Modulation-doped In0.3Ga0.7As/In0.29Al0.71As heterostructures grown on GaAs by step grading

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Abstract
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 1012 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 nonparabolic 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*10-14 s while the classical relaxation time determined from the measured mobility and calculated m* is 1.5*10-12 s.