The external gettering effect, due to P, was used to improve the electrical properties of polycrystalline wafers. After annealing (900C, 4h), it was found that the effective diffusion lengths of minority carriers attained or exceeded the thickness of the wafers. After annealing at 850C for 4h, the improvements were less marked, and hydrogenation was required in order to obtain the same increase in effective diffusion length. Secondary ion mass spectrometric analyses indicated that the gettered impurities were mainly Fe, Cu, and Ni. Some limited regions of the wafers were only slightly improved. It was found, after chemical etching, that these regions contained a high density of sub-grain. boundaries. A mechanism for the gettering effect was proposed which took account of dissolved impurities in the grains and of impurities which segregated to dislocations. It was suggested that the additivity of the hydrogenation effect might be due to the neutralization of recombination centers which were related to O atoms that were segregated at dislocations.

I.Perichaud, S.Martinuzzi: Journal de Physique III, 1992, 2[3], 313-24