Release of basal plane dislocations from a helical threading mixed dislocation in 4H-SiC

We identified a threading mixed dislocation (TMD) as the origin of a single Shockley-type stacking fault (1SSF) in 4H-SiC. X-ray topography before ultraviolet (UV) irradiation and photoluminescence imaging after exposure confirmed this relationship. The origin was characterized by three TMD segments with distinct configurations and two basal-plane dislocation releases between them, partially exhibiting a helical structure. We speculate that the helical structure associated with TMD formation is driven by kinetics and dynamics of backfilling in flat-bottomed pits during spiral growth. Factors such as inclination toward the basal plane, release of basal-plane components, and reconstruction into other TMD types likely contribute to this transformation. These findings provide critical insights into the mechanisms behind expandable TMDs and their role in stacking fault expansion, offering guidance for improving the long-term reliability of SiC power devices.