Chemical bonding effect of Ge atoms on B diffusion in Si

We perform first-principles density-functional calculations to study the chemical bonding effect of Ge atoms on the diffusion pathway and migration barrier of a B dopant in Si. The binding energy of a B-Ge pair is extremely small, thus, it is ruled out that the pairing of the B and Ge atoms immobilizes the B atom. When a Ge atom is located in the first neighborhood of a substitutional B, the B impurity is still likely to diffuse via an interstitialcy mechanism by forming a pair with a self-interstitial (I-s) without pair dissociation, similar to that previously suggested in pure Si. We find that the presence of the Ge atom increases the migration barrier by a sizable amount, which can affect the B diffusivity, while the formation energy of the stable I-s-B-Ge complex is little affected. The effect of the Ge atom is most significant in the first neighborhood of the B interstitial, thus, the Ge chemical bonding effect plays a role in the retardation of B diffusion observed in SiGe alloys.