First principles study of As-vacancy interaction and the ring mechanism of diffusion in the presence of Ge in Si

We performed first principles calculations to study the As-vacancy interaction and the ring mechanism of diffusion in the presence of Ge in Si in neutral and positively charged states. We discovered that the vacancy barrier decreases substantially when the vacancy hops around the ring. We believe that this indicates that the existence of As atoms can lower the vacancy migration barrier. The vacancy migration barrier is also decreased when Ge atoms are present in the vicinity. We made calculations on the As-vacancy ring mechanism in crystalline Ge and found that the formation energy and migration barriers of the vacancy are smaller than those in crystalline Si. These results support our conclusion that As diffusion can be enhanced by the presence of Ge, and provide physical insight into As diffusion in Si1-xGex.