Germanium

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Germanium
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Outline

• Brief History of Germanium
• Why Germanium?
• Chemical and Physical Properties of Ge
• Germanium Occurrence Value
• Mobility
• Temperature and Thermal conductivity of Ge
• Sources Consulted

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Why Germanium?

• First Transistor was made of Germanium
• Want to know why it is not as popular as Silicon?
• Want to Understand how its thermal and electrical
  properties behave with varying temperature

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History of Germanium

• Dmitri Mendeleev predicted the existence 1871 and
  called it EkaSilicon
• Clemens Winkler discovered Germanium in 1886.
• Economically Significant after 1945, when its
  properties as a semiconductor were recognized.
• Found in Argyrodite (Sulfide of germanium
  silver).

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First 1950s Transistors

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Germanium Chemical and Physical Properties

• Atomic Number 32
• Grayish-white, Brittle
• Electronic Configuration Ar3d104s24p2
• Valence Electrons 4
• Atomic Weight 72.59 gm.mol-1
• Density (g/cm3) 5.35
• Melting point 947oC.
• Oxides at 600-700oC

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• Ge has diamond like FCC crystal structure
• Indirect gap
• Band Gap of Ge, E(ev) 0.66 at T 300K,
• 0.75 at 0k. Si, E(ev) 1.12 at T 300K,
  1.17 at 0k

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• Ge is indirect gap semiconductor

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Carrier Mobility

• Carrier Concentration ? Eg/KbT, ratio of band gap
  to temperature
• If the ratio is large?low concentration
  conductivity will be low. (intrinsic)
• Small Band Gap width mean higher mobility

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Carrier Mobility at room temperaturecm2/volt-sec

• Crystal Electrons Holes
• Diamond 1800 1200
• Si 1300 500
• Ge 4500 3500
• InAs 33,000 460

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Germanium Occurence

• Zinc ore and coal ash ? proccesed using Zone
  refining
• Chemically ? GeO2 2H2 -gt Ge 2H2O
• One can grow Ge crystal using Czochralski method

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Germanium Value

• In 1998 the cost of germanium was about US1.70
  per gram. The year end price for zone-refined
  germanium has (generally) decreased
• 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)

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Thermal Transport Properties of Ge

• Electron Excitation -? E gt Eg
• As Temp. increases electrons thermally excited
• Electrons excitation is due to phonon scattering.
• K m ½CvVl where Cv is specific heat
  capacity
• V phonon velocity, l phonon mean free
  path.

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K(T) vs T
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• Thermal conductivity of Ge is increasing by 1/T
  at high temperature.
• Phonon scattering is decaying by 1/T as well.
• This is making Germanium unstable at high
  temperature
• Therefore transistors made of Ge can loose their
  PN junction properties malfunction. This is the
  reason manufacturers look after Silicon.

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Uses of Ge

• Mainly in Semi-Conductor Industry
• Transistors, Diodes etc.
• Infrared Spectroscopes -? efficient response to
  Infrared light
• Alloying with Silicon (SiGe) to create
• high speed integrated circuits
• Effective in killing some type of Bacteria

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Sources

• Article from Texas tech university
• Article UC Berkeley Lawrence Berkley Laboratory
• Wikipedia
• Ashcroft/Mermin Solid State physics (book)