets in Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1987, 35, 6182– 6194, DOI: 10.1103/PhysRevB.35.6182Google Scholar68https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsVWnsbw%253D&md5=f2e31cef82444da65df62df291204fe8Acoustic deformation potentials and heterostructure band offsets in semiconductorsCardona, Manuel; Christensen, Niels E.Physical Review B: Condensed Matter and Materials Physics (1987), 35 (12), 6182-94CODEN: PRBMDO; ISSN:0163-1829.The abs. hydrostatic deformation potentials calcd. by J. A. Verges, et al., (1982) for tetrahedral semiconductors with the linear muffin-tin-orbital method must be screened by the dielec. response of the material before using them to calc. electron-phonon interaction. This screening can be estd. by using the midpoint of an av. dielec. gap evaluated at special (Baldereschi) points of the band structure. This dielec. midgap energy (DME) was related to the charge-neutrality point (Tersoff, J., 1984) to evaluate band offsets in heterojunctions and Schottky-barrier heights. Band offsets obtained with this method for several heterojunctions are tabulated, and compared with existing exptl. results and other theor. calcns. The DME's are tabulated, and compared with those based on charge-neutrality points.
- 69Li, Y.-H.; Gong, X. G.; Wei, S.-H. Ab initio All-electron Calculation of Absolute Volume Deformation Potentials of IV-IV, III-V, and II-VI Semiconductors: The Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 245206, DOI: 10.1103/PhysRevB.73.245206Google Scholar69https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvFCgtb0%253D&md5=885f504cdae67febdf534bab954e9433Ab initio all-electron calculation of absolute volume deformation potentials of IV-IV, III-V, and II-VI semiconductors: The chemical trendsLi, Yong-Hua; Gong, X. G.; Wei, Su-HuaiPhysical Review B: Condensed Matter and Materials Physics (2006), 73 (24), 245206/1-245206/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We calc. systematically the abs. vol. deformation potential (AVDP) of the Γ8v valence band max. (VBM) and the Γ6c conduction band min. (CBM) states for all group IV, III-V, and II-VI semiconductors. Unlike previous calcns. that involve various assumptions, the AVDPs are calcd. using a recently developed approach that is independent of the selection of the ref. energy levels. We find that although the vol. deformation potentials of the CBM state are usually large and always neg., those of the VBM state are usually small and always pos. The AVDP of the VBM state decreases as the p-d coupling increases, e.g., in the II-VI compds. The AVDP of CBM decreases as the ionicity increases. Our calcd. chem. trends of the AVDPs are explained in terms of the AO energy levels and coupling between these orbitals.
- 70Varley, J. B.; Samanta, A.; Lordi, V. Descriptor-Based Approach for the Prediction of Cation Vacancy Formation Energies and Transition Levels. J. Phys. Chem. Lett. 2017, 8, 5059– 5063, DOI: 10.1021/acs.jpclett.7b02333Google Scholar70https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFyrurjK&md5=65a28aa7efc87cf4b081712a9cc22fc0Descriptor-based approach for the prediction of cation vacancy formation energies and transition levelsVarley, Joel B.; Samanta, Amit; Lordi, VincenzoJournal of Physical Chemistry Letters (2017), 8 (20), 5059-5063CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Point defects largely det. the obsd. optical and elec. properties of a given material, yet the characterization and identification of defects has remained a slow and tedious process, both exptl. and theor. We demonstrate a computationally-cheap model that can reliably predict the formation energies of cation vacancies as well as the location of their electronic states in a large set of II-VI and III-V materials using only parameters obtained from the bulk primitive unit cell (2-4 atoms). We apply our model to ordered alloys within the CdZnSeTe, CdZnS, and ZnMgO systems and predict the positions of cation vacancy charge-state transition levels with a mean abs. error of < 0.2 eV compared to the explicitly calcd. values, showing useful accuracy without the need for the expensive and large-scale calcns. typically required. This suggests the properties of other point defects may also be predicted with useful accuracy from only bulk-derived properties.
- 71Schleife, A.; Fuchs, F.; Rödl, C.; Furthmüller, J.; Bechstedt, F. Branch-point Energies and Band Discontinuities of III-nitrides and III-/II-oxides from Quasiparticle Band-structure Calculations. Appl. Phys. Lett. 2009, 94, 012104, DOI: 10.1063/1.3059569Google Scholar71https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXkvVCrug%253D%253D&md5=a62968ae457463c41f4e616e8b0a72e8Branch-point energies and band discontinuities of III-nitrides and III-/II-oxides from quasiparticle band-structure calculationsSchleife, A.; Fuchs, F.; Roedl, C.; Furthmueller, J.; Bechstedt, F.Applied Physics Letters (2009), 94 (1), 012104/1-012104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using quasiparticle band structures based on modern electronic-structure theory, we calc. the branch-point energies for zinc blende (GaN, InN), rocksalt (MgO, CdO), wurtzite (AlN, GaN, InN, ZnO), and rhombohedral crystals (In2O3). For InN, CdO, ZnO, and also In2O3 the branch-point energies are located within the lowest conduction band. These predictions are in agreement with observations of surface electron accumulation (InN, CdO) or conducting behavior of the oxides (ZnO, In2O3). The results are used to predict natural band offsets for the materials investigated. (c) 2009 American Institute of Physics.
- 72Shapera, E. P.; Schleife, A. Database-Driven Materials Selection for Semiconductor Heterojunction Design. Advanced Theory and Simulations 2018, 1, 1800075, DOI: 10.1002/adts.201800075Google ScholarThere is no corresponding record for this reference.
- 73Walsh, A.; Catlow, C. R. A.; Zhang, K. H. L.; Egdell, R. G. Control of the Band-gap States of Metal Oxides by the Application of Epitaxial Strain: The Case of Indium Oxide. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 161202(R) DOI: 10.1103/PhysRevB.83.161202Google Scholar73https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXlsV2ktLc%253D&md5=50d4c1a74160380d7ce3293607967dc1Control of the band-gap states of metal oxides by the application of epitaxial strain. The case of indium oxideWalsh, Aron; Catlow, C. Richard A.; Zhang, K. H. L.; Egdell, Russell G.Physical Review B: Condensed Matter and Materials Physics (2011), 83 (16), 161202/1-161202/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We demonstrate that metal oxides exhibit the same relationship between lattice strain and electronic band gap as nonpolar semiconductors. Epitaxial growth of ultrathin [111]-oriented single-crystal In2O3 films on a mismatched YSZ substrate reveals a net band-gap decrease, which is dissipated as the film thickness is increased and the epitaxial strain is relieved. Calcn. of the band-gap deformation of In2O3, using a hybrid d. functional, confirms that, while the uniaxial lattice contraction along [111] results in a band-gap increase due to a raise of the conduction band, the lattice expansion in the (111) plane caused by the substrate mismatch compensates, resulting in a net band-gap decrease. These results have direct implications for tuning the band gaps and transport properties of oxides for application in optoelectronic devices.
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, 15178-15196. https://doi.org/10.1039/D3TC02756B
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- Taikyu Kim, Cheol Hee Choi, Jae Seok Hur, Daewon Ha, Bong Jin Kuh, Yongsung Kim, Min Hee Cho, Sangwook Kim, Jae Kyeong Jeong. Progress, Challenges, and Opportunities in Oxide Semiconductor Devices: A Key Building Block for Applications Ranging from Display Backplanes to 3D Integrated Semiconductor Chips. Advanced Materials 2023, 35
(43)
https://doi.org/10.1002/adma.202204663
- Michael Lorenz, Holger Hochmuth, Holger von Wenckstern, Marius Grundmann. Flexible hardware concept of pulsed laser deposition for large areas and combinatorial composition spreads. Review of Scientific Instruments 2023, 94
(8)
https://doi.org/10.1063/5.0142085
- Dongwook Kim, Hyeonju Lee, Youngjun Yun, Jaehoon Park, Xue Zhang, Jin-Hyuk Bae, Sungkeun Baang. Analyzing Acceptor-like State Distribution of Solution-Processed Indium-Zinc-Oxide Semiconductor Depending on the In Concentration. Nanomaterials 2023, 13
(15)
, 2165. https://doi.org/10.3390/nano13152165
- Haojie Li, Zhengyuan Wu, Pengfei Tian, Jinchai Li, Junyong Kang, Guoqi Zhang, Zhilai Fang. AlInGaN nanocrystal seeded growth of weak p-type β-(In
0.1
Ga
0.9
)
2
O
3
nanowires and nanobelts. CrystEngComm 2023, 25
(25)
, 3674-3681. https://doi.org/10.1039/D3CE00317E
- Kammutty Musliyarakath Abdul Shekkeer, Junchen Deng, Kuan Yew Cheong, Kadiarakath Manathparambil Riyas, Hock Jin Quah. Alteration in growth temperatures of metal-organic decomposed GaxCe1-xOyNz passivation layer in nitrogen/oxygen/nitrogen ambient. Ceramics International 2023, 49
(9)
, 14760-14770. https://doi.org/10.1016/j.ceramint.2023.01.072
- Xilai Liu, Chunxiang Zhao, Chunyao Niu, Yu Jia. Computational and experimental studies on band alignment of ZnO/InxGa2−xO3/GaN heterojunctions. The Journal of Chemical Physics 2023, 158
(13)
https://doi.org/10.1063/5.0134277
- Hao Wang, Behrouz Movahhed Nouri, Hamed Dalir, Volker J. Sorger, , . 30 GHz plasmonic slot MoTe2 photodetector integrated with silicon photonic circuits at telecom wavelength. 2023, 38. https://doi.org/10.1117/12.2651013
- Vadim MORARI, Victor ZALAMAI, Emil V. RUSU, Veaceslav V. URSAKI, Pascal COLPO, Ion M. TIGINYANU, , , . Study of (GaxIn1-x)2O3 thin films produced by aerosol deposition method. 2023, 12. https://doi.org/10.1117/12.2642127
- Junting Chen, Junlei Zhao, Sirui Feng, Li Zhang, Yan Cheng, Hang Liao, Zheyang Zheng, Xiaolong Chen, Zhen Gao, Kevin J. Chen, Mengyuan Hua. Formation and Applications in Electronic Devices of Lattice‐Aligned Gallium Oxynitride Nanolayer on Gallium Nitride. Advanced Materials 2023, 35
(12)
https://doi.org/10.1002/adma.202208960
- N.N. Yakovlev, A.V. Almaev, V.I. Nikolaev, B.O. Kushnarev, A.I. Pechnikov, S.I. Stepanov, A.V. Chikiryaka, R.B. Timashov, M.P. Scheglov, P.N. Butenko, D.A. Almaev, E.V. Chernikov. Low-resistivity gas sensors based on the In2O3-Ga2O3 mixed compounds films. Materials Today Communications 2023, 34 , 105241. https://doi.org/10.1016/j.mtcomm.2022.105241
- Eric Welch, Pablo Borges, Luisa Scolfaro. Hybrid density functional theory study of substitutional Gd in
β
-Ga2O3. Physica B: Condensed Matter 2023, 651 , 414558. https://doi.org/10.1016/j.physb.2022.414558
- Sai Lyu. Band offsets at the interfaces between
β
−
Ga
2
O
3
and
Al
2
O
3
. Physical Review Materials 2023, 7
(1)
https://doi.org/10.1103/PhysRevMaterials.7.014603
- Dongwook Kim, Hyeonju Lee, Bokyung Kim, Sungkeun Baang, Kadir Ejderha, Jin-Hyuk Bae, Jaehoon Park. Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance. Materials 2022, 15
(19)
, 6763. https://doi.org/10.3390/ma15196763
- Kammutty Musliyarakath Abdul Shekkeer, Kuan Yew Cheong, Hock Jin Quah. Growth of Quaternary GaxCe1-xOyNz passivation layer for silicon based metal-oxide-semiconductor capacitor. Materials Chemistry and Physics 2022, 290 , 126549. https://doi.org/10.1016/j.matchemphys.2022.126549
- Nasir Alfaraj, Kuang-Hui Li, Laurentiu Braic, Mohamed Nejib Hedhili, Zaibing Guo, Tien Khee Ng, Boon S. Ooi. Optical and interfacial characteristics of a heterojunction between (2¯01)-oriented single-domain β-(In
0.072
Ga
0.928
)
2
O
3
and α-Al
2
O
3
crystals. Optical Materials Express 2022, 12
(8)
, 3273. https://doi.org/10.1364/OME.462192
- Paul Lee, Minh Nhut Le, Gahye Kim, Sung Min Kwon, Jeong‐Wan Jo, Jaehyun Kim, Yong‐Hoon Kim, Sung Kyu Park, Kyunghan Ahn, Myung‐Gil Kim. Efficient Oxygen‐Vacancy Suppression and Electrical Stabilization of Solution‐Processed In
2
O
3
:Q (Q
=
S, Se) Thin‐Film Transistor with Chalcogen Alloying. Advanced Electronic Materials 2022, 8
(7)
https://doi.org/10.1002/aelm.202101250
- Manoj K. Jamarkattel, Adam B. Phillips, Indra Subedi, Abasi Abudulimu, Ebin Bastola, Deng-Bing Li, Zhaoning Song, Xavier Matthew, Yanfa Yan, Randy J. Ellingson, Nikolas J. Podraza, Michael J. Heben. Properties of Co-Sputtered $(\text{In}_{\mathrm{X}}\text{Ga}_{(1-\mathrm{X})})_{2}\mathrm{O}_{3}$ Layers Used in CdTe Solar Cells. 2022, 0972-0974. https://doi.org/10.1109/PVSC48317.2022.9938695
- Mahitosh Biswas, Hiroyuki Nishinaka. Thermodynamically metastable
α
-,
ε
- (or
κ
-), and
γ
-Ga2O3: From material growth to device applications. APL Materials 2022, 10
(6)
https://doi.org/10.1063/5.0085360
- Ziheng Wang, Zehao Lin, Mengwei Si, Peide D. Ye. Characterization of Interface and Bulk Traps in Ultrathin Atomic Layer-Deposited Oxide Semiconductor MOS Capacitors With HfO2/In2O3 Gate Stack by C-V and Conductance Method. Frontiers in Materials 2022, 9 https://doi.org/10.3389/fmats.2022.850451
- Yuri Ogura, Yuta Arata, Hiroyuki Nishinaka, Masahiro Yoshimoto. Alloying In
2
O
3
and Ga
2
O
3
on AlN templates for deep-ultraviolet transparent conductive films by mist chemical vapor deposition. Japanese Journal of Applied Physics 2022, 61
(SC)
, SC1037. https://doi.org/10.35848/1347-4065/ac4688
- Wenshan Chen, Xiangyu Xu, Jiaye Zhang, Jueli Shi, Jiawei Zhang, Wencheng Chen, Qijin Cheng, Yuzheng Guo, Kelvin H. L. Zhang. (In
x
Ga
1−
x
)
2
O
3
Thin Film Based Solar‐Blind Deep UV Photodetectors with Ultra‐High Detectivity and On/Off Current Ratio. Advanced Optical Materials 2022, 10
(7)
https://doi.org/10.1002/adom.202102138
- Kar Yeow Tan, Hock Jin Quah. Growth of metal‐organic decomposed ternary
Ga
x
Ce
y
O
z
films by nitrogen‐infused wet oxidation for metal‐oxide‐semiconductor capacitor. International Journal of Energy Research 2022, 46
(5)
, 5756-5770. https://doi.org/10.1002/er.7520
- Alexandra Papadogianni, Takahiro Nagata, Oliver Bierwagen. The electrical conductivity of cubic (In
1−x
Ga
x
)
2
O
3
films (x ≤ 0.18): native bulk point defects, Sn-doping, and the surface electron accumulation layer. Japanese Journal of Applied Physics 2022, 61
(4)
, 045502. https://doi.org/10.35848/1347-4065/ac4ec7
- Alexandra Papadogianni, Charlotte Wouters, Robert Schewski, Johannes Feldl, Jonas Lähnemann, Takahiro Nagata, Elias Kluth, Martin Feneberg, Rüdiger Goldhahn, Manfred Ramsteiner, Martin Albrecht, Oliver Bierwagen. Molecular beam epitaxy of single-crystalline bixbyite
(
In
1
−
x
Ga
x
)
2
O
3
films (
x
≤
0.18
): Structural properties and consequences of compositional inhomogeneity. Physical Review Materials 2022, 6
(3)
https://doi.org/10.1103/PhysRevMaterials.6.033604
- Khue Nguyen, Pavle V. Radovanovic. Defects and impurities in colloidal Ga
2
O
3
nanocrystals: new opportunities for photonics and lighting. Canadian Journal of Chemistry 2022, 100
(1)
, 1-8. https://doi.org/10.1139/cjc-2021-0203
- Joel B. Varley. First-principles calculations of structural, electrical, and optical properties of ultra-wide bandgap (Al$$_x$$Ga$$_{1-x}$$)$$_2$$O$$_3$$ alloys. Journal of Materials Research 2021, 36
(23)
, 4790-4803. https://doi.org/10.1557/s43578-021-00371-7
- Isa Hatipoglu, Daniel A. Hunter, Partha Mukhopadhyay, Martin S. Williams, Paul R. Edwards, Robert W. Martin, Winston V. Schoenfeld, G. Naresh-Kumar. Correlation between deep-level defects and functional properties of β-(Sn
x
Ga1-
x
)2O3 on Si photodetectors. Journal of Applied Physics 2021, 130
(20)
https://doi.org/10.1063/5.0068186
- Xinyi Xia, Chaker Fares, Fan Ren, Anna Hassa, Holger von Wenckstern, Marius Grundmann, S. J. Pearton. Al Composition Dependence of Band Offsets for SiO
2
on α-(Al
x
Ga
1−x
)
2
O
3. ECS Journal of Solid State Science and Technology 2021, 10
(11)
, 113007. https://doi.org/10.1149/2162-8777/ac39a8
- Cheng-Yi Huang, Mau-Phon Houng, Sufen Wei, Cheng-Fu Yang. Depositions of In2xGa2−2xO3-based films and their application in the fabrication of a thin-film transistor. Modern Physics Letters B 2021, 35
(29)
https://doi.org/10.1142/S0217984921410116
- Han-Yin Liu, Zhen-Yuan Huang. Investigation of p-NiO/N-Ga₀.₃Zn₀.₇O Heterojunction Photodiodes for Ultraviolet-B Detection. IEEE Sensors Journal 2021, 21
(19)
, 21486-21493. https://doi.org/10.1109/JSEN.2021.3104826
- Johannes Feldl, Martin Feneberg, Alexandra Papadogianni, Jonas Lähnemann, Takahiro Nagata, Oliver Bierwagen, Rüdiger Goldhahn, Manfred Ramsteiner. Bandgap widening and behavior of Raman-active phonon modes of cubic single-crystalline (In,Ga)2O3 alloy films. Applied Physics Letters 2021, 119
(4)
https://doi.org/10.1063/5.0056532
- A. Dive, J. Varley, S. Banerjee.
