Fabrication of independently contacted and tuneable 2D-electron-hole systems in GaAs/AlGaAs double quantum wells

We have investigated the properties of closely spaced, but electrically separated two-dimensional electron-hole systems formed in GaAs/AlGaAs double quantum wells (QWs). These novel structures were fabricated using MBE by applying a special Si and C modulation doping technique in order to form intrinsically both a high-quality two-dimensional electron (2DEG) and hole gas (2DHG) with a separation of less than 1500 إ. The devices are additionally equipped with buried p+-GaAs back-gates, which have been fabricated by regrowth over a patterned substrate. Reliable independent contacts to each of the 2D-systems have been achieved by a stepwise annealing technique for the p- and n-type metallisation. We have done so-called `dragʹ measurements to study the interaction effects between the two systems, from which we could conclude on the non-parabolic subband dispersion of the 2DHGs.