Abstract
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.
Highlights
Monoclinic β-Ga2O3 can potentially be used in high-power electronics,1–4 as solar-blind photo detectors,5 gas sensors,6 or thin film transistors,7 because of its beneficial material properties such as a large Baliga’s figure of merit, a large breakdown field8 of 8 MV cm−1, and a high bandgap energy of 4.6–5 eV.3Another interesting polymorph of the wide bandgap material is its orthorhombic modification, denoted as κ-Ga2O3 and being isostructural to κ-Al2O3, making the growth of κ-(Al,Ga)2O3 for any cation composition seem possible
Storm et al presented pulsed laser deposition (PLD) grown thin films on (00.1)Al2O3 with a maximum Al content of x = 0.38, which was increased by growth on a κ-Ga2O3 template up to x = 0.65.10
The chemical cation composition of the whole wafer was determined by energy-dispersive X-ray spectroscopy (EDX) performed with a FEI Nova Nanolab 200 equipped with an Ametek EDAX detector on 49 positions on the 2 in. wafer
Summary
Monoclinic β-Ga2O3 can potentially be used in high-power electronics, as solar-blind photo detectors, gas sensors, or thin film transistors, because of its beneficial material properties such as a large Baliga’s figure of merit, a large breakdown field of 8 MV cm−1, and a high bandgap energy of 4.6–5 eV.. Monoclinic β-Ga2O3 can potentially be used in high-power electronics, as solar-blind photo detectors, gas sensors, or thin film transistors, because of its beneficial material properties such as a large Baliga’s figure of merit, a large breakdown field of 8 MV cm−1, and a high bandgap energy of 4.6–5 eV.3 Another interesting polymorph of the wide bandgap material is its orthorhombic modification, denoted as κ-Ga2O3 and being isostructural to κ-Al2O3, making the growth of κ-(Al,Ga)2O3 for any cation composition seem possible. The chemical, structural, and optical material properties, namely crystal structure, surface morphology, optical bandgap energy, dielectric function, and refractive index will be discussed in dependence on the cation composition
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