The band-gap energy distribution of Pb centers on oxidized (100) Si wafers has been determined and compared with interface electrical trap density Dit. Two different Pb centers are observed on (100) Si: Pb0, which has the structure ⋅Si≡Si3, and is essentially identical to the sole Pb center observed on (111) Si; and Pb1, of presently uncertain identity, but clearly different in nature from Pb0. By electric field-controlled electron paramagnetic resonance (EPR) and capacitance-voltage (C-V) measurements, it is found that Pb0 has its (0↔1) electron transition at Ev+0.3 eV and its (1↔2) transition at Ev+0.85 eV. Similarly, Pb1 has its (0↔1) transition at Ev+0.45 eV and its (1↔2) transition at Ev+0.8 eV. The Pb band-gap density correlates qualitatively and quantitatively with the electrical trap density Dit from C-V analysis; nonbonded Pb orbitals are found to be the source of about 50% of the characteristic traps in dry-oxidized, unannealed (100) Si wafers.

Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 interface in metal-oxide-silicon (MOS) structures was examined by electric-field-controlled electron paramagnetic resonance (EPR) and capacitance-voltage (C-V) analysis on the same samples. Chips of (111)-oriented silicon were dry-oxidized for maximum Pb and trap density, and metallized with a large MOS capacitor for EPR and adjacent small dots for C-V measurements. Analysis of C-V data shows two Dit peaks of amplitude 2×1013 eV−1 cm−2 at Ev+0.26 eV and Ev+0.84 eV. The EPR spin density reflects addition or subtraction of an electron from the singly occupied paramagnetic state and shows transitions of amplitude 1.5×1013 eV−1 cm−2 at Ev+0.31 eV and Ev+0.80 eV. This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ⋅Si≡Si3 is a major source of interface electronic traps in the 0.15–0.95 eV region of the Si band gap in unpassivated material.

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We report the observation of both silicon and nitrogen paramagnetic defect centers using X-band and Q-band electron spin resonance microwave excitation frequencies. By using two different microwave frequencies along with a computer analysis of the resonance lineshapes, we have been able to confirm and extend earlier observations regarding the chemical identity of these paramagnetic defects. Specifically, we provide additional evidence that the silicon dangling bond, i.e., K center, is an unpaired electron on a silicon atom bonded to three nitrogen atoms in stoichiometric silicon nitride. We further demonstrate that the g tensor of the K center exhibits very little anisotropy and that the lineshape is broadened primarily by hyperfine interactions of the nitrogens bonded to the silicon atom. We also confirm that the recently observed nitrogen dangling-bond resonance in silicon nitride is indeed due to a hyperfine interaction with a nitrogen nucleus. This improved understanding of these two important paramagnetic defects may be of importance in eliminating or perhaps exploiting their chemical properties.