Thesis presented December 07, 2005

Abstract:
This work is a numerical study of point defect diffusion in semi-conductors such as Si and SiGe. As macroscopic gradients of concentrations are the result of atomic moves, a multi-scale approach can be used.
Ab initio calculations are highly useful when investigating atomic interactions, and, when linked with geometric minimization algorithms they give access to stable and transition states. The macroscopic movement can then be simulated using kinetic Monte Carlo calculations.
We detail, in this work, the geometry and the energetic cost of most stable points defects of Si and SiGe. This includes vacancies, dumbbell [110] interstitials, hexagonal interstitals and four-folded coordinated defects. We study their movements and use this information in thermodynamical simulations to show that several regimes exist for the diffusion, depending on the interactions between mediators. In the case of the vacancy assisted diffusion, the differences observed in diffusivity are explained by the existence of the di-vacancies and their dissociation mechanisms.
This study shows that the coupling between atomistic and macroscopic simulations is required to explain diffusion mechanisms.

Keywords:
Point defect, semi-conductor, silicon, vacancy, interstitial

On-line thesis.