Investigation of Avalanche Capability of 1200V 4H-SiC MPS Diodes and JBS Diodes

In this work, the avalanche capability of 1. 2kV 4H-SiC JBS and MPS diodes in single-pulse Unclamped Inductive Switching (UIS) tests is investigated and compared. It is found that the width (W) of wide P+ region has great effects on the device avalanche capability. The experimental results show that the avalanche capability gets increased with W when W=3-8μm, then declines when W exceeds 8μm. TCAD Simulation is carried out to study the device behavior in the avalanche mode. It is revealed that the electric field under avalanche condition is crowded at the corners of the pn junction, which leads to avalanche current crowding and unbalanced current distribution issues. Current non-uniformity coefficient (k) is used to characterize the severity of the current unbalance. Simulation results indicate that k declines with W when W=3-8μm, then get increased when W exceeds 8μm, which is consistent with the optimal design in the experimental results. Based on the study, an optimal MPS diode structure design with W=8μm is obtained and an avalanche capability improvement of 9%~ 28% is achieved by the experiments.