Abstract
In order to investigate recrystalization processes in obtaining photoconduction, evaporated CdS films have been annealed; the photosensitivity and the spectro-photosensitivity of the films have been measured. Dark resistivities in excess of 106Ω cm have been obtained by the heat-treated at 500 °C for 30 minutes in air. In the heat-treated films, a remarkable increase in photosensitivity is produced. The photosensitivity is strongly dependent on the resistivity of films, and it is independent of evaporation rate, substrate temperature, film thickness, and heat treatment conditions. The photosensitivity increases monotonically as the resistivity increases, but photoconductivity is not recognized below the resistivities of 104Ω cm. The characteristics of spectro-photosensitivity of CdS films show the maximum sensitivity at the wavelength of 5340Å. In films treated in air, photocurrent decreases remarkably in the range of the wavelength from approximately 5100Å to 5300Å. On the other hand, such a phenomenon is not observed in films treated in vacuum. Therefore, photoconducting properties of CdS films are found to be profoundly influenced by oxygen sorption due to annealing.
