Bright Future with Gallium Nitride
November 2, 2015
Laser projectors in cell phones, laser headlights in cars, high-performance fiber optics capable of transmitting terabytes of data in homes and offices—all this will soon become the order of the day thanks to production technology based on a chemical called gallium nitride.
Scientists from the Polish Academy of Sciences’ Institute of High Pressure Physics in Warsaw are working to improve their pioneering method of growing gallium nitride crystals in a project designed to enable production of next-generation electronic and optoelectronic devices based on gallium nitride (GaN) and silicon carbide (SiC).
The project’s manager, Prof. Michał Leszczyński, who is also deputy CEO of technology company TopGaN, a spin-off from the Institute of High Pressure Physics established in 2001, talks to Karolina Olszewska.
In simple terms, gallium nitride is a semiconductor that is used in light-emitting diodes (LEDs) and laser diodes. It is also the key material for a variety of next-generation electronic and optoelectronic devices. Are lasers based on nitride semiconductors in common use today?
They are predominantly used in white LEDs. Last year our [Japanese] colleagues Isamu Akasaki, Hiroshi Amano and Shuji Nakamura won the Nobel Prize in Physics [for inventing the blue light-emitting diode, using Polish gallium nitride crystals in the process].This is a huge industry, worth more than 10 billion euros in annual sales. LEDs are produced by many Japanese and [South] Korean companies, and in Europe by companies including Osram.
Another big market is Blu-ray laser diodes for players and game consoles. Small violet lasers are used to read and record on such discs. In the future, lasers based on nitride semiconductors—green, blue, and ultraviolet—will create entirely new markets, including those for laser projectors and laser televisions.
Is it true that the image from such a laser projector will be so realistic that we won’t be able to tell it from the view outside the window?
The picture will be perfect. Red lasers based on gallium arsenide (GaAs) and green and blue ones based on gallium nitride (GaN) will be used for the production of such projectors. Mixing these three colors in different proportions makes it possible to render any color seen by the human eye. This will be a huge market. With time, such a projector for displaying videos and photos will appear in every mobile phone. Projectors based on gallium nitride will come in various sizes—from those for cell phones to increasingly larger televisions to large outdoor screens and cinema projectors. Mitsubishi already produces laser TVs, but these are not based on nitride lasers at this time. Although the technology is imperfect, these televisions offer a picture with remarkable color resolution.
Further markets include telecommunications, the automotive market, and medicine. Is that correct?
What is known as last-mile telecommunications technology is another major application of nitride lasers in the future. Plastic fiber optics will be used to transmit terabytes of data between computers, sensors and detectors. This will be possible in every home, airplane, ship and car, adding up to an unimaginably enormous market. Tens or even hundreds of lasers will be needed for every building.
There are also niche applications including communications in the military and cancer detection in medicine. We have been working with hospitals in this area. Our lasers make it possible to detect cancer at an early stage without having to collect a sample of the tumor. The doctor lets in light through an endoscope that stimulates a cell in the body with a specific color to illuminate. Healthy cells glow with a different color than malignant cells.
There is also a third possible application. At the moment, light-emitting diodes produce white LED light. They are extremely expensive because they cannot be powered too intensely, because then their lighting efficiency becomes too low. This is not the case with laser light. It will be possible to use lasers instead of LEDs. Although these are more complex devices, they may prove to be cheaper and their light is more directional. A diode emits light in all directions, while in the case of lasers we have strong intense light only in one direction. The newest, most expensive BMW and Audi cars no longer have LED-based headlights; they have laser headlights. This is an intelligent type of light because when there is an obstacle, it can be focused in a different direction. However, laser diodes still have much lower performance than LEDs. Researchers are trying to change that; we’ll see which technology takes over. When it comes to the automotive industry, I’m betting on lasers with light responding to changing conditions.
Polish scientists have made a major contribution to the production of laser diodes. Is it realistic to expect that Polish companies will secure pole position for themselves internationally in these promising markets?
We have created several unique technologies in Poland. It all started with crystals. Twenty years ago Poland was the only country to produce substrates [for the production of light-emitting diodes]. And that wasn’t easy—the technology required very high pressure of around 10,000 atmospheres and a temperature of 1,500 degrees Celsius. We were able to create such conditions. And, although it later turned out that a gallium nitride substrate could be made with different methods so the pressure method was eventually abandoned, it must be remembered that it was Poland where the impulse that gave rise to further technologies came from.
