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Semiconductor
A class of materials, such as silicon and germanium,
whose electrical properties lie between those of conductors
(such as copper and aluminum) and insulators (such as glass
and rubber). The term is also used to denote electronic
devices made from
semiconductor materials.
At the atomic level, semiconductors are crystals that in
their pure state are resistive,
but when the proper impurities
are added (this process is called doping)
in trace amounts (often measured in parts per billion),
display much lower resistance
along with other interesting and useful properties.
Depending on the selection of impurities added,
semiconductor material of two electrically-different types
can be created -- one that is electron-rich
(called N-type, where N stands for
Negative), or one that is electron-poor
(called P-type, where P stands for
Positive).
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