Properties of vacuum-evaporated CdS thin films

Thin films of highly purified CdS have been prepared by the vacuum evaporation method. The source has been maintained at 850οC and a semi-closed system has been used for evaporation. The following properties of the films have been studied, viz: (1) dark and photoconductivity as functions of temperature and thickness of the films (2) Hall mobility and carrier concentration at room temperature (3) optical absorption and spectral response and (4) structural studies by X-ray diffraction. The resistivity of the films varies from 0.15 to 3.7 Ω·cm as the thickness of the films decreases from 13600 to 1200 Å. The transmittance of the films has been found to be 80-90%. The results for Hall mobility and carrier concentration show that the comparatively low resistivity of CdS films obtained by us is primarily due to high carrier concentration. The photoconductive gain increases with a decrease in film thickness. The effect of heat treatment in air on dark and photoconductivity has been studie