Investigation of the Suitability of 1200-V Normally-Off Recessed-Implanted-Gate SiC VJFETs for Efficient Power-Switching Applications

A recessed-implanted-gate (RIG) 1290-V normally-off (N-OFF) 4H-SiC vertical-channel JFET (VJFET), fabricated with a single masked ion implantation and no epitaxial regrowth, is evaluated for efficient power conditioning applications. The relationship between the VJFET´s on-state resistance and current gain is elucidated. Under high-current-gain operation, which is required for efficient power switching, the 1200-V N-OFF (enhancement mode) VJFET exhibits a prohibitively high on-state resistance. Comparison with 1200-V normally-on VJFETs, fabricated on the same wafer, confirms experimentally that the strong gate-depletion-region overlap required for 1200-V N-OFF blocking is the principal contributor to the prohibitively high specific on-state resistance observed under high-current-gain VJFET operation. Perfecting the 1200-V edge termination structure, which can reduce the theoretical drift specific ON-state resistance from 2.2 to 1.5 mOmega ldr cm², has a negligible impact in decreasing the channel-dominated 1200-V N-OFF VJFET resistance. The RIG VJFET channel-region optimization simulations (assuming a single commercial implantation and no epitaxial regrowth) revealed that, although aggressively increasing channel doping lowers the resistance, the corresponding reduction in the source mesa width can prohibitively limit manufacturability.