Variational wave functions used in the variational Monte Carlo (VMC) method are extensively improved to overcome the biases coming from the assumed variational form of the wave functions. We construct a highly generalized variational form by introducing a large number of variational parameters to the Gutzwiller-Jastrow factor as well as to the one-body part. Moreover, the projection operator to restore the symmetry of the wave function is introduced. These improvements enable to treat fluctuations with long-ranged as well as short-ranged correlations. A highly generalized wave function is implemented by the Pfaffians introduced by Bouchaud et al., together with the stochastic reconfiguration method introduced by Sorella for the parameter optimization. Our framework offers much higher accuracy for strongly correlated electron systems than the conventional variational Monte Carlo methods.

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.

Epitaxial ε-gallium oxide (Ga2O3) thin films incorporated with In were successfully grown by mist chemical vapour deposition (CVD) on c-plane sapphire substrates for bandgap tuning.

In this study, epitaxial ε-Ga2O3 thin films are successfully grown on cubic (111) MgO and (111) yttria-stablized zirconia (YSZ) substrates by mist chemical vapor deposition. Pure-phase hexagonal ε-Ga2O3 thin films are grown on the two substrates with a c-axis orientation determined by X-ray diffraction (XRD) 2θ–ω scanning. XRD pole figure measurements reveal that the in-plane orientation relationship between the (0001) of ε-Ga2O3 and the (111) of the two substrates is ε-Ga2O3 ∥ substrates . Using (111) MgO substrates with a 2.5% lattice mismatch, the epitaxial ε-Ga2O3 films are successfully grown at a low temperature of 400 °C. The optical direct and indirect bandgaps of pure ε-Ga2O3 thin films are estimated as 5.0 and 4.5 eV, respectively.

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In this study, ε-(AlxGa1−x)2O3 alloy films were grown on c-plane AlN templates by mist chemical vapor deposition. The Al content of two samples was determined by Rutherford backscattering analysis. The lattice constant of the ε-(AlxGa1−x)2O3 alloy films followed Vegard's law, and the Al contents of other samples were determined to be as high as x = 0.395 by Vegard's law. The direct bandgap was obtained in the range of 5.0–5.9 eV by transmittance measurements. The valence-band offset between ε-(Al0.395Ga0.605)2O3 and ε-Ga2O3 was analyzed to be 0.2 eV, and the conduction-band offset was calculated to be 0.7 eV by X-ray photoelectron spectroscopy. The ε-(AlxGa1−x)2O3/ε-Ga2O3 interface band discontinuity was type I. Our experimental results will be important for the actual application of ε-(AlxGa1−x)2O3/ε-Ga2O3 heterojunction devices.

Epitaxial ε-Ga2O3 thin films with smooth surfaces were successfully grown on c-plane AlN templates by mist chemical vapor deposition. Using X-ray diffraction 2θ–ω and φ scans, the out-of-plane and in-plane epitaxial relationship was determined to be (0001) ε-Ga2O3 ∥ (0001)AlN. The gallium/oxygen ratio was controlled by varying the gallium precursor concentration in the solution. While scanning electron microscopy showed the presence of large grains on the surfaces of the films formed for low concentrations of oxygen species, no large grains were observed under stoichiometric conditions. Cathodoluminescence measurements showed a deep-level emission ranging from 1.55–3.7 eV; however, no band-edge emission was observed.

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