In this study, ε-Ga2O3 thin films were grown by mist chemical vapor deposition on a hexagonal (0001) GaN template and a cubic (111) SrTiO3 (STO) substrate. By analyzing the obtained X-ray diffraction (XRD) φ-scans, it was found that the ε-Ga2O3 epitaxial thin films grown on both GaN and STO exhibited an orthorhombic structure. In addition, a method was proposed to distinguish between hexagonal and orthorhombic structures on the basis of the relationships between the 2θ and χ angles for these structures, obtained from the XRD studies. Finally, a mechanism was discussed on the basis of angle relationships, where three rotational domains were observed for orthorhombic ε-Ga2O3 on GaN and STO. Transmission electron microscopy was then employed to determine whether the ε-Ga2O3 thin films on the GaN template and STO substrate consisted of columnar ε-Ga2O3 comprising small domains and intermediate layers between the ε-Ga2O3 film and the substrate.

In this study, single-phase ε-gallium oxide (Ga2O3) thin films were heteroepitaxially grown on c-plane sapphire substrates.

LiNbO3 and LiTaO3 substrates are used in wide-bandwidth applications such as surface acoustic wave filter and show structural similarity to α-Ga2O3. In this study, we demonstrated the phase control of Ga2O3 epitaxial thin films, grown by mist chemical vapor deposition, on the (0001) planes of LiNbO3 and LiTaO3 substrates using α-Fe2O3 buffer layers. κ-Ga2O3 thin films were grown epitaxially on bare LiNbO3 and LiTaO3 substrates. Conversely, the insertion of the α-Fe2O3 buffer layer led to the preferential growth of the α-Ga2O3 epitaxial thin films. X-ray diffraction (XRD) φ-scan results revealed that the α-Ga2O3 thin films were grown along the same in-plane direction as that of the substrates. Besides, the XRD φ-scan results indicated that twin-free α-Ga2O3 was grown on the LiNbO3 and LiTaO3 substrates with the α-Fe2O3 buffer layers. The x-ray rocking curve scans of the asymmetric plane of α-Ga2O3 showed that the full width at half maximum values of α-Ga2O3 on the LiNbO3 and LiTaO3 substrates with the buffer layers were smaller than that of the c-plane α-Al2O3 substrate with and without the buffer layer. In addition, we grew the (11-20) and (1-100) planes of the α-Ga2O3 epitaxial thin films on the (11-20) and (1-100) planes of LiNbO3 substrates with the α-Fe2O3 buffer layer, respectively. This study showed that LiTaO3 and LiNbO3 are promising substrates for the epitaxial growth of α-Ga2O3 and κ-Ga2O3.

This study demonstrates the formation of the van der Waals epitaxy of the ε-gallium oxide (Ga 2 O 3 ) thin film on cleaved synthetic mica via mist chemical vapor deposition. Orthorhombic ε-Ga 2 O 3 (001) was epitaxially grown on synthetic mica (001). The analysis using transmission electron microscopy revealed an in-plane orientation of ε-Ga 2 O 3 [010] || synthetic mica [010]. However, the most thermodynamically stable β-Ga 2 O 3 was grown at the film-substrate interface. The optical direct bandgap of the ε-Ga 2 O 3 thin film grown by van der Waals epitaxy was estimated to be 5.0 eV, which was the same as for the heteroepitaxially grown ε-Ga 2 O 3 thin film on other substrates. Besides, after ε-Ga 2 O 3 thin film was grown on the synthetic mica substrates that are cleaved sufficiently thin, the sample could be bent or cut with scissors. These results denote that the epitaxial ε-Ga 2 O 3 thin films grown by van der Waals epitaxy can be applied to flexible electronics.

AbstractBendable p-type NiO and n-type In2O3 thin films were epitaxially grown on synthetic mica using mist chemical vapor deposition. It was found that at a growth temperature of 400 °C, epitaxially grown cubic (111) NiO thin films developed twin rotational domains, and the epitaxial relationship between each domain and the substrate was (111) NiO [1-10] or [10-1] || (001) synthetic mica [100]. In the visible light region, the epitaxial NiO thin films showed high transparencies, and their cut-offs appeared in the UV region. Additionally, at a growth temperature of 500 °C, cubic (111) In2O3 thin films with and without Sn doping were epitaxially grown on synthetic mica. As a result of the plasma oscillation of free carriers, Sn-doped In2O3 thin films exhibited reflection characteristics in the infrared region, while maintaining their visible light transmission characteristics. Furthermore, compared with non-doped In2O3, Sn doping decreased the sheet resistance by two digits.