Light-emitting diode

In 1907, British engineer Henry Joseph Round noticed that silicon carbide crystals glowed yellow when voltage passed through them. In 1993, Shuji Nakamura's blue LED at Nichia sent the company's revenue from ¥20 billion to ¥80 billion in eight years. Between these moments lay 86 years of convergence: the LED didn't require genius—it required quantum mechanics, purified semiconductors, and the military-industrial complex to create enough gallium arsenide for someone to experiment with color.

Round's 1907 observation was a curiosity without a theory. Oleg Losev, a Soviet radio technician, saw the same glow in carborundum junctions in 1923 and correctly intuited it was quantum mechanics in reverse—electrons falling across an energy gap, emitting photons instead of absorbing them. His 1927 papers described "cold light." But Losev worked during Stalin's purges, died of starvation in the Siege of Leningrad in 1942, and his work vanished into irrelevance.

The LED required three convergences Losev never witnessed: quantum band theory to explain why some materials emit light efficiently, the p-n junction to control electron flow, and pure semiconductor crystals in industrial quantities. Russell Ohl's 1940 discovery of the p-n junction at Bell Labs gave the LED its fundamental architecture. WWII radar programs stockpiled gallium, indium, and arsenic for microwave detectors.

On October 9, 1962, Nick Holonyak Jr.—a 33-year-old physicist and the first doctoral student of transistor co-inventor John Bardeen—created the first practical visible LED at GE's lab near Syracuse, New York. He mixed gallium arsenide with phosphorus, tuning the bandgap to 1.98 eV—exactly the energy of red photons. GE sold these red LEDs for $260 each. The color spectrum expanded through bandgap engineering. In 1972, George Craford at Monsanto invented the first yellow LED and boosted brightness tenfold.

But blue remained impossible. Blue photons require 2.7+ eV, demanding wide-bandgap semiconductors. By 1990, Sony, IBM, 3M, and Toshiba had abandoned gallium nitride as a dead end. Nakamura chose GaN precisely because the giants had quit. Working at Nichia, he spent 1988-1993 solving p-type doping by heating magnesium-doped GaN in nitrogen. His 1993 blue LED was 1,000 times brighter than previous attempts.

Blue unlocked white. By coating a blue InGaN LED with yellow phosphor, engineers created functional white light. Nakamura, Akasaki, and Amano won the 2014 Nobel Prize "for the invention of efficient blue LEDs, which has enabled bright and energy-saving white light sources." Global LED lighting saved an estimated 1,400 terawatt-hours annually by 2020.