Gallium(III) arsenide

Gallium arsenide (GaAs) is a laser diodes and solar cells.

Applications

GaAs advantages

GaAs has some electronic properties which are superior to Gunn diodes for generation of microwaves.

Another advantage of GaAs is that it has a direct band gap, which 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 lasers possible).

Because of its high switching speed, GaAs would seem to be ideal for computer applications, and for some time in the 1980s many thought that the microelectronics market would switch from silicon to GaAs. The first attempted changes were implemented by the supercomputer vendors Cray Computer Corporation, Convex, and Alliant in an attempt to stay ahead of the ever-improving CMOS microprocessor. Cray eventually built one GaAs-based machine in the early 1990s, the Cray-3, but the effort was not adequately capitalized, and the company filed for bankruptcy in 1995.

Silicon's advantages

Silicon has three major advantages over GaAs for integrated circuit manufacture. First, silicon is abundant and cheap to process. Silicon's greater physical strength enables larger wafers (maximum of ~300 mm compared to ~150 mm diameter for GaAs). Si is highly abundant in the Earth's crust, in the form of silicate minerals. The economy of scale available to the silicon industry has also reduced the adoption of GaAs.

The second major advantage of Si is the existence of insulators. Silicon dioxide can easily be incorporated onto silicon circuits, and such layers are adherent to the underlying Si. GaAs does not form a stable adherent insulating layer.

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

GaAs heterostructures

Complex layered structures of gallium arsenide in combination with magnetic semiconductor.

Solar cells and detectors

Another important application of GaAs is for high efficiency solar cells. In 1970, the first GaAs heterostructure solar cells were created by indium gallium phosphide layers were developed as the basis of a triple junction solar cell which held a record efficiency of over 32% and can operate also with light as concentrated as 2,000 suns. This kind of solar cell powers the robots Spirit and Opportunity, which are exploring Mars' surface. Also many solar cars utilize GaAs in solar arrays.

Complex designs of Al_xGa_1-xAs-GaAs devices can be sensitive to infrared radiation (QWIP).

GaAs diodes can be used for the detection of x-rays. ^[4]

Light emission devices

GaAs has been used to produce (near-infrared) laser diodes since the early 1960s.^[5]

Single crystals of gallium arsenide can be manufactured by the Bridgeman technique, as the Czochralski process is difficult for this material due to its mechanical properties. However, an encapsulated Czochralski method is used to produce ultra-high purity GaAs for semi-insulators.

GaAs is often used a substrate material for the epitaxial growth of other III-V semiconductors including: InGaAs and GaInNAs.

Safety

The toxicological properties of gallium arsenide have not been thoroughly investigated. On one hand, due to its arsenic content, it is considered highly toxic and metalorganic precursors have been reported recently in a review.^[6]

See also

• Electronics
• Field effect transistor
• Heterostructure emitter bipolar transistor
• Integrated circuit
• Semiconductor
• Semiconductor devices
• solar cell
• magnetic semiconductor

Related materials

• Aluminium arsenide
• Indium arsenide
• Gallium antimonide
• Gallium phosphide
• Aluminium gallium arsenide
• Indium gallium arsenide
• Gallium arsenide phosphide
• Gallium nitride
• MOVPE
• Trimethylgallium
• Arsine

References

1. ^ Alferov, Zh. I., V. M. Andreev, M. B. Kagan, I. I. Protasov, and V. G. Trofim, 1970, ‘‘Solar-energy converters based on p-n Al_xGa_1-xAs-GaAs heterojunctions,’’ Fiz. Tekh. Poluprovodn. 4, 2378 (Sov. Phys. Semicond. 4, 2047 (1971))]
2. ^ Nanotechnology in energy applications, pdf, p.24
3. ^ Nobel Lecture by Zhores Alferov, pdf, p.6
4. ^ Glasgow University report on CERN detector
5. ^ R. C. Miller, F. M. Ryan and P. R. Emtage, “Uniaxial Strain Effects in Gallium Arsenide Laser Diodes,” 7th Intl. Conf. Phys. Semicond., Academic Press, Paris, 1964.
6. ^ Environment, health and safety issues for sources used in MOVPE growth of compound semiconductors; D V Shenai-Khatkhate, R Goyette, R L DiCarlo and G Dripps, Journal of Crystal Growth, vol. 1-4, pp. 816-821 (2004); doi:doi:10.1016/j.jcrysgro.2004.09.007

• Semiconductor Today: Online resource covering compound semiconductors and advanced silicon materials and devices