Determination of ellipsometric parameters of a thin dielectric GaAs film between helium and air environments in the range containing resonant frequencies

The study presents the results of theoretical calculation of the first and second ellipsometric parameters ρ and Δ for a 2 μm thick GaAs thin film enclosed between air and helium environments. The behavior of the angular reflection spectrum for S- and P-polarized waves near the phonon resonance was determined with the medium parameters WTO = 269 см–1; WLO = 292 см–1. The obtained curves of angular spectra R(θ) allowed us to determine the number of reflection peaks near the frequency ΩTO – 2 peaks for GaAs at S polarization, 3 at P polarization, and near ΩLO – 3 peaks at S polarization, 5 at P polarization. Having analyzed the graphs of angular and frequency spectra, we can see the jump-like behavior of Δ. Ellipsometry is the most accurate non-destructive method for determining the optical parameters of surfaces and interfaces for different media. The accuracy of this method can be improved by taking into account the absorption of the media under consideration. Then the refractive index will have a complex form, and the Fresnel formulas will become complex values. The frequency spectrum allows us to see the change in the behavior of the ellipsometry parameters in the forbidden frequency region and also to notice the acceleration of their change when approaching the resonance frequencies.