Band-Gap Tuning of Electron Beam Evaporated Cds Thin Films

The effect of evaporation rate on structural, morphological, and optical properties of electron beam evaporated CdS thin films has been investigated. CdS thin film was deposited by electron beam evaporation method in 12nm/min and 60nm/min evaporation rates on glass substrates. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis-NIR spectroscopy and Atomic Force Microscopy (AFM) were used to characterize the thin films. The xray diffraction analysis confirms that the films have polycrystalline hexagonal phase and exhibit preferred orientation along the (002) plane. The crystallite size was calculated and found to increase from 23 to 30 nm by increasing the deposition rate. Results of Atomic Force Microscopy revealed that the RMS roughness values of the CdS films decreased as the deposition rate increased. The relation between deposition rates and optical properties of deposited films was also investigated. It was found that stoichiometric properties and band gap values of the deposited films are correlated to the deposition rates. These dependencies are associated with the Cd/S ratio variation by the deposition rate. The optical band gap values of CdS films increased slightly in a range of 2.32–2.34 eV for deposition rate varied from 12nm/min and 60nm/min.