Oxides as Semiconductors

When?

Monday 21 February 2011, 16:00

Where?

02ATI02

Open to:

Staff, Students

Speaker:

C.F. McConville, Department of Physics, University of Warwick, Coventry CV4 7AL UK

Oxide semiconductors have enormous potential for new and innovative uses and may also improve existing device applications. The fact that some of these materials, such indium tin oxide in a low quality form, have seen significant industrial use as transparent conducting oxides (TCO’s) has perhaps contributed to the belated recognition of their possibilities as semiconductors in their purer form.  Here, the surface and bulk electronic properties of several epitaxially grown high-quality oxide semiconductors (In2O3, CdO, and ZnO) will be discussed. 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 [1,2]. Both the valence band density of states and the surface electronic properties of the oxide semiconductors have been studied using high-resolution photoemission spectroscopy.  A common property of these oxide semiconductors is found to be the presence of a (quantized) surface electron accumulation layer [3,4], which is in marked contrast to the electron depletion generally observed at the surface of conventional compound semiconductors. Additionally, hydrogen is found to be a donor and native defects have a propensity to be donors in already n-type material. The origin of these phenomena will be discussed in terms of the band structure of these semiconducting oxides and their potential application in devices.

References:

1.            A. Walsh, et al. Phys. Rev. Lett. 100, 167402 (2008)

2.            P.D.C. King, T.D. Veal, et al. Phys. Rev. Lett. 101, 116808 (2008)

3.            L.F.J. Piper, P.D.C. King, et al. Phys. Rev. B, 78, 165127 (2008)

4.            P.D.C. King, T.D. Veal, C.F. McConville, et al. Phys. Rev. Lett. 104, 256803 (2010)