Physical properties of CdS films prepared by chemical bath deposition at different deposition temperatures

The relationship between microstructure and energy band gap of CdS films prepared by chemical bath deposition was studied. The growth rate, structural properties, optical properties, surface morphologies and film composition of CdS films prepared at different deposition temperatures were investigated by profilometer, X-ray diffractometer(XRD), transmission electron microscopy(TEM), UV-Vis spectrophotometer, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) respectively and the interrelationship among them was analyzed. As the deposition temperature increased, the growth rate and the H(002) interplanar distance increased, while the energy band gap decreased. Meanwhile, the film surface became smoother. In combination with the EDS results, it was found that the sulfur content in the CdS films increased with the deposition temperature increasing and the Cd/S atomic ratio was closer to 1:1. It could be inferred that the increase of lattice constant resulted in the decrease of the energy band gap. The variation of lattice constant could be ascribed to the variation of sulfur content in CdS films which was influenced by deposition temperature. The reaction between OH^- and thiourea was accelerated as the deposition temperature increased, which led to higher S^2- concentration in the reaction solution. More sulfur participated in the CdS films resulting in a decrease of sulfur vacancies. A decrease of sulfur vacancies indicated an improvement of the crystallinity of CdS films and led to an increase of lattice constant which became closer to that of CdS bulk materials.