Ab initioinvestigation of boron diffusion paths in germanium

Abstract

Experimental data indicate that boron diffuses very differently in Ge than in Si. To examine the kinetics of boron diffusion, density functional calculations were performed on a variety of boron diffusion mechanisms, including interstitial and vacancy-mediated paths, as well as a correlated exchange mechanism. It was found that although vacancy and correlated exchange mechanisms possess high diffusion barriers comparable with experiment, the barrier for interstitial-mediated diffusion lies around $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and is similar to those found for boron diffusion in Si. This estimate is well below the experimental activation energy. The difference is attributed to the failure of the theory to include the effect of electronic excitations.