β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor (EG ∼4.8 eV), which promises generational improvements in the performance and manufacturing cost over today's commercial wide bandgap power electronics based on GaN and SiC. However, overheating has been identified as a major bottleneck to the performance and commercialization of Ga2O3 device technologies. In this work, a novel Ga2O3/4H-SiC composite wafer with high heat transfer performance and an epi-ready surface finish has been developed using a fusion-bonding method. By taking advantage of low-temperature metalorganic vapor phase epitaxy, a Ga2O3 epitaxial layer was successfully grown on the composite wafer while maintaining the structural integrity of the composite wafer without causing interface damage. An atomically smooth homoepitaxial film with a room-temperature Hall mobility of ∼94 cm2/Vs and a volume charge of ∼3 × 1017 cm-3 was achieved at a growth temperature of 600 °C. Phonon transport across the Ga2O3/4H-SiC interface has been studied using frequency-domain thermoreflectance and a differential steady-state thermoreflectance approach. Scanning transmission electron microscopy analysis suggests that phonon transport across the Ga2O3/4H-SiC interface is dominated by the thickness of the SiNx bonding layer and an unintentionally formed SiOx interlayer. Extrinsic effects that impact the thermal conductivity of the 6.5 μm thick Ga2O3 layer were studied via time-domain thermoreflectance. Thermal simulation was performed to estimate the improvement of the thermal performance of a hypothetical single-finger Ga2O3 metal-semiconductor field-effect transistor fabricated on the composite substrate. This novel power transistor topology resulted in a ∼4.3× reduction in the junction-to-package device thermal resistance. Furthermore, an even more pronounced cooling effect is demonstrated when the composite wafer is implemented into the device design of practical multifinger devices. These innovations in device-level thermal management give promise to the full exploitation of the promising benefits of the UWBG material, which will lead to significant improvements in the power density and efficiency of power electronics over current state-of-the-art commercial devices.
Bibliographical noteFunding Information:
Funding for efforts by Y.S., D.S., and S.C. was provided by the Air Force Office of Scientific Research (AFOSR) Young Investigator Program (grant no. FA9550-17-1-0141, Program Officers: Dr. Brett Pokines and Dr. Michael Kendra, also monitored by Dr. Kenneth Goretta). S.C. also thanks fruitful discussions with Marco D. Santia and Stefan C. Badescu at the Air Force Research Laboratory (AFRL). Work by J.H.L. and T.H. was supported in part by AFRL/AFMC through SBIR contract no. FA8650-19-C-2902. Efforts by C.M.G. and S.Z. were performed in part at the NIST Center for Nanoscale Science and Technology. H.-L.H. and J.H. acknowledge support by the AFOSR GAME MURI Program (grant no. FA9550-18-1-0479, Program Officer: Dr. Ali Sayir). Electron microscopy was performed in the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State university. A.B. and S.K. acknowledge the II–VI foundation Block Gift Program and AFOSR (Grant no. FA9550-18-1-0507, Program Officer: Dr. Ali Sayir) for financial support. This work was performed in part at the Utah Nanofab sponsored by the College of Engineering and the Office of the Vice President for Research. Y.Z. and X.W. appreciate the support from the National Science Foundation (NSF, grant no. CBET-1804840) and the MN Futures Award.
© 2021 American Chemical Society.
- composite substrate
- fusion bonding
- gallium oxide (GaO)
- low-temperature metal organic vapor phase epitaxy (MOVPE)
- thermal boundary resistance (TBR)
- thermal management
- ultrawide bandgap (UWBG) semiconductor devices