The diffusion and reactions of H in GaN were described by applying differential equations for the concentration profiles of H species, charged dopants and carriers; with the simultaneous solution of Poisson’s equation. This approach avoided the simplifying assumptions of local equilibrium among states, and local charge neutrality, which had previously been used to treat high-temperature H behavior in uniform layers. This led to a more general modelling scheme which encompassed non-equilibrium conditions and space-charge effects. Density-functional theory, which had previously been used to treat equilibrium H energies, was here used to examine activation barriers and wave-function overlaps that affected the rates of relevant H and carrier reactions. This then guided the selection of the mechanisms to be included, and influenced the evaluation of some rate parameters. The model was applied to H-containing p-n junctions, with detailed consideration of the reversible, metastable electrical activation of H-passivated Mg acceptors that was observed experimentally under forward bias. The calculations indicated that interstitial H2 was the H state which resulted from such activation, and this conclusion was supported by a good agreement between the predicted and observed onset temperatures for re-passivation under open-circuit annealing. When modelling the more complex activation process, experimentally observed qualitative features were reproduced by choosing relative carrier-capture cross sections which were in accord with ab initio theoretical considerations. In other model calculations, H was shown to be expelled from the carrier-depleted zone of p-n junctions; thus causing H redistribution under reverse bias.

Theoretical Description of H Behavior in GaN p-n Junctions. S.M.Myers, A.F.Wright: Journal of Applied Physics, 2001, 90[11], 5612-22