This study demonstrated homoepitaxial growth of Ge-doped β-Ga2O3 thin films on β-Ga2O3 substrates via mist chemical vapor deposition (CVD) using GeI4, a water-soluble Ge precursor. The carrier concentration of the Ge-doped β-Ga2O3 thin films was controlled by varying the Ge precursor concentration in the solution. A mobility of 66 cm2V-1s-1 was obtained at a carrier density of 3.4×1018 cm-3 using oxygen gas. X-ray diffraction (XRD) scans revealed that homoepitaxial Ge-doped β-Ga2O3 thin films were grown on β-Ga2O3 without phase separation. However, the XRD rocking curves revealed that the mist CVD- grown Ge-doped β-Ga2O3 was slightly degraded compared to the substrate as the Ge concentration increased. The surface morphologies of the Ge-doped β-Ga2O3 exhibited atomically flat surfaces with a root mean square roughness of less than 1 nm. These results indicate that the Ge-doped β-Ga2O3 thin films prepared by mist chemical vapor deposition are promising for device applications.
The resistive switching temperature associated with the metal−insulator transition (MIT) of epitaxial VO 2 thin films grown on flexible synthetic mica was modulated by bending stress. The resistive switching temperature of polycrystalline VO 2 and V 2 O 5 thin films, initially grown on synthetic mica without a buffer layer, was observed not to shift with bending stress. By inserting a SnO 2 buffer layer, epitaxial growth of the VO 2 (010) thin film was achieved, and the MIT temperature was found to vary with the bending stress. Thus, it was revealed that the bending response of the VO 2 thin film depends on the presence or absence of the SnO 2 buffer layer. The bending stress applied a maximum in-plane tensile strain of 0.077%, resulting in a high-temperature shift of 2.3 °C during heating and 1.8 °C during cooling. After 10 4 bending cycles at a radius of curvature R = 10 mm, it was demonstrated that the epitaxial VO 2 thin film exhibits resistive switching temperature associated with MIT.
Herein, we demonstrate β-(AlxGa1-x)2O3 thin films that were coherently grown on a (010) β-Ga2O3 substrate using mist chemical vapor deposition (CVD). X-ray diffraction and reciprocal space mapping results revealed that the β-(AlxGa1-x)2O3 thin films were of high-crystalline quality and were grown coherently to attain an Al content of 18.3% as measured by Rutherford backscattering spectroscopy. Importantly, based on their surface morphologies, the coherently grown β-(AlxGa1-x)2O3 thin films have atomically flat surfaces. These results indicate that mist CVD is a promising technique for β-(AlxGa1-x)2O3/β-Ga2O3 heterojunction devices.
Gallium oxide (Ga 2 O 3 ) possesses five polymorphs: α, β, γ, κ (ε), and δ. Although the first four polymorphs have been well-studied, there are few reports on δ-Ga 2 O 3 . Here, we demonstrate the epitaxial growth of metastable δ-Ga 2 O 3 thin films by mist chemical vapor deposition using β-Fe 2 O 3 buffer layers. X-ray diffraction (XRD) 2θ−ω scan pattern revealed that (004) κ-Ga 2 O 3 grew on (111) yttria-stabilized zirconia (YSZ) without a buffer layer or with a bcc-In 2 O 3 buffer layer, whereas (222) δ-Ga 2 O 3 grew on (222) β-Fe 2 O 3 . The β-Fe 2 O 3 buffer layer led to the epitaxial growth of the δ-Ga 2 O 3 thin film. The lattice mismatch between the equivalent crystal structures of β-Fe 2 O 3 and δ-Ga 2 O 3 triggered this growth. XRD analysis shows that δ-Ga 2 O 3 grew epitaxially on the β-Fe 2 O 3 buffer layer/YSZ substrate in both the out-of-plane and in-plane orientations, and the lattice constant inferred from the diffraction peaks was estimated to be 9.255 Å. Reciprocal space mapping results indicated that the δ-Ga 2 O 3 grown on β-Fe 2 O 3 was fully relaxed. Selected area electron diffraction images confirmed that the δ-Ga 2 O 3 exhibited a cubic bixbyite structure. The optical band gap of δ-Ga 2 O 3 was 4.3 or 4.9 eV, as calculated from reflection electron energy loss spectroscopy. We successfully grew a δ-Ga 2 O 3 epitaxial thin film for the first time. KEYWORDS: δ-Ga 2 O 3 , β-Fe 2 O 3 , bixbyite structure, epitaxial growth, mist CVD
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