On the electrical and optical properties of CdS films thermally deposited by a modified source

CdS films were prepared by a physical vacuum deposition technique on an amorphous (glass) substrate using a modified evaporation source. The effect of the processing conditions (the film thickness, substrate temperature and the deposition rate) were considered in comparison with the normal evaporation source. A van der Pauw four-probe arrangement was used for measuring the electrical resistivity, which varies between 0.1×104 and 8.18×104 Ω cm. It decreases with increasing film thickness, and decreasing deposition rate and substrate temperature. This was attributed to the effect of crystallite size, the degree of preferred orientation, internal microstrain and the stoichiometry. From spectrophotometric measuring and using an approximate formula, the optical parameters (n, k, α) were evaluated. The values of the refractive indices and the energy gaps were evaluated and correlated with the preparation parameters.