The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in physics this year for the three scientists. Isamu Akasaki is rewarded (Meijo University, Nagoya, Japan), Hiroshi Amano (University of Nagoya, Japan), and Shuji Nakamura (University of California, Santa Barbara, USA).
From the 70s of the twentieth century, these three researchers measured the the challenge of the physics of semiconductor materials and devices, which was to create a light emitting diode emitting blue light. Red and green LEDs were available from the late 60s of the twentieth century. The finale of their research was to create a blue LED in 1993, making the spectrum emitted by the light emitting diodes in the visible light range complete. The wide range of possible applications, from lighting dwellings after recording on optical discs, opened up thanks to humanity.
LEDs when compared with the bulbs are ten times more energy efficient, they work a hundred times longer and are much much more resistant to vibration and shock. Assuming that 20..30% of the electricity produced in the world is consumed for lighting, wide adaptation of lighting based on LEDs need to significantly reduce the consumption of electricity in the world and, consequently, reduce the amount emitted into the atmosphere of carbon dioxide.
As a distant echo of the words Alfrea Nobel committee to give this year’s Nobel Prize summed up by saying that the invention of the blue LED is a “huge profit for the whole of humanity.”
Towards blue LEDs
The blue LED’s operate on the same principle to the Reds and Greens brothers. The two semiconductor layers – one a second n-doped P, adjacent to each other. Through application of a voltage to these layers – from p to n, causing additional electrons to flow from the conduction band of the doped n-type layer for the valence band of p-type doped layer, where the fill hole.
If electrons can exceed the energy gap without scooping or descent momentum, that is the minimum conduction band and valence band maximum are located next to each other in the shoot, each recombination of electron-hole pairs produces a photon whose energy is equal to energy is the energy gap of the material from which the diode is built.
Materials which have a simple band gap are effective materials for the construction of LEDs, however, are unique among semiconductor where the majority of silicon at the helm, takes a break inclined. Most light emitting diodes, with blue Nobel Prize winners at the head, are constructed of materials with a simple band gap based on the elements of the III and V of the periodic table of elements.
Red and green LEDs are made, respectively, with the gala arsenide and gallium phosphide. In simplified to produce the next color with a shorter wavelength, you need to pair your gal with a lighter element of Group V – Nitrogen – whose smaller size results in a tighter binding of atoms in the structure and widening the energy gap.
The search for methods for the use of gallium nitride and its energy gap for emission enlightened started in ’50 twentieth century, even before the debut of the red Leda in 1962. By the early 70s of the twentieth century, scientists have not achieved much. It turned out that growing the GaN-u (as is often called the material – ed. Crowd.) Size of the circuit is too difficult, not to mention their respective doping.
outlook brightened only when a new technique of growing crystals appeared in the semiconductor industry. It was a technique of growing crystals layer by layer. MOVPE (metalorganic vapor phase epitaxy, ang. metalorganic vapor epitaxy ) allowed for cultivation of GaN-u doped p-type and n-type. In 1986, after a decade of effort, researchers failed to find a recipe for creating a system . GaN was applied on an aluminum nitride layer, which in turn was applied to the sapphire substrate. Basis of sapphire and aluminum nitride provided the correct growth of gallium nitride crystals. Nakamura working independently reached the same result in 1991.
magnesium doping of gallium nitride and zinc allowed to grow crystals doped p-type, but they were not able to effectively accept electrons. Fortunately, completely by chance, Amano and Akasaki discovered in the late 80s of the twentieth century that the sample GaN-in after examining a scanning electron microscope better absorb electrons. Nakamura discovered why. The reason for this phenomenon fact that during crystal growth, the dopant complexes formed with the hydrogen that is present as an impurity in a sample derived from the precursors used in the MOVPE. Electron beam irradiation of crystals, led to the destruction of these complexes, as well as heating of the crystal.
The last step to construct effective, the blue LED was the use of the concept of heterostructures. The led’s based on gallium nitride, as in front of them led’s created based on gallium arsenide, other semiconductors of the same group are combined into layers. The origin of atoms from the same “family” ensures that, despite the different energy gaps and refractive indices, these materials are structurally compatible with each other. With appropriate selection of the layers electrons and holes are able to recombine emitting a photon easily with a smaller volume, which improves the efficiency of the LED. The use of optical properties of materials can increase efficiency even more.
first blue LED made by Amano Akasakiego composed of a GaN layer in the nitride-alumina. Nakamura turn countered gallium nitride, indium gallium nitride and the created InGaN, AlGaN structure. By 1993 Nakamura has created a small, blue LEDs that shine as much as a candle. Emission occurred in those elements of a layer of zinc-doped indium gallium nitride, sandwiched between two layers of aluminum gallium nitride, doped nip, which in turn was placed between layers of the same doped GaN-u. Publication describing this structure is a milestone development of semiconductor technology, and has been, so far, quoted more than 3,000 times.
Blue LEDs have the potential not only to reduce global energy consumption. Based and gallium nitride optoelectronic components have many applications. Is placed in computers, televisions and mobile phones. In many third world countries that use solar lamps, among other blue LEDs replace the previously used kerosene lamps.
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