Scalable Growth and Properties of (Al <i> _x </i> Ga ₁ ₋ <i> _x </i> ) ₂ O ₃ Thin Films on 2‐ and 4‐Inch Sapphire via Close‐Coupled Showerhead MOCVD

A series of (Al x Ga 1 − x ) 2 O 3 thin films were deposited using an AIXTRON Close‐Coupled Showerhead (CCS) metalorganic chemical vapour deposition (MOCVD) system to study aluminium (Al) incorporation into the β‐Ga 2 O 3 lattice. Films ≈1.2 μm thick were grown on 2‐inch and 4‐inch c‐plane sapphire substrates. A linear relationship between film composition and precursor ratio indicated near‐ideal alloying behaviour. Growth kinetics were composition‐dependent, where Al incorporation reduced growth rates compared to gallium (Ga), although pure Al 2 O 3 grew faster than intermediate alloys. The films exhibited high optical transmittance (82–88%), with a tuneable bandgap increasing with Al content. Morphological changes and increased roughness were observed up to Al x = 0.42, suggesting a possible phase transition. X‐ray diffraction, rocking curve measurements and pole figure confirmed the monoclinic β‐phase for the Ga 2 O 3 only film, with strong, well‐defined Bragg peaks. For Al 2 O 3 , only the substrate and nucleation layer reflections were visible, consistent with epitaxial Al 2 O 3 growth on sapphire. The largest rocking curve full width half maximum was observed for samples with Al content x equals 0.12 and 0.42, which can be correlated with significant changes in the thin film surface morphology. The successful extension from 2‐inch to 4‐inch wafers highlights the scalability and uniformity of the CCS MOCVD process.