Thermal boundary conductance in standalone and nonstandalone GaN/AlN heterostructures predicted using machine-learning interatomic potentials

GaN/AlN interfaces are essential in advanced high-power and high-frequency electronic devices, where effective thermal management is crucial for optimal performance and reliability. This work investigates the thermal boundary conductance (TBC) of standalone and nonstandalone GaN/AlN heterostructures using nonequilibrium molecular dynamics (NEMD) driven by accurate machine learning interatomic potentials trained from density-functional theory calculations. For the standalone interface, the TBC is found to be $\ensuremath{\sim}600\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at room temperature after quantum correction. The result revises previous NEMD predictions ($400--2000\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$) using empirical interatomic potentials. When a second GaN/AlN interface is brought close to the original interface, the TBC of the original interface can increase to $1000\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, and this value gradually decreases with increasing distance between the two interfaces. When more interfaces are introduced in proximity, the original interface's TBC can be further enhanced to above $1150\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. After comparing double interfaces, superlattices, and random multilayers, it is concluded that such enhancement of TBC is not caused by the emergence of superlattice modes but rather by the ballistic transport of the existing phonon modes of each material. Additionally, a ``critical separation distance'' (${l}_{\mathrm{cs}}$) is defined as the threshold beyond which the two interfaces no longer influence each other and behave independently. ${l}_{\mathrm{cs}}$ is determined by the mean free path of the phonons filtered by the interfaces that transport in the middle layer between two interfaces. Our findings provide insights into the thermal transport mechanisms that may aid the design of future electronic devices.