The role of lighter and heavier embedded nanoparticles on the thermal conductivity of SiGe alloys

TL;DR

This study uses an atomistic ab initio approach to compare how lighter and heavier embedded nanoparticles affect the thermal conductivity of SiGe alloys, revealing that Ge nanoparticles reduce conductivity more effectively than Si ones.

Contribution

It introduces an exact Green's function calculation for nanoparticle scattering rates and compares it with the Born approximation, providing insights into nanoparticle size effects on thermal conductivity.

Findings

Embedding Ge nanoparticles reduces thermal conductivity by 20% more than Si nanoparticles.

The Born approximation performs well despite differences with the exact method.

Larger nanoparticle sizes up to 60 nm can be investigated using the Born approximation.

Abstract

We have used an atomistic {\it ab initio} approach with no adjustable parameters to compute the lattice thermal conductivity of Si$_{0.5}$Ge$_{0.5}$ with a low concentration of embedded Si or Ge nanoparticles of diameters up to 4.4 nm. Through exact Green's function calculation of the nanoparticle scattering rates, we find that embedding Ge nanoparticles in $\text{Si}_{0.5}\text{Ge}_{0.5}$ provides 20% lower thermal conductivities than embedding Si nanoparticles. This contrasts with the Born approximation which predicts an equal amount of reduction for the two cases, irrespective of the sign of the mass difference. Despite these differences, we find that the Born approximation still performs remarkably well, and it permits investigation of larger nanoparticle sizes, up to 60 nm in diameter, not feasible with the exact approach.