On the local structure of optically active Er centers in Si

We report high resolution (<0.05 cm^-1) photoluminescence (PL) spectra of erbium implanted float-zone (FZ) and Czochralski grown (CZ) silicon. We show that the PL spectrum of cubic Er centers observed in CZ-Si annealed at 900°C is the dominant emission in FZ-Si for the same annealing conditions. We assign it to isolated, interstitial erbium. We observe also two other kinds of optically active Er centers with lower than cubic site symmetry: (i) O-related (found only in CZ Si) and (ii) those related to radiation defects. We conclude that coimplantation with light elements does not lead to the formation of Er-codopant complexes, but rather to Er forming complexes with implantation induced lattice defects.