Misorientation in GaAs on Si Grown by Migration-Enhanced Epitaxy

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Abstract
The misorientation of GaAs grown on Si(100) by migration-enhanced epitaxy is investigated using X-ray diffraction. In addition to the usual tilt misorientation of GaAs with respect to the Si substrate, almost all of the GaAs layers are found to exhibit a misorientation of rotation about the substrate surface normal. The misorientation depends systematically on the initial growth conditions such as the substrate off-orientation and the nucleation conditions of the first GaAs monolayer, which include growth initiations by Ga- or As-supply first and simultaneous supply of Ga and As4 with various V/III flux ratios. A model which describes the observed tilt is proposed, based on the relaxation of misfits perpendicular to the Si surface. Reducing unnecessary misorientation leads to better crystal quality even for thick (∼4 µm) samples including strained-layer superlattices, which can provide a very low dislocation density. The surface etch-pit densities are 6.2×104 cm-2 for the thick sample with a rotation angle β=2°, and 3.1×105 cm-2 for β=12°, even though they are grown under identical conditions except for the initial growth conditions.