We report on a high-resolution photoluminescence and absorption study with the application of external stress and magnetic fields on the 0.97-eV ($G$) line. We determine the symmetry of the related center to be monoclinic $I$. It is shown that satellite lines $E$, $E^{\prime }$, and $E^{*}$, which are observed in luminescence or absorption, are local modes of the $G$-line center. The low-energy local modes $E$ and $E^{\prime }$ both exhibit isotope effects upon ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ implantation of the Si samples. The doublet structure due to ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ gives evidence that one substitutional carbon atom is incorporated in the complex. We observe a nonthermalizing and stress-independent triplet structure of the $G$ line in luminescence as well as in absorption with intensities almost identical to the natural abundances of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$. This establishes our basic model of substitutional carbon atom interacting with a single silicon atom, ${\mathrm{Si}}^{*}$, in a prominent position. Relaxation of the complex leads to a symmetry lowering from a trigonal $〈111〉$ defect configuration to a monoclinic $I\left(C_{1h}\right)$ symmetry with a (110) mirror plane. Two particular models are discussed in detail, one being a ${\mathrm{C}}_S-{\mathrm{Si}}_I$ dumbbell having relaxed off a bond-centered $〈111〉$ position, the other being a carbon-vacancy complex similar to the electron-paramagnetic-resonance $\mathrm{S}\mathrm{i}-E$ center.

• Received 23 June 1981

DOI:https://doi.org/10.1103/PhysRevB.24.5874