Blue Light: A Fascinating Journey (Nobel Lecture).

“In the beginning there was light”, emphasizes how closely light is tied to our lives. Light is indispensable for mankind and for many other creatures, and humans have pursued light sources since ancient times. Starting with flames, humans have developed electric light bulbs, fluorescent lamps, and then semiconductor light-emitting devices (lightemitting diodes (LEDs) and laser diodes (LDs)) in the second half of the last century. Although these light sources cover a wide wavelength range, the development of high-energy light sources has largely lagged behind. The development of an efficient blue LED had been a long-term dream for researchers worldwide, as it is indispensable for realizing LED-based full-color displays and general lighting applications. Drastic improvements in the crystal quality of gallium nitride (GaN) and the ability to control the conductivity in both pand n-type nitride semiconductors 3] in the late 1980s, have enabled the production of high-brightness GaN-based pn junction blue/ultraviolet (UV) LEDs, high-performance blue-violet LDs, and many other novel devices. These successes triggered the opening of an entirely new field of electronics. In this Review, I would like to describe the historical progress that led to the invention of the first p-n junction blue/ UV LED and related optical devices.

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