Abstract
This chapter focuses on the influence of thermal evaporation conditions and subsequent light and heat treatments on the atomic structure. Molecular structure of sulfur-based amorphous chalcogenides is more sensitive to preparation conditions and various treatments compared to Se-rich materials. Vacuum-deposited amorphous chalcogenide films from an As–S system prepared by thermal evaporation methods with different rates are studied in the chapter. The changes in the Raman spectra of thermally evaporated amorphous As2S3 films after light treatment are interpreted in terms of rearrangement of bonding configurations of molecular species that exist just after evaporation. As the evaporation temperature or deposition rate is increased, irradiation with band-gap light, As-enriching and/or even more annealing of the films induces the formation of microcrystallites. The reversible photo-induced changes in well-annealed films involve negligible small changes in bonding statistics. Only in the medium-range order, discernable change occurs. Irreversible changes in the Raman spectra of slowly deposited films with illumination are direct evidence for gross structural changes caused by optical irradiation. Photopolymerization mechanism is used to depict this behavior. The results in the chapter show that the films become sulfur-deficient as the deposition rate increased, because of partial fragmentation of As2S3 into As3S2 and sulfur during the deposition. Fast-deposited films are unstable and phase separation occurred upon light irradiation.
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