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

Abstract

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.

Band Offsets at κ-([Al,In]xGa1–x)2O3/MgO Interfaces

“…However, it should be noted that in principle every core level could be used for this purpose. Supplementary Figure S4 and are in agreement with recently determined values from transmission spectroscopy 24,25 . It should be mentioned that for higher In contents the band gap determined by this method might be overestimated, as the onset of the inelastic background and the core level peak start to partially overlap, making a determination of the constant background difficult.…”

“…The elliptically-segmented target for the κ-(InxGa1-x)2O3 alloy layers was a (In0.4Ga0.6)2O3/Ga2O3 target with additional 1.5 at.% SnO2 in each segment and for the κ-(AlxGa1-x)2O3 alloy layers a (Al0.4Ga0.6)2O3/Ga2O3 or a (Al0.2Ga0.6)2O3/Ga2O3 target with additional 2 at.% SnO2 in each segment for both targets was employed, respectively. The exact target geometries can be found in References 24,25,45 . The presence of tin is necessary to facilitate the growth of the Ga2O3 based layers in the metastable orthorhombic modification for the PLD deposition method [18][19][20]23 .…”

“…Recently, one report even achieved conductive doping of this phase by Si or Sn incorporation, which is necessary for a variety of device applications 36 . However, in PLD and MBE growth, tin is necessary as catalyst to stabilize the orthorhombic modification at all, but is not incorporated in the thin film layer as active donor element [18][19][20][23][24][25]44 . Further, several reports already deal with the alloying of this phase with indium 23,25,38 or aluminum 24,40 in a broad composition range, including bandgap engineering and the evolution of lattice constants.…”

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

“…[ 6 ] The second‐most stable structure is the orthorhombic κ ‐phase, for which ternary PLD thin films were already reported. [ 7–11 ] The third‐most stable polymorph is the rhombohedral α‐phase.…”

Epitaxial Growth of κ‐(AlxGa1−x)2O3 Layers and Superlattice Heterostructures up to x = 0.48 on Highly Conductive Al‐Doped ZnO Thin‐Film Templates by Pulsed Laser Deposition

“…Research on the In as well as Al alloy systems of the κ ‐phase is still relatively scarce, as up to now only reports on PLD [ 23–25,50,51 ] as well as mist CVD [ 16,44 ] growth are available. However, these alloys can be grown phase pure in a broad composition range [ 23–25,50 ] of and .…”