In
2
O
3
−
Ga
2
O
3
Alloys as Potential Buffer Layers in
Cd
Te
Thin-Film Solar Cells. Physical Review Applied 2021, 15
(3)
https://doi.org/10.1103/PhysRevApplied.15.034028
References
ARTICLE SECTIONSThis article references 73 other publications.
- 1Walsh, A.; Da Silva, J. L. F.; Wei, S.-H.; Korber, C.; Klein, A.; Piper, L. F. J.; DeMasi, A.; Smith, K. E.; Panaccione, G.; Torelli, P.; Payne, D. J.; Bourlange, A.; Egdell, R. G. Nature of the Band Gap of In2O3 Revealed by First-Principles Calculations and X-Ray Spectroscopy. Phys. Rev. Lett. 2008, 100, 167402, DOI: 10.1103/PhysRevLett.100.1674021https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXltFOlurw%253D&md5=913b840052042078c7bf8442f03bddbbNature of the Band Gap of In2O3 Revealed by First-Principles Calculations and X-Ray SpectroscopyWalsh, Aron; Da Silva, Juarez L. F.; Wei, Su-Huai; Korber, C.; Klein, A.; Piper, L. F. J.; DeMasi, Alex; Smith, Kevin E.; Panaccione, G.; Torelli, P.; Payne, D. J.; Bourlange, A.; Egdell, R. G.Physical Review Letters (2008), 100 (16), 167402/1-167402/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for In2O3 is found significantly closer to the bottom of the conduction band than expected from the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of In2O3 exhibit a small dispersion and the conduction band min. is positioned at Γ. However, direct optical transitions give a minimal dipole intensity until 0.8 eV below the valence band max. The results set an upper limit on the fundamental band gap of 2.9 eV.
- 2Ellmer, K. Past Achievements and Future Challenges in the Development of Optically Transparent Electrodes. Nat. Photonics 2012, 6, 809– 817, DOI: 10.1038/nphoton.2012.2822https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhslCntLzF&md5=9387299074a07fd9aa9f35c7f70d9867Past achievements and future challenges in the development of optically transparent electrodesEllmer, KlausNature Photonics (2012), 6 (12), 809-817CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Transparent conductive electrodes play important roles in information and energy technologies. These materials, particularly transparent conductive oxides, are widely used as transparent electrodes across tech. fields such as low-emissivity coatings, flat-panel displays, thin-film solar cells and org. light-emitting diodes. This Review begins by summarizing the properties and applications of transparent conductive oxides such as In2O3, SnO2, ZnO and TiO2. Owing to the increasing demand for raw materials - esp. indium - scientists are currently searching for alternatives to indium tin oxide. Carbon nanotube and metal nanowire networks, as well as regular metal grids, have been investigated for use as transparent conductive electrodes. This Review compares these materials and the recently 'rediscovered' graphene with today's established transparent conductive oxides.
- 3Pearton, S. J.; Yang, J.; Cary, P. H.; Ren, F.; Kim, J.; Tadjer, M. J.; Mastro, M. A. A Review of Ga2O3 Materials, Processing, and Devices. Appl. Phys. Rev. 2018, 5, 011301, DOI: 10.1063/1.50069413https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXotFSgsw%253D%253D&md5=145f298a1ae45c7ab9dcf874b84fc732A review of Ga2O3 materials, processing, and devicesPearton, S. J.; Yang, Jiancheng; Cary, Patrick H.; Ren, F.; Kim, Jihyun; Tadjer, Marko J.; Mastro, Michael A.Applied Physics Reviews (2018), 5 (1), 011301/1-011301/56CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)A review. Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (ε) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. The performance of technol. important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger crit. elec. field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielecs. for gate formation, and passivation are discussed. (c) 2018 American Institute of Physics.
- 4Lorenz, M. The 2016 Oxide Electronic Materials and Oxide Interfaces Roadmap. J. Phys. D: Appl. Phys. 2016, 49, 433001, DOI: 10.1088/0022-3727/49/43/4330014https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1anu7Y%253D&md5=19f887f4fb5274766b5c1d20f992f000The 2016 oxide electronic materials and oxide interfaces roadmapLorenz, M.; Rao, M. S. Ramachandra; Venkatesan, T.; Fortunato, E.; Barquinha, P.; Branquinho, R.; Salgueiro, D.; Martins, R.; Carlos, E.; Liu, A.; Shan, F. K.; Grundmann, M.; Boschker, H.; Mukherjee, J.; Priyadarshini, M.; DasGupta, N.; Rogers, D. J.; Teherani, F. H.; Sandana, E. V.; Bove, P.; Rietwyk, K.; Zaban, A.; Veziridis, A.; Weidenkaff, A.; Muralidhar, M.; Murakami, M.; Abel, S.; Fompeyrine, J.; Zuniga-Perez, J.; Ramesh, R.; A. Spaldin, N.; Ostanin, S.; Borisov, V.; Mertig, I.; Lazenka, V.; Srinivasan, G.; Prellier, W.; Uchida, M.; Kawasaki, M.; Pentcheva, R.; Gegenwart, P.; Granozio, F. Miletto; Fontcuberta, J. PrydsJournal of Physics D: Applied Physics (2016), 49 (43), 433001/1-433001/53CODEN: JPAPBE; ISSN:0022-3727. (IOP Publishing Ltd.)A review. Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addn. to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-vol. ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelecs., piezoelecs., power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on 'oxide electronic materials and oxide interfaces'. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theor. considerations behind both present and future applications in many technol. important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topol. oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action 'towards oxide-based electronics' which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chem., which even after many years of very successful development shows in short intervals novel insights and achievements.
- 5Gonçalves, G.; Barquinha, P.; Pereira, L.; Franco, N.; Alves, E.; Martins, R.; Fortunato, E. High Mobility a-IGO Films Produced at Room Temperature and Their Application in TFTs. Electrochem. Solid-State Lett. 2010, 13, H20– H22, DOI: 10.1149/1.3257613There is no corresponding record for this reference.
- 6Huang, W.-L.; Hsu, M.-H.; Chang, S.-P.; Chang, S.-J.; Chiou, Y.-Z. Indium Gallium Oxide Thin Film Transistor for Two-Stage UV Sensor Application. ECS J. Solid State Sci. Technol. 2019, 8, Q3140– Q3143, DOI: 10.1149/2.0251907jss6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVymtL7P&md5=acfd81d9893fb64c7bdba196d02753bcIndium gallium oxide thin film transistor for two-stage UV sensor applicationHuang, Wei-Lun; Hsu, Ming-Hung; Chang, Sheng-Po; Chang, Shoou-Jinn; Chiou, Yu-ZungECS Journal of Solid State Science and Technology (2019), 8 (7), Q3140-Q3143CODEN: EJSSBG; ISSN:2162-8769. (Electrochemical Society)In this work, indium gallium oxide (IGO) thin film transistor (TFT) was fabricated by radio-frequency (RF) sputtering. The transmittance of the TFT shows larger than 80% cross the visible light region. As a wide bandgap and high transparency semiconducting material, IGO is a potential candidate for UV-detection applications.Measured in the dark, the IGO TFT exhibits a threshold voltage of 0.9 V, mobility of 2.66 cm2/Vs, on-off ratio of 1.21×106, subthreshold swing of 0.41 V/dec. The TFT was then employed to detect UV light and the sensing properties are investigated. The IGO phototransistor has a high responsivity of 5.012 A/W and a rejection ratio of 1.65×105. The above results reveal that IGO phototransistor is a brilliant multi-functional device, which can serve as either a switch component or a UV sensor.
- 7Kim, Y. G.; Kim, T.; Avis, C.; Lee, S.-H.; Jang, J. Stable and High-Performance Indium Oxide Thin-Film Transistor by Ga Doping. IEEE Trans. Electron Devices 2016, 63, 1078– 1084, DOI: 10.1109/TED.2016.25187037https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFerurnE&md5=5ce5baba01d5548be4d5da1f36b7593aStable and high-performance indium oxide thin-film transistor by Ga dopingKim, Youn Goo; Kim, Taehun; Avis, Christophe; Lee, Seung-Hun; Jang, JinIEEE Transactions on Electron Devices (2016), 63 (3), 1078-1084CODEN: IETDAI; ISSN:0018-9383. (Institute of Electrical and Electronics Engineers)Research on a replacement of amorphous silicon for a thin-film transistor (TFT) and large area electronics has been driven by costly vacuum processed indium-gallium-zinc oxide (IGZO). Even though widely studied, the performances still require improvement, and a wide no. of other materials have been tested. While indium-zinc oxide, IGZO, indium-zinc-tin oxide (ZTO), and ZTO have been widely investigated, gallium-doped indium oxide (IGO) has not been under highlight. Here, we report the use of simple and cost effective spin-coated IGO TFT using spin-coated AlOx gate dielec. We achieved high mobility over 50 cm2/Vs and high stability. The thin films are studied by transmission electron microscopy, X-ray diffraction, XPS, Raman spectra, at. force microscopy, and field-effect measurements. Analyses reveal the strong dependence between crystallinity, mobility, and stability. All TFTs show excellent operation, with champion characteristics for the 10% Ga-doped InOx, revealing a mobility of 52.6 cm2/Vs, on/off ratios of 108, and VTH variation of <0.1 V during 1 h of stress measurement.
- 8von Wenckstern, H.; Splith, D.; Werner, A.; Müller, S.; Lorenz, M.; Grundmann, M. Properties of Schottky Barrier Diodes on (InxGa1-x)2O3 for 0.01 ≤ x ≤ 0.85 Determined by a Combinatorial Approach. ACS Comb. Sci. 2015, 17, 710– 715, DOI: 10.1021/acscombsci.5b000848https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs12qurrL&md5=a25f1c78c7e6baa196aab19a87c779acProperties of Schottky Barrier Diodes on (InxGa1-x)2O3 for 0.01 ≤ x ≤ 0.85 Determined by a Combinatorial Approachvon Wenckstern, H.; Splith, D.; Werner, A.; Mueller, S.; Lorenz, M.; Grundmann, M.ACS Combinatorial Science (2015), 17 (12), 710-715CODEN: ACSCCC; ISSN:2156-8944. (American Chemical Society)We investigated properties of an (InxGa1-x)2O3 thin film with laterally varying cation compn. that was realized by a large-area offset pulsed laser deposition approach. Within a two inch diam. thin film, the compn. varies between 0.01 ≤ x ≤ 0.85, and three crystallog. phases (cubic, hexagonal, and monoclinic) were identified. We obsd. a correlation between characteristic parameters of Schottky barrier diodes fabricated on the thin film and its chem. and structural material properties. The highest Schottky barriers and rectification of the diodes were found for low indium contents. The thermal stability of the diodes is also best for Ga-rich parts of the sample. Conversely, the series resistance is lowest for large In content. Overall, the (InxGa1-x)2O3 alloy is well-suited for potential applications such as solar-blind photodetectors with a tunable absorption edge.
