Monday, April 1, 2013




1907 - H.J. Round discovered electroluminescence when using silicon carbide and a cats whisker. Oleg Losev independently discovered the phenomena the same year.
London, United Kingdom
1920s - Oleg V. Losev studied the phenomena of light emitting diodes in radio sets. His first work on 'LEDs' involved a report on light emission from SiC. In 1927 he published a detailed report but his work was not well known until the 1950s when his papers resurfaced.
Saint Petersburg, Russia
1961 - Bob Biard and Gary Pittman developed the Infrared LED at Texas instruments. This was the first modern LED. It was discovered by 'accident' while TI tried to make a laser diode. The discovery was made during a test of a tunnel diode using a zinc diffused area of a GaAs (Gallium Arsenide) semi-insulating substrate.
Dallas, Texas

Photo: Robert Biard
1961 - Gary Pittman worked together with Robert Biard. He had started working in 1958 with semiconductor GaAs for creation of early solar cells. This lead him into the group working on tunnel diodes (lasers). A failed attempt to make a laser lead to the infrared LED.
Dallas, Texas
1962 - Nick Holonyack Jr. develops the red LED, the first LED of visible light. He used GaAsP (Gallium Arsenide Phosphide) on a GaAs substrate. General Electric.
Syracuse, New York

1972 - M. George Craford creates the first yellow LED at Monsanto using GaAsP. He also develops a brighter red LED. 
St. Louis, Missouri

Photo: Semicon West 2012
1979 - Shuji Nakamura develops the world's first blue LED using GaN (Gallium nitride). It wouldn't be until the 1990s that the blue LED would become low cost for commercial production. 
Tokushima, Japan

Photo: Randy Lamb, UC Santa Barbara
1976 - Thomas P. Pearsall develops special high brightness LEDs for fiber optic use. This improves communications technology worldwide. Paris, France
Photo: T.P. Pearsall

light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Appearing as practical electronic components in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible,ultraviolet, and infrared wavelengths, with very high brightness.
When a light-emitting diode is switched on,electrons  are able to recombine with electron holes within the device, releasing energy in the form of photons . This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. However, LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorscent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as aviation lighting , automotive lighting, advertising, general lighting, and traffic signals . LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players and other domestic appliances. LEDs are also used in seven-segment display.

Discoveries and early devices

Green electroluminescence from a point contact on a crystal of SiCrecreates H.J.Round's original experiment from 1907.
Electroluminescence as a phenomenon was discovered in 1907 by the British experimenterH.J.Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Russian Oleg Vladimirovich Losev reported creation of the 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 Braunsteinof 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 gallium antimonide(GaSb), GaAs, indium phosphide(InP), and silicon-germanium(SiGe) alloys at room temperature and at 77 kelvins.
In 1961 American experimenters Robert Biard and Gary Pittman, working at Texas 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 by Nick Holonyak,Jr., while working at General Electric Company. Holonyak first reported this breakthrough in the journal Applied Physics Letters on the December 1, 1962. 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.

Commercial development

The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays, first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches (see list of signal uses). Until 1968, visible and infrared LEDs were extremely costly, in the order of US$200 per unit, and so had little practical use. The Monsanto Company was the first organization to mass-produce visible LEDs, using gallium arsenide phosphide (GaAsP) in 1968 to produce red LEDs suitable for indicators. Hexlett Packard (HP) introduced LEDs in 1968, initially using GaAsP supplied by Monsanto.planar process invented by Dr. Jean Hoerni at Fairchild Semiconductor . The combination of planar processing for chip fabrication and innovative packaging methods enabled the team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. These methods continue to be used by LED producers.
These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors grew widely available and also appeared in appliances and equipment. In the 1970s commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the

LED display of a TI-30 scientific calculator (ca. 1978), which uses plastic lenses to increase the visible digit size
As LED materials technology grew more advanced, light output rose, while maintaining efficiency and reliability at acceptable levels. The invention and development of the high-power white-light LED led to use for illumination, which is fast replacing incandescent and fluorescent lighting(see list of illumination applications) .
Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with rising power output, it has grown increasingly necessary to shed excess heat to maintain reliability, so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high-power LEDs bear little resemblance to early LEDs.

The blue and white LED

Illustration of Haitz's law Light output per LED as a function of production year; note the logarithmic scale on the vertical axis
The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGan.Its development built on critical developments in GaNnucleation on sapphire substrates and the demonstration of p-type doping of GaN, developed by Isamu Aksakiand H. Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide(ITO) on (AlGaInP/GaAs). 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 (donw-convertedyellow 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 rise exponetially, with a doubling occurring approximately every 36 months since the 1960s, in a way similar to Moore's law. This trend is generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science, and has been called Haitz's law after Dr. Roland Haitz.
In 2001 and 2002, processes for growing gallium nitride(GaN) LEDs on sillicon were successfully demonstrated. In January 2012, Osram demonstrated high-power InGaN LEDs grown on Silicon substrates commercially. It has been speculated that the use of six-inch silicon wafers instead of two-inch sapphire wafers and epitaxy manufacturing processes could reduce production costs by up to 90%

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