Gallium(III) oxide
Encyclopedia
Gallium oxide (Ga2
O3
) is a chemical compound
used in vacuum deposition
and as part of the manufacturing of semiconductor device
s.
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,δ,γ and ε. Of these modifications β-Ga2O3 is the most stable form.
(TEM) and energy-dispersive X-ray spectroscopy
(EDS). Such analysis showed that the resulting structures were wool-like and gray in color.
SEM reveals that the products consist of wire-like nanostructures and sheet-type structures. The TEM image shows the ribbon-like structure of Ga2O3. The EDS confirms that the nanostructures obtained are in fact Ga2O3.
The nanoribbon and nanosheets structures of Ga2O3 are pure, structurally uniform, single crystalline and free from dislocation. The structure of nanoribbons and nanosheets, that is, their wave-like and sheet-like shape, also indicates that their growth is as a result of growth kinetics, vapor-liquid-solid (VLS) method and vapor-solid method (VS). VLS and VS are two common growth mechanisms for nanowires. The VLS process, catalytic-assisted in nature, is one in which the metal particle is located at the growth of the wire and acts as the catalytic active site. For the VS process, oxide vapor, which is evaporated from the starting oxide at a higher temperature xone, directly deposits on a substrate at a lower temperature region and grows into ribbon-like nanostructures.
is a procedure that can be used to determine optical functions of the β-Ga2O3.
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
O3
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
) is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
used in vacuum deposition
Vacuum deposition
Vacuum deposition is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub-atmospheric pressure on a solid surface. The layers may be as thin as one atom to millimeters thick . There may be multiple layers of different materials...
and as part of the manufacturing of semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
s.
Preparation
Gallium oxide is precipitated in hydrated form upon neutralizationNeutralization
In chemistry, neutralization, or neutralisation is a chemical reaction in which an acid and a base react to form a salt. Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water:Y and X represent a monovalent cation and anion...
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,δ,γ and ε. Of these modifications β-Ga2O3 is the most stable form.
Preparation Methods for the Five Modifications
- β-Ga2O3 is prepared by heating nitrate, acetate, oxalate or other organic derivatives above 1000˚C.
- α-Ga2O3 can be obtained by heating β-Ga2O3 at 65kbars and 1100˚C for 1 hour giving a crystalline structure. 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˚C-500˚C.
- δ-Ga2O3 is obtained by heating Ga(NO3)3 at 250˚C.
- ε-Ga2O3 is prepared by briefly heating δ-Ga2O3 at 550˚C for 30 minutes.
Crystal Structure
The β-Ga2O3, with a melting point of 1740˚C, is the most stable crystalline modification. The oxide ions are in a distorted cubic closest packing arrangement, and the gallium (III) ions are in distorted tetrahedral and octahedral sites, with Ga-O bond distances of 1.83 and 2.00 Å respectively. These distortions are in fact the reasons for the great level of stability of β-Ga2O3.Applications and Uses
Gallium(III) oxide is an important functional material. It has been studied in the use of lasers, phosphors and luminescent materials, has been shown to demonstrate catalytic properties and has also been used as an insulating barrier in tight junctions. The stable oxide of gallium, monoclinic β-Ga2O3, has current applications 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.Nanotechnology
Nanoribbons and nanosheets of Ga2O3 can be synthesized either by high temperature reaction of Ga0 with water or by evaporation of GaN at high temperature in the presence of oxygen. Analysis of the products of the thermal evaporation reaction is done using X-ray diffraction , scanning electron microscopy (SEM), transmission electron microscopyTransmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
(TEM) and energy-dispersive X-ray spectroscopy
X-ray spectroscopy
X-ray spectroscopy is a gathering name for several spectroscopic techniques for characterization of materials by using x-ray excitation.-Characteristic X-ray Spectroscopy:...
(EDS). Such analysis showed that the resulting structures were wool-like and gray in color.
SEM reveals that the products consist of wire-like nanostructures and sheet-type structures. The TEM image shows the ribbon-like structure of Ga2O3. The EDS confirms that the nanostructures obtained are in fact Ga2O3.
The nanoribbon and nanosheets structures of Ga2O3 are pure, structurally uniform, single crystalline and free from dislocation. The structure of nanoribbons and nanosheets, that is, their wave-like and sheet-like shape, also indicates that their growth is as a result of growth kinetics, vapor-liquid-solid (VLS) method and vapor-solid method (VS). VLS and VS are two common growth mechanisms for nanowires. The VLS process, catalytic-assisted in nature, is one in which the metal particle is located at the growth of the wire and acts as the catalytic active site. For the VS process, oxide vapor, which is evaporated from the starting oxide at a higher temperature xone, directly deposits on a substrate at a lower temperature region and grows into ribbon-like nanostructures.
Optical Uses
It is important to accurately determine the optical functions as these are essential for device simulations and improvement in material preparation. The thin Ga2O3 films are of commercial interest as gas sensitive material and Ga2O3 based glasses are among the best optical materials used in advanced technologies. EllipsometryEllipsometry
Ellipsometry is an optical technique for the investigation of the dielectric properties of thin films....
is a procedure that can be used to determine optical functions of the β-Ga2O3.
Catalyst
β-Gallium (III) oxide is also very important in the production of catalysts . It is needed for the preparation of Ga2O3-Al2O3 catalyst. The preparation of this catalyst involves reacting Al2O3 with aqueous solutions of gallium nitrate, followed by evaporation to dryness at 393K, and calcining in air (i.e.thermal decomposition of the compound) for 4 hours at 823K.See also
- Vacuum depositionVacuum depositionVacuum deposition is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub-atmospheric pressure on a solid surface. The layers may be as thin as one atom to millimeters thick . There may be multiple layers of different materials...
- NanotechnologyNanotechnologyNanotechnology is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres...
- Scanning electron microscopy
- Transmission electron microscopyTransmission electron microscopyTransmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
- EllipsometryEllipsometryEllipsometry is an optical technique for the investigation of the dielectric properties of thin films....