Donor levels in Si nanowires determined by hybrid-functional calculations

The accurate determination of doping levels is critical in the optimization of devices. However, the experimental identification of these levels in thin nanowires is not straightforward, while the accurate calculation of these ionization energies is challenging. We study typical donors in 110 and 111 silicon nanowires, showing that (i) the donor wave function is highly localized in the quantum confinement regime; (ii) there is a simple connection between the hyperfine constant and ionization energy; (iii) the ionization energies are deeper than those obtained within standard density-functional theory, though the difference decreases for larger wires; (iv) the doping efficiency for diameters d>10 nm is comparable with that of bulk silicon at room temperature. © 2009 The American Physical Society.