- 9Kranert, C.; Lenzner, J.; Jenderka, M.; Lorenz, M.; von Wenckstern, H.; Schmidt-Grund, R.; Grundmann, M. Lattice Parameters and Raman-active Phonon Modes of (InxGa1-x)2O3 for x < 0.4. J. Appl. Phys. 2014, 116, 013505, DOI: 10.1063/1.48868959https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFSlsr%252FM&md5=75ddadbd64a9e62b9589aa3465d77273Lattice parameters and Raman-active phonon modes of (InxGa1-x)2O3 for x < 0.4Kranert, Christian; Lenzner, Joerg; Jenderka, Marcus; Lorenz, Michael; von Wenckstern, Holger; Schmidt-Grund, Ruediger; Grundmann, MariusJournal of Applied Physics (Melville, NY, United States) (2014), 116 (1), 013505/1-013505/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We present X-ray diffraction and Raman spectroscopy investigations of (InxGa1-x)2O3 thin films and bulk-like ceramics in dependence of their compn. The thin films grown by pulsed laser deposition have a continuous lateral compn. spread allowing the detn. of phonon mode properties and lattice parameters with high sensitivity to the compn. from a single 2-in. wafer. In the regime of low indium concn., the phonon energies depend linearly on the compn. and show a good agreement between both sample types. We detd. the slopes of these dependencies for eight different Raman modes. While the lattice parameters of the ceramics follow Vegard's rule, deviations are obsd. for the thin films. Further, we found indications of the high-pressure phase InGaO3 II in the thin films above a crit. indium concn., its value depending on the type of substrate. (c) 2014 American Institute of Physics.
- 10Shannon, R. D.; Prewitt, C. T. Synthesis and Structure of Phases in the In2O3-Ga2O3 System. J. Inorg. Nucl. Chem. 1968, 30, 1389– 1398, DOI: 10.1016/0022-1902(68)80277-510https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXks1agtro%253D&md5=4f9b48da0fbf8c5517190b3f66e79b56Synthesis and structure of phases in the indium sesquioxide-gallium sesquioxide systemShannon, R. D.; Prewitt, C. T.Journal of Inorganic and Nuclear Chemistry (1968), 30 (6), 1389-98CODEN: JINCAO; ISSN:0022-1902.Compns. Ga2-xInxO3 (x = 0.0-1.0) having the β-Ga2O3 structure were prepd. in the powder form and as single crystals by several techniques and characterized by x-ray and resistivity measurements. The compn. InGaO3 transforms at high pressures to a new phase, InGaO3 II. InGaO3 II has a simple hexagonal oxide structure which is the 1st structure reported contg. Ga3+ in 5-fold coordination. The cell parameters are: a 3.310 ± 0.002, c 12.039 ± 0.002 A.; Z = 2; ρ(calcd.) = 6.756; and the space group is P63/mmc. Interat. distances obtained from least-sqs. refinement results are In-O(1)[×2], 3.010 A.; In-O(2)[×6], 2.174 A.; Ga-O(1)[×3], 1.911 A.; and Ga-O(2)[×2], 1.973 A. InGaO3 II is isotypic with hexagonal YAlO3, and its structure is related to that of YMnO3, which contains 5 coordinated Mn3+. 20 references.
- 11Kneiß, M.; Hassa, A.; Splith, D.; Sturm, C.; von Wenckstern, H.; Lorenz, M.; Grundmann, M. Epitaxial Stabilization of Single Phase κ-(InxGa1-x)2O3 Thin Films up to x = 0.28 on c-Sapphire and κ-Ga2O3(001) Templates by Tin-Assisted VCCS-PLD. APL Mater. 2019, 7, 101102, DOI: 10.1063/1.512057811https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFaksr7J&md5=8ae376374581a0b013f39056fe5f9cc7Epitaxial stabilization of single phase κ (InxGa1-x)2O3 thin films up to x = 0.28 on c-sapphire and κ -Ga2O3(001) templates by tin-assisted VCCS-PLDKneiss, M.; Hassa, A.; Splith, D.; Sturm, C.; von Wenckstern, H.; Lorenz, M.; Grundmann, M.APL Materials (2019), 7 (10), 101102/1-101102/10CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)High-quality (InxGa1-x)2O3 thin films in the orthorhombic κ -phase were grown by pulsed-laser deposition (PLD) on c-sapphire substrates as well as PLD-grown κ -Ga2O3 thin film templates. We varied the In-content 0 = x = 0.38 of the layers using a single, elliptically segmented, and tin-doped (In0.4Ga0.6)2O3/Ga2O3 target, employing the vertical continuous compn. spread (VCCS) PLD-technique. A stoichiometric transfer of In and Ga from the target to the thin films has been confirmed, suggesting that the formation of volatile Ga2O and In2O suboxides is not a limiting factor in the tin-assisted growth mode. For all x, the thin films crystd. predominantly in the κ -modification as demonstrated by XRD 2θ -ω scans. However, for x > 0.28, phase sepn. of the cubic bixbyite and the κ -phase occurred. The κ -Ga2O3 template increased the cryst. quality of the κ -(InxGa1-x)2O3 thin film layers remarkably. Epitaxial, but relaxed growth with three in-plane rotational domains has been found for all thin films by XRD κ -scans or reciprocal space map measurements. Smooth surface morphologies (Rq < 3 nm) for all phase pure thin films were evidenced by at. force microscopy measurements, making them suitable for multilayer heterostructures. The compn.-dependent in- and out-of plane lattice consts. follow a linear behavior according to Vegard's law. A linear relationship can also be confirmed for the optical bandgaps that demonstrate the feasibility of bandgap engineering in the energy range of 4.1-4.9 eV. The results suggest κ -(InxGa1-x)2O3 as a promising material for heterostructure device applications or photodetectors. (c) 2019 American Institute of Physics.
- 12Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118, 8207– 8215, DOI: 10.1063/1.156406012https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjtlSisLw%253D&md5=05a44dc5890abc3dfa8e1ef5338a4781Hybrid functionals based on a screened Coulomb potentialHeyd, Jochen; Scuseria, Gustavo E.; Ernzerhof, MatthiasJournal of Chemical Physics (2003), 118 (18), 8207-8215CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)Hybrid d. functionals are very successful in describing a wide range of mol. properties accurately. In large mols. and solids, however, calcg. the exact (Hartree-Fock) exchange is computationally expensive, esp. for systems with metallic characteristics. In the present work, we develop a new hybrid d. functional based on a screened Coulomb potential for the exchange interaction which circumvents this bottleneck. The results obtained for structural and thermodn. properties of mols. are comparable in quality to the most widely used hybrid functionals. In addn., we present results of periodic boundary condition calcns. for both semiconducting and metallic single wall carbon nanotubes. Using a screened Coulomb potential for Hartree-Fock exchange enables fast and accurate hybrid calcns., even of usually difficult metallic systems. The high accuracy of the new screened Coulomb potential hybrid, combined with its computational advantages, makes it widely applicable to large mols. and periodic systems.
- 13Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 50, 17953– 17979, DOI: 10.1103/PhysRevB.50.1795313https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2sfjslSntA%253D%253D&md5=1853d67af808af2edab58beaab5d3051Projector augmented-wave methodBlochlPhysical review. B, Condensed matter (1994), 50 (24), 17953-17979 ISSN:0163-1829.There is no expanded citation for this reference.
- 14Kresse, 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.54.1116914https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28Xms1Whu7Y%253D&md5=9c8f6f298fe5ffe37c2589d3f970a697Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis setKresse, 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.
- 15Blöchl, P. E.; Jepsen, O.; Andersen, O. K. Improved Tetrahedron Method for Brillouin-zone Integrations. Phys. Rev. B: Condens. Matter Mater. Phys. 1994, 49, 16223– 16233, DOI: 10.1103/PhysRevB.49.1622315https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2cXks1Gqtb0%253D&md5=d1aa48b406bfccde3e58d26cbf21a809Improved tetrahedron method for Brillouin-zone integrationsBlochl, Peter E.; Jepsen, O.; Andersen, O. K.Physical Review B: Condensed Matter and Materials Physics (1994), 49 (23), 16223-33CODEN: PRBMDO; ISSN:0163-1829.Several improvements of the tetrahedron method for Brillouin-zone integrations are presented. (1) A translational grid of k points and tetrahedra is suggested that renders the results for insulators identical to those obtained with special-point methods with the same no. of k points. (2) A simple correction formula goes beyond the linear approxn. of matrix elements within the tetrahedra and also improves the results for metals significantly. For a required accuracy this reduces the no. of k points by orders of magnitude. (3) Irreducible k points and tetrahedra are selected by a fully automated procedure, requiring as input only the space-group operations. (4) The integration is formulated as a weighted sum over irreducible k points with integration wts. calcd. using the tetrahedron method once for a given band structure. This allows an efficient use of the tetrahedron method also in plane-wave-based electronic-structure methods.
- 16Onuma, T.; Saito, S.; Sasaki, K.; Goto, K.; Masui, T.; Yamaguchi, T.; Honda, T.; Kuramata, A.; Higashiwaki, M. Temperature-Dependent Exciton Resonance Energies and their Correlation with IR-active Optical Phonon Modes in β-Ga2O3 Single Crystals. Appl. Phys. Lett. 2016, 108, 101904, DOI: 10.1063/1.494317516https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVWqs74%253D&md5=517b6df3b9978d3e7e81446b2eea1893Temperature-dependent exciton resonance energies and their correlation with IR-active optical phonon modes in β-Ga2O3 single crystalsOnuma, T.; Saito, S.; Sasaki, K.; Goto, K.; Masui, T.; Yamaguchi, T.; Honda, T.; Kuramata, A.; Higashiwaki, M.Applied Physics Letters (2016), 108 (10), 101904/1-101904/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Temp.-dependent exciton resonance energies Eexciton in β-Ga2O3 single crystals are studied by using polarized reflectance measurement. The Eexciton values exhibit large energy changes at 179-268 meV from 5 to 300 K. The IR-active Au and Bu optical phonon modes are selectively obsd. in the IR ellipsometry spectra by reflecting the polarization selection rules. The LO phonon energies can be divided into 3 ranges: ℏωLO = 35-48, 70-73, and 88-99 meV. The broadening parameters, which are obtained from the reflectance measurements, correspond to the lower 2 ranges of ℏωLO at low temp. and 75 meV >150 K. The large Eexciton changes with temp. in β-Ga2O3 are originated from the exciton-LO-phonon interaction. (c) 2016 American Institute of Physics.
- 17Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Y.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstübner, U.; Vines, L. Iron and Intrinsic Deep Level States in Ga2O3. Appl. Phys. Lett. 2018, 112, 042104, DOI: 10.1063/1.502013417https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsl2iu74%253D&md5=67c0fa08a94280c035424b2f4553a0ffIron and intrinsic deep level states in Ga2O3Ingebrigtsen, M. E.; Varley, J. B.; Kuznetsov, A. Yu.; Svensson, B. G.; Alfieri, G.; Mihaila, A.; Badstubner, U.; Vines, L.Applied Physics Letters (2018), 112 (4), 042104/1-042104/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using a combination of deep level transient spectroscopy, secondary ion mass spectrometry, proton irradn., and hybrid functional calcns., we identify two similar deep levels that are assocd. with Fe impurities and intrinsic defects in bulk crystals and mol. beam epitaxy and hydride vapor phase epitaxi-grown epilayers of β-Ga2O3. First, our results indicate that FeGa, and not an intrinsic defect, acts as the deep acceptor responsible for the often dominating E2 level at ∼0.78 eV below the conduction band min. Second, by provoking addnl. intrinsic defect generation via proton irradn., we identified the emergence of a new level, labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2* are found to be consistent with its intrinsic origin. As such, contradictory opinions of a long standing literature debate on either extrinsic or intrinsic origin of the deep acceptor in question converge accounting for possible contributions from E2 and E2* in different exptl. conditions. (c) 2018 American Institute of Physics.
- 18Geller, S. Crystal Structure of β-Ga2O3. J. Chem. Phys. 1960, 33, 676– 684, DOI: 10.1063/1.173123718https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF3MXisF2gsg%253D%253D&md5=a1369607c308a8592f2a30ffa0f7e6bcCrystal structure of β-Ga2O3Geller, S.Journal of Chemical Physics (1960), 33 (), 676-84CODEN: JCPSA6; ISSN:0021-9606.The monoclinic crystal has cell dimensions a = 12.23, b = 3.04, c = 5.80 A., β = 103.7°. There are 4 mols. per unit cell. The most probable space group is C32h-C2/m; the atoms are in 5 sets of special positions 4i: (000, 1/2 1/2 0) ± (x0z). There are 2 kinds of co.ovrddot.ordination for Ga+++ in this structure, tetrahedral and octahedral. Av. interionic distances are: tetrahedral Ga-O; 1.83 A.; octahedral Ga-O, 2.00 A.; tetrahedron edge O-O, 3.02 A.; and octahedron edge O-O, 2.84 A. Because of the reduced co.ovrddot.ordination of half of the metal ions, the d. of β-Ga2O3 is lower than that of α-Ga2O3. The av. Ga-O distances in the structure account for the fact that although the Ga+++ is substantially larger than the Al+++, its quant. preference for tetrahedrally co.ovrddot.ordinated sites when substituted for Fe+++ in the Fe garnets is nearly the same as that of the Al+++ ion. The magnetic aspects of the β-Ga2O3 structure are discussed, and a possible Fe2O3 isomorph may be expected to be at least antiferromagnetic with a Neel temp. of about 700°K.
- 19Prozheeva, V.; Hölldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F. Effects of Alloy Composition and Si-doping on Vacancy Defect Formation in (InxGa1-x)2O3 Thin Films. J. Appl. Phys. 2018, 123, 125705, DOI: 10.1063/1.502224519https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXms1Ggtb8%253D&md5=3675ad4d0b4012ffd8cce25e97fb83cbEffects of alloy composition and Si-doping on vacancy defect formation in (InxGa1-x)2O3 thin filmsProzheeva, V.; Holldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F.Journal of Applied Physics (Melville, NY, United States) (2018), 123 (12), 125705/1-125705/6CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Various nominally undoped and Si-doped (InxGa1-x)2O3 thin films were grown by pulsed laser deposition in a continuous compn. spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterization technique in order to investigate the effect of alloy compn. and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concns. changing to In2O3-like behavior along with the increase in the indium fraction. Increasing indium concn. is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron satn. trapping in VIn-like defects, suggesting a vacancy concn. of at least mid-1018 cm-3 independent of the indium content. This is a solid soln. study. (c) 2018 American Institute of Physics.
