A ternary, orthorhombic κ-(AlxGa1−x)2O3 thin film was synthesized by combinatorial pulsed laser deposition on a 2 in. in diameter c-sapphire substrate with a composition gradient. Structural, morphological, and optical properties were studied as a function of the alloy composition. The thin film crystallized in the orthorhombic polymorph for Al contents of 0.07 ≤ x ≤ 0.46, enabling bandgap engineering from 5.03 eV to 5.85 eV. The direct optical bandgap and the c-lattice constant, as well, show a linear dependence on the cation composition. XRD measurements, especially 2θ-ω- and ϕ-scans, revealed the growth of κ-(AlxGa1−x)2O3 in [001]-direction and in three rotational domains. The surface morphology was investigated by atomic force microscopy and reveals root mean square surface roughnesses below 1 nm. Furthermore, the dielectric function (DF) and the refractive index, determined by spectroscopic ellipsometry, were investigated in dependence on the Al content. Certain features of the DF show a blue shift with increasing Al concentration.
