Injection-Stimulated Vacancy Reordering in p-Type Silicon at 76°K

Electron injection into p-type silicon at 76°K has been observed to reduce the lifetime degradation rate due to 60Co gamma irradiation at 76°K. By comparing isochronal annealing data between 76° and 300°K with similar data obtained by Watkins in EPR studies, the lifetime degradation at 76°K is seen to be due primarily to recombination through vacancies. Since the activation energy of motion of silicon vacancies is known to depend strongly on charge state, the injection-stimulated reduction in degradation rate at 76°K has been related to vacancy reordering which occurs when the injected electron density is sufficiently large to modify the vacancy charge state from neutral (mobile above 160°K) to negative (mobile above 60°K). Quantitative estimates of the vacancy-reordering rate in the presence of excess electrons show this model to be consistent with the observed phenomena.