It was found that the density of paramagnetic defects in hydrogenated tetrahedral amorphous material, and the Urbach slope of the optical absorption edge, could be reduced by annealing at 300C; with little effect upon the optical gap. This led to a reduction in the dark conductivity, and to an increase in the photosensitivity. The effect was attributed to the migration of H through the C-C network; permitting better passivation of dangling bonds, and a modification of the more weakly-bonded sp2 clusters with narrower local band-gaps.

Reduction in Defect Density by Annealing in Hydrogenated Tetrahedral Amorphous Carbon. N.M.J.Conway, A.Ilie, J.Robertson, W.I.Milne, A.Tagliaferro: Applied Physics Letters, 1998, 73[17], 2456-8