LAUSR

A defect dynamics model is proposed for the positive synergistic effect of neutron- and gamma-ray-irradiated silicon NPN transistors. The model considers a gamma-ray induced transformation and annihilation of the neutron-induced divacancy defects in the p-type base region of the transistor. The derived model of the base current predicts a growth function of the gamma-ray dose that approaches exponentially an asymptotic value, which depends linearly on the neutron-induced initial displacement damage (DD), and a linear decay function of the dose whose slope depends quadratically on the initial DD. Variable fluence and dose neutron-gamma ray irradiation experiments are carried out, and we find all of the novel dose and fluence dependence predicted by the proposed model are confirmed by the measured data. Our work, hence, identifies that the defect evolution under gamma-ray irradiation, rather than the widely-believed interface Coulomb interaction, is the dominating mechanism of the synergistic effect. Our work also paves a way for the modification of displacement defects in silicon by gamma ray irradiation.