Cu0*: A metastable configuration of the {Cus,Cui} pair in Si

First-principles theory shows that the substitutional-interstitial copper pair in Si (Si-Cus Cui) has a metastable state with Cui very near a tetrahedral interstitial site in a trigonal Cus-Si Cui configuration that exhibits three low-frequency pseudolocal vibrational modes. The lowest of them, at 40cm-1, has A1 symmetry and is the likely source of the phonon sidebands observed at 52cm-1 in the photoluminescence band of a defect known as Cu0*.