Optical band gap and refractive index dispersion parameters of In–Se–Te amorphous films

Different compositions of Inx(Se0.75Te0.25)100 − x (where 0 ≤ x ≤ 10 at.%) chalcogenide glasses were prepared by the usual melt quench technique. Chalcogenide thin films of these glasses were prepared by using thermal evaporation method. The film transmittance (T(λ)) at normal incidence for these films was measured in the wavelength range 400–2500 nm using a double beam spectrophotometer. Successfully applying Swanepoel's method helps us to determine the film thickness and the real (n) and imaginary (k) parts of the complex index of refraction with high accuracy. Optical absorption measurements show that, the fundamental absorption is due to the allowed non-direct transitions. It was found that, the addition of In content leads to the increase of the refractive index increases while the optical band gap decreases. The obtained results are well discussed in terms of the chemical bond approach and the cohesive energy.

Research Highlights
► Study the effect of the replacement of Se and Te atoms by Indium on the optical properties of In-Se-Te.
► Accurately determination of the film thickness based on the interference fringes.
► Determine the optical constants such as the optical band gap, refractive index with high accuracy.
► The observed results of the refractive index were discussed in terms of the electronic polarizability.
► The obtained results of the optical band gap and absorption coefficient were discussed in terms of the chemical bond approach.