Modelling of neutron radiation-induced defects in thick low gain avalanche detectors

Abstract Low gain avalanche detectors (LGADs) are poised for deployment in the intense radiation environments of future particle physics experiments. These advanced silicon sensors incorporate an additional moderately doped p + layer (in p-type substrate having n + as the high doping layer) to create a high electric field region, facilitating impact ionisation. This design imparts LGADs with superior timing capabilities, high signal-to-noise ratio, and radiation hardness compared to traditional silicon sensors. Given their application in particle colliders where they are exposed to high levels of charged and neutral hadrons, understanding LGAD behaviour under such conditions is critical to optimise their performance. In this study, we use the Silvaco technology computer-aided design simulation platform to evaluate the performance of neutron-irradiated LGADs against the available measurement results. The simulations incorporate the neutron radiation damage model, previously developed at the University of Delhi for traditional silicon sensors. However, LGADs also exhibit an acceptor removal mechanism, particularly in the gain layer, which is not accounted for in the existing model. Further, a distinctive feature of the LGAD is the importance of charge multiplication or impact ionisation even at small bias voltages. There is a need to optimise the impact-ionisation parameters, both for non-irradiated and neutron-irradiated LGADs. To address this, the present neutron radiation damage model is extended for thick (300 µ m) neutron-irradiated LGAD structures, where the acceptor removal mechanism and optimised impact ionisation model are integrated in the simulation framework. By exploiting the results, these LGAD parameters are optimised to successfully reproduce and explain experimental data for thick LGADs, full depletion voltage ( V FD ) and charge collection (CC). This validation of our model is crucial for optimising radiation-hard LGAD designs, essential for mitigating increased dark current and decreased CC efficiency in high-neutron-fluence environments.