January 1, 2000
Inventor of Blue, Green, White LEDs and Blue Laser Leaves Japanese Company for U.S. University
Shuji Nakamura's Research Likely to Lead to Whole New Way of Lighting
Santa Barbara, Calif. -- Shuji Nakamura--the creator of blue, green and white LEDs and the blue laser--has accepted an appointment to the faculty of the College of Engineering at the University of California at Santa Barbara. Nakamura, known for his technological wizardry with semiconducting gallium nitrides, comes to the Santa Barbara faculty from Nichia Chemical Industries in Tokushima, Japan, where he has conducted his research since 1979 and headed the Department of Research & Development since 1993.
UCSB Chancellor Henry Yang, whose academic area of expertise is aerospace engineering, said, "Nakamura has achieved remarkable creative feats with the new semiconductors based on gallium nitrides. What a pleasure it is for UCSB to welcome such a world-class researcher to Santa Barbara. The gallium nitride group here at the College of Engineering--six outstanding professors and their 30 brilliant graduate students--is truly top-notch; they are pioneers among university researchers in making the blue laser. Nakamura's joining our group is like mounting the jewel in the semiconductor crown at Santa Barbara. I would like to acknowledge the enthusiastic efforts of many of our colleagues and friends of UCSB during the recruitment."
Nakamura said that Santa Barbara's expertise in gallium nitride material--making and devices is key to his deciding to come to this University. But his decision was two-fold. Before he chose a particular university, he had to decide to leave industry for academia.
Said Nakamura, "I am very grateful to Nichia for the superb research opportunities they have provided me. But I felt that I had come to a crossroads in my life. There is a spectrum of orientation for research that ranges, let us say, from the purely commercial to the purely academic. I decided that an academic context would now be better for my work."
Santa Barbara's Dean of Engineering Matthew Tirrell hailed Nakamura's arrival as a clear-cut example of "strength building on strength. What it took for us to attract the leader of this new semiconductor revolution was our existing premier group. Quality attracts quality."
One of the key outcomes of Nakamura's research at Santa Barbara will likely be a whole new way of lighting. He has already made the invention--the white LED--which will likely lead to replacing the incandescent light bulbs of the world (the lighting method invented by Thomas Edison in 1878) with semiconductor-based devices. The white LED (Light Emitting Diode) has been described as the holy grail of semiconductor optoelectronic engineers.
Innovative MOCVD Technique
Nakamura's road to that invention began with his development of a new technique for Metal-Organic Chemical Vapor Deposition (MOCVD). With the conventional MOCVD technique, semiconductors are made by flowing reactant gases over a substrate. Nakamura pioneered a method whereby the gases flow in two directions instead of one, thereby improving the material quality.
That novel MOCVD technique enabled Nakamura to make a blue LED. And the blue LED lead to the white LED and the blue laser.
Semiconductors are made of a crystal of a material such that electrons moving from higher to lower energy levels in the crystalline structure emit photons of light whose frequency (color) is determined by the extent of the gap between the energy levels. Optoelectronic engineers call the difference in energy levels the "band gap." The gap that an electron traverses to give off a blue photon is greater than that for any other visible color, so the electron has to have more energy to give off the higher frequency blue photon.
But that semiconductor picture is a little too simplified for understanding Nakamura's breakthrough in the making of the blue LED. A blue LED consists of a two-sided crystal such that the "sides" represent an n-type and a p-type semiconductor. The n-type conducts electrons, and the p-type conducts holes, which are the absence of electrons. The electrons flow along in one direction, and the holes in the other. The place in the crystal where the electrons fall into or are injected into the holes is called the junction, and that is where the photons--the particles of light--are emitted.
What Nakamura did was to figure out how to grow the crystal so that it would have the n and p semiconductor structure that would create "quantum wells" for the electrons at the junction. One key thing he did to create the wells was to add indium to the gallium nitride crystal. Without the indium, the gallium nitride crystal produces a higher frequency ultraviolet light, which is not visible. The addition of indium results in lowering the frequency of the emitted photons to visible blue, but the indium also creates the quantum well effect, so that electrons falling into the passing holes first fall into the well and therefore collect en mass before being injected into the holes. That massing in the well creates a more vigorous injection.
