In this paper we show that nickel partially remains in the solid solution after Rapid Thermal Treatments (RTPs), so it can be detected by recombination lifetime techniques such as SPV and Elymat (based on photocurrent measurements). A quantification of nickel contamination based on lifetime measurements is provided. However, partial nickel segregation at wafer surface is observed even in RTPs by surface recombination velocity measurements. As a consequence, the near-surface region is depleted by nickel and a specific thermal treatment with very fast quenching is required to detect nickel in the volume by DLTS. Finally, the results about the electrical activity of nickel in carrier recombination and generation are compared to TOF-SIMS analyses at the oxide-silicon interface and to TEM analyses of nickel precipitates at wafer surface.