It was recalled that experiments had shown that B diffusivity decreased rapidly as the Ge concentration was increased to 40%, but that the cause of this decrease remained unclear. Here, an ab initio derived energy database was used to fit classical potential models in order to simulate B diffusion in SiGe on larger lengths and time-scales than were possible by using ab initio models. A set of Stillinger-Weber potential parameters for Ge-B and Si-Ge-B was constructed here which permitted the molecular dynamics study of B diffusion in SiGe alloys. Molecular dynamics simulations of B diffusion in Si, as compared to that in SiGe alloys, suggested that differing trapping mechanisms predominated. That is, the B in Si was trapped in substitutional positions, whereas the B in SiGe alloys was trapped in interstitial positions. The number of B interstitials increased as the Ge concentration increased, reached a maximum at 50%Ge, and then decreased as the amount of Ge increased to 100%. At the same time, the number of Si/Ge interstitials followed the opposite trend. That is, their numbers decreased, reached a minimum at 50%Ge and then increased again as the Ge concentration increased. This confirmed ab initio predictions and provided insights into the origin of retarded B diffusion in SiGe alloys.

Molecular Dynamics Simulations of Boron Diffusion in SiGe. L.Wang, P.Clancy: Journal of Applied Physics, 2004, 96[4], 1939-46