Heat treatment studies on silver gallium diselenide (AgGaSe2) crystals

Silver gallium diselenide (AgGaSe2) is an important material for nonlinear optical frequency generation in the infrared region. Crystals have been difficult to produce in high optical quality form because of the presence of precipitates in as-grown material. A post-growth heat treatment process has been developed to remove these precipitates and render the crystals usable for optical applications. However, the details of the chemical interdiffusion processes involved in this method have not been well understood. In this study, the heat treatment procedure was analyzed through mass transport measurements and phase identification by powder X-ray diffractometry. A chemical mass balance model, and how it relates to our current understanding of the phase equilibrium in the Ag2Se-Ga2Se3 pseudobinary system are presented. The estimated flux, based on Knudsen's equation, has enabled us to predict the optimum annealing time for a given temperature and crystal size.