- 20Schmidt-Grund, R.; Kranert, C.; Bontgen, T.; von Wenckstern, H.; Krauß, H.; Grundmann, M. Dielectric Function in the NIR-VUV Spectral Range of (InxGa1-x)2O3 Thin Films. J. Appl. Phys. 2014, 116, 053510, DOI: 10.1063/1.489152120https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXht1KksrvN&md5=0cf97c8d4b0ab35cffe159bb8f56ed50Dielectric function in the NIR-VUV spectral range of (InxGa1-x)2O3 thin filmsSchmidt-Grund, R.; Kranert, C.; Boentgen, T.; von Wenckstern, H.; Krauss, H.; Grundmann, M.Journal of Applied Physics (Melville, NY, United States) (2014), 116 (5), 053510/1-053510/7CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)We detd. the dielec. function of the alloy system (InxGa1-x)2O3 by spectroscopic ellipsometry in the wide spectral range from 0.5 eV to 8.5 eV and for In contents ranging from x = 0.02 to x = 0.61. The predicted optical transitions for binary, monoclinic β-Ga2O3, and cubic bcc-In2O3 are well reflected by the change of the dielec. functions' lineshape as a function of the In content. In an intermediate compn. range with phase-sepd. material (x ≈ 0.3...0.4), the lineshape differs considerably, which we assign to the presence of the high-pressure rhombohedral InGaO3-II phase, which we also observe in Raman expts. in this range. By model anal. of the dielec. function, we derived spectra of the refractive index and the absorption coeff. and energy parameters of electronic band-band transitions. We discuss the sub-band gap absorption tail in relation to the influence of the In 4d orbitals on the valence bands. The data presented here provide a basis for a deeper understanding of the electronic properties of this technol. important material system and may be useful for device engineering. (c) 2014 American Institute of Physics.
- 21von Wenckstern, H.; Kneiß, M.; Hassa, A.; Storm, P.; Splith, D.; Grundmann, M. A Review of the Segmented-Target Approach to Combinatorial Material Synthesis by Pulsed-Laser Deposition. Phys. Status Solidi B 2020, 257, 1900626, DOI: 10.1002/pssb.20190062621https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitlyms7nF&md5=1e12c15dcdda939efdb6df2c11a3a372A Review of the Segmented-Target Approach to Combinatorial Material Synthesis by Pulsed-Laser Depositionvon Wenckstern, Holger; Kneiss, Max; Hassa, Anna; Storm, Philipp; Splith, Daniel; Grundmann, MariusPhysica Status Solidi B: Basic Solid State Physics (2020), 257 (7), 1900626CODEN: PSSBBD; ISSN:0370-1972. (Wiley-VCH Verlag GmbH & Co. KGaA)Combinatorial material synthesis has led to a significant acceleration in the optimization of multinary compds. and a more efficient usage of source and substrate materials. Various growth methods, including phys. vapor deposition, can be adopted to realize material libraries. Herein, two approaches to combinatorial material synthesis based on ablation of segmented targets during pulsed-laser deposition are reviewed. For these two processes, either laterally or radially segmented targets are utilized and allow the creation of lateral and vertical compn. spreads, resp. Radially segmented targets can addnl. be used to synthesize a discrete binary material library. Both approaches are introduced by calcg. the expected material distribution with a simple geometric plasma expansion model. Then, exptl. detd. elemental distributions and growth rates are compared to predictions and it is demonstrated that differences between calcd. and exptl. data contain vital information on the influence of, for example, thermodn. processes on the growth mechanism.
- 22Vines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M. Electrical Conductivity of In2O3 and Ga2O3 after Low Temperature Ion Irradiation; Implications for Intrinsic Defect Formation and Charge Neutrality Level. J. Phys.: Condens. Matter 2018, 30, 025502, DOI: 10.1088/1361-648X/aa9e2a22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhsFygurjO&md5=fd0cd7d4c51f1e50f1e7560f0274adcbElectrical conductivity of In2O3 and Ga2O3 after low temperature ion irradiation; implications for instrinsic defect formation and charge neutrality levelVines, L.; Bhoodoo, C.; von Wenckstern, H.; Grundmann, M.Journal of Physics: Condensed Matter (2018), 30 (2), 025502/1-025502/6CODEN: JCOMEL; ISSN:0953-8984. (IOP Publishing Ltd.)The evolution of sheet resistance of n-type In2O3 and Ga2O3 exposed to bombardment with MeV 12C and 28Si ions at 35 K is studied in situ. While the sheet resistance of Ga2O3 increased by more than 8-fold as a result of ion irradn., In2O3 showed a more complex defect evolution and became more conductive when irradiated at the highest doses. Heating up to room temp. reduced the sheet resistivity somewhat, but Ga2O3 remained highly resistive, while In2O3 showed a lower resistance than as deposited samples. Thermal admittance spectroscopy and deep level transient spectroscopy did not reveal new defect levels for irradn. up to 2 × 1012 cm-2. A model where larger defect complexes preferentially produce donor like defects in In2O3 is proposed, and may reveal a microscopic view of a charge neutrality level within the conduction band, as previously proposed.
- 23King, P. D. C.; Veal, T. D.; Fuchs, F.; Wang, C. Y.; Payne, D. J.; Bourlange, A.; Zhang, H.; Bell, G. R.; Cimalla, V.; Ambacher, O.; Egdell, R. G.; Bechstedt, F.; McConville, C. F. Band Gap, Electronic Structure, and Surface Electron Accumulation of Cubic and Rhombohedral In2O3. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 205211, DOI: 10.1103/PhysRevB.79.20521123https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvFyhtbc%253D&md5=eb6fd198231cbef4b3383cb1c844cf11Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3King, P. D. C.; Veal, T. D.; Fuchs, F.; Wang, Ch. Y.; Payne, D. J.; Bourlange, A.; Zhang, H.; Bell, G. R.; Cimalla, V.; Ambacher, O.; Egdell, R. G.; Bechstedt, F.; McConville, C. F.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (20), 205211/1-205211/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The bulk and surface electronic structure of In2O3 has proved controversial, prompting the current combined exptl. and theor. investigation. The band gap of single-cryst. In2O3 is detd. as 2.93±0.15 and 3.02±0.15 eV for the cubic bixbyite and rhombohedral polymorphs, resp. The valence-band d. of states is investigated from x-ray photoemission spectroscopy measurements and d.-functional theory calcns. These show excellent agreement, supporting the absence of any significant indirect nature of the In2O3 band gap. Clear exptl. evidence for an s-d coupling between In 4d and O 2s derived states is also obsd. Electron accumulation, recently reported at the (001) surface of bixbyite material, is also shown to be present at the bixbyite (111) surface and the (0001) surface of rhombohedral In2O3.
- 24Swallow, J. E. N.; Varley, J. B.; Jones, L. A. H.; Gibbon, J. T.; Piper, L. F. J.; Dhanak, V. R.; Veal, T. D. Transition from Electron Accumulation to Depletion at β-Ga2O3 Surfaces: The Role of Hydrogen and the Charge Neutrality Level. APL Mater. 2019, 7, 022528, DOI: 10.1063/1.505409124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjtVGru7w%253D&md5=fe7b421ae053736c23e30989e6c1d53bTransition from electron accumulation to depletion at β-Ga2O3 surfaces: The role of hydrogen and the charge neutrality levelSwallow, J. E. N.; Varley, J. B.; Jones, L. A. H.; Gibbon, J. T.; Piper, L. F. J.; Dhanak, V. R.; Veal, T. D.APL Materials (2019), 7 (2), 022528/1-022528/8CODEN: AMPADS; ISSN:2166-532X. (American Institute of Physics)The surface electronic properties of bulk-grown β-Ga2O3 (201) single crystals are investigated. The band gap is found using optical transmission to be 4.68 eV. High-resoln. x-ray photoemission coupled with hybrid d. functional theory calcn. of the valence band d. of states provides insights into the surface band bending. Importantly, the std. linear extrapolation method for detg. the surface valence band max. (VBM) binding energy is found to underestimate the sepn. from the Fermi level by ∼0.5 eV. According to our interpretation, most reports of surface electron depletion and upward band bending based on photoemission spectroscopy actually provide evidence of surface electron accumulation. For uncleaned surfaces, the surface VBM to Fermi level sepn. is found to be 4.95 ± 0.10 eV, corresponding to downward band bending of ∼0.24 eV and an electron accumulation layer with a sheet d. of ∼5 × 1012 cm-2. Uncleaned surfaces possess hydrogen termination which acts as surface donors, creating electron accumulation and downward band bending at the surface. In situ cleaning by thermal annealing removes H from the surface, resulting in a ∼0.5 eV shift of the surface VBM and formation of a surface electron depletion layer with upward band bending of ∼0.26 eV due to native acceptor surface states. These results are discussed in the context of the charge neutrality level, calcd. bulk interstitial hydrogen transition levels, and related previous exptl. findings. (c) 2019 American Institute of Physics.
- 25Nagata, T.; Hoga, T.; Yamashita, A.; Asahi, T.; Yagyu, S.; Chikyow, T. Valence Band Modification of a (GaxIn1-x)2O3 Solid Solution System Fabricated by Combinatorial Synthesis. ACS Comb. Sci. 2020, 22, 433439, DOI: 10.1021/acscombsci.0c00033There is no corresponding record for this reference.
- 26King, P. D. C.; Veal, T. D.; Payne, D. J.; Bourlange, A.; Egdell, R. G.; McConville, C. F. Surface Electron Accumulation and the Charge Neutrality Level in In2O3. Phys. Rev. Lett. 2008, 101, 116808, DOI: 10.1103/PhysRevLett.101.11680826https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtFWltrrK&md5=e15c564b1e0560b21cb9aa23a3f474b1Surface electron accumulation and the charge neutrality level in In2O3King, P. D. C.; Veal, T. D.; Payne, D. J.; Bourlange, A.; Egdell, R. G.; McConville, C. F.Physical Review Letters (2008), 101 (11), 116808/1-116808/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)High-resoln. x-ray photoemission spectroscopy, IR reflectivity and Hall effect measurements, combined with surface space-charge calcns., are used to show that electron accumulation occurs at the surface of undoped single-cryst. In2O3. From a combination of measurements performed on undoped and heavily Sn-doped samples, the charge neutrality level is shown to lie ∼0.4 eV above the conduction band min. in In2O3, explaining the electron accumulation at the surface of undoped material, the propensity for n-type cond., and the ease of n-type doping in In2O3, and hence its use as a transparent conducting oxide material.
- 27Lovejoy, T. C.; Chen, R.; Zheng, X.; Villora, E. G.; Shimamura, K.; Yoshikawa, H.; Yamashita, Y.; Ueda, S.; Kobayashi, K.; Dunham, S. T.; Ohuchi, F. S.; Olmstead, M. A. Band Bending and Surface Defects in β-Ga2O3. Appl. Phys. Lett. 2012, 100, 181602, DOI: 10.1063/1.471101427https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmtlGqs7s%253D&md5=48382782a6c5523dba943133949f216bBand bending and surface defects in β-Ga2O3Lovejoy, T. C.; Chen, Renyu; Zheng, X.; Villora, E. G.; Shimamura, K.; Yoshikawa, H.; Yamashita, Y.; Ueda, S.; Kobayashi, K.; Dunham, S. T.; Ohuchi, F. S.; Olmstead, M. A.Applied Physics Letters (2012), 100 (18), 181602/1-181602/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Surface band bending and surface defects on the UV-transparent conducting oxide β-Ga2O3 (100) are studied with hard x-ray photoemission spectroscopy and scanning tunneling microscopy. Highly doped β-Ga2O3 shows flat bands near the surface, while the bands on nominally undoped (but still n-type), air-cleaved β-Ga2O3 are bent upwards by > 0.5 eV. Neg. charged surface defects are obsd. on vacuum annealed β-Ga2O3, which also shows upward band bending. D. functional calcns. show O vacancies are not likely to be ionized in the bulk, but could be activated by surface band bending. The large band bending may also hinder formation of ohmic contacts. (c) 2012 American Institute of Physics.
- 28Navarro-Quezada, A.; Alamé, S.; Esser, N.; Furthmüller, J.; Bechstedt, F.; Galazka, Z.; Skuridina, D.; Vogt, P. Near Valence-band Electronic Properties of Semiconducting β-Ga2O3 (100) Single Crystals. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 195306, DOI: 10.1103/PhysRevB.92.19530628https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtF2lurvM&md5=87c0a49c3be11c955027cd184f299d63Near valence-band electronic properties of semiconducting β-Ga2O3 (100) single crystalsNavarro-Quezada, A.; Alame, S.; Esser, N.; Furthmueller, J.; Bechstedt, F.; Galazka, Z.; Skuridina, D.; Vogt, P.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (19), 195306/1-195306/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)β-Ga2O3 is a transparent wide-band-gap semiconductor that has attracted considerable interest in recent years due to its suitable elec. cond. and transparency in the UV spectral region. In this work we investigate the electronic properties of the near valence-band-edge region for semiconducting β-Ga2O3 (100) bulk single crystals using core-level photoelectron spectroscopy and ab initio theory within the framework of d. functional theory and the GW approach. We find good agreement between the exptl. results and the theor. calcns. This is explained by the hybridization of the Ga 3d and O 2s states, similar as for In2O3.
- 29King, P. D. C.; Veal, T. D.; Schleife, A.; Zúñiga-Pérez, J.; Martel, B.; Jefferson, P. H.; Fuchs, F.; Muñoz-Sanjosé, V.; Bechstedt, F.; McConville, C. F. Valence-band Electronic Structure of CdO, ZnO, and MgO from X-ray Photoemission Spectroscopy and Quasi-particle-corrected Density-functional Theory Calculations. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 79, 205205, DOI: 10.1103/PhysRevB.79.20520529https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmvFyiurY%253D&md5=4366fa00f414c9f91a0b17dd25666ae6Valence-band electronic structure of CdO, ZnO, and MgO from x-ray photoemission spectroscopy and quasi-particle-corrected density-functional theory calculationsKing, P. D. C.; Veal, T. D.; Schleife, A.; Zuniga-Perez, J.; Martel, B.; Jefferson, P. H.; Fuchs, F.; Munoz-Sanjose, V.; Bechstedt, F.; McConville, C. F.Physical Review B: Condensed Matter and Materials Physics (2009), 79 (20), 205205/1-205205/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The valence-band d. of states of single-cryst. rock-salt CdO(001), wurtzite c-plane ZnO, and rock- salt MgO(001) are investigated by high-resoln. x-ray photoemission spectroscopy. A classic two-peak structure is obsd. in the VB-DOS due to the anion 2p-dominated valence bands. Good agreement is found between the exptl. results and quasi-particle-cor. d.-functional theory calcns. Occupied shallow semicore d levels are obsd. in CdO and ZnO. While these exhibit similar spectral features to the calcns., they occur at slightly higher binding energies, detd. as 8.8 eV and 7.3 eV below the valence band max. in CdO and ZnO, resp. The implications of these on the electronic structure are discussed.
