Photo-dependence of sub-<i>T</i>_grelaxation in a-Se thin films

Abstract

Abstract The structural relaxation in amorphous selenium, below T g, involves bond breaking and reformation. Its kinetics is governed by both the enthalpic departure from equilibrium and the temperature. The characteristics of the relaxation can be inferred from the dependence of T g on heating rate and on ageing. In particular the relaxation rate can be deduced from the displacement of T g, at constant heating rate, with the ageing time. A study of the ageing of thin films of amorphous selenium under illumination, shows that light can produce a significant increase of the relaxation rate. The spectral response of this phenomenon exhibits an important fall of photon energy below 2·2 eV. The influence of the annealing temperature on the photo-dependence of the relaxation rate is also examined. Results are compared to different observations of photostructural changes in glassy chalcogenides. From a comparison of the spectral response of the observed phenomenon, with both the optical absorption spectrum and the luminescence excitation spectrum, it is deduced that the non-radiative recombination of excitons via self-trapped excitons (C3 +, C1 − pairs) can play a part in the enhancement of bond breaking and rearrangement during structural relaxation.