Epitaxial stabilization of single phase κ-(InxGa1−x)2O3 thin films up to x = 0.28 on c-sapphire and κ-Ga2O3(001) templates by tin-assisted VCCS-PLD

• Published in: APL materials Vol. 7; no. 10; pp. 101102 - 101102-10
• Main Authors: Kneiß, M., Hassa, A., Splith, D., Sturm, C., von Wenckstern, H., Lorenz, M., Grundmann, M.
• Format: Journal Article
• Language: English
• Published: AIP Publishing LLC 01.10.2019
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.5120578

High-quality (InxGa1−x)2O3 thin films in the orthorhombic κ-phase were grown by pulsed-laser deposition (PLD) on c-sapphire substrates as well as PLD-grown κ-Ga2O3 thin film templates. We varied the In-content 0 ≤ x ≤ 0.38 of the layers using a single, elliptically segmented, and tin-doped (In0.4Ga0.6)2O3/Ga2O3 target, employing the vertical continuous composition spread (VCCS) PLD-technique. A stoichiometric transfer of In and Ga from the target to the thin films has been confirmed, suggesting that the formation of volatile Ga2O and In2O suboxides is not a limiting factor in the tin-assisted growth mode. For all x, the thin films crystallized predominantly in the κ-modification as demonstrated by XRD 2θ-ω scans. However, for x > 0.28, phase separation of the cubic bixbyite and the κ-phase occurred. The κ-Ga2O3 template increased the crystalline quality of the κ-(InxGa1−x)2O3 thin film layers remarkably. Epitaxial, but relaxed growth with three in-plane rotational domains has been found for all thin films by XRD ϕ-scans or reciprocal space map measurements. Smooth surface morphologies (Rq < 3 nm) for all phase pure thin films were evidenced by atomic force microscopy measurements, making them suitable for multilayer heterostructures. The composition-dependent in- and out-of plane lattice constants follow a linear behavior according to Vegard’s law. A linear relationship can also be confirmed for the optical bandgaps that demonstrate the feasibility of bandgap engineering in the energy range of 4.1–4.9 eV. The results suggest κ-(InxGa1−x)2O3 as a promising material for heterostructure device applications or photodetectors.