Mechanisms of defect formation in ingots of 4H silicon carbide polytype

The methods of optical microscopy and X-ray diffractometry have been used to study the features of defect structure in ingots of the SiC-4H polytype; the ingots have featured different diameters and have been grown by the modified Lely method on seeds with deviations of several degrees from the exact orientation (0001)C in the direction $\langle11\bar20\rangle$ (off-cut (0001) seeds). The slip bands observed in the crystals are extended along the $[11\bar20]$ direction and correspond to the secondary slip system of threading dislocations $a/3\langle11\bar20\rangle$ $\{\bar1100\}$ for hexagonal close packing (HCP) crystals. Low-angle dislocation boundaries directed along $[1\bar100]$ accommodate the disorientation of neighboring domains, which results from their mutual rotation around the [0001] axis. Enlargement of ingots leads to some increase in the dislocation density, mainly due to threading edge dislocations. The average density of micropipes is in the range of 5–20 cm$^{-2}$ and practically remains unchanged as the ingot size is increased.