Photoconductivity in Neutron-Irradiated p-Type Si

Photoconductivity spectra of p-type silicon after fission neutron irradiation at ∼13°K and isochronal annealing up to 360°K have been measured in the wavelength range 1.2–5 μ. Neutron irradiation increases the photoconductivity in the measured wavelength range. The 3.9-μ photoconductivity band, which has been correlated with the divacancy, appears immediately after the irradiation and starts to grow upon annealing around 170°K. The growth rate becomes rapid around 350°K. The energy level at Ev+0.42 eV, which has been correlated with interstitial dopant atoms, also appears immediately after the irradiation and grows upon annealing in the temperature range 250°–360°K. The results indicate that the neutron damage region is localized, and they are consistent with a model in which the outer part of the region consists of a divacancy-rich region surrounded by an interstitial-rich region. The presence of shallow traps in neutron-irradiated silicon has been assumed in order to explain the temperature dependence of the photoconductivity.