Effect of thermal annealing on structural and optical properties of In doped Ge-Se-Te chalcogenide thin films

Thin films of Ge_10–xSe₆₀Te₃₀In_x (x = 0, 2, 4 and 6) were developed by thermal evaporation technique. The annealing effect on the structural properties of Ge_10–xSe₆₀Te₃₀In_x (x = 0, 2, 4 and 6) films has been studied by X-ray diffraction (XRD). The XRD results indicate amorphous nature of the as-prepared films whereas crystalline phases in annealed films were identified. Structural parameters such as average crystallite size, strain, and dislocation were determined for different annealing temperatures. Effect of annealing on optical constants of prepared films has been explored using UV-Vis spectrophotometer in the wavelength range of 400 nm to 1000 nm. Various optical constants were determined depending on annealing temperature. It has been noticed that the film transparency and optical bandgap E_g have been reduced whereas the absorption coefficient α and extinction coefficient k increased with increasing annealing temperature. It was found that the prepared samples obey the allowed direct transition. The reduction in optical bandgap with annealing temperature has been described by Mott and Davis model. Due to annealing dependence of the optical parameters, the investigated material could be utilized for phase change memory devices.