Influence of base carrier lifetime on the characteristics of 4H-SiC BJTs

The optimum range of the base electron lifetime (τnB0) in silicon carbide (SiC) bipolar junction transistors (BJTs) is qualitatively investigated in this paper, considering both the static and dynamic performance. The TCAD simulation results show that there is tradeoff between the current gain (β) and the turn-off time (tF). With τnB0 increasing, both β and tF increase. However, with a fixed base width, the base transport factor tends toward saturation when τnB0 exceeds certain value. Thus, the eclectic values of base electron lifetime with different base thickness are obtained. The influence of the base drive current is also discussed. According to the charge control theory, the excessive storage charge caused by overdrive has a great influence on turn-off delay time (tD). To solve this, a suitable base drive current is necessary. For the common 4H-SiC BJT structure, appropriate base drive under variable base and collector doping concentration is suggested.