Four-copper complexes in Si and the Cu-photoluminescence defect: A first-principles study

Complexes containing four Cu impurities in Si are systematically investigated using density functional theory. The complexes include various combinations of substitutional and interstitial copper. The structures, formation and binding energies, approximate gap levels, and vibrational spectra are calculated and the results compared to the measured properties of the Cu_PL defect. The best candidate out of those investigated is the Cu_s1Cu_i3 complex recently proposed by Shirai. The estimated positions of the gap levels of Cu_s1Cu_in, with n=0,...,3, suggest a straightforward explanation as to why only the defects Cu_s and Cu_s1Cu_i3 occur in high-resistivity material.