
Gallium(III) oxide

Gallium(III) trioxide is an inorganic compound with the formula Ga2O3. It exists as several polymorphs, all of which are white, water-insoluble solids. Although no commercial applications exist, 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.
Preparation.
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.
Reactions.
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, .
With HCl, it forms gallium trichloride GaCl3.
It can be reduced to gallium suboxide (gallium(I) oxide) Ga2O by H2. or by reaction with gallium metal:
Structure.
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.
ε-Ga2O3 films deposited by metalorganic vapour phase epitaxy show a columnar structure with orthorhombic crystal symmetry. Macroscopically, this structure is seen by X-ray crystallography as hexagonal close packed.
Potential applications.
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.
ε-Ga2O3 thin films deposited on sapphire show potential applications as solar-blind UV photodetector.
Thin Ga2O3 films are of commercial interest as gas sensitive materials and Ga2O3. Ellipsometry is a procedure that can be used to determine optical functions of the β-Ga2O3.
β-Ga2O3 is used in the production of Ga2O3-Al2O3 catalyst.