  We consider the electronic transport properties of phosphorus (P) doped
silicon nanowires (SiNWs). By combining ab initio density functional theory
(DFT) calculations with a recursive Green's function method, we calculate the
conductance distribution of up to 200 nm long SiNWs with different
distributions of P dopant impurities. We find that the radial distribution of
the dopants influences the conductance properties significantly: Surface doped
wires have longer mean-free paths and smaller sample-to-sample fluctuations in
the cross-over from ballistic to diffusive transport. These findings can be
quantitatively predicted in terms of the scattering properties of the single
dopant atoms, implying that relatively simple calculations are sufficient in
practical device modeling
