Abstract

This chapter examines the effect of preexcitation with the light of band-gap energy on trapping and thermal generation in selenium and selenium-rich As–Se alloy films by several techniques. Unique and intriguing features of chalcogenide vitreous semiconductors are the photoinduced changes appearing as a nearly parallel shift of the optical absorption edge to lower energy (so-called photodarkening effect) after irradiation with band-gap light. Such irradiation also causes changes in a wide variety of other properties—mechanical, physicochemical, photoelectronic, and so forth. The latter provides a valuable opportunity for the evaluation of light-induced changes of the gap states. There is a strong evidence to suggest that most of the reported photoinduced optical and structural changes affect the band-gap states. Several research groups have devoted considerable efforts to experiments that probe the gap states near mobility edges and within mobility gap. This is not a simple matter; no single experiment gives complete and unequivocal information, thus making it necessary to bring together data from a wide range of measurements, stationary as well as transient.

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