Spectroscopic ellipsometry investigation of electronic states and optical properties of thin films from Ge30AsxSe70-x system

Abstract This paper deals with the investigation of the optical properties of thin films from the Ge30AsxSe70-x system. The complex permittivity, e ^ = e 1 + i e 2 , and the optical band gap, Egopt, were determined by spectroscopic ellipsometry measurements. The spectra of e2 in the ultraviolet spectral range were analysed on the base of the existing literature data for the valence band spectra obtained by X-ray photoelectron spectroscopy. It was found that the absorption in the spectral range 2.0–6.5 eV is related to the bonding and anti-bonding p-orbitals of Ge, Se and As atoms. The temperature coefficients of linear expansion, refractive index and the band gaps were determined. The evaluated values for the non-linear refractive index, γ, and the two-photon absorption coefficient, β, showed that the thin films exhibit a highly non-linear refractive index at the telecommunication wavelength.