Light emitting diode (LED)
What is LED?
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Light emitting diode are PN junction diode which emit electromagnetic radiation mostly in infrared region or visible region of electromagnetic spectrum. When an electric current flows through it.
LEDs are generally made up of iii-v compound semiconductor such as GaAs which have a direct band gap.
Working principle
They work on the principle that flow of electric current through a forward bised PN diode causes the injection of minority carrier into the region where they can recombine with majority carrier thus producing electromagnetic radiation. The effect is known as injections electroluminescence.
Indirect band gap semiconductor such as silicon or germanium, where the electrons in the conduction band have a momentum different from holes in valence band. This type of radiative recombination is unlikely to occur generally the recombination releases heat to lattice in such cases.
The wavelength of limited radiation is given by
λ=hc/Eg
Where,
h =planck's constant
c = velocity of light
Eg = band gab energy.
