Dual action of light in photodarkened Ge–As–S films

Abstract

In annealed chalcogenide films, thinner than 1 mm, highly expressed photodarkening (PD) can be fully restored after prolonged illumination. It was supposed that this light annealing effect (LAE) results from the dual action of light, which provokes not only increase of network disorder at PD but also decrease of disorder leading to photobleaching (PB), competing with PD. To confirm it, the changes of two parameters of disorder are studied: the Tauc slope B 1/2 , dependent on network bonding character, and the Urbach energy E u , associated with tailing of the band edges. It is found that B 1/2 decreases during PD and increases when PB overcomes the PD, which is direct evidence that the basis of the LAE is the dual action of light. The changes of disorder defined by E u are found to be mostly inversely related to the changes of B 1/2 . The peculiarities of this relationship after various treatments are presented and the problem of the correspondence of both parameters of disorder is discussed.

Dual Effects of Photo-Darkening and Photo-Bleaching in Ge-Se Films

“…The dual action of light was shown earlier in Ge-As-S [22,23] and in Ge-As-Se [24] films. In essence, this shows the reversibility of the processes for which Elliott has created a unified model [25].…”

Photo-induced phenomena in chalcogenide glasses

“…that As 2 S 3 and GeS 2 expand under illumination. It is also known that GeAs-S(Se) ternary glasses possess a unique characteristic, photoinduced volume compaction (Hamanaka et al, 1976;Calvez et al, 2009;Arsova and Vateva, 2012). Nevertheless, all these glasses exhibit photodarkening.…”

Dynamic variations of the light-induced effects in a-Ge_xSe_100-x films: experiment and simulation

“…Recent studies demonstrate that the transition between these two effects becomes apparent with an increase of the exposure time. This demonstrates the dual role of light for occurrence of PIEs in ChG [25][26][27]. It also has been found that light-induced effects are composition dependent and can transition from photodarkening to photobleaching with change from Ge-deficient to Ge-rich material [28].…”