Question

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

Answer 1

Light-emitting diode (LED) is a forward biased p-n junction diode which emits visible light when energized. The light energy is produced by the recombination of electrons and holes at the junction. Emit radiation in the infrared region.

If light - emitting diode is reverse-biased, then no light would be emitted at all.

In-fact, the LED can be damaged on being reverse-biased.

The emission of light from a light-emitting diode can be explained with the help of mechanism of spontaneous emission. We know that there are two distinct energy bands in a semiconductor, the conduction (higher energy) and the valence (lower energy) bands. There may also be energy bands $\left(E_D\right)$ due to donor inpurities near the conduction band or acceptor impurities $\left(E_A\right)$ near the valence band. When electron falls from higher to lower energy level containing holes, the energy in the form of light radiating is released. Generally, radiative transistions occur, Sometimes, non-radiative transitions may occur.