Carbon related defects and iron distribution in cast-grown polycrystalline silicon

The present cast-grown polycrystalline Si has a significantly larger grain size exceeding 1 cm, which is large enough as compared with the minority carrier diffusion length. Therefore, the grain boundaries do not play an important role in deteriorating the solar cell performances, and the defects and impurities in a grain strongly affect the conversion efficiency. In the region where the minority carrier lifetime was relatively short, there were many etch-pits in the grain. Oppositely, the relatively longer lifetime region had little amount of etch-pits. The carbon concentration was measured by /spl mu/-FT-IR and SIMS. The substitutional carbon concentrations in each region were almost the same as the solid solubility limit at the melting point. SIMS profile indicated that the carbon concentration partly exceeded the solubility limit. The iron distribution was studied by /spl mu/-XRF at Spring-8. Large amount of iron existed at the regions where there were many etch-pits, and also line-shape defects with etch-pits. The structure of iron K absorption edge was scanned in the near edge region to analyze the electrical state of the iron. The result indicated that the some trapped iron existed as an oxidized iron.