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Short note: Light emitting diode

Short answer

A light-emitting diode (LED) is a PN junction device that emits light under forward bias via electron-hole recombination in direct band-gap materials like GaAsP or GaN. Colour depends on bandgap. A series resistor limits current; typical forward voltage is 1.8-3.3V, current 5-20mA. Used for indicators, displays, lighting, and optical communication.

Write a short note on light emitting diode (LED).

A light emitting diode (LED) is a PN junction diode that emits light when forward biased. It is made from direct band-gap compound semiconductors such as gallium arsenide phosphide (GaAsP), gallium phosphide (GaP) and gallium nitride (GaN), not from silicon.

Principle

Under forward bias, electrons from the n-region and holes from the p-region cross the junction and recombine. In a direct band-gap material the energy released by recombination is given out as photons (electroluminescence). The photon energy equals the band gap: E = hf, so the colour (wavelength) depends on the material.

 +Vcc o--[ R ]--|>|--o GND      Symbol: --|>|-- with
                 LED             arrows pointing out

A series resistor limits the current: R = (Vs − VF)/IF. Example: Vs = 5 V, VF = 2 V, IF = 10 mA gives R = 300 Ω.

Characteristics

  • Forward drop 1.8 to 3.3 V (red about 1.8 V, blue/white about 3.2 V), typical current 5 to 20 mA.
  • Low reverse breakdown voltage (about 5 V), so it must not be reverse biased.
  • Fast switching (nanoseconds), long life, low power, small size.
MaterialColour
GaAsinfrared
GaAsPred/yellow
GaPgreen
GaN/InGaNblue/white

Applications: indicator lamps, seven-segment displays, remote controls (infrared), optocouplers, lighting, traffic signals and fibre optic transmitters.

✓ Answer checked by Claude Opus 5.5 (high effort)

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