Transport properties of InGaAs/GaAs Heterostructures with $\delta$-doped quantum wells

The lateral transport of electrons in single- and double-well pseudomorphic GaAs/$n$-InGaAs/GaAs heterostructures with quantum wells 50–100 meV deep and impurity $\delta$-layers in the wells, with concentrations in the range 10$^{11}<N_s<10^{12}$ cm$^{-2}$, has been investigated. Single-well structures with a doped well at the center exhibit a nonmonotonic temperature dependence of the Hall coefficient and an increase in low-temperature electron mobility with an increase in the impurity concentration. The results obtained indicate that the impurity-band electron states play an important role in the conductivity of these structures. Involvement of the impurity band also allows to explain adequately the characteristics of the conductivity of double-well structures; in contrast to single-well structures, band bending caused by asymmetric doping is of great importance. The numerical calculations of conductivity within the model under consideration confirm these suggestions.