Effect of annealing time on optical and electrical properties of CdS thin films

Cadmium sulphide (CdS) is semiconductor compound of II–VI group. Thin film of CdS widely used in the applications such as, a buffer layer in copper indium diselenide (CIS) hetrojunction based solar cells, transistors, photo detectors and light emitting diodes. Because of the ease of making like chemical bath deposition (CBD), screen printing and thermal evaporation. It is extensively used in the CIS based solar cells as a buffer layers. The buffer layers usually used for reducing the interface recombination of the photo generated carriers by means of improving the lattice mismatch between the layers. The optimum thickness and the optoelectronics properties of CdS thin films like, optical band gap, electrical resistivity, structure, and composition etc., are to be considering for its use as a buffer layer. In the present study the CdS thin film were grown by simple dip coating method. In this method we had prepared 0.1M Cadmium-thiourea precursor solution. Before the deposition process of CdS, glass substrate has been cleaned using Methanol, Acetone, Trichloroethylene and De-ionized (DI) water. After coating of precursor layer, it was heated at 200 °C for themolysis. Then after CdS films were annealed at 200 °C for different time and studied its influence on the optical transmission, band gap, XRD, raman and the electrical resistivity. As increasing the annealing time we had observed the average transmission of the films was reduce after the absorption edge. In addition to the blue shift of absorption edge was observed. The observed optimum band gap was around 2.50 eV. XRD and raman analysis confirms the cubuc phase of CdS. Hot probe method confirms the n-type conductivity of the CdS film. Hall probe data shows the resistivity of the films was in the order of 103 Ωcm. Observed data signifies its future use in the many optoelectronics devices.