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Zhang Guoyi is a professor at the School of Physics, Peking University, and a doctoral tutor.
Energy-efficient, long-life semiconductor lighting products are leading the green revolution in the lighting industry. With the breakthrough of the third-generation semiconductor material GaN and the advent of blue and green LEDs, countries around the world have invested heavily in the launch of national-level semiconductor lighting plans.
As the earliest research unit of GaN semiconductor materials in China, the Institute of Physics of Peking University has a heavy responsibility for the industrialization of GaN-based lasers and semiconductor lighting. How to occupy a place in semiconductor technology under the condition that existing technology and investment are relatively backward compared with foreign countries. Professor Zhang Guoyi of the center recently told reporters that the final application field of third-generation semiconductors will be very extensive. The key of current research is to find the right direction. Effectively integrate resources.
Selected GaN semiconductor research
The Institute of Physics of Peking University has been working with the Research Center for Wide Band Gap Semiconductors and GaN for 15 years.
Nitride semiconductors are called third-generation semiconductors. The first generation is germanium and silicon. The representative application field is integrated circuit, which has caused revolution in the field of information processing. The second generation is III-V compound semiconductor based on gallium arsenide and indium phosphide. The application field is Information communication has caused revolutions in the fields of semiconductor lasers, fiber-optic communications, broadband networks, and other information transmission and storage; the third generation of white light prepared by III-V compound semiconductors based on gallium nitride, indium nitride, and aluminum nitride LEDs, mainly used in semiconductor lighting, are currently revolutionizing the field of lighting.
Zhang Guoyi introduced that GaN has a good performance as a semiconductor luminescent material around 1943. Later, with the support of the State Key Laboratory of Artificial Microstructures and Mesoscopic Physics, Peking University selected nitride semiconductor materials and conducted a year of research, but the project is difficult to obtain support from national projects. The reason is very simple. At that time, nitride semiconductors were only recognized from the basic performance, and it is still unknown whether the blue and green light-emitting tubes can be successfully produced. Domestic attention to LED materials is still focused on silicon carbide materials. At that time, a US company had made blue light-emitting tubes with silicon carbide. Although the luminous efficiency was very low, it was a precedent for success.
The turnaround appeared in 1994. Japan's Nichia Corporation used GaN materials to make samples of the light-emitting tubes. The luminous efficiency is more than 100 times stronger than that of silicon carbide LEDs. In this context, the Center was supported by the National Natural Science Foundation in 1995, and the National Natural Science Foundation of China was awarded the special award at the end of the project. For the first time, an improved low-voltage-MOCVD method was proposed. A single crystal thin film such as gallium nitride was successfully grown on a sapphire substrate, and its electrical and optical properties such as structural characteristics, defects and background carrier concentration were studied. Good results have been obtained by reactive ion etching and ohmic contact characteristics, which lays a solid foundation for the research of gallium nitride-based blue light-emitting diodes.
Market urging production
"Nitride semiconductors are very strange. It is characterized by market leading technology, technology leading to the study of physical mechanisms, and the technology is mature. There is no need to worry about the fact that there is no such thing as a common development for scientists and engineers. Space.†Zhang Guoyi introduced that at that time, blue light-emitting tubes and lasers had already seen huge market demand and economic benefits. The research of nitrides has become one of the focuses of international competition in the high-tech field.
With the support of the subject and funds, the first blue light-emitting diode in China was developed in 1997, and then several units actively requested cooperation. At the end of 1999, under the promotion of Peking University Science and Technology Development Department and other units, Heilongjiang Province Dazheng Investment Group became the owner of this technology industrialization. In April 2000, Shanghai Peking University Blu-ray Technology Co., Ltd. (now known as Shanghai Blu-ray Technology Co., Ltd.) was established. It is located in Shanghai with a registered capital of 70 million yuan. Now the company's scale has grown to more than 300 million yuan, and the estimated output value this year is about 180 million yuan. Subsequently, a wide-bandgap semiconductor research center was established at Peking University, which is the first professional wide-bandgap semiconductor research center in China.
As the core personnel to realize the industrialization of GaN-based blue light-emitting diode technology, Zhang Guoyi believes that the key factor for the success of high-tech industrialization depends on whether investors and technology can effectively integrate. On the one hand, investors must thoroughly understand the laws governing the development of high technology, and there must be a process for the transformation of scientific and technological achievements. On the other hand, the technical side must also clarify the maturity of technical achievements, grasp the market prospects of the project, and innovate in time.
