Quantitative analysis of EPR and electron-nuclear double resonance spectra of D centers in amorphous silicon: Dangling versus floating bonds

We report a quantitative analysis of the EPR and electron-nuclear double resonance (ENDOR) data associated with the D center in amorphous Si and show that they support the recent suggestion that D centers are not dangling bonds (threefold-coordinated Si atoms) as commonly believed but instead are ‘‘floating bonds’’ (fivefold-coordinated Si atoms). The localization properties of the D-center wave function are shown to be significantly different from those of the $P_b$ center at the Si-${\mathrm{SiO}}_2$ interface and from model calculations of dangling bonds. They are, on the other hand, consistent with the predicted properties of floating bonds. We conclude that floating bonds are a stronger candidate for the D center. It is suggested that ENDOR data in ${}_{}{}^{29}{}_{}{}^{}\mathrm{enriched}$ material may provide a further test of this conclusion.