Hydrogen flip model for light-induced changes of amorphous silicon

We propose a new metastable defect associated with hydrogen atoms in amorph ous silicon. A higher energy metastable state is formed when H is flipped t o the backside of the Si-H bond at monohydride sites. The defect is describ ed by a double-well potential energy. The dipole moment of this "H-flip" de fect is larger and increases the infrared absorption. This defect accounts for large structural changes observed on light soaking including larger inf rared absorption and volume dilation.