Influence of annealing temperature on tuning the band gap of Mn-doped ZnS thin films deposited by spray pyrolysis technique

Transition metal (Mn)-doped II-VI binary (ZnS) semiconductor (Zn_{1- x} Mn _x S, where, x = 0.1, 0.3, 0.5 and 0.7 M) thin films were deposited onto glass substrates using a spray pyrolysis deposition technique at 350 °C. The as-deposited film was found to be homogeneous and smooth for x = 0.3 M. Annealing temperature greatly affects the film morphology. So the effect of annealing temperature on the structural, optical and electrical properties of the Zn_0.70Mn_0.30S thin films was studied to explore the suitable application of these films in optoelectronics devices. The lattice defects and the internal dislocation density are found to decrease with the annealing temperature, causing improved crystallinity of the film. The decrease in dislocation density suggests an increase in the crystallinity of the film. The optical transmittance of the thin films increases with increasing annealing temperature, and the optical band gap is found to be red-shifted from 3.45 to 3.05 eV. The redshift in the band gap is due to the decrease in the amorphous phase in the thin film owning to annealing. The electrical conductivity of the films was also found to be improved by thermal treatment which may be attributed to the increased crystallinity.