Germanium - PowerPoint by u0dbBu

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									Germanium
                    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
              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
           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).
    First 1950’s Transistors

       Germanium Chemical and Physical
                 Properties
 Atomic Number = 32
 Grayish-white, Brittle
 Electronic Configuration = [Ar]3d104s24p2
 Valence Electrons = 4
 Atomic Weight = 72.59 gm.mol -1
 Density (g/cm3) = 5.35
 Melting point = 947oC.
 Oxides at 600-700oC
   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
   Ge is indirect gap
    semiconductor
                         E  , P  q;




     E   ; p  q


    p   / c
                Carrier Mobility
   Carrier Concentration  Eg/KbT, ratio of band gap
    to temperature

   If the ratio is largelow concentration &
    conductivity will be low. (intrinsic)

                 u  e / m *
   Small Band Gap width mean higher mobility
            Carrier Mobility
          at room temperature
                    cm2/volt-sec




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


   Zinc ore and coal ash  proccesed using Zone refining
   Chemically  GeO2 + 2H2 -> Ge + 2H2O
   One can grow Ge crystal using Czochralski method
            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
      • 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)
Thermal Transport Properties of
             Ge
   Electron Excitation - E > Eg

   As Temp. increases electrons thermally excited

   Electrons excitation is due to phonon scattering.

   K m = ½*Cv*V*l ; where Cv is specific heat capacity
     V = phonon velocity, l = phonon mean free path.
K(T) vs T
   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.
                    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
               Sources
 Article from Texas tech university
 Article UC Berkeley & Lawrence Berkley
  Laboratory
 Wikipedia
 Ashcroft/Mermin Solid State physics
  (book)

								
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