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
Si
Ge
InAs
1800
1300
4500
33,000
1200
500
3500
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)