Purely wurtzite phase needle crystals and epitaxial layers of GaN were grown by the ammonothermal method using an NH4I mineralizer. The inclusion of zincblende phase GaN was effectively eliminated by increasing the growth temperature higher than 500 degrees C. Accordingly, an approximately 20-mu m-thick GaN epitaxial layer was achieved on the Ga-polar face of a c-plane GaN seed wafer at 520 degrees C. Although the characteristic deep state emission band dominated the room temperature photoluminescence spectrum, the near-band-edge emission of GaN was observed for both the needle crystals and the epitaxial layers. These results encourage one to grow better quality GaN crystals at a high growth rate under high-temperature growth conditions. (C) 2010 Elsevier B.V. All rights reserved.