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 CuPL defect. The best candidate out of those investigated is the Cuₛ₁Cuᵢ₃ complex recently proposed by Shirai et al. [J. Phys: Condens. Matter 21, 064249 (2009)]. The estimated positions of the gap levels of Cuₛ₁Cuᵢₙ, with $n=0,...,3$, suggest a straightforward explanation as to why only the defects Cuₛ and Cuₛ₁Cuᵢ₃ occur in high-resistivity material.