A comparative study of nonpolar a-plane and m-plane AlN grown on 4H-SiC by plasma-assisted molecular-beam epitaxy

AlN has been grown on 4H-SiC m  -plane (11¯00) and a  -plane (112¯0) substrates by RF-plasma-assisted molecular-beam epitaxy. Similarities and differences between the two growth orientations are discussed. High-quality AlN can be obtained in both orientations when grown in the metastable 4H-crystal structure. For both epilayer orientations Al-rich conditions were necessary to stabilize the 4H-polytype. 4H-AlN for both growth directions shows very narrow X-ray rocking curves widths less than 100 arcsec. a-plane 4H-AlN exhibited a much smoother morphology than m-plane 4H-AlN. On the other hand, reflection high-energy diffraction intensity oscillations in the initial growth stage were observed only for m-plane AlN.