The Characteristics of a P-N Diode
A P-N diode is an electronic component that consists of two pieces of semiconductor material --- one P-type, the other N-type --- fitted face to face with a wire fastened to the end of each semiconductor. The entire assembly is coated in plastic to make a small, short tube with a wire coming out of each end. Electrically, a P-N diode allows current to flow through it easier in one direction than in the other.
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The Basic N-P diode
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Pure silicon semiconductor material is not very good at conducting electricity --- hence the name. When this material is baked in an oven, with a carefully selected gas, a small number of atoms are introduced into the material which changes its electrical behavior. This process is called "doping," and if it is done with one gas the results is an N-type semiconductor --- a semiconductor with extra electrons suspended in the material. With a different gas, a P-type semiconductor is produced --- with an absence of electrons --- called "holes."
When these two materials are used together, a variety of electrical effects can be produced. Just putting the two materials together produces a diode. When electrical potential is applied in one direction, the electrons and holes are pushed together and current flows. When electrical potential is applied in the other direction, the holes and electrons are pulled apart and no current flows.
LEDs
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It was discovered, quite by accident, that diodes made with certain semiconductor materials glowed when used. A little research led to a whole new way to make light: Light Emitting Diodes (LEDs). These lights are cheap to make, use very little power, burn cool and last forever.
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Laser Diodes
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If the P-N junction is highly polished and there is a special resonating cavity, an LED can produce laser light. These are the sources of the lights used with optic fiber communications.
Zener Diodes
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Zener diodes are the first of a new breed of diodes that have a more complex behavior profile than simply allowing current to flow in one direction and not in the other. A typical zener diode allows current to flow freely in one direction, but not in the other; however, when the potential becomes high enough in the "wrong" direction there is a breakdown that allows current that flow in this direction. This breakdown does not harm the zener diode. It can happen frequently with no harm to the diode. These more complex diodes --- with specific breakdown voltages --- allow zener diodes to be used in complex logic circuits that control switching and control circuits.
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