When an SBD with a conventional structure is reverse-biased, the depletion region extends into the semiconductor as shown below. The area of the triangle formed by the electric breakdown field and the depletion region width represents the withstand voltage of an SBD. The depletion region depth is inversely proportional to the dopant concentration. Increasing the dopant concentration helps reduce the resistance of silicon and therefore the forward voltage (VF) of the SBD, but at the expense of withstand voltage (i.e., triangle area). The electric breakdown field of SiC is nearly 10 times that of silicon. As shown below, it is therefore possible to increase the withstand voltage (i.e., triangle area) of a SiC SBD relative to a Si SBD, even if it is heavily doped.
In addition, since the depletion layer is less stretched by the higher concentration, the thickness of the chip can be thinner than in the case of Si. The thickness of the semiconductor (Si or SiC) can be considered as series resistance in the forward direction, and so the forward voltage can be improved by reducing the thickness.