Optical properties of amorphous Se90-XIn10SbX thin film alloys.

Ternary thin film alloys of Se 90-X In 10 Sb 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 ≥ 10 4 cm −1 . The refractive index (n), complex dielectric constant ( ε ), band tailing parameter (B), plasma frequency (ω p ), single oscillator parameters (E o and 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 L and ω p values at the composition where Sb = 4 at% was correlated to the usual chemical threshold at this composition. [ABSTRACT FROM AUTHOR]