Nobel Prize for Blue LEDs

October 10, 2014

The 1960s television series, "Voyage to the Bottom of the Sea,"[1] was loosely based on the 1961 movie of the same name.[2] One interesting part of the movie was that the captain (played by Walter Pidgeon) of the nuclear submarine, Seaview, could smoke cigars while on board. Perhaps smoking was safer aboard a nuclear submarine than a conventional submarine, since there wasn't any hydrogen present from overcharged batteries.

Episode 20, season 1, of the television series was entitled, The Invaders, and it guest-starred Robert Duvall as Zar, a member of a previous race of humans placed in suspended animation at the bottom of the sea. Humans of Zar's time had advanced intelligence; and, fortunately for the plot, Zar is able to learn English in just a few hours. While on a tour of the ship, Zar notices the incandescent lighting, and he comments how humans of the present-day had not yet learned how to create light without heat.

Just a few years into the future, red light-emitting diodes (LEDs) were produced from gallium arsenide phosphide (GaAsP), and these produced light with nearly no heat. By the mid-1970s, Fairchild Optoelectronics was selling red LEDs for about five cents each. There followed a long march of research in similar III-V semiconductor materials to produce shorter wavelength colors, from orange and yellow through green. These "traffic light" colors allowed a good variety in indicator lights on electronic equipment.

Missing from the color mix was blue, since these III-V materials could not produce blue-light because their band gap was too small. The band gap, which is the difference in energy between the electrons in the valence and conduction bands, essentially sets the wavelength that a semiconductor can efficiently emit light.

Pure gallium arsenide (GaAs) has a band gap of 1.43 electron volts (eV), corresponding to the infrared wavelength of 867 nm. Alloying with other elements, such as gallium phosphide (GaP), pushes the emission to shorter wavelengths. You can calculate the wavelength λ from the energy E with this simple formula involving the Planck constant h and the speed of light c.

As light-emitting diode technology progressed, gallium nitride (GaN) loomed as a possible blue light material, since its band gap of 3.4 eV pegged it as a possible emitter of very short wavelength light; in fact, the wavelength of 364 nm corresponding to the band gap energy is ultraviolet light. One problem was that a diode junction needs n-doped and p-doped material, and an electron-deficient p-type material was elusive.

Another problem was manufacture of the gallium nitride, itself. Gallium nitride has a melting point greater than 2500 °C, so the Czochralski process used to make large silicon crystals is not possible. Shuji Nakamura, while working at Nichia Corporation (Tokushima, Japan), developed a metalorganic vapor phase epitaxy process for growth of thin films of GaN on sapphire (Al₂O₃).

These films could be doped with silicon, to produce n-type material, and magnesium, to produce p-type material. Nakamura discovered that high temperature annealing of Mg-doped GaN in a nitrogen atmosphere after electron irradiation would produce a suitable p-type material. The electron irradiation effect was discovered by Isamu Akasaki, and Hiroshi Amano at Nagoya University. Eventually, high brightness blue LEDs were manufactured from InGaN, as well as violet and ultraviolet LEDs.

Red, green, and blue light-emitting diodes. Nowadays, these devices are more likely to be surface mount, rather than these through-hole types. (Via Wikimedia Commons.)

While blue LEDs are useful in their own right, their main utility arises from the fact that white light can be created from red, green, and blue sources. There are some problems with this approach, since the different LEDs will age at different rates, and the color will shift. White light can even be created from a mix of proper wavelengths of blue and yellow light, or by using an ultraviolet LED to illuminate a white phosphor similar to the type used in white fluorescent lamps.

The CIE 1931 Color Space. This diagram allows an estimate of what color results from a mixture of primary colors at the periphery. (Wikimedia Commons image by Sakurambo. Click for larger image.)

Change is difficult when the advantages for change are not that apparent. I personally bypassed compact fluorescent lighting, since its disadvantages, especially slow turn-on, cheap construction, and environmental problems, did not outweigh its presumed advantages. However, I've purchased quite a few LED lamps.

I saw special advantage in placing an LED lamp in the high ceiling of a stairway where its long life will preclude many a dangerous ladder excursions for bulb replacement. There's no question that LED lighting is a winning technology. As I tell my family, after the initial investment, it's like getting light for free. LED lamps use one-seventh the electrical power of an equivalent incandescent lamp.

I once worked on an electron phosphor project for which 100 lumens per watt of just yellow light was seen as significant. Laboratory LEDs have achieved more than 300 lumens/watt, compared with about 70 for fluorescent lamps and 15 for incandescent lamps. LED lifetime approaches 100,000 hours, and the bulbs I've purchased are claimed to last for 22.8 years of typical use (It must be true because of the decimal point, LOL!). About 19% of the world's electricity is used for lighting.

