A new model for afterpulsing in neutron irradiated single-photon avalanche diodes

This paper presents a modeling approach to quantify afterpulsing in neutron-irradiated SPADs by combining an established analytical trapping/de-trapping model with trap parameters taken from published defect data and from NIEL displacement-damage scaling, and with the device fields and geometry obtained from numerical device simulation. The model assessment is performed for a 180 nm CMOS SPAD design and the model predicts a 28% increase in afterpulsing probability following exposure to a 1 MeV-neutron equivalent fluence of 4.29 × 10 10 n/cm 2 . The predicted magnitude and the predicted monotonic increase with excess bias are consistent with the afterpulsing levels and bias dependence reported in previous works for CMOS SPADs at comparable displacement-damage levels. A Monte-Carlo uncertainty analysis shows that, although the absolute afterpulsing probability inherits a wide uncertainty from the trap activation energies, the predicted relative increase is robust. The work provides a quantitative framework for predicting afterpulsing in irradiated SPADs, supporting the design of radiation-hardened devices for extreme environments such as space exploration and nuclear instrumentation.