Optical centers and oxygen in Er-ion implanted silicon

Systematic photoluminescence (PL) studies of silicon co-implanted with erbium and oxygen are presented. We find a strong dependence of PL spectra on the ratio of O/Er. For samples with Er peak concentration of 1 × 10¹⁹ cm^-3, annealed at 800°C, the well-defined Er luminescence spectra arising from Er³⁺-centers with cubic site symmetry have been observed to dominate the PL spectra in the O/Er ratio of one to two. In addition, Rutherford backscattering spectrometry (RBS) and channeling measurements revealed significant recovery of the crystal quality in the same O/Er ratio. In the O/Er ratio larger than 5, other lines emerge in the PL spectrum, and the PL from cubic symmetry centers decreases in intensity. We suggest that the origins of optical centers with cubic site symmetry are Er³⁺ ions in tetrahedral sites coupled with O, while oxygen aggregation around Er ions becomes predominant in the O/Er ratio larger than 5.