Local vibrational modes of impurities in diamond

Local vibrational modes induced by defect complexes involving nitrogen and silicon impurities in different configurations are calculated using Keating potentials in a supercell model. Both the frequency and the vibrational amplitudes of atoms in the complexes are determined for each mode. It is found that defect complexes involving interstitial impurities produce high-frequency localized modes and substitutional impurities produce low-frequency quasilocalized modes. The bond-center Si interstitial is found to have higher lattice energy than the substitutional Si-vacancy pair complex, and hence is less stable. Suggestive atomic models are given based on the present calculations.