How is Semiconductor
made from Silicon?
Semiconductor devices are made primarily of silicon ("Si").
silicon forms rigid crystals because of its four valence (outermost)
electron structure - one Si atom bonds to four other Si atoms
forming a very regularly shaped diamond pattern.
Pure silicon is not a conductor because there are no
free electrons; all the electrons are tightly bound to neighboring
To make silicon conducting, producers combine or "dope" pure silicon
with very small amounts of other elements like boron or phosphorus.
Phosphorus has five outer valence electrons. When three silicon
atoms and one phosphorus atom bind together in the basic silicon
crystal cell of four atoms, there is an extra electron and a net
This type of material is called n-type silicon. The extra electron
in the crystal cell is not strongly attached and can be released by
normal thermal energy to carry current; the conductivity depends on
the amount of phosphorus added to the silicon.
Boron has only three valance electrons. When three silicon atoms and
one boron atom bind with each other there is a "hole" where another
electron would be if the boron atom were silicon. This gives the
crystal cell a positive net charge (referred to as p-type silicon),
and the ability to pick up an electron easily from a neighboring
The resulting migration of electron vacancies or holes acts like a
flow of positive charge through the crystal and can support a
current. It is sometimes convenient to refer to this current as a
flow of positive holes, but in fact the current is really the result
of electrons moving in the opposite direction from vacancy to