Effect of Annealing on the Properties of ZnxCd1-xS Thin Film Growth by RF Magnetron Co-sputtering

Abstract

ZnxCd1-xS thin films at low zinc content have been deposited on bare soda lime glass substrates using RF magnetron co-sputtering of CdS and ZnS for the first time to investigate annealing effect on the structural and optical properties of the thin films. The as-deposited films were annealed in O2/N2 ambient at annealing temperature ranging 200-500°C. The composition of the films was controlled by varying RF power of CdS and ZnS in such a ratio so that zinc content in the thin films was low. The composition, structural, optical and surface morphological properties of the films was investigated using EDX, XRD, UV-Vis spectrophotometer and FESEM. The annealed films were observed hexagonal wurtzite structure with strong preferential orientation along (002) diffraction peak. Crystallinity of the films increased with increasing annealing temperature below 400°C whereas beyond 400°C new peaks were observed along with decreasing trend of (002) diffraction peak. Optical absorption and transmission spectra were recorded within the range 300-900nm. With increasing annealing temperature, the band gap of the annealed films once decreased and then abruptly increased at around 400°C. The decreased bandgap may have been due to possible increase in the crystalline nature of the material. From SEM, it was observed that the thin films were formed by different clusters of grains which later changed to isolated grains as the annealing temperature increased. This work confirms that annealing temperature has overbearing influence on the ZnxCd1-xS thin film properties deposited by RF magnetron co-sputtering.