Positron lifetime measurements of wafers showed that the bulk lifetime was 246ps. Most of the samples exhibited a defect lifetime of 287ps, which was attributed to mono-vacancy plus impurity complexes at a concentration of 7 x 1016/cm3. Very heavily doped n-type samples exhibited a defect lifetime of 332 to 340ps. The defects in these samples exhibited di-vacancy characteristics but changed their configuration, at low temperatures, to give a mono-vacancy type of defect. The concentration of these defects was close to 1017/cm3. Both types of defect were stable against rapid thermal annealing at up to 850C, and were neutral. It was suggested that the formation of the di-vacancy type of defect might be related to a discrepancy between the carrier concentration and the total dopant concentration.

J.Mahony, P.Mascher: Physical Review B, 1997, 55[15], 9637-41