Synchrotron X-ray topography analysis of the distribution and formation mechanisms of low angle grain boundaries in PVT-Grown 4H-SiC crystal

The distribution and formation mechanisms of low-angle grain boundaries (LAGBs) in physical vapor transport (PVT) grown 4H-SiC crystals are investigated by synchrotron monochromatic beam X-ray topography (SMBXT) combined with ray-tracing simulation, focusing on the facet region and its adjacent area that were not covered in previous studies. Two spatially distinct threading edge dislocation (TED)-LAGB networks are identified: the one within the facet is interpreted as originating from misorientations between threading screw dislocations (TSDs) acting as growth centers, while the one adjacent to the facet is explained by extending the horseshoe-shaped growth step model previously reported at the wafer scale from a single pair of fronts to multiple interacting sets, each originating from an individual spike generated by TSDs and micropipes at the facet edge. The encounter of these multiple spike-driven fronts incorporates prismatic slip dislocations induced by radial temperature gradients and accounts for the formation of TED-LAGBs along all three <11¯00> directions, as well as the coexistence of multiple 1/3[112¯0] Burgers vector variants within a single continuous network. These findings extend the horseshoe-shaped step-flow framework to a new geometric regime and provide a more complete understanding of LAGB formation across the full wafer.