Formation Mechanism of Two Types of Polytype Transformation in off-axis 4H-SiC Boules

The morphology and distribution of polytypes are studied by confocal laser scanning microscopy (CLSM) and Micro-Raman spectroscopy. Based on the experimental results, two possible formation mechanisms of foreign polytypes are proposed. One phenomenon is that the polytype transition interface tilts toward the seed crystal plane, which is related to the step flow growth mechanism. By reducing the crystal growth rate at the starting point of the step, this foreign polytypes can be effectively avoided. Another phenomenon is that the polytype transition interface is parallel to the seed crystal plane, which usually occurs in the later growth stage. This is related to the increase of the temperature of the growth front, which is also confirmed by the theoretical simulation results obtained by commercial VR™-PVT SiC software.