Effect of Sb on the optical properties of the Ge-Se chalcogenide thin films

Thin films of Ge30−xSbxSe70 (x=0, 5, 10 and 15) were prepared by thermal evaporation technique. All samples were confirmed as amorphous according to XRD results. The complex dielectric functions and optical parameters of the films determined by using the Swanepoel's method from transmittance spectra at room temperature in the range of wavelength 400-1100 nm. It has been found that by increasing Sb content, the optical band gap decreases, while the refractive index and the extinction coefficient increase. The optical energy gap of the films under test was discussed in terms of the chemically ordered model (COM) and random covalent network model (RCNM). We confirmed, using Raman spectroscopy, by addition of Sb the intensity of Ge-Ge and Ge-Se bands decreased; however, Sb-Se, and Se-chain band increased, in agreement with COM and RCNM. The results of the refractive index were studied using the Wemple equation. The variations of the refractive index and real part of dielectric constant associated with the changes of the density were examined with the well-known Lorentz-Lorenz relation. The experimental results were found to be in good agreement with those of theoretical ones.