Optical properties and structure of thin films from the system GeSe2–Sb2Se3–AgI

Chalcohalide glasses from the GeSe2–Sb2Se3–AgI system were synthesized by taking preliminary prepared GeSe2, Sb2Se3 and AgI in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films from the above system were deposited using vacuum thermal evaporation at different conditions on optical glass substrates BK-7. Using X-ray microanalysis it was found that the film composition differs in a certain degree from the bulk composition. Optical transmission and reflection measurements were carried out in the spectral range 400–2500 nm. The optical constants of films thicker than 400 nm (refractive index, n, and absorption coefficient, k) and the film thickness (d) were calculated using a method developed by Konstantinov. The values of n change from 2.38 for thin GeSe2 films up to 3.48 for thin Sb2Se3 films while the optical band gap decreased from 1.92 eV to 1.29 eV, respectively. After exposure to light the photo-induced changes in the optical parameters were negligible for GeSe2 and Sb2Se3 films and increase for some of the ternary samples. Using IR spectroscopy some conclusions about changes in the film structure were drawn.