Compositional dependence of the optical constants of amorphous GexAs20Se80−x thin films

Abstract

This paper reports the effect of replacement of selenium by germanium on the optical constants of chalcogenide GexAs20Se80−x (where x = 0, 5, 10, 15 and 20 at.%) thin films. Films of GexAs20Se80−x glasses were prepared by thermal evaporation of the bulk samples. The transmission spectra, T(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Swanepoel, based on the use of the maxima and minima of the interference fringes, has been applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing germanium content is found to affect the refractive index and the extinction coefficient of the GexAs20Se80−x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing germanium content the refractive index decreases while the optical band gap increases.