Aging process of photosensitive chalcogenide films deposited by electron beam deposition

Highlights: → Ge15Sb20S65 and As30Se50Te20 chalcogenide amorphous films were deposited by EBD. → The structure of both bulk and thin film has been studied by far-IR and Raman spectroscopy. → Both films were found to be photosensitive as manifested by the shift of their optical band-gap. → Aging was found to induce also morphological changes, as growth of arsenic trioxide micro-crystals. - Abstract: Chalcogenide films attract broad interest due to their use as optical components like narrow band-pass filters, omnidirectional reflectors cladding, all-optical signal processing devices or optochemical sensors. Ge15Sb20S65 and As30Se50Te20 chalcogenide amorphous films were deposited by electron beam deposition (EBD) using their corresponding bulk glasses as targets. The structure of both bulk and thin film has been studied by far-IR and Raman spectroscopy. This study investigated an ordinary aging behavior of the chalcogenide films by exposing them to natural light under atmospheric conditions for a period of six months. Both films were found to be photosensitive as manifested by the shift of their optical band-gap to shorter or longer wavelength depending on chemical composition. Aging was found to induce also morphological changes, most notably the likely growth of arsenic trioxide micro-crystals on the surface of As30Se50Te20 films. Such effects were discussed in terms of photo-oxidation and photo-hydrolysis phenomena, the extent of which was found to be relatively limited for Ge25Sb10S65 films. The larger stability of the latter films against crystal growth at the surface was associated with the ability of germanium to bond to diffusing oxygen atoms in germanium-oxysulfide tetrahedral arrangements.