STRAIN RELAXATION OF COMPOSITIONALLY GRADED INXGA1-XAS BUFFER LAYERS FOR MODULATION-DOPED IN0.3GA0.7AS/IN0.29AL0.71AS HETEROSTRUCTURES

Modulation-doped In0.3Ga0.7As/In0.29Al0.71As heterostructures have been grown on GaAs substrates by molecular beam epitaxy using a compositionally step-graded InxGa1-xAs buffer layer. We found that the buffer layer produces essentially total relaxation with < 2 X 10(6)/cm2 dislocations present in the In0.3Ga0.7As layer. The structural perfection of this layer is reflected in the electrical and galvanomagnetic properties of its two-dimensional electron-gas channel which has a sheet-electron density of 1.2 X 10(12)/cm2, peak mobilities of 9 300 cm2/V s at room temperature and 31000 cm2/V s at 77 K, and a mobility anisotropy of approximately 4% along orthogonal [110] directions.