Thermal annealing induced evolution of AgIn5Se8 phase from Ag/In2Se3 bilayer thin film

In the present report, we have investigated the AgIn₅Se₈ phase formation upon annealing the Ag/In₂Se₃ bilayer film prepared by the thermal evaporation technique. The optical, morphology as well as structural parameters was tuned with different annealing temperature. The prominent crystalline phase developed at 250 °C annealing where as there is no signal of this phase in the as-prepared film (amorphous). The analysis using XRD study showed the amorphous to crystalline phase transformation with annealing. The indirect as well as the direct band gap is found to be increased with annealing (up to 150 °C) and then decreased due to the growing up new phase as explained by phase transformation and decrease in density of localized states. The formation of dangling bonds at the surface near the crystallite sites during crystallization process reduces the band gap. The Tauc parameter change shows the degree of chemical disorderness in the films. The transmittivity, absorption coefficient, oscillator energy, refractive index, dispersion energy and extinction coefficient are found to be changed accordingly with annealing condition. The micro structural study done by Scanning Electron Microscopy shows the formation of crystallites upon annealing. The Raman study of these films supports the formation of new phase.