Absorption measurements in neutron irradiated silicon

Silicon samples have been neutron irradiated at 76 °K with fluences sufficient to allow measurement of the 1.7 μ divacancy band at 76 °K. The growth of the divacancy concentration and the recovery of the edge absorption were studied as a function of annealing temperature between 76 °K and 550 °K. Immediately after irradiation the divacancy concentration is about 25 per cent of its maximum value which is attained at 330 °K, the temperature at which the divacancies begin to anneal out. Increases in the 1.7 μ band intensity and recovery of the edge absorption can also be achieved at 76 °K by illuminating the sample with intense sub-bandgap light or white light. The experimental results suggest a neutron-induced cluster model in which the cluster is a vacancy-rich region whose annealing characteristics are controlled by the liberation and motion of vacancies. The injection effects can be explained by analogy to the charge state dependent mobility of the Si vacancy.