# Reduced thermal conductivity of epitaxial GaAs on Si due to symmetry-breaking biaxial strain

## TL;DR

This study reveals that small in-plane biaxial stress in epitaxial GaAs on Si significantly reduces its thermal conductivity by breaking crystal symmetry, impacting heat dissipation in silicon photonics devices.

## Contribution

It demonstrates the first direct link between biaxial stress and reduced thermal conductivity in epitaxial GaAs, combining experimental and ab initio methods.

## Key findings

- Thermal conductivity of GaAs decreases by up to 19% under 250 MPa biaxial stress.
- Biaxial stress enhances phonon-phonon scattering by breaking cubic symmetry.
- Residual thermal stress must be minimized to optimize heat dissipation in III-V/Si photonic devices.

## Abstract

Epitaxial growth of III-V semiconductors on Si is a promising route for silicon photonics. Threading dislocations and the residual thermal stress generated during growth are expected to affect the thermal conductivity of the III-V semiconductors, which is crucial for efficient heat dissipation from photonic devices built on this platform. In this work, we combine a non-contact laser-induced transient thermal grating technique with ab initio phonon simulations to investigate the in-plane thermal transport of epitaxial GaAs-based buffer layers on Si, employed in the fabrication of III-V quantum dot lasers. Surprisingly, we find a significant reduction of the in-plane thermal conductivity of GaAs, up to 19%, as a result of a small in-plane biaxial stress of 250 MPa. Using ab initio phonon calculations, we attribute this effect to the enhancement of phonon-phonon scattering caused by the in-plane biaxial stress, which breaks the cubic crystal symmetry of GaAs. Our results indicate the importance of eliminating the residual thermal stress in the epitaxial III-V layers on Si to avoid the reduction of thermal conductivity and facilitate heat dissipation. Additionally, our results showcase potential means of effectively controlling thermal conductivity of solids with external strain/stress.