Charged impurity scattering and mobility in gated silicon nanowires

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-B\"uttiker Green's 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 ${\text{HfO}}_{2}$ than in bulk Si. Acceptors might, however, strongly hinder the flow of electrons in thin nanowires embedded in ${\text{SiO}}_{2}$. (5) The perturbative LBTE largely fails to predict the correct mobilities in quantum-confined nanowires.