Effect of oxidation on structural, optical and electrical properties of CdS thin films grown by sputtering

CdS thin films of 150 nm thick were grown by sputtering technique on top of commercially available FTO coated glass substrates. The films are oxidized by subsequently annealed in oxygen ambient at 350 °C. XRD, EDX, FTIR analysis, UV–vis spectrometry and Hall Effect measurement were used to characterize the films. XRD studies confirm the polycrystalline nature of the deposited films with phase transition from hexagonal CdS to orthorhombic CdS:CdO mixed structure. It has been observed from the UV–vis and EDX characterizations that the band gap increases with the increase of oxygen concentration incorporated to the annealed CdS thin films as well as with the increase of the oxidation time. Band gaps of the films were found to be in the range of 2.52 – 2.89 eV. CdS and CdO stretching vibration was observed from the FTIR spectra. The film resistivity and mobility are observed to change inversely with the inclusion of O2 in the CdS thin films.