A vapor phase growth process involving the reaction of Ga vapor and ammonia has been used to grow needle- and platelet-shaped single crystals of GaN at 1130degreesC. Introduction of the NH3 only at high temperatures reduced the nucleation density, minimized the amount of GaN crust on the Ga source and resulted in larger crystals. A processing map has been constructed with respect to ammonia flow rate and total pressure at 1130degreesC to achieve control of growth in different crystallographic directions. Platelet growth of GaN was favored using low V/III ratios achieved via low ammonia flow rates and/or low total ammonia pressures and/or an increase in the Ga source temperature. Crystals with aspect ratios c/a < 1 were obtained at 1130degreesC, 430 Torr, and 25-75 sccm of ammonia. Raman spectroscopy revealed that the best platelets were grown at 1130degreesC using ammonia flow rates of 60 sccm and a Ga source temperature of 1260degreesC. Seeded growth from previously grown needles and platelets at lateral and vertical rates of similar to 25 and similar to 10 mum/h, respectively, was achieved using these growth parameters. (C) 2002 Published by Elsevier Science B.V.