What are light-emitting diodes and why are they prized as light sources?

Subject: Science and Tech

Section: Msc

What are diodes?

A diode is a small electronic component with two terminals, an anode and a cathode, designed to allow current flow in only one direction.
It operates based on a p-n junction, where a p-type material with positive charge carriers (holes) meets an n-type material with negative charge carriers (electrons).
This junction allows electrons to move easily from the n-type to the p-type material, creating a one-way current flow.
The anode is connected to the p-type material, and the cathode is connected to the n-type material. Initially, some electrons move from the n-side to the p-side, creating a layer between them without free electrons or holes.
When a suitable voltage is applied, more electrons flow from the n-side to the p-side, allowing current to move from the anode to the cathode. However, if the voltage is reversed, the current won’t flow in the opposite direction.

What is an LED?

An LED, or Light-Emitting Diode, is a type of diode that emits light through a process called electroluminescence.
Within the diode’s p-n junction, when electrons with higher energy levels meet and fill holes, they release energy in the form of light.
The visible light emitted depends on the frequency of this energy. The phenomenon is regulated by the band gap, ensuring that the emitted light falls within the visible part of the electromagnetic spectrum.

What is called the Band Gap?

The band gap is a characteristic of materials, representing the energy difference between the lower and higher energy levels that electrons can occupy.
In conductive materials,electrons flow freely when energized by an electric field, while insulators prevent electron flow due to insufficient energy.
The band gap is the energy barrier electrons must overcome to conduct current.
In LEDs, the energy released during electron-hole recombination corresponds to the band gap.
Engineers can tailor the band gap of the p-n junction in LEDs by selecting specific materials, allowing for the emission of visible light when an electric current is applied.

What colours can an LED produce?

LEDs can produce all three primary colours—red, green, and blue—allowing for a diverse range of colours when combined.
However, the development of blue LEDs faced challenges, as scientists struggled to create crystals of gallium nitride, a compound capable of emitting blue light, with the required properties.
Breakthroughs in epitaxy, a layer-by-layer material-building process, led to the invention of bright blue LEDs in the late 1980s.Three Japanese researchers, Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura, received the 2014 Nobel Prize in Physics for their significant contributions to this achievement.

Advantages of LED lights:

The advantages of LEDs, in line with Haitz’s law, include a substantial decrease in cost and a significant increase in light output for a given frequency of light.
Even before Haitz’s law,LEDs were valued for their efficiency compared to incandescent bulbs and fluorescent lamps.
Their durability, light contrast, and energy efficiency contribute to cost savings and reduced material waste.

Applications of LED lights:

LEDs find applications in various fields, from consumer electronics like smartphones and TV screens to industrial uses such as signboards, greenhouse lighting for plants, barcode scanners, and air quality monitoring.
Modern LEDs can produce different colours, operate at various frequencies, and be embedded in the skin, and organic LEDs offer enhanced light emission.
Ongoing research explores more efficient LEDs using materials like perovskites.

Source: TH