- 30Moses, P. G.; Van de Walle, C. G. Band Bowing and Band Alignment in InGaN Alloys. Appl. Phys. Lett. 2010, 96, 021908, DOI: 10.1063/1.329105530https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXnsValtg%253D%253D&md5=1338c895900ffcf26637e7830b9da0e3Band bowing and band alignment in InGaN alloysMoses, Poul Georg; Van de Walle, Chris G.Applied Physics Letters (2010), 96 (2), 021908/1-021908/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)We use d. functional theory calcns. with the HSE06 hybrid exchange-correlation functional to investigate InGaN alloys and accurately det. band gaps and band alignments. We find a strong band-gap bowing at low In content. Band positions on an abs. energy scale are detd. from surface calcns. The resulting GaN/InN valence-band offset is 0.62 eV. The dependence of InGaN valence-band alignment on In content is found to be almost linear. Based on the values of band gaps and band alignments, we conclude that InGaN fulfills the requirements for a photoelectrochem. electrode for In contents up to 50%. (c) 2010 American Institute of Physics.
- 31Peelaers, H.; Steiauf, D.; Varley, J. B.; Janotti, A.; Van de Walle, C. G. (InxGa1-x)2O3 Alloys for Transparent Electronics. Phys. Rev. B: Condens. Matter Mater. Phys. 2015, 92, 085206, DOI: 10.1103/PhysRevB.92.08520631https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XivVOnurs%253D&md5=7e6c49c8687400f2b1b306eeee680c26(InxGa1-x)2O3 alloys for transparent electronicsPeelaers, Hartwin; Steiauf, Daniel; Varley, Joel B.; Janotti, Anderson; Van de Walle, Chris G.Physical Review B: Condensed Matter and Materials Physics (2015), 92 (8), 085206/1-085206/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)(InxGa1-x)2O3 alloys show promise as transparent conducting oxides. Using hybrid d. functional calcns., band gaps, formation enthalpies, and structural parameters are detd. for monoclinic and bixbyite crystal structures. In the monoclinic phase the band gap exhibits a linear dependence on alloy concn., whereas in the bixbyite phase a large band-gap bowing occurs. The calcd. formation enthalpies show that the monoclinic structure is favorable for In compns. up to 50% and bixbyite for larger compns. This is caused by In strongly preferring sixfold oxygen coordination. The formation enthalpy of the 50:50 monoclinic alloy is much lower than the formation enthalpy of the 50:50 bixbyite alloy and also lower than most monoclinic alloys with lower In concn.; these trends are explained in terms of local strain. Consequences for expt. and applications are discussed.
- 32Oshima, T.; Fujita, S. Properties of Ga2O3-based (InxGa1-x)2O3 Alloy Thin Films Grown by Molecular Beam Epitaxy. Phys. Status Solidi C 2008, 5, 3113– 3115, DOI: 10.1002/pssc.20077929732https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXpsVyhuro%253D&md5=7925c1ca2221aa78c120015fb02729bbProperties of Ga2O3-based (InxGa1-x)2O3 alloy thin films grown by molecular beam epitaxyOshima, Takayoshi; Fujita, ShizuoPhysica Status Solidi C: Current Topics in Solid State Physics (2008), 5 (9), 3113-3115CODEN: PSSCGL; ISSN:1862-6351. (Wiley-VCH Verlag GmbH & Co. KGaA)A series of Ga2O3-based (InxGa1-x)2O3 alloy thin films were grown on c-plane Al2O3 substrates with a thin Ga2O3 buffer layer by plasma-assisted MBE. At growth temps. of 700° and higher, even with a slight inclusion of In2O3 to Ga2O3, for example, the film of (In0.08Ga0.92)2O3, exhibited a rough surface and degraded transmission spectrum resulting from phase sepn. of In2O3. Due to low temp. growth at 600°, however, the phase sepn. was suppressed for the In compn. ≤35%, which was confirmed by x-ray diffraction measurement, and the films exhibited high transmittance over 85% with sharp absorption edges. The bandgap could be tuned from 5.0-4.0 eV. The results encourage the application of (InxGa1-x)2O3 thin films in short-wavelength optical devices.
- 33Regoutz, A.; Egdell, R.; Morgan, D.; Palgrave, R.; Téllez, H.; Skinner, S.; Payne, D.; Watson, G.; Scanlon, D. Electronic and Surface Properties of Ga-doped In2O3 Ceramics. Appl. Surf. Sci. 2015, 349, 970– 982, DOI: 10.1016/j.apsusc.2015.04.10633https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXntlGgsLw%253D&md5=e9497081343790fc4db705e9ad92596cElectronic and surface properties of Ga-doped In2O3 ceramicsRegoutz, A.; Egdell, R. G.; Morgan, D. J.; Palgrave, R. G.; Tellez, H.; Skinner, S. J.; Payne, D. J.; Watson, G. W.; Scanlon, D. O.Applied Surface Science (2015), 349 (), 970-982CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)The limit of soly. of Ga2O3 in the cubic bixbyite In2O3 phase was established by x-ray diffraction and Raman spectroscopy to correspond to replacement of around 6% of In cations by Ga for samples prepd. at 1250°. D. functional theory calcns. suggest that Ga substitution should lead to widening of the bulk bandgap, as expected from the much larger gap of Ga2O3 as compared to In2O3. However both diffuse reflectance spectroscopy and valence band x-ray photoemission reveal an apparent narrowing of the gap with Ga doping. It is tentatively concluded that this anomaly arises from introduction of Ga+ surface lone pair states at the top of the valence band and structure at the top of the valence band in Ga-segregated samples is assigned to these lone pair states. In addn. photoemission reveals a broadening of the valence band edge. Core x-ray photoemission spectra and low energy ion scattering spectroscopy both reveal pronounced segregation of Ga to the ceramic surface, which may be linked to both relief of strain in the bulk and the preferential occupation of surface sites by lone pair cations. Surprisingly Ga segregation is not accompanied by the development of chem. shifted structure in Ga 2p core XPS assocd. with Ga+. However expts. on ion bombarded Ga2O3, where a shoulder at the top edge of the valence band spectra provide a clear signature of Ga+ at the surface, show that the chem. shift between Ga+ and Ga3+ is too small to be resolved in Ga 2p core level spectra. Thus the failure to observe chem. shifted structure assocd. with Ga+ is not inconsistent with the proposal that band gap narrowing is assocd. with lone pair states at surfaces and interfaces.
- 34von Wenckstern, H.; Splith, D.; Purfürst, M.; Zhang, Z.; Kranert, C.; Müller, S.; Lorenz, M.; Grundmann, M. Structural and Optical Properties of (In,Ga)2O3 Thin Films and Characteristics of Schottky Contacts Thereon. Semicond. Sci. Technol. 2015, 30, 024005, DOI: 10.1088/0268-1242/30/2/02400534https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXit1ygsr0%253D&md5=99f3012eb139364fea9f0e4bfa2c9469Structural and optical properties of (In, Ga)2O3 thin films and characteristics of Schottky contacts thereonvon Wenckstern, H.; Splith, D.; Purfuerst, M.; Zhang, Z.; Kranert, Ch.; Mueller, S.; Lorenz, M.; Grundmann, M.Semiconductor Science and Technology (2015), 30 (2), 24005/1-24005/7, 7 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)We report on structural and optical properties of a (InxGa1-x)2O3 thin film having a monotonic lateral variation of the indium content x (0 ≤ x ≤ 0.9). The growth condition for each In content is similar allowing precise detn. of the dependence of material properties on x. For low In content (x < 0.15) the thin film has monoclinic crystal structure; for highest In contents (x > 0.8) the cubic bixbyite phase is predominant. For intermediate alloying we observe addnl. the rhombohedral InGaO3(II) crystallog. phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (InxGa1-x)2O3 and photo response measurements for x < 0.1.
- 35Yang, F.; Ma, J.; Luan, C.; Kong, L. Structural and Optical Properties of Ga2(1-x)In2xO3 films Prepared on α-Al2O3 (0001) by MOCVD. Appl. Surf. Sci. 2009, 255, 4401– 4404, DOI: 10.1016/j.apsusc.2008.10.12935https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXpvFSitw%253D%253D&md5=147cc7a7f8cc0019b9ce061e6b323a12Structural and optical properties of Ga2(1-x)In2xO3 films prepared on α-Al2O3 (0001) by MOCVDYang, Fan; Ma, Jin; Luan, Caina; Kong, LingyiApplied Surface Science (2009), 255 (8), 4401-4404CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Ga2(1-x)In2xO3 thin films with different indium content x [In/(Ga + In) at. ratio] were prepd. on α-Al2O3 (0 0 0 1) substrates by the metal org. chem. vapor deposition (MOCVD). The structural and optical properties of the Ga2(1-x)In2xO3 films were investigated in detail. Microstructure anal. revealed that the film deposited with compn. x = 0.2 was polycryst. structure and the sample prepd. with x up to 0.8 exhibited single cryst. structure of In2O3. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The av. transmittance for the films in the visible range was over 90%.
- 36Zhang, Z.; von Wenckstern, H.; Lenzner, J.; Lorenz, M.; Grundmann, M. Visible-blind and Solar-blind Ultraviolet Photodiodes Based on (InxGa1-x)2O3. Appl. Phys. Lett. 2016, 108, 123503, DOI: 10.1063/1.494486036https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvVCltL4%253D&md5=233d1f6efa45ed6b1195cf33b394e67cVisible-blind and solar-blind ultraviolet photodiodes based on (InxGa1-x)2O3Zhang, Zhipeng; von Wenckstern, Holger; Lenzner, Joerg; Lorenz, Michael; Grundmann, MariusApplied Physics Letters (2016), 108 (12), 123503/1-123503/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)UV and deep-UV selective photodiodes from visible-blind to solar-blind were realized based on a Si-doped (InxGa1-x)2O3 thin film with a monotonic lateral variation of 0.0035 < x < 0.83. Such layer was deposited by employing a continuous compn. spread approach relying on the ablation of a single segmented target in pulsed-laser deposition. The photo response signal is provided from a metal-semiconductor-metal structure upon backside illumination. The absorption onset was tuned from 4.83 to 3.22 eV for increasing x. Higher responsivities were obsd. for photodiodes fabricated from indium-rich part of the sample, for which an internal gain mechanism could be identified. (c) 2016 American Institute of Physics.
- 37Michel, J.; Splith, D.; Rombach, J.; Papadogianni, A.; Berthold, T.; Krischok, S.; Grundmann, M.; Bierwagen, O.; von Wenckstern, H.; Himmerlich, M. Processing Strategies for High-Performance Schottky Contacts on n-Type Oxide Semiconductors: Insights from In2O3. ACS Appl. Mater. Interfaces 2019, 11, 27073– 27087, DOI: 10.1021/acsami.9b0645537https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlSntbnN&md5=e32c825ad1d3131c600b3c557c8cae7cProcessing strategies for high-performance Schottky contacts on n-type oxide semiconductors: insights from In2O3Michel, Jonas; Splith, Daniel; Rombach, Julius; Papadogianni, Alexandra; Berthold, Theresa; Krischok, Stefan; Grundmann, Marius; Bierwagen, Oliver; von Wenckstern, Holger; Himmerlich, MarcelACS Applied Materials & Interfaces (2019), 11 (30), 27073-27087CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Prepn. of rectifying Schottky contacts on n-type oxide semiconductors, such as indium oxide (In2O3), is often challenged by the presence of a distinct surface electron accumulation layer. Here, the authors investigated the material properties and elec. transport characteristics of platinum contact/indium oxide heterojunctions to define routines for the prepn. of high-performance Schottky diodes on n-type oxide semiconductors. Combining the evaluation of different Pt deposition methods, such as electron-beam evapn. and (reactive) sputtering in an (O and) Ar atm., with oxygen plasma interface treatments, the authors identify key parameters to obtain Schottky-type contacts with high electronic barrier height and high rectification ratio. Different photoelectron spectroscopy approaches are compared to characterize the chem. properties of the contact layers and the interface region toward In2O3, to analyze charge transfer and plasma oxidn. processes as well as to evaluate the precision and limits of different methodologies to det. heterointerface energy barriers. An oxygen-plasma-induced passivation of the semiconductor surface, which induces electron depletion and generates an intrinsic interface energy barrier, is found to be not sufficient to generate rectifying platinum contacts. The dissoln. of the functional interface oxide layer within the Pt film results in an energy barrier of ∼0.5 eV, which is too low for an In2O3 electron concn. of ∼1018 cm-3. A reactive sputter process in an Ar and O atm. is required to fabricate rectifying contacts that are composed of platinum oxide (PtOx). Combining oxygen plasma interface oxidn. of the semiconductor surface with reactive sputtering of PtOx layers results in the generation of a high Schottky barrier of ∼0.9 eV and a rectification ratio of up to 106. An addnl. oxygen plasma treatment after contact deposition further reduced the reverse leakage current, likely by eliminating a surface conduction path between the coplanar Ohmic and Schottky contacts. We conclude that processes that allow us to increase the oxygen content in the interface and contact region are essential for fabrication of device-quality-rectifying contacts on various oxide semiconductors.
