Abstract
In present work, Variable Angle Spectroscopic Ellipsometer (VASE) is used to determine the optical properties of thermally evaporated thin films Se15Te62.5Ge22.5 and to Se10Te67.5Ge22.5 from 0.8 to 5.1 eV.The experimental data of VASE parameters were fit using two group of models to extract the dielectric function. First group consist from mixtures of several Gaussian, and one Tauc-Lorentz (TL group ). The other group is a mixed from several Gaussian and one Cody-Lorentz dispersion functions (CL group). The models' factors such as resonance, optical band gap, Urbach energies, oscillator's amplitude and width for both Se15Te62.5Ge22.5 and Se10Te67.5Ge22.5 films were estimated. Extinction coefficients and refractive indices as function of photon energy of the films were calculated. Both models perform very equally and precisely adequate to the experimental data. However the CL model shows a good accuracy in recounting dielectric function at the beginning absorption area.