Evaluation of space radiation effects on HgCdTe avalanche photodiode arrays for Lidar applications

We report the results from proton and gamma ray radiation testing of HgCdTe avalanche photodiode (APD) arrays developed by Leonardo DRS for space lidar receivers. The devices were tested with ~60 MeV protons up to 100 krad(Si) without the read-out integrated circuit (ROIC) and 30 krad(Si) with the ROIC. We also measured the transient responses with the device fully powered and the APD gain set to >1000. The detectors output a large current impulse in response to each proton hit, which could saturate the ROIC but recovered within 1 μs. The APD dark currents increased linearly with the proton dose. The quantum efficiency and APD gain decreased slightly with dose. The dark currents due to the radiation damage went up many times after the devices were warmed to room temperature and cooled to 80K again. The radiation damage was found to completely anneal after baking the device at 85°C or higher. These results showed the HgCdTe APD arrays are suitable for use in space lidar for typical Earth orbiting and planetary missions provided that provisions are made to heat the detector chip to 85°C when the system performance is impacted.