The removal rates of charge carriers from degenerate p-type and n-type samples which had been bombarded with 1MeV and 2.5MeV electrons at 4.7K were studied. The production rate of the primary defects which survived recombination during low-temperature irradiation, as well as the annealing of radiation-induced defects, was considered. In degenerate B-doped material (2 x 1019/cm3), the removal rate of charge carriers during irradiation at 4.7K was high: 1.3 and 4.0/cm at 1 and 2.5MeV, respectively. These removal rates were higher than the production rates that were calculated by using a threshold displacement energy of 40eV (0.6/cm at 1MeV). At irradiation doses of more than about 1018/cm2, an additional non-linear increase in the electrical resistivity was observed. The small fraction of defects which annealed out in degenerate p-type material at low temperatures suggested that isolated vacancies were mainly paired with substitutional B during irradiation at 4.7K. In degenerate n-type material, a much smaller carrier removal rate was observed and, for the first time, it was noted that the production rate of defects substantially increased during low-temperature irradiation. This was thought to be related to changes in the occupancy of defect states that were close to the conduction band. No annealing was observed, below room temperature, in the case of n-type material. Measurements of diffuse X-ray scattering, after room-temperature annealing of samples that had been irradiated to the highest dose, revealed quite similar defect concentrations to those in degenerate n-type and p-type material. These defect concentrations were also quite similar to those in slightly doped Si. These observations represented the first evidence that the low carrier removal rates in n-type Si reflected only the electrical properties of the defects, and not an instability of the Frenkel pairs.

P.Ehrhart, V.V.Emtsev, D.S.Poloskin, H.Zillgen: Materials Science Forum, 1995, 196-201, 151-6