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

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 (& lambda;) with nmax at & lambda;max depending on x was revealed in the films at & lambda; = 240-500 nm. It was established that as the concentration of Ge decreases, nmax increases, and & lambda;max red shifts. Based on the Wemple-DiDomenico model, the nonlinear coefficients & chi;(3) and n2 characterizing the synthesized films were calculated as a function of x. The highest & chi;(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.

Automated summary

Four non-crystalline GexSe100-x (x = 15-25 at. %) films were synthesized by vacuum-thermal deposition of glassy Ge-Se alloys. The films were found to be semiconductors with an indirect band gap energy of 2.0-2.07 eV, as determined by spectroscopic ellipsometry. Anomalous dispersion of the refractive index was observed in the films at wavelengths of 240-500 nm, with the maximum refractive index and its corresponding wavelength depending on the Ge concentration. The highest values of the nonlinear coefficients & chi;(3) and n2 were achieved in the film with a Ge concentration of 15 at. %. The results can be utilized for the development of Ge-Se optical filters with adjustable blue absorption band edge.