Ab initiocalculations of doping mechanisms in SrTiO₃

Abstract

A density functional plane-wave pseudopotential method is used to study the formation energy of a number of acceptor- and donor-type defects in SrTiO3 as a function of oxidizing atmosphere and doping levels in the bulk crystal. Of the three donor defects (VO, NbTi and AlSr) and two acceptor defects (NaSr and AlTi) considered in this study, NbTi and NaSr impurities are predicted to have the largest effect on electrical conductivity. The Al impurity is amphoteric and AlTi and AlSr can compensate one another. However, the relative abundance of AlTi and AlSr is found to depend on the oxidizing conditions. In a highly oxidizing environment AlTi is preferred, resulting in p-type material. Therefore, the Al self-compensation mechanism is predicted to be less effective in conditions where the oxygen partial pressure is high.