Solution Based Cation-Exchange Process to Control Optoelectronic Properties of Cadmium Sulphide Thin Films

The control of optoelectronic properties of cadmium sulphide films, by a simple solution based ion exchange process, is an important aspect for various applications. The effect of post doping of certain metal ions on chemical bath deposited cadmium sulphide thin films has been studied in this work. An alkaline bath has been developed to obtain highly homogeneous CdS films on various substrates. X-ray diffraction of these films reveals that as deposited material is amorphous. The energy dispersive x-ray analysis confirms that a reasonable amount of cations can be incorporated into these films without affecting its atomic structure. Optical absorption and electrical conductivity measurements suggest that there is a clear effect of cation-exchange with respect to lead, silver and copper ions. Electrical conductivity is significantly improved by copper ions, this change is close to five orders of magnitude with respect to intrinsic films. These results clearly show that both substitutional and interstitial mechanisms are involved in the cation-exchange process of these films.