LEDs_physics

The light-emitting diode (LED) is a common light source in electrical devices. It may be used in various ways, from your phone to enormous advertising billboards. However, they are most commonly seen in devices that display the time and various forms of data.

When an electric current passes through a light-emitting diode (LED), it emits light. When current travels through an LED, electrons recombine with holes, resulting in light. LEDs enable electricity to flow in one direction but prevent it from flowing oppositely.

The LED sign is a normal diode symbol with two little arrows indicating light emission. Let us learn more about LEDs.

Structure Of LEDs

LEDs are strongly doped p-n junction diodes that emit spontaneous radiation when biassed forward. The diode is encased in a transparent cover that allows the emitted light to escape.

The manufacturing of an LED is identical to that of a standard p-n junction diode, except that gallium, phosphorus, and arsenic components are utilised instead of silicon or germanium.

Silicon is the most extensively utilised material in typical p-n junction diodes because it is less temperature-sensitive, but we require current sensitivity in the case of LEDs.

Three layers make up a light emitting diode (LED): p-type semiconductor, n-type semiconductor, and depletion layer. A depletion zone, also known as a depletion layer, separates the p-type and n-type semiconductors.

Working Of LEDs

• An LED works in forward bias conditions. The minority electrons are sent from p to n, whereas the minority holes are sent from n to p when the diode is forward biassed. 
• The concentration of minority carriers grows along the junction border. The extra minority carriers recombine at the intersection with the majority charged carriers.
• The size of the depletion area narrows when free electrons and holes recombine in the depletion region. As a result, more charge carriers pass across the p-n junction.
• Before they recombine at the depletion zone, some charge carriers from the p-side and n-side pass the p-n junction. Some n-type semiconductor free electrons, for example, pass the p-n junction and recombine with holes in the p-type semiconductor. Similarly, p-type semiconductor holes traverse the p-n junction and recombine with free electrons in the n-type semiconductor.
• As a result, recombination occurs in both the p-type and n-type semiconductors.
• Before recombining with holes in the valence band, free electrons in the conduction band release energy in the form of light.
• The energy is emitted in the form of heat in conventional diodes. However, energy is emitted in the form of photons in light-emitting diodes. This phenomenon is known as electroluminescence. As the forward voltage rises, the light intensity rises, eventually reaching a maximum.

Applications of LEDs

Light-emitting diodes are very useful and important in our everyday lives. Here are some of the common applications of LEDs:

• An LED is often used as an On/Off indicator bulb for electrical devices.
• LEDs are used in calculators, clocks and watches, thermometers, signs, and other self-lighting displays.
• Since they consume very little energy, LEDs are currently widely employed in light motor vehicles and two-wheelers, residential illumination, traffic signals, portable torches, and diverse indication lamps.
• The virtually monochromatic light generated by an LED can also be coherent under specific conditions. Optical fibre telecommunications, laser printers, card readers, and laser pointers feature LEDs.
• The backlight of a television consumes a lot of energy. The use of LEDs can result in a significant reduction in power consumption. LEDs can be a cost-effective option for the corners of the television. Better contrast is achieved by placing LEDs immediately behind the display. LEDs have mostly replaced CFLs and LCDs when it comes to TV backlighting.
• The backlighting structure of the smartphone may be slimmer and created at a lower cost thanks to the usage of LED. LED prices may differ as per the size of the smartphone display.

Conclusion

LEDs produce light energy on the application of current through the device. On the forward bias application of the diode, electrons are sent from n to p (in which they are minority carriers), and holes are sent from p to n (where they are minority carriers). Compared to the equilibrium concentration (i.e., when there is no bias), the concentration of minority carriers rises at the junction border. As a result, there are extra minority carriers at the junction border on both sides of the junction, which merge with majority carriers. The radiation is emitted in the form of photons during recombination. The emitted photons have an energy equal to or somewhat less than the bandgap. Therefore, when the diode’s forward current is low, the light emitted is low.