We demonstrate that when vertical threading dislocations in (0001) GaN are imaged in plan-view by transmission electron microscopy, a surface-relaxation contrast operates in addition to that due to the strain fields of dislocations passing through the specimen. We show that all three dislocation types (edge, screw, and mixed) can be detected in the same image using g=(112̄0) and 18° specimen tilt from [0001], allowing total densities to be assessed properly. The type of an individual dislocation can also be readily identified.
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