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.