Effect of Ge concentration on optical properties of films synthesized by vacuum-thermal evaporation of glassy Ge–Se alloys

Abstract

Four non-crystalline GexSe100−x (x = 15−25 at. %) films were obtained by vacuum-thermal deposition of glassy Ge–Se alloys. With the use of spectroscopic ellipsometry, it was determined that the films are semiconductors with indirect band gap energy Eg = 2.0−2.07 eV. An anomalous dispersion of the refractive index n (λ) with nmax at λmax depending on x was revealed in the films at λ = 240−500 nm. It was established that as the concentration of Ge decreases, nmax increases, and λmax red shifts. Based on the Wemple-DiDomenico model, the nonlinear coefficients χ(3) and n2 characterizing the synthesized films were calculated as a function of x. The highest χ(3) and n2 values are achieved in the films at x = 15 at. %. The results obtained can be used for the development and creation of Ge–Se optical filters with an adjustable blue absorption band edge.