The anisotropy of H+ diffusion in wurtzite-type samples was treated by using density-functional theory, and the effects of this anisotropy upon trapping by charged and neutral sinks were examined via numerical solutions of the time-dependent diffusion problem. The results clarified recent results of the modelling of experimentally observed H+ drift in reverse-biased GaN pn junctions; where the effective capture radius for the trapping of H+ by Mg– was much larger than that expected for isotropic diffusion. The diffusion anisotropy was found to introduce qualitative changes into the solution of the classical Onsager problem of trapping by electrostatic attraction in the presence of an externally applied electric field.
Trapping with Anisotropic Diffusion in an Applied Field - H+ in Mg-Doped GaN. S.M.Myers, A.F.Wright: Journal of Applied Physics, 2003, 93, 2608-17