Thermal boundary resistance of direct van der Waals bonded GaN-on-diamond

Carbide forming interlayers, such as amorphous silicon nitride, are typically used for GaN-on-diamond heterogenous integration. This interlayer has a low thermal conductivity, introducing an additional extrinsic interfacial thermal resistance. It may therefore be advantageous to omit this layer, directly bonding GaN-to-diamond (van der Waals bond). However, weakly bonded interfaces are known to increase the intrinsic thermal boundary resistance. An adapted acoustic mismatch model has been implemented to assess which bonding approach is the most optimal for low thermal resistance GaN-on-diamond. A high thermal boundary resistance of 200 m2 K GW−1 is predicted for weakly bonded GaN-to-diamond interfaces, which is close to the measured value of 220 ± 70 m2 K GW−1, and ∼7× higher than values measured when a 10's nm-thick SiN interlayer is included. Covalently bonded interfaces are therefore critical for achieving low thermal resistance GaN-on-diamond.