Comparative Evaluation of Forward Voltage Degradation due to Propagating and Converted Basal Plane Dislocations

This study investigated the relationship between the forward voltage degradation induced by SSF expansion and (a) BPD density in substrates and epitaxial layers of SiC, and (b) the temperature during the application forward current to the pin diodes. The Vf shift caused by the BPDs in the drift layer simply depended on the BPD density. However, no correlation was initially observed between the Vf shift and BPD density in the substrate; instead a strong correlation was observed between the Vf shift and the device temperature measured when applying the current stress. Thus when we selected samples which show the same temperature at that time, a correlation was observed between the Vf shift and the BPD density in the SiC substrate, with the slope corresponding to the former, drift layer relationship. Therefore, due to the high BPD density in the SiC substrate, suppressing the Vf shift due to BPD density in this region is highly important, and a combination of approaches is therefore proposed in order to reduce the overall forward voltage degradation.