PVT growth of bulk AlN crystals with low oxygen contamination

We have performed growth and characterization of bulk aluminum nitride (AlN). Crystalline boules have been prepared by physical vapor transport (PVT), i.e. sublimation and recondensation of AlN at temperatures exceeding 2000 degreesC in nitrogen atmosphere. The dense boules are up to 15 mm in height and 2 inch in diameter and consist of high-purity AlN grains up to 5 mm in size. Oxygen was identified to be main impurity, strongly influencing seeding and material transport during growth. Chemical analysis shows that the grown material contains less than 100 ppm wt oxygen. The AlN crystals exhibit high structural quality and a texture in c-axis direction. Optical absorption data taken at different temperatures are discussed in connection with oxygen contamination. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.