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This paper establishes a direct correlation between the arrangement of bright and dark contrast in phase-contrast microscopy images and the in-plane Burgers-vector direction of threading edge dislocations in GaN. By first calibrating this relationship on ammonothermal GaN with independently verified Burgers vectors, the authors then successfully applied it to hydride vapor phase epitaxy-grown GaN, with results confirmed by TEM and CBED. The findings reveal that phase contrast primarily reflects the sum of in-plane normal strain components, offering a nondestructive optical method for dislocation characterization.
Phase-contrast microscopy can now nondestructively reveal the in-plane Burgers-vector direction of threading edge dislocations in GaN, bypassing the need for destructive TEM.
Phase-contrast microscopy enables rapid, nondestructive observation of threading dislocations in GaN, but the relationship between dislocation contrast and the Burgers vector has not been established. Here, we demonstrate that the in-plane Burgers-vector direction of threading edge dislocations in GaN can be determined from the arrangement of bright and dark contrast in phase-contrast microscopy images. The relationship was first established for threading edge dislocations in ammonothermal GaN whose Burgers vectors were independently determined by X-ray topography and was subsequently applied to hydride vapor phase epitaxy-grown GaN. The Burgers vector predicted from the phase contrast was verified by weak-beam dark-field TEM and large-angle convergent-beam electron diffraction. For the threading edge dislocations examined, the direction obtained by rotating the direction from the minimum of the dark contrast to the maximum of the bright contrast by 90{\deg} counterclockwise coincided with the Burgers-vector direction. Analysis based on the photoelastic effect further suggests that the phase contrast primarily reflects the sum of the two in-plane normal strain components, {\epsilon}xx + {\epsilon}yy, around the dislocation. These results demonstrate that phase-contrast microscopy can be used as a nondestructive optical method for determining the in-plane Burgers-vector direction of threading edge dislocations in GaN.