Annealing-induced phase transformation in InSeTe thin films and its structural, optical and morphological changes for optoelectronic applications.

InSe and InTe have great importance in various device fabrications. The present report is based on the annealing-induced phase formation of both InSe and InTe from InSeTe thin films at different annealing temperatures as found from the XRD analysis and well supported by the Raman study. The average crystallite size increased with a decrease in the dislocation density. The surface morphology changed with annealing and increased in particle size as noticed from the FESEM images. The uniform distribution and presence of constituent elements in the film were verified using EDX data. The increase in transmittance is accompanied by a decrease in extinction coefficient, optical density and increase in skin depth with annealing. The increase in optical bandgap from 0.418 eV to 0.645 eV upon annealing at 250 °C is associated with a decrease in disorder. The steepness parameter increased and the value decreased with annealing. The refractive index decreased with an increase in oscillator energy and decrease in dispersion energy. The quality factor, dielectric loss, optical conductivity and electrical susceptibility decreased. The optical electronegativity and plasma frequency increased with annealing. There is a significant change in the non-linear susceptibility and non-linear refractive index with annealing. The observed changes in the film structure and optical behaviour are due to the annealing-induced phase formation from the InSeTe host matrix upon annealing. Such materials are suitable for optoelectronic and phase change devices.