Optical properties of amorphous Se_90-XIn₁₀Sb_Xthin film alloys

Ternary thin film alloys of Se_90-XIn₁₀Sb_X(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 (E_g) 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 (ω_p), single oscillator parameters (E_oand E_d) and lattice dielectric constant (ε_L) 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 E_g, E_d, ε_Land ω_pvalues at the composition where Sb = 4 at% was correlated to the usual chemical threshold at this composition.