Switch-on transient of shallow-profile bipolar transistors

This paper presents 2-D computer simulations of the switch-on characteristics of shallow-profile silicon bipolar transistors with a focus on the current distribution and the base charge storage time calculations. From the simulations, we learned that 1) although the initial turn-on current predominantly flows through the edge of the emitter, after the transient, most current flows under the emitter, not through the edge; 2) a fast rise in collector current can be accomplished by a small voltage overdrive which causes a peak transient current larger than the final dc value at the emitter edge and 3) the charge storage time derived from the transient simulation is not necessarily the same as the one derived from the quasi-static method. The latter does not take the nonuniform current distribution into account.