A crack-free aluminum nitride (AlN) template layer was grown on a (0 0 0 1) sapphire substrate at 1450 degrees C using a thin (100 nm) protective AlN layer grown at 1065 degrees C by hydride vapor-phase epitaxy (HVPE). Full-width at half-maximum (FWHM) values of X-ray rocking curves (XRCs) for (0 0 0 2) and (1 0 (1) over bar 0) planes of the AlN layer were 378 and 580 arcsec, respectively. The formation of voids was observed at the interface between the thin protective AlN layer and the sapphire substrate due to decomposition reaction of sapphire during heating up to 1450 degrees C. The voids relaxed the tensile stress in the AlN layer, which resulted in the suppression of cracks. (C) 2009 Published by Elsevier B.V.