P. Palestri et al., A better insight into the performance of silicon BJT's featuring highly nonuniform collector doping profiles, IEEE DEVICE, 47(5), 2000, pp. 1044-1051
This paper investigates the effects of highly nonuniform collector doping p
rofiles on the speed and breakdown performance of silicon bipolar transisto
rs. Monte Carlo and drift diffusion simulation results point out that a thi
n highly doped layer adjacent to the base collector junction can improve th
e 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 o
f this layer.