Saturation current improvement in 1200 V normally-off SiC VJFETs using non-uniform channel doping

Excellent performance and record inverter efficiency have been reported for 1200 V normally-off silicon carbide (SiC) vertical channel junction field effect transistors (VJFETs) with uniform channel doping. Optimally designed normally-off SiC VJFETs typically have a threshold voltage of approximately +1 V and pentode-like output characteristics with clear saturation. Some applications require significant surge or pulsed current capability thus it is desirable to increase saturation current density while maintaining normally-off operation. This paper reports the use of non-uniform channel doping in a normally-off SiC power VJFET to achieve a 28-48% increase in saturation current and 13% decrease in on-resistance compared to the uniform channel case. This results in a specific on-resistance of 2.5 mΩ·cm² and saturation current density of 1275 A·cm^-2 at 25°C. Forward drain leakage at V_gs= 0 V and V_ds= 1100 V (measurement setup limit) is very similar for both channel doping profiles and remains less than 55 uA (1.75 mA·cm^-2) at 150°C for the non-uniform channel SiC VJFET. The total switching energy for non-uniform channel devices was 194 μJ compared to 190 μJ for uniform channel devices.