Ultra‐Wide Bandgap Semiconductor of Cubic‐Phase AlN/Diamond Heterojunction for Radio Frequency Electronics

ABSTRACT While diamond stands as the preeminent paradigm for next‐generation high‐power and radio‐frequency electronics, its practical application has been bottlenecked by the lack of a stable and high‐quality ultra‐wide bandgap gate dielectric/barrier layer. Here, we report a transformative breakthrough in achieving the single‐domain heteroepitaxy of cubic AlN on (001) diamond via MOCVD. By strategically exploiting a nitrogen‐for‐hydrogen substitution mechanism, we successfully circumvent diamond's chemical inertness and the thermodynamic metastability of the cubic phase. Microscopic analysis reveals that the formidable 22.8% lattice mismatch is accommodated by a periodic 6:7 domain‐matching epitaxy model, relieving residual strain to 2.45% and enabling a record‐low RMS roughness of 0.74 nm. Most significantly, this structurally seamless, polarization‐free Type‐II interface induces a high‐performance two‐dimensional hole gas with a record room‐temperature hole mobility of 314 cm 2 V −1 s −1 at a sheet density of 3.2 × 10 12 cm −2 . Utilizing this platform, normally‐off diamond FET was demonstrated, providing a definitive roadmap for high‐symmetry, high‐mobility diamond power and RF electronics.