VS - Lighting Systems - Lighting - 998542

14

From Xenon to LED

14.1. What is LED technology about? LEDs or Light Emitting Diodes belong in the semiconductor diode family. Diodes are electronic devices that allow electrical current to flow in only one direction. Diodes are built by bringing two slightly different materials together to form a P/N junction (Positive/Negative). LEDs are different to power commutation diodes used in automotive alternators. The materials that are used in LEDs are not silicon-based semiconductors but materials that allow light emission.

LED chip structure

p-contact

The material used in the LED governs the colour of the light that is emitted.

Anode

p-crystal n-crystal

Active layer

l InGaN material (Indium Gallium Nitride) is used for violet, blue, and green LEDs.

Substrate

l InGaAlP material (Indium Gallium Aluminum Phosphide) is used for green, yellow, orange, and red LEDs.

Cathode

n-contact

Slight changes in the composition of these primary allows to change the colour of the emitted light.

In a P/N junction, the N side contains negative charge carriers, that are called “electrons”, and the P side contains positive charge carriers, that are called “holes”, which indicate the absence of electrons. When a forward voltage is applied to the P/N junction, electrons move from the N side towards the P side and holes move from the P side towards the N side.

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