Band-gap narrowing of TiO 2 films induced by N-doping

Abstract

N-doped TiO 2 films were deposited on n + -GaN/Al 2O 3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 °C in flowing N 2 gas. The N-doping concentration was ∼8.8%, as determined from X-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at 1.18 and 2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N-doping and contributes to band-gap narrowing by mixing with the O 2p valence band.