Modeling high-level free carrier injection in advanced bipolar junction transistors

This paper presents a comprehensive study on the effects of high-level free-carrier injection on the current transport of bipolar junction transistors (BJTs). Detailed information for the free-carrier concentration, electric field, and drift and diffusion current components in the quasi-neutral base (QNB) under high-level injection are calculated using the modified ambipolar transport equation and using several different approximations for the majority-carrier current in the QNB. Our results suggest that the widely used zero majority current approximation gives rise to a larger error compared to other lesser known approximations.