The contribution of the Nobel laureates: blue LEDs fill the world with new light

Only the combination of red, green and blue light is able to create the white light that illuminates the world around us. Despite the high risks and the multiple efforts required of the research community, both in universities and in industry, the production of blue LED light remained an unsolved challenge for three whole decades - until the three winners of the 2014 Nobel Prize in Physics came along and turned the 21st century into the century of the LED

Isamu Akasaki, Hiroshi Amano and Shoji Nakamura won the 2014 Nobel Prize in Physics For the invention of a new energy - an efficient and environmentally friendly lighting source - the blue light emitting diode (LED). In the spirit of Alfred Nobel's will, the prize is given for an invention with an important and useful contribution to humanity; With the use of blue LEDs, it is possible to produce white light in a new way. With the advanced LED lamps today we have more efficient and long-term alternatives to old lighting sources.

When Akasaki, Amano and Nakamura arrive in Stockholm in early December to participate in the Nobel Prize ceremony, they will hardly be able to ignore the lighting that comes from their invention radiating from all the windows of the city. The white LED bulbs are energy efficient bulbs, stable over time and emit bright white light. Moreover, and unlike fluorescent bulbs, they do not contain the toxic metal mercury.

Red and green light-emitting diodes have been known to us for almost half a century, but there was a real need for blue light in order to bring about a real breakthrough in lighting technologies - only the combination of red, green and blue light is able to create the white light that illuminates the world around us. Despite the high risks and the multiple efforts required of the research community, both in universities and in industry, the production of blue LED light remained an unsolved challenge for three whole decades.

Akasaki worked together with Amano at Nagoya University while Nakamura was employed by Nichiya Kemeikles, a small company in Tokushima. Once they received the blue light beams from their semiconductors, the gates were opened for fundamental changes in lighting technologies. Incandescent bulbs illuminated the twentieth century; The twenty-first century was defined by LED bulbs.

Saving energy and resources

A light emitting diode consists of several semiconductor materials arranged in several layers. In an LED bulb, electricity is converted directly into light particles, photons, which leads to increased efficiency compared to other light sources, where most of the electricity turns into heat and only a small part is converted into light. In incandescent bulbs, as well as in halogen bulbs, an electric current is used to heat a filament coil that causes light to be emitted from it. In fluorescent bulbs, a discharge of gas is obtained, which creates both heat and electricity.
Unlike these lighting sources, the new LED bulbs consume less energy to emit light. Moreover, these bulbs undergo constant improvement and become more and more efficient while achieving a higher luminous flux (measured in lumen units) per unit input of electricity (measured in watt units). The most recent record is a rate of over 300 lumens/watt, a rate equal to 16 standard light bulbs and close to 70 fluorescent bulbs. In light of the fact that about a quarter of the world's electricity consumption is devoted to lighting purposes, the very energy-efficient LEDs contribute to saving the earth's energy resources.
The heart of the LED bulb.

A light emitting diode consists of several layers of semiconductor materials. An electric current moves electrons from the n-layer and holes from the p-layer to the active layer, where they fuse together while emitting light. The wavelength of light depends entirely on the nature of the semiconductor used. The LED bulb itself is no bigger than a grain of sand.
Blue LED light.

The light emitting diode in this bulb consists of several different layers of the material gallium nitride (GaN). By mixing it with indium (In) and aluminum (Al), the laureates were able to increase the efficiency of the bulb.

LEDs also last longer than other bulbs. Incandescent bulbs tend to operate for 1,000 hours, since the heat emitted over time destroys the filament itself, while fluorescent bulbs tend to operate for about 10,000 hours. LEDs can operate for 100,000 hours, which significantly reduces material wear and tear.

Create light inside a semiconductor

LED technology was born from the same place where mobile phones, computers and all other modern electronic components and equipment based on quantum phenomena were born. A light-emitting diode consists of several layers: an n-type layer with an excess of negatively charged electrons and a p-type layer with a lack of electrons, which is known as a layer with an excess of positively charged holes.
Between them is placed an active layer to which the negative electrons and positive holes drain when an electric current is applied to the semiconductor. When electrons and holes meet they fuse to create light. The wavelength of the light depends entirely on the type of semiconductor - blue light appears in short wavelengths of the spectrum and can only be obtained in certain materials.
The first publication that presented the emission of light from a semiconductor appeared back in 1907 by Henry J. Round, a colleague of Guglielmo Marconi, an Italian electrical engineer who won the Nobel Prize in Physics in 1909, for his contribution to the development of wireless telegraphy. Then, in the twenties and thirties of the twentieth century, in the USSR, the scientist Oleg V. Losev carried out more in-depth studies regarding the emission of light. At the same time, the two researchers lacked the appropriate understanding to fully understand the phenomenon. It will be several more decades before the prerequisites for the exact theoretical description of this quantum phenomenon, electroluminescence, emerge.

