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The Junction
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Field Effect TransistorsNormally, semiconductors don't have many free electrons.
Since electric current relies on those free electrons, the amount
of current that can travel through an isolated semiconductor is negligible.
Put a slab of silicon, for example, in the middle of a circuit and
it will stop the current in its tracks.
But things change if you put an electric field near that silicon. Bringing a positively-charged metal plate up close will attract the negatively-charged electrons from inside the body of the semiconductor. These electrons stream to the surface—suddenly there is an abundance of free electrons creating a pathway for the blocked current. Where once there was a stopped passage, electricity can now flow. By controlling the voltage on the metal plate, you can easily flip the current through the semiconductor on and off. On top of that, the current traveling through the semiconductor will be an exact replica of the signal sent to the metal plate—only larger. The transistor has amplified the original signal. Since this transistor depends on an electric field, it's known as a Field Effect transistor. Copyright 1999, ScienCentral, Inc, and The American Institute of Physics. No portion of this web site may be reproduced without written permission. All Rights Reserved. |
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