A Two-Dimensional Characterization of Low-Gain Avalanche Diodes for Low-LET Microdosimetry

A low-gain avalanche diode (LGAD) achieves intrinsic gain and is thus of interest for low-linear-energy-transfer (LET) microdosimetry. A novel LGAD device with two geometric configurations was characterized using an ion microprobe with proton energies of 1, 1.8, 3, and 8 MeV as well as carbon ions with an energy of 2 MeV/u using the SIRIUS accelerator at the Australian Nuclear Science and Technology Organisation (ANSTO). A 2-D assessment of charge collection in the device showed distinct regions in the detector with gain and without gain. The gain of the device was characterized for all ion configurations and at different reverse biases. The gain did not monotonically increase with a larger reverse bias and was also observed to reduce with lower proton energies and carbon ions. This is due to an increase of the induced charge density in the device for higher LET ions resulting in charges being screened from the strong localized electric field in the gain layer. Thus, due to the nonlinear behavior of these devices with the deposited energy, a thorough investigation is required for the assessment of these devices for microdosimetry in proton therapy, heavy ion therapy, and space radiation.