A better insight in the performance of silicon bjt's featuring highly non-uniform collector doping profiles

This paper investigates the effects of highly nonuniform collector doping profiles on the speed and breakdown performance of silicon bipolar transistors. Monte Carlo and drift diffusion simulation results point out that a thin highly doped layer adjacent to the base collector junction can improve the device cut off frequency without deteriorating significantly the maximum oscillation frequency and the breakdown voltage, provided the voltage drop across this layer is lower than an effective threshold of approximately 1.2 V. Guidelines are given for choosing the doping, position, and thickness of this layer.