Optical and structural properties of antimony-doped CdS thin films

Abstract

Optical and structural investigations of antimony-doped cadmium sulphide thin films prepared by a modified chemical deposition process are described. The samples were prepared in an aqueous medium at a deposition temperature of 85 ± 2 °C and a pH of around 8.5. The samples were doped with various concentrations of Sb 3+ in the concentration range 0.005–1 wt.%. Measurements of the absorption coefficient in the energy range 1.6–3.5 eV for both CdS and CdS:Sb crystalline thin films have been carried out. A careful analysis of the absorption coefficients indicated the crystalline character of the samples studied; a similar diagnosis was obtained from the X-ray and SEM analyses. The absorption coefficient is of the order of 10 4 cm −1, and the optical energy bandgap decreases with increasing doping concentration, typically from 2.47 to 1.7 eV. The absorption edge shifts towards the higher-wavelength side and becomes broader as the doping concentration is increased. The samples are polycrystalline, and the crystallinity increases after doping up to a 0.075 wt.% doping level and decreases thereafter. In both cases the samples consist of phases of cubic and hexagonal structures. Additional peaks corresponding to Sb 2S 3 orthorhombic phases and some other small peaks due to excess Cd and S have also been observed.