Question

Describe the construction and working of light emitting diodes (LED). State it’s any two uses.

Answer 1

Hint: LED is basically a general-purpose diode with light emitting properties. For a photon to be released, energy has to be released within the diode. A diode can release energy by combining electrons and holes.

Complete answer:
Light emitting diode is basically a light emitting device which is made up of semiconductor components. Though it is much similar to the general-purpose diode, the special property of being able to emit light in multiple colours distinguishes it.
Aluminium-gallium-arsenide (AlGaAs) is commonly used in LEDs. It has the added advantage of possessing strongly bonded atoms, and thereby making conduction pretty much impossible as there are no free electrons. Like any other diode an LED too is doped with impurity, which disturbs the electron hole balance with the material and creates an internal potential difference. They either provide excess electrons known as free electrons or reduce the number of electrons, creating a lack of electrons also known as excess holes in the orbits of atoms present within.
An LED is a p-n junction diode and is a two-lead semiconductor light source. As the potential difference is being applied across it, the holes which are present on it combine with the holes. And this recombination makes the electron hole system to release energy, and this energy release is in the form of photons with an energy level in the visible spectrum, therefore emitting light.
This process is also known as electroluminescence. The wavelength of the photon emitted is dependent on the energy band gap in the semiconductor.

Note:
The colour of an LED is determined by the wavelength of the photon released. And this wavelength in turn depends on the energy released by the combination of electron and hole. Other than visible light infrared light is produced in LED by using Gallium Arsenide instead of using aluminium gallium arsenide.