Thermal Conductivity of GaAs/Ge Nanostructures

TL;DR

This study systematically investigates the thermal conductivities of GaAs/Ge superlattice nanostructures, revealing how interface density and alloy phase separation influence heat transport, with implications for thermoelectric applications.

Contribution

It provides new experimental insights into nanoscale thermal transport in GaAs/Ge superlattices and alloys, aiding future thermoelectric material design.

Findings

Thermal conductivity decreases with increasing interface density.

Alloys exhibit phase separation and lower thermal conductivities.

Ultrafast thermoreflectance effectively measures nanoscale heat transport.

Abstract

Superlattices are promising low-dimensional nanomaterials for thermoelectric technology that is capable of directly converting low-grade heat energy to useful electrical power. In this work, the thermal conductivities of GaAs/Ge superlattice nanostructures were investigated systematically in relation to their morphologies and interfaces. Thermal conductivities were measured using ultrafast time-domain thermoreflectance and were found to decrease with increasing interface densities, consistent with our understanding of microscopic phonon transport in the particle regime. Lower thermal conductivities were observed in (GaAs)0.77(Ge2)0.23 alloys; transmission electron microscopy study reveals phase separation in the alloys. These alloys can be interpreted as fine nanostructures, with length scales comparable to the periods of very thin superlattices. Our experimental findings help gain fundamental insight into nanoscale thermal transport in superlattices and are also useful for future improvement of thermoelectric performance using superlattice nanostructures.