Energy Dependence of Neutron Damage in Silicon

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Abstract
The carrier removal produced in 10‐ and 100‐Ω·cm, vacuum‐floating‐zone, n‐type silicon by neutrons from a bare 235U reactor was measured and compared with that produced by 14‐MeV neutron irradiation of the same samples. Carrier removal rates were obtained from conductivity measurements at 283°K following irradiations at 300°K. The measured 14 MeV‐to‐reactor‐neutron‐damage ratio is 2.8±0.5 for the 10‐Ω·cm silicon, and 2.9±0.6 for the 100‐Ω·cm silicon. Very similar isochronal annealing was observed between 300 and 500°K following 14‐MeV and reactor‐neutron irradiation. This suggests that 14‐MeV and reactor‐neutron irradiation produce the same kinds of defects in n‐type silicon. Total scattering cross‐section data for silicon, information on nonisotropic scattering, and the Lindhard model for silicon recoil energy loss to ionization were used to calculate the average energy per cm spent in silicon displacement collisions per incident neutron between 0.2 and 14 MeV. There is general agreement between the calculated energy spent in silicon displacements as a function of neutron energy and the energy dependence of the reported monoenergetic neutron irradiation‐produced carrier removal rates in n‐type silicon. Dividing the predicted energy spent in collisions per neutron‐cm by the carrier removal rate gives an average of 0.85 keV with a standard deviation of 0.38 keV per carrier removed for previously reported monoenergetic neutron irradiations. Using the carrier removal rates measured at 283°K for the 10‐Ω·cm n‐type silicon of this investigation, the average energy spent in collisions per carrier removed is 1.25±0.15 keV for the reactor neutron irradiation and 0.94±0.08 keV for the 14‐MeV neutron irradiation.