Direct observation of excess carrier distribution in 4H-SiC power diodes

The first direct measurements of electrically injected carrier distributions in the base of 4H-SiC power diodes are reported. A novel approach of combining micron-resolution free-carrier absorption technique with optical imaging of e-h recombination radiation was applied to study the spatial and temporal plasma build-up. The excess carrier distributions both along and across the base region were examined during forward biasing within a 50-250 A/cm/sup 2/ range. The revealed local deviations of carrier density and lifetimes are attributed to inherent structural imperfections of the epilayer. Numerical device simulation demonstrated a good agreement with experiment and validated the importance of actual lifetime, contact, and emitter injection parameters to the overall plasma formation.