Effect of Sn addition on the optical constants of Ge–Sb–S thin films based only on their measured reflectance spectra

Abstract

In this work, different compositions of homogenous Snx(Ge1Sb2S7)100−x (0⩽x⩽9at.%) thin films were prepared by thermal evaporation method. The film reflectance R(λ) was measured in wavelength range 400–2500nm. A straight forward analysis proposed by Minkov based on the maximum and minimum envelopes of the reflection spectra have been applied to drive the complex index of refraction and film thickness with high accuracy. Addition of Sn content to Snx(Ge1Sb2S7)100−x thin films was found to affect the refractive index and the extinction coefficient for these films. The dispersion of the refractive index was discussed in terms of the single oscillator Wemple–DiDomenico model. The absorption mechanism of the prepared films obeys the rule of the allowed non-direct optical transitions. The refractive index increases while the optical band gap decreases with increasing Sn content. The compositional dependence of the optical band gap for the Snx(Ge1Sb2S7)100−x thin films was discussed in terms of the chemical bond approach. The plasma frequency, dielectric loss, dissipation factor and the optical conductivity of these films have been investigated.