Question

True or False? I found it true but < WHY > ?

A BJT with doping concentrations of Ne= Nc = 10^18 cm-3, and Nb=10^16 cm-3, with a very narrow base can potentially have a high current gain but will for sure have a low output resistance.

Answer 1

Yes Its true .. The intention for a narrow base is to avoid recombination of minority charges being injected by the emitter , so that they can be swept away at by the high electric field prevalent in the CB junction , and thus we see amplification The more we reduce the base width the less recombination occurs and helps increase the amplification factor But there's a limit to this . By reducing the base width to a considerable width we see base width modulation , an effect seen due to increase in reverse bias of CB junction. Reducing beyond that would give so much acceleration to the electrons that they would strike other atoms and create newer e-h pairs that would create further e- h pairs and thus reduce the output resistance causing breakdown ·