Reversible photodarkening in As2S3 nanolayers

The dependence of reversible photodarkening on film thickness has been measured for island type As2S3 layers embedded in a dielectric SiO matrix, when the layer effective thicknesses are comparable with the scale of the intermediate-range order. The photostimulated shift of the optical absorption edge to smaller energies increases when the As2S3 layer thickness decreases (from 0.08 eV for continuous films to 0.23 eV for composite multilayer structures with As2S3 layers of 0.7 nm effective thickness). This feature is related to confinement of the photoexcited carrier diffusion length with decreasing As2S3 cluster sizes. A gradual decrease of the absorption coefficient with decreasing As2S3 cluster sizes is caused by As-O and S-S bond formation at the As2S3-SiO interface. (C) 1998 Elsevier Science B.V. All rights reserved.