Limitations on injection efficiency in power devices

In this paper the mechanisms of bandgap narrowing, Shockly-Read-Hall (SRH) recombination, Auger recombination, and carrier-carrier and carrier-lattice scattering are included in an exact one-dimensional model of a bipolar transistor. The transistor is used as a vehicle for studying the relative importance of each of these phenomena in determining emitter efficiency in devices with emitter junction depths of 1µm to 8µm. It is shown that band gap narrowing is the dominant influence for devices with shallow emitters of 2µm or less and that SRH recombination dominates for emitter depths greater than 4µm. Calculations are also presented showing the effects of the emitter surface concentration and high level injection on the current gain for devices with emitter junction depths of 1 µm to 8µm. It is shown that there is an optimum surface concentration of cm^-3for the 1µm emitter depth but no optimum under 10²¹cm^-3for devices with emitter depths greater than 4µm.