APD Rise Time Measurements for 50–300-keV Ions

In this paper, we report the rise time of three silicon reach-through avalanche photodiodes (APD) when measuring alpha particles and low-energy ions in the energy range from 50 to 300 keV. The APDs were custom manufactured by Hamamatsu Photonics and differ by their doping manufacturing method (p-type or n-type) and their depletion layer thickness (30 or 150 μm). Our findings are summarized as follows: 1) the rise time is largely a function of detector drift layer thickness and 2) the rise time is mostly independent of ion species. The measured rise time values were comparable to ~1.5 ns for the two 30 μm APDs at the operational bias voltages. In combination with the timing electronics, such as constant fraction discriminators, a less than 1-ns response time resolution will be achievable for these APDs. These new findings are valuable for applying APDs for suprathermal particle measurements in space physics, enabling simplified time-of-flight and energy systems, and high count rate applications.