Gap states in amorphous silicon—dangling and floating bonds

Abstract

It is shown that the primitive intrinsic defects in amorphous Si (a-Si) are threefold- and fivefold-coordinated Si atoms. A variety of experimental and theoretical information indicates that both these defects are likely to play a role in determining the properties of a-Si. Both have localized states in the energy gap. Electron-spin-resonance (ESR) data show that the dominant paramagnetic defect is more likely to be fivefold-coordinated Si (floating bond). A luminescence peak at ∼0.9 eV, on the other hand, is likely to be due to threefold-coordinated Si (dangling bond). In hydrogenated a-Si (a-Si:H), interstitial H (either at a “bond center” or “channel” site) may also have a state in the gap.