Origin of the ESR signal withg=2.0055 in amorphous silicon

Defect-state wave functions for threefold- and fivefold-coordinated Si atoms in amorphous silicon clusters have been calculated with use of a first-principles linear combination of the atomic orbitals method in order to clarify the origin of the ESR signal with g=2.0055 in amorphous silicon. The wave function of the defect state originating from the threefold-coordinated Si atom is strongly localized on this atom. On the other hand, that for the fivefold-coordinated Si atom is extended on this atom and its nearest neighbors. By comparing these results with the observed hyperfine structure of the ESR signal, we conclude that the origin of this ESR signal is the threefold-coordinated Si atoms.