New measurements are presented for multi-stage InGaAs avalanche photodiodes (APDs) which have the potential to
perform GHz-rate single photon counting in linear mode. No increase in dark current was measured for an 11-device
sample of 5-stage APDs following 717 hours of accelerated aging under bias at 50°C, during an initial lifetime study.
Impulse response times of 0.45 ns, 0.9 ns, and 1.1 ns were measured directly for 6-, 8-, and 10-stage APDs, respectively,
operated at a nominal gain of M=10. To assess the suitability of the technology for a NASA optical communications
application, separate samples of 5-stage APDs were irradiated by 1- and 2-MeV protons at the University of
Washington's Center for Experimental Nuclear Physics and Astrophysics (UW CENPA) and by 63.5-MeV protons at
the University of California Davis, Crocker Nuclear Laboratory (UCD CNL). Good agreement between calculated non-ionizing
energy loss (NIEL) and observed damage was found for the low-energy protons at fluences of 1010 and 1011 cm-2. A NIEL calculation successfully predicted the damage observed following a 5×1010 cm-2 dose of 63.5-MeV protons by
extrapolating from 2 MeV data, which suggests that displacement damage is the dominant mechanism.