Urbach's tail in the absorption spectra of the ordered vacancy compound CuGa3Se5

The presence of Urbach's tail in the absorption coefficient spectra just be low the fundamental absorption edge is observed in several samples of the o rdered vacancy compound CuGa3Se5 at different temperatures below 300 K. An empirical relation that takes into account the effect of structural disorde r and modification in the contribution of the thermal term, caused due to t he deviation from the ideal stoichiometry 1:3:5, is proposed to explain the change of Urbach's energy with temperature. The phonon energy involved in the electron-phonon interaction, in the absence of structural disorder, is estimated to be around 30 meV. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.