Formation and evolution of micropipes in SiC crystals

Based on experimental observations of spiral steps at the growth front of SiC ingots, we propose that micropipes may originate from screw dislocation pairs with opposite Burgers vectors or from screw dislocation groups with the same Burgers vectors. Impurity particles attached at the growing surface interacting with the spiral steps may enhance the formation of micropipe defects. It has also been found that micropipes not only can originate from the second-phase inclusion, but terminate at it. According to experimentally observed ramification of micropipes, we propose that the extension of micropipes along the off-oriented direction will result in them splitting and terminating. Therefore, cambering the crystal seeds may be helpful to grow SiC crystals with a low density of micropipes. During the combination and interaction procedures, micropipes can be created at the infalls of low angle boundaries, and have an identical evolution along the [0001] extending direction in 6H-SiC, and 15R-SiC as well. These results will help to understand micropipe formation and evolution mechanisms, and hence help control micropipe density.