Understanding the microstructures of triangular defects in 4H-SiC homoepitaxial

Triangular defects are frequently observed in 4H-SiC homoepitaxial layers and their existence is reported to greatly degrade the performance of corresponding p-n junction diodes. Regarding the formation mechanisms of these defects, there have been a few models postulated before, which will be briefly reviewed here. In this study, we have observed a significant number of triangular defects in a 150mm n^-/n⁺ commercial 4H-SiC homoepitaxial wafer using Nomarski Microscopy and Synchrotron X-ray topography (SXRT). The observed defects show varying morphology and complexity. In order to investigate their complex microstructures and gain insight on the formation mechanism, selected triangular defects were characterized by high resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. Results confirm that all the triangular defects have a 3C-SiC nature. In addition, {111} twins and double positioning boundaries (DPBs) were frequently observed inside the triangular defects. Based on these observations, a model has been developed to interpret the formation mechanism of these defects. In this model, the introduction of downfall particle during epitaxy creates a large triangular on-axis terrace, on which 3C-SiC crystals nucleate 2-dimensionally and grow under no constraint, eventually overgrown by 4H-SiC growth steps.