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The aim of this study is to prove that vacancy clusters (Vx) are effective at gettering Cu impurities in Si. The structure of V-Cu complexes in Si was determined by positron annihilation spectroscopy, namely positron lifetime, coincidence Doppler broadening, and first-principles calculation. Cu impurities were introduced by ion implantation in Si wafers in which Vx were induced by Si implantation beforehand. By annealing the obtained samples, consecutive reactions between V and Cu were observed: formation of V6Cux complexes at 500 °C, transformation into V2Cuy at 600 °C, and finally decomposition into V and Cu at 700 °C. Our calculations indicate that the V-Cu complexes progressively become more Cu-rich compositions with increasing temperature, as V6Cu form at 500 °C, and transform into V2Cu2 through to V2Cu4 at 600 °C where the formation energy reaches the maximum. [ABSTRACT FROM AUTHOR]