HIGH-DENSITY AND HIGH-MOBILITY TRANSPORT CHARACTERISTICS IN GATED UNDOPED GAAS ALXGA1-XAS HETEROSTRUCTURES/

The two-dimensional electron gas which is formed at the interface in u ndoped GaAs/AlxGa1-xAs heterostructures by the electric field generate d by a top gate is studied. The barrier region consists of an Al0.3Ga0 .7As/Al0.5Ga0.5As superlattice to prevent undesirable tunneling throug h the barrier. Therefore, we are able to achieve high electron densiti es exceeding 10(16) m(-2) with sufficient small gate leakage currents in a MISFET like device for the first time. Despite the high electron density in the sample rather high mobilities of about 100 m(2) V s(-1) can be maintained at low temperatures. The population of the second s ubband is studied from Shubnikov-de Haas measurements in these devices . The role of intersubband scattering is important for understanding t he magneto-transport experiments. (C) 1997 Elsevier Science Ltd.