On the influence of the inner δ-layer on the low-temperature resistance saturation in gated Si-δ-doped double-layered GaAs

During measurements of the temperature dependence of the conductivity of a gated Si-δ-doped GaAs structure with two 'deep' δ-layers in the depletion regime, a resistance saturation was observed when the temperature decreased below 1 K, instead of the exponential growth expected for the variable-range hopping (VRH) mechanism. A possible origin of this saturation is analysed, related to a quantum capacitance effect in the inner δ-layer. In addition, results of the investigation of the influence of a depleting gate voltage V_g on the longitudinal 2D resistivity ρ_xx and Hall effect in a double-layered Si-δ-doped GaAs sample are presented.