Piezo-Urbach rule for acoustoelectric domains in GaAs

The acoustoelectric-domain-induced changes of the absorption coefficient of GaAs at the fundamental absorption edge have been found to be an exponential function of energy. Such data are analyzed here in terms of the electric microfield model of Urbach's rule. The fit between theory and experiment demonstrates the relevance and importance of the electric microfield model with the electron-hole interaction included and yields values for the piezoelectric microfields in mature domains of ≅ 4 × ${10}^4$ V/cm.