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are materials whose electrical conductivity is intermediate between
that of the good conductors and insulators. Germanium (Ge) and Silicon (Si)
are semiconductors which are very useful in electronics.
Structure and Characteristics of Ge and Si:
Electrical conductivity of a semiconductor can be drastically changed
by adding a small quantity of a suitable impurity to molten
semiconductor and allowing it to recrystallize.
This process of adding impurity to pure semiconductor is known as
Doped semiconductors are of two types:
of Hole Movement: In a p-type
semiconductor, one of the 4 bonds between an impurity and a
germanium/silicon atom, has a vacancy for an electron. This empty
space or vacancy is known as a hole. When an electric field is
applied to the crystal, an electron from the neighbouring
atom jumps into the hole creating a fresh hole in its previous place.
This process repeats itself many times and the hole effectively moves
towards the negative potential.
and Working of p - n Junction Diode
semiconductor is joined together with n-type semiconductor, the
boundary between them is called p-n junction.
If a germanium or silicon crystal is doped in such a way that half of
it is p-type and
the other half is n-type then we get a p-n junction diode. The p side forms
the anode and the n side forms the cathode of the diode.
of diffusion at the junction, few electrons go from n region to p
region. As a result, n-region is at a small positive
potential with respect to p region. Similarly few holes go from
p region to n region. As a
result, p region is
at small negative potential with respect to n region.
The region near the junction (thickness about 10-6m) is
depleted of holes and electrons and it is called depletion region.
The result of build up of positive and negative charges near the
junction is to set up a potential difference. It is called a potential
Forward-biased p-n Junction
of a Semiconductor Diode (or Semiconductor Devices in General) Over
of Semiconductor Diode and Vacuum Diode