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

Abstract

In this theoretical study, we examine the influence of dimensionality, size reduction, and heattransport direction on the phonon-drag contribution to the Seebeck coefficient of silicon nanostructures. Phonon-drag contribution arises from the momentum transfer between out-of-equilibrium phonon populations and charge carriers, and 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 acconout 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 nanstructures. Our results support the recent experimental findings, showing that a part of phonon drag contribution survives in 100 nm silicon nanostructures