Single-Crystalline High-Quality β‑Ga₂O₃ Pseudosubstrate on Sapphire through Sputtering for Epitaxial Deposition

Solid-phase epitaxy (SPE) of β-Ga₂O₃ thin films by radio frequency (RF) sputtering, followed by crystallization through high-temperature postdeposition annealing, is employed on sapphire substrates, yielding a high-quality pseudosubstrate for subsequent buffer growth via MOCVD and LPCVD. Low roughness (<0.5 nm) and sharp single-crystalline diffraction peaks corresponding to the (-201), (-402), and (-603) reflections of β-Ga₂O₃ were observed in the SPE β-Ga₂O₃ film and the subsequent epitaxial buffer layer. N-doped Ga₂O₃ film grown by LPCVD on SPE Ga₂O₃ film showed step-assisted growth mode with reasonable electronic behavior, with 45 cm²/V·s mobility at a bulk carrier concentration of 1.3 × 10¹⁷ cm^-3. These results suggest that SPE Ga₂O₃ is a promising pathway to advance the development of β-Ga₂O₃ on foreign substrates.