Growth process and properties of CdS thin films prepared by chemical bath deposition at different pH values

Abstract

CdS thin films were successfully fabricated on glass substrates in different pH solutions by chemical bath deposition (CBD). The influences of pH value on the thickness, growth process, structure as well as on the optical properties of CdS film were investigated. The as-deposited films exhibited pure cubic phase structure, indicating that the pH had no significant effect on the crystal structure of CdS film. The optical transmittance spectra demonstrated that the films deposited at 11.7 and 11.8 pH exhibited relatively high transmittance in the long wavelength. And the optical band gaps decreased from 2.42 to 2.31 eV with increasing pH values. Subsequently, the growth process of CdS films was studied by analyzing the morphologies and particles sizes at different growing stages of the deposition. It was found that the particle clusters produced by homogeneous reaction acted as nucleation sites during the deposition process, and CdS preferred to grow on their surface. As a result, the sizes of clusters expanded with deposition time until a continuous film was formed, and the duration to obtain a continuous film reduced with decreasing pH values. Hence, a growth mode of CdS film on the glass substrate was proposed, i.e. the film was formed by the connection of expanded particle clusters produced by homogeneous reaction.