Thick single-crystal rhombohedral boron nitride as a substrate platform enabling high-performance III-V electronics

Monolayer hexagonal boron nitride (hBN) provides an atomically flat interface ideal for encapsulation and tunneling applications ¹ . Beyond the monolayer limit, thick boron nitride (BN) emerges as a mechanically resilient dielectric, efficient thermal conductor, and epitaxial platform for high-power electronics, deep-UV optoelectronics, and quantum emitters ^2–6 . However, wafer-scale synthesis of single-crystalline BN with controlled thickness remains a challenge. Here we present a solid–liquid interface-mediated epitaxy method that enables wafer-scale, thickness-tunable single-crystal rhombohedral BN (rBN) on atomically flat Ni(111). Introducing Si into Ni at the growth temperature forms a Ni–Si surface liquid layer that enhances B and N solubility and rBN thickness controllability, while underlying Ni(111) enforces epitaxial alignment of rBN. The resulting single-crystal rBN films can be transferred onto SiC to direct the epitaxy of AlN/GaN/AlGaN heterostructures for high-electron-mobility transistors (HEMTs). Compared with direct growth of GaN on SiC, thick rBN-buffered GaN shows ~91% lower screw dislocation density, ~93% reduced residual stress, and improved on-state current, on/off ratio, and reduced current collapse in HEMTs. This strategy establishes thick rBN as a universal platform for next-generation ultra-wide-bandgap electronics and quantum optoelectronics.