Microstructural Gradational Properties of Sn-Doped Gallium Oxide Heteroepitaxial Layers Grown Using Mist Chemical Vapor Deposition

This study examined the microstructural gradation in Sn-doped, n-type Ga2O3 epitaxial layers grown on a two-inch sapphire substrate using horizontal hot-wall mist chemical vapor deposition (mist CVD). The results revealed that, compared to a single Ga2O3 layer grown using a conventional single-step growth, the double Ga2O3 layers grown using a two-step growth process exhibited excellent thickness uniformity, surface roughness, and crystal quality. In addition, the spatial gradient of carrier concentration in the upper layer of the double layers was significantly affected by the mist flow velocity at the surface, regardless of the dopant concentration distribution of the underlying layer. Furthermore, the electrical properties of the single Ga2O3 layer could be attributed to various scattering mechanisms, whereas the carrier mobility of the double Ga2O3 layers could be attributed to Coulomb scattering owing to the heavily doped condition. It strongly suggests the two-step-grown, lightly-Sn-doped Ga2O3 layer is feasible for high power electronic devices.

Synthesis of Stoichiometric SrTiO3 and Its Carrier Doping from Air-Stable Bimetallic Complexes

We demonstrate the synthesis of perovskite oxide SrTiO₃ with ideal cation stoichiometry and homogeneous La doping using air-stable Sr-Ti and La-Ti bimetallic peroxo complexes with a 1:1 cation ratio. Phase-pure SrTiO₃, La₂Ti₂O₇, and LaTiO₃ were successfully synthesized by thermal decomposition of those complexes. La-doped SrTiO₃ was obtained by mixing the Sr-Ti and La-Ti complexes in an acid solution, followed by thermal decomposition. La-doped SrTiO₃ showed systematic chemical trends in the lattice constant and electrical conduction. Not only those bulk polycrystals but also cation-stoichiometric SrTiO₃ epitaxial thin films were grown with an atomically flat surface from the Sr-Ti complex.

Epitaxial growth of bismuth oxyhalide thin films using mist CVD at atmospheric pressure

We report the epitaxial growth of bismuth oxyhalide BiOX (X = Cl, Br, and I) thin films using mist chemical vapour deposition at atmospheric pressure. The thin films grown under optimum conditions possessed atomically flat surfaces and high crystallinity, where the lattice constants of BiOX were controlled by epitaxial strain.

Epitaxial Stabilization of SrCu3O4 with Infinite Cu3/2O2 Layers

We report the epitaxial thin-film synthesis of SrCu₃O₄ with infinitely stacked Cu₃O₄ layers composed of edge-sharing CuO₄ square planes, using molecular-beam epitaxy. Experimental and theoretical characterizations showed that this material is a metastable phase that can exist by applying tensile biaxial strain from the (001)-SrTiO₃ substrate. SrCu₃O₄ shows an insulating electrical resistivity in accordance with the Cu²⁺ valence state revealed by X-ray photoelectron spectroscopy. First-principles calculations also indicated that the unoccupied d_3z²-r² band becomes substantially stabilized owing to the absence of apical anions, in contrast to A₂Cu₃O₄Cl₂ (A = Sr, Ba) with an A₂Cl₂ block layer and therefore a trans-CuO₄Cl₂ octahedron. These results suggest that SrCu₃O₄ is a suitable parent material for electron-doped superconductivity based on the Cu₃O₄ plane.

Control of Polar Orientation and Lattice Strain in Epitaxial BaTiO3 Films on Silicon

Conventional strain engineering of epitaxial ferroelectric oxide thin films is based on the selection of substrates with a suitable lattice parameter. Here, we show that the variation of oxygen pressure during pulsed laser deposition is a flexible strain engineering method for epitaxial ferroelectric BaTiO₃ films either on perovskite substrates or on Si(001) wafers. This unconventional growth strategy permits continuous tuning of strain up to high levels (ε > 0.8%) in films greater than one hundred nanometers thick, as well as selecting the polar axis orientation to be either parallel or perpendicular to the substrate surface plane.