Culture. Nurture. Tincture. Enrapture.

The colorful history of the LED

LEDs (Light Emitting Diode) are tiny sparkling indicators. You probably heard the name before but I am sure you don‘t know how ubiquitous they are. Nowadays, any video game or film disk are read by LEDs. More cards each year are equipped with LED indicators. We use them for transmitting signals, maybe even including your internet connection. Nighttime lighting? That‘s probably LEDs too. But as common as they are, few actually know WHEN they were invented. Like many such stories, it is more winding and complex than you could expect. In fact, it came pretty close to never coming to be, at least in the way we know them. We need to go back to its humble beginnings to appreciate that.

LEDs emit light by exploiting the structure of semiconductors. In a word, by passing a current through some semiconductors, you can make some of its electrons move. The key here is that, contrary to metals, those electrons cannot flow freely. They can “live“ only at specific energy levels. By moving from one energy level to another, electrons will emit light to get rid of their excess energy. The important part here is that the difference in energy is quite specific. This means that with the appropriate semiconductor, we can ensure that those electrons produce light of exactly the colour we want.

Like many scientific discoveries, this was first observed by accident. At the time an assistant of radio pioneer Marconi, Henry J. Round reported seeing light emission from silicon carbide. He seemed in some way quite confused by it and couldn‘t explain it. Release in February 1907, that little note led to no following publications or research. It could have easily been to end of it right there: just a curious observation with a strange new material.

No, the LED would truly be birth about twenty years later. Let me introduce you to the true father of the LED: Oleg Vladimirovich Losev. This Soviet laboratory technician had no formal education. Yet in his short 40-year life, he published more than 43 papers in leading European journals and was granted 16 patents as sole author. Much of his groundbreaking work deserves recognition but his work on the LED specifically requires our attention today. In the mid-1920s, Losev would in turn observe light emission from silicon carbide crystals when a current was passed through them. That‘s all the motivation he needed to plunge headfirst into the subject. In 1927, he published his first paper on the subject. From that first paper, Losev shows a great understanding of the technology. In 16 papers published between 1924 and 1930, he provided a comprehensive study of the LED. He recognized the temperature dependence of the emission, the light spectrum produced and the current-voltage characteristics of semiconductors. All those aspects are crucial to modern LED production. He closely followed this paper with a patent (intitulated “Light Relay“), pointing out right here and there its potential in communication. Not bad for a self-made scientist.

Either way, the floodgates were now open.

From 1930, multiple papers on LEDs would spur out of multiple laboratories throughout Europe. The first LEDs emitted multiple colours but, in time, researchers discovered that specific and pure semiconductor crystals could produce more precise colours. In 1958, Egon Loebner and Rubin Braunstein created the first green LED. In 1962, Nick Holonyak Jr. invented the first truly practical LED - a red one. This was the first reproductable LED that was visible to the eye. Red LEDs would start as light indicators and calculator displays. Brighter reds would come gradually, peaking with laser diodes in the 1970s. More colours would also follow suit. Green, of course, but yellow too. But one colour escaped our grasp: blue.

This was a huge problem.

Why? Well, without vital blue light, LEDs cannot produce white light. This limited the LED immensely. In 1969, Maruska and Tietjen succeeded in growing single crystals of GaN (a nitride semiconductor). They found that GaN had a bandgap energy of about 3.39 eV - just in the blue spectrum. Predictably, the race for the blue LED soon followed. However, researchers were quick to discover a big problem. Sure, you could grow GaN crystals but obtaining crystals pure and large enough for p-type conduction (required for semiconductors) was a pain. For that reason, interest in GaN was quickly replaced by fresh discoveries in zinc-based semiconductors.

But where others left, Isamu Akasaki saw promise. Much later than author researchers, Akasaki started his quest for the blue LED in the 1970s. After years and years of failures, Akasaki and his student Hiroshi Amano finally achieved the first high-quality GaN crystal in 1985. Progress would take the pace from there, leading to the first true blue LED in 1989. Shuji Nakamura would later improve GaN quality and brightness even further, making the first blue diode laser possible. This deservedly made headlines. LEDs could now produce white light.

LEDs have completely replaced gas and incandescent sources which were cumbersome, fragile and costly. Unless you haven't updated your computer in several years, you're probably reading these words with white LEDs. The LED‘s march forward is still ongoing. In later years, we have achieved organic LEDs (OLED) producing even more efficient lighting. The LED has revolutionized our world and for the better. It now stands as one of our best tools to guarantee a more sustainable and less power-hungry future. We just need to remember that the LED was not a gift but rather the outcome of years of sweat and stubbornness. I expect our next revolution to be much the same.

Anyway, that is all for today. See you next time.

References

  • The life and times of the LED — a 100-year history, NIKOLAY ZHELUDEV (2007)
  • Isamu Akasaki, Key inventions in the history of nitride-based blue LED and LD, Journal of Crystal Growth, Volume 300, Issue 1, 2007, Pages 2-10, ISSN 0022-0248
  • His Blue LEDs Changed How We Light Our World - Nearly 30 years ago, Isamu Akasaki dazzled journalists with a bright pen light, JEFF HECHT, 08 APR 2021, IEEE Spectrum
  • Hall, R. N., Fenner, G. E., Kingsley, J. D., Soltys, T. J. & Carlson, R. O. Phys. Rev. Lett. 9, 366–368 (1962).
  • Holonyak, N. & Bevacqua, S. F. Appl. Phys. Lett. 1, 82–83 (1962).
  • Nathan, M. I., Dumke, W. P., Burns, G., Dill, F. H. & Lasher, G. Appl. Phys. Lett. 1, 62–63 (1962).
  • Quist, T. M. et al. Appl. Phys. Lett. 1, 91–92 (1992).
  • Loebner, E. E. IEEE Trans. Electron Dev. 23, 675–699 (1976).
  • Novikov, M. A. in Ahead of the Time Ch. 1, 7–31 (N. I. Lobachevsky State Univ. of Nizhniy Novgorod Publishing, 2006).
  • Losev, O. V. Soviet patent 12191 (1929).
  • Round, H. J. Electr. World, 49, 308 (1907).