Abstract
This work deals with the preparation of cadmium sulfide (CdS) thin films by chemical bath deposition. The influence of the solution temperature is investigated in this study. We suggest that activation energy of the deposition rate measurement can be a tool for determining the nature of the deposition mechanism. We found that at low solution temperature, the growth mechanism proceeds via the ion by ion process, and found the corresponding activation energy equal to 0.06 eV. However, at higher solution temperature, the film deposition became via the cluster by cluster process, the growth rate activation energy is equal to 0.48 eV. The films' structural and optical properties were studied by x-ray diffraction analysis and UV-visible spectrophotometry. Structural analysis revealed that the deposited films have a cubic structure, and the crystallite size decreases with increasing deposition temperature. The transmission spectra of the film, in the visible range, show a high transmission coefficient (70%). The transmittance data analysis indicates that the optical band gap is closely related to the solution temperature. From this analysis, a direct band gap ranging from 2.21 to 2.34 eV was deduced. From the electrical characterization we inferred that CdS films are n-type and their dark conductivities reduced with increasing bath solution temperature. From the photoconductivity measurements we concluded that films deposited at low temperatures (less than 60 degrees C) or high temperatures (higher than 70 degrees C) have good optoelectronic properties suitable for utilization as a buffer layer in thin film solar cells.