This paper investigated the growth of (AlxGa1−x)2O3 thin films on semi-insulating (010) Ga2O3 substrates over the entire Al composition range (0% < x ≤ 100%) via metalorganic chemical vapor deposition (MOCVD). For the Al composition x < 27%, high quality single phase β-(AlxGa1−x)2O3 was achieved. A mixture of β and γ phases existed in (AlxGa1−x)2O3 when Al composition ranged between 27% and 40%, whereas a single γ-phase was observed for the films with Al composition x > 40%. The transition from the β to γ phase in AlGaO alloys was observed from x-ray diffraction spectra. The growth of γ-phase AlGaO with higher Al content was further confirmed via atomic resolution scanning transmission electron microscopy imaging and nanodiffraction. Compositional and statistical analyses performed on data acquired from atom probe tomography provided insight on the local compositional homogeneity in AlGaO films with different Al compositions. For AlGaO with pure β or γ phases, the Al composition distribution showed homogeneity with similar Al composition values as extracted from the x-ray diffraction peak positions. For AlGaO films with mixed β and γ phases, inhomogeneity in the Al composition distribution became more obvious in the nm scale. A mechanism was proposed for the observed phase transformation between β and γ phases in MOCVD growth of AlGaO films.

In this paper, we investigated the evolution of microstructural chemistry of metal organic chemical vapor deposition grown (010) (AlxGa1−x)2O3 films with varying Al contents, x = 0.10–1.0, using atom probe tomography (APT). At a low Al content (x ≤ 0.25), the films are homogeneous, where layer inhomogeneity appears at a high Al content (x > 0.25). Further increasing the Al content up to x ≥ 0.60 results in a homogeneous (AlxGa1−x)2O3 layer. This change in microstructural features was linked to the phase transformation of (AlxGa1−x)2O3 using a manifold learning approach to capture the governing features hidden in the data dimensionality. Combining APT to unsupervised machine learning enables APT to be an independent material characterization tool to investigate the microstructure, chemical composition, and phase related information.

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We characterized unintentionally doped β-(Al0.19Ga0.81)2O3 for its structural, band, and electrical properties by using a variety of material and electrical characterization methods such as atom probe tomography (APT), transmission electron microscope, X-ray photoelectron spectroscopy (XPS), capacitance-voltage measurement, and a temperature dependent forward current-voltage measurement. A 115 nm thick β-(Al0.19Ga0.81)2O3 film was grown by molecular beam epitaxy on Sn doped Ga2O3 substrates. Reciprocal space mapping shows a lattice matched (Al0.19Ga0.81)2O3 layer. Both APT and TEM results confirm a sharp β-(Al0.19Ga0.81)2O3/β-Ga2O3 interface. XPS measurements show conduction band offsets of 2.78 ± 0.25 eV and 0.79 ± 0.25 eV between the SiO2/β-(Al0.19Ga0.81)2O3 and β-(Al0.19Ga0.81)2O3/β-Ga2O3 interfaces, respectively. Extracted room temperature Schottky Barrier Heights (SBHs) after zero field correction for Pt, Ni, and Ti were 2.98 ± 0.25 eV, 2.81 ± 0.25 eV, and 1.81 ± 0.25 eV, respectively. The variation of SBHs with metals clearly indicates the dependence on work function.

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