Gallium(III) trioxide is an inorganic compound with the formula Ga2O3. It exists as several polymorphs, all of which are white, water-insoluble solids. Ga2O3 is an intermediate in the purification of gallium, which is consumed almost exclusively as gallium arsenide. The thermal conductivity of β-Ga2O3 is at least one order of magnitude lower than the other wide bandgap semiconductors, such as GaN and SiC. It is further reduced for related nanostructures which are usually used in electronic devices. Heterogeneous integration with high thermal conductivity substrates such as diamond and SiC helps heat dissipation of β-Ga2O3 electronics.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Gallium trioxide is precipitated in hydrated form upon neutralization of acidic or basic solution of gallium salt. Also, it is formed on heating gallium in air or by thermally decomposing gallium nitrate at 200–250 ˚C. It can occur in five different modifications, α, β, γ, δ, and ε. Of these modifications β-Ga2O3 is the most stable form.
β-Ga2O3 is prepared by heating nitrate, acetate, oxalate or other organic derivatives above 1000 °C. Epitaxial thin films of β-Ga2O3 can be deposited on sapphire substrate at temperatures between 190 °C and 550 °C.
α-Ga2O3 can be obtained by heating β-Ga2O3 at 65 kbars and 1100 °C. The hydrated form can be prepared by decomposing precipitated and "aged" gallium hydroxide at 500 °C.
γ-Ga2O3 is prepared by rapidly heating the hydroxide gel at 400–500 °C. A more crystalline form of this polymorph can be prepared directly from gallium metal by a solvothermal synthesis.
δ-Ga2O3 is obtained by heating Ga(NO3)3 at 250 °C.
Gallium(III) trioxide is amphoteric. It reacts with alkali metal oxides at high temperature to form, e.g., NaGaO2, and with Mg, Zn, Co, Ni, Cu oxides to form spinels, e.g. MgGa2O4.
It dissolves in strong alkali to form a solution of the gallate ion, Ga(OH)− 4.
β-Ga2O3, with a melting point of 1900 ˚C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions occupy distorted tetrahedral and octahedral sites, with Ga-O bond distances of 1.83 and 2.00 Å respectively.
α-Ga2O3 has the same structure (corundum) as α-Al2O3, wherein Ga ions are 6-coordinate. γ-Ga2O3 has a defect spinel structure similar to that of γ-Al2O3.
Gallium(III) oxide has been studied in the use of lasers, phosphors, and luminescent materials. It has also been used as an insulating barrier in tight junctions. Monoclinic β-Ga2O3 is used in gas sensors and luminescent phosphors and can be applied to dielectric coatings for solar cells. This stable oxide has also shown potential for deep-ultraviolet transparent conductive oxides, and transistor applications.
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