A semi-local and hybrid Hartree–Fock density functional study was made of native defects in three oxide semiconductors: ZnO, SrTiO3, and SnO. The defect that was responsible for the n-type conductivity of ZnO was debated, in which the O vacancy, Zn interstitial, their complexes, and residual H impurity were considered candidates. The results indicated that the O vacancy introduced a deep and localized in-gap state, whereas the Zn interstitial was a shallow donor and hence could be a source of carriers. In view of the formation energies, the O vacancy was likely to form with a substantial concentration under O-poor conditions, but the Zn interstitial was unlikely. It was therefore proposed that the O vacancy was relevant to the non-stoichiometry of ZnO and that a source other than the native defects, such as the H impurity, had to be considered for the n-type conductivity. For SrTiO3, the O vacancy and its complexes were regarded as being the origins of some of the remarkable electrical and optical properties. Significant roles for the Ti antisite were suggested in order to gain new insights into the defect-induced properties. Two types of Ti antisite, both of which were off-centered from the Sr site but in different directions, exhibited low formation energies under Ti-rich conditions, as did the O vacancy. They could explain optical properties such as visible-light emission, deep-level absorption, and ferro-electricity in reduced SrTiO3. As an example of p-type conductors, SnO was investigated, with the focus concentrated upon acceptor-like native defects. Under O-rich conditions, the Sn vacancy and O interstitial were found to be energetically favourable. The Sn vacancy introduced shallow acceptor levels and could therefore be a source of carriers. The O interstitial exhibited no in-gap levels and was inactive hence it terms of the carrier generation and compensation. This defect was a key to the understanding of the structures of intermediate compounds between SnO and SnO2.

Native Defects in Oxide Semiconductors: a Density Functional Approach. F.Oba, M.Choi, A.Togo, A.Seko, I.Tanaka: Journal of Physics - Condensed Matter, 2010, 22[38], 384211