Self-heating is a critical problem for $\mathrm{Ga}\mathrm{N}$-based devices in high-power and high-frequency applications. Heat dissipation in the latest $\mathrm{Ga}\mathrm{N}$-on-diamond technology lies in increasing the interfacial thermal conductance (ITC) of the $\mathrm{Ga}\mathrm{N}$/diamond interface. In this work, we systematically investigated the effect of interplay between morphology and thickness of a $\mathrm{Si}\mathrm{N}$ interlayer on the ITC of the $\mathrm{Ga}\mathrm{N}$/diamond interface through molecular dynamics simulations. It is found that as the thickness of the interlayer increases, for amorphous $\mathrm{Si}\mathrm{N}$, the ITC ($G_{\mathrm{amo}}$) decreases monotonically. However, for a crystalline-$\mathrm{Si}\mathrm{N}$ interlayer, the ITC ($G_{\mathrm{cry}}$) shows a nonmonotonic behavior, firstly decreasing, then experiencing an abnormal increase, and finally decreasing again. The ratio of $G_{\mathrm{cry}}$ to $G_{\mathrm{amo}}$ reaches 3.23 as the $\mathrm{Si}\mathrm{N}$ thickness increases to 10 nm. Our calculated results show good agreement with reported experimental values from different research teams. Since amorphous and crystalline structures represent two extreme morphologies, our calculated results can be considered as the high and low limits for the ITC of the $\mathrm{Ga}\mathrm{N}$/diamond interface with a $\mathrm{Si}\mathrm{N}$ interlayer. Further spectral analysis and lattice dynamics calculations reveal that the effect of the morphology and the thickness of the $\mathrm{Si}\mathrm{N}$ interlayer on the ITC is governed by the interplay among different mechanisms of phonon-disorder scattering, thermalization by inelastic scattering, and the phonon bridge effect. The findings here provide guidance for optimizing interlayers in facilitating thermal transport of $\mathrm{Ga}\mathrm{N}$-on-diamond devices.

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• Heat transfer
• Phonons
• Thermal transport
• III-V semiconductors
• Multilayer thin films
• Nitrides
• Solid-solid interfaces
• Molecular dynamics