We present variable temperature resistivity and magnetotransport data for GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells, which are Be doped in the central part of the wells at doping concentrations ranging from moderate levels to well above the degenerate limit. We provide an investigation of possible transport mechanisms. For nondegenerate structures, the activation of free carriers with a measured activation energy of ${\mathit{E}}_{\mathrm{act}}$=29–36 meV is close to the binding energy of the Be acceptor in ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As/GaAs center-doped quantum wells. The dopant concentration corresponding to the transition from being nondegenerate to the degenerate limit is <6×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$. For degenerate conditions, the variable-range-hopping 2D transport with ρ∼exp(${\mathit{T}}_0$/T${)}^{1/3}$, Mott’s law, which is observed at lower temperatures, occurs due to the strong localization of holes in the impurity potential fluctuations. For higher temperatures, the observed thermally activated transport is discussed in terms of the excitation of holes from the symmetric ground state into the antisymmetric excited states. The calculated intersubband energies according to a self-consistent solution of the coupled Poisson and Schrödinger equations are in good quantitative agreement with the experimental data. © 1996 The American Physical Society.

• Received 18 September 1995

DOI:https://doi.org/10.1103/PhysRevB.53.1357