Photoinduced Effects in Amorphous Semiconductors

Abstract

A wide range of reversible effects is induced when light absorbed by an amorphous lattice. The spatial distribution of the released energy during the non-radiative recombination of the photoexited e-h pairs creates short and medium range order effects. Point or coordination defects induced when the energy is locally absorbed, while structural changes caused by bond rearrangements and atom movements induced when the released energy has been distributed over several lattice points. The coordination defects are produced when weak bonds break under illumination (fast process). It is believed that in a-Si:H, the singly occupied dangling bond is the dominant metastable defect, while in the chalcogenide glasses or films, intimate pairs of charged defects are induced. A slower stabilization process, such as hydrogen diffusion accompanies the formation of dangling bonds in the case of a-Si:H or lattice rearrangements that lead to the formation of random pairs of charged defects, in the chalcogenides. In contrast the medium and the long range order effects, even though are connected to lattice rearrangements, in most of the cases, they are not related with the creation of metastable dangling bonds. The majority of the metastable structural rearrangements seems to be a pure property of the lone pair electrons of the chalcogenide elements. For a detailed review see Shimakawa et al [1].