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