Scatterings image

A Nobel Prize graphic depicts the increase in efficiency from oil lamp to modern LED. [Illustration: Johan Jarnestad/Royal Swedish Academy of Sciences]

Amid the run-up to the 2015 International Year of Light celebration, the Swedish Academy has conferred this year’s Nobel Prize in Physics on three inventors of blue LEDs—Isamu Akasaki and Hiroshi Amano of Nagoya University, Japan, and Shuji Nakamura of the University of California, Santa Barbara, USA. The Academy cited the three scientists for their role in creating a technology that has “enabled bright and energy-saving white light sources.”
 
For all three researchers, work on blue LEDs came to fruition in Japan in the 1990s, after long and unsuccessful efforts by numerous scientists, including the three 2014 physics laureates themselves, to create such devices. The key to the blue-LED breakthrough turned out to be an interlocking set of developments more than 20 years in the making. These included the creation of new techniques for growing crystals of gallium nitride (GaN), a material that had previously been identified as having the right band gap but that was notoriously difficult to manufacture; breakthroughs in p-doping of GaN and of alloys of the material necessary to create efficient semiconductor heterojunctions; and the fashioning of increasingly sophisticated heterostructures and quantum wells to boost quantum efficiencies.
 
The research groups of Akasaki and Amano, working together at Nagoya University, and Nakamura, then employed at Nichia Chemical Corporation in Japan, contributed pivotal work at virtually every stage of this decades-long journey. The path culminated in landmark papers by both groups in 1995-96 in which they reported blue laser emissions from GaN devices.
 
The Swedish Academy specifically stressed the work’s importance at a fulcrum point in human energy history. The blue LED, they noted, represents a crucial component in cheap LED lighting that has begun, finally, to displace incandescent and fluorescent lighting in a meaningful way. (Commonly, blue LEDs serve as a light source that excites a phosphor, which converts the energy into white light.) In large part because of the team’s efforts, according to the Academy, whereas “incandescent light bulbs lit the 20th century, the 21st century will be lit by LED lamps.”