Radiation hardness of high gain avalanche photodiodes

In this paper, we report on evaluation of radiation hardness of deep diffused, high gain avalanche photodiodes (APDs). We have performed experiments on 2 mm × 2 mm APDs to quantify the degradation in performance over a range of particle fluences. Eight APDs were irradiated at the Paul Scherrer Institut (Switzerland) with 72 MeV protons ranging from a fluence of 1 × 10⁸ protons/cm² to 2 × 10¹² protons/cm² with an equivalent 1 MeV neutron fluence of ∼2 × 10⁸ n/cm² to 5 × 10¹² n/cm². The performance parameters measured include quantum efficiency (QE), gain, noise, and leakage current. Cooling and annealing measurements were also performed to explore options for reversing the effects of the damage sites within the APD. Our measurements show that our APDs have a minimal loss of performance in noise and QE up to about 1 × 10¹² n/cm². Beyond this neutron fluence, we see a decrease in QE and increase in noise. We were able to reverse the performance degradation of the higher irradiated APDs with moderate cooling and with annealing at 100°C.