Environmental effects on dangling and floating bonds in amorphous Si

Since bond angles in a-Si have distortions of order 10°, we have calculated defect state wave functions and energies for numerous configurations of non-ideal dangling and floating bonds in a-Si using Bethelattice terminated clusters and a tight-binding approach. We find that energy eigenvalue for the dangling bond is highly dependent on deviations from ideality while the wave function amplitudes are much less so. Exactly the opposite holds for the floating bond. These results are consistent with experimental data if one assumes that the defect state is a dangling bond but is inconsistent with the assumption of a floating bond.