Quenching of impact ionization in heavy-ion induced electron-hole pair plasma tracks in wide bandwidth avalanche photodetectors

Optoelectronics such as Si avalanche photodiodes (APDs) used in space are subjected to background cosmic radiation including highly energetic heavy ions. As these swift ions pass through a device, they lose energy by promoting free electron-hole pairs. The resultant ionization track is an extremely dense two-component free carrier plasma with submicron radial diameters. Within the track, injected space charge is high enough to severely distort the local electric field, which perturbs the current transient or impulse response induced on the device electrodes. In this paper, the time-resolved ion beam induced current response of a low breakdown bias, high-frequency Si APD has been observed for a sequence of front side irradiations with MeV heavy ions species with different track geometries. These results are compared with focused picosecond laser experiments, where injection levels are controlled from low to high. Ion induced tracks are found to effectively quench the avalanche process. Simulations using Synopsis technology computer aided design are performed to clarify the role of screening in quenching avalanche mechanisms under the conditions prevalent here.