Mechanism of photostructural changes in mixed-chalcogen As–S–Se glasses investigated by Raman spectroscopy

Abstract

The structure and photosensitivity of chalcogen-rich As–S–Se glasses are investigated ex situ and in situ. The Raman spectra of these glasses exhibit three well-defined bands associated with Se-based, S-based and mixed Se–S based structural units. The deconvolutions of these bands show a coherent correlation between intensity and composition. It is then shown that the magnitude of photoexpansion and photorefraction measured ex situ increases continuously with Se content therefore indicating a central role of Se atoms in the mechanism of photostructural changes. The key role of Se is indeed directly observed and confirmed using in situ Raman characterization. It is shown that the band associated with Se–Se oscillators decays continuously during photostructural changes. Furthermore, it is shown that the kinetics of Raman decay closely matches the kinetics of photoexpansion when measured simultaneously. Overall these results demonstrate the central contribution of Se–Se fragment during sub-bandgap irradiation which is consistent with the presence of Se lone pair states at the top of the valence band.