Minggu, 18 September 2011

Light emission

Physical function
An LED is a special type of semiconductor diode.
Like a normal diode, an LED consists of a chip of semiconducting material is fully charged, or in-bulb, with impurities to create a structure called a pn junction.
-Charge carriers - electrons and holes flow into the junction from electrodes with different voltage.
When an electron meets a hole, he fell into a lower energy level, and release energy in the form of photons.

Light emission
The wavelength of light emitted, and therefore its color, depending on the difference in the energy band of the material that forms a pn junction.
A normal diode, typically made of silicon or germanium, emits visible light near infrared, but the material used for an LED have a difference between the energy band near infrared light, visible, and near ultraviolet.

Substrate LED
LED development began with infrared and red devices made with gallium arsenide.
Perkembagan in materials science have enabled the production of tools with shorter wavelengths, producing light with varied colors.

Conventional LEDs are made from inorganic mineral that varies, resulting in the following colors:
* Aluminum gallium arsenide (AlGaAs) - red and infrared
* Gallium aluminum phosphide - green
* Gallium arsenide / phosphide (GaAsP) - red, orange-red, orange, and yellow
* Gallium nitride (GaN) - green, pure green (or emerald green), and blue
* Gallium phosphide (GaP) - red, yellow, and green
* Zinc selenide (ZnSe) - blue
* Indium gallium nitride (InGaN) - turquoise and blue
Aluminum gallium indium phosphide * - orange-red, orange, yellow, and green
* Silicon carbide (SiC) - blue
* Diamond (C) - ultraviolet
* Silicon (Si) - blue (under development)
* Sapphire (Al2O3) - blue

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