Activated mechanisms in amorphous silicon: An activation-relaxation-technique study

At low temperatures, dynamics in amorphous silicon occurs through a sequence of discrete activated events that locally reorganize the topological network. Using the activation-relaxation technique, a database containing over 8000 such events is generated, and the events are analyzed with respect to their energy barrier and asymmetry, displacement and volume expansion/contraction. Special attention is paid to those events corresponding to diffusing coordination defects. The energetics is not clearly correlated with the displacement, nor with the defect density in well-relaxed configurations. We find however some correlation with the local volume expansion: it tends to increase by about 4eV/^3. The topological properties of these events are also studied; they show an unexpectedly rich diversity.