How does a diode work?

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How does a diode work?

Or more precicely how does a semiconductor such as silicon only allow current to flow one way around a circuit?
 
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Janus
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The silicon isn't pure, it is "doped" by adding a small impurity, By carefully choosing what you use to dope the silicon with, you can ened up with two types of material called N or P. Th difference being how many electrons are in the outer shell of the doping material. A diode is made by joining together two sections of N and P material and attaching a wire to each.

If a voltage is applied in one direction All the electrons in the N material are drawn away from the Junction with the P material. Since the P material doesn't have any free electrons to "give" to the N material, no current flows.

If you reverse the voltage direction, the free electrons will flow from the N material into The P material (which readily accepts them). These electrons are replaced by new electrons entering through the wire attached to the N material, while the wire attached to the P material draws electrons out(making room for more electrons from the N material). A current flows.

This is somewhat of a rough explanation, but it should give you the basic idea.
 

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