Our research team is well over 100 strong. In 2001, the director of the Institute of High Pressure Physics, Prof. Sylwester Porowski, started a company to eventually produce lasers. That’s how TopGaN came into being. The technology was contributed by the Institute of High Pressure Physics, and Andrzej Kasprowiak, who is now the company’s CEO, contributed zl.30 million from his private funds.
Does this mean that a laser diode factory will soon be built in Poland?
We are trying to make this happen. For the time being we are creating a pilot production line in Warsaw. At the moment, the company is producing very good violet-blue lasers on a laboratory scale, yet these are relatively expensive because they are produced in small runs. We sell these lasers to customers including producers of atomic clocks, which require specialized lasers of appropriate wavelength and capacity. Such clocks can be used in space and in devices that are synchronized and communicate with one another. This includes underwater communication, for example in submarines and in the fishing sector—blue light is poorly absorbed by water, and additionally it is difficult to detect with some kind of sonar.
We often take part in trade fairs for electronic equipment. We are asked when we will start producing [our lasers] in millions of units. But such a scale of production requires building a factory. For now, production is being carried out on a laboratory scale. We are in for a major step up from 10,000 to 5 million units a year. We are preparing a major investment project to get the pilot [production] line off the ground. If it works well, it will be multiplied in the factory. This is our vision of development. The factory will operate in Poland in collaboration with Polish industry.
If new equipment is purchased, the number of lasers produced will increase and they will be more reliable. It is worth knowing that such a laser is smaller than a particle of sand. A laser strip is 2-3 microns wide and half a millimeter in length. This is really a miracle of nature that it’s possible to extract light with a power of several watts from such a small device. The pilot line will ensure semi-industrial production with consistent results and an output on the order of half a million units a year, for example.
Such a line will take around three years to build and then a decision will be made on whether Poland should go ahead with building a factory to meet the demand for projectors and last-mile communication as well as automotive lights.
Some of the research in this area is subsidized with public money. Your technology continues to develop and has the potential to strengthen the position of the Polish economy internationally. Does this mean you don’t have to worry about the financial side of things?
[Our] substrate technology consists of several dozen elements. All the money that we have received so far in the form of grants has been used to finance various strains of research. [Our latest] project—the full technical name of which is “Optimizing the disorientation of GaN and SiC substrates for the production of electronic and optoelectronic devices”—is in part financed with funds granted to us by the National Center for Research and Development. The subject of research here is the substrate used for the deposition of epitaxial layers of either gallium nitride or silicon carbide. We produce gallium nitride on our own or in partnership with the Ammono company, which is run by graduates of the University of Warsaw’s Faculty of Physics. It is difficult to grow such crystals. Usually, all semiconductor crystals are created using a method developed by the great Polish scientist Jan Czochralski: the material is melted, a tiny crystal is inserted, and a large crystal grows on this tiny crystal. However, gallium nitride is almost impossible to melt because this requires temperatures of thousands of degrees Celsius and high pressure. Therefore other methods are used; it’s just that these are imperfect. Above all, crystals grow very slowly and have many defects. [Polish researchers] were the first to patent technology for the production of the gallium nitride substrate. Currently, the Japanese produce substrates larger than the Polish ones, but these are inferior in quality. [Polish crystals] are too small for large-scale production. That’s why we must increase the dimensions of our crystals.
Silicon carbide is the next element. In addition to laser diodes, TopGaN produces layers for use in transistors. We make them on silicon carbide substrates that we buy from either the United States or China. Thanks to an idea from our colleague Marcin Sarzyński, Ph.D., we have managed to patent this method: it’s possible to create a structure on the surface of silicon carbide thanks to which transistors will be much cheaper.
The Czochralski Method
Polish-born and German-educated chemist and metallurgist Jan Czochralski (1885-1953) invented a process to grow single crystal silicon, a method that is still widely used. It is said that in 1916, while he was working at a metallurgical lab in Berlin, Czochralski absent-mindedly dipped his pen in a container of liquid tin that he had melted instead of a nearby inkwell. A thin metal filament appeared on the nib. Czochralski examined it using X rays and found that he had obtained a tin monocrystal.
