OPTICAL AND STRUCTURAL-PROPERTIES OF ANTIMONY-DOPED CDS THIN-FILMS

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 degrees C and a pH of around 8.5. The samples were doped with various concentrations of Sb3+ 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 Sb2S3 orthorhombic phases and some other small peaks due to excess Cd and S have also been observed.