Direct Detection of keV-scale Electrons in Single-Photon Avalanche Diode-Based Detectors

Photomultiplier tubes (PMTs), despite being almost a century old, are still the most suitable photodetector for many astroparticle physics experiments, such as neutrino telescopes. One example of such a project is the Pacific Ocean Neutrino Experiment (P-ONE), a proposed deep-ocean neutrino telescope to be deployed off the coast of Canada that will monitor a few cubic kilometers of sea water with thousands of photodetectors. While the baseline design uses PMTs, incorporating single-photon avalanche diodes (SPADs), with their precise photon counting and sub-nanosecond time resolution, could greatly improve the detector pointing resolution. However, the requirements of large photosensitive areas with low single-photon noise levels limits their use. A proposed solution is to use a hybrid photomultiplier tube instead: a PMT where the dynode chain is substituted by a SPAD array. Used in this configuration, SPADs need to directly detect electrons with O(100 eV - 10 keV) energies. Here we present a systematic study of direct electron detection in a prototype SPAD and a commercially available array to guide the design of a SPAD tailored for a hybrid photodetector.