We report the role of N in epitaxial films of anatase $\mathrm{Ti}{\mathrm{O}}_2$. The films were artificially grown with a two-step temperature-tuned epitaxy which utilized the high-temperature cubic phase of $\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ substrates. The preparation of highly crystallized anatase with various N concentrations $(C_{\mathrm{N}}⩽3.85\mathrm{at.}\%)$ allowed us to identify the optimum dopant concentration $(C_{\mathrm{N}}=1–2\mathrm{at.}\%)$. At higher doping levels, N is found to be difficult to substitute for O having been predicted to contribute to the band-gap narrowing, giving rise to the undesirable deep-level defects. In addition, a study by x-ray and Raman spectroscopy revealed that the growth of anatase became more difficult, and the stable phase was shifted to rutile at the higher N concentrations.

• Received 5 March 2005

DOI:https://doi.org/10.1103/PhysRevB.72.115124