Tech Stories: The Blue LED.

[Cyberpunk]

The blue LED. Most people think of it as a mundane thing, largely relegated to fancy power indications on things such as toasters and kettles. Others think of Christmas lights with a cool blue glow. But the blue LED is a fairly recent invention, with quite a story behind it. Here, I hope to explain its story, and the role it plays in modern electronics. Quite simply, without this small unobtrusive device, many of the modern gadgets and appliances would not be possible. 

 

Up to about 1993, there was no such thing as a viable blue LED. Without it, there would be no such thing as your smart phone, your LED TV, smart watches, modern flatscreen computer monitors, and the blue circular power light on your toaster. The blue LED was such an important invention, that the creators were awarded the Nobel Prize for Physics in 2014. This is the story of the blue LED. 

 

It begins in 1907. This is the year that Electroluminescence as a phenomenon was discovered by the English experimenter Henry J. Round. He used a crystal of silicon carbide and two metal needles to show that when a current was passed through the crystal, it emitted a dim glow. Silicon Carbide, though primarily used in sandpaper, is actually a semi-conductor, and Henry Round had actually made a diode. Hence the term Light Emitting Diode. Though this was experimented with for years, including notable works by Russian inventor Oleg Losev in the late 1920’s, it was decades before a practical use could be found for this phenomenon.  

 

Rubin Braunstein of the Radio Corporation of America (RCA) reported on infrared emission from gallium arsenide and other semiconductor alloys in 1955. This was followed up in 1961 at Texas Instruments by James R. Biard and Gary Pittman discovered near-infrared (900 nm) light emission from a tunnel diode they had constructed on a gallium arsenide substrate. The same technique would be used at General Electric (GE) by Nick Holonyak Jnr to create a more visible spectrum LED. His diode produced a faint red light that was nonetheless visible to the naked eye. Over the next decade, various chemical compositions were used to produce yellow and green LEDs, and increase the brightness of the light emitted from these diodes. The red-orange LEDs proved to be the brightest, and most cost effective to manufacture at this time, with original sales being to the military, and Hewlett Packard, and finally appearing in consumer products such as pocket calculators in the early 1970’s. Soon, LEDs were popping up all over the place, from early digital watches, to computer displays. But a colour was proving to be elusive. Blue. 

 

The idea of a blue LED was very desirable, as blue light is a necessary part of producing a full spectrum colour. The primary colours of red, green and blue, can be mixed to make other colours, and when mixed fully, produce white light. The reason why at this time we were stuck with various hues of red, green and yellow, but not blue is down to the physics of how an LED works. To put it simply, an LED is made up of multiple layers of semi-conductor materials. When a current is passed through the LED, it emits light at the frequency the semi-conducting material allows. Because the frequency of blue light is much higher than red, green, or yellow, it required much more exotic materials and production processes to reproduce. 

 

Some of the early blue LEDs were produces at RCA in 1972, while they were trying to produce a TV which used LEDs instead of phosphors in Cathode Ray Tubes. The first blue-violet LED was created using magnesium-doped gallium nitride as a semi-conductor. That first blue LED was developed by Herb Maruska and Wally Rhines. They began by figuring out how to grow crystals of gallium nitride, and then doping them with magnesium. Today, magnesium-doping of gallium nitride remains the basis for all commercial blue LEDs and laser diodes. In the early 1970s, these devices were too dim for practical use, and with RCA being in financial trouble in the mid 70’s, research into gallium nitride devices slowed, and then halted. 

Bell Laboratories and Japanese company Matsushita worked with magnesium-doped gallium nitride for years before coming to the conclusion that the material was just too tough to work with, and unlikely to produce blue LED’s that were bright enough, and cost effective to manufacture. It wasn’t until the 1980’s that a string of breakthroughs was made in Japan. Isamu Akasaki and Hiroshi Amano in Nagoya were working on developing the important gallium nitride deposition on sapphire substrates and the demonstration of p-type doping of gallium nitride. They called this method “Low temperature, buffer layered technology”. This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like Blu-ray. The results of this research were made available publicly. In 1993, high-brightness blue LEDs were demonstrated by Shuji Nakamura of Nichia Corporation using a gallium nitride growth process, for his company Nichia. Nichia was known for making phosphorus for florescent light tubes, and cathode ray tubes, but were looking to diversify into new products.  

 

Shuji Nakamura made his first breakthrough by using thermal annealing instead of an electron beam which resulted in a higher quality LED, but appeared more violet than blue. His second breakthrough was to create a double header structure within the semiconductor layer. Basically, a sandwich of iridium infused gallium nitride, and the existing magnesium-doped gallium nitride crystals. This narrowed the frequency of the light that was emitted, producing a true blue light. 

 

Finally, in late 1993, Nichia and Shuji Nakamura unveiled their blue LED. This LED was one hundred times brighter, and more vivid that the LEDs of the past. Nichia put the LED into production, and followed it with a high intensity white LED in 1995. The white LED was made by adding a yellow phosphor to the blue LED, creating white light. Other companies followed suit and began to make their own version of blue LEDs, creating an explosion of LEDs on the market, and many companies finding uses for them.  

 

Now blue LEDs have been miniaturized, along with their other coloured cousins to create high density, high resolution LED displays, used in TVs, monitors, watches, tablets and phones. The white LED created a revolution in lighting technology, used in screen backlights, to energy efficient household light bulbs. Not to mention home lighting is now more versatile and colourful than ever, with RGB lights creating vivid displays, and mood lighting. Another advancement from the blue LED arrived in 1996 when Nakamura continued his work and invented the first efficient blue laser. The benefits of blue laser were immediate cause for excitement within the data storage field. Up until this point lasers used in data storage devices were only red. Because of the wavelength of the laser light, there was a limit on how much could be stored on a disc. A blue laser, with its higher wavelength, would enable much more data to be stored on the same size disc. 

[spatular]

 

that's really cool! (although i didn't understand a lot of it)

 

34 minutes ago, Cyberpunk said:

Without it, there would be no such thing as your smart phone, your LCD TV, smart watches, modern flatscreen computer monitors,

sorry i have to nitpick slightly - lcd tv/monitors used to use other light sources for backlight.

[Cyberpunk]

7 minutes ago, spatular said:

 

that's really cool! (although i didn't understand a lot of it)

 

sorry i have to nitpick slightly - lcd tv/monitors used to use other light sources for backlight.

Yeah. They used to use florescent tubes at one point.

[shinymcshine]

It's funny when I recall red LEDs from the 80s as power hungry devices - LED watches didn't have constant display, but press to show for a few seconds. Then LCD took primacy for watches and calculators with LED usually constrained to mains connection for constant ( but self illuminated) display.

 

Then in the late 90s someone I knew brought a white LED torch into work (trial sample) with 2 AAs lasting 12 hrs constant use, bright light too.

[one-armed dwarf]

https://www.japantimes.co.jp/news/2021/04/03/national/isamu-akasaki-dies/

 

The blue LED inventor Isamu Akasaki has died