Annealing of multicrystalline wafers in Ar, at temperatures above 700C, irreversibly increased the recombination strength of extended defects. External gettering, when used at the same temperatures, reduced the recombination strength. It was observed that, in light-beam induced current scans at 80K, the contrast of extended defects was enhanced and additional defects were detected. The same features were found initially at 80K, as well as at 300K after annealing. That is, light-beam induced current scans at low temperatures detected so-called sleeping defects. These did not recombine at 300K, but were activated by later heat treatment. The results could be explained in terms of Shockley-Read-Hall statistics, involving the presence of deep and shallow energy levels in the band-gap which were associated with impurity-defect interaction.

Detection and characterisation of 'sleeping' defects in silicon S.Martinuzzi, I.Périchaud, S.McHugo: Solid State Phenomena, 1998, 63-64, 53-60