Physical Modeling and Scaling Properties of 4H-SiC Power Devices

4H silicon carbide (4H-SiC) has great potential for use as a material for power devices owing to its superior electrical properties. The distinctive feature of 4H-SiC is the high avalanche breakdown field and its anisotropy. In order to realize 4H-SiC power devices that make the best use of the excellent physical properties, device simulation, considering anisotropic physical properties is indispensable. This paper reports on the modeling of anisotropic impact ionization coefficients for device simulation, and the effect of anisotropic impact ionization coefficients on the avalanche breakdown of 4H-SiC power devices. We show that the avalanche breakdown voltage is degraded due to the anisotropy of impact ionization coefficients, which is caused by the lateral field at the termination structure. In addition, we precisely evaluate the effect of the high avalanche breakdown field of 4H-SiC on the performance of power devices. Scaling theory is applied for the design of power devices. A new figure of merit (HFOM) is derived as an invariant of scale transformation, which is a function of avalanche breakdown field and regarded as a measure of the performance of the power device.