Hydrogen-mediated model for defect metastability in hydrogenated amorphous silicon

We propose a hydrogen-mediated model for defect metastability in hydrogenated amorphous silicon which associates the creation of paramagnetic defects with the transfer of hydrogen between the dilute and clustered phases of bonded hydrogen. Hydrogen in the clustered phase is predominantly paired on sites which we identify as weak Si-Si bonds when unhydrogenated. An elementary statistical-mechanics calculation based on this model accounts for the observed thermally activated paramagnetic defect density and also rationalizes the changes in spin density observed following electron irradiation and hydrogen evolution.