Speaker
Dr
Christoph Janowitz
(Humboldt University Berlin)
Description
A growing number of transparent conducting oxides (TCO’s) combining transparency for visible light with good electrical conductivity has been found and studied. The carrier concentration can be varied in some cases making them either more semiconducting- or metal- like. The preferential doping is n-type while p-type is hard to achieve and only some attempts have been reported. No consensus on the doping mechanism and the preferential donor has been reached. Depending on the doping level these materials can be regarded to zero approximation as degenerate semiconductors. Another concept to understand the peculiar behavior often observed in thin films is the so called charge accumulation layer on the surface giving the basis for the conductivity. In this contribution the electronic structure of high quality single crystals of In2O3 and Ga2O3 is discussed giving access to the intrinsic bulk properties. ARPES on in situ cleaved single crystals is especially used to obtain the bulk bandstructure in comparison to DFT calculations, the fundamental gaps and the effective masses. Special emphasis is laid on the states in the gap. An investigation of the states in the vicinity of EF by ARPES yields results in disagreement with the two dimensional charge accumulation layer model and suggest, that electron phonon coupling leading to polaron states may be an essential ingredient to TCO physics. Finally an overview on recent results obtained by resonant photoemission and X-ray absorption spectroscopy is given. The data can be interpreted in a way that the doping is facilitated by intrinsic defect states in the gap. These states form by configuration interaction leading to opened d-shells and interaction with the ligands.
Author
Dr
Christoph Janowitz
(Humboldt University Berlin)
