Characteristics of Neutron Damage in Silicon

The production and annealing behavior of the divacancy and the $A$ center in fission-neutron-irradiated silicon was studied by infrared absorption, using the 1.8-, 3.9-, and 12-μ bands. The production rate of the divacancy was found to be high, about 5.7 ${\mathrm{cm}}^{-1\mathrm{}}$, and to be enhanced by the presence of boron (∼2×${10}^{17}$ atoms per ${\mathrm{cm}}^3$), but not by the presence of oxygen (∼1×${10}^{18}$ atoms per ${\mathrm{cm}}^3$). The annealing of divacancies in neutron-irradiated Si required an activation energy of 1.25 eV, as in electron-irradiated Si, indicating that most of the divacancies were removed by diffusion to sinks. The annealing results also indicate that the local defect concentrations in the damaged regions can be as high as ∼${10}^{20}$ defects ${\mathrm{cm}}^{-3\mathrm{}}$, in which the divacancies still retain their individual properties as far as their infrared absorption and annealing properties are concerned. The production rate of the $A$ center was found to be extremely low. The near-edge absorption band was also studied. About 95% of the near-edge band disappeared upon annealing in the same broad temperature range as did the divacancies. From these results, it was concluded that the majority of the total volume in localized damage regions produced by the fission-neutron irradiation of silicon is rich in divacancies and is still crystalline.