Effects of Confinement and Orientation on the Thermoelectric Power Factor of Silicon Nanowires

Abstract

It is suggested that low dimensionality can improve the thermoelectric (TE) power factor of a device, offering an enhancement of the ZT figure of merit. In this work the atomistic sp3d5s*-spin-orbit-coupled tight-binding model and the linearized Boltzmann transport theory is applied to calculate the room temperature electrical conductivity, Seebeck coefficient, and power factor of narrow 1D silicon nanowires (NWs). We present a comprehensive analysis of the thermoelectric coefficients of n-type and p-type NWs of diameters from 12nm down to 3nm, in [100], [110], and [111] transport orientations at different carrier concentrations. We find that the length scale at which the influence of confinement on the power factor can be observed is at diameters below 7nm. We show that contrary to the current view, the effect of confinement and geometry on the power factor originates mostly from changes in the conductivity which is strongly affected, rather than the Seebeck coefficient. In general, enhanced scattering at these diameter scales strongly degrades the conductivity and power factor of the device. We identify cases, however, for which confinement largely improves the channel's conductivity, resulting in ~2-3X power factor improvements. Our results may provide guidance in the design of efficient low dimensional thermoelectric devices.

49 pages, 11 figures

References in corpus (11)

• Impact of Phonon Surface Roughness Scattering on Thermal Conductivity of Thin Si Nanowires
• Mobility in Semiconducting Graphene Nanoribbons: Phonon, Impurity, and Edge Roughness Scattering
• Silicon nanowire band gap modification
• Electron- and phonon transport in silicon nanowires: an atomistic approach to thermoelectric properties
• Bandstructure Effects in Silicon Nanowire Electron Transport
• Electron Transport in Silicon Nanowires: The Role of Acoustic Phonon Confinement and Surface Roughness Scattering
• Significant enhancement of hole mobility in [110] silicon nanowires compared to electrons and bulk silicon
• Bandstructure Effects in Silicon Nanowire Hole Transport
• On the Bandstructure Velocity and Ballistic Current of Ultra Narrow Silicon Nanowire Transistors as a Function of Cross Section Size, Orientation and Bias
• Design space for low sensitivity to size variations in [110] PMOS nanowire devices: The implications of anisotropy in the quantization mass
• Analysis of Thermoelectric Properties of Scaled Silicon Nanowires Using an Atomistic Tight-Binding Model