Noise effects in bipolar junction transistors at cryogenic temperatures: Part II

In Part II of this investigation, a characterization of the output noise current generator i
0
of modern planar bipolar junction transistors (BJT's) for common-base configuration with the input ac open circuited is developed and verified at temperatures ranging from 60 to 300 K. It is shown that at low temperatures, for those devices where recombination processes in the emitter-base space-charge region become very pronounced, the resulting noise for these processes shows less than full shot noise. This noise reduction can show up at temperatures slightly below room temperature for such devices. (Generation-recombination effects described in Part I may still become important at temperatures below 110 K.) Also, it is demonstrated that an important parameter to monitor in taking these measurements, at least at low temperatures, is the alpha cutoff frequency fα if the low-frequency theory is to be realized.