COMPARISON OF CdS AND ZnS THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION

In this paper, we reported a comparative study of process and structural characterization of cadmium sulfide (CdS) and zinc sulfide (ZnS) thin films by chemical bath deposition (CBD) technique. Their deposition process is similar which clearly shows three different growth phases, a none-film one, a quasi-linear one, and a saturation one. And the growth rate of CBD-CdS is higher than that of CBD-ZnS. Through calculating the activation energy of reaction, we can conclude that the rate determining step of CBD-CdS in the deposition process is a chemical one, in contrast with the CBD-ZnS in which the determining step can be a diffusion step. The XRD analysis of the as-deposited films shows that the CBD-CdS films present cubic and hexagonal mixed structure and CBD-ZnS films are in cubic ZnS structure. The deposition time significantly influenced the crystal structure of CdS thin film. Transmission measurement shows that when the wavelength is below 500 nm, the optical transmission of CBD-ZnS film is higher than that of CBD-CdS film. Optical transmission of both CBD-ZnS and CBD-CdS films is about 90% when the wavelength is over 600 nm. The band gap (Eg) value of CBD-CdS is about 2.41 eV and that of CBD-ZnS is about 3.51 eV.