MISORIENTATION IN GAAS ON SI GROWN BY MIGRATION-ENHANCED EPITAXY

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 (approximately 4 mum) samples including strained-layer superlattices, which can provide a very low dislocation density. The surface etch-pit densities are 6.2 X 10(4) cm-2 for the thick sample with a rotation angle beta = 2-degrees, and 3.1 x 10(5) cm-2 for beta = 12-degrees, even though they are grown under identical conditions except for the initial growth conditions.