The influence of lattice polarity on wurzite GaN{0 0 0 1} decomposition was investigated using an in situ gravimetric monitoring (GM) method with freestanding GaN(0 0 0 1). At temperatures below about 820degreesC, the decomposition rate of GaN(0 0 0 1) was faster than that of GaN(0 0 0 (1) over bar). On the other hand, the decomposition rate of GaN(0 0 0 (1) over bar) was faster than that of GaN(0 0 0 1) at temperatures between about 850degreesC and 950degreesC. The relation between the decomposition rate and the H-2 partial pressure (P-H2) indicates that the rate-limiting reactions are N(surface) + H-3/2(2)(g) -->NH3(g) at lower temperatures, but Ga(surface) + H-1/2(2)(g) --> GaH(g) at higher temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.