The influence of shallow core-level hybridization on the electronic structure of the post-transition metal oxides ZnO, CdO, In 2O 3, and SnO 2 has been investigated using high-resolution soft x-ray emission and absorption spectroscopies. Synchrotron radiation excited O K α emission spectra provide a direct measure of the O 2p partial density of states and shallow core-level hybridization for this series of transparent conducting materials and reveal significant mixing of O 2p and shallow-core metal d states for ZnO, CdO, and In 2O 3. The experimental data are compared with local density approximation and tight-binding band structure calculations and with previous experimental determinations of direct and indirect band gaps. Rocksalt CdO, bixbyite In 2O 3, and rutile SnO 2 all adopt structures with metal cations in sites with locally centrosymmetric coordination. This prevents hybridization of O 2p states with metal 4d states at the zone center, but mixing away from F leads to indirect band gaps for CdO and In 2O 3. A revised value for the lowest indirect band gap in CdO is proposed and the overall trends in the band gap are discussed in terms of the separation between O 2p and metal 4d states. The experimental investigation has been extended to study the effects of Sn doping in In 2O 3.
|Number of pages||14859370|
|Journal||Physical Review B: Condensed Matter and Materials Physics|
|Publication status||Published - Oct 2003|