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electronics A material, typically crystaline, which allows
current to flow under certain circumstances. Common
semiconductors are silicon, germanium, gallium arsenide.
Semiconductors are used to make diodes, transistors and
other basic "solid state" electronic components.
As crystals of these materials are grown, they are "doped"
with traces of other elements called donors or acceptors
to make regions which are n- or p-type respectively for the
electron model or p- or n-type under the hole model.
Where n and p type regions adjoin, a junction is formed which
will pass current in one direction (from p to n) but not the
other, giving a diode.
One model of semiconductor behaviour describes the doping
elements as having either free electrons or holes dangling
at the points in the crystal lattice where the doping elements
replace one of the atoms of the foundation material. When
external electrons are applied to n-type material (which
already has free electrons present) the repulsive force of
like charges causes the free electrons to migrate toward the
junction, where they are attracted to the holes in the p-type
material. Thus the junction conducts current.