Study of the radiation-induced damage mechanism in proton irradiated low gain avalanche detectors and its thermal annealing dependence

In this study the effects of proton irradiation and annealing on Low Gain Avalanche Detectors (LGADs) are investigated. Two LGADs and one p-in-n diode, produced by CNM (Centre Nacional de Microelectrònica 2018), were irradiated with 24 GeV∕c -protons to a fluence of 1×10$^{14}$n$_{eq}$∕cm$^{2}$ and annealed at 60°C for up to 5000 min . The sensors have an active area of 3×3mm$^{2}$ and a thickness of 277 $\mu$m . Current– and capacitance–voltage measurements, as well as laser measurements using the transient-current-technique were carried out to study the change of gain and the electric field after irradiation and consecutive annealing steps. The reduction of gain after irradiation is the main concern when using LGADs in high energy physics experiments. After annealing the sensors, no recovery of gain was observed. Different ways to measure the gain layer depletion voltage are discussed.