Electronic structure and origin of visible-light activity of C-doped cubic In2O3 from first-principles calculations

The origin of the experimentally observed band gap narrowing and red-shift of the adsorption edge of cubic In2O3 induced by C doping has been investigated using density functional theory calculations. We have compared the stability of all these doped systems based on the calculated formation energy as a function of the oxygen chemical potential. The calculated electronic structures show that: (I) at low C concentration, substitutional replacement of O by C could lead to small gap narrowing, owing to C 2p states below the conduction band minimum while interstitial C doping does not induce band gap narrowing; and (II) at high C concentration, C2p states mix well with O 2p states above the valence band, which may account for the experimentally observed red-shift of the absorption edge.