With the addition of a little more indium, the blue light emitting device can be turned into a green light emitting device. Before Nakamura the green in full-color displays was phosphorescent yellowish. But his blue LED technology now makes greens in huge full panel displays (of which there are now some 200 worldwide) really green.
And the green light in existing traffic lights in St. Paul, Minn., or at the corner of Patterson and University in Goleta, Calif. (where UCSB is located), can be purely green emitting devices. Heretofore, the green of traffic lights has been created by filtering out all but green light from a light source emitting at the full spectrum of visible light. Those pure green semiconductor-based traffic lights require half as much energy to operate as their full-spectrum-filtered-to-green predecessors.
Nakamura's next step was to put a novel phosphor over his blue chip to get a white light. Though still a little too bluish for straightforward commercial application, the resultant white LED translates, for instance, into a flashlight that can shine for 35 hours instead of the present limit for an incandescent flashlight bulb of six hours.
The 60-watt light bulb in that lamp next to your reading chair is putting out a lot of electromagnetic energy in the infrared part of the spectrum; that excess radiation can't be seen, but it can be felt as heat. So the idea is to replace those inefficient incandescent light bulbs of the world with white LEDs for a reduction in the energy needed to power lights bulbs. And the absence of the infrared radiation means lights putting out no heat, thereby reducing air-conditioning costs.
Not only will these soon-to-be white LEDs use half as much energy to shine, they will also last orders of magnitude longer than the conventional light bulb. Imagine changing light bulbs once every 50 years!
At the same time, the mid-1990s, when Nakamura was using his blue LEDs to make white LEDs, he was adapting his blue LED technology to make a blue laser.
With LEDS the photons emitted are in a range of similar frequencies--i.e., the blue. With lasers, the frequency of the photons is all the same. To amplify a single frequency of light in a crystal, Nakamura figured out how to etch a highly polished mirror on each side of the crystal so that the light bouncing back and forth between the mirrors moves to resonating at the same frequency. His breakthrough work consisted not only of making the mirrors on the crystal but also enabling the crystal to take the high current necessary to create the high-frequency blue laser light.
So what's a blue laser good for? Substitute blue lasers for the infrared lasers used in compact-disc players and get five times as much data on the CD. Blue lasers may eventually mean as much as a 35-fold increase in the amount of information that can be contained on a CD. And blue lasers presage not only more data on CDs, but also DVDs.
All of Nakamura's dazzling innovations--the blue, green and white LEDs and the blue laser--depend on the use of the semiconducting material gallium nitride. Current research developments based on the material seem to herald a semiconductor revolution in which gallium nitride is replacing gallium arsenide as the material of choice. Though gallium is common to both materials, it is the move from its combination with arsenic to combination with nitrogen that is key. The latter unlike the former is environmentally friendly.
Nakamura's position in the vanguard of the gallium nitride revolution is evident from the press he's been getting in the United States. In the last few months he has figured prominently in articles in Forbes, Fortune, and Scientific American.
Nakamura, who is 45-years-old, grew up on the southern island of Shikoku, Japan, and received his degrees from the University of Tokushima, Japan.
He is the recipient of numerous prestigious awards including most recently the 1994 and 1997 Japan Society of Applied Physics awards, the Nikkei 1995 Best Products and 1996 Excellent Products awards, the 1996 Society of Information Display Special Recognition Award, the 1996 IEEE Laser and Electro-Optics Society Engineering Achievement Award, the 1996 Nishina Memorial Award, the 1997 Ohkochi Grand Technology Prize, the 1997 Materials Research Society Medal, and the 1998 IEEE Jack A. Morton Award.
The author of 150 scientific papers and two books, Nakamura holds 80 Japanese and ten U.S. patents.
Media ContactTony Rairden