Comprehensive mobility study of silicon nanowire transistors using multi-subband models

Abstract

Spatial confinement is important in advanced More Moore devices, such as nanowire transistors (NWTs), where the basic charge transport properties must be revised beyond the bulk crystal assumptions. This work presents a comprehensive and general overview of the electron mobility in aggressively-scaled Si NWTs in order to demonstrate the effect of quantum confinement on this topic, establishing its dependence on numerous physical factors (shape, diameter, and orientation). The mobility evaluation makes use of a unique simulation framework and innovative multi-subband calculations of the scattering rates. We show that (1) the effect of surface roughness scattering is more pronounced at higher sheet densities, (2) ionized impurity scattering seriously degrades the mobility in highly-doped NWTs, and (3) the cross-section shape affects directly the subband parameters and the mobility, with the elliptical NWTs giving the best performance for the same cross-sectional area.

Keywords

• silicon nanowire field-effect transistors
• one-dimensional multi-subband scattering models
• confined charge transport
• Poisson-Schroödinger solvers
• Kubo-Greenwood formalism