Electrical characterization of band gap states in C-doped TiO2 films

We report on band gap states in C-doped TiO2 films that were prepared by oxidative annealing of sputtered TiC films at 550°C in flowing O2 gas. Deep-level optical spectroscopy measurements revealed three deep levels located at ∼0.86, ∼1.30, and ∼2.34eV below the conduction band. The first level is probably attributable to the intrinsic nature of TiO2, whereas the latter two levels are newly introduced by the C-doping. In particular, the pronounced 2.34eV band contributes to band gap narrowing by mixing with the O 2p valence band. Additionally, the 0.86 and 1.30eV levels can be active as an efficient generation-recombination center.