The History of LED Technology

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It is nice to turn on that LED flashlight and feel the comfort of being able to see in the dark.  Did you ever wonder how it works?  Or, where the technology came from?  LED technology has actually enjoyed a rather long history.  It is not as new as most people believe.  LED, or light-emitting diode, lighting started out as a very dim, yellow light but progressed to the very bright light we see today.

British scientist Henry J. Round of Marconi Labs discovered that the junction of a semi-conductor produced light in 1907.  Silicon Carbide (SiC) was used in these early experiments.  This early light was very dim.  It was not bright enough to stimulate further research.  LEDs were forgotten until the 1920s when experiments began in Germany and Russia.  Russian researcher Oleg Vladimirovich Losev produced the first LED but his research never made it out of his own country.  At the same time Bernhard Gudden and Robert Wichard Pohl, of Germany, experimented with phosphor materials made from Zinc Sulphide with Copper (ZnS:Cu).  These experiments did not yield much light either.  The term “electroluminescence” came about in 1936 after a published report by George Destriau on the light produced by passing an electric current through Zinc Sulfide powders. 

In the 1950s, British experiments in electroluminescence, using a semiconductor called Gallium Arsenide (GaAs), led to the development of the first infrared light-emitting diode.  It was reported that these early laboratory LEDs had to be kept in liquid nitrogen during operation and significant effort was required to produce lights that could function at room temperature.  The Radio Corporation of America (RCA) led the charge, with Rubin Braunstein.  Braunstein discovered and reported the production of infrared light using various semiconductor alloys in 1955.  Bob Biard and Gary Pittman, of Texas Instruments, followed suit and continued experimenting with the infrared light produced from electricity applied to Gallium Arsenide.  Nick Holonyak Jr., at General Electric Company, produced the first visible spectrum light, a red light, in 1962.  This discovery earned him the moniker, “Father of the light-emitting diode.”  Holonyak was later at the University of Illinois at Urbana-Champaign and a graduate student of his, M. George Craford, invented the first yellow LED and eventually a much brighter red and red-orange LED in 1972. 

Craford started using a Gallium Phosphide (GaP) substrate to produce a brighter red and also orange.  This led to the use of Gallium Phosphide itself, which emitted a pale green light.  Craford took it a step further and used a dual GaP chip system (one red and one green) to produce a yellow light.  The Russians experimented with Silicon Carbide to produce a yellow light at about the same time but, due to the inefficiency of the light, they were not as well accepted as their U.S. counterparts.  The end of the decade brought about purer green light.

The 1980s brought forth the first superbright LEDs.  The use of Gallium Aluminium Arsenide Phosphide (GaAlAsP) produced these bright reds, then yellows and finally greens.  The next progression, in the 1990s, found experimenters using Indium Gallium Aluminium Phosphide (InGaAlP) to produce ultra bright LEDs of orange-red, orange, yellow, and green.  Blue LEDs made their first appearance in the early part of this decade, as well.   These were first produced using, once again, Silicon Carbide.  Due to the dim quality this was soon replaced with Gallium Nitride (GaN).  Shortly after, Indium Gallium Nitride (InGaN) LEDs were introduced, producing high intensity blue and green lights. 

These super-bright blue chips were used to produce white light.   The chip is coated with fluorescent phosphors, which absorbs the blue light and re-emit’s a white light.  This same technology can be used to produce a wide array of visible colors.  This has also helped to produce higher intensity colored lights.

The process to get from the very dim, low output LEDs of the early 20th century to the high intensity lights of today was a slow road, but the current “end result” has been worth it.  The intensity of light and availability of colors has made it useful in many applications.  The early scientists may never have imagined their accidental discoveries would lead to such varied uses of this electroluminescence.  As the science progressed the uses increased and the availability grew.  LEDs are found in most homes and businesses in modern society.  So, although it was a slow crawl across the color spectrum to get to the technology of today, it has certainly been worth it.

-Ben Anton, 2007
http://www.lightsandknives.com/led-technology-history.htm