Aluminum nitride (AlN) is a true bulk-grown native substrate for III-nitrides. The crystals are grown by seeded physical vapor transport (PVT) using AlN seeds. AlN has high thermal conductivity ( comparable to, and perhaps higher than SiC), high bulk resistivity (>1x10(11) Ohm cm), high bulk-breakdown field (7-8 MV/cm), the highest surface acoustic wave (SAW) velocity and since it has the smallest lattice constant of the III-nitrides all AlInGaN compositions grown on AlN are in compression, thus making it easier to grow crack-free epitaxy. Additionally, AlN is transparent down to nearly 200 nm, making it attractive for deep UV LED structures. AlN has excellent cleavage planes making it suitable for edge-emitting lasers and low cost manufacturing. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim