External gettering by P diffusion was applied to interstitial O rich wafers which contained extended crystallographic defects such as dislocations, twins and grain boundaries. It was found that P diffusion sharply increased the minority carrier diffusion length when the O content was lower than 6 x 1017/cm3, but was less effective (or impaired the diffusion length) when the O content was of the order of 1018/cm3. In the latter case, light beam induced current mappings showed that, when extended crystallographic defects were present, the carrier length increased around the defects and decreased in homogeneous regions. It was suggested that the O precipitates which formed in O-rich samples induced an internal gettering which contributed to the cleaning of extended defects (in the same manner as P diffusion) but degraded the carrier length in the grains.

S.Martinuzzi, I.Perichaud: Materials Science Forum, 1994, 143-147, 1629-34