Positron lifetime measurements were made of as-grown and deformed monocrystalline samples. The bulk lifetime of positrons was deduced to be 253ps. A defect lifetime of 300ps was found in wafer material and in annealed bulk material. This lifetime corresponded to electrically neutral complexes, with a mono-vacancy nature, which existed in concentrations that ranged from moderate, to high, multiples of 1016/cm3. Clustering of these vacancy-type complexes into small voids occurred only after high-temperature pre-deformation of the samples. These larger clusters annealed out in a broad stage at temperatures of between 400 and 650C.

J.Mahony, G.Tessaro, P.Mascher, H.Siethoff, H.G.Brion: Materials Science Forum, 1995, 196-201, 1449-54