Optical properties of ZnO thin films on LiNbO3 and LiTaO3 substrates grown by pulsed laser deposition

Optical properties such as transmittance, optical band gap and room temperature photoluminescence were investigated for ZnO thin films grown on LiNbO3 and LiTaO3 substrates by pulsed laser deposition method. The c-axis oriented ZnO films were grown epitaxially on (0001) LiNbO3 and (0001) LiTaO3 substrates. The transmittance of the films was over 90%. Peaks attributed to excitons were shown in absorption spectra, indicating that the thin films had high crystallinity. Photoluminescence spectra with the maximum peak at 540 nm were observed at room temperature, which seemed to be ascribed to excess zinc and (or) oxygen vacancy in the ZnO films caused by diffusion of Li from the substrates into the films during the deposition.