Significant impact of Al1− <i>x</i> Ga <i>x</i> N interlayer on GaN/AlN thermal boundary conductance

AlN/GaN heterostructures are central to high-power and high-frequency electronics, including RF devices, power converters, and AI accelerators. An intermediate Al1−xGaxN (AlGaN) layer is often present, either unintentionally during growth or intentionally to induce a 2D electron gas, yet its impact on the interfacial thermal boundary conductance (TBC) remains unknown due to the lack of reliable measurement and modeling methods. Here, we report a first-principles-based evaluation of the TBCs of AlN/AlGaN, AlGaN/GaN, and AlN/AlGaN/GaN interfaces over the full alloy range (0 ≤ x ≤ 1). This is realized by the development of accurate deep learning interatomic potentials based on first-principles simulations. Contrary to other material systems where mixed interlayers enhance thermal coupling, we find that an AlGaN interlayer markedly degrades the TBC between GaN and AlN, explaining the observations in experiments. Finally, we show that if the Al composition transitions sigmoidally from 0 to 1 across the AlN/GaN interface, it can remarkably increase the TBC compared to an abrupt or a linear transition. This work is expected to shed light on accurate thermal analysis and electro-thermal co-design of future AlGaN-based devices.