First principles calculations of dopant solubility based on strain compensation and direct binding between dopants and group IV impurities

We investigated binding between dopant atoms such as boron and arsenic and various elements in group IV (e.g., C, Ge, Sn, and Ph) to explore opportunities for increasing dopant solubility, which is becoming critical for nanoscale semiconductor technology. Using first principles calculations, we find the dominant component of binding to be global strain compensation. We find negligible direct local binding between B and Ge, in contrast to some suggestions in the literature. Considering strain compensation and negative deviation from Vegard's law of lattice parameter for SiGe, we predict the enhancement of boron segregation ratio across epitaxial Si/SiGe interfaces, which agrees well with previous experimental observations. Due to nearest neighbor binding plus substantial strain compensation, Sn may have some promise for enhancing B solubility. For C/As, the first nearest neighbor interaction is repulsive. However, the large negative induced strain due to carbon overcompensates this effect in the solubility, and thus As is predicted to weakly segregate from Si into epitaxial carbon-doped Si. (c) 2006 American Vacuum Society.