Question

How is a light emitting diode fabricated ? Briefly state is working. Write any two important advantages of LEDs over the conventional incandescent low power lamps.

Answer 1

LED is fabricated by

(i) Heavy doping of both the p and n region.

(ii) Providing a transparent covers so that light comes out.

Working : When the diode is forward biased , electrons are sent from n$\to$p and holes from p$\to$n . At the junction boundary , the excess minority carriers on the either side of photon $h\nu =E_g$.

GaAs (Gallium Arsenide) : Band gap of semiconductors used to manufacture LED's should be $1.8eV$ to $3eV$ . These materials have band gap which is suitable to produce desired visible light wavelengths.

Advantages :

(i) Low operational voltage and less power consumption.

(ii) Fast action and no warm-up time required.

(iii) Long life and ruggedness.

(iv) Fast on-off switching capability.