FABRICATION OF INDEPENDENTLY CONTACTED AND TUNABLE 2D-ELECTRON-HOLE SYSTEMS IN GAAS ALGAAS DOUBLE-QUANTUM WELLS/

We have investigated the properties of closely spaced, but electricall y separated two-dimensional electron-hole systems formed in GaAs/AlGaA s double quantum wells (QWs). These novel structures were fabricated u sing MBE by applying a special Si and C modulation doping technique in order to form intrinsically both a high-quality two-dimensional elect ron (2DEG) and hole gas (2DHG) with a separation of less than 1500 Ang strom. The devices are additionally equipped with buried p(+)-GaAs bac k-gates, which have been fabricated by regrowth over a patterned subst rate. Reliable independent contacts to each of the 2D-systems have bee n achieved by a stepwise annealing technique for the p- and n-type met allisation. We have done so-called 'drag' measurements to study the in teraction effects between the two systems, from which we could conclud e on the non-parabolic subband dispersion of the 2DHGs. (C) 1998 Elsev ier Science S.A. All rights reserved.