Spectroscopic ellipsometry characterization of photoinduced phenomena in Ge25Sb5Se70 films using the Cody–Lorentz parameterized model

Abstract

Variable angle spectroscopic ellipsometry (VASE) was employed to examine the photoinduced effect on the optical properties of Ge25Sb5Se70 thin films, that were prepared by thermal evaporation method. The measurements were carried out at room temperature and in the UV–vis–NIR (near infrared) spectral region for photon wavelengths from 280 to 1000 nm. For data analysis, we employed linear combination consist from two Cody–Lorentz (CL) dispersion model in the entire measured photon range. The photo bleaching (increase in bandgap) was identified by this model. The behavior of the Cody–Lorentz model parameters with the time of light illumination is discussed in detail. To obtain a good fitting to the variation of fundamental CL amplitude with the time of exposer, we proposed a simple phenomenological model based on the alternation of bond formation and breaking. Good agreement between calculated and experimental data is obtained.