Published online by Cambridge University Press: 15 February 2011
GaN decomposition was studied above 800°C in flowing H2 and N2 for pressures ranging from 10 to 700 torr. From careful weighings of the GaN film on sapphire before and after annealing, the rates for GaN decomposition, Ga surface accumulation, and Ga desorption were obtained. An enhancement in the GaN decomposition rate was observed in H2 pressures greater than 100 torr. Even with this enhanced GaN decomposition, the Ga desorption rate is nearly constant at higher pressures. As a result, Ga droplets accumulate on the surface. For N2 pressures ranging from 76 to 400 torr no net enhancement in the GaN decomposition rate is observed and the GaN decomposition rate is reduced compared to identical annealing conditions in H2. This suggests that HI- is acting chemically to reduce the barrier for GaN decomposition. This may occur through a surface mediated dissociation of H2 followed by the formation of more mobile and volatile hydrogenated N and Ga species. The significance of this study for GaN growth is that by increasing the GaN decomposition, the Ga atoms diffuse farther and subsequently re-incorporate into the growing lattice, increasing the GaN crystal quality. Connections between the enhanced GaN decomposition rate and the coalescing of nucleation layer during the ramp to high temperature and the consequences for the high temperature growth are discussed.