8-, 3.3-, and 3.9-μ Bands in Irradiated Silicon: Correlations with the Divacancy

The annealing behavior and the uniaxial stress response of the radiation-induced defects causing the 1. 8-, 3. 3-, and 3. 9- infrared absorption bands were studied after 45-MeV-electron and fast-neutron irradiation. The results indicate that these three bands all arise from the same defect. The defect exhibits two kinds of stress response, as evidenced by the dichroism induced in the bands: one due to electronic redistribution and the other due to atomic redistribution among the allowable orientations. We determine that the defect has an atomic symmetry along a 〈111〉 direction and a transition dipole close to a perpendicular 〈110〉 direction. The activation energies for atomic reorientation and for annealing of the defect are the same, about 1. 2 eV. Correlation of these results with the previous EPR studies indicates that the defect giving rise to these bands is the divacancy. Using the one-electron molecular-orbital model deduced for the divacancy from the EPR studies, some suggestions are given as to the nature of the optical transitions involved.