Effect of Annealing Temperature on Structural and Optical Properties of N-Doped ZnO Films

Nitrogen-doped ZnO (ZnO:N) films are prepared by thermal oxidation of sputtered Zn3N2 layers on Al2O3 substrates. The correlation between the structural and optical properties of ZnO:N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn3N2 films are transformed into ZnO:N films after annealing above 600°C. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO:N films: the NO acceptor and the double donor (N2)O. Due to the No acceptor, the hole concentration in the film annealed at 700°C is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy.