Chalcogenide thin films of Se82.5Te15Sb2.5 with different thickness (50e300 nm) are prepared by thermal
evaporation technique. Crystalline phases of the deposited films are identified by x-ray diffraction (XRD).
The influence of the film thickness and annealing temperature on the structure is studied by using XRD.
The XRD studies show that the crystallinity improved by increasing film thickness and annealing temperature.
Furthermore, the particle size and the crystallinity increase whereas dislocation density and
strain decrease with increasing both the film thickness and annealing temperature. Transmittance and
reflectance of the films are measured in wavelength range 300e2500 nm. It is found that, the optical
energy gap, Eg, decreases and the localized state tails, Ee, increases by increasing film thickness and
annealing temperature. Dispersion of the refractive index is described using WempleeDiDomenico
(WDD) single oscillator model. Dispersion parameters are calculated as a function of the film thickness
and annealing temperature.