Direct imaging of reverse-bias leakage through pure screw dislocations in GaN films grown by molecular beam epitaxy on GaN templates

Excess reverse-bias leakage in GaN films grown by molecular beam epitaxy on GaN templates is 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 GaN films under reverse bias. Two samples with similar total dislocation density (∼109 cm−2) but with pure screw dislocation density differing by an order of magnitude were compared. We found that the density of reverse-bias leakage spots correlates well with pure screw dislocation density, not with mixed dislocation density. Thus, pure screw dislocations have a far more detrimental impact on gate leakage than edge or mixed dislocations.