Exploring the potential of Low Gain Avalanche Detectors for low-energy ion spectrometry

Low Gain Avalanche Detectors (LGADs) have emerged as key sensors for High Energy Physics and related applications due to their excellent time resolution and enhanced signal-to-noise ratio. However, their use in low-energy ion spectrometry has generally been limited by gain suppression effects, arising from the high ionization densities produced by such ions within the multiplication layer, which leads to a reduction of the gain and a non-linear detector response with ion energy. In this work, we investigate an alternative detection configuration aimed at mitigating this effect by shifting the region of highest ionization density away from the gain layer. Alpha spectrometry measurements in the energy range 3-9 MeV were performed by irradiating the detector from both the frontside (multiplication layer side) and the backside of the devices. Additionally, potential gain suppression effects when the detected particles are photons were evaluated using an X-ray tube operated at 40 kV, with irradiation from both the front and back sides. The results show that backside irradiation leads to a higher and more uniform gain and a linear relationship between generated charge and alpha particle energy. In particular, a gain of 3-4 is obtained for backside irradiation, while a nearly constant gain of ≈ 2 is achieved for frontside irradiation. In addition, the achieved energy resolution (1%–2%) is comparable to that of standard PiN detectors fabricated under the same conditions. Finally, the gain response to X-rays was found to be very similar to that observed for alpha particles, suggesting that no gain suppression is observed in the studied LGADs for backside irradiation. These findings demonstrate the potential of LGADs for low-energy ion spectrometry, particularly in applications where low deposited energy makes enhanced signal-to-noise ratio a critical advantage.