Working of light emitting diode(LED)

The holes lie in the valence band, while the free electrons are in the conduction band. When there is a forward bias in the p-n junction, the electron which is a part of the n-type semiconductor material would overrun the p-n junction and join with the holes in the p-type semiconductor material. Therefore regarding the holes, the free electrons would be at the higher energy bands.

When this movement of free electron and hole takes place, there is a change in the energy level as the voltage drops from the conduction band to the valance band. There is a release of energy due to the motion of the electron. In standard diodes, the release of energy in the manner of heat. But in LED the release of energy in the form of photons that would emit the light energy. The entire process is known as electroluminescence, and the diodes are known as a light-emitting diode.

In LED, energy discharged in light form hinges on the forbidden energy gap. One could manipulate the wavelength of the light produced. Therefore, from its wavelength, the light colour and its visibility or cannot be controlled. The colour and wavelength of the light emitted can be determined by doping it with several impurities.