Light-emitting diodes (LEDs) are narrow-band light sources based on semiconductor
components, with wavelengths ranging from the infrared to the ultraviolet. The first
LEDs were studied and constructed during the 1950s and 1960s in several laboratories.
They emitted light at different wavelengths, from the infrared to the green. However,
emitting blue light proved to be a difficult task, which took three more decades to
achieve. It required the development of techniques for the growth of high-quality
crystals as well as the ability to control p-doping of semiconductors with high bandgap,
which was achieved with gallium-nitride (GaN) only at the end of the 1980s. The
development of efficient blue LEDs also required the production of GaN-based alloys
with different compositions and their integration into multilayer structures such as
heterojunctions and quantum wells.
The invention of efficient blue LEDs has led to white light sources for illumination.
When exciting a phosphor material with a blue LED, light is emitted in the green and red
spectral ranges, which, combined with the blue light, appears as white. Alternatively,
multiple LEDs of complementary colours (red, green and blue) can be used together.
Both of these technologies are used in today's high-efficiency white electroluminescent
light sources. These light sources, with very long lifetimes, have begun to replace
incandescent and fluorescent lamps for general lighting purposes. Since lighting
represents 20-30% of our electrical energy consumption, and since these new white
light sources require ten times less energy than ordinary light bulbs, the use of efficient
blue LEDs leads to significant energy savings, of great benefit to mankind.
This year’s Nobel Prize in Physics honours the inventors of efficient blue LEDs: I.
Akasaki, H. Amano and S. Nakamura.