HIGH-MOBILITY AND HIGH SHEET ELECTRON-DENSITY IN SELECTIVELY DOPED INALAS/INGAAS HETEROSTRUCTURES GROWN BY MBE ON GAAS

A selectively doped InAlAs/InGaAs heterostructure, which combines both high mobility and high sheet electron density with a high-resistivity buffer layer, is examined by MBE on GaAs using either InAlAs or InGaAs ternary buffer layers. Lower In compositions increase the mobility and sheet electron density of the channel by reducing misfit dislocations and enlarging the conduction-band discontinuity between InAlAs and InGaAs. With an InAlAs buffer, the mobility reaches its maximum 7980 cm2/V.s and the sheet electron density is 2.8 X 10(12) cm-2, at an In composition of 0.3. The resistivity of the InAlAs buffer was greater than 10(8) OMEGA/cm2. The InGaAs buffer made a slightly higher mobility possible at the same In composition, although its resistivity was too low (about 10(5) OMEGA/cm2) for FET applications.