Spectroscopic ellipsometry characterization of Ge30-xSbx Se70 films using combinations of multiple dispersion functions

Variable angle spectroscopic ellipsometry (VASE) was employed to study the optical properties of Ge30-xSbx Se70 (x = 0, 5, 10, 15 and 25) films in the UV-vis-NIR (near infrared) spectral region for photon energies from 0.7 to 5 eV. The spectrum of imaginary parts of dielectric for all films is characterized by several peaks. Two groups of linear combination of oscillators were employed for the analysis of these spectra. First combination consists from one Tauc-Lorentz oscillator with more than one Gaussian oscillators (TL + G). Second one Cody-Lorentz oscillator with more than one Gaussian (CL + G) oscillators. Both groups of models behave very similarly and accurately fit to the experimental data. However the Second group models is more accurate in describing dielectric function in the absorption onset region. The effect of Sb content on models' parameters (Lorentz oscillator amplitude, resonance energy, oscillator width, optical band gap, and Urbach energy) is discussed.