How+They+Work

O.k. so we know that LEDs are small but very useful little lights. They are efficient and produce relatively little heat. The question now is how do they work? First, some helpful terms… **Diode-** is a device that allows current to pass in only one direction. **Semiconductor**- a material that has a conductivity between a conductor and an insulator; electricity can pass through them, but not very easily **Impurities**- additional elements added to the semiconductor **Doping**- the process of adding very small amounts of impurities to the semiconductor **Conduction Band-** the partially filled outer shell where electrons can move freely. **Free electrons**- valence electrons that have gained enough energy to break away from the atom, but are still loosely attached to that atom in the conduction band. **N-type semiconductor**- a mixture that makes up one-half of the diode; contains extra free electrons **Hole-** the absence of an electron in a valence shell; these holes behave very much like particles **P-type semiconductor**- a mixture that makes up the other half of the diode; contains extra holes.

A n LED is made up of terminal pins, a diode, semiconductor material, and a plastic casing. Seems simple right? Not quite… You see, what goes on inside the diode and semiconductor is a lot more complicated than one would expect. The semiconductor is usually made of silicon, an element that only conducts electricity at high voltages. In the diode, there needs to be a P-type semiconductor and an N-type semiconductor right next to each other with an electrode touching both types. P-type semiconductors are doped with elements that would allow the material extra holes in it, while N-type semiconductors are doped with elements that give the material extra electrons. P-type semiconductors are called P-type because the extra holes give the material a positive charge. The N-type is called N-type because of the extra electrons, which give the material a negative charge. When placed next to each other in the diode, the electrons from the n-type material fill the holes of the p-type material. This leaves a space in the middle called the depletion zone, where there is no charge. The negative end of a circuit is attached to the n-type semiconductor and the positive end to the p-type material. Just add electricity, and the holes in the p-type material are attracted to the negative electrode attached to the n-type material. At the same time, the electrons in the n-type material are attracted to the positive electrode connected to the p-type material. Diagrams from []  With enough electricity, electrons can be displaced from their holes, allowing them to move freely. Electrons can move all throughout the P-type and N-type materials, which means no more depletion zone. Now here's the cool part. When the electrons fall into the holes, they go to a lower energy orbital. When this happens, they can let go of some of their energy, which is released in the form of... wait for it... LIGHT!! As long as there is a currant running through the diode, the constant movement of holes and electrons keeps the light coming. By using different combos of semiconductors and doping elements, we can change just how much an electron loses when it falls into a hole. Different energy losses mean different wavelengths, which means different colors! We can create the whole visible spectrum //and// infrared waves just by changing the elements used in the p-type and n-type semiconductors.

Information above provided with the help of howstuffworks.com

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Harris, Tom. "HowStuffWorks "How Light Emitting Diodes Work"" //Howstuffworks "Electronics"// Web. 06 Jan. 2010. .

"The Valence Shell." Web. 08 Jan. 2010. .

Wagner, Doris J. "Holes." //Rensselaer Polytechnic Institute (RPI) :: Architecture, Business, Engineering, IT, Humanities, Science//. Web. 08 Jan. 2010. .