Two-band electron transport in a double quantum well

The carrier densities and mobilities have been measured for the first two populated subbands in a GaAs double quantum well (DQW) as a function of the top gate voltage Vg. The densities and quantum mobilities (μᵢq, $i=1,2$) were obtained from the de Haas-Shubnikov oscillations. The transport mobilities (μᵢᵗ) were determined from the semiclassical low-field magnetoresistance with intersubband scattering taken into account. At 0.320.3em0exK the experimental data on both μᵢᵗ and μᵢq, as a function of Vg, lie on two curves which cross at the resonance point as expected from theoretical considerations. At 1.090.3em0exK and 4.20.3em0exK the μᵢᵗ curves no longer cross at resonance, but show a gap. The reason for this is not known. The mobilities have been calculated in the low-temperature limit within the Boltzmann framework by assuming that they are limited by scattering due to ionized impurities located at the outside interfaces. The assumption of short-range scattering is justified by the relatively small value of the ratio μᵢᵗ∕μᵢq that is measured in the present system. The theoretical values obtained for μᵢᵗ and μᵢq are in reasonable agreement with the experiment for all values of Vg examined. We have also calculated the resistivity and intersubband scattering rates of the DQW as a function of Vg and again find good agreement with measured values.