Effect of annealing and γ-irradiation on the properties of CuInSe₂ thin films

We study the structural and optical properties of CuInSe₂ thin films with the effect of annealing and γ-irradiation. CuInSe₂ thin films have been successfully deposited by spray pyrolysis technique. The as-deposited films exhibited single phase, polycrystalline and chalcopyrite structure with (112) the preferred orientation, which were confirmed by X-ray diffraction (XRD) analysis. However, selected area diffraction (SAD) analysis revealed that the films showed single crystal nature in some of the regions. An increase in the lattice constants was observed for annealed and irradiated thin films. The theoretical XRD pattern was simulated with the experimental pattern of as-deposited CuInSe₂ thin films. The optical band gaps of the films were found to increase from 0.9 to 1.0 and 1.06 eV on annealing the films in vacuum at 653 K for 1 h and γ-irradiation, respectively. In the case of irradiated samples, the second transition at 1.27 eV was observed, which was assigned to optical transition from split off valence band to the conduction band minimum (from Γ_7v⁵ to Γ_6c¹). The Burstein-Moss shift was observed in annealed and γ-irradiated CuInSe₂ films. The Mott parameters were evaluated for CuInSe₂ thin films.