Evaluation of GaAs FETs for cryogenic readout

Low-frequency, low-noise, low-power cryogenic electronics to read out photodetectors is being investigated for the star-tracking telescope of the Gravity Probe B spacecraft. We report our initial findings from evaluating more than 20 types of GaAs FETs, both commercial and non-commercial, for this application. Most exhibit useable dc characteristics at cryogenic temperatures, although gate leakage and hysteretic effects (presumably due to charge trapping) could be troublesome. Low-frequency noise (based primarily on grounded-gate measurements) at 4 K is '1/f-like' and for the quietest GaAs FETs appears to be at least as low as the lowest noise values reported for Si MOSFETs at 4 K. Further investigation is needed in several areas.