Light emitting diodes (LED) "consist of layers of semiconductor materials. The light is generated in the interface of an n-type and an p-type layer. The n-type layer (left: dark blue) is silicon doped with atoms of certain other elements which have one more valence electron than silicon. The p-type layer (left: light-blue) contains fewer of these charge carriers - positive holes can be viewed as the charge carriers of the p-type layer.
By applying an external electrical potential with n-type layer to the negative terminal p-type layer to the positive terminal electrons and holes moves towards each other and connect in the interface of the two layers. The result: Light is emitted. A current of a few milliamps is sufficient to shine. The light emitted has a certain colour depending on the materials used. Indium-gallium-aluminium-phosphide (InGaAlP) is used in diodes emitting red, orange, yellow light...." (Bild der Wissenschaft 4/2002).

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