Though copper can be quenched interstitially inp-type silicon, it precipitates completely within 10–15 h at room temperature. The decay of concentration of interstitial copper inp-Si was monitored by capacitance–voltage characteristics(C–V)and surface photovoltage (SPV). It is shown that the time constant of change of minority carrier diffusion length, as measured by SPV, correlates well with the precipitation of interstitial copper. The capture cross section of interstitial copper is estimated to be in the range10−15–10−17 cm2.It is shown that interstitial copper is far less deleterious than iron and can limit the diffusion length of commercialp-Si wafers only if its concentration is above1013 cm−3.However, copper precipitates may be detrimental to lifetime even for much lower copper concentrations. ©1997 American Institute of Physics.