Calculation of the emitter efficiency of bipolar transistors

The emitter efficiency of a bipolar transistor is calculated taking heavy doping effects such as impurity band formation and band tailing into account. It is shown that in most cases these effects, rather than the minority carrier lifetime in the emitter are limiting the transistor current gain. This allows us to define an effective emitter impurity profile for use in current transport calculations. The influence of the emitter and base impurity profiles upon the gain is studied, and experimental results are presented showing that the knowledge of the impurity profiles is sufficient to predict the one-dimensional current gain.