Designing $\mathrm{Ta}\mathrm{C}$ Virtual Substrates for Vertical ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ Power Electronics Devices

Journal Article · 27 September 2024 · PRX Energy

DOI: https://doi.org/10.1103/PRXEnergy.3.033007 · OSTI ID:2448447

Roberts, Dennice M. ; Hachtel, Jordan A.; Haegel, Nancy M. ; Miller, Moira K.; Rice, Anthony D. ; Tellekamp, M. Brooks

Power electronics are critical for a sustainable energy future, playing a key role in electrification and integration of renewable energy sources into the grid. Advances in ultrawide band gap materials are needed to handle higher powers in smaller form factors while reducing electrical and thermal losses. High $\mathrm{Al}$ content ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ is theoretically capable of meeting these demands, but its impact in power electronics has been severely restricted by a lack of substrates that can satisfy conductivity, lattice matching, and/or thermal expansion requirements. We demonstrate that electrically conductive $\mathrm{Ta}\mathrm{C}$ can be used as a virtual substrate for ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ heteroepitaxy. Scaleably sputtered $\mathrm{Ta}\mathrm{C}$ grown on ${\mathrm{Al}}_2{\mathrm{O}}_3$ , followed by high-temperature face-to-face annealing, produces a thin film $\mathrm{Ta}\mathrm{C}$ template with an effective hexagonal lattice constant matched to ${\mathrm{Al}}_{0.70}{\mathrm{Ga}}_{0.30}\mathrm{N}$ . Annealing of the $\mathrm{Ta}\mathrm{C}$ promotes recrystallization, significantly improving crystallinity and reducing crystalline defects from as-deposited columnar grains to a step-and-terrace surface morphology, enabling the subsequent growth of high-quality ${\mathrm{Al}}_{0.70}{\mathrm{Ga}}_{0.30}\mathrm{N}$ by molecular beam epitaxy. X-ray diffraction and scanning transmission electron microscopy confirm that the ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ layer is heteroepitaxially aligned, strain-free, and lattice-matched, transitioning abruptly from $\mathrm{Ta}\mathrm{C}$ to ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ without intermediate phases. These results demonstrate $\mathrm{Ta}\mathrm{C}$ virtual substrates as electrically conductive, lattice-matched, and thermally compatible templates for vertical ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ devices that can meet the growing power needs of a sustainable energy future. Published by the American Physical Society 2024

• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR)
• OSTI ID: 2448447
• Journal Information: PRX Energy, Journal Name: PRX Energy Journal Issue: 3 Vol. 3; ISSN 2768-5608
• Publisher: American Physical SocietyCopyright Statement
• Country of Publication: United States
• Language: English