Interplay between morphology and thickness of a SiN interlayer for enhanced thermal transport across the GaN/diamond interface

Self-heating is a critical problem for GaN-based devices in high-power and high-frequency applications. Heat dissipation in the latest GaN-on-diamond technology lies in increasing the interfacial thermal conductance (ITC) of the GaN/diamond interface. In this work, we systematically investigated the effect of interplay between morphology and thickness of a SiN interlayer on the ITC of the GaN/diamond interface through molecular dynamics simulations. It is found that as the thickness of the interlayer increases, for amorphous SiN, the ITC (Gamo) decreases monotonically. However, for a crystalline-SiN interlayer, the ITC (Gcry) shows a nonmonotonic behavior, firstly decreasing, then experiencing an abnormal increase, and finally decreasing again. The ratio of Gcry to Gamo reaches 3.23 as the SiN 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 GaN/diamond interface with a SiN interlayer. Further spectral analysis and lattice dynamics calculations reveal that the effect of the morphology and the thickness of the SiN 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 GaN-on-diamond devices.