Temperature dependence of the Urbach edge in GaAs

Abstract

The temperature dependence of the optical-absorption edge (Urbach edge) of GaAs is measured in semi-insulating and n-type GaAs (n=2×1018 cm−3) over the temperature range from room temperature to 700 °C. Both the optical absorption and the temperature are measured using a diffuse reflectance technique. The characteristic energy of the exponential absorption edge is found to increase linearly with temperature, from 7.5 meV at room temperature to 12.4 meV at 700 °C, for semi-insulating GaAs. The temperature dependent part of the width of the Urbach edge for semi-insulating GaAs is six times smaller than predicted by the standard theory where the edge width is proportional to the phonon population.