Entropic Influence on the Aggregation Physics of Interstitial Point Defects in Silicon

The evolution of self-interstitials and their aggregates during the annealing of ion-implanted silicon has received a tremendous amount of attention because of their strong, non-linear effects on the diffusion of dopants. The implantation process leads to extensive lattice damage, which must be healed by thermal annealing. Also generated by the implantation process is a large number of self-interstitials which lead to enhanced dopant diffusion during annealing known as Transient Enhanced Diffusion, or TED. A major obstacle to understanding and quantitatively predicting TED is the formation of a variety of self-interstitial aggregates, which range from small amorphous three-dimensional clusters, to planar stacking-faults with various crystallographic orientations. In the present study, we use large-scale constant-stress MD simulations to dynamically simulate the evolution of an ensemble of highly supersaturated self-interstitials at various temperatures and pressures. We show that the simulated interstitial clustering into various types of planar structures exhibits a complex thermodynamic-kinetic phase diagram that is sensitively controlled by entropic factors. The observations are studied with a recently developed approach that maps out the potential energy landscape in the vicinity of the defect cluster and allows for the total (classical) free energy to be analyzed.