An optical study of defects in silicon irradiated with fast neutrons

Crystals of silicon which were pure, and either monocrystalline or polycrystalline, or were doped with oxygen, or with carbon and oxygen have been irradiated at room temperature with fast neutrons to doses in the range 10 15 -10 20 n 0 cm -2 . After irradiation, measurements were made of the strengths of the induced electronic absorption due to divacancies at 1.7 mu m and that due to band tailing below fundamental edge ( lambda =1.05 mu m) together with the vibrational one-phonon absorption below the Raman frequency omega R (band mode) and intrinsic local-mode features just above omega R . These features were independent of the degree of crystal perfection and the presence of impurities. Annealing studies showed a major stage near 150 degrees C when all the divacancies were lost; the anneal temperature decreased systematically with increasing n degrees dose and was reduced further in the polycrystalline samples, but was unaffected by the impurities.