Pure White Light; the Holy Grail of LEDs
Source/Type: Reference Materials

April 4, 2001... A number of lighting concerns, including the major manufactures such as General Electric, Philips, and Sylvania, have long pursued the dream of developing a pure white Light Emitting Diode (LED) as the next logical replacement for conventional lighting sources. Compound semiconductor laboratories all over the world have been working in this direction for many years as "white LEDs" are obviously an environmentally attractive, smaller, significantly longer-lived, and ultimately less expensive source of light compared to incandescent, halogen, and fluorescent lighting. The route to a white solid state LED is clearly through the development of progressively more efficient blue spectrum LEDs (which include green, blue, violet, and ultraviolet). For many years, materials scientists and physicists felt that Zinc Selenide (ZnSe) or silicon carbide (SiC) would be the most likely compound semiconductor combinations to achieve the goal. Each of those compound semiconductor combinations have proved they can achieve blue, and have fielded devices, but not at the brightness levels needed to achieve the required revolution in lighting.

It took a brilliant photonic scientist named Shuji Nakamura, who at the time was working with Nichia Chemicals in Japan, to show the world that gallium nitride (GaN) was the most practical route. Dr. Nakamura, who has since moved to the United States to become a professor at the University of California Santa Barbara, built upon a long history of GaN development which began in the US at RCA Laboratories, under Professor Jacques Pankove, as well as other GaN developers in Asia and the former Soviet Union. But it was Dr. Nakamura's breakthrough work in the mid-1990s that made blue spectrum solid state LEDs and Laser Diodes (LDs) real. He grew his breakthrough GaN-based devices epitaxially, by MOCVD, on a sapphire substrate. Because of his long association with Nichia, that company remains in the technological lead for blue spectrum work. Many other companies are now in the field, all have moved solidly over to GaN epitaxial growth using various substrates (sapphire and SiC being the most popular) and most use MOCVD production platforms. Some white LEDs have already been fielded, fashioned into night lights, flashlights, and as sources of ambient light and for toys. But the true replacement for the ordinary white lightbulb remains in the future... though not as distant a future as before. Considerable global development work is now underway to perfect the most practical and manufacturable ways of combining colors to create the desired hues of white LEDs, coating and packaging of the lamps, and producing the long-lived light sources required. When perfected, truly pure white LEDs will, indeed, replace power-hungry sources upon which we are currently dependent. When perfected and prolific, the global environment will ultimately be the real winner.

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