Radiation Tolerance of Proton-Irradiated LGADs

Low gain avalanche detectors (LGADs), silicon sensors with intrinsic charge amplification, are being considered as a possible technology for tracking and timing in the high luminosity upgrade of the CERN Large Hadron Collider. In order to work in such an environment, LGADs must be sufficiently radiation hard. The characterisation before and after irradiation of properties, such as gain, charge collection, spatial homogeneity, space charge, and leakage current, is vital for assessing the performance and viability of LGADs. This paper presents the results obtained from the study of LGADs irradiated with 24-GeV/c protons up to a maximum fluence of $10^{15}~\text{n}_{\text {eq}}/\text{cm}^2$ . The characterisation was performed mainly by means of the transient current technique with red and infrared laser pulses. It was found that the gain decreases with increasing fluence. At a fluence of $10^{15}~\text{n}_{\text {eq}}/\text{cm}^2$ , the charge collected is similar to that of a normal p-i-n diode. Whilst this might be explained by an effective acceptor removal, it was also found that there are clear signs of a double junction in these devices, after irradiation. In addition, the spatial charge collection homogeneity before and after irradiation was evaluated.