Introduction LED

Definition:
LED technology Physical function
An LED is a special type of semiconductor diode. Like a normal diode, it consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side, or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers - electrons and electron holes flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon as it does so.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever shorter wavelengths, producing light in a variety of colors.

LEDs are usually built on a n-type substrate, with electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it gets absorbed and turns into additional heat.

Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following 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
gallium arsenide phosphide (GaAsP) - red, orange-red, orange, and yellow
gallium phosphide (GaP) - red, yellow and green
gallium nitride (GaN) - green, pure green (or emerald green), and blue
indium gallium nitride (InGaN) - near ultraviolet, bluish-green and blue
silicon carbide (SiC) as substrate - blue
silicon (Si) as substrate - blue (under development)
sapphire (Al2O3) as substrate - blue
zinc selenide (ZnSe) - blue
diamond (C) - ultraviolet
aluminum nitride (AlN), aluminum gallium nitride (AlGaN) - near to far ultraviolet

• Features and Benefits of LED