Coherent phonon scattering effects on thermal transport in thin semiconductor nanowires

TL;DR

This paper investigates how coherent phonon scattering influences thermal transport in thin semiconductor nanowires, revealing a crossover from localized to Ohmic behavior and explaining experimental data with a combined scattering model.

Contribution

It introduces a scalable transfer-matrix method to model phonon transport and explains the linear thermal conductivity in nanowires through a mixed scattering mechanism.

Findings

Crossover from localized to Ohmic phonon conductance.

Long-wavelength phonons behave nearly ballistically.

Boundary defects weaken localization effects.

Abstract

The thermal conductance by phonons of a quasi-one-dimensional solid with isotope or defect scattering is studied using the Landauer formalism for thermal transport. The conductance shows a crossover from localized to Ohmic behavior, just as for electrons, but the nature of this crossover is modified by delocalization of phonons at low frequency. A scalable numerical transfer-matrix technique is developed and applied to model quasi-one-dimensional systems in order to confirm simple analytic predictions. We argue that existing thermal conductivity data on semiconductor nanowires, showing an unexpected linear dependence, can be understood through a model that combines incoherent surface scattering for short-wavelength phonons with nearly ballistic long-wavelength phonons. It is also found that even when strong phonon localization effects would be observed if defects are distributed throughout the wire, localization effects are much weaker when defects are localized at the boundary, as in current experiments.