Characterization of horseshoe-shaped defects in 4H-SiC thick homoepitaxial layers

We report horseshoe-shaped protuberance defects encountered in growing thick homoepitaxial films on 4° off c-axis 4H-silicon carbide substrates. Their morphology, polytype and formation mechanism are investigated by optical microscopy, laser microscopy, micro-Raman spectroscopy, micro-photoluminescence spectroscopy and defect tracking experiments. The defects are observed to protrude from the surrounding area with a facet of (0001) at an angle of about 3.06°. Concomitantly, surface undulations develop and extend about hundreds of microns from the defect perpendicular to the direction of step flow. No polytype inclusions are found in these defects. The defect tracking reveals that the defects are not directly related to the existence of dislocations. We think that the formation of the defects origin from the occurrence of giant step bunching and subsequent faceting.