  Modulation-doped AlGaAs/GaAs heterostructures are utilized extensively in the
study of quantum transport in nanostructures, but charge fluctuations
associated with remote ionized dopants often produce deleterious effects.
Electric field-induced carrier systems offer an attractive alternative if
certain challenges can be overcome. We demonstrate a field-effect transistor in
which the active channel is locally devoid of modulation-doping, but silicon
dopant atoms are retained in the ohmic contact region to facilitate reliable
low-resistance contacts. A high quality two-dimensional electron gas is induced
by a field-effect and is tunable over a wide range of density. Device design,
fabrication, and low temperature (T= 0.3K) transport data are reported.
