Optical absorption tails in Cd 0.97Zn 0.03Te and CdS at elevated temperatures

Abstract

Low energy optical absorption in Cd 0.97Zn 0.03Te and CdS has been studied at temperatures up to 1014 and 1161 K, respectively, by measurements of the incandescence spectra of wafers of both materials. Exponential absorption (Urbach) tails were observed, characterised by a spreading energy which increased exponentially with increasing temperature. This contrasts with the inverse temperature dependence widely assumed to be the high temperature limit for this parameter. It may be that defects are dominating the absorption tail at high temperatures in these samples, rather than phonon induced electric fields.