Optical band gap tuning and study of strain in CdS thin films

In this work we have taken advantage of the control of strains at the CdS films-substrate interfaces to obtain films with tunable energy band gap. We found that on decreasing the amount of strain at the layer-substrate interface, the energy band gap of the films also decreases. Thus, we could obtain CdS films with energy band gap between 2.26 and 2.5eV. The CdS films were deposited on glass slide substrates by the chemical bath deposition method using an ammonia-free cadmium-sodium citrate system. The amount of strain at the CdS-glass substrate interface was controlled by the amount of cadmium ions in the chemical deposition process. The higher the concentration of cadmium ions, the higher the amount of strain at the layer-substrate interfaces. The properties of the CdS films were determined by X-ray diffraction and optical transmission spectroscopy measurements.