The method invented by Czochralski enabled the development of the contemporary electronics industry. The Czochralski process is used to produce silicon, gallium arsenide and germanium monocrystals, which are used in the production of electronic components such as integrated circuits, diodes, transistors and processors.
Today the Czochralski process is used industrially to grow huge single crystals, mainly monocrystalline silicon, weighing up to half a ton. This requires a very precise control of the crystal growth process. The parameters are controlled with the use of electronic components made from materials obtained by the same method.
White LED light enables companies to create smartphone and computer screens, LED TVs and light bulbs that last longer and use less electricity than traditional bulbs. White LED light is made from combining light from every other color, but its creation was not possible until three Japanese scientists—Isamu Akasaki, Hiroshi Amano and Shuji Nakamura—invented the blue light-emitting diode (LED) in the early 1990s. The scientists used carefully created crystals of gallium nitride produced in Poland and jointly earned the 2014 Nobel Prize in Physics for their work. Blue was the last and most difficult advance required to create fully white LED light.
White LED lamps are steadily replacing other sources of light because they use less power and last longer than old-style bulbs.
The Warsaw scientists started their project in 2013 and are due to complete it later this year. The project is financed with funds available under the European Union’s Innovative Economy Operational Programme. The total cost of the project is nearly zl.2.5 million. The National Center for Research and Development has provided almost zl.2 million to help finance it. TopGaN contributed the remainder from its own funds.
The TopGaN team is made up of scientists from the Institute of High Pressure Physics in Warsaw. They include the company’s founder, Prof. Sylwester Porowski and gallium nitride substrate experts Prof. Michał Boćkowski and Prof. Izabella Grzegory (who is also director of the Institute of High Pressure Physics). Prof. Michał Leszczyński and Prof. Czesław Skierbiszewski handle the production of epitaxial layers. Prof. Piotr Perlin and Prof. Tadeusz Suski contribute their expertise in laser diodes. Prof. Stanisław Krukowski and Prof. Izabela Gorczyca are theoreticians who support the group with their calculations.
Gallium Nitride: Technology of the Future
Gallium nitride can emit light of any color of the rainbow. It is now the basic material used in the production of blue lasers, which read compact discs in Blu-ray players and video game consoles. The lasers are the size of a pinhead and the amount of data that can be written on a compact disc by means of blue light is several times larger than with previous laser technology.
Gallium nitride crystals also offer hope for the development of better light-emitting diodes (LED). Experts say such diodes will find application in laser TV projectors. The projectors will be so small that it will be possible to build them into various devices, such as laptops, mobile phones and even watches. The technology will also make it possible to reduce the size of computers to that of a pen, with the keyboard displayed on the desk and the image on the wall.
Additionally, gallium nitride has several useful properties that can be applied in the optical industry and other sectors. For example, it is a much better thermal conductor than silicon. As a result, it could be used in hybrid cars, with no need for an independent cooling system. This will make the hybrid car design simpler and reduce the cost of such vehicles.
Ammono, a Polish firm set up by four graduates and doctoral students—from the University of Warsaw Faculty of Physics and the Warsaw University of Technology Faculty of Chemistry—has outdistanced some of the largest research centers in the United States, Japan and Europe in producing large pure crystals of gallium nitride—a method hailed as a technology of the future.
Set up in 1992, the firm worked for years to improve its production process. Initially, their crystals were small and contained many impurities, making them look like coarse salt. The firm entered the international market when it started to offer crystals with a length of 25 and 38 millimeters.
Today Ammono makes crystals suitable for laser production lines. The company has patent protection for its large gallium nitride crystals, which are now the best in the world, according to the Ammono researchers, Robert Dwiliński, Leszek Sierzputowski, Roman Doradziński and Jerzy Garczyński. These crystals are produced in autoclaves with a temperature of 400-500 degrees Celsius and pressure of up to 5,000 atmospheres. They grow slowly from tiny seeds immersed in ammonium, just like salt crystals on a thread immersed in a water solution of salt. The process takes weeks but the crystals obtained in this way are of top quality.
Experts say the global market for gallium nitride substrates is growing by double-digit figures every year and is expected to be worth $1 billion within the next few years. The Ammono researchers say they are shooting for at least 15 percent of this market.