Optical Properties of Thermally Evaporated (As2Se3)100-xAgx Thin Films

We obtained amorphous thin films by evaporation and condensation in three component systems based on As, Se and Ag. The aim was to investigate the influence of the third component on the thin film structure and optical properties. The refractive index and the film thickness were determined from the upper and lower envelopes of the optical transmission spectra, measured in the spectral range 400 – 2500 nm.The absorption coefficient (α) was determined after extrapolation the values of n in the region of strong absorption (where α ≥ 104 cm-1) and its spectral distribution was discussed. The dispersion of the refractive index was analyzed in terms of single-oscillator Wemple-DiDomenico model. The shift of the optical absorption edge was described using the non-direct transition model, proposed by Tauc. Optical band gap was calculated from the Tauc plot αhν=B(EgTauc – hν)2 and the compositional dependence of the optical gap was discussed. In order to realize photoinduced changes in the films, they were illuminated by He-Ne laser and their transmission spectra were measured before and after illumination. The shift of the absorption edge of as – deposited and illuminated films was investigated and discussed as a function of the films composition.