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Question

Heavily doped p-n junction diode which emits light when it is forward biased is/are :

A
zener diode
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B
photo-diode
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C
light emitting diode
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D
all of the above
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Solution

The correct option is D light emitting diode
Answer: C

Light emitting diodes are made from a very thin layer of fairly heavily doped semiconductor material and depending on the semiconductor material used and the amount of doping, when forward biased an LED will emit a coloured light at a particular spectral wavelength.

When the diode is forward biased, electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable number of these photons can leave the junction and radiate away producing a coloured light output.


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