Nakamura cracked the blue LED by growing GaN on a sapphire buffer layer.

For years the LED made red and green light but not blue, and without blue there could be no full-color display or white light. The blocker was gallium nitride: it grew as n-type but nobody could get p-type GaN, so the device would not emit.

At small Nichia Chemical Industries, a lone company in rural Japan, Shuji Nakamura took on the problem. He first built a novel two-flow MOCVD reactor that let him grow high-quality crystal.

He found that growing a low-temperature GaN buffer layer on sapphire gave good crystal, and crucially he discovered that annealing magnesium-doped GaN in a hydrogen-free nitrogen atmosphere activated the p-type dopant. This was the step the field had missed.

In 1993 Nichia shipped the world's first efficient blue LEDs, and with a phosphor some of that blue converted to yellow, producing the first bright white LED. Nakamura won the 2014 Nobel Prize in Physics for the invention.