Analysis of BJT’s, Pseudo-HBT’s, and HBT’s by Including the Effect of Neutral Base Recombination

An analytical study of the effect of neutral base recombination on various transistor performance characteristics is presented. Using an approximate life time model which is suitable for BJT’s, pseudo-HBYs, and HBT’s with small variations in bandgap, closed form analytical relations for common emitter current gain, Early voltage and base and emitter delay times are derived including the effect of neutral base recombination. The relations show that the current gain 3 and Early voltage 1-4 and, as a result, the figure of merit current gain-Early voltage product ( j1-1) drop rapidly as the recombination increases. They also show that emitter delay time increases with an increase in the neutral base recombination while base delay time decreases though these delay times are not strong function of neutral base recombination. Computer simulations (MEDICI) are also shown for comparing with analytical results.