Crossover from photodarkening to photobleaching in a-Ge_xSe_100-x thin films

Abstract

In this Letter, we present the interesting results of photodarkening (PD), transition toward photostability, and a slow crossover from PD to photobleaching when composition of the chalcogenide glassy thin film changes from Ge-deficient to rich. A subsequent Raman analysis on these as-prepared and irradiated samples provide the direct evidence of photoinduced structural rearrangement, i.e., photocrystallization of Se and the removal of edge-sharing GeSe4 tetrahedra. Further, our experimental results clearly demonstrate that light-induced effects can be effectively controlled by choosing the right composition and provide valuable information on synthesizing photostable/sensitive glasses.

Role of Ge:As ratio in controlling the light-induced response of a-GexAs35−xSe65 thin films

“…Notably, the cross over from PD to PB occurs through a photostable phase. A similar crossover from PD to PB has been observed recently in binary Ge x Se 100−x thin films at x = 30 by Kumar et al 20.…”

Photo- and thermally-induced changes in the optical properties of Ge-S-Se amorphous films

“…Amorphous films of germanium chalcogenides (Ge-S, Ge-Se, Ge-S-Se, Ge-Sb-S systems) as well as respective glasses possess a nano-heterogeneous structure [6,12,18,[21][22][23][24][25][26][27][28][29]. The basic elements of structural network in glasses and films with the germanium content above 25% are tetrahedrons GeS n Se 4-n (n = 0 -4).…”

“…However, the matrix of germanium chalcogenide glasses and films contains a considerable amount of structural fragments with homopolar bonds Ge-Ge, S-S and Se-Se . In these cases, germanium chalcogenide films contain a higher concentration of homopolar bonds [12,18,23]. When illuminating the films, there take place break and reswitch of Ge-Ge, S-S and Se-Se bonds and formation of the heteropolar ones Ge-S(Se) [12,15,16,23].…”

“…In recent decades, intensively studied are photoinduced effects in amorphous films of germanium chalcogenides [11][12][13][14][15][16][17][18]. First of all, in view of practical applications, these materials are attractive if accounting the fact that they do not contain the poisonous arsenic.…”

“…Second, in these films under illumination one can observe both effects of photodarkening and photobleaching (growth of the pseudogap and optical transparency). Moreover, while germanium sulfide films are characterized only by photobleaching [13][14][15], the films Ge x Se 100-x demonstrate both effects: photodarkening in Ge-dificient (x<20) and photobleaching in Ge-rich (x>20) samples [11,12,[16][17][18].…”