Optical properties of amorphous As-Se and Ge-As-Se thin films

Amorphous As-Se and Ge-As-Se thin films were prepared by thermal evaporatio n. From parameters of the Wemple-DiDomenico model, the values of the third- order non-linear susceptibility were estimated using the generalized Miller 's rule. Measurements of photodarkening at 78 K showed that the optical gap and the slope of the optical absorption edge are intercorrelated, The kine tics of the photoinduced shift of the gap are described using a stretched e xponential law. A possible role of the concentration of Se atoms on the rat e of photodarkening on one hand and of the network rigidity (measured by th e mean coordination number) on the other are briefly discussed. (C) 1999 El sevier Science B.V. All rights reserved.