- 38Rombach, J.; Papadogianni, A.; Mischo, M.; Cimalla, V.; Kirste, L.; Ambacher, O.; Berthold, T.; Krischok, S.; Himmerlich, M.; Selve, S.; Bierwagen, O. The Role of Surface Electron Accumulation and Bulk Doping for Gas-Sensing Explored with Single-Crystalline In2O3 Thin Films. Sens. Actuators, B 2016, 236, 909– 916, DOI: 10.1016/j.snb.2016.03.07938https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XkvFOnu7c%253D&md5=e8e979d3bfdf3f57b5b6920697b467f3The role of surface electron accumulation and bulk doping for gas-sensing explored with single-crystalline In2O3 thin filmsRombach, Julius; Papadogianni, Alexandra; Mischo, Markus; Cimalla, Volker; Kirste, Lutz; Ambacher, Oliver; Berthold, Theresa; Krischok, Stefan; Himmerlich, Marcel; Selve, Soeren; Bierwagen, OliverSensors and Actuators, B: Chemical (2016), 236 (), 909-916CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)Single cryst. and textured In2O3 thin films with (1 1 1) surface orientation, grown by plasma-assisted mol. beam epitaxy, were used as a model system to study the role of bulk and surface electron accumulation layer conductance for ozone sensing. Both conductance contributions, which add to the total film conductance, were systematically varied. The resulting ozone sensitivity was detd. by total conductance measurements in synthetic air with defined ozone concn. using UV irradn. instead of heating to regenerate the In2O3 surface. Depletion of the surface electron accumulation by an oxygen plasma treatment, confirmed by XPS, rendered the films ozone insensitive. The ozone response of films with an accumulation layer was increased by thickness redn. or by designing the bulk of the film semi-insulating using deep acceptor doping by Mg. Our results of using electron accumulation layers for gas sensing and bulk doping by deep acceptors to increase sensitivity can be generalized to other gas sensing materials. The use of single cryst. films allows selecting the most sensitive crystallog. surface orientation and may have further advantages over polycryst. films, such as increased stability and sensing speed.
- 39Veal, T. D.; Jefferson, P. H.; Piper, L. F. J.; McConville, C. F.; Joyce, T. B.; Chalker, P. R.; Considine, L.; Lu, H.; Schaff, W. J. Transition from Electron Accumulation to Depletion at InGaN Surfaces. Appl. Phys. Lett. 2006, 89, 202110, DOI: 10.1063/1.238797639https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXktlak&md5=b14fb532a9578efd68907d2f3b43d496Transition from electron accumulation to depletion at InGaN surfacesVeal, T. D.; Jefferson, P. H.; Piper, L. F. J.; McConville, C. F.; Joyce, T. B.; Chalker, P. R.; Considine, L.; Lu, Hai; Schaff, W. J.Applied Physics Letters (2006), 89 (20), 202110/1-202110/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)The compn. dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1-xN films (0 ≤ x ≤ 1) was studied using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band min. (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approx. x = 0.3. The results are consistent with the compn. dependence of the band edges with respect to the charge neutrality level.
- 40Kajiyama, K.; Mizushima, Y.; Sakata, S. Schottky Barrier Height of n-InxGa1-xAs Diodes. Appl. Phys. Lett. 1973, 23, 458, DOI: 10.1063/1.165495740https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXjtFOitg%253D%253D&md5=36c14898e87f403b143525b8a0b70f17Schottky barrier height of n-indium gallium arsenide (n-InxGa1-xAs) diodesKajiyama, K.; Mizushima, Y.; Sakata, S.Applied Physics Letters (1973), 23 (8), 458-9CODEN: APPLAB; ISSN:0003-6951.The barrier heights, ΦB, of Au/n-InxGa1-xAs diodes were measured by the capacitance-voltage and satn. current methods. The compn. dependence of the barrier height is ΦB (eV) = 0.95 - 1.90x + 0.90x2. A low barrier height with a relatively wide band gap is obtained in this system.
- 41Lüth, H. Research on III-V Semiconductor Interfaces: Its Impact on Technology and Devices. Physica Status Solidi (a) 2001, 187, 33– 44, DOI: 10.1002/1521-396X(200109)187:1<33::AID-PSSA33>3.0.CO;2-9There is no corresponding record for this reference.
- 42Wei, S.-H.; Zunger, A. Role of Metal d States in II-VI Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 8958, DOI: 10.1103/PhysRevB.37.895842https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1cXkvVSjsrk%253D&md5=4a52c17c7dabbdc3b5fe4eb181336e72Role of metal d states in II-VI semiconductorsWei, S. H.; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1988), 37 (15), 8958-81CODEN: PRBMDO; ISSN:0163-1829.All-electron band-structure calcns. and photoemission expts. on II-VI semiconductors both exhibit a metal d subband inside the main valence band. It has nevertheless been customary in pseudopotential and tight-binding approaches to neglect the metal d band by choosing Hamiltonian parameters which place this band inside the chem. inert at. cores. By using all-electron self-consistent electronic-structure techniques (which treat the outermost d electrons in the same way as other valence electrons) and by comparing the results to those obtained by methods which remove the d band from the valence spectrum, the effects on valence properties were studied. For II-VI semiconductors p-d repulsion and hybridization (1) lower the band gaps, (2) reduce the cohesive energy, (3) increase the equil. lattice parameters, (4) reduce the spin-orbit splitting, (5) alter the sign of the crystal-field splitting, (6) increase the valence-band offset between common-anion II-VI semiconductors, and (7) modify the charge distributions of various II-VI systems and their alloys. P-d repulsion is also responsible for the occurrence of deep Cu acceptor levels in II-VI semiconductors (compared with shallow acceptors of Zn in III-V), for the anomalously small band gaps in chalcopyrites, and for the neg. exchange splitting in ferromagnetic MnTe.
- 43Varley, J. B.; Weber, J. R.; Janotti, A.; Van de Walle, C. G. Oxygen Vacancies and Donor Impurities in β-Ga2O3. Appl. Phys. Lett. 2010, 97, 142106, DOI: 10.1063/1.349930643https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXht1Gns7bJ&md5=73782eef178ad7fa1e75df78e496b428Oxygen vacancies and donor impurities in β-Ga2O3Varley, J. B.; Weber, J. R.; Janotti, A.; Van de Walle, C. G.Applied Physics Letters (2010), 97 (14), 142106/1-142106/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using hybrid functionals we have investigated the role of O vacancies and various impurities in the elec. and optical properties of the transparent conducting oxide β-Ga2O3. We find that O vacancies are deep donors, and thus cannot explain the unintentional n-type cond. Instead, we attribute the cond. to common background impurities such as Si and H. Monoat. H has low formation energies and acts as a shallow donor in both interstitial and substitutional configurations. We also explore other dopants, where substitutional forms of Si, Ge, Sn, F, and Cl are shown to behave as shallow donors. (c) 2010 American Institute of Physics.
- 44Karazhanov, S. Z.; Ravindran, P.; Vajeeston, P.; Ulyashin, A.; Finstad, T. G.; Fjellvag, H. Phase Stability, Electronic Structure, and Optical Properties of Indium Oxide Polytypes. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 075129, DOI: 10.1103/PhysRevB.76.07512944https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtVWqsbbE&md5=5cc91051bdbb67b7a3a92d3f6b9fe4ccPhase stability, electronic structure, and optical properties of indium oxide polytypesKarazhanov, S. Zh.; Ravindran, P.; Vajeeston, P.; Ulyashin, A.; Finstad, T. G.; Fjellvag, H.Physical Review B: Condensed Matter and Materials Physics (2007), 76 (7), 075129/1-075129/13CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Structural phase stability, electronic structure, optical properties, and high-pressure behavior of polytypes of In2O3 in three space group symmetries I213, Ia3, and R3 were studied by 1st-principles d.-functional calcns. From structural optimization based on total energy calcns., lattice and positional parameters were established, which are in good agreement with the corresponding exptl. data except for I213, where the symmetry anal. for optimized structure indicates that it arrived at the Ia3 phase. In2O3 of space group symmetry Ia3 is found to undergo a pressure-induced phase transition to the R3 phase at pressures around 3.8 GPa. From the anal. of band structure coming out from the calcns. within the local d. and generalized gradient approxns., In2O3 of space group symmetry I213 and R3 are indirect band gap semiconductors, while the other phase of space group Ia3 is having direct band gap. The calcd. carrier effective masses for all these three phases are compared with available exptl. and theor. values. From charge-d. and electron localization function anal., these phases have dominant ionic bonding with noticeable covalent interaction between In and O. The magnitudes of the absorption and reflection coeffs. for In2O3 with space groups Ia3 and R3 are small in the energy range 0-5 eV, indicating that these phases can be regarded and classified as transparent.
- 45Mryasov, O. N.; Freeman, A. J. Electronic Band Structure of Indium Tin Oxide and Criteria for Transparent Conducting Behavior. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 64, 233111, DOI: 10.1103/PhysRevB.64.23311145https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXovV2qsro%253D&md5=6df82de30ad4bd7eb3b010f0725253a6Electronic band structure of indium tin oxide and criteria for transparent conducting behaviorMryasov, O. N.; Freeman, A. J.Physical Review B: Condensed Matter and Materials Physics (2001), 64 (23), 233111/1-233111/3CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Indium-based transparent conductors, notably indium tin oxide (ITO), have a wide range of applications due to a unique combination of visible light transparency and modest cond. A fundamental understanding of such an unusual combination of properties is strongly motivated by the great demand for materials with improved transparent conducting properties. Here we formulate conditions for transparent conducting behavior on the basis of the local d. full-potential linear muffin-tin orbital electronic band structure calcns. for Sn-doped In2O3 and available exptl. data. We conclude that the position, dispersion, and character of the lowest conduction band are the key characteristics of the band structure responsible for its electro-optical properties. Further, we find that this lowest band is split with Sn doping due to the strong hybridization with dopant s-type states and this splitting contributes to both the decrease of the plasma frequency and the mobility of the carriers.
- 46Furthmüller, J.; Bechstedt, F. Quasiparticle Bands and Spectra of Ga2O3 Polymorphs. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 115204, DOI: 10.1103/PhysRevB.93.115204There is no corresponding record for this reference.
- 47Hajnal, Z.; Miró, J.; Kiss, G.; Réti, F.; Deák, P.; Herndon, R. C.; Kuperberg, J. M. Role of Oxygen Vacancy Defect States in the n-type Conduction of β-Ga2O3. J. Appl. Phys. 1999, 86, 3792, DOI: 10.1063/1.37128947https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlvFWht7g%253D&md5=18fc2c6c7448d58d7642c51e52040171Role of oxygen vacancy defect states in the n-type conduction of β-Ga2O3Hajnal, Zoltan; Miro, Jozsef; Kiss, Gabor; Reti, Ferenc; Deak, Peter; Herndon, Roy C.; Kuperberg, J. MichaelJournal of Applied Physics (1999), 86 (7), 3792-3796CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)Based on semiempirical quantum-chem. calcns., the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equil. geometries and formation energies of neutral and doubly ionized vacancies were calcd. Using the calcd. donor level positions of the vacancies, the high temp. n-type conduction is explained. The vacancy concn. is obtained by fitting to the exptl. resistivity and electron mobility.
- 48Swallow, J. E. N. Influence of Polymorphism on the Electronic Structure of Ga2O3. Chem. Mater. 2020, 32, 8460– 8470, DOI: 10.1021/acs.chemmater.0c0246548https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXitVeju7bM&md5=a15f97f6d4857fec636c475c0fd61889Influence of Polymorphism on the Electronic Structure of Ga2O3Swallow, Jack E. N.; Vorwerk, Christian; Mazzolini, Piero; Vogt, Patrick; Bierwagen, Oliver; Karg, Alexander; Eickhoff, Martin; Schormann, Jorg; Wagner, Markus R.; Roberts, Joseph W.; Chalker, Paul R.; Smiles, Matthew J.; Murgatroyd, Philip; Razek, Sara A.; Lebens-Higgins, Zachary W.; Piper, Louis F. J.; Jones, Leanne A. H.; Thakur, Pardeep K.; Lee, Tien-Lin; Varley, Joel B.; Furthmuller, Jurgen; Draxl, Claudia; Veal, Tim D.; Regoutz, AnnaChemistry of Materials (2020), 32 (19), 8460-8470CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The search for new wide-band-gap materials is intensifying to satisfy the need for more advanced and energy-efficient power electronic devices. Ga2O3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theor. approaches to gain insights into their structure-electronic structure relationships. Valence and conduction electronic structure as well as semicore and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron d. functional theory and many-body perturbation theory, provides detailed understanding of the spectroscopic results. The calcd. spectra provide very accurate descriptions of all exptl. spectra and addnl. illuminate the origin of obsd. spectral features. This work provides a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device generations.
- 49Scofield, J. Theoretical photoionization cross sections from 1 to 1500 keV, 1973.There is no corresponding record for this reference.
- 50Persson, C.; Zunger, A. s-d Coupling in Zinc-blende Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 68, 073205, DOI: 10.1103/PhysRevB.68.07320550https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXntV2gu7k%253D&md5=2ee875f84bc050ffbd0ce2324fb7870as-d coupling in zinc-blende semiconductorsPersson, Clas; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (2003), 68 (7), 073205/1-073205/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)Most zinc blende semiconductors have a single anion-like s state near the bottom of the valence band, found in d.-of-states (DOS) calcns., and seen in photoemission. Here, we discuss the case where two s-like peaks appear, due to strong s-d coupling. Indeed, away from the k = 0 Brillouin zone center, cation d states and anion s states can couple in zinc blende symmetry. Depending on the energy difference ΔEsd = Esanion - Edcation, this interaction can lead to either a single or two s-like peaks in the DOS and photoemission. We find four types of behaviors: (i) in GaP, GaAs, InP, and InAs, ΔEsd is large, giving rise to a single cation d peak well below the single anion s peak; (ii) similarly, in CdS, CdSe, ZnS, ZnSe, and ZnTe, we see also a single s peak, but now the cation d is above the anion s. In both (i) and (ii) the s-d coupling is very weak. For (iii) in GaN and InN, the local d. approxn. (LDA) predicts two s-like peaks bracketing below and above the cation d-like state. Correcting the too low binding energies of LDA by LDA + SIC (self-interaction correction) still leaves the two s-like peaks. The occurrence of two s-like peaks represents the fingerprint of strong s-d coupling. And (iv) in CdTe, LDA predicts a single s-like peak just as in case (ii) above. However, LDA + SIC correction shifts down the cation d state closer to the anion s band, enhancing the s-d coupling, and leading to the appearance of two s-like peaks. Case (iv) is a remarkable situation where LDA errors cause not only quant. energetic errors, but actually leads to a qual. effect of a DOS peak that exists in LDA + SIC but is missing in LDA. We predict that the double-s peak should be obsd. in photoemission for GaN, InN, and CdTe.
