Gallium-related 0.875-eV photoluminescence defect spectrum in irradiated silicon

The 0.875-eV (Ga1) photoluminescence defect spectrum in gallium-doped irradiated silicon is studied in high resolution and in uniaxial stress and homogeneous magnetic fields. The spectrum exhibits one- and two-phonon Stokes satellites of the no-phonon Ga1 line due to the coupling of quasilocalized vibrational modes of quantum energy {}{ω}=56.3 meV. Temperature-controlled measurements reveal two electronic excited states at energies of 5.1 and 6.0 meV in excess of the upper Ga1 level. These three states are strongly mixed by uniaxial stress resulting in a nonlinear stress response. The symmetry of the defect is determined to be rhombic I (C₂ᵥ) from the linear portion of the stress response. Complicated Zeeman spectra of Ga1 are fully identified as spin-(1/2)--to--spin-(1/2) transitions at a center of C₂ᵥ point-group symmetry. An isotope effect observed in ¹³enriched silicon gives evidence that the optical defect incorporates carbon in addition to gallium. A defect model is discussed on the basis of the experimental results.