Characteristics of gain degradation in proton irradiated Low Gain Avalanche Detectors

Low Gain Avalanche Detectors (LGADs) provide high time resolution at moderate charge gain, making them essential for high-energy physics experiments, such as those at the High Luminosity Large Hadron Collider. However, their performance is significantly impacted by radiation induced defects, particularly at high hadron fluences. This study is devoted to the characterization of degradation mechanisms in LGADs irradiated with 24 GeV/c protons at fluences ranging from 10 12 to 10 16 cm -2 . Carrier lifetime ( τ R ) variations examined using the microwave probed photoconductivity transients revealed a significant reduction of τ R from >10 μs in non-irradiated samples to <1 ns at the highest fluence irradiated sensors, indicating increased densities of defects acting as deep-level recombination centers. Photoionization and deep level transient spectroscopy techniques have been employed to identify radiation induced defects. The impact of these defects on the electric field distribution and internal gain in LGADs was comprehensively analyzed using Synopsys TCAD Sentaurus and MATLAB simulations. The results indicate a substantial reduction in gain from 26 for non-irradiated sensors to a negligible its value for 10 16 cm -2 fluence irradiated LGADs due to a simultaneous reduction of effective doping concentration, decreased τ R and enhanced trapping. The study provides a versatile methodology for correlating electrical and spectroscopic measurements with defect characterization, offering valuable insights for optimizing LGAD design in radiation-rich environments.