Hybrid density functional calculations are carried out to investigate the behavior of holes in ${\mathrm{Sr}\mathrm{Ti}O}_3$. As in many other oxides, it is shown that a hole tend to localize on one oxygen forming an ${\mathrm{O}}^{-}$ anion with a concomitant lattice distortion; therefore a hole polaron. The calculated emission energy from the recombination of the localized hole and a conduction-band electron is about 2.5 eV, in good agreement with experiments. Therefore the localization of the hole or self-trapping is likely to be responsible for the green photoluminescence at low temperature, which was previously attributed to an unknown defect state. Compared to an electron, the calculated hole polaron mobility is three orders of magnitude lower at room temperature. In addition, two ${\mathrm{O}}^{-}$ anions can bind strongly to form an O${}_2{}^{2-}$ peroxide anion. No electronic states associated with the $O_2{}^{2-}$ peroxide anion are located inside the band gap or close to the band edges, indicating that it is electronically inactive. We suggest that in addition to the oxygen vacancy, the formation of the $O_2{}^{2-}$ peroxide anion can be an alternative to compensate acceptor doping in ${\mathrm{Sr}\mathrm{Ti}O}_3$.

• Received 7 May 2014
• Revised 25 June 2014

DOI:https://doi.org/10.1103/PhysRevB.90.035202