- 51Fuchs, F.; Bechstedt, F. Indium-oxide Polymorphs from First Principles: Quasiparticle Electronic States. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 155107, DOI: 10.1103/PhysRevB.77.15510751https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXlsVGktbw%253D&md5=7c9918c14851840394558fc5e4b4fc9dIndium-oxide polymorphs from first principles: Quasiparticle electronic statesFuchs, F.; Bechstedt, F.Physical Review B: Condensed Matter and Materials Physics (2008), 77 (15), 155107/1-155107/10CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The electronic structure of In2O3 polymorphs is calcd. from first principles using d. functional theory (DFT) and many-body perturbation theory (MBPT). DFT calcns. with a local exchange-correlation (XC) functional give the relaxed at. coordinates of the two stable polymorphs. Their electronic structure, i.e., the band structure and d. of states, is studied within MBPT. The quasiparticle equation is solved in two steps. As the zeroth approxn. for the XC self-energy the nonlocal potential resulting from a HSE03 hybrid functional is used. In the sense of a self-consistent procedure G0W0 quasiparticle corrections are computed on top. The calcd. direct quasiparticle gaps at Γ amt. to 3.3 eV (rhombohedral) and 3.1 eV (cubic). The rhombohedral polymorph is found to exhibit a near degeneracy of the valence-band maxima at the Γ point and on the Γ-L line, while the valence-band max. of the cubic polymorph occurs near Γ. Interconduction band transitions are identified as possible origin of conflicting exptl. reports, claiming a much larger difference between the direct and indirect gap. The results for gaps, d-band positions, and d. of states are compared with available exptl. data.
- 52Fuchs, F.; Furthmüller, J.; Bechstedt, F.; Shishkin, M.; Kresse, G. Quasiparticle Band Structure based on a Generalized Kohn-Sham Scheme. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 115109, DOI: 10.1103/PhysRevB.76.11510952https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtFeqt7fI&md5=ef0914feed4c7203ad821c666df823c4Quasiparticle band structure based on a generalized Kohn-Sham schemeFuchs, F.; Furthmuller, J.; Bechstedt, F.; Shishkin, M.; Kresse, G.Physical Review B: Condensed Matter and Materials Physics (2007), 76 (11), 115109/1-115109/8CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We present a comparative full-potential study of generalized Kohn-Sham (gKS) schemes with explicit focus on their suitability as starting point for the soln. of the quasiparticle equation. We compare G0W0 quasiparticle band structures calcd. upon local-d. approxn. (LDA), screened-exchange, HSE03, PBE0, and Hartree-Fock functionals for exchange and correlation (XC) for Si, InN, and ZnO. Furthermore, the HSE03 functional is studied and compared to the generalized gradient approxn. (GGA) for 15 nonmetallic materials for its use as a starting point in the calcn. of quasiparticle excitation energies. For this case, the effects of self-consistency in the GW self-energy are also analyzed. It is shown that the use of a gKS scheme as a starting point for a perturbative quasiparticle correction can improve upon the deficiencies found for LDA or GGA starting points for compds. with shallow d bands. For these solids, the order of the valence and conduction bands is often inverted using local or semilocal approxns. for XC, which makes perturbative G0W0 calcns. unreliable. The use of a gKS starting point allows for the calcn. of fairly accurate band gaps even in these difficult cases, and generally single-shot G0W0 calcns. following calcns. using the HSE03 functional are very close to expt.
- 53Ley, L.; Pollak, R. A.; McFeely, F. R.; Kowalczyk, S. P.; Shirley, D. A. Total Valence-band Densities of States of III-V and II-VI Compounds from X-ray Photoemission Spectroscopy. Phys. Rev. B 1974, 9, 600– 621, DOI: 10.1103/PhysRevB.9.60053https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXhtFClsbY%253D&md5=d78a05cbcbffbc1ff9e665a1a4bc6743Total valence-band densities of states of [Groups] III-V and II-VI compounds from x-ray photoemission spectroscopyLey, L.; Pollak, R. A.; McFeely, F. R.; Kowalczyk, S. P.; Shirley, D. A.Physical Review B: Solid State (1974), 9 (2), 600-21CODEN: PLRBAQ; ISSN:0556-2805.A comprehensive survey of the total valence-band x-ray-photoemission spectra of 14 semiconductors is reported. The x-ray photoelectron spectra of cubic GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdTe, and HgTe, and of hexagonal ZnO, CdS, and CdSe were obtained from freshly cleaved single crystals, in the 0-50-eV binding-energy range, by using monochromatized Al Kα (1486.6 eV) radiation. The binding energies of the outermost d shells are reported. They were detd. relative both to the top of the valence bands (EBV) and to the Fermi level of a thin layer of Au that was vapor deposited after each run (EBF). These data also yielded accurate measures of sample charging. The Fermi level fell near the center of the gap for 6 samples, near the top for 2, and near the bottom for 3. Evidence for an apparent increase in core d-level spin-orbit splitting over free-atom values was interpreted as a possible spreading of a Γ7 and a Γ8 level from the upper (d3/2) Γ8 level by a tetrahedral crystal field. The s, p valence-band spectra showed 3 main peaks, with considerable structure on the least-bound peak. A discussion is given of the validity of comparing the valence-band (VB) spectrum I'(E) with VB d. of states, including cross-section modulation, final-state modulation, and relaxation effects. Characteristic binding energies of spectra features in I'(E) are tabulated. In addn., the energies of the characteristic symmetry points L3, X5, W2, Σ1min., W1, X3(L1), X1, L1, and Γ1 are given for the 11 cubic compds. These are compared with uv photoemission spectroscopy results where available and with theor. band-structure results where available. The energies calcd. by using the relativistic-orthogonalized-plane-wave approach with Xαβ exchange agree very well with expt., on the whole. In particular, they predict the important ionicity gap X3-X1 quite accurately. The ds. of states calcd. by using the empirical-pseudopotential method provided a useful basis for relating features in I'(E) to energies of the characteristic symmetry points. Band-structure calcns. in combination with x-ray-photoemission spectra appears to provide a very powerful approach to establishing the total valence-band structure of semiconductors.
- 54Erhart, P.; Klein, A.; Egdell, R. G.; Albe, K. Band Structure of Indium Oxide: Indirect Versus Direct Band Gap. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 153205, DOI: 10.1103/PhysRevB.75.15320554https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXltVSgsLg%253D&md5=9bfb8b973344fb98a131cb2b8c3bd9e0Band structure of indium oxide: Indirect versus direct band gapErhart, Paul; Klein, Andreas; Egdell, Russell G.; Albe, KarstenPhysical Review B: Condensed Matter and Materials Physics (2007), 75 (15), 153205/1-153205/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)The nature of the band gap of In oxide is still a matter of debate. Based on optical measurements the presence of an indirect band gap was suggested, which is 0.9 to 1.1 eV smaller than the direct band gap at the Γ point. This could be caused by strong mixing of O 2p and In 4d orbitals off Γ. The authors have performed extensive d. functional theory calcns. using the LDA+U and the GGA+U methods to elucidate the contribution of the In 4d states and the effect of spin-orbit coupling on the valence band structure. Although an indirect band gap is obtained, the energy difference between the overall valence band max. and the highest occupied level at the Γ point is <50 meV. The exptl. observation cannot be related to the electronic structure of the defect free bulk material.
- 55Wei, S.-H.; Nie, X.; Batyrev, I. G.; Zhang, S. B. Breakdown of the Band-gap-common-cation Rule: The Origin of the Small Band Gap of InN. Phys. Rev. B: Condens. Matter Mater. Phys. 2003, 67, 165209, DOI: 10.1103/PhysRevB.67.16520955https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXjvVKnsbk%253D&md5=c98fd287274834b31befd3c84871662eBreakdown of the band-gap-common-cation rule: the origin of the small band gap of InNWei, Su-Huai; Nie, Xiliang; Batyrev, Iskander G.; Zhang, S. B.Physical Review B: Condensed Matter and Materials Physics (2003), 67 (16), 165209/1-165209/4CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)It is well accepted that the band gap of a semiconductor compd. increases as the at. no. decreases. However, recent measurements of the small band gap of InN (Eg ∼ 0.9 eV) suggest that this rule may not hold for the common-cation In compds. Using a band-structure method that includes band-gap correction, we systematically study the chem. trends of the band-gap variation in III-V semiconductors. The calcd. InN band gap is 0.85 ± 0.1 eV, much smaller than previous exptl. value of ∼1.9 eV. The InN band-gap anomaly is explained in terms of at.-orbital energies and the band-gap deformation potentials.
- 56Wei, S.-H.; Zunger, A. Predicted Band-gap Pressure Coefficients of all Diamond and Zinc-blende Semiconductors: Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 60, 5404, DOI: 10.1103/PhysRevB.60.540456https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXlt1yjs70%253D&md5=e5fd953bf853520618f5819ee277e8f6Predicted band-gap pressure coefficients of all diamond and zinc-blende semiconductors: Chemical trendsWei, Su-Huai; Zunger, AlexPhysical Review B: Condensed Matter and Materials Physics (1999), 60 (8), 5404-5411CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)We have studied systematically the chem. trends of the band-gap pressure coeffs. of all Group IVA, IIIA-VA, and IIB-VIA semiconductors using first-principles band-structure method. We have also calcd. the individual "abs." deformation potentials of the valence-band max. (VBM) and conduction-band min. (CBM). We find that (1) the vol. deformation potentials of the Γ6c CBM are usually large and always neg., while (2) the vol. deformation potentials of the Γ8v VBM state are usually small and neg. for compds. contg. occupied valence d state but pos. for compds. without occupied valence d orbitals. Regarding the chem. trends of the band-gap pressure coeffs., we find that (3) apΓ-Γ decreases as the ionicity increases (e.g., from Ge → GaAs → ZnSe), (4) apΓ-Γ increases significantly as anion at. no. increases (e.g., from GaN → GaP → GaAs → GaSb), (5) apΓ-Γ decreases slightly as cation at. no. increases (e.g., from AlAs → GaAs → InAs), (6) the variation of apΓ-L are relatively small and follow similar trends as apΓ-Γ, and (7) the magnitude of apΓ-X are small and usually neg., but are sometimes slightly pos. for compds. contg. first-row elements. Our calcd. chem. trends are explained in terms of the energy levels of the at. valence orbitals and coupling between these orbital. In light of the above, we suggest that "empirical rule" of the pressure coeffs. should be modified.
- 57Li, Y.-H.; Gong, X. G.; Wei, S.-H. Ab Initio All-Electron Calculation of Absolute Volume Deformation Potentials of IV-IV, III-V, and II-VI Semiconductors: The Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 245206, DOI: 10.1103/PhysRevB.73.24520657https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvFCgtb0%253D&md5=885f504cdae67febdf534bab954e9433Ab initio all-electron calculation of absolute volume deformation potentials of IV-IV, III-V, and II-VI semiconductors: The chemical trendsLi, Yong-Hua; Gong, X. G.; Wei, Su-HuaiPhysical Review B: Condensed Matter and Materials Physics (2006), 73 (24), 245206/1-245206/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We calc. systematically the abs. vol. deformation potential (AVDP) of the Γ8v valence band max. (VBM) and the Γ6c conduction band min. (CBM) states for all group IV, III-V, and II-VI semiconductors. Unlike previous calcns. that involve various assumptions, the AVDPs are calcd. using a recently developed approach that is independent of the selection of the ref. energy levels. We find that although the vol. deformation potentials of the CBM state are usually large and always neg., those of the VBM state are usually small and always pos. The AVDP of the VBM state decreases as the p-d coupling increases, e.g., in the II-VI compds. The AVDP of CBM decreases as the ionicity increases. Our calcd. chem. trends of the AVDPs are explained in terms of the AO energy levels and coupling between these orbitals.
- 58Mann, J. B.; Meek, T. L.; Allen, L. C. Configuration Energies of the Main Group Elements. J. Am. Chem. Soc. 2000, 122, 2780– 2783, DOI: 10.1021/ja992866e58https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXhs1Wktb8%253D&md5=dab049932dd3ad097093f524650cb1a5Configuration Energies of the Main Group ElementsMann, Joseph B.; Meek, Terry L.; Allen, Leland C.Journal of the American Chemical Society (2000), 122 (12), 2780-2783CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Configuration energies (CEs), formerly called spectroscopic electronegativities, are an attempt to quantum mech. define, and extend, the important chem. concept of electronegativity. In a previous paper (J. Am. Chem. Soc. 1989, 111, 9003) we reported high-resoln. exptl. values obtained from the National Institutes of Science and Technol. spectroscopic energy level tables using the formula CE = (nεs + mεp)/(n + m); n and m are the no. of s and p electrons and εs and εp are their multiplet-averaged one-electron energies, for the 34 s and p-block atoms H→Xe. This CE definition is a direct extension of N. Bohr's introduction of electron configurations to quantum mech. rationalize the periodic table (hence its designation as configuration energy). Here we give exptl. nos. for the remaining 8 sixth row representative atoms plus Zn, Cd, and Hg. In addn., we have carried out high accuracy numerical Dirac-Hartree-Fock solns. for all 45 atoms. Results from these calcns. closely parallel the exptl. values and enable us to est. some of the at. multiplet levels for which no exptl. data exist. CE leads to nos. which are interpretable as an "electron attracting power" in the same manner as the traditional scales of Pauling and Allred & Rochow. They are also strongly correlated with at. energy level spacings, therefore providing an addnl. interpretability compatible with energy level data and the MO diagrams that dominate much of contemporary chem. Likewise, CEs are able to rationalize the origin of the metalloid band (diagonal line sepg. metals from nonmetals) in the periodic table and the new detn. of sixth row CEs permit designation of bismuth and polonium as metalloids, clarifying their previous uncertain classification between metal and metalloid.
- 59Fischer, C. F. Average-energy-of-configuration Hartree-Fock Results for the Atoms Helium to Radon. At. Data Nucl. Data Tables 1973, 12, 87– 99, DOI: 10.1016/0092-640X(73)90014-459https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXjtVOrsw%253D%253D&md5=c7b272a39353aa4c72c5eed8b5af2af3Average-energy-of-configuration Hartree-Fock results for the atoms helium to radonFischer, Charlotte FroeseAtomic Data and Nuclear Data Tables (1973), 12 (1), 87-99CODEN: ADNDAT; ISSN:0092-640X.Table I of the paper [Atomic Data, 1972, 4, 301] is actually for the lowest term of the configuration rather than for the av.-energy-of-the-configuration, as the paper implies. For configurations contg. 4f electrons the results of that paper correspond to an incorrect energy expression. When the energy of the lowest term is also the av. energy as for complete groups or complete groups plus (or minus) one electron, all atomic parameters are correct except for the total energy which is too high by the amt. q(q - 1) [2/95 - 2/195]F2(4f,4f), where q is the no. of 4f electrons. In all other cases, the radial functions were detd. from an energy expression too low by the same amt. The at. properties are reasonably accurate but the energy is too low. Table I for the av.-energy-of-the-configuration is given.
- 60Herman, F.; Skillman, S. Atomic Structure Calculations; Prentice-Hall: Englewood Cliffs, NJ, 1963.There is no corresponding record for this reference.
