Effect of annealing conditions on structural transformation of ZnS thin film

Thin films of ZnS and ZnS doped with Cu and Al, i.e. ZnS:Cu, ZnS:[Cu, Al] with the thickness up to 1 μm were deposited by electron-beam evaporation (EBE) from three ZnS, ZnS:Cu and ZnS:[Cu, Al] targets onto ceramic BaTiO ₃ and glass substrates heated up to 150-200°C. The films were annealed at the atmospheric pressure in S₂-rich ambient atmosphere at 600-1000°C. The ZnS films were doped with Cu and Cl using the thermal treatment in a mixture of ZnS with the compounds of Cu and Cl. The ZnS:Cu and ZnS:[Cu, Cl] films were Ga co-doped by annealing in the S₂-rich ambient atmosphere with additional vapors of Ga. The duration of each annealing was one hour. X-ray diffraction (XRD) technique and atomic force microscopy (AFM) were used for the investigation. Thin films deposited from different targets have only zincblende crystal structure. The annealing of ZnS, ZnS:Cu films at 1000°C in S₂-rich atmosphere both with and without Ga co-doping does not result in the change of crystal structure. The diffusion of Cu and Cl into ZnS lattice at the annealing leads to phase transition from zincblende to wurtzite structure at 800°C, change of texture and increase of grain size. The phase transition temperature depends on the presence, type and ratio of doping elements. It was shown that Ga and Cl act as activators of recrystallization processes at the annealing.