Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous pow...

The perovskite structure—a review of its role in ceramic science and technology

Opaque minerals of common granitic rocks were studied microscopically. The granitoids were divided into (i) a magnetite-bearing magnetite-series and (ii) a magnetite-free ilmenite-series. Each series has the following characteristic assemblages of accessary minerals: Magnetite-series: Magnetite (0.1-2 vol.%), ilmenite, hematite, pyrite, sphene, epidote, high ferric/ferrous (and high Mg/Fe) biotite; Ilmenite-series: Ilmenite (less than 0.1 vol.%), pyrrhotite, graphite, muscovite, low ferric/ferrous (and low Mg/Fe) biotite. The mineral assemblages imply a higher oxygen fugacity in the magnetite-series granitoids than in the ilmeniteseries granitoids during solidification of the granitic magmas. The boundary separating the two series is probably near the Ni-NiO buffer. The magnetite-series granitoids are considered to have been generated in a deep level (upper mantle and lowest crust) and not to have interacted with C-bearing materials; whereas the ilmenite-series granitoids were generated in the middle to lower continental crust and mixed with C-bearing metamorphic and sedimentary rocks at various stages in their igneous history. The former carries porphyry copper-molybdenum deposits and the latter accompanies greisen-type tin-wolframite deposits. Lack of porphyry copper deposits in the Mesozoic orogeny belts in East Asia is related to a general paucity of the magnetite-series granitoids in this terrane.

https://www.jstage.jst.go.jp/article/shigenchishitsu1951/27/145/27_145_293/_pdf

The Magnetite-series and Ilmenite-series Granitic Rocks

Sol–gel coatings on metals for corrosion protection

This is a review article on the current status and future prospects of the research and development on gallium oxide (Ga2O3) power devices. Ga2O3 possesses excellent material properties, in particular for power device applications. It is also attractive from an industrial viewpoint since large-size, high-quality wafers can be manufactured from a single-crystal bulk synthesized by melt–growth methods. These two features have drawn much attention to Ga2O3 as a new wide bandgap semiconductor following SiC and GaN. In this review, we describe the recent progress in the research and development on fundamental technologies of Ga2O3 devices, covering single-crystal bulk and wafer production, homoepitaxial thin film growth by molecular beam epitaxy and halide vapor phase epitaxy, as well as device processing and characterization of metal–semiconductor field-effect transistors, metal–oxide–semiconductor field-effect transistors and Schottky barrier diodes.

https://iopscience.iop.org/article/10.1088/0268-1242/31/3/034001/pdf

Recent progress in Ga2O3 power devices

Polymorphism of Ga2O3 and the System Ga2O3—H2O

Reaction series for subalkaline igneous rocks based on different oxygen pressure conditions

The results of a phase-equilibrium study of mixtures lying on the join eucryptite-silica in the system LizO-Al2O3–SiO2 are presented. Hydrother-mal techniques were used to obtain equilibrium relations among the crystalline phases at low temperature. The upper limits of stability of the naturally occurring forms of LiAlSiO, (eucryptite), LiA1SizO6 (spodumene), and LiA1Si4O10 (petalite) were found to be 972°, 500°, and 680°c., respectively. Each of these minerals (low forms) was synthesized. An approximate diagram depicting equilibria among the phases is presented.

Compositional and Stability Relationships Among the Lithium Aluminosilicates: Eucryptite, Spodumene, and Petalite

The system Al2O3-SiO2-H2O

A study of the system Al2O3–Ga2O3–H2O has resulted in the determination of equilibrium diagrams for the systems Al2O3–Ga2O3 and Al2O3.-H2O–Ga2O3.H2O. Extensive solid solution characterizes the α-Al2O3 and β-Ga2O3 structures at high temperatures, but it is shown that below 810°C. a compound, GaAlO3, and a new series of (Al, Ga)2O3 structures are stable. Among the hydrates, a complete series of diaspore solid solutions extends from Al2O3.H2O to Ga2O3.H2O. Boehmite solid solutions extend to approximately the composition 70Al2O3.H2O, 30Ga2O3.H2O.

E. F. Osborn

Papers

Polymorphism of Ga2O3 and the System Ga2O3—H2O

Reaction series for subalkaline igneous rocks based on different oxygen pressure conditions

Compositional and Stability Relationships Among the Lithium Aluminosilicates: Eucryptite, Spodumene, and Petalite

The system Al2O3-SiO2-H2O

The System Alumina‐Gallia‐Water