Matryoshka Phonon Twinning in alpha-GaN

TL;DR

This study reveals a unique Matryoshka phonon dispersion in alpha-GaN, which enhances anharmonicity and reduces thermal conductivity, providing insights for thermal management in power semiconductors.

Contribution

It uncovers the first observation of Matryoshka phonon twinning in alpha-GaN and demonstrates its impact on phonon scattering and thermal transport.

Findings

Matryoshka phonon dispersion confirmed by experiments and calculations.

Phonon twinning increases anharmonicity and three-phonon scattering.

Thermal conductivity in alpha-GaN is significantly reduced due to phonon topology.

Abstract

Understanding lattice dynamics is crucial for effective thermal management in high-power electronic devices because phonons dominate thermal transport in most semiconductors. This study utilizes complementary inelastic X-ray and neutron scattering techniques and reports the temperature-dependent phonon dynamics of alpha-GaN, one of the most important third-generation power semiconductors. A prominent Matryoshka phonon dispersion is discovered with the scattering tools and confirmed by the first-principles calculations. Such Matryoshka twinning throughout the three-dimension reciprocal space is demonstrated to amplify the anharmonicity of the related phonon modes through creating abundant three-phonon scattering channels and cutting the phonon lifetime of affected modes by more than 50%. Such phonon topology effectively contributes to the reduction of the in-plane thermal transport, thus the anisotropic thermal conductivity of alpha-GaN. The results not only have significant implications for engineering the thermal performance and other phonon-related properties of alpha-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically important semiconductors.