A new metastable defect which was associated with H atoms in amorphous material was proposed. A higher-energy metastable state was formed when H was flipped to the reverse side of the Si-H bond at monohydride sites. The defect was described in terms of a double-well potential energy. The dipole moment of this so-called H-flip defect was larger, and increased the infra-red absorption. This defect accounted for large structural changes which were observed upon light-soaking; including greater infra-red absorption and volume dilation.

Hydrogen flip model for light-induced changes in amorphous silicon R.Biswas, Y.P.Li: Physical Review Letters, 1999, 82[12], 2512-5