Invited Paper EM-ThM3
Trends in Surface Electronic Properties of Oxide Semiconductors
Thursday, November 12, 2009, 8:40 am, Room B1
| Session: |
Oxide Semiconductors |
| Presenter: |
T.D. Veal, University of Warwick, UK |
| Authors: |
T.D. Veal, University of Warwick, UK
P.D.C. King, University of Warwick, UK
C.F. McConville, University of Warwick, UK
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| Correspondent: |
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Oxide semiconductors have enormous potential for new and innovative uses and may also improve existing device applications. However, the fundamental properties of some of the oxide semiconductors (such as In2O3, Ga2O3 and CdO) remain either controversial or largely unknown. The semiconducting oxides have traditionally been grown using low cost, low quality techniques, such as sputtering, resulting in poor microstructure material with high levels of impurities and defects. The fact that some of these materials in their low quality form have seen significant industrial use as transparent conductors has perhaps contributed to the belated recognition of their possibilities as semiconductors in their purer form. Relatively recently, with the advent of high-purity oxide semiconductor films by high-quality growth methods, such as molecular-beam epitaxy and metal-organic vapor phase epitaxy, the fundamental properties have begun to emerge and the material characteristics have been vastly improved. Here the surface and bulk electronic properties of several such high-quality oxide semiconductors (In2O3, CdO, SrTiO3, ZnO and SnO2) will be reported. Optical, electrical and structural properties of the semiconducting oxide films will be presented, including data on the revision of the band gap of In2O3 from 3.7 eV to less than 3.0 eV [1]. Both the valence band density of states and the surface electronic properties of the oxide semiconductors have been studied using high-resoultion photoemission spectroscopy [1,2]. A common property of the materials with a high size and electronegativity mismatch between the cation and oxygen atoms is found to be the presence of a surface electron accumulation layer [3,4] which is in marked contrast to the electron depletion generally observed at the surface of conventional compound semiconductors. The origin of this phenomenon will be discussed in terms of the band structure of the semiconducting oxides. The five groups where the samples were grown are gratefully acknowledged. [1] P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang,
G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville,
Phys. Rev. B 79 (2009) in press.
[2] P. D. C. King, T. D. Veal, A. Schleife, J. Zúñiga-Pérez, B. Martel, P. H. Jefferson, F. Fuchs,
V. Muñoz-Sanjosé, F. Bechstedt, and C. F. McConville, Phys. Rev. B 79 (2009) 205205.
[3] P. D. C. King, T. D. Veal, D. J. Payne, A. Bourlange, R. G. Egdell, C. F. McConville,
Phys. Rev. Lett, 101 (2008) 116808.
[4] P. D. C. King, T. D. Veal, P. H. Jefferson, J. Zúñiga-Pérez, V. Muñoz-Sanjosé, and
C. F. McConville, Phys. Rev. B 79 (2009) 035203.