Uniaxial stress study of photoluminescence defects created by noble-gas implantation into silicon

We report uniaxial stress measurements on the $I_1$ photoluminescence spectrum in silicon at 1.0182 eV associated with a multivacancy or self-interstitial complex, and on similar spectra arising from modifications of the $I_1$ defect by implantation of the noble gases He, Ne, Ar, Kr, and Xe. The splittings are in all cases due to orientational degeneracy effects and all defects belong to the $C_{3v}$ symmetry group except the Xe defect which has tetragonal symmetry. In the former cases, the splitting rates are unusually small and highly nonlinear even at stresses as low as 100–200 MPa. We give evidence for excited states and suggest that they are mixed by the stress with the optical ground states causing the nonlinearities. It is concluded that the lack of electronic degeneracy—obvious from the present stress measurements and recent Zeeman data—is due to large internal local strains around the defects. Thermal dissociation energies of ≊50 meV are found for all of the defects. The line shifts under temperature variation do not follow the band-gap shift as is characteristic of deep defects.