Simulation of anisotropic breakdown in 4H-SiC diodes

The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. The authors' numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams a one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in the design and characterization of 4H-SiC power devices.