Radiation damages of silicon avalanche photodiodes in analog mode used in space lidars

Abstract

Silicon avalanche photodiodes (Si APD) in linear mode operation have been used in spaceborne lidars around Mars, Mercury, Earth, and the Moon over the past 25 years. We have been monitoring the space radiation damages to some of these Si APDs over their mission lifetimes. It was found that the Si APD performance degradation depended on the location of the Si APDs inside the lidars and the thickness of the shielding materials around them. The major accumulated radiation effect was found to be the increase of the dark currents. Most of the radiation damage remained after weeks of annealing at room temperature. Heating the devices at high temperature could anneal the radiation damage to certain extent. Recently, the lidar on the Global Ecosystem Dynamics Investigation (GEDI) mission captured many individual pulse waveforms from transient radiation events from the Si APDs. We subsequently conducted a single event effects (SEE) test of a GEDI Engineering Model Si APD using 64 MeV protons to reproduce the anomalous pulse waveforms observed from GEDI in orbit. In this paper, we will present a summary of the Si APD performance monitored from several space lidars developed by and operated at NASA Goddard Space Flight Center. We will also present the laboratory test data from the recent SEE tests.