Investigating irradiation effects and space charge sign inversion in n-type Low Gain Avalanche Detectors

Abstract: Low Gain Avalanche Detectors built on n-type substrate (nLGADs) have been developed by IMB-CNM to enhance the detection of low-penetrating particles, with a wide range of applications from medicine, industry to synergies with developments for high-energy physics (HEP). In this work, irradiation effects on nLGADs were investigated through proton irradiation at the CERN PS-IRRAD facility up to proton fluences of $10^{14}\,\mathrm{cm}^{-2}$. Electrical characterization before and after irradiation reveals space charge sign inversion of the n-type bulk, leading to significant modifications in the depletion behavior and electric field distribution. Utilizing UV TCT and TPA-TCT measurements, the impact of irradiation on the electric fields and the gain are studied in more detail, confirming a change of sensor depletion and a reduced electric field in the gain layer. The results suggest that donor removal in nLGADs is stronger pronounced already at lower fluences compared to acceptor removal in traditional p-type LGADs. These findings provide not only first insights into the effects of irradiation on nLGADs but also contribute to the development of methods to quantify the donor removal.