Orientation control of β-NaGaO2 thin film: a precursor for β-CuGaO2 as a thin-film solar cell absorber

The beta-NaGaO2 thin film is a precursor film for the fabrication of a beta-CuGaO2 thin film by ion exchange, which is expected to be applicable to a thin film solar cell. The beta-NaGaO2 thin films were fabricated by electron beam evaporation, and they showed substrate dependence of the crystal orientation, which is in contrast to the recently reported beta-NaGaO2 films obtained by sputtering that exhibited no substrate dependence. The difference observed for evaporation and sputtering was discussed based on the kinetic energy of the particles impinging on the substrate during the deposition. An appropriate orientation of the beta-NaGaO2 film for ion exchange was discussed in terms of the in-plane shrinkage generated during the ion exchange from beta-NaGaO2 to -CuGaO2. (c) 2017 The Ceramic Society of Japan. All rights reserved.