Origin of the 0.97 eV luminescence in irradiated silicon

Optical detection of magnetic resonance studies are described for the well-studied optical center with zero phonon line at 0.97 eV in irradiated silicon. Analysis of the S=1 ODMR spin Hamiltonian reveals a low symmetry (C_lh) center and a resolved ²⁹Si hyperfine interaction with a single silicon atom. In a specially enriched ¹³C doped sample we find additional hf interactions with two equivalent carbon atoms. At elevated temperatures, the defect reorients easily from one C_lh distortion to another around a common 〈111t> axis; during this reorientation the spin density remains located on the same silicon atom and the same carbon pair. From these results we construct a model comprising two adjacent (substitutional) carbon atoms and an interstitial silicon atom which has distorted out from a bond-centered position. We conclude that the same defect gives rise to the Si-G11 EPR spectrum when positively charged.