On the surface morphology and transport properties of chemical bath deposited CoxCd1−xS thin films: A correlation

CoxCd1−xS (0 ≤ x ≤ 0.5) thin composite films were grown onto glass micro slides from an aqueous alkaline medium using a chemical bath deposition process. A complex liquid phase was formed by the addition of equimolar (1 M) volumes of cadmium sulphate, thiourea and cobaltous sulphate. For deposition, various preparative parameters, viz., speed, temperature, pH, and time were selected as optimized earlier. The chemical composition and surface morphology of these films were determined by an Energy Dispersive Spectroscopy (EDS) and the Scanning Electron Microscopy (SEM), respectively. EDS revealed the film composites to be Cd-rich. SEM revealed polycrystalline randomly oriented crystallites of elongated rhomboids with sharp and clear edges having leaf like appearance (up to x = 0.1). Optical studies revealed that the absorption increased with the increase of Co content in CdS lattice. The strong absorption edge also shifted towards the longer wavelength side and hence the band gap of the materials decreased with the increase of Co content. The temperature and composition dependence of electrical conductivity and thermoelectric power were studied and analyzed to determine the characteristic film properties and to understand the mechanism of an electrical conduction. A continuous decrease in electrical conductivity has been observed when x was varied from 0 to 0.5. The thermo power measurements showed n-type conduction. The observed results are interpreted and supported by the microscopic observations on these films.