Universal feature of photo-induced volume changes in chalcogenide glasses

We have investigated in chalcogenide glasses the microscopic processes caused by illumination using tight-binding molecular dynamics computer simulation. After photon absorption we treated the excited electron and hole independently. We found covalent bond breaking in amorphous networks with photo-induced excited electrons, whereas excited holes contribute to the formation of inter-chain bonds. We also observed a correlated macroscopic volume change of the amorphous sample. Our results provide a new and universal description, which can explain simultaneously the photo-induced volume expansion and shrinkage. This model is supported by the results of recent measurements.