Local heating and photostructure transformations in chalcogenide vitreous semiconductors

Abstract To explain the photostructure transformation mechanism many authors are still using chemical reactions in a solid state, models of valence-alternation pairs, ground and excited quasi-stable state transition, etc. An induced anisotrophy produced by light in chalcogenide vitreous semiconductor (ChVS) films of various compositions has been discovered. A specific characteristics of the phenomenom is the fact having turned the polarization plane of the exciting light through π/2 we can record a new axis, i.e., optically re-recorded the direction of anisotropy. These new data allow the following statements to be made. 1. (1)Normally isotropic ChVS filmsconsists of anisotropic structural elements, whose optical axes are oriented at random. 2. (2)Photo-induced changes in the optical properties of ChVS are associated with the generation of local phonons during photo-induced electron recombination, the local heating of small micooregions, and the subsequent hardening of them. To confirm the model we carried out experiments to determine the effect of the mean temperature of the film on its photosensitivity; examined thermostability and photosensitivity for saturated and unsaturated states; proved that there are no two stable quasi-stationary states. i.e., ground and excited ones, but that there is a continuous series of glass states with different degrees of order and, accordingly, structure, inclination of fundamental absorption edge, etc. It was concluded that local heating is the main cause of photostructure transformations, while possible chemical reactions in a phase and the availability of valence-alternaion pairs were defined by the specific character of the ChVS compositions investigated and the particular experimental conditions employed.