Question

What is an LED? Give the principle of its operation with a diagram.

Answer 1

1. LED is a p-n junction diode which emit visible or invisible light when it is forward bias.

2. It converts electrical energy to light energy.

3. It consists of p-layer, n-layer and substrate. External resistance in series with biasing source is required to limit forward current through LED. It has anode and cathode.

           Circuit symbol of LED

                           Inside view of LED

  Schematic diagram to explain recombination process

4. When a p-n junction is forward bias, conduction band electron on n-side and valence band hole on p side diffuse across the junction.

5. When they cross junction, they become excess minority carriers. These excess minority carriers recombine with oppositely charged majority carriers in the respective region.

6. During the recombination process energy is released is the form of light or heat.

7. The colour of the light is determined by the energy band gap of the material.

8. LED’s with wide range colours such as blue (Sic), green (AlGaP), red(GaAsP), white(GaInN) is also available.