Structure of Er-O complexes in crystalline Si

The local structure around Er3+ ions in Er+O doped silicon has been investigated by extended x-ray absorption spectroscopy. By comparing samples obtained by molecular-beam epitaxy and ion implantation a common structure comes out. Er is linked to five or six O atoms at around 2.24 Angstrom and there is a well defined Er-O-Si bond angle of 135degrees and an Er-Si separation of 3.6 Angstrom. The Er-Si distance is appreciably longer than that found in the more stable structures from ab-initio calculations and a discussion on the possible site for Er is presented.