Electronic structure and spectral properties of paramagnetic point defects in Si3N4

The geometric and electronic structure and the optical, vibrational, and magnetic properties of paramagnetic point defects in Si3N4 have been studied by means of ab initio quantum-chemical methods. Using cluster models and gradient-corrected density functional theory or configuration interaction (CI) wave functions, we have studied the N(3)equivalent to Si-. and Si-2=N-. paramagnetic point defects, also known as K-0 and N-0 centers, respectively. The computed ground-state properties, in particular the hyperfine coupling constants of N(3)equivalent to Si-. and Si-2=N-.. the vibrational spectra of the corresponding hydrogenated centers, N(3)equivalent to Si-H and Si-2=N-H, and the valence density of states are correctly described, showing the adequacy of the cluster models used for the study of point defects in silicon nitride. The optical transitions associated with N and K centers have been computed by means of CI calculations. The results are compared with those of the analogous defects in SiO2, the nonbridging oxygen and the E' center, respectively. [S0163-1829(99)12741-3].