Effects of nitrogen doping on optical properties of TiO2 thin films

Abstract

The potential for extending the optical absorption range of TiO2 by doping with nonmetallic elements was examined in nitrogen-containing TiO2 thin films. Thin films of TiO2-xNx were synthesized on glass and silicon substrates by ion-beam-assisted deposition to obtain a wide range of nitrogen concentrations. The compositions of the films were determined by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. The structures of the films were analyzed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The optical properties of the films were measured by UV-Vis spectroscopy and ellipsometry. A characteristic decreasing trend in band-gap values of the films was observed within a certain range of increasing dopant concentrations. As the nitrogen concentration increased, the structure of the films evolved from a well-defined anatase to deformed anatase. The reduced band gaps are associated with the N 2p orbital in the TiO2-xNx films.