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Abstract: Co-precipitation of copper and nickel in silicon bicrystals produced by wafer-bonding has been investigated. Transmission electron microscopy and energy-dispersive X-ray analysis show two types of precipitates: copper-rich silicide particles that contain a small partial mole fraction of 5% of nickel and nickel-rich particles containing a partial mole fraction between 15% and 25% of copper. Both types of precipitates are found inside large precipitate colonies typical for copper precipitation in silicon in the absence of nickel co-doping. Thermodynamically these precipitates can be assigned to the known binary metal silicide phases Cu3Si and NiSi2 and a solid solution of a second metal species therein. [Copyright &y& Elsevier]

Abstract: We report temperature-dependent LBIC-measurements on copper–nickel co-diffused Czochralski-silicon bicrystals focussing on the distribution and the recombination properties of the metal-precipitated defects. The samples had been hydrophobically wafer-bonded from two n-type materials with slightly different doping concentration and thermal history. LBIC analyses in cross-section geometry reveal substantially different spatial distributions of metal-related precipitates between the two crystals. This behaviour is explained by oxygen-related microdefects present in one wafer, acting as efficient nucleation sites. A precipitate-free zone was found below the surface but not beneath the bonding interface. At isolated colonies LBIC contrasts in the range of 50% have been observed indicating strong carrier recombination at such defects. [Copyright &y& Elsevier]

Abstract: Multicrystalline silicon materials for photovoltaic applications inherently contain extended defects like grain boundaries, dislocations, microdefects and in some cases also second phase precipitates due to high concentrations of light elements (carbon, nitrogen or oxygen) and transition metal impurities. The latter are known to reduce the minority carrier lifetime and hence should be removed by gettering during solar cell processing. This paper discusses the influence of extended defects on the spatial distribution of copper- and nickel-related silicide precipitates for a model system containing a small angle grain boundary and in one part silicon oxide pecipitates partly associated with punched-out dislocations. Phosphorus-diffusion gettering under conditions of mostly precipitated metal impurities is discussed in terms of quantitative simulations. It is shown that two regimes can be distinguished where gettering kinetics are either limited by precipitate dissolution or phosphorus in-diffusion. Finally, binding of metal impurities to dislocations is considered and its effect on gettering kinetics is illustrated in terms of gettering simulations. [Copyright &y& Elsevier]