Divacancy in silicon: Hyperfine interactions from electron-nuclear double-resonance measurements. II

The Si-$G7$ EPR spectrum, which is attributed to the negative charge state of the divacancy in silicon, was investigated by electron-nuclear double resonance. Hyperfine interactions between the unpaired defect electron and various ²⁹Si nuclei were determined to obtain detailed information about the electron wave function. A total number of 33 hyperfine tensors was determined, of which 20 belong to a general class shell of atoms and 13 to a mirrorplane class shell. In this way the divacancy electron was probed in a region containing more than 100 lattice sites around the defect. Most hyperfine tensors exhibited approximate axial symmetry, a majority of these having their axial direction along a $〈111〉$ crystal bond direction. An analysis of the interactions is given, using a wave function that is a linear combination of atomic orbitals. From a further theoretical approach of the defect wave function, using extended H\"uckel theory, preliminary results are given. In their discussion data from the positive divacancy are also included. In agreement with previous conclusions, the largest general class and mirrorplane class interactions were identified with the nearest-neighbor shells of both types. Further matching between hyperfine tensors and specific shells of lattice sites could not yet be made.