Transition from strong to weak localization in the split-off impurity band in two-dimensional p-GaAs/AlGaAs structures

A crossover from strongly localized behavior to weak localization (SL-WL) was observed in two-dimensional modulation-doped GaAs/Al_0.3Ga_0.7 As structures as the impurity concentration increased. In this case, it was observed that the low-temperature dependence of the conductivity changed its character (from exponential to logarithmic) and the magnetoresistance changed its sign (from linear negative to root positive). For 2D structures, it is shown that this transition proceeds in the impurity band separated from the valence band by the mobility gap, whereas the effective mass in the impurity band is larger than in the valence band.