6kV 4H-SiC BJTs with Specific On-resistance Below the Unipolar Limit using a Selectively Grown Base Contact Process

High-voltage (6 kV) 4H-SiC NPN BJTs are demonstrated using a novel self-aligned selectively grown base contact process. The devices exhibit specific on-resistance values (R_on,sp) as low as 28 mOmegacm², the lowest reported to date and below the unipolar limit. The current gain in the active region is found to be 3 and closely related to the depth of the isolation trench. The open-base turn-off curves exhibit a storage time of 0.4 mus, providing evidence for conductivity modulation in SiC high-voltage BJTs for the first time. Blanket growth devices fabricated on the same wafer as the selective growth devices show higher R_on,sp and current gain values as a result of a deeper isolation trench.