Features of the conductivity and magnetoresistance of doped two-dimensional structures near a metal-insulator transition

Theoretical and experimental studies of the conductivity and magnetoresistance of selectively doped structures of GaAs/AlGaAs quantum well structures near a metal-insulator phase transition have been reviewed. Special attention is focused on the role of the structure of impurity bands, which are narrow in the absence of intentional compensation and, in the case of doping of barriers, include the partially filled upper Hubbard band. It has been shown that the indicated structures exhibit (i) specific mixed conductivity, which can, in particular, include the contribution from delocalized states in the impurity band; (ii) the virtual Anderson transition, which is suppressed with an increase in disorder owing to compensation or with an increase in the concentration of a dopant; (iii) slow relaxations of the hopping magnetoresistance caused by the Coulomb glass effects, including, in particular, the states of the upper Hubbard band; and (iv) the suppression of the negative interference magnetoresistance owing to the spin effects.