Optical properties of amorphous Se90-XIn10SbX thin film alloys

•Flash evaporation in high vacuum used to obtain amorphous thin films of Se90-XIn10SbX.•Sb was added to critical Se90In10 glasses.•Ceiling of the Sb additive stretched beyond the usually reported 10 at%.•Trends in the optical properties discussed on the basis of chemical bond approach.•A chemical threshold observed at Sb = 4 at% with shift in trends of optical constants.

Ternary thin film alloys of Se90-XIn10SbX (x = 1, 4, 10, 15 and 20) were synthesised by flash evaporation of the pre-melt quenched bulk samples under a vacuum of 10−5 Torr. Optical absorption analysis pointed to indirect allowed transitions as the mechanism of excitation across the energy gap. The optical band gap (Eg) was evaluated on the basis of Wemple-Didomenico single oscillator model and Tauc's extrapolation method in the spectral region where the absorption coefficient, α ≥ 104 cm−1. The refractive index (n), complex dielectric constant (ε), band tailing parameter (B), plasma frequency (ωp), single oscillator parameters (Eo and Ed) and lattice dielectric constant (εL) were deduced for each alloy. The compositional dependence of optical and dielectric parameters was explained on the basis of chemical bond approach. The observed shift in the trends of Eg, Ed, εL and ωp values at the composition where Sb = 4 at% was correlated to the usual chemical threshold at this composition.