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Gallium arsenide (GaAs) is a chemical compound composed of gallium and arsenic. It is an important semiconductor, and is used to make devices such as microwave frequency integrated circuits, infrared light-emitting diodes and laser diodes.
Properties
| General |
| Name | Gallium arsenide |
| Chemical Formula | Ga As |
| Appearance | Dark gray cubic crystals |
| Structure |
Formula weight | 144.64 amu |
| Lattice constant | 0.56533 nm |
| Crystal structure | Zincblende |
Physical |
| State of matter at STP | solidA solid is a state of matter, characterized by a definite volume and a definite shape (i. it resists deformation). Within a solid, atoms/ molecules are relatively close together, or "rigid"; however, this does not prevent the solid from becoming deformed |
| Melting pointThe melting point of a solid is the temperature at which it changes state from solid to liquid. When considered as the temperature of the reverse change, it is referred to as the freezing point . For example, the melting point of the element mercury is 23 at SP | 1513 KThe kelvin (symbol: K is the SI unit of temperature, and is one of the seven SI base units. It is defined by two facts: zero kelvin is absolute zero (when molecular motion stops), and one kelvin is the fraction 1/273. 16 of the thermodynamic temperature o |
| Boiling pointAlternate use: Boiling Point, English title of Kitano Takeshi's film 3-4X Jugatsu The boiling point of a substance is the temperature at which it can change state from a liquid to a gas throughout the bulk of the liquid. A liquid may change to a gas at te at SP | ? |
| Specific gravity | 5.318 |
| Electronic |
| Band gap at 300K | 1.424 eV |
| Electron effective mass | 0.067 me |
| Light hole effective mass | 0.082 me |
| Heavy hole effective mass | 0.45 me |
| Electron mobility at 300 K | 9200 cm2/V·s |
| Hole mobility at 300 K | 400 cm2/V·s |
Precautions |
| Toxic | YES |
| Decompostion products | Highly toxic arsenic fumes |
SI units were used where possible. |
The electronic properties of GaAs are superior to silicon's. It has a higher saturated electron velocity and higher electron mobility, allowing it to function at frequencies in excess of 250 GHz. Also, GaAs devices generate less noise than silicon devices.
Another advantage of GaAs is that it has a direct bandgap. This means that it can be used to emit light. Silicon has an indirect bandgap, and so is very poor at emitting light. (Nonetheless, recent advances may make silicon LEDs and lasers possible).
Silicon has two major advantages over GaAs. First, silicon is cheap. This is for several reasons: silicon's large wafer size (maximum of ~300mm compared to ~150mm diameter), high strength allowing for easier processing, and of course the scale of the economy.
The second major advantage is the existence of silicon dioxide—one of the best known insulators of any kind. Silicon dioxide can easily be incorporated into silicon circuits wherever a good insulator is required. GaAs circuits must either use the intrinsic semiconductor itself or silicon nitride ; neither comes close to the extremely good properties of silicon dioxide.
Complex layered structures of gallium arsenide in combination with Aluminum arsenide (AlAs) or the alloy AlxGa1-xAs can be grown using molecular beam epitaxy (MBE). Because GaAs and AlAs have almost the same lattice constant, the layers have very little induced strain, which allows them to be grown almost arbitrarily thick.
Gallium arsenide integrated circuits are commonly used in mobile phones, satellite communications, microwave point-to-point links, and some radar systems.
Cray Research attempted to make a GaAs-based supercomputer, the Cray-3, in the early 1990s. The venture failed, and the company filed for bankruptcy in 1995.
See also semiconductor, electronics, integrated circuit, semiconductor devices, field effect transistor
