Low-temperature photodarkening of the AsxSe100-x system prepared by PECVD

Films of the amorphous AsxSe100-x system were prepared by plasma-enhanced c hemical vapor deposition (PECVD) using different gas ratios of the hydrides , AsH3 and H2Se. In the Se-rich region the optical bandgap decreased with i ncreasing As content, in agreement with measurements made on films prepared by evaporation. The temperature dependence of the optical gap (77-300 K) c ould be described by Fan's one-phonon approximation, indicating that electr on-phonon interaction (thermal disorder) plays the most important role. Mea surements of photodarkening at 77 K showed that the decrease of the optical gap and the slope of the Tauc plot are intercorrelated. The kinetics of th e photoinduced shift could be best described by a stretched-exponential law . (C) 2000 Elsevier Science B.V. All rights reserved.