Relaxation processes in amorphous As-S and AS-Se films

The relaxation of optical, mechanical and chemical properties of as-evaporated amorphous As-S and As-Se films while storing them at room temperature is investigated. The AsxS1-x films with arsenic content 0.3 < x < 0.4 are found to undergo maximal changes. It is shown that the phenomenon of dark self-enhancement of holograms ( an increase of diffraction efficiency over time without any special treatment) can be used as an efficient method for investigation of relaxation processes in the amorphous chalcogenide films. The changes of diffraction efficiency in amorphous As2S3 films have been measured as a function of ageing time and recording light intensity. The relaxation processes can be described by stretched exponential function often called as the Kohlraush- Williams - Watts function K(t) = K-0 exp [-(t/tau(r))(n)] where tau(r) is relaxation time of the process, n - a parameter, characterizing the relaxation process. It is assumed that the reason for the relaxation processes lies in internal mechanical stresses arising in the films during their preparation. A mechanism based on the photo-induced stress relaxation and viscous now of amorphous semiconductor has been discussed.