Gallium arsenide

This article is about the chemical compound. For the record label, see Gallium Arsenide.

Related Topics:
Record label - Gallium Arsenide

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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 (ie, MMICs), infrared light-emitting diodes and laser diodes.

Related Topics:
Compound - Gallium - Arsenic - Semiconductor - Microwave - Integrated circuit - MMIC - Infrared - Light-emitting diode - Laser diode

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Properties

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General

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Namegallium arsenide

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Chemical FormulaGaAs

Related Topics:
Ga - As

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AppearanceDark gray cubic crystals

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Structure

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Formula weight144.64 u

Related Topics:
Formula weight - U

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Lattice constant0.56533 nm

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Crystal structurezincblende

Related Topics:
Crystal structure - Zincblende

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Physical

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State of matter at STPsolid

Related Topics:
State of matter - STP - Solid

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Melting point at SP1513 K

Related Topics:
Melting point - SP - K

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Boiling point at SP?

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Specific gravity5.318

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Electronic

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Band gap at 300 K1.424 eV

Related Topics:
Band gap - EV

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Electron effective mass0.067 me

Related Topics:
Electron - Effective mass

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Light hole effective mass0.082 me

Related Topics:
Light hole - Effective mass

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Heavy hole effective mass0.45 me

Related Topics:
Heavy hole - Effective mass

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Electron mobility at 300 K9200 cm2/(V·s)

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Hole mobility at 300 K400 cm2/(V·s)

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Precautions

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ToxicYES

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Decompostion productsHighly toxic arsenic fumes

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SI units were used where possible.

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GaAs has some electronic properties which 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 when operated at high frequencies. They can also be operated at higher power levels than the equivalent silicon device because they have higher breakdown voltages. These properties have made GaAs circuitry common in mobile phones, satellite communications, microwave point-to-point links, and some radar systems.

Related Topics:
Silicon - Noise - Mobile phone - Satellite - Radar

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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).

Related Topics:
Direct bandgap - Indirect bandgap - LED - Laser

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Its high switching speed makes GaAs seemingly ideal for computer uses, and for some time in the 1980s many thought that it was only a matter of time before the entire market switched off of silicon. The first to attempt this were the supercomputer vendors, with Cray, Convex and Alliant all running GaAs projects in order to stay ahead of the ever-improving CMOS microprocessor. The closest to production was the Cray-3, built to one example in the early 1990s, but the effort was so costly the venture failed and the company filed for bankruptcy in 1995.

Related Topics:
Supercomputer - Cray - Convex - Alliant - CMOS - Cray-3 - 1995

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Silicon has three major advantages over GaAs. First, silicon is cheap. This is for several reasons: silicon's large wafer size (maximum of ~300 mm compared to ~150 mm diameter), higher strength allowing for easier processing, and of course the scale of the economy.

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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.

Related Topics:
Silicon dioxide - Insulator - Silicon nitride

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The third, and perhaps most important, advantage is that silicon posesses a much higher hole mobility. This allows the fabrication of higher-speed P-channel field effect transistors, which are required for CMOS logic. A lack of a fast CMOS structure means that GaAs logic circuits have much higher power consumption, which has made them unable to compete with silicon logic circuits.

Related Topics:
Hole - Field effect transistors - CMOS

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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.

Related Topics:
Aluminum arsenide - Al_xGa_1-xAs - Molecular beam epitaxy - Strain

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See also semiconductor, electronics, integrated circuit, semiconductor devices, field effect transistor

Related Topics:
Semiconductor - Electronics - Integrated circuit - Semiconductor devices - Field effect transistor

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