Controlling the optical constants of thermally-evaporated Ge10Sb30S60 chalcogenide glass films by photodoping with silver

We have analysed the effect of silver content on the optical properties of Ag-doped Ge10Sb30S60 chalcogenide glass films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of compositions Agx(Ge0.1Sb0.3S0.6)100−x, with x≲8 at.%, were obtained by successively photodissolving thin (around 10 nm) layers of silver. The optical constants (n,k) have been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence. The dispersion of the refractive index of the Ag-photodoped chalcogenide films is analysed within the single-effective-oscillator approach. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the refractive index of the Ag-doped samples increases with the Ag content, whereas the optical band gap, Egopt, decreases from 1.97 ± 0.01 to 1.67 ± 0.01 eV. These results are consistent with the hypothesis that the photodoped Ag is a structure modifier in the a-Ge10Sb30S60 films.