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WHAT IS led? HISTORY AND DEVELOPMENTS
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A light-emitting-diode (LED)
(pronounced /ˌɛliːˈdiː/), is a semiconductor diode that emits light
when an electric current is applied in the forward direction of the
device, as in the simple LED circuit. The effect is a form of
electroluminescence where incoherent and narrow-spectrum light is
emitted from the p-n junction.
LEDs are widely used as indicator lights on electronic devices and
increasingly in higher power applications such as flashlights and area
lighting. An LED is usually a small area (less than 1 mm2) light
source, often with optics added to the chip to shape its radiation
pattern and assist in reflection. The color of the emitted light
depends on the composition and condition of the semiconducting
material used, and can be infrared, visible, or ultraviolet. Besides
lighting, interesting applications include using UV-LEDs for
sterilization of water and disinfection of devices and as a grow light
to enhance photosynthesis in plants.
Discovery and development
The first known report of a light-emitting solid-state diode was made
in 1907 by the British experimenter H. J. Round of Marconi Labs.[6]
Russian Oleg Vladimirovich Losev independently created the first LED
in the mid 1920s; his research, though distributed in Russian, German
and British scientific journals, was ignored, and no practical use was
made of the discovery for several decades. Rubin Braunstein of the
Radio Corporation of America reported on infrared emission from
gallium arsenide (GaAs) and other semiconductor alloys in
1955.Braunstein observed infrared emission generated by simple diode
structures using GaSb, GaAs, InP, and Ge-Si alloys at room temperature
and at 77 K. In 1961, experimenters Bob Biard and Gary Pittman working
at Texas Instruments,found that gallium arsenide gave off infrared
radiation when electric current was applied. Biard and Pittman were
able to establish the priority of their work and received the patent
for the infrared light-emitting diode.
The first practical visible-spectrum (red) LED was developed in 1962
by Nick Holonyak Jr., while working at General Electric Company. He
later moved to the University of Illinois at Urbana-Champaign.Holonyak
is seen as the "father of the light-emitting diode". M. George Craford,
a former graduate student of Holonyak's, invented the first yellow LED
and 10x brighter red and red-orange LEDs in 1972.
Shuji Nakamura of Nichia Corporation of Japan demonstrated the first
high-brightness blue LED based on InGaN borrowing on critical
developments in GaN nucleation on sapphire substrates and the
demonstration of p-type doping of GaN which were developed by I.
Akasaki and H. Amano in Nagoya. In 1995, Alberto Barbieri at the
Cardiff University Laboratory (GB) investigated the efficiency and
reliability of high-brightness LEDs demonstrating very high result by
using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs)
LED. The existence of blue LEDs and high efficiency LEDs quickly led
to the development of the first white LED, which employed a
Y3Al5O12:Ce, or "YAG", phosphor coating to mix yellow (down-converted)
light with blue to produce light that appears white. Nakamura was
awarded the 2006 Millennium Technology Prize for his invention.
The development of LED technology has caused their efficiency and
light output to increase exponentially, with a doubling occurring
about every 36 months since the 1960s, in a similar way to Moore's
law. The advances are generally attributed to the parallel development
of other semiconductor technologies and advances in optics and
material science. This trend is normally called Haitz's Law after Dr.
Roland Haitz.
From Wikipedia, the free encyclopedia
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