Diffusion in the presence of excess Ga metal was measured using optical and microprobe techniques. The coefficient was found to be concentration-dependent and anisotropic, with faster diffusion occurring in directions perpendicular to the hexagonal c-axis. The anisotropy in the activation energy was 0.2eV. At 940 to 1240K, the linear concentration-dependent diffusion indicated an activation energy, for defect migration, of 2.39eV perpendicular to the c-direction and one of 2.21eV for diffusion parallel to the c-direction.

E.D.Jones, H.Mykura: Journal of the Physics and Chemistry of Solids, 1980, 41[11], 1261-5