The effects of emitter region recombination and bandgap narrowing on the current gain and the collector lifetime of high-voltage bipolar transistors

It is shown that the “apparent bandgap narrowing” ΔEgapp in heavily doped silicon, deduced from the electrical measurements on bipolar transistors using minority-carrier mobility values is consistent with the values extracted from the luminescence data. Using an empirical fit to this ΔEgapp as a function of doping and the lifetime model applicable to heavily doped diffused layers, it is demonstrated by numerically computing the current gain of n+-p-ν-n+ transistors that the experimental current gain can be predicted with excellent accuracy. Using these models for estimating the hole current injected into the heavily doped emitter region, it is shown that the observed dependence of collector lifetime of high-voltage transistors on the parameters of the emitter region can be adequately explained. High-voltage n+-p-ν-n+ transistors having different emitter junction depths and emitter surface doping concentrations are studied in the present work to compare the experimental results with the theoretical calculations of current gain and collector lifetime. © 1989 IEEE