Impact of sulfur content on structural and optical properties of Ge20Se80-xSx chalcogenide glasses thin films

Chalcogenide system Ge₂₀Se_80-xS_x (x = 0, 15 and 30%) thin films were prepared by thermal evaporation technique. The amorphous state of the samples was confirmed according to XRD. The structural changes occurring upon replacement Se by S was investigated using Raman spectroscopy. The optical properties of the as-deposited Ge₂₀Se_80-xS_x thin films have been studied by analysis the transmittance T(λ) measured at room temperature in the wavelength range 200-2500 nm using Swanepoel's method. Urbach energy (E_e) and optical band gap (E_g) were strongly affected by sulfur concentration in the sample. The refractive index evaluated through envelope method was extrapolated by Cauchy dispersion relationship over the whole spectral range. Moreover, the dispersion of refractive index was analyzed in terms of the single-oscillator Wemple-Di Domenico model. The third-order nonlinear susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) were calculated and discussed for different Ge₂₀Se_80-xS_x (x = 0, 15 and 30%).