Structure, optical and electronic properties of solid solution Zn(O,S) thin films and the effect of annealing

Structure, optical and electronic properties of solid solution thin films of Zn(O,S) developed by spray pyrolysis are investigated, and the effect of annealing is investigated for a possible improvement in its electrical properties. A variation in the initial sulphur (S) precursor concentration with fixed Zn-precursor concentration during the spray deposition produces a solid solution of ZnO and ZnS. Both the lower (80%) concentrations of the S-precursor cause isovalent substitution in the system, retaining hexagonal ZnO and cubic ZnS structures, respectively, whereas other concentrations lead to the formation of films in a phase-separated solid solution of ZnO and ZnS. A strain-induced shift in optical band gap in the range of 3.3–3.6 eV is unique in the system with a strong bowing effect. A post-annealing at 370 °C in air is found to improve electron mobility in the film, whereas the annealing in argon ambient improves its electrical conductivity.