Analysis of hyperfine structure in chalcogen-doped silicon and germanium nanowires

Due to the confinement effect, the donor wave functions in nanostructures are highly localized on the defect and can even be deformed by the local geometry of the system. This can have relevant consequences on the hyperfine structure of the defect that can be exploited for advanced electronic applications. In this work we employ ab initio density functional calculations to explore the hyperfine structure of S and Se substitutional defects in silicon and germanium nanowires. We show that, if the tetrahedral symmetry is preserved, the hyperfine contact term is only marginally dependent on the nanowire orientation, while it can undergo drastic changes if the symmetry is lost. In addition, we provide an analysis of the strain dependence of the hyperfine structure for the different orientations of the nanowires.