Tight-binding molecular dynamics calculations were used to study the spatial extent and time-scale of the structural relaxation which followed a change in the charge state of dangling bonds in hydrogenated amorphous material. The structural relaxation was found to be local, and involved mainly large displacements (more than 0.01nm) of the nearest neighbors of the dangling bond and of a few nearby H atoms. The calculated optical transition levels had the D- level below both the D0 levels, and the D+ level above the D0 levels. A smooth energy surface was found for transitions between the neutral and charged dangling-bond configurations. Molecular dynamics simulations showed that the electron levels relaxed within tens of ps, following electron capture or emission by a dangling bond. However, large oscillations of the gap levels could be present as a result of a strong coupling between the charge and the local structure. The results did not appear to support the Cohen-Leen-Rasmussen slow relaxation model or the Branz-Fedders D structural memory model.

R.Biswas, Q.Li, Y.Yoon, H.M.Branz: Physical Review B, 1997, 56[15], 9197-200