Effect of nitrogen and carbon doping on electronic properties of SrTiO3

The energy band structures of nitrogen(N)-doped and carbon(C)-doped SrTiO3 are calculated based on the first-principles density-functional theory. The substitution of N(C) for O may introduce isolated states above the top of O 2p valence band, but the band gap narrowing driven by mixing of N(C) with O 2p states is very small. Our results are consistent with experimental data of N-doped SrTiO3, where the absorption of visible light arises from the N 2p states localized above the valence-band maximum of SrTiO3, rather than the band gap narrowing.