Role of Dimensionality and Size in Controlloing the Drag Seebeck Coefficient of Doped Silicon Nanostructures: A Fundamental Understanding

TL;DR

This theoretical study investigates how the size, shape, and heat flow direction of silicon nanostructures affect the phonon-drag contribution to their thermoelectric properties, providing insights aligned with recent experiments.

Contribution

The paper introduces a comprehensive theoretical model that accounts for anisotropy, boundary effects, and spin-orbit coupling to quantify phonon drag in silicon nanostructures.

Findings

Phonon drag contribution persists in 100 nm silicon nanostructures.

Size and geometry significantly influence the phonon-drag effect.

The model aligns with recent experimental observations.

Abstract

In this theoretical study, we examine the influence of dimensionality, size reduction, and heat-transport direction on the phonon-drag contribution to the Seebeck coefficient of silicon nanostructures. Phonon-drag contribution, which arises from the momentum transfer between out-of-equilibrium phonon populations and charge carriers, significantly enhances the thermoelectric coefficient. Our implementation of the phonon drag term accounts for the anisotropy of nanostructures, such as thin films and nanowires, through the boundary- and momentum-resolved phonon lifetime. Our approach also takes into account the spin-orbit coupling which turns out to be crucial for hole transport. We reliably quantify the phonon drag contribution at various doping levels, temperatures, and nanostructure geometries for both electrons and holes in silicon nanostructures. Our results support the recent experimental findings, showing that a part of phonon drag contribution survives in 100 nm silicon nanostructures.