- 61Vurgaftman, I.; Meyer, J. R.; Ram-Mohan, L. R. Band Parameters for III-V Compound Semiconductors and their Alloys. J. Appl. Phys. 2001, 89, 5815– 5875, DOI: 10.1063/1.136815661https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXkt1Wrt74%253D&md5=cf8f5276c819c0a694a621e86c3d827bBand parameters for III-V compound semiconductors and their alloysVurgaftman, I.; Meyer, J. R.; Ram-Mohan, L. R.Journal of Applied Physics (2001), 89 (11, Pt. 1), 5815-5875CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)A review with 1001 refs. We present a comprehensive, up-to-date compilation of band parameters for the technol. important III-V zinc blende and wurtzite compd. semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calcns., we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temp. and alloy-compn. dependences where available. Heterostructure band offsets are also given, on an abs. scale that allows any material to be aligned relative to any other.
- 62Wu, J.; Walukiewicz, W.; Shan, W.; Yu, K. M.; Ager, J. W.; Li, S. X.; Haller, E. E.; Lu, H.; Schaff, W. J. Temperature Dependence of the Fundamental Band Gap of InN. J. Appl. Phys. 2003, 94, 4457– 4460, DOI: 10.1063/1.160581562https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXnsVWhur0%253D&md5=ecc91761222248b13d7a4706692ed570Temperature dependence of the fundamental band gap of InNWu, J.; Walukiewicz, W.; Shan, W.; Yu, K. M.; Ager, J. W.; Li, S. X.; Haller, E. E.; Lu, Hai; Schaff, William J.Journal of Applied Physics (2003), 94 (7), 4457-4460CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)The fundamental band gap of InN films grown by MBE were measured by transmission and photoluminescence spectroscopy as a function of temp. The band edge absorption energy and its temp. dependence depend on the doping level. The band gap variation and Varshni parameters of InN are compared with other Group III nitrides. The energy of the photoluminescence peak is affected by the emission from localized states and cannot be used to det. the band gap energy. Based on the results obtained on two samples with distinctly different electron concns., the effect of degenerate doping on the optical properties of InN is discussed.
- 63Tippins, H. H. Optical Absorption and Photoconductivity in the Band Edge of β-Ga2O3. Phys. Rev. 1965, 140, A316– A319, DOI: 10.1103/PhysRev.140.A31663https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXks1Oqs7g%253D&md5=01581b3d252ce2533abeaea3b50246daOptical absorption and photoconductivity in the band edge of β-Ga2O3Tippins, H. H.Physical Review (1965), 140 (1A), 316-19CODEN: PHRVAO; ISSN:0031-899X.Optical absorption and photocond. were observed in the uv in single crystals of nominally pure β-Ga2O3. At room temp. a steep absorption edge, characteristic of a band-to-band transition, is observed at 2700 A. The edge is shifted approx. 100 A. toward shorter wavelengths when the temp. is reduced to 77°K. Photocond. begins coincident with the absorption edge at 77°K., but could not be detected at room temp. A model is proposed in which the absorption arises as a result of excitation of an electron from the O 2p band to the Ga 4s band. Calcns. using this model and the Born-Haber cycle are in good agreement with the observed band gap of 4.7 ev. The much smaller band gap of β-Ga2O3 as compared with sapphire is due to the reduced coordination no. of the ions involved in the transition.
- 64Varley, J. B.; Schleife, A. Bethe-Salpeter Calculation of Optical-absorption Spectra of In2O3 and Ga2O3. Semicond. Sci. Technol. 2015, 30, 024010, DOI: 10.1088/0268-1242/30/2/02401064https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXit1ygs74%253D&md5=d2b3cafee0b2749f35fd4b24b9c2f3b4Bethe-Salpeter calculation of optical-absorption spectra of In2O3 and Ga2O3Varley, Joel B.; Schleife, AndreSemiconductor Science and Technology (2015), 30 (2), 24010/1-24010/5, 5 pp.CODEN: SSTEET; ISSN:0268-1242. (IOP Publishing Ltd.)Transparent conducting oxides keep attracting strong scientific interest not only due to their promising potential for 'transparent electronics' applications but also due to their intriguing optical absorption characteristics. Materials such as In2O3 and Ga2O3 have complicated unit cells and, consequently, are interesting systems for studying the physics of excitons and anisotropy of optical absorption. Since currently no exptl. data is available, for instance, for their dielec. functions across a large photon-energy range, we employ modern first-principles computational approaches based on many-body perturbation theory to provide theor.-spectroscopy results. Using the Bethe-Salpeter framework, we compute dielec. functions and we compare to spectra computed without excitonic effects. We find that the electron-hole interaction strongly modifies the spectra and we discuss the anisotropy of optical absorption that we find for Ga2O3 in relation to existing theor. and exptl. data.
- 65Wei, S.-H.; Zunger, A. Calculated Natural Band Offsets of all II-VI and III-V Semiconductors: Chemical Trends and the Role of Cation d Orbitals. Appl. Phys. Lett. 1998, 72, 2011, DOI: 10.1063/1.12124965https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXisValtLk%253D&md5=748c0289622ef2e2d806e9ae6e83b510Calculated natural band offsets of all II-VI and III-V semiconductors: Chemical trends and the role of cation d orbitalsWei, Su-Huai; Zunger, AlexApplied Physics Letters (1998), 72 (16), 2011-2013CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using first-principles all-electron band structure method, we have systematically calcd. the natural band offsets ΔEv between all II-VI and sep. between III-V semiconductor compds. Fundamental regularities are uncovered: for common-cation systems ΔEv decreases when the cation at. no. increases, while for common-anion systems ΔEv decreases when the anion at. no. increases. We find that coupling between anion p and cation d states plays a decisive role in detg. the abs. position of the valence band max. and thus the obsd. chem. trends.
- 66Wei, S.-H.; Zunger, A. Role of d Orbitals in Valence-Band Offsets of Common-Anion Semiconductors. Phys. Rev. Lett. 1987, 59, 144, DOI: 10.1103/PhysRevLett.59.14466https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsVWmtr8%253D&md5=6e378e78e911e4dd3859f08c2579982fRole of d orbitals in valence-band offsets of common-anion semiconductorsWei, Su Huai; Zunger, AlexPhysical Review Letters (1987), 59 (1), 144-7CODEN: PRLTAO; ISSN:0031-9007.All-electron first-principles electronic structure calcns. of core levels were made on common-anion semiconductors AlAs-GaAs and CdTe-HgTe and contrary to previous expectations, the valence-band offsets are decided primarily by intrinsic bulk effects and the interface charge transfer has but a small effect on these quantities. The failure of previous models results primarily from the omission of cation d orbitals.
- 67Van de Walle, C. G.; Martin, R. M. Absolute Deformation Potentials: Formulation and Ab initio Calculations for Semiconductors. Phys. Rev. Lett. 1989, 62, 2028– 2031, DOI: 10.1103/PhysRevLett.62.202867https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXksVGmsrk%253D&md5=0a862095ddf2e99fab3c0424985451ec"Absolute" deformation potentials: formulation and ab initio calculations for semiconductorsVan de Walle, Chris G.; Martin, Richard M.Physical Review Letters (1989), 62 (17), 2028-31CODEN: PRLTAO; ISSN:0031-9007.The subjects of this paper are the proper inclusion of long-range electrostatic terms in the theory of electronic deformation potentials, a way to include these terms by using supercells in ab initio d.-functional methods, and calcns. for selected semiconductors. The connection with the heterojunction problem is described. The results are compared with previous model theories and with expt.
- 68Cardona, M.; Christensen, N. E. Acoustic Deformation Potentials and Heterostructure Band Offsets in Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1987, 35, 6182– 6194, DOI: 10.1103/PhysRevB.35.618268https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXlsVWnsbw%253D&md5=f2e31cef82444da65df62df291204fe8Acoustic deformation potentials and heterostructure band offsets in semiconductorsCardona, Manuel; Christensen, Niels E.Physical Review B: Condensed Matter and Materials Physics (1987), 35 (12), 6182-94CODEN: PRBMDO; ISSN:0163-1829.The abs. hydrostatic deformation potentials calcd. by J. A. Verges, et al., (1982) for tetrahedral semiconductors with the linear muffin-tin-orbital method must be screened by the dielec. response of the material before using them to calc. electron-phonon interaction. This screening can be estd. by using the midpoint of an av. dielec. gap evaluated at special (Baldereschi) points of the band structure. This dielec. midgap energy (DME) was related to the charge-neutrality point (Tersoff, J., 1984) to evaluate band offsets in heterojunctions and Schottky-barrier heights. Band offsets obtained with this method for several heterojunctions are tabulated, and compared with existing exptl. results and other theor. calcns. The DME's are tabulated, and compared with those based on charge-neutrality points.
- 69Li, Y.-H.; Gong, X. G.; Wei, S.-H. Ab initio All-electron Calculation of Absolute Volume Deformation Potentials of IV-IV, III-V, and II-VI Semiconductors: The Chemical Trends. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 245206, DOI: 10.1103/PhysRevB.73.24520669https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XmvFCgtb0%253D&md5=885f504cdae67febdf534bab954e9433Ab initio all-electron calculation of absolute volume deformation potentials of IV-IV, III-V, and II-VI semiconductors: The chemical trendsLi, Yong-Hua; Gong, X. G.; Wei, Su-HuaiPhysical Review B: Condensed Matter and Materials Physics (2006), 73 (24), 245206/1-245206/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We calc. systematically the abs. vol. deformation potential (AVDP) of the Γ8v valence band max. (VBM) and the Γ6c conduction band min. (CBM) states for all group IV, III-V, and II-VI semiconductors. Unlike previous calcns. that involve various assumptions, the AVDPs are calcd. using a recently developed approach that is independent of the selection of the ref. energy levels. We find that although the vol. deformation potentials of the CBM state are usually large and always neg., those of the VBM state are usually small and always pos. The AVDP of the VBM state decreases as the p-d coupling increases, e.g., in the II-VI compds. The AVDP of CBM decreases as the ionicity increases. Our calcd. chem. trends of the AVDPs are explained in terms of the AO energy levels and coupling between these orbitals.
- 70Varley, J. B.; Samanta, A.; Lordi, V. Descriptor-Based Approach for the Prediction of Cation Vacancy Formation Energies and Transition Levels. J. Phys. Chem. Lett. 2017, 8, 5059– 5063, DOI: 10.1021/acs.jpclett.7b0233370https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFyrurjK&md5=65a28aa7efc87cf4b081712a9cc22fc0Descriptor-based approach for the prediction of cation vacancy formation energies and transition levelsVarley, Joel B.; Samanta, Amit; Lordi, VincenzoJournal of Physical Chemistry Letters (2017), 8 (20), 5059-5063CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Point defects largely det. the obsd. optical and elec. properties of a given material, yet the characterization and identification of defects has remained a slow and tedious process, both exptl. and theor. We demonstrate a computationally-cheap model that can reliably predict the formation energies of cation vacancies as well as the location of their electronic states in a large set of II-VI and III-V materials using only parameters obtained from the bulk primitive unit cell (2-4 atoms). We apply our model to ordered alloys within the CdZnSeTe, CdZnS, and ZnMgO systems and predict the positions of cation vacancy charge-state transition levels with a mean abs. error of < 0.2 eV compared to the explicitly calcd. values, showing useful accuracy without the need for the expensive and large-scale calcns. typically required. This suggests the properties of other point defects may also be predicted with useful accuracy from only bulk-derived properties.
- 71Schleife, A.; Fuchs, F.; Rödl, C.; Furthmüller, J.; Bechstedt, F. Branch-point Energies and Band Discontinuities of III-nitrides and III-/II-oxides from Quasiparticle Band-structure Calculations. Appl. Phys. Lett. 2009, 94, 012104, DOI: 10.1063/1.305956971https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXkvVCrug%253D%253D&md5=a62968ae457463c41f4e616e8b0a72e8Branch-point energies and band discontinuities of III-nitrides and III-/II-oxides from quasiparticle band-structure calculationsSchleife, A.; Fuchs, F.; Roedl, C.; Furthmueller, J.; Bechstedt, F.Applied Physics Letters (2009), 94 (1), 012104/1-012104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)Using quasiparticle band structures based on modern electronic-structure theory, we calc. the branch-point energies for zinc blende (GaN, InN), rocksalt (MgO, CdO), wurtzite (AlN, GaN, InN, ZnO), and rhombohedral crystals (In2O3). For InN, CdO, ZnO, and also In2O3 the branch-point energies are located within the lowest conduction band. These predictions are in agreement with observations of surface electron accumulation (InN, CdO) or conducting behavior of the oxides (ZnO, In2O3). The results are used to predict natural band offsets for the materials investigated. (c) 2009 American Institute of Physics.
- 72Shapera, E. P.; Schleife, A. Database-Driven Materials Selection for Semiconductor Heterojunction Design. Advanced Theory and Simulations 2018, 1, 1800075, DOI: 10.1002/adts.201800075There is no corresponding record for this reference.
- 73Walsh, A.; Catlow, C. R. A.; Zhang, K. H. L.; Egdell, R. G. Control of the Band-gap States of Metal Oxides by the Application of Epitaxial Strain: The Case of Indium Oxide. Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 161202(R) DOI: 10.1103/PhysRevB.83.16120273https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXlsV2ktLc%253D&md5=50d4c1a74160380d7ce3293607967dc1Control of the band-gap states of metal oxides by the application of epitaxial strain. The case of indium oxideWalsh, Aron; Catlow, C. Richard A.; Zhang, K. H. L.; Egdell, Russell G.Physical Review B: Condensed Matter and Materials Physics (2011), 83 (16), 161202/1-161202/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)We demonstrate that metal oxides exhibit the same relationship between lattice strain and electronic band gap as nonpolar semiconductors. Epitaxial growth of ultrathin [111]-oriented single-crystal In2O3 films on a mismatched YSZ substrate reveals a net band-gap decrease, which is dissipated as the film thickness is increased and the epitaxial strain is relieved. Calcn. of the band-gap deformation of In2O3, using a hybrid d. functional, confirms that, while the uniaxial lattice contraction along [111] results in a band-gap increase due to a raise of the conduction band, the lattice expansion in the (111) plane caused by the substrate mismatch compensates, resulting in a net band-gap decrease. These results have direct implications for tuning the band gaps and transport properties of oxides for application in optoelectronic devices.
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ARTICLE SECTIONSThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.0c16021.
XPS core levels and associated analysis, optical transmission and absorption spectra, XPS semicore levels, DFT of semicore levels accounting for SOC, DFT calculated band gap deformation potentials (PDF)
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