Interpretation of the change in optical constants of different compositions of Ge–Se–In in terms of cohesive energy

Abstract

Compositional dependencies of the optical and physical properties of as-deposited amorphous GexSe90−xIn5 films (with 5≤x≤30at%), prepared by thermal evaporation have been studied. The optical energy gap Egopt is derived from Tauc's extrapolation in the strong absorption region in terms of transmission and reflection spectra. The relationship between the optical gap and chemical composition of the GexSe90−xIn5 (with 5≤x≤30at%) amorphous system is discussed in terms of the chemical bond approach. The refractive index, n and film thickness, d have been determined by an envelope method using transmission spectra. It is observed that the refractive index, n of GexSe90−xIn5 thin films increases with increasing x, over the entire spectral range, which is related to both the increased density and average coordination number.