Gallium arsenide
| Crystal structure | |||||||||||||||||||
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| __ Ga 3+ __ As 3− | |||||||||||||||||||
| Crystal system |
cubic |
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| Space group |
F 4 3 m (No. 216) |
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| Lattice parameters |
a = 565.33 pm |
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| General | |||||||||||||||||||
| Surname | Gallium arsenide | ||||||||||||||||||
| Ratio formula | GaAs | ||||||||||||||||||
| Brief description |
dark gray solid |
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| properties | |||||||||||||||||||
| Molar mass | 144.64 g mol −1 | ||||||||||||||||||
| Physical state |
firmly |
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| density |
5.31 g cm −3 |
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| Melting point |
1238 ° C |
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| Vapor pressure |
984 h Pa (1238 ° C) |
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| solubility |
reacts with water |
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| safety instructions | |||||||||||||||||||
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| MAK |
not specified, as carcinogenic |
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| Thermodynamic properties | |||||||||||||||||||
| ΔH f 0 |
−71.0 kJ / mol |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
The binary compound gallium arsenide ( GaAs ) is a semiconductor material that can be semiconducting ( doped with elements from groups II, IV or VI of the periodic table ) or semi-insulating (undoped). The connections and epitaxial layers that build up on this substrate material are required for the production of electronic components that are used in high-frequency applications and for converting electrical signals into optical signals.
Crystal structure
Gallium arsenide crystallizes in the cubic crystal system in the space group F 4 3 m (space group no. 216) with the lattice parameter a = 5.653 Å and four formula units per unit cell and is isotypic to the structure of the zinc blende . The crystal structure consists of two face-centered cubic lattices ( cubic closest packing of spheres ), which are built up by gallium ( group III) or arsenic (group V) atoms and which are offset from one another by a quarter of the spatial diagonal of the cubic unit cell. The gallium atoms thus occupy half of the tetrahedral gaps in the packing of arsenic atoms and vice versa. Gallium arsenide is an intrinsic direct semiconductor with a band gap of 1.424 eV at room temperature (300 K ). The density of the compound is 5.315 g / cm 3 , its melting point is 1238 ° C.
application areas
In basic research and the semiconductor industry, GaAs is mainly used in the context of the aluminum gallium arsenide material system for the production of semiconductor heterostructures . Components made of gallium arsenide have a transit frequency that is around ten times as high as their comparable silicon counterparts . They have less noise and electrical circuits built with them have lower energy requirements than their direct silicon equivalents. Gallium arsenide is a base material for high electron mobility transistors and Gunn diodes , which are used in high frequency technology. This can be used to build low-noise high-frequency amplifiers (LNA), which are used, among other things, in cell phones , in satellite communication or in radar systems.
In addition, gallium arsenide is used to send information through fiber optic networks with the help of lasers or surface-emitting lasers and to supply satellites with energy from solar cells ( photovoltaics ). In everyday life, gallium arsenide is used in light and laser diodes ranging from infrared to yellow.
Another application of gallium arsenide in research is its use as a photocathode in inverse photoemission spectroscopy , where in particular a spin polarization of the electron beam can be generated with gallium arsenide .
The fiber optic temperature measurement represents an application for gallium arsenide. Here, the glass tips of fiber optic sensors with a gallium arsenide crystal be fitted which will be evaluated in terms of its ability to change the position of his band edge under the influence of temperature.
Nevertheless, gallium arsenide has not been able to replace silicon as a mass semiconductor for more everyday applications. The main reasons for this are the significantly higher prices of the significantly rarer raw materials gallium and arsenic compared to the extremely common element silicon, as well as the more complex technology for the production of single crystals. This high technological effort simultaneously limits the mass and the diameter of the gallium arsenide single crystals. In addition, insulating areas can be produced more easily in silicon - usually in the form of silicon dioxide - than is possible in gallium arsenide. Since no good p-channel field effect transistors can be implemented in GaAs due to the significantly lower mobility of its conductive defects (the so-called "holes") compared to silicon , CMOS circuit technology is not possible in GaAs; as a result, the energetic advantage of GaAs is reversed for many purposes.
Health hazards
The poisonous arsenic is used in the production of GaAs. The volatile, poisonous intermediate products during the production of GaAs, such as the arsenic acid formed during the etching of GaAs, are also problematic . Gallium arsenide can cause cancer in humans.
Manufacturing
The production of gallium arsenide single crystals ( crystal growth ) takes place from a melt of the two elements gallium and arsenic using steam pressure-controlled crucible pulling processes , for example liquid encapsulated Czochralski or vertical gradient freeze processes ( LEC or VGF processes). State of the art are wafers with a diameter of 150 mm, the possibility of manufacturing wafers with a diameter of 200 mm being demonstrated. GaAs or AlGaAs layers can be produced epitaxially on corresponding substrates; such layers are also single crystals . This usually takes place at a rate of approx. 1 µm / h, depending on the epitaxy process.
See also
literature
- S. Adachi: GaAs and related materials: Bulk semiconducting and superlattice properties. World Scientific, Singapore 1994, ISBN 981-02-1925-3 .
- O. Madelung, M. Schulz, H. Weiss: Semiconductors: Technology of Si, Ge and SiC. In: Landolt-Bornstein - Group III: Condensed Matter. 17c, Springer, Berlin 1984, ISBN 0-387-11474-2 .
- M. Schulz, H. Weiss: Semiconductors: Technology of III-V, II-VI and non-tetrahedrally bonded compounds. In: Landolt-Bornstein - Group III: Condensed Matter. 17d, Springer, Berlin 1984, ISBN 0-387-11779-2 .
Web links
- Physical properties of Gallium Arsenide (GaAs) . Ioffe Institute St. Petersburg, accessed on June 10, 2010 (English).
- Katherine Bourzac: The Better Semiconductor . Technology Review, May 26, 2010, accessed June 10, 2010.
Individual evidence
- ↑ a b c ioffe.ru: Basic Parameters of Gallium Arsenide (GaAs)
- ^ Entry on gallium arsenide. In: Römpp Online . Georg Thieme Verlag, accessed on May 30, 2014.
- ↑ a b c data sheet gallium arsenide from AlfaAesar, accessed on February 7, 2010 ( PDF )(JavaScript required) .
- ↑ a b c d e Entry on gallium arsenide in the GESTIS substance database of the IFA , accessed on February 8, 2018(JavaScript required) .
- ↑ Entry on gallium arsenide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on January 24, 2017. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-5.
- ↑ I. Uschmann, T. Kämpfer, F. Zamponi, A. Lübcke, U. Zastrau, R. Loetzsch, S. Höfer, A. Morak, E. Förster: Investigation of fast processes in condensed matter by time-resolved X- ray diffraction . In: Applied Physics A: Materials Science & Processing . tape 96 , no. 1 , 2009, p. 91-98 , doi : 10.1007 / s00339-009-5187-1 .
- ^ Medical thermometer. Principles and applications of fiber optic temperature measurement (PDF; 214 kB)