Influence of vacuum annealing on the photoresponse of thermally evaporated cadmium telluride thin films

Highlights: • CdTe thin films were deposited by thermal evaporation. • The films were subsequently annealed in vacuum at 200, 300 or 400 °C. • Structural, compositional, optical, electrical characterization were conducted. • Band gap was not affected, but resistivity decreased by 2 orders of magnitude. • The photocurrent and photoresponse were markedly increased. -- Abstract: Post-deposition annealing of thin films can induce significant changes in their properties. Annealing in vacuum is particularly important because it elucidates the influence of thermal energy rather than the effects of chemical interactions with a specific ambient. Cadmium telluride (CdTe) is one of the most promising materials for photovoltaic applications. Annealing in cadmium chloride has been established as the standard method to activate the efficiency of CdTe. Nevertheless, annealing CdTe in vacuum was rarely investigated. In this work, CdTe thin films were grown by thermal evaporation, and subsequently subjected to annealing in vacuum. The resulting changes in the structural, chemical, optical, and photoelectric properties of the films were investigated. Annealing caused substantial changes in the crystallinity, surface morphology, surface chemical composition, light absorption, photocurrent and photoresponse of the films.