Persistent Photoconductivity in Si-dopedAlxGa1−xAs

Persistent photoconductivity in Si-doped molecular-beam epitaxial ${\mathrm{Al}}_{0.28}$ ${\mathrm{Ga}}_{0.72}$As was studied. The carrier concentration decreases with time according to a simple power law. The decay is explained semiquantitatively by an effective-mass-like model of the impurity with a wave packet centered near but not at the $\Gamma$ point in the Brillouin zone. The shift of the impurity wave function in k space may be explained in terms of long-range composition ordering in the AlAs-GaAs system. Other physical properties may also be influenced by periodic composition fluctuations observed in many semiconducting alloys.