Acoustic Phonon Characteristics of Gallium Oxide Single Crystals Investigated with Brillouin-Mandelstam Light Scattering Spectroscopy

TL;DR

This study investigates the anisotropic acoustic phonon properties of gallium oxide single crystals using Brillouin-Mandelstam spectroscopy, revealing key insights into phonon velocities and their impact on thermal conduction.

Contribution

It provides detailed measurements of bulk and surface acoustic phonons in gallium oxide, highlighting anisotropy and its implications for thermal and electrical transport modeling.

Findings

Average acoustic phonon velocities are 5250 m/s and 4990 m/s.

Surface acoustic phonons propagate about half as fast as bulk phonons.

Anisotropy in phonon velocities influences heat conduction in gallium oxide.

Abstract

We report an investigation of the bulk and surface acoustic phonons in gallium oxide ultra-wide bandgap single crystals along various crystallographic directions using Brillouin-Mandelstam spectroscopy. Pronounced anisotropy in the acoustic phonon dispersion and velocities was observed across different crystal orientations. The measured average acoustic phonon velocities for the crystallographic directions of interest are 5,250 m/s and 4,990 m/s. The surface acoustic phonons propagate approximately twice as slowly as the bulk acoustic phonons. Our results suggest that the anisotropy of heat conduction in gallium oxide results from the difference in phonon velocities rather than the phonon lifetime. The obtained information for bulk and surface acoustic phonons can be used for developing accurate theoretical models of phonon scattering and optimization of thermal and electrical transport in this technologically important ultra-wide bandgap semiconductor.