  In highly doped uncompensated p-type layers within the central part of
GaAs/AlGaAs quantum wells at low temperatures we observed an activated behavior
of the conductivity with low activation energies (1-3) meV which can not be
ascribed to standard mechanisms. We attribute this behavior to the
delocalization of hole states near the maximum of the narrow impurity band in
the sense of the Anderson transition. Low temperature conduction $\epsilon_4$
is supported by an activation of minority carriers - electrons (resulting from
a weak compensation by back-ground defects) - from the Fermi level to the band
of delocalized states mentioned above. The corresponding behavior can be
specified as virtual Anderson transition. Low temperature transport ($<4$ K)
exhibits also strong nonlinearity of a breakdown type characterized in
particular by S-shaped I-V curve. The nonlinearity is observed in unexpectedly
low fields ($<10$ V/cm). Such a behavior can be explained by a simple model
implying an impact ionization of the localized states of the minority carriers
mentioned above to the band of Anderson-delocalized states.
