LED — Definition
Definition
Imagine a tiny electronic component that glows when you connect it correctly to a power source, much like a miniature light bulb, but without a filament that heats up. That's essentially what a Light Emitting Diode, or LED, is.
At its heart, an LED is a special type of semiconductor device, specifically a p-n junction diode. You might recall that a p-n junction is formed by joining a p-type semiconductor (rich in 'holes' or positive charge carriers) with an n-type semiconductor (rich in 'electrons' or negative charge carriers).
When an LED is connected in 'forward bias' – meaning the positive terminal of the battery is connected to the p-side and the negative terminal to the n-side – something fascinating happens. The applied voltage pushes the electrons from the n-side towards the p-side, and simultaneously, the holes from the p-side towards the n-side. These charge carriers meet at the 'depletion region' of the p-n junction.
Here's the crucial part: when an electron from the n-side encounters a hole from the p-side, they 'recombine.' In many semiconductors, this recombination process releases energy. In the case of an LED, this released energy is in the form of light photons. This phenomenon is called 'electroluminescence.' It's like the electron and hole 'annihilate' each other, and in doing so, they give off a tiny packet of light energy.
The color of the light emitted by an LED isn't random; it's precisely determined by the specific semiconductor material used to make the diode. Different materials have different 'bandgap energies.' The bandgap energy dictates the energy of the photons that can be emitted, and higher energy photons correspond to shorter wavelengths (like blue or UV light), while lower energy photons correspond to longer wavelengths (like red or infrared light).
For instance, gallium arsenide (GaAs) typically emits infrared light, while gallium nitride (GaN) emits blue light. This direct relationship between material properties and emitted light color is a key characteristic of LEDs, making them versatile for various applications from indicator lights to high-efficiency general illumination.