Preparation and optical dispersion and absorption of Ag-photodoped GexSb40-xS60 (x = 10, 20 and 30) chalcogenide glass thin films

We have analysed the effect of silver content on the optical properties of Ag-photodoped amorphous GexSb40-xS60 (with x = 10, 20 and 30 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Agy(GexSb40-xS60)100-y, with y ∼< 10 at.%, were prepared by successively photodissolving about 10 nm thick layers of silver. The film thickness and optical constants have been accurately determined by a refined envelope method, based upon the two envelope curves of the optical-transmission spectrum, obtained at normal incidence. The dispersion of the linear refractive index of the Ag-photodoped chalcogenide films is analysed in terms of the Wemple-DiDomenico single-effective-oscillator model. We have found that the maximum change in the index of refraction, between the Ag-photodoped and the undoped material, is about 0.08, when the Ag-concentration reaches the level of saturation of around 10 at.%. On the other hand, the Tauc gap, Egopt, decreases notably, with increasing Ag-content: for instance, in the particular case of x = 10 at.%, the smallest Ge-content, Egopt decreases from 1.97 down to 1.67 eV