Integration of polycrystalline Ga2O3 on diamond for thermal management

Gallium oxide (Ga2O3) has attracted great attention for electronic device applications due to its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is significantly lower than that of other wide bandgap semiconductors such as SiC, AlN, and GaN, which will impact its ability to be used in high power density applications. Thermal management in Ga2O3 electronics will be the key for device reliability, especially for high power and high frequency devices. Similar to the method of cooling GaN-based high electron mobility transistors by integrating it with high thermal conductivity diamond substrates, this work studies the possibility of heterogeneous integration of Ga2O3 with diamond for the thermal management of Ga2O3 devices. In this work, Ga2O3 was deposited onto single crystal diamond substrates by atomic layer deposition (ALD), and the thermal properties of ALD-Ga2O3 thin films and Ga2O3-diamond interfaces with different interface pretreatments were measured by Time-domain Thermoreflectance. We observed a very low thermal conductivity of these Ga2O3 thin films (about 1.5W/m K) due to the extensive phonon grain boundary scattering resulting from the nanocrystalline nature of the Ga2O3 film. However, the measured thermal boundary conductance (TBC) of the Ga2O3-diamond interfaces is about ten times larger than that of the van der Waals bonded Ga2O3-diamond interfaces, which indicates the significant impact of interface bonding on TBC. Furthermore, the TBC of the Ga-rich and O-rich Ga2O3-diamond interfaces is about 20% smaller than that of the clean interface, indicating that interface chemistry affects the interfacial thermal transport. Overall, this study shows that a high TBC can be obtained from strong interfacial bonds across Ga2O3-diamond interfaces, providing a promising route to improving the heat dissipation from Ga2O3 devices with lateral architectures.