Phonon transport across GaN-diamond interface: The nontrivial role of pre-interface vacancy-phonon scattering

Abstract

Diamond substrate with superior thermal conductivity has been the most promising heat sink to solve the heat dissipation issues in GaN-based power electronics. The phonon transport behaviors across the GaN-diamond interface crucially determine the thermal performance and still remain largely unexplored especially considering the presence of pre-interface vacancies. Herein, the influence of localized high-concentration Ga/N atomic vacancies on phonon transport across the GaN-diamond interface is fully investigated using non-equilibrium molecular dynamics. The calculated interface thermal resistance (ITR) of the perfect GaN-diamond interface at room temperature is approximately 1.5 m2·K/GW, consistent with prediction of the diffusion mismatch model. After introducing the Ga/N vacancies at a concentration of 30%, the existence of vacancy-phonon scattering increases the interfacial thermal resistance (ITR) by up to 67%. Analyzing the phonon density of states and the spectral heat current, the heat flux contributed by GaN high-frequency phonons decreases after introducing vacancy defects. This is attributed that the vacancy-phonon scattering in GaN enhances anharmonic phonon scattering, and the phonon energy is redistributed among different phonon modes. Moreover, the collective vibration of propagation phonons is disrupted randomly by the vacancy-phonon scattering. This work aims to understand the influence of vacancy-phonon scattering on the phonon transport across GaN-diamond interface and provide helpful guidance to engineering such interface for better heat dissipation performance.