Charge-state calculations, based upon density-functional theory, were used to study the formation energy of H in wurtzite and zincblende samples as a function of the Fermi level. A comparison of these results revealed appreciable differences, including a 0.56eV lower formation energy for H2 in wurtzite, and different configurations for H2 and H- in the 2 crystal structures. In addition, H- was found to be equally stable at bond-centered and anti-bonding sites in wurtzite, whereas it was unstable at a bond-centered site in zincblende samples. The N-H+ stretching-mode vibration frequencies, the clustering of H+ in p-type material and diffusion barriers for H- were investigated in wurtzite. A diffusion barrier of 1.6eV was found for H- in wurtzite. This was significantly lower than a previous estimate, and a tendency to H+ clustering in p-type material was detected.

Influence of Crystal Structure on the Lattice Sites and Formation Energies of Hydrogen in Wurtzite and Zincblende GaN. A.F.Wright: Physical Review B, 1999, 60[8], R5101-4