Investigation of structural, morphological and optical properties of cadmium sulphide (CdS) thin films at different Cd/S concentration deposited by chemical technique

Abstract

CdS thin films with different Cd/S molar ratios have been prepared on glass substrates at 200 °C using simple and cost effective chemical technique having Cadmium Acetate Dihydrate (C₄H₈CdO₄·2H₂O) and Thiourea (CH₄N₂S) salts as sources for Cd and S respectively. Irrespective of Cd/S molar ratio, the crystalline nature with Cubic crystal system of cadmium sulphide thin films with preferential orientation (111) were determined by X-ray diffraction analysis with crystallite size between 1.5 and 2 nm. Crystallite size increases as the Cd/S molar ratio decreases up to 0.8 and then decreases for lower Cd/S molar ratio. Microstructural parameters such as strain, dislocation density and crystallite size were calculated. The broadened diffraction peaks indicated nano sized particles of the film material. Film coated with Cd/S molar ratio equal to 0.8 has lowest values of lattice strain and dislocation density confirming the improved crystallinity of the thin films. The surface morphology of the films was studied by scanning electron microscope analysis. The surface topography of the film was studied by atomic force microscope indicated that the film is evenly coated and has uniform grain sizes. Element stoichiometry was derived from EDS. The optical characteristic of Transmittance, Absorbance and Band gap Energy was studied by UV–Visible Spectrometer. The optical measurement shows the presence of direct transition with energy band gap between 2.4 and 2.7 eV.