Germanium

Germanium (pronounced /dʒɚˈmeɪniəm/) is a chemical element with the symbol Ge and atomic number 32. This is a lustrous, hard, silver-white metalloid that is chemically similar to tin. Germanium forms a large number of organometallic compounds and is an important semiconductor material used in transistors. It is named after the country of Germany.

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Notable characteristics

Germanium is a hard, grayish-white element that has a metallic luster and the same crystal structure as diamond. In addition, it is important to note that germanium is a semiconductor, with electrical properties between those of a metal and an insulator. In its pure state, this metalloid is crystalline, brittle and retains its lustre in air at room temperature. Zone refining techniques have led to the production of crystalline germanium for semiconductors that have an impurity of only one part in 10¹⁰. Along with gallium, bismuth, antimony and water, it is one of the few substances that expands as it freezes. The oxide form, Germanium dioxide, also has the unusual property of having a high refractive index for visible light, but transparent to infrared light.

History

In 1871, germanium (Latin Germania for Germany) was one of the elements that Dmitri Mendeleev predicted to exist as a missing analogue of the silicon group (Mendeleev called it "ekasilicon"). The existence of this element was proven by Clemens Winkler in 1886. This discovery was an important confirmation of Mendeleev's idea of element periodicity.

The development of the germanium transistor opened the door to countless applications of solid state electronics. From 1950 through the early 1970s, this area provided an increasing market for germanium, but then high purity silicon began replacing germanium in transistors, diodes, and rectifiers. Silicon has superior electrical properties, but requires much higher purity samples—a purity which could not be commercially achieved in the early days. Meanwhile, demand for germanium in fiber optics communication networks, infrared night vision systems, and polymerization catalysts increased dramatically. These end uses represented 85% of worldwide germanium consumption for 2000 Germanium differs from silicon in that the supply of silicon is limited by production capacity only while that for germanium is limited by the shortage of exploitable sources.

Applications

Unlike most semiconductors, germanium has a small band gap, allowing it to efficiently respond to infrared light. It is therefore used in infrared spectroscopes and other optical equipment which require extremely sensitive infrared detectors. Its oxide's index of refraction and dispersion properties make germanium useful in wide-angle camera lenses and in microscope objective lenses.

Germanium transistors are still used in some stompboxes by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era, most notably the Dallas Arbiter Fuzz Face. Vintage stompboxes known to contain germanium transistors have shown marked increases in collector value for this reason alone.

Germanium is a highly important infra-red optical material and can be readily cut and polished into lenses and windows. It is used particularly as the front optic in thermal imaging cameras working in the 8 to 14 micron wavelength range for passive thermal imaging and for hot-spot detection in military and fire fighting applications. The material has a very high refractive index (4.0) and so needs to be anti-reflection coated. Particularly, a very hard special antireflection coating of diamond-like carbon (DLC) (refractive index 2.0)is a good match and produces a diamond-hard surface that can withstand much environmental rough treatment.

The alloy Silicon germanide (commonly referred to as "silicon-germanium", or SiGe) is rapidly becoming an important semiconductor material, for use in high speed integrated circuits. Circuits utilising the properties of Si-SiGe junctions can be much faster than those using silicon alone.   Other uses:

• Alloying agent (see below)
• Phosphor in fluorescent lamps
• catalyst
• High purity germanium single crystal detectors can precisely identify radiation sources (e.g. for airport security)
• Germanium substrate wafers for high-efficiency multi-junction solar cells for space applications

Certain compounds of germanium have low toxicity to mammals, but have toxic effects against certain bacteria. This property makes these compounds useful as chemotherapeutic agents.

Germanium is useful for single crystal neutron or synchrotron X-ray monochromator for beamlines. The reflectivity has advantages over silicon in neutron and High energy X-ray applications.

High purity Germanium crystals are used in detectors for gamma spectroscopy.

FDA research has concluded that germanium, when used as a nutritional supplement, "presents potential human health hazard".^[2]

In recent years germanium has seen increasing use in precious metal alloys. In sterling silver alloys, for instance, it has been found to reduce firescale, increase tarnish resistance, and increase the alloy's response to precipitation hardening (see Argentium sterling silver).

Occurrence

This element is found in argyrodite (sulfide of germanium and silver); coal; germanite; zinc ores; and other minerals. See also Category:Germanium minerals

Germanium is obtained commercially from zinc ore processing smelter dust and from the combustion by-products of certain coals. A large reserve of this element is therefore in coal sources.

This metalloid can be extracted from other metals by fractional distillation of its volatile tetrachloride. This technique permits the production of ultra-high purity germanium.

Value

In 1998 the cost of germanium was about US$1.70 per gram. The year end price for zone-refined germanium has (generally) decreased since then^{[3][4][5][6][7]}:

1999.....$1,400 per kilogram (or $1.40 per gram)

2000.....$1,250 per kilogram (or $1.25 per gram)

2001.....$890 per kilogram (or $0.89 per gram)

2002.....$620 per kilogram (or $0.62 per gram)

2003.....$380 per kilogram (or $0.38 per gram)

2004.....$600 per kilogram (or $0.60 per gram)

2005.....$660 per kilogram (or $0.66 per gram)

2006.....$880 per kilogram (or $0.88 per gram)

Compounds

Some inorganic germanium compounds include Germane or Germanium tetrahydride (GeH₄), Germanium tetrachloride (GeCl₄), and Germanium dioxide (germania) (GeO₂). Some organic compounds of germanium include tetramethylgermane or tetramethyl germanium, (Ge(CH₃)₄), and tetraethylgermane or tetraethyl germanium, (Ge(C₂H₅)₄). Recently a new organogermanium compound isobutylgermane ((CH₃)₂CHCH₂GeH₃), was reported as the less hazardous liquid substitute for toxic germane gas in semiconductor applications. Germanium also occurs in the III oxidation state, but only in the Ge₂⁶⁺ cation, Ge(III) is never found otherwise.^[8]

See also

• Category:Germanium compounds
• Germane
• Germanide

Properties

Pure germanium is known to spontaneously extrude very long screw dislocations, referred to as germanium whiskers. The growth of these whiskers is one of the primary reasons for the failure of older diodes and transistors made from germanium, as, depending on what they end up touching, they may lead to an electrical short.

References

• Los Alamos National Laboratory – Germanium

1. ^ Germanium: germanium(II) chloride compound data. WebElements.com. Retrieved on 2007-12-10.
2. ^ Tao, S.H. and Bolger, P.M. (June 1997). "Hazard Assessment of Germanium Supplements". Regulatory Toxicology and Pharmacology 25 (3): 211-219.
3. ^ (January 2003) "Germanium". U.S. Geological Survey Mineral Commodity Summaries: 2. [1].
4. ^ (January 2004) "Germanium". U.S. Geological Survey Mineral Commodity Summaries: 2. [2].
5. ^ (January 2005) "Germanium". U.S. Geological Survey Mineral Commodity Summaries: 2. [3].
6. ^ (January 2006) "Germanium". U.S. Geological Survey Mineral Commodity Summaries: 2. [4].
7. ^ (January 2007) "Germanium". U.S. Geological Survey Mineral Commodity Summaries: 2. [5].
8. ^ Germanium: germanium(III) hydride compound data. WebElements.com. Retrieved on 2007-12-10.

• WebElements.com – Germanium