Hydrogen-mediated models for metastability in a-Si : H: role of dihydride bonding

Two hydrogen-mediated models for defects in hydrogenated amorphous silicon (a-Si:H) based on hydrogen pairing have previously been proposed. One model based on the clustered hydrogen phase detected by nuclear magnetic resonan ce accounts well for several near-equilibrium properties, and in particular for the defect creation during hydrogen effusion. The second model based o n hydrogen-collisions forming metastable pairs at arbitrary sites accounts for aspects of light-induced generation of metastable defects. We describe a unified model subsuming both the clustered-phase and hydrogen-collision m odels. The model is based on sites which bond two pairs of hydrogens. We di scuss evidence that the site may be involved with dihydride bonding observe d by infrared absorption spectroscopy. (C) 2000 Published by Elsevier Scien ce B.V. All rights reserved.