First-principles density-functional calculations were used 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 was extremely small. Therefore, it was ruled out that pairing of the B and Ge atoms immobilized the B atom. When a Ge atom was located in the first-nearest neighborhood of substitutional B, the B impurity was still likely to diffuse via an interstitialcy mechanism by forming a pair with a self-interstitial (Is) without pair dissociation; similar to that previously suggested for pure Si. It was found that the presence of the Ge atom increased the migration barrier by a sizable amount, which could affect the B diffusivity, while the formation energy of the stable Is-B-Ge complex was little affected. The effect of the Ge atom was most significant in the first-nearest neighborhood of the B interstitial. Therefore, the Ge chemical bonding effect played a role in the retardation of B diffusion observed in SiGe alloys.

Chemical Bonding Effect of Ge Atoms on B Diffusion in Si. J.Bang, J.Kang, W.J.Lee, K.J.Chang, H.Kim: Physical Review B, 2007, 76[6], 064118