Excess reverse-bias leakage in GaN films, grown by molecular beam epitaxy onto GaN templates, was correlated with the presence of pure screw dislocations. A scanning current–voltage microscope was used to map the spatial locations of leakage current on high-quality films under reverse bias. Two samples with a similar total dislocation density (109/cm2), but with a pure screw dislocation density which differed by an order of magnitude, were compared. It was found that the density of reverse-bias leakage spots correlated well with the pure screw dislocation density; not with the mixed dislocation density. It was concluded that pure screw dislocations had a far more detrimental effect upon gate leakage than did edge or mixed dislocations.

Direct Imaging of Reverse-Bias Leakage through Pure Screw Dislocations in GaN Films Grown by Molecular Beam Epitaxy on GaN Templates. J.W.P.Hsu, M.J.Manfra, R.J.Molnar, B.Heying, J.S.Speck: Applied Physics Letters, 2002, 81[1], 79-81