The diffusion of Ga and N adatoms on wurtzite (00•¯1) and (00•1) surfaces was analyzed by using density functional theory. The calculations revealed very different diffusivities of Ga and N adatoms on equilibrium surfaces. Whereas Ga was very mobile at typical growth temperatures, the diffusivity of N was some orders of magnitude lower. It was also found that the presence of excess N strongly increased the Ga diffusion barrier. On (00•1), the barrier increased from 0.4 to 1.8eV while, on (00•¯1), it increased from 0.2 to 1.0eV. It was therefore concluded that excess N at the surface, which could appear under N-rich conditions, appreciably reduced the mobility of Ga adatoms. This was attributed to the formation of strong Ga-N bonds, which had to be broken during adatom migration.

Adatom diffusion at GaN(00•1) and (00•¯1) surfaces T.Zywietz, J.Neugebauer, M.Scheffler: Applied Physics Letters, 1998, 73[4], 487-9