LEDs

1
LEDs

• Kang Bae
• Material Science
• MEEN 3344

2
What is LED

• LED stands for Light Emitting Diode.
• LED is a semiconductor device that produces
  infrared lights when electric current is applied
  to the device
• This process is also called Electroluminescense

3
HISTORY OF LED

• Radio Corporation of America first reported on
  infrared emission from gallium arsenide in 1955.
• Texas Instrument found Gallium Arsenide emits
  infrared lights when electric current were
  applied 1961.
• GE developed the first working LED in 1962.

4
How LED works

• A LED is a semiconductor diode that consists of a
  chip of semiconducting material that creates a
  p-n junction.
• P-N junction is where current flows and it flows
  from the p-side to the n-side
• Charge-carriers - electrons and electron holes -
  flow into the junction
• releases energy in the form of a photon.
• The wavelength of the light emitted distinguishes
  LEDs color
• Examples of colors
• aluminum gallium arsenide (AlGaAs) - red and
  infrared
• aluminum gallium phosphide (AlGaP) - green
• aluminum gallium indium phosphide (AlGaInP) -
  high-brightness orange-red, orange, yellow, and
  green
• diamond (C) - ultraviolet

5
Uses of LED

• flash lights.
• LED Display
• Bicycle lights
• Traffic signs and signals
• Mouse for computers
• Cars (Lexus tailamp)

6
Advantages and Disadvantage

• Lasts longer than incandescent lights
• Extremely durable and less heat
• Lights up in microseconds
• High ambient temperature cause overheat.
• More efficient, lower power usage than
  incandescent lights.

7
References

• Whatis June 18 2001, Nov 9 2006
  http//whatis.techtarget.com/definition/0,,sid9_gc
  i213613,00.html
• Wikipedia Nov 9 2006, Nov 9 2006
  http//en.wikipedia.org/wiki/LED_28Light-emitting
  _diode29Physical_function