Description:
<jats:title>Abstract</jats:title><jats:p>The energy gap <jats:italic>E</jats:italic><jats:sub>g</jats:sub> is accurately determined from interband Landau level transitions observed in spectral measurements of photoconductivity at low temperatures in an external magnetic field. The temperature dependence of the optical absorption coefficient is measured on samples with different slopes of the exponential Urbach absorption edge. The results are compared with empirical formulae reported for <jats:italic>E</jats:italic><jats:sub>g</jats:sub>(<jats:italic>x, T</jats:italic>). In the temperature region 10 to 300K, the best agreement is found for the rclation published by Seiler et al., but with a modified value of the temperature coefficient.</jats:p>