Growth of Nitrogen-Polar 2H-AlN on Step-Height-Controlled 6H-SiC(000(1)over-bar) Substrate by Molecular-Beam Epitaxy

200-nm-thick N-polar AlN layers were grown on 6H-SiC(000 (1) over bar) substrates with 6-bilayer-high steps by molecular-beam epitaxy. During N-polar AlN growth, multinucleation growth occured easily, increasing the surface roughness of AlN. By reducing supersaturation (nucleation probability), the surface roughness was improved. The FWHMs of (0002) and (01 (1) over bar(2) over bar) omega-scan diffraction peaks of the AlN layer were 120 and 210 arcsec, respectively. The formation of stacking-mismatch boundaries (SMBs) was successfully suppressed by step-height control of the SiC substrate and the initial layer-by-layer growth. Most of the threading dislocations (TDs) were generated at the step edges of the SiC surfaces. The density of TDs in the AlN layers was 2 x 10(9) cm(-2). (C) 2012 The Japan Society of Applied Physics