On the role played by the silicon substrate in the crystallization, photo-vitrification and photo-oxidation of As50Se50 layers

The role played by the silicon substrate in the fight-induced vitrification of As50Se50 thin films is analyzed. It is demonstrated that these films can crystallize into different structures, depending on the substrate they are attached to. Photo-oxidation when the illuminated film is deposited on silicon can be enhanced due to a chemical reaction of the chalcogenide material with Si, which produces arsenic that would be then oxidized. The spectral irradiance of the light source employed also influences the photo-amorphization phenomenon, because the existence of a larger proportion of photons with higher energy will probably cause a larger degree of disorder in the films. Finally, the reversible structural changes induced by light in As50Se50 layers are accompanied by reversible photo-darkening.