ELECTRICAL CHARACTERIZATION OF PSEUDOMORPHIC GAAS/INGAAS/ALGAAS AND ALGAAS/INGAAS/ALGAAS MODULATION DOPED FIELD-EFFECT TRANSISTOR-TYPE HETEROSTRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY

We studied the influence of the indium composition y, growth temperature T(s) and InGaAs quantum-well channel thickness d(ch) on the 300 and 77 K Hall electrical properties of pseudomorphic modulation doped field effect transistor (MODFET)-type heterostructures grown by molecular-beam epitaxy. In agreement with Nguyen et al., we find an optimum channel thickness of 90 angstrom for an indium composition y = 0.25 of the channel. Significant improvements in sheet resistivity rho(s) and in carrier concentration n(so) were obtained by using AlGaAs doped barriers on both sides of the pseudomorphic channel. We were thus able to obtain a two-dimensional electron gas sheet density n(so) as high as 4.0 x 10(12) cm-2 at 77 K, which is among the highest values ever reported for MODFETs on GaAs.