Charged impurity scattering and mobility in gated silicon nanowires

TL;DR

This study investigates how charged impurities affect electron mobility in gated silicon nanowires, revealing differences between dopant types, impurity positioning effects, and limitations of traditional modeling approaches.

Contribution

It provides a detailed analysis of impurity scattering effects on mobility in silicon nanowires using advanced computational methods, highlighting the importance of dopant type and placement.

Findings

Phosphorous dopants behave as tunnel barriers, Boron as Fano resonances.

Mobility varies significantly with dopant type and carrier density.

Impurity position and nanowire environment critically influence resistance and mobility.

Abstract

We study the effects of charged impurity scattering on the electronic transport properties of <110>-oriented Si nanowires in a gate-all-around geometry, where the impurity potential is screened by the gate, gate oxide and conduction band electrons. The electronic structure of the doped nanowires is calculated with a tight-binding method and the transport properties with a Landauer-Buttiker Green functions approach and the linearized Boltzmann transport equation (LBTE) in the first Born approximation. Based on our numerical results we argue that: (1) There are large differences between Phosphorous (P) and Boron (B) doped systems, acceptors behaving as tunnel barriers for the electrons, while donors give rise to Fano resonances in the transmission. (2) As a consequence, the mobility is much larger in P- than in B-doped nanowires at low carrier density, but can be larger in B-doped nanowires at high carrier density. (3) The resistance of a single impurity is strongly dependent on its radial position in the nanowire, especially for acceptors. (4) As a result of subband structure and screening effects, the impurity-limited mobility can be larger in thin nanowires embedded in HfO2 than in bulk Si. Acceptors might, however, strongly hinder the flow of electrons in thin nanowires embedded in SiO2. (5) The perturbative LBTE largely fails to predict the correct mobilities in quantum-confined nanowires.