TRANSITION FROM ONE-SUBBAND TO 2-SUBBAND OCCUPANCY IN THE 2-DEG OF BACK-GATED MODULATION-DOPED GAAS-ALXGA1-XAS HETEROSTRUCTURES

We present experimental investigations of the transition from one- to two-subband occupancy in the two-dimensional electron gas (2DEG) of back-gated modulation-doped GaAs-AlxGa1-xAs heterostructures. A combination of front and back gates allows us to control the subband energies in the 2DEG, so that we are able to maintain single-subband occupation for carrier densities as high as 9×1011 cm-2 and achieve double-subband occupancy for carrier densities as low as 5×1011 cm-2. These devices are used to map out the phase diagram of subband occupancy as a function of total carrier density and back-gate bias. Our results are in good agreement with the predictions of a recent theoretical model of the electronic structure of back-gated heterostructures. © 1995 The American Physical Society.