NOBLE-GAS-RELATED DEFECTS IN SI AND THE ORIGIN OF THE 1018 MEV PHOTOLUMINESCENCE LINE

The implantation of noble-gas ions in Si results in the appearance of photoluminescence centers that are closely associated with the intrins ic-defect luminescence at 1018 meV. We present the results of a theore tical study aimed at identifying these defects. The calculations are p erformed in molecular clusters at the ab initio and approximate ab ini tio Hartree-Fock levels. Our predictions are as follows. (i) Interstit ial noble-gas impurities are not associated with the luminescence and their activation energies for diffusion are large. (ii) Noble-gas atom s do not become substitutional, but are strongly repelled by vacancies instead. This suggests an unusual vacancy-enhanced diffusion mechanis m. (iii) Noble-gas-divacancy complexes are very stable and their calcu lated properties show them to be excellent candidates as the defects r esponsible for the noble-gas-related photoluminescence. (iv) Larger va cancy aggregates (up to the hexavacancy) cannot be responsible for the observed luminescence, although the formation of a hexavacancy-noble- gas complex could nicely explain the disappearance of the luminescence at higher temperatures. (v) Our results imply that the 1018-meV line is due to the neutral divacancy.