High-injection carrier dynamics generated by MeV heavy ions impacting high-speed photodetectors

Abstract

The generation of single event transients generated by the impact of high-energy ions in high-speed photodetectors leads to bit error rate degradation in optical communications in radiation hard environments such as space. High-energy heavy ions, in particular, generate a submicron electron-hole pair plasma with a picosecond temporal profile that results in ultrahigh-injection carrier dynamics which induce large space-charge effects. These space-charge effects disturb the local electric field, thereby determining the peak and duration of a single event transient. In this paper, we examine the transient response of Si p-i-n photodetectors irradiated with focused single MeV heavy ions for a range of ion energies chosen to ensure the same end of range but different average plasma densities. We discuss the role of high-injection effects on the evolving spatiotemporal response with the aid of three-dimensional technology computer-aided design software. The result of both measurement and simulation points to charge collection being dominated by three clearly separable phases: (a) an ultrafast bandwidth-limited response which follows the excitation function, (b) an ambipolar diffusion-dominated expansion phase where space-charge screening limits the extracted current, and (c) a bipolar phase where the external field penetrates the electron-hole pair plasma resulting in rapid collection by drift.