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/Alo(0.33)Ga(0.67)As 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 nu=1 and nu=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 nu=1 and nu=2 regions in the disorder-magnetic-field phase diagrams. Thermal studies show a spin gap at filling factor nu=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.