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Earlier we reported an observation at low temperatures of activationconductivity with small activation energies in strongly doped uncompensatedlayers of p-GaAs/AlGaAs quantum wells. We attributed it to Andersondelocalization of electronic states in the vicinity of the maximum of thenarrow impurity band. A possibility of such delocalization at relatively smallimpurity concentration is related to the small width of the impurity bandcharacterized by weak disorder. In this case the carriers were activated fromthe "bandtail" while its presence was related to weak background compensation.Here we study an effect of the extrinsic compensation and of the impurityconcentration on this "virtual" Anderson transition. It was shown that anincrease of compensation initially does not affect the Anderson transition,however at strong compensations the transition is suppressed due to increase ofdisorder. In its turn, an increase of the dopant concentration initially leadsto a suppression of the transition due an increase of disorder, the latterresulting from a partial overlap of the Hubbard bands. However at largerconcentration the conductivity becomes to be metallic due to Mott transition.

Suppression of the virtual Anderson transition in a narrow impurity band of doped quantum well structures