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Semiconductor, solid or liquid material,
able to conduct electricity at room temperature more readily than
an insulator, but less easily than a metal. Electrical
conductivity, which is the ability to conduct electrical current
under the application of a voltage, has one of the widest ranges of
values of any physical property of matter. Such metals as copper,
silver, and aluminum are excellent conductors, but such insulators
as diamond and glass are very poor conductors. At low temperatures,
pure semiconductors behave like insulators. Under higher
temperatures or light or with the addition of impurities, however,
the conductivity of semiconductors can be increased dramatically,
reaching levels that may approach those of metals.
Semiconductor devices have many
varied applications in electrical engineering. Recent engineering
developments have yielded small semiconductor chips containing
hundreds of thousands of transistors. These chips have made
possible great miniaturization of electronic devices. More
efficient use of such chips has been developed through what is
called complementary metal-oxide semiconductor circuitry, or CMOS,
which consists of pairs of p- and n-channel transistors controlled
by a single circuit. In addition, extremely small devices are being
made using the technique of molecular-beam epitaxy.
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