First observation of temperature dependent lightinduced response of Ge25As10Se65 thin films

Ge rich ternary chalcogenide glasses (ChG) exhibit photobleaching (PB) when illuminated with bandgap light and such an effect is originating from the combined effect of intrinsic structural changes and photo-oxidation. In a sharp contradict to these previous observations, in this letter, we demonstrate for the first time that Ge rich Ge25As10Se65 ChG thin films exhibit photodarkening (PD) at 20 K and PB at 300 and 420 K for continuous illumination of ~ 3 hours. Strikingly, the temporal evolution of PD/PB show distinct characteristics at the temperatures of illumination and provide valuable information on the light induced structural changes. Further, structure specific far infrared (FIR) absorption measurements give direct evidence of different structural units involved in PD/PB at the contrasting temperatures. By comparing the lightinduced effects in vacuum and air, we conclude that intrinsic structural changes dominate over photo-oxidation in the observed PB in Ge25As10Se65 ChG thin films.