Influence of thickness and annealing on optical constants of Se82.5Te15Sb2.5 chalcogenide thin films

•Se82.5Te15Sb2.5 films are deposited by thermal evaporation technique.•The effect of thickness is studied for annealed films at 400 K by XRD.•Se82.5Te15Sb2.5 films have indirect optical band gaps.•Absorption coefficient increases by increasing annealing temperature and film thickness.•The optical parameters are depending on heat treatment and the film thickness.

Chalcogenide thin films of Se82.5Te15Sb2.5 with different thickness (50–300 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 300–2500 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 Wemple–DiDomenico (WDD) single oscillator model. Dispersion parameters are calculated as a function of the film thickness and annealing temperature.

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