New quaternary Ge-Se-Sb-Ag optical materials: Blue shift in absorption edge and evaluation of optical parameters

We report the effect of replacement of antimony by silver on the optical constants of new quaternary chalcogenide Ge20Se60Sb20−xAgx (x = 0, 5, 10, 15 and 20 at.%) thin films. Films of Ge20Se60Sb20−xAgx 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 nm to 2500 nm. A straightforward analysis proposed by Swanepoel has been applied to derive the real and imaginary parts of the complex index of refraction. Increasing silver content is found to affect the refractive index and the extinction coefficient of the studied films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing silver content the static refractive index decreases from 2.71 to 2.49 while the optical band gap increases from 1.37 eV to 1.55 eV.