Chemical Properties
Gallium arsenide contains 48.2% gallium and 51.8% arsenic and is considered an intermetallic compound. It occurs as cubic crystals with a dark gray metallic sheen. Gallium arsenide is electroluminescent in infrared light. Gallium arsenide readily reacts with oxygen in air, forming a mixture of oxides of gallium and arsenic on the crystal surface. Gallium arsenide presents the following properties: hardness, 4.5; thermal expansion coefficient, 5.9×10
6; thermal conductivity, 0.52Wunits; specific heat, 0.086 cal/g/ ℃; intrinsic electron concentration, 10
7; energy gap at room temperature, 1.38 eV; electron mobility, 8800 cm
2/V/s; effective mass for electrons, 0.06m
0; lattice constant,5.6–54 AO; dielectric constant, 11.1; intrinsic resistivity at 300K＝3.7×10
8Ωcm; electron lattice mobility at 300K＝ 10,000 cm2/V/s; intrinsic charge density at 300K＝1.4 10
6 cm
-3; electron diffusion constant at 300K＝310 cm2/s; and hole diffusion constant＝11.5 cm2/s.
Garlic odor when moistened. Finely divided gallium arsenide can react vigorously with steam, energetic acids, and oxidizers to evolve arsine gas, and can release arsenic fumes when heated to decomposition. The molten form attacks quartz.
Physical properties
Gray cubic crystal; density 5.316 g/cm3; melts at 1,227°C; hardness 4.5 Mohs; lattice constant 5.653?; dielectric constant 11.1; resistivity (intrinsic) at 27°C, 3.7x10
8 ohm-cm.
Uses
Gallium arsenide, GaAs, is considered a possible substitute for silicon substrates, based on its potential for high speed applications where it can operate at high (1.9 GHz) frequencies using low power consumptions and high sensitivity. One reason that GaAs technology has not fulfilled its promise is that silicon technology has dramatically improved in the interim, particularly with improvements in speed, and has reduced the cost-effectiveness of pursuing GaAs development
Uses
In semiconductor applications (transistors, solar cells, lasers).Gallium arsenide is among the most widely used intermetallic semiconductor components (Harrison, 1986; McIntyr and Sherin, 1989). Gallium arsenide is also incorporated into light-emitting diodes and photovoltaic cells, while gallium alloys are used for dental amalgam as a low toxicity replacement for mercury.
Uses
Gallium arsenide is electroluminscent in infrared light and is used
for telephone equipment, lasers, solar cell, and other electronic devices. GaAs is used as the substrate of the infrared low-pass filter.
Production Methods
Gallium (Ga) and arsenic (As), heated in a vacuum to eliminate oxygen, are filled in the silica boat
and the boat is vacuum-sealed in a silica tube. A single crystal is obtained by putting the silica tube
into the horizontal Stockbarger furnace with three zones: A (605℃), B (1250℃) and C (1100℃),
and by transporting the tube in the direction A→B→C with the speed of 2 cm/h. The Czochralski
method can also be used (refer to InAs).
The vapor phase method can be used to deposit the thin films. For instance, the GaAs single
crystal is grown on the low temperature area by heating the closed tube filled with GaAs together
with I2, Cl2, or HCl gas with a temperature gradient. Using this method, we can grow the
epitaxial layer.
Preparation
Gallium arsenide is prepared by passing a mixture of arsenic vapor and hydrogen over gallium(III) oxide heated at 600°C: Ga2O3 + 2As + 3H2 2GaAs + 3H2OThe molten material attacks quartz. Therefore, quartz boats coated with carbon by pyrolytic decomposition of methane should be used in refining the compound to obtain high purity material. Gallium arsenide is produced in polycrystalline form as high purity, single crystals for electronic applications. It is produced as ingots or alloys, combined with indium arsenide or gallium phosphide, for semiconductor applications.
General Description
Dark gray crystals with a metallic greenish-blue sheen or gray powder. Melting point 85.6°F (29.78°C).
Air & Water Reactions
Stable in dry air. Tarnishes in moist air. Insoluble in water.
Reactivity Profile
GALLIUM ARSENIDE can react with steam, acids and acid fumes. Reacts with bases with evolution of hydrogen. Attacked by cold concentrated hydrochloric acid. Readily attacked by the halogens. The molten form attacks quartz.
Hazard
Toxic metal. Questionable carcinogen
Fire Hazard
Flash point data for GALLIUM ARSENIDE are not available; however, GALLIUM ARSENIDE is probably combustible.
Flammability and Explosibility
Non flammable
Safety Profile
Confirmed carcinogen.
Mddly toxic by intraperitoneal route. Most
arsenic compounds are poisons. Can react
with steam, acids, and acid fumes to evolve
the deadly poisonous arsine. Molten gallium
arsenide attacks quartz. When heated to
decomposition it emits very toxic fumes of
As. See also ARSENIC COMPOUNDS and
GALLIUM COMPOUNDS.
Carcinogenicity
Carcinogenesis.
Gallium is antineoplastic in several
human and murine cancer cell lines and in some in vivo
cancers. It has been used experimentally in patients in the
treatment of lymphatic malignancies (including multiple
myelomas) and for urothelial malignancies. However,
the dissociation of gallium arsenide into gallium and arsenic
is a factor to take into account. A considerable number of
studies have evaluated the carcinogenic potential of arsenic
and various arsenic compounds.
Structure and conformation
The space lattice of gallium arsenide (GaAs) belongs to the cubic system T
d2, and its zincblende-type structure has a lattice constant of a=0.5654 nm and a distance to its nearest
neighbor of 0.244 nm.
