Tuning the insulator–quantum Hall liquid transitions in a two-dimensional electron gas using self-assembled InAs

We investigate the transport properties of two-dimensional electron gases (2DEG's) formed in a GaAs/Al0.33Ga0.67As quantum well, where InAs has been inserted into the center of the GaAs well. Depending on the growth conditions, the InAs forms either self-assembled quantum dots or dashes, and due to the resulting strain fields repulsive short-range scattering is experienced by the conduction electrons in the 2DEG. In a perpendicular magnetic field there are transitions between quantum Hall liquids at filling factors ν=1 and ν=2 and the insulating phase. Depending on the amount of InAs coverage, the degree of disorder in the 2DEG can be varied, changing the relative size of the ν=1 and ν=2 regions in the disorder--magnetic-field phase diagrams. Thermal studies show a spin gap at filling factor ν=1, which collapses as the magnetic field is decreased. Microscopic information about the dots was obtained from structural characterization, as well as from conductance measurements through individual dots isolated using a submicron split gate.