Public Physic Colloquium in the Summer Terms 2010 in Münster
Place:     Germany, 48149 Münster, Wilhelm-Klemm-Str. 10, IG I, HS 2
Time:     Thursday, 01.07.2010  16:00 h c.t.
Colloquium Coffee at 15:45 h  at the Lecture Hall

Electronic structure, thermodynamics and kinetics of point defects in transparent conductive oxides
K. Albe, TU-Darmstadt

Transparent conducting oxies (TCO) represent a special class of materials combining electrical conductivity with transparency for visible light. They play a key role in optoelectronic applications such as photovoltaics and are used in conjunction with organic semiconductors in flat panel displays and so called ”smart windows”. Common features of the prototype TCO materials ZnO, SnO₂ and In₂O₃ are intrinsic n-type conductivity, extraordinary n-type dopability, absence of p-type conductivity and asymmetric effective masses. Thus far, theoretical results on the energetics of intrinsic point defects obtained from local density functional theory are at odds with experimental findings which is partly due to the LDA band-gap problem. In this contribution, hybrid functional calculations which contain a portion of non-local Hartree-Fock exchange are presented, which show a strong propensity towards n-type behavior for all TCO materials consistent with experiment and reveal fundamental differences in the defect chemistry of In₂O₃, SnO₂ and ZnO.
Additionally, calculated migration energies for all relevant defects are presented. Due to the different crystal structures the diffusion behavior is also substantially different for the investigated materials. The structural peculiarities are especially important for indium oxide where we show that the low energy migration processes do not contribute to the diffusion. In that case additional migration pathes with different barriers need to be active for larger displacements to take place. While for cation interstitials we observe a general trend for all materials, the oxygen interstitials migration is very different. A qualitatively different behavior is also found for the cation vacancies. Tin oxide which shows a notably high anisotropy which is not found for the other materials. The results are discussed by focussing on the technological importance especially in the context of organic light emitting diodes.