The influence of lattice polarity of wurzite GaN(0001) on its decomposition rate was investigated using an in situ gravimetric monitoring (GM) method with freestanding GaN(0001) substrates. At temperatures between 800degreesC and 850degreesC, the decomposition rate of GaN(0001) was faster than that of GaN(0001). On the other hand, the decomposition rate of GaN(0001) was faster than that of GaN(0001) at temperatures between 900degreesC 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) + 3/2H(2)(g)-->NH3(g) at lower temperatures, but Ga(surface) + 1/2H(2)(g)-->GaH(g) at higher temperatures. In addition, we used the GM method to measure the growth rate of GaN(0001)on freestanding GaN(0001) substrates. In the low-temperature region, GaN(0001) grew faster than GaN(O 0 0 1), whereas GaN(0001) grew faster than GaN(000 (1) over bar).in the high-temperature region. (C) 2002 Elsevier Science B.V. All rights reserved.