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

High-quality (InxGa1-x)(2)O-3 thin films in the orthorhombic kappa-phase were grown by pulsed-laser deposition (PLD) on c-sapphire substrates as well as PLD-grown kappa-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)(2)O-3/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 kappa-modification as demonstrated by XRD 2 theta-omega scans. However, for x > 0.28, phase separation of the cubic bixbyite and the kappa-phase occurred. The kappa-Ga2O3 template increased the crystalline quality of the kappa-(InxGa1-x)(2)O-3 thin film layers remarkably. Epitaxial, but relaxed growth with three in-plane rotational domains has been found for all thin films by XRD phi-scans or reciprocal space map measurements. Smooth surface morphologies (R-q < 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 kappa-(InxGa1-x)(2)O-3 as a promising material for heterostructure device applications or photodetectors. (C) 2019 Author(s).