Formation Mechanisms of Polytype-Induced Parallel Slits in Off-Axis 4H-SiC Crystals

This study presents systematic research of the parallel slits originating from the polytype boundaries in the 4H silicon carbide (4H-SiC) single crystals grown by the physical vapor transport (PVT) method. Through the analysis of longitudinal slices of SiC crystals, it was verified that the foreign polytype inclusions generated at the crystal edges, when propagating into the interior, form densely packed micropipe (MP) bundles originating from the foreign polytypes. The generation of observed slits parallel to the [1 1 2̅ 0] crystallographic direction may be associated with the agglomeration of MPs, and these slits could potentially penetrate the entire crystal along the growth direction. Then, the thermal field conditions responsible for slit formation were investigated through control experiments, guided by numerical simulations. It was concluded that the edge temperature gradient plays a crucial role in its development. Building on these findings, the growth mechanism responsible for the formation and elimination of the polytypes that led to the slits was refined. Our research provides valuable insights into avoiding defects in SiC crystal growth using the PVT method.