Germanium is the chemical element with atomic number 32, symbol Ge. It
belongs to group 14 of the periodic table.
This metalloid is semiconductor and crystallizes with the same structure as
diamond, just like silicon. It has five natural isotopes, including 76Ge, which
is weakly radioactive. At least 27 radioisotopes have been synthesized.
Almost all of the germanium is recovered in zinc smelters (fusion by-product).
The first transistors had germanium as their substrate.
Germanium has 32 known isotopes, with a mass number varying from 58 to 89, as
well as 13 nuclear isomers. Five of these isotopes are found in nature 70Ge,
72Ge, 73Ge, 74Ge and 76Ge, the latter being very slightly radioactive,
disintegrating by double beta disintegration in selenium 76 with a half-life of
1.78 ¡Á 1021 years9 (130 billion of times the age of the universe). The stable
isotope 74Ge is the most common, with a natural abundance of around 36%, the
least common being 76Ge (around 7%)
Deposit
Germanium can be found in many places. Currently, it is recovered as a
by-product from zinc sphalerite ores (chemical formula of the mineral: ZnS,
cubic).
It is present in germanite (which contains up to 9%, cubic), renierite10
(tetragonal), argyrodite (4Ag2S ¡¤ GeS2, or Ag8GeS6, orthorhombic) and in other
ores11, which are not exploited .
It is a rare element, its content in the earth's crust is very low, around 1.5
ppm12.5. It is found in trace amounts in the ashes of certain types of coal
(called ¡°vitrain¡± (en)) after refining these. In France, it is also present in
Pb-Zn veins.
World production in 2004 was estimated at 40 t (China, USA, etc.) 5. China
produced 79% of the world's supply in 200613.
Germanium tetrachloride (a volatile liquid which boils at 86 ¡ă C and can be
distilled) is an intermediate for the purification of germanium metal or its
oxide, GeO2. The technique allows the production of ultra-high purity germanium.
Zone refining techniques have led to the production of crystalline germanium for
semiconductor of purity 10−9: 99.999 999 99% (only 0.1 ppb of impurity) 5.
Applications
Germanium bowl
The transistor effect was observed in 1948 in germanium5. It served as a
semiconductor substrate until silicon took its place, around the 1970s.
Germanium transistors are still used today as the main components of some effect
pedals for electric guitar, called "fuzz" ", For their supposedly particular
sound and which would be appreciated by lovers of" 1970s "sounds. Today, it is
more used in the high frequency field, for the production of low drop diodes
(about 0.3 V, detection application) of the diode station and in multi-junction
photovoltaic cells for space and terrestrial after concentration. It is also
found in the alloy or multilayer state with silicon (SiGe). Originally, the
reasons for its alternating deposition with Si rested on the possibility of
making the band gap between Si and Ge direct (this property being important for
opto-electronic applications). This technique is also used to introduce
constraints which improve the mobility of the carriers in the field effect
transistors. The SiGe transistors are bipolar heterojunction transistors which
are commonly used in the field of microwaves in weak signal amplification (low
noise factor).
Its second use is in glasses, thanks to its infrared transparency. The structure
of germanium cannot be destroyed by neutron radiation, as for steel. On the
other hand, fast neutron irradiation introduces point defects which anneal
around 200 ¡ă C.
In 2007, the main applications were the manufacture of optical fibers (35%),
infrared optics (20%), catalysts (20%) 14, electronics (15%) and certain types
of photovoltaic cells.
In the 1980s, germanium was considered to be one of the eight strategic raw
materials essential in wartime as well as in peacetime15.
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magnesium bismuth manganese chromium cobalt titanium
Tungsten vanadium niobium indium molybdenum antimony
rhenium germanium zirconium cadmium hafnium
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