Introduction

In 2014, the Royal Swedish Academy of Sciences declared that “the 21st century will be lit by LED lamps,” recognizing the pivotal role of Light-Emitting Diodes (LEDs) in shaping the future of lighting technology.
This article delves into the fascinating world of diodes, LEDs, and their significance in modern technology.

Understanding Diodes

Diode Basics: A diode is a small electronic component with two terminals, an anode and a cathode. Its primary function is to allow current flow in one direction only, thanks to a p-n junction.
P-N Junction: A p-n junction consists of two adjacent materials: a p-type with positive charge-carriers called holes and an n-type with negative charge-carriers – electrons. Electrons can flow easily from the n-type to the p-type but not the other way, granting the diode its one-way current control.
Anode and Cathode: The anode terminal is connected to the p-type material, while the cathode is connected to the n-type material. These terminals define the diode’s directionality.

Electroluminescence: LEDs are diodes that emit light. Electrons, with higher energy levels than holes, release energy when they occupy holes in the p-n junction. If this energy falls within the visible spectrum, light is emitted – a phenomenon known as electroluminescence.
Band Gap: LEDs achieve specific light colors by ensuring that electron-hole recombination releases a precise amount of energy, determined by the band gap.

Energy Levels: Electrons can only have distinct energy values and occupy particular energy levels. These electrons tend to occupy the lowest energy levels available, leading to conductors, insulators, and materials with a band gap.
Band Gap’s Role: A band gap represents the energy threshold required for electrons to move from lower to higher energy levels, allowing materials to conduct electricity.
LEDs and Band Gap: In LEDs, the energy emitted during electron-hole recombination corresponds to the band gap, determining the light’s color.

Historical Context: Scientists developed red and green LEDs over four decades before achieving blue LEDs. The challenge lay in creating gallium nitride crystals with precise properties for electroluminescence.
Primary Colors: LEDs can produce red, green, and blue light, offering a versatile color palette. Combining different LEDs enables a broad spectrum of colors on display boards and screens.
Breakthrough: Japanese researchers, Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura, made a significant breakthrough in the late 1980s, creating a bright blue LED using gallium nitride. Their achievement earned them the 2014 Nobel Prize in Physics.

Efficiency: LEDs outperform incandescent bulbs and fluorescent lamps in terms of luminous efficacy, emitting more light per watt of power.
Durability: LEDs are highly durable, reducing material waste and maintenance costs.
Diverse Applications: LEDs find applications in diverse fields, from consumer electronics and signage to greenhouse lighting and air quality monitoring.
Color Versatility: LEDs can emit various colors and frequencies, catering to a wide range of applications.

Haitz’s Law: Similar to Moore’s law, LEDs have followed Haitz’s law, predicting cost reduction and increased light output over time.
Innovations: Ongoing research explores skin-embedded LEDs, organic LEDs, and efficient LEDs made from perovskites, promising further advancements in lighting technology.