Growth mechanism of CdS film prepared by chemical bath deposition

In this paper, sodium citrate was adopted as a complexing agent and ammonia merely served as pH adjustor to investigate the growth mechanism of CdS film. The growth rate, structural properties, surface morphology, microstructure, and optical properties of CdS films were studied by profilometer, X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spectrophotometer, respectively. The SEM images show that CdS films prepared with higher ammonia concentration have lower nucleation density on substrate. SEM and EDS results show that the formation of Cd(OH) ₂ is not required in the growth of CdS film. As the ammonia concentration increases, the sites that previously adsorbed S^2- are taken by OH^- which leads to lower S^2- density on substrate. CdS film forms through direct reaction of Cd²⁺ with the S^2- which are adsorbed on the substrate. Lower S^2- density on the substrate results in the decrease of particle density on the substrate. The as-deposited CdS films have relatively high-average transmittance (~80 %) in the wavelength range from 500 to 1,000 nm which makes them suitable to be used in solar cell.