First-principle-based full-dispersion Monte Carlo simulation of the anisotropic phonon transport in the wurtzite GaN thin film

Abstract

In this study, we developed a first-principle-based full-dispersion Monte Carlo simulation method to study the anisotropic phonon transport in wurtzite GaN thin film. The input data of thermal properties in MC simulations were calculated based on the first-principle method. The anisotropy of thermal conductivity in bulk wurtzite GaN is found to be strengthened by isotopic scatterings and reduced temperature, and the anisotropy reaches 40.08% for natural bulk GaN at 100 K. With the GaN thin film thickness decreasing, the anisotropy of the out-of-plane thermal conductivity is heavily reduced due to both the ballistic transport and the less importance of the low-frequency phonons with anisotropic group velocities. On the contrary, it is observed that the in-plane thermal conductivity anisotropy of the GaN thin film is strengthened by reducing the film thickness. And the anisotropy reaches 35.63% when the natural GaN thin film thickness reduces to 50 nm at 300 K with the degree of specularity being zero. The anisotropy is also improved by increasing the surface roughness of the GaN thin film. V

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Matryoshka phonon twinning in α-GaN

“…The anisotropic thermal conductivity of -GaN recently attracted intensive attention because it is critical for heat management in power electronics, where -GaN is a key component. However, the answer remains controversial: some reported that the out-of-plane thermal conductivity is greater than the in-plane one while others showed opposite results [5,6,19,20] Recent reports suggest that the in-plane thermal conductivity is smaller than the out-of-plane one, with a relatively strong anisotropy of 12% [19,20]. Here, we will investigate the roles of phonon group velocity and scattering rates on the anisotropic lattice thermal conductivity.…”

“…For example, existing experimental measurements of the phonon dispersion relation of -GaN are limited to ambient conditions, and the phonon scattering processes and the temperature effects are mostly unexplored [9,10]. Moreover, the anisotropic thermal transport of -GaN along a (inplane) and c (out-of-plane) axis directions remains controversial due to the challenges in transport measurements [7,[11][12][13][14][15][16][17][18] and calculations [19][20][21]. Therefore, a more comprehensive understanding of the phonon dynamics is pivotal to investigating the thermal transport and other thermodynamics properties of GaN.…”

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