Effect of the doping gradient of 4H-SiC aluminum-implanted floating field rings for edge termination

4 H-silicon carbide (4 H-SiC) has been investigated and utilized for power semiconductor devices because of its wider bandgap than silicon (Si) and hence higher critical electric field and breakdown voltage. Furthermore, the thermal conductivity of 4 H-SiC is more than 2 times greater than that of Si, making it attractive for power devices operating at higher powers and higher temperatures. Edge termination is inevitable for power semiconductor devices. In this work, we investigated the effect of the doping gradient of aluminum-implanted floating field rings (FFRs) in the edge termination structure of 4 H-SiC power devices via TCAD simulation. For the 4 H-SiC n-drift layer with a thickness of 40 μm and a doping concentration of 2 × 1015 cm−3, four doping gradients of the Al-doped FFRs were simulated: 0.25, 0.33, 0.4, and 0.5 μm/decade. The simulation results revealed that, for the edge termination structure with 35 3 μm-wide FFRs, the effect of the doping gradient of FFRs on the breakdown voltage is relatively small, and the highest breakdown voltage is 6011 V with a doping gradient of 0.4 μm/decade. However, as the number of FFRs decreases to 26, the effect of the doping gradient of the FFRs on the breakdown voltage becomes highly significant. The highest breakdown voltage is 5710 V with a doping gradient of 0.25 μm/decade, but the lowest breakdown voltage is only 2835 V as the doping gradient increases to 0.5 μm/decade.