Drain avalanche breakdown and gate instabilities in 4H-SiC MESFETs

With a 2-D numerical simulator, avalanche breakdown in 4H-SiC MESFETs with a recessed-gate structure has been studied. The breakdown voltage of the 4H-SiC MESFET is determined by impact ionization as well as conductivity modulation. The dependence of the breakdown voltage on gate bias is due to the change of the electric field distribution. A thermal model must be included to take the self-thermal effects into account and a positive coefficient of breakdown voltage is obtained. The anisotropy parameters are included into the model for the first time and the orientation dependence of the breakdown characteristics is explained.