Saddle-point configurations for self-interstitial migration in silicon

Reaction paths between low-energy configurations of a self-interstitial in crystalline silicon are studied using two methods of sampling and analysis, one of which (the discretized path method) has not been previously applied to studying defect mobility. Given two minimum-energy defect configurations, a discretized path method is shown to provide an efficient means of determining the saddle-point configuration along the reaction path. Conversely, for a known transition state configuration, eigenmode analysis enables one to find the stable configurations that are connected by the saddle. The results, obtained here using the Stillinger-Weber potential model, reveal two basic mechanisms of self-interstitial migration, a jump process involving the center of a distributed self-interstitial and a rotation of the defect configuration about this center. Since the lowest activation energy given by the present saddle-point analysis corresponds to a transition that does not involve the defect configuration of the lowest energy, it suggests that considering the formation and migration components of a defect activation energy separately can be misleading in identifying the dominant mechanism for mobility.