Some properties of thin films of chemically deposited cadmium sulphide

Abstract

Physical, optical and electrical properties of thin films of chemically deposited CdS are reported. As-deposited films were composed of hexagonal crystals with a diameter of 0.1 to 0.2 μm. The band gaps for as-deposited and hydrogen annealed samples were 2.45 and 2.38 eV, respectively. The resistivity of as-deposited films was ca. 10 9 ω cm and was lowered by both vacuum and hydrogen annealing. The resistivity was lower than 0.05 ω cm after annealing at 450°C in hydrogen saturated with Cd vapour. Atomic concentration measurements showed3the films to be stoichiometric, with hydrogen annealing having no detectable effect on the stoichiometry. X-ray photoelectron spectra showed that a surface layer of sulphate was present on both the single crystal and the film after air exposure. Secondary ion mass spectrometry revealed that the films contained impurities traceable to the deposition solution components, e.g. organics from the thiourea, chlorine, cadmium oxide and hydroxide. The impurities were not present in sufficient amounts to be detected by XPS. Hydrogen annealing the film reduced the concentration of impurities from the deposition solution, but introduced contaminants from the substrate.