Revisiting phonon thermal transport in two-dimensional gallium nitride: higher-order phonon-phonon and phonon-electron scattering

TL;DR

This study revisits phonon thermal transport in 2D-GaN, revealing that higher-order phonon-phonon scattering, especially four-phonon processes, significantly reduces thermal conductivity, while phonon-electron interactions are negligible at high carrier concentrations.

Contribution

It demonstrates the importance of accurately calculating fourth-order interatomic force constants and shows four-phonon scattering dominates thermal conductivity reduction in 2D-GaN.

Findings

Four-phonon scattering reduces thermal conductivity by 65.6%.

Fourth-order IFCs are sensitive to atomic displacement and overestimation occurs with non-convergent calculations.

Phonon-electron interactions have negligible effects at high charge carrier concentrations.

Abstract

Two-dimensional gallium nitride (2D-GaN) has great potential in power electronics and optoelectronics. Heat dissipation is a critical issue for these applications of 2D-GaN. Previous studies showed that higher-order phonon-phonon scattering has extremely strong effects on the lattice thermal conductivity of 2D-GaN, which exhibits noticeable discrepancies with lattice thermal conductivity calculated from molecular dynamics. In this work, it is found that the fourth-order interatomic force constants (4th-IFCs) of 2D-GaN are quite sensitive to atomic displacement in the finite different method. The effects of the four-phonon scattering can be severely overestimated with non-convergent 4th-IFCs. The lattice thermal conductivity from three-phonon scattering is reduced by 65.6% due to four-phonon scattering. The reflection symmetry allows significantly more four-phonon processes than three-phonon processes. It was previously thought the electron-phonon interactions have significant effects on the lattice thermal conductivity of two-dimensional materials. However, the effects of phonon-electron interactions on the lattice thermal conductivity of both n-type and p-type 2D-GaN at high charge carrier concentrations can be neglected due to the few phonon-electron scattering channels and the relatively strong four-phonon scattering.