Electron-nuclear double-resonance and electron-spin-resonance study of silicon dangling-bond centers in silicon nitride

We report the first observation of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ nearest-neighbor hyperfine interactions with an unpaired electron on silicon dangling-bond centers, K centers, in silicon nitride generated by ultraviolet or gamma irradiation. We observe this interaction using electron-nuclear double-resonance (ENDOR) spectroscopy. Our results indicate that the unpaired electron’s wave function is (1–3)% localized on each nitrogen atom bonded to the central silicon atom. We find that the hyperfine coupling constant of the nitrogens bonded to the silicon is 4.6 G. Combining our ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ ENDOR results with a computer analysis of ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine spectra obtained in standard electron-spin-resonance measurements, we find that the unpaired electron is approximately 70% localized on the central silicon atom. We also find that the g tensor of the K center exhibits very little anisotropy. Our results unambiguously demonstrate that the K-center defects are silicons bonded to nitrogen atoms with the unpaired spin density primarily on the silicon. This result is of some importance since these centers appear to be the dominant deep electron and hole trapping center in a rather wide variety of silicon nitride films.