Direct Role of Hydrogen in the Staebler-Wronski Effect in Hydrogenated Amorphous Silicon

We report a hydrogen-related defect that establishes the direct role of hydrogen in stabilizing the silicon dangling bonds created in the Staebler-Wronski effect in hydrogenated amorphous silicon. A specific NMR signal due to paired hydrogen atoms occurs only after optical excitation, exists at an intensity that is consistent with the density of optically induced silicon dangling bonds, and anneals at temperatures that are consistent with the annealing of the optically induced silicon dangling bonds. At this defect the hydrogen atoms are $2.3\pm 0.2Å$ apart.