  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, 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 thermal management of
Ga2O3 devices. In this work, Ga2O3 was deposited onto single crystal diamond
substrates by ALD and the thermal properties of ALD-Ga2O3 thin films and
Ga2O3-diamond interfaces with different interface pretreatments were measured
by TDTR. We observed very low thermal conductivity of these Ga2O3 thin films
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 are about 10 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 are about 20% smaller
than that of the clean interface, indicating interface chemistry affects
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.
