Performance transition from full- to semi-superjunction geometries in 4H-SiC

We present a numerical exploration of the trade-off between specific on-resistance and breakdown voltage in silicon carbide superjunction (SJ) devices along the [0001] crystal orientation. Our study spans vertical-symmetric full-SJ geometry to the hybrid configurations that integrate SJ and non-SJ layers, so-called semi-SJ geometries. In semi-SJ devices, where the SJ layer is thinner than the optimal thickness required for full-SJ devices to sustain a given breakdown voltage, performance is notably inferior compared to full-SJ devices. A systematic performance analysis relative to the SJ layer thickness reveals a shift in the breakdown path. While full-SJ devices undergo breakdown through a peak electric field at the n- and p-pillar interface in conjunction with the anisotropic impact ionization process, the breakdown path transitions to parallel to [0001] through the center of the n-pillar as the SJ layer thickness decreases. This path switching in semi-SJ devices is attributed to a reduced electric field at the pillar interface, compared to full-SJ counterparts, due to the lower optimal doping density in the SJ layer. This reduction in optimal doping density is driven by the enhancement of the electric field caused by the non-SJ layer. To counterbalance the increase in the ionization integral resulting from the intensified electric field, the peak electric field at the pillar interface must be lowered, which necessitates a reduction in the doping density of the SJ layer.