Blue LED chip

A blue LED chip is a square of crystal about the size of a grain of sand. Inside it, a few layers far thinner than a wavelength of light turn electric current directly into blue light, at about 450 nanometers.

It's grown on a wafer of sapphire. In a reactor, hot gases carrying gallium, indium and nitrogen flow over the wafer, and crystal layers build up atom by atom. First come thick layers of gallium nitride, the lower ones doped, usually with silicon, to carry spare electrons. Then several very thin layers of indium gallium nitride separated by gallium nitride: the quantum wells where light is made. Next comes gallium nitride doped with magnesium, which carries holes, places missing an electron. A film of indium tin oxide spreads current over the top, metal pads are added, and the wafer is cut into thousands of chips.

When current flows, electrons and holes meet in the quantum wells and release their energy as blue light. In a white LED, a phosphor turns part of that blue into yellow.

Isamu Akasaki, Hiroshi Amano and Shuji Nakamura shared the 2014 Nobel Prize in Physics for the work, which hinged on making magnesium-doped gallium nitride conduct.