The red light emitting diode was invented in the late fifties. These diodes were used, for example, in clocks and digital calculators, or as on/off status indicators in various applications. At an early stage it was understood that there is an important need to create a short wavelength light emitting diode that includes extremely powerful photons - a blue light emitting diode - in order to create white light. Many laboratories have tried to achieve this, but without success.

challenging the conventions

Award winners challenged established truths; They worked hard and took many risks. They built their own equipment, conceived the technology from scratch and conducted thousands of experiments. Most of the time they failed, but they did not despair; It was one of the highest level laboratory arts.
The researchers chose the material gallium nitride and in the end they succeeded in their endeavours, although many others had failed before them. In the first stage, the material was considered suitable for producing blue light, but many practical difficulties were discovered. No researcher has been able to make the gallium nitride crystal of high enough quality. In addition, it was not possible to form the p-type layers in this material.
Despite all these difficulties, Akasaki was convinced by previous experiments that the choice of this material was correct, and continued to work in this direction with Amano, who was a doctoral student at Nagoya University. The researcher Nakamura who worked at the Nichia company as Michaels also chose gallium nitride, before moving on to the alternative material zinc selenide, which others believed to be a better material for this use.

let there be light

In 1986, Akasaki and Amano were the first to successfully synthesize a high-quality gallium nitride crystal by placing a layer of aluminum nitride on top of a sapphire substrate and preparing gallium nitride over this surface. In the late XNUMXs, researchers were involved in a breakthrough in the creation of a p-type layer. Coincidentally, researchers Akasaki and Amano discovered that their material glowed more brightly when examined under a scanning electron microscope.

This observation implied that the electron beam from the microscope made the p-layer more efficient. In 1992 they were able to present their first diode that emitted bright blue light.
Nakamura began developing his blue LED in 1988. Two years later, he too succeeded in creating high-quality gallium nitride. He came up with his ingenious trick to produce the crystal by preparing a thin layer of gallium nitride at a low temperature and then preparing additional layers at a high temperature.
Nakamura was also able to explain why Akasaki and Amano were able to form the p-layer: the electron beam removed the hydrogen atom that prevented the formation of the p-layer. In his laboratory, Nakamura converted the electron beam with a simpler and cheaper method: by heating the material he was able to create a functional p layer in 1992. Thus, Nakamura's solution was different from that of Akasaki and Amano.

During the 90s both research groups managed to improve the blue LEDs, making them more efficient. The researchers developed different gallium nitride alloys using metals such as aluminum and indium, and the overall structure of the halides became more and more complex.

The three researchers also developed the blue laser in which the blue LED, the size of a grain of sand, is a key and essential component. Unlike the diffused light of the blue LED, a blue laser emits an extremely narrow beam. Since the blue light has a short wavelength, it can be transmitted more closely; With the help of the blue light you can store four times the amount of information than with the help of infrared light. This increase in storage capacity soon led to the development of Blu-ray discs that allow for longer playback times, and also to the development of better laser printers. Many household electrical products also utilize LED technology. They illuminate the LCD screens in television monitors, computers and mobile phones, and they also provide the flash and bulb in cameras.

LED bulbs consume less energy to emit light than older light sources. The efficiency is measured in units of light flux (luminous flux, measured in lumen units) per unit of electricity input (measured in watt units). About a quarter of the world's electricity consumption is devoted to lighting purposes, and thus the very energy-efficient LEDs contribute to saving the earth's energy resources.

A bright revolution
The inventions of the prize winners brought about a revolution in the field of lighting technologies. Even today, many researchers are developing new, efficient, cheaper and more advanced bulbs. White LEDs can be produced in two different ways. One way is to use blue light to stimulate the phosphor material so that it glows in red and green light. When all the colors merge together white light is created. The second method is to assemble the bulb from three different LEDs: one red, one green and one blue, and allow the human eye to blend the three colors together into white light.

Therefore, LED bulbs are flexible lighting sources, which are already used in several applications in the field of lighting - millions of different types of colors can be produced; The shades and intensity of the colors can be adjusted as required; Billboards in full colors, several hundred square meters in size, flash, change their color and their patterns - and all of this can be controlled with the help of computers. The possibility to control the type of light also implies that LED lights can adapt to our biological clock as well as artificial lighting for growing crops. The LED bulb also holds great promise in increasing the quality of life of more than 1.5 billion people who currently lack access to an organized electricity grid, in light of the fact that the low electricity requirements provide the possibility to operate the LED bulbs with the help of cheap local solar energy. Moreover, contaminated water can be disinfected with the help of LED bulbs that emit light in the ultraviolet range.