Inclined Partial Dislocations in Nitride Semiconductors.

We investigate a-type threading edge dislocations (TEDs) and (a+c)-type threading mixed dislocations (TMDs) in (0001) gallium nitride grown on (111) silicon, using the short depth-of-field of a scanning transmission electron microscope equipped with an aberration corrector. Almost all are inclined to the growth direction. While TMDs are known to dissociate into two partial dislocations bounding a prismatic stacking fault, we also observe a similar dissociation of TEDs. Both types of dislocation have straight c-axis segments separated by jogs that displace the dislocation core along an a-axis direction. Jogs on TEDs appear abrupt, with a localized displacement of the whole core by a translation in the basal plane. Conversely, jogs on TMDs are distributed along the dislocation core, giving a variety of structures where individual atom columns are displaced by ±(1/6)[01-10] from one region to the next. Tetrahedral Ga-N bonding, which is preserved in straight TMDs with Drum stacking fault reconstructions, is not maintained in jogs on either type of threading dislocation. We thus expect them to be electro-optically active centers that may have deleterious effects on nitride devices.