In 2014, Japanese engineers Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura were awarded the Nobel Prize in Physics for their contributions to creating efficient blue light-emitting diodes. Now, you might be wondering what was so revolutionary about making a blue LED that garnered a Nobel Prize.
The History of Light-Emitting Diodes
By applying a potential difference across a silicon carbide (SiC) crystal, English engineer H.J. Round created the first diode that was able to emit electrically produced light in 1907. By varying the potential difference applied across the SiC crystal, he could change the color of the light emitted. This happens through a process we call electroluminescence: the emission of light when a solid interacts with an electrical field. J.R. Haynes demonstrated that this emission of light was due to the interaction of holes and electrons in a p-n junction.
How do LEDs Work?
LEDs are electronic devices that are illuminated by electron movement in a semiconductor material. A semiconductor has conductive properties that lie somewhere between conductors like copper and insulators like rubber. LEDs are typically made from aluminum gallium arsenide (AlGaAs) doped with electron holes to make it more conductive. A diode consists of a section of an N-type semiconductor attached to a section of a P-type semiconductor forming a p-n junction. When current flows, the negatively charged electrons move in one direction whilst the positively charged holes move in the opposite direction. The holes exist in lower energy states causing a free electron to lose energy as it falls into a hole. The lost energy is emitted as a photon of light.
The Blue LED Problem
To create different LED colors, scientists experimented to see what happened when currents were passed through different materials with unique molecular makeups. You can imagine how slow this trial-and-error process was. The ideal compound was supposed to efficiently produce protons, be thermally stable, and be relatively cheap to produce in large amounts. The necessary materials to create red and green LEDs were found early on but the right one for blue remained elusive. The largest energy gap of all was needed to create a light with a blue wavelength.
Blue Light at the End of the Tunnel
In 1972, researchers at Stanford used magnesium-doped gallium nitride to try and create a blue LED as it had a wide energy gap. However, when built, the LED emitted green light, not blue. It was only in 1993 when Japanese scientists Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura figured out how to produce blue LEDs. They precisely engineered and grew gallium nitride crystals that produced the desired energy gap, which was refined to be feasible for mass production. Many consider the invention of the blue LED one of the most significant engineering advancements of the 20th century.
The Impact of The Blue LED
LEDs have revolutionized many scientific and commercial applications requiring light. For many of these applications, a pure white light was required. No single LED can produce pure white light as it combines multiple wavelengths. Combining red, green, and blue in equal amounts appears visibly as white light. Hence, many of the applications of LEDs we have today would not exist without the blue LED.
LEDs are much more energy-efficient, long-lasting, and produce less heat than previous lighting technologies. They are also more affordable and by replacing conventional light bulbs LEDs can cut the world's energy requirements for lighting by around 25%. LED technology is used in the back-lit screens of phones, TVs, and laptops.
Works Cited
NobelPrize.org. (2014). The Nobel Prize in Physics 2014. [online] Available at: https://www.nobelprize.org/prizes/physics/2014/summary/ [Accessed 1 Oct. 2024].
Veritasium (2024). Why It Was Almost Impossible to Make the Blue LED. YouTube. Available at: https://www.youtube.com/watch?v=AF8d72mA41M&ab_channel=Veritasium [Accessed 1 Oct. 2024].
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