Effect of the Doping Gradient of 4H-SiC Aluminum-implanted Floating Field Rings for Edge Termination

4H-silicon carbide (4H-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 4H-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 4H-SiC power devices via TCAD simulation. For the 4H-SiC n-drift layer with a thickness of 40 µm and a doping concentration of 2×10 ¹⁵ 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 3µm-wide FFRs, the effect of the doping gradient of FFRs on the breakdown voltage is relatively small, and the highest breakdown voltage is 5945 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 5597 V with a doping gradient of 0.25 µm/decade, but the lowest breakdown voltage is only 2789 V as the doping gradient increases to 0.5 µm/decade.