Properties of graded Inx0Ga1-xAs layers grown by molecular beam epitaxy

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Abstract
Modulation-doped In0.5Al0.5As/In0.5Ga0.5As heterostructures on compositionally graded Inx0Ga1-xAs buffer layers on (001) GaAs substrates were prepared by molecular beam epitaxy. An investigation of samples is reported, which have different initial In compositions x0=0, 0.12, 0.18, 0.24, 0.5 in the linearly graded buffer. The sample with x0=0.18 shows the highest electron mobility and the highest electron density, which are 9.3*103 cm2 V-1 S-1 and 3*1012 cm-2 at 300 K respectively, of the investigated samples. The smallest photoluminescence linewidth of 18 meV was measured from both samples with x0=0.12 and 0.18. A small lattice tilt of 1.4 mrad between the relaxed In0.5Ga0.5As layer and substrate and a smooth surface was achieved for x0=0.18.