[otw_is sidebar=otw-sidebar-1]LIGHT EMITTING DIODE

A pn jinction diode which wmit light when forwar biased kbown aa light emiting diode LED.



It consists of N-type layer placed on a P-type substrate by a  diffusion.Then a thinP-type laye is placed on the

N-type layer.The metal connection to both the layers forms anode and cathode terminal when light falls on the junction recombination of electrons with holes take place.After passing through the P-region the light emitted through the window arranged at the top of the surface.




When the LED is forward biased,the electrons and holes move towards the junction and the recombination takes place.After recombination,the electron ,lying in the conduction bands of n-region,fall into the holes lying in the valance band of a P-reigion.The difference of energy between the conduction band and valance band is radiated in the form of light energy.


The LED’s radiate liight in different colors such as Red,Green,Yellow,Blue,etc.Some of the LED’s emit infrarwd (invisible) light also.The color of the light depends upon the type of the semiconductor used.

Semiconducor Materials used for LED

  • Gallium Arsenide sulphide (GaAsS) emits Red
  • Gallium Phosphide(GaP) emits yellow
  • Gallium Nitride (GaN) emits blue






LED’s  are used to:

  1. Displays
  2. Indicating power On/Off conddition
  3. in optical swtching application
  4. Transmit light energy to fiber optical cable.
  5. For image sensong circuits in pocture phones.