  Similar to the enhanced low-dose-rate sensitivity (ELDRS) effect of
ionization damage, an enhanced low-flux senstivity (ELFS) effect has been
reported in ions/neutron irradiation on n-type silicon or PNP transistors.
However, the existing mechanism and simulation dominated by the diffusion
dynamics give much higher transition flux than the experimental observations.
In this work, we develop a new model based on the annealing of defect clusters
for the ELFS effect. Simulations considering Si-interstitial-mediated
inter-cluster interactions during their annealing processes successfully
reproduce the ELFS effect. The ratio of Si interstitials captured by defect
clusters to those dissipating off on the sample edges or re-merging into the
bulk is found as the key parameter dominating the enhancement factor (EF) of
the ELFS effect. We also establish a compact parametric model based on the
mechanism, which is found to provide a good quantitative description of the
experimental results. The model predicts the existence of nonsensitive regions
at sufficiently low and high fluxes as well as a non-trivial fluence and
temperature dependence of the enhancement factor.
