AlN bulk crystals grown on SiC seeds

AlN layers with thickness between 0.1 and 3 mm were grown on on-axis and off-axis (0 0 0 1), Si-face SiC seeds by physical vapor transport (PVT) from an AlN powder source. A two-step deposition process was developed for the growth of thick layers. Cracks formed in the AlN layers due to the thermal expansion mismatch between AlN and SiC were observed to decrease with increase in AlN thickness. AlN grown on on-axis SiC was primarily Al-polar, but contained N-polar inversion domains (IDs) revealed by wet etching in hot, aqueous phosphoric acid or potassium hydroxide solutions. Regions of opposite polarity on basal plane surfaces were imaged by piezoresponse force microscopy (PFM). IDs were not observed in crystals grown on off-axis seeds. The influence of SiC seed orientation and stability on the polarity of the AlN layers is discussed.