AVALANCHE MULTIPLICATION IN FORWARD-ACTIVE AND REVERSE-ACTIVE MODE BIPOLAR JUNCTION TRANSISTORS

Impact ionization in the reverse-biased base-collector space-charge la yer of the bipolar junction transistor (BJT) can cause an avalanche co llector current as well as a reverse (or negative) base current. We de velop analytical models to predict and compare avalanche phenomena in the BJT biased under forward-active and under reverse-active operation s. The models consider a position-dependent electric field in the spac e-charge layer, the effect of the non-uniform doping profile, and the excess free carriers associated with the current passing through the s pace-charge layer. For the specified device make-up and parameters use d, our results suggest that avalanche is more prominent in the reverse -active BJT than the forward-active BJT. The physics underlying this o ccurrence is given, and experimental data obtained from an advanced BJ T is included in support of the models.