Alfred Nobel established his eponymous prize to reward "those who, during the preceding year, shall have conferred the greatest benefit on mankind." Since it is now apparent that development of the blue LED has conferred a great benefit on mankind, this years' Nobel Prize in Physics was awarded to its three principal inventors, Shuji Nakamura, Isamu Akasaki, and Hiroshi Amano.[3-11]

While Isamu Akasaki and Hiroshi Amano did some important fundamental research on gallium nitride at Nagoya University, the actual invention of the blue LED is credited to Nakamura (see figure).[12] Nakamura, who is now professor at the Materials Department, the College of Engineering, the University of California, Santa Barbara, did this research while at Nichia Corporation, and he was awarded about $200 for his efforts. In 2005, after filing suit for a larger share of this profitable discovery, Nakamura was awarded about nine million dollars. His share of the Nobel Prize money is a little more than $350,000, with Akasaki and Amano getting the same amounts.

Fig. 3 of US Patent No. 6,900,465, "Nitride semiconductor light-emitting device, by Shuji Nakamura, Shinichi Nagahama, Naruhito Iwasa, and Hiroyuki Kiyoku, May 31, 2005. The priority date of this 31 page patent is December 2, 1994. (Via Google Patents.)[12]

A statement by the Royal Swedish Academy of Sciences, which makes selections for the physics prize, recalls that "Despite considerable efforts, both in the scientific community and in industry, the blue LED had remained a challenge for three decades.” It continues that LED lighting “holds great promise for increasing the quality of life for over 1.5 billion people around the world who lack access to electricity grids."[3]

Akasaki, 85, a Japanese citizen, works at Meijo University and Nagoya University.[3,5,7,11]. He was was born in Chiran, Japan, graduated from Kyoto University in 1952, and received his Ph.D. in 1964 from Nagoya University.[5] Amano, 54, a Japanese citizen, is a professor at Nagoya University.[5] He was born in Hamamatsu, Japan, and he received his Ph.D. from Nagoya University in 1989.[5,7,11] Shuji Nakamura, 60, born in Ehime, Japan, is a US citizen.[3,5,11]

Shuji Nakamura at the University of California, Santa Barbara. Nakamura is listed as an inventor on more than a hundred patents. (UCSB image by Randall Lamb.)[3]

Nakamura, who is an electrical engineer, received his undergraduate and Ph.D. degrees from the University of Tokushima. He was awarded his Ph.D. in 1994, coincident with his blue LED research at Nichia Corporation.[3,5] He was been awarded the Millennium Technology Prize in 2006, and he was elected to the U.S. National Academy of Engineering in 2003.[3] He joined the University of California, Santa Barbara, in 2000, taking the Cree Chair in the Solid State Lighting and Display Center in 2001.[3] He is a founder of Soraa, a developer of gallium nitride solid-state lighting technology.

Aside from the lighting application, blue LEDs are used in the aptly-named Blu-Ray DVD players. The short wavelengths are useful for stuffing a greater number of bits into optical fibers, and ultraviolet LEDs are used for sterilizing drinking water.[5,9] Professor Olle Inganas, a member of the prize committee from Linkoping University, is quoted by BBC News as saying, "These uses are what would make Alfred Nobel very happy."[6] Said Nakamura shortly after announcement of the award, "I hope that energy-efficient LED light bulbs will help reduce energy use and lower the cost of lighting worldwide.”[3]

References:

1. Voyage to the Bottom of the Sea (Television Series, 1964–1968, Created by Irwin Allen) on the Internet Movie Database.
2. Voyage to the Bottom of the Sea (1961, Irwin Allen, Director) on the Internet Movie Database.
3. Andrea Estrada, "UCSB Materials Professor Shuji Nakamura Wins Nobel Prize in Physics," University of California, Santa Barbara, Press Release, October 6, 2014.
4. Daniel Clery, "Creators of blue LEDs win Nobel physics prize," Science, October 7, 2014.
5. Hamish Johnston, "Isamu Akasaki, Hiroshi Amano and Shuji Nakamura win 2014 Nobel Prize for Physics," Physics World, October 7, 2014.
6. Jonathan Webb, "Invention of blue LEDs receives physics Nobel," BBC News, October 7, 2014.
7. Niklas Pollard, "Nobel Prize for physics goes to inventors of low-energy LED light," Reuters, October 7, 2014.
8. Scott Neuman, "3 Scientists Win Nobel In Physics For Development Of Blue LED," NPR, October 7, 2014.
9. The 2014 Nobel prizes: Physics - Blue's brothers, The Economist, October 7, 2014.
10. Japanese, American Win Nobel Physics Prize for LED Invention, VOA News, October 7, 2014.
11. Oliver Staley, "Energy-Saving LED Lights Win Nobel Physics Prize," Bloomberg News, October 7, 2014.
12. Shuji Nakamura, Shinichi Nagahama, Naruhito Iwasa, and Hiroyuki Kiyoku, "Nitride semiconductor light-emitting device," US Patent No. 6,900,465, May 31, 2005.