Question

What is LED? Explain its principle, construction and working.

Hint:

LEDs are energy-efficient and used widely in indicators, displays, and lighting due to their low power consumption and long life.

Answer 1

LED (Light Emitting Diode):
An LED is a semiconductor device that emits light when an electric current flows through it. It is a \(p\)-\(n\) junction diode that emits photons during the process of electron-hole recombination. Principle:
The working of an LED is based on the principle of electroluminescence, where light is emitted when a forward-biased \(p\)-\(n\) junction diode recombines electrons and holes near the junction.
The energy released during this recombination is emitted in the form of photons (light). Construction:


LED is made using semiconductor materials like gallium arsenide (GaAs), gallium phosphide (GaP), etc.

It consists of a \(p\)-type and an \(n\)-type semiconductor.

The LED is housed in a transparent plastic casing to allow emitted light to escape.

The longer lead is the anode (+), and the shorter lead is the cathode (–).

Working:


When a forward voltage is applied, electrons from the \(n\)-side and holes from the \(p\)-side move toward the junction.

They recombine near the junction. The electrons lose energy.

This energy is released as photons (light).

The color of light depends on the bandgap energy of the material used.