Scanning infra-red microscopy, mapping, Fourier transform infra-red spectroscopy, and minority carrier diffusion length measurements were combined in order to study precipitates in annealed wafers of Czochralski material and to evaluate their recombination strength; with or without metallic contamination. The effect of P diffusion was also investigated. After 2-step annealing (750C, 16h; 900C, 24 or 96h), scanning infra-red microscopy revealed the presence of precipitates, while light beam-induced current mapping indicated a ring-like distribution of recombination centers and minority carrier diffusion length collapses to 2. The presence of Cu contamination did not significantly modify these observations when precipitates formed. The occurrence of P diffusion near to the surface shrank the precipitates which were revealed by MIRB, but did not suppress the ring-like patterns which were seen in light beam-induced current maps, and slightly increased the carrier diffusion length. The results suggested that the recombination strength of precipitates did not depend upon metallic decoration, but was more likely to depend upon interfacial states between the precipitates and the host crystal, or upon associated extended defects.

C.Veve, N.Gay, M.Stemmer, S.Martinuzzi: Journal de Physique III, 1995, 5[9], 1353-63