Structure And Characteristics Study Of4H-SiC BJT Power Devices

Bipolar junction transistors (BJTs) are attractive candidates for4H-SiC power-switching devices because of the absence of a critical gate oxide in the device structure, the possibility of conductivity modulation in the drift layer, and nearly zero offset voltage.In this paper, the development of4H-SiC BJT is briefly reviewed and BJT’s fundamental working principles are introduced. Two dimensional numerical analysis tool ATLAS is used to help investigate the electrical characteristics of4H-SiC BJT. In order to obtain true and reliable simulation results, physical models of4H-SiC are established. Vertical4H-SiC BJT and lateral4H-SiC BJT are both studied in this paper. For vertical4H-SiC BJT, influence of geometrical effects on current gain is studied. By optimizing Emitter width and Emitter-Base distance, a high current gain of BJT is acquired. And then, current gain and breakdown voltage as a function of base width for different base doping is investigated to acquire a trade-off between current gain and breakdown voltage.Lateral4H-SiC BJT is also studied in this paper. Based on double RESURF4H-SiC BJT, by applying base field plate, collector-base depletion extension into base region is suppressed greatly. And by optimizing base doping and base width, high current gain is acquired under high breakdown voltage. At last, performances of lateral4H-SiC BJT and vertical4H-SiC BJT are compared. Results show that lateral4H-SiC BJT has an overwhelming advantage of current gain over vertical4H-SiC BJT under the comparable breakdown voltage. However, due to the inherent disadvantage of lateral power devices, specific on resistance of vertical4H-SiC BJT is much higher than that of vertical4H-SiC BJT.