Extremely high conductivities in modulation-doped GaAs and (GaIn)As quantum wells with AlAs/GaAs type-II-superlattice barriers

We present a new structure to reduce impurity scattering in remotely doped GaAs and (GaIn)As single quantum wells by using heavy-mass X-electrons in the short-period AlAs/GaAs superlattice barriers to smooth the potential fluctuations of the ionized Si dopants. In 10-nm GaAs SQW electron mobilities as high as 120 m²/Vs at electron densities of 1.2 10¹⁶ m^-2 are obtained in the one-subband conductivity mode without any parallel conductance. In the case of (GaIn)As SQW the reduction of the impurity scattering manifests itself in the increase of the single particle relaxation time. The design limits to achieve these ultra-high conductivities in terms of layer sequence and growth parameters are discussed