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 beta. Long-term operation in common-emitter mode results in negligible V-F or beta degradation, if the base plate is maintained at 25 degrees C. A greater degradation of beta 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 beta reduction. It is also shown that the beta degradation can be reversed by annealing at >= 200 degrees C, suggesting the possibility of degradation-free operation of SiC BJTs, when operating in pulsed current mode at >= 200 degrees C temperatures.