Electronic state of interstitial Cu in bulk Si: Density functional calculations

Abstract

The behavior of the interstitial Cu atom in an otherwise clean Si crystal has been examined by means of density functional calculations. It is found that Cu basically stays at the tetrahedral site with hardly any electrons promoted from the 3d to the 4sp shells. Our calculations confirm the well-known fact that interstitial Cu in Si donates its 4s electron to the surrounding lattice. The 4s state is found to be very diffuse as the resulting Cu+ ion is effectively screened by the Si environment. When the precision in calculations is lowered, Cu starts moving away from the tetrahedral site. The results of our calculations with atomic-type orbitals emphasize the importance of using a consistent basis set: if Si atoms in the vicinity of the impurity are treated differently from remaining Si atoms and the basis sets are not both sufficiently complete, artificial confinement of electrons will occur.