Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 15: Focus Session: Crystalline n-type semiconducting oxides - SnO2, Ga2O3, and In2O3 for novel devices (HL, jointly with O)
HL 15.9: Topical Talk
Monday, March 11, 2013, 18:15–18:45, H2
Surface electron accumulation layers in oxide semiconductors — •Tim Veal — University of Liverpool, Liverpool, UK
In contrast to the electron depletion at the surface of almost all n-type semiconductors, electron accumulation has long been known to occur at ZnO surfaces. It has recently been found to be characteric of several other oxide semiconductors, including CdO [1,2], In2O3 [3] and SnO2. They all have a significant size and electronegativity mismatch between their cation and anion. As a result, they have a particularly low Γ-point conduction band minimum which is ultimately responsible for the propensity for electron accumulation. As well as the existence of an electron-rich layer, it has been found, using angle-resolved photoemission spectroscopy (ARPES), to be quantized into 2D subbands [1]. Moreover, the conventional one-electron picture of surface space-charge in semiconductors is shown to be inconsistent with the electronic structure observed directly from ARPES, indicating that many-body interactions play a large role in the surface electronic properties of these oxides. Such interactions lead to a depth-dependent shrinkage of the semiconductor band gap, resulting in a surface band gap which differs from the bulk value [1]. The most recent studies have focussed on the influence of depositing alkali metals onto these surfaces. Many collaborators are acknowledged for samples and ARPES expertise.
[1] P. D. C. King, T. D. Veal et al., PRL 104, 256803 (2010); [2] P. D. C. King, T. D. Veal et al., PRB 79, 035203 (2009); [3] P. D. C. King, T. D. Veal et al., PRL 101, 116808 (2008)