Properties of ZnS Thin Films Prepared by CBD under Different Concentration of Complexing Agent

ZnS thin films were deposited on glass substrates using chemical bath deposition. The zinc sulfate and thiourea were used as precursors along with a stable complexing agent of sodium citrate in ammonia/ammonium chloride (pH=10.5) buffer solution. The ratio of Zn and complexing agent was changed from 6:1 to 1:1 by varying concentrations of the complexing agent. X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-vis spectrophotometer were used to investigate the structure, micrograph and optical characteristics of the ZnS thin films respectively. The concentration of sodium citrate has an effect on the crystalline size and crystallization. For the as-deposited thin films, the values of transmittances and Eg are about 85% and 3.8 eV respectively. However, they are decreased to 75% and 3.4 eV respectively after annealing. In addition, the concentration of the complexing agent has no remarkable influence on both the transmittance and the energy gap. The results show that the ZnS thin films with resistivity of 4.34×104 Ωcm are suitable for optoelectronic applications.