Oxygen‐assisted photoinduced structural transformation in amorphous Ge–S films

Abstract

We report our results of continuous illumination of Ge46S54 chalcogenide glass films with bandgap light in air. The outcome of this process is the formation of Ge–S backbone depleted in germanium. We relate this to consumption of some of the germanium available in the initial material due to the occurrence of a photoinduced oxidation. This is proved using energy dispersion spectroscopy which shows the presence of 17.68 at.% oxygen in the glass post‐radiation. Raman spectra demonstrate that the initial material shows breathing modes, characteristic for Ge46S54 glass. After prolonged illumination Raman spectra reveal structure characteristic for the composition of the Ge–S backbone close to Ge33S67. The oxide forms a film on the surface and this changes the surface relief, studied by atomic force microscopy, but the oxidation is not surface‐limited. The oxidation process in these glasses is discussed and the higher priority of germanium oxidation compared to the oxidation of sulphur is stated.

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

“…Usually, PD is explained by bond changes in chalcogenide atoms, accompanied with changes in the interactions of their LP electrons, which lead to increase of network disorder. On the other hand, the irreversible PB is related either to short and medium ordering processes in the network [5,9,10] Ge-rich compositions and intense laser illumination [11] it is attributed typically to certain near-surface photo-oxidation. However, in our experiments LAE appears also after illumination in vacuum where the oxidation could be suppressed (e.g.…”

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

“…The increase of the ES peak area would mean that the structure is compacting, in contrary to its opening during the PD, and the thickness of the films reduces, as measured in this work. The second reason of the PB process could be the well known phenomenon of photo-oxidation in these materials, which can occur during illumination of Ge-based chalcogenide thin films in air [13,15]. Although there are some speculations that both elements Ge and Se could oxidize, following our experience [15], we believe that the only element that could form oxides in the system should be Ge.…”

“…The second reason of the PB process could be the well known phenomenon of photo-oxidation in these materials, which can occur during illumination of Ge-based chalcogenide thin films in air [13,15]. Although there are some speculations that both elements Ge and Se could oxidize, following our experience [15], we believe that the only element that could form oxides in the system should be Ge. We have not observed vibrations of Ge-O bonds at 520-650 cm -1 [30], and believe that this process presumably should be excluded from the explanation of the studied phenomena.…”

“…It is reported [13,14] that in contrast to As-based chalcogenides in which photo-darkening effect was observed, Ge-based chalcogenide glasses undergo photo-induced darkening and/or bleaching effect. A few models have proposed that the intrinsic structural changes and/or photo-oxidation are responsible for photo-induced bleaching and for other structural modifications [15][16][17].…”

Oxygen assisted photoinduced changes in Ge39Ga2S59 amorphous thin film

“…Also in GeS 2 and (GeS 2 ) 0.6 (Ga 2 S 3 ) 0.4 amorphous films illuminated by Mercury lamp equipped with a cut-off filter at 330 nm, the photooxidation limited by oxygen diffusion was suggested to be responsible for observed photoinduced bleaching of the films [6]. Oxygen assisted photoinduced structural transformation was observed in amorphous Ge-S films illuminated by 441.6 nm line of a He-Cd laser [7]. Employing Raman spectroscopy, depletion of germanium was found in the post irradiated film, ranging from the Ge-S backbone of virgin Ge 46 S 54 film to a backbone close to Ge 33 S 67 .…”