During the 1990s, developments by scientists at the Nichia Corporation in Japan helped pave the way for the creation of blue Light Emitting Diodes. This series of breakthroughs essentially enabled the production of LEDs in any colour and also led to the creation of numerous environmentally-friendly lighting products.
LEDs are everywhere. From displays at airports and train stations to traffic lights and everyday household appliances. Yet these efficient light sources have only been refined for commercial use over the past two decades. And before the Nichia Corporation's numerous patents (and work by their many scientists, including Shuji Nakamura), the only LEDs available were yellow and red.
However, once all three fundamental colours - yellow, red and blue - were present, they could be used to create any other colour, including white.
With respect to blue LEDs, it all began at Nichia in the late 1980s and early 1990s. As part of a long line of innovations by Nichia scientists, Nakamura and his colleagues created the first high-brightness GaN (gallium nitride) LED to produce blue light.
Up until that point, most scientists were working on zinc selenide to try to create blue LEDs. The breakthrough at Nichia was the use of gallium nitride - and the daily modification (over a period of eighteen months) of a Metalorganic Chemical Vapour Deposition system (MOCVD). The result was the Two-Flow MOCVD, and using this machine it was possible to produce the highest quality gallium nitride crystals in the world at that time.
The previously missing colour opened the door to advancements in several fields, the most notable being blue LEDs that could be used to produce energy-efficient LED lights - an environmentally-friendly alternative to traditional light bulbs.
Since that time, blue, green, white and UV LEDs, as well as blue laser diodes, have all been produced, with applications including energy efficient lamps, TVs, new DVD formats, and blue lasers for the transmission of information over optical fibres.
LEDs are semiconductor devices that emit incoherent narrow-spectrum light when electrically stimulated. The 1992 patent entitled "Method of vapour-growing semiconductor crystal and apparatus for vapour-growing the same" was one of several patents which helped lead to the creation of blue LEDs, and came as one of a line of Nichia developments in the area.
The invention was achieved by creating a method of growing in vapour phase a semiconductor crystal film consisting of a nitrogen compound. Specifically, it's a method where a reaction gas is blown on the surface of a substrate.
This was achieved by using what Shuji Nakamura called the Two-Flow MOCVD reactor. Normally a MOCVD system would have a single gas flow, but Nakamura and his colleagues added another sub-flow with an inactive gas blowing perpendicular to the substrate. The result was the suppression of the large thermal convection that occurs when growing a crystal at 1,000 degrees.
Using this system, extremely high-quality gallium nitride crystals were produced.