Performance Limits of Vertical Unipolar Power Devices in GaN and 4H-SiC

GaN and 4H-SiC are emerging wide-bandgap semiconductors that have unipolar power-device figures-of-merit 350-400x higher than silicon, but precise design and performance information on GaN has been unavailable due to lack of ionization rate data in that material. In this paper we calculate performance limits of unipolar vertical drift regions in GaN using recently published impact ionization data, and compare these limits to those of silicon and 4H-SiC. To assist in the design of power devices, we include equations for the doping and thickness of optimum unipolar drift regions in both materials.