Defect states at floating and dangling bonds in amorphous Si

Defect-state wave functions and energies are calculated for dangling bonds and recently proposed "floating bonds" in a-Si, using a Bethe-lattice terminated nine-atom cluster and a tight-binding approach. The dangling-bond state is much more localized than the floating-bond state, consistent with a rigorous result we prove for the wave-function amplitudes. Our results suggest that the D-state electron-spin-resonance signal in a-Si:H arises from dangling bonds.