Uniform Luminescence at Breakdown in 4H-SiC 4°-Off (0001) p–n Diodes Terminated With an Asymmetrically Spaced Floating-Field Ring

Conventional floating-field rings, which are used to reduce the peak electric field at the periphery of power devices, cause nonuniform avalanche multiplication when applied to planar junctions formed on 4H-SiC substrates misoriented from (0001) toward [1120]. Accordingly, a novel asymmetrically spaced floating-field ring (AS-FFR) was applied to 4H-SiC 4°-off (0001) p-n diodes and found to be effective against such nonuniform avalanche multiplication; that is, luminescence at breakdown was nearly uniform when the spacing between the edge of the anode and the inner edge of the AS-FFR was 2.0 μm in the [1̅1̅20] direction and 1.5 μm in the [112̅0] direction. This result should contribute to exploring the possibility of 4H-SiC power devices with higher avalanche ruggedness.