  Because of its ultrawide bandgap, high breakdown electric field, and large
area affordable substrates grown from the melt, beta Ga2O3 has attracted great
attention recently for potential applications of power electronics. However,
its thermal conductivity is significantly lower than those of other wide
bandgap semiconductors, such as AlN, SiC, GaN, and diamond. To ensure reliable
operation with minimal selfheating at high power, proper thermal management is
even more essential for Ga2O3 devices. Similarly to the past approaches aiming
to alleviate selfheating in GaN HEMTs, a possible solution has been to
integrate thin Ga2O3 membranes with diamond to fabricate Ga2O3 on diamond
lateral MESFET or MOSFET devices by taking advantage of the ultra high thermal
conductivity of diamond. Even though the TBC between wide bandgap semiconductor
devices such as GaN HEMTs and a diamond substrate is of primary importance for
heat dissipation in these devices, fundamental understanding of the Ga2O3
diamond thermal interface is still missing. In this work, we study the thermal
transport across the interfaces of Ga2O3 exfoliated onto a single crystal
diamond. The Van der Waals bonded Ga2O3 diamond TBC is measured to be 17
MWm2K1, which is comparable to the TBC of several physical vapor deposited
metals on diamond. A Landauer approach is used to help understand phonon
transport across perfect Ga2O3 diamond interface, which in turn sheds light on
the possible TBC one could achieve with an optimized interface. A reduced
thermal conductivity of the Ga2O3 nanomembrane is also observed due to
additional phonon membrane boundary scattering. The impact of the
Ga2O3substrate TBC and substrate thermal conductivity on the thermal
performance of a power device are modeled and discussed.
