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Microscopic Mechanisms of Low Lattice Thermal Conductivity in AlxGa1−xN Alloys Revealed by Neuroevolution Machine-Learning Potential

Yuwen Zhang1,2, Tao Ouyang3, Zheyong Fan4, and Wu Li1,5,*

  • *Contact author: wu.li.phys2011@gmail.com
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PRX Energy 5, 023013 – Published 18 June, 2026

DOI: https://doi.org/10.1103/df1n-9bll

Abstract

Understanding thermal transport in AlxGa1−xN alloys is critical for the reliable thermal management of high-power electronic devices. However, theoretical predictions of lattice thermal conductivity κℓ based on the traditional Abele’s virtual crystal approximation (VCA) significantly deviate from experimental measurements, and these discrepancies have long been attributed to finite-size effects. Unlike the traditional VCA, which homogenizes atomic masses and bonding environments, we explicitly incorporate both mass disorder and interatomic force constant (IFC) disorder by directly performing Boltzmann transport equation calculations on large special quasirandom structures, aiming to uncover their impact on lattice thermal transport. Our results show that mass disorder plays a dominant role in suppressing κℓ by significantly enhancing the anharmonic scattering of low-frequency phonons, whereas the heat-carrying capacity of high-frequency phonons is completely eliminated due to substantially reduced group velocities and strong harmonic scattering. In comparison, IFC disorder mainly increases anharmonic scattering rates but has negligible influence on the group velocities of low-frequency phonons. When both disorder types are accounted for, the predicted thermal conductivities align closely with experimental observations. This indicates that the previously reported overestimations from VCA are not due to finite-size effects. We also find that the alloy scattering model based on perturbation theory significantly overestimates the harmonic scattering rates of high-frequency phonons, despite their negligible contribution to thermal conductivity. These findings highlight the necessity of atomistic disorder modeling in wide-bandgap alloys and provide critical insights for thermal design in AlxGa1−xN-based electronics.

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Understanding the thermal transport of AlxGa1−xN alloys is critical for the thermal management of high-power electronic devices. However, predictions based on the virtual crystal approximation deviate from experiments, with discrepancies long attributed to finite-size effects. In this work, the authors resolved this discrepancy by explicitly incorporating both mass disorder and interatomic force-constant (IFC) disorder into phonon transport calculations, enabling accurate thermal-conductivity predictions in close agreement with experiments. These results show that mass disorder dominates the suppression of lattice thermal conductivity by enhancing anharmonic scattering of low-frequency phonons and eliminating high-frequency contributions through reduced group velocities and strong harmonic scattering. In comparison, IFC disorder mainly increases anharmonic scattering but has little influence on low-frequency group velocities. This work clarifies the microscopic origin of low thermal conductivity in AlxGa1−xN alloys and introduces a quantitative, transferable methodology for systematically separating and combining mass and IFC disorder, advancing phonon-transport studies in disordered systems.

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PRX Energy 5, 023013– Published 18 June, 2026
  • Received 7 February 2026
  • Revised 17 April 2026
  • Accepted 12 May 2026
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