Light emitting diode

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Introduction

Alight-emitting diode(LED) is asemiconductorlight source. LEDs are used as indicator lamps in many devices and are increasingly used for otherlighting. Introduced as a practical electronic component in 1962,early LEDs emitted low-intensity red light, but modern versions are available across thevisible,ultravioletandinfraredwavelengths, with very high brightness.

When a light-emittingdiodeis forwardbiased(switched on),electronsare able torecombinewithelectron holeswithin the device, releasing energy in the form ofphotons. This effect is calledelectroluminescenceand thecolorof the light (corresponding to the energy of the photon) is determined by theenergy gapof the semiconductor. An LED is often small in area (less than 1mm2), and integrated optical components may be used to shape its radiation pattern.LEDs present manyadvantagesover incandescent light sources includinglower energy consumption, longerlifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current andheat managementthan compactfluorescent lampsources of comparable output.

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Light-emitting diodes are used in applications as diverse as replacements foraviation lighting,automotive lighting(particularly brake lamps, turn signals and indicators) as well as intraffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology.InfraredLEDs are also used in theremote controlunits of many commercial products including televisions, DVD players, and other domestic appliances.

History

Discoveries and early devices

Green electroluminescence from a point contact on a crystal ofSiCrecreatesH. J. Round’s original experiment from 1907.

Electroluminescenceas a phenomenon was discovered in 1907 by the British experimenterH. J. RoundofMarconi Labs, using a crystal ofsilicon carbideand acat’s-whisker detector.RussianOleg Vladimirovich Losevreported on the creation of a first LED in 1927.His research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades. Rubin Braunstein of theRadio Corporation of Americareported on infrared emission fromgallium arsenide(GaAs) and other semiconductor alloys in 1955.Braunstein observed infrared emission generated by simple diode structures usinggallium antimonide(GaSb), GaAs,indium phosphide(InP), andsilicon-germanium(SiGe) alloys at room temperature and at 77kelvin.

In 1961, American experimenters Robert Biard and Gary Pittman working atTexas Instruments,found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED.

The first practical visible-spectrum (red) LED was developed in 1962 byNick Holonyak Jr., while working atGeneral Electric Company.Holonyak is seen as the "father of the light-emitting diode".M. George Craford,a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T.P. Pearsall created the first high-brightness, high efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths.

Until 1968,

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