MODULATION-DOPED IN0.3GA0.7AS/IN0.29AL0.71AS HETEROSTRUCTURES GROWN ON GAAS BY STEP GRADING

Modulation-doped In0.3Ga0.7As/In0.29Al0.71As heteroepitaxial layers were grown on GaAs substrates by molecular beam epitaxy using compositionally graded buffer step layers. The misfit strain in the x = 0.3 layer, which contains the two-dimensional electron gas channel, is relaxed by 96% as determined by x-ray diffraction. Transmission electron microscopy reveals that the active layer is dislocation-free. The sheet electron density of the channel is of the order 10(12) cm-2 and the mobility is 9340 cm2 V-1 s-1 at room temperature and 42290 cm2 V-1 s-1 at cryogenic temperatures. The effective mass of the electrons, m* = 0.066m0, is greater by about 20% than that expected of this ternary alloy, due principally to the non-parabolic correction at the Fermi level. Shubnikov-de Haas oscillations measured at 1.6 K as a function of magnetic field show that the quantum relaxation time is 8.8 x 10(-14) s while the classical relaxation time determined from the measured mobility and calculated m* is 1.5 x 10(-12) s.