Investigation of optical band-gap and related optical properties in thin-films of Ge containing Se-Te-Sn alloys

Abstract The optical band-gap and related optical properties of some Germanium containing quaternary (i.e., third generation) alloys of SeTeSnGe (STSG) have been studied. For the optical characterization of prepared thin-films, we analyzed the transmission spectrum (wavelength range: 400 – 2500 nm) and then we estimated some significant optical parameters (e.g., the absorption index and refractive index). Based on the dispersion parameters, we calculated the optical band-gap and the complex dielectric constant. Further, we determined the single-oscillator dispersion parameters and the high dielectric constant e∞ and used the Wemple and Di-Domenico model for understanding these parameters. The volume and surface energy loss functions (i.e. VELF and SELF respectively), as well as the dissipation factor, were also determined. The detailed studies show that the different optical parameters have significant compositional dependence. The optical band gap is decreased by increasing the Ge concentration in the parent STS glass.