Electronic transport through Si nanowires: Role of bulk and surface disorder

We calculate the resistance and mean free path in long metallic and semiconducting silicon nanowires (SiNW's) using two different numerical approaches: a real-space Kubo method and a recursive Green's-function method. We compare the two approaches and find that they are complementary: depending on the situation a preferable method can be identified. Several numerical results are presented to illustrate the relative merits of the two methods. Our calculations of relaxed atomic structures and their conductance properties are based on density functional theory without introducing adjustable parameters. Two specific models of disorder are considered: Unpassivated, surface reconstructed SiNW's are perturbed by random on-site (Anderson) disorder whereas defects in hydrogen passivated wires are introduced by randomly removed H atoms. The unpassivated wires are very sensitive to disorder in the surface whereas bulk disorder has almost no influence. For the passivated wires, the scattering by the hydrogen vacancies is strongly energy dependent and for relatively long SiNW's (L > 200 nm) the resistance changes from the Ohmic to the localization regime within a 0.1-eV shift of the Fermi energy. This high sensitivity might be used for sensor applications.