PHOTOSTRUCTURAL TRANSFORMATIONS IN AMORPHOUS-CHALCOGENIDE SEMICONDUCTORS

The mechanism of photoinduced structural transformations in amorphous As2S3 is studied with the differential IR Fourier spectroscopy technique in the 400 to 100 cm-1 region. It is established that the irreversible photostructural effect observed in freshly evaporated thin films is accompanied by switching of homopolar chemical bonds into heteropolar ones. The stage of reversible photodarkening is realized in a-AS2S3 samples after a first cycle of photoexposure and thermoannealing. The corresponding destruction-polymerization reaction is opposite to that obtained for irreversible changes. The whole scheme of photo- and thermoinduced structural transformations in a-As2S3 is presented as a multicyclic process of coordination defect formation and annihilation.