Characterization of the Stability of Current Gain and Avalanche-Mode Operation of 4H-SiC BJTs

The stability of the electrical characteristics of SiC n-p-n bipolar junction transistors (BJTs) is investigated under long-term avalanche-mode, dc, and pulsed-current operation. There is absolutely no change in the blocking I-V characteristics after a 934-h repetitive avalanche stress test. Long-term operation of the base-emitter diode (open-collector mode) alone does not result in any degradation of the ON-state voltage drop V_F or current gain β. Long-term operation in common-emitter mode results in negligible V_F or β degradation, if the base plate is maintained at 25°C. A greater degradation of β results upon increasing the base-plate temperature. The same total electrical charge, if passed through the BJT as a pulsed current, instead of a dc current, results in smaller β reduction. It is also shown that the β degradation can be reversed by annealing at ≥200°C, suggesting the possibility of degradation-free operation of SiC BJTs, when operating in pulsed current mode at ≥200°C temperatures.