Question

What is LED? Show its (v-i) characteristics drawing circuit diagram.

Answer 1

Hint :A light emitting diode is a special heavily doped p-n junction diode that emits spontaneous radiation when forward biased. It is used to convert electrical energy in the form of light energy. This energy will be emitted in the form of infra-red radiations.

Complete Step By Step Answer:
A light emitting diode is a special heavily doped p-n junction diode that emits spontaneous radiation when forward biased.
When a p-n junction will be forward biased, the electrons from the p-side of the diode will form the conduction band to the valence. This process is equivalent to the falling of electrons from a higher energy state (conduction band) to a lower energy state (valence band).
A light emitting diode is used to convert electrical energy into light energy. LEDs emit light that is produced by the combination of electrons and holes at the junction of p-n junction diodes. The process in which the light is emitted by applying an electrical source of energy is known as electro-luminescence.
The light emitted from the light emitting diode can be explained on the basis of the mechanism of spontaneous emission. As there are two energy bands in the semiconductor that are conduction band and valence band. When the electrons combined with holes fall from the conduction band to the valence band, the energy is released in the form of a light.
The diagram of V-I circuit is given below

The V-I characteristics of LED are the same as that of the elementary semiconductor say silicon diode. Knee voltage of the LED is much higher than that of Si diode.
The graph of V-I characteristic of LED is given as

Note :
When the light emitting diode is reverse biased, there will be no emission of light. In-fact, light emitting diodes will get damaged when reverse biased. LEDs made of elemental semiconductors like germanium and silicon emit energy in the form of infra-red radiations.