Solubility limit and material properties of a κ-(AlxGa1−x)2O3 thin film with a lateral cation gradient on (00.1)Al2O3 by tin-assisted PLD

• Main Authors: A. Hassa, C. Sturm, M. Kneiß, D. Splith, H. von Wenckstern, T. Schultz, N. Koch, M. Lorenz, M. Grundmann
• Format: Article
• Language: English
• Published: AIP Publishing LLC 2020-02-01
• Series: APL Materials
• Online Access: http://dx.doi.org/10.1063/1.5141041

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.