Hole mobility in low-doped silicon nanowires: An atomistic approach

We performed first-principle calculations by the Density Functional Theory in order to study the scattering properties of silicon nanowires with two different crystalline orientations, [100] and [110], and different types of dopants. The nanowire axis orientation is found to have a strong influence on transmission, which can alter the normal behavior of dopants. Boron, a p-type dopant, can act indeed as a strong scatterer in the conduction band of [100]-oriented silicon nanowires. Using Boltzmann transport theory, we calculated the charge mobility of boron-doped silicon nanowires with different diameters. Although the scattering strength is shown to be strongly dependent on dopant locations and wire cross-sectional size, the hole mobilities are rather insensitive. It was found that the doping density and the nanowire width strongly influence the hole mobility. It was also found that in small diameter nanowires scattering by neutral impurities can be quite significant and act as a limiting factor to the mobility. At low doping densities, the hole mobility increases monotonically with the width of the nanowire.