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

TL;DR

This study investigates electronic transport in silicon nanowires, comparing numerical methods and analyzing how bulk and surface disorder affect resistance, with implications for sensor technology.

Contribution

It introduces a combined numerical approach to analyze disorder effects in SiNWs and provides detailed insights into how different types of disorder influence conductance.

Findings

Surface disorder greatly affects un-passivated SiNWs.

Hydrogen vacancies cause energy-dependent scattering in passivated SiNWs.

Resistance can shift from Ohmic to localized within 0.1 eV energy change.

Abstract

We calculate the resistance and mean free path in long metallic and semiconducting silicon nanowires (SiNWs) 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: Un-passivated, surface reconstructed SiNWs are perturbed by random on-site (Anderson) disorder whereas defects in hydrogen passivated wires are introduced by randomly removed H atoms. The un-passivated 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 SiNWs (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.