Epitaxy of nonpolar AlN on 4H-SiC (1-100) substrates

AlN has been grown on 4H-SiC (1-100) substrates by rf-plasma molecular beam epitaxy. The epilayers assume a metastable 4H structure to match the in-plane stacking arrangement of the substrate. Initial two-dimensional nucleation of 4H-AlN is revealed by reflection high-energy electron diffraction. The epitaxial quality is evidenced by narrow x-ray diffraction ω-scan linewidths less than 70 arcsec for both symmetric and asymmetric reflections. The AlN growth surface exhibits a smooth and anisotropic morphology similar to that of GaN (1-100). Large residual stress is present in the epilayers, consistent with incomplete relaxation of misfit strain during growth.