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.