Post-growth annealing of CdS crystals grown by physical vapor transport

Abstract

In this study, the photoluminescent and electric properties of as-grown CdS crystals and the effects observed after post-growth annealing in a cadmium, sulphur, and selenium overpressure were investigated. Bulk CdS crystals were grown by physical vapor transport (PVT) from high-purity starting materials, and two types of as-grown crystals, one “dark” and the other “clear” were obtained both having a medium resistivity of 106 – 108 Ω · cm. The “dark”-type crystals are cadmium rich, as evidenced by an emission peak centered around 2.07 eV, which may be attributed to sulphur vacancies, while in the “clear” crystals, this emission is less pronounced. Heat treatment under a cadmium-vapor atmosphere has the effect of decreasing the resistivity by approximately 5 orders of magnitude, while sulphur annealing at 500°C, increases the resistivity of the as-grown crystals by 4 orders of magnitude and creastes a new emission peak centered around 620 nm (2 eV).