OPTICAL REFLECTIVITY STUDY OF PHOTODISSOLUTION KINETICS IN GESE3 VITREOUS THIN-FILMS

Optical reflectivity measurements on amorphous GeSe3 obtained by flash evaporation and photodoped with Ag have been carried out. Cooling the sample during Ag evaporation avoids Ag diffusion but when the sample returns to room temperature photodissolution always occurs even in absolute darkness. The ratio between Ag and GeSe3 thicknesses for a complete photodissolution of Ag film is about 1/3. After complete photodissolution the thickness of the photodoped region follows the relation dPR = dAg + dGeSe. The rate of the phenomenon increases when GeSe3 is previously exposed. The kinetics of the process are determined from an optical model. This optical model requires values of the optical constants of each layer: GeSe3, photodoped region and Ag. A method taking into account the thick glass substrate and thin film effects gives the constants ni and ki of the film from transmission and reflection measurements in the wavelength range 0.4-3 μm. From these values, the reflectivity-time dependence of the multi-layer system Ag-photodoped region-GeSe3 during photodoping is calculated and can be compared with the time dependence of the electrical resistance of the Ag layer. © 1990.