The two most common
materials used in the
making of semiconductors
are silicon and
germanium.
Sand on the beach is
silicon and they say
that germanium can be
obtained from chimney
soot.
So you can see that the
raw materials are
extremely common.
However they do have to
be purified to an
extraordinary degree.
When purified they have
a crystalline
construction like salt
and sugar.
The atoms which make up
the materials are
rigidly locked together
in a pattern (a LATTICE)
in which the electrons,
in the atoms, are unable
to move.
This means that pure
silicon and germanium
are good insulators.
After purification,
precise amounts of
impurities are added
(the materials are
DOPED).
These impurities fit
into the lattice but
have associated
electrons which are free
to move about and
produce a flow of
electric current.
There is therefore a
surplus of negative
electrons and the
material is called
N-type semiconductor.
Other types of
impurities can be added
to pure silicon and
germanium. These produce
a shortage of electrons
in the lattice.
Therefore there are
HOLES in the lattice.
Electrons can jump into
these holes, producing a
flow of holes.
It's like sitting in a
row of chairs in the
doctor's waiting room.
When someone gets up and
goes into the surgery
there is an empty chair
(a hole).
People (electrons) move
along nearer to the
surgery and a hole
travels in the opposite
direction.
Since there is a
shortage of negative
electrons there is an
overall positive charge
and the material is
called P-type
semiconductor.
The resistance of
semiconductors is about
half way between
conductors and
insulators.
Hence the name,
semiconductors.
Semiconductors are used
in semiconductor devices
such as diodes,
transistors, integrated
circuits etc.
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