Thermal stability of defects in plastically deformed silicon studied by positron lifetime spectroscopy

Defects in phosphorus-doped float-zone silicon single crystals plastically deformed at 800 degrees C were studied by the positron lifetime technique. The lifetime measurements were performed for the undeformed, as-deformed and all annealed samples at temperatures varying from 20 K to 300 K. Three kinds of defects including vacancy clusters, dislocation-bound vacancies and undisturbed dislocations are induced by deformation. It is proposed that the dislocation could be charged and this was well proved by fitting the experimental positron lifetime with all possible positron trapping models. The fitted results indicate that during the annealing process dislocation-bound vacancies are quite stable and they cannot be annealed out until a thermal treatment at 1300 degrees C, when the negatively charged dislocation acts as shallow positron traps which influence significantly the measured average positron lifetime. The density of the dislocation line decreases unconspicuously below the annealing temperature of 1000 degrees C, and the transition rate between the related defects of the dislocation line and vacancies is almost constant.