The nucleation and initial growth kinetics of GaN on sapphire grown using hydride vapor phase epitaxy technique were measured over a broad range of typically employed growth conditions. GaN nucleation and growth were investigated by a series of short time growth and quench experiments. Atomic force microscopy was used to examine the island density, size, and shape as a function of growth time and substrate temperature. The nucleation temperatures were studied over the range of 985-1100degreesC. As the temperature increased, the island density decreased due to adatom desorption and higher surface diffusion rates. The initial growth islands transformed from an irregular shape to a hexagonal shape and secondary nucleation was observed as the temperature increased. The activation energy for adatom surface diffusion was estimated to be similar to2.3 eV on the nitridated (0 0 0 1) sapphire. At high temperatures (greater than or equal to1050degreesC), different surface processes, including adatom desorption and island mobility were taking place. (C) 2003 Elsevier B.V. All rights reserved.