HIGH-RESOLUTION X-RAY-DIFFRACTION OF EPITAXIAL LAYERS ON VICINAL SEMICONDUCTOR SUBSTRATES

For a misoriented (hkl) substrate crystal, the (hkl) lattice plane normal and surface normal do not coincide. Rocking curve measurements of a sample with an epitaxial layer grown on such a substrate show a variation of substrate epitaxial layer peak distances with rotation around the surface normal of the sample. The variation in angular peak distances is frequently attributed to a relative tilt of the epitaxial layer with respect to the substrate. For exactly oriented substrates the lattice of the epitaxial layer is tetragonally distorted because of the lattice parameter difference. We show that for fully strained epitaxial layers of semiconductors with the zinc blende structure the variation in peak distance is due to distortion of the tetragonal symmetry, caused by the anisotropic elasticity of these materials. The effects of misorientation are calculated quantitatively and simulated by using an effective asymmetry, consisting of the asymmetry angle of the lattice plane plus a projection of the misorientation onto the diffraction plane.