COMPOSITION DEPENDENCE OF PHOTOINDUCED AND THERMALLY-INDUCED BLEACHINGS OF AMORPHOUS GE-S AND GE-S-AG FILMS

Photoinduced and thermally induced bleachings of as-deposited GexS100-x and (Ge0.3S0.7)100-yAgy films were systematically studied in the ranges of 21 less-than-or-equal-to x less-than-or-equal-to 42 and 0 less-than-or-equal-to y less-than-or-equal-to 67 using optical transmission measurement. The bleachings for the Ge-S system show a maximum at around the stoichiometric composition GeS2, whereas that for the Ge-S-Ag system become smaller with an increase of the Ag content and vanish above 40 at. %. The composition dependence for the Ge-S system can reasonably be explained by an increase in the Ge-S bond density and subsequent decrease of short- and medium-range disordering. The bleaching rates, which are relatively small for Ge-rich films, are considered to be associated with the flexibility of the local network structure. The photo-oxidation phenomenon, which is observed for the films illuminated in air, also shows a maximum at around GeS2. The composition dependence for the bleaching of Ag-containing Ge30S70 films can be understood in a similar way to the Ge-S system. The vanishing at y congruent-to 40 is associated with a thermodynamically stable phase at that composition for the Ge-S-Ag system.