Carbon impurities in SrTiO₃ from first principles

Perovskite oxides have attracted both experimental and theoretical attention due to their high permittivities, with SrTiO₃ used in waveguides, high capacity computer memory cells and dielectric elements in electronic devices. Different growth methods yield various qualities of material, and thin-films growth using organic precursors makes carbon contamination highly probable. Using density functional calculations, we have investigated various structural configurations of carbon in SrTiO₃, and analysed the associated electronic properties and vibrational modes for carbon doped cubic SrTiO₃. We find that carbon substitution of host species in SrTiO₃ could be either electrically active, such as in the substitution of Sr or O, or electrically passive, which is the case with the iso-electronic substitution of Ti. The highly characteristic vibrational modes predicted for the different configurations provide a route to experimental identification. Additionally, formation energies suggest that C_Ti is generally more favourable, but under O-lean conditions oxygen substitution becomes significant, and for p-type material substitution of Sr is also possible.