Oxygen-assisted photoinduced structural transformation in amorphous Ge-S films

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.