“Shanghai Blu-ray Technology Co., Ltd. is the first enterprise in China to engage in gallium nitride-based blue light epitaxial wafers and chip production. It belongs to the upstream industry, with high technical content and relatively large capital investment. It is far from enough to transfer technology only. The key is to Establish a technical team of the company."
At present, Peking University and Shanghai Blu-ray Technology Co., Ltd. have formed a benign mechanism for technological innovation interaction. The company and Peking University established a research center combining production, education and research. The preliminary basic research was completed at Peking University, and the pilot stage was completed in the company and then invested in industrialization. This not only promoted the construction of disciplines at Peking University, but also provided new technical resources for the company.
Lighting application is only one of them
Gallium nitride materials are widely used. At present, the world's countries value the application of lighting. In fact, gallium nitride based materials are widely used. For example, blue light lasers based on GaN materials can be widely used in information storage, such as Blu-ray DVD; deep ultraviolet detectors can be used for UV guidance and early warning in national defense, and at the same time, they can be made into deep ultraviolet light tubes. Lasers have many applications in medical and chemical industries.
"The future application of GaN materials is lighting or lasers, or electronic devices. It is not easy to say that it is possible that the future application of lighting is just the tip of the iceberg. So far, countries in lighting have paid more attention to development. It is also fast, because its applicability is more obvious and clearer.†Zhang Guoyi pointed out that the final application field of the third generation semiconductor may be very extensive.
Since April 2002, Peking University has undertaken the development tasks of the national “863†major project GaN-based laser and the Beijing Science and Technology Plan project GaN-based blue-violet laser. In view of the difficulties of wide-bandgap semiconductor GaN-based lasers, the center explores and studies the GaN-based laser epitaxy and device structure calculation and optimization design, MOCVD epitaxial growth and characterization, device micromachining technology and cavity structure. . A series of advances have been made in key scientific and technical issues such as quantum wells for gallium nitride based materials, MOCVD growth of superlattice and waveguide structures, and preparation of ridge waveguide laser diode devices.
In the second half of 2004, the GaN-based laser chip was developed to obtain the optically pumped stimulated emission of a prototype device of a gallium nitride-based ridge waveguide laser. The stimulated emission with a wavelength of about 405 nm was realized for the first time, and then the electricity was realized. Stimulated emission of a ridge-waveguide gallium nitride-based laser diode. This band of lasers is the light source for the next generation of Blu-ray DVD disc systems.
“Every country is very concerned about the research of GaN-based semiconductors. In the competition, we must find new growth points. The LEDs will continue to be used. The lasers should be further improved. Another important research area is the GaN single crystal lining. The bottom material." Zhang Guoyi pointed out that sapphire is currently a gallium nitride single crystal substrate material, but because sapphire is not conductive, the thermal conductivity is not good, and so on, it is not the best choice. Another turning point in the development of nitrides is the breakthrough on GaN substrates.
It is understood that GaN-based dilute magnetic semiconductors and spintronics are also one of the current research directions of the center. Zhang Guoyi introduced that the dilute magnetic semiconductor is to make the material both semiconductor and ferromagnetic. The magnetic rotation is divided into two states: spin up and spin down. It is predicted that this kind of research can increase the storage density of the optical disc, change the storage speed and operation speed of the computer, and form an LED with a positive light on the light-emitting device.
Gallium nitride research has a long way to go
"China's DVD industry, due to intellectual property and patent issues, has almost no profit. After the Blu-ray DVD stage, whether the core technology, light source is a key issue."
According to market research firm ABI Research, Blu-ray DVD will occupy about 30% of the optical storage market in three years, and the market size will reach tens of billions of dollars. Currently, the market for Blu-ray DVDs is basically Japan. Zhang Guoyi pointed out that Blu-ray DVD may take another three to five years to fully occupy the market. As the unit that undertakes the national project of GaN-based laser research, the center has great responsibility, opportunities and challenges in the development of practical GaN-based short-wavelength lasers in China.
At present, the center has formed an excellent team to study nitride semiconductors, as well as technicians with long-term laboratory experience. Zhang Guoyi pointed out: "In terms of scientific research, funding is an important issue, but in this team of more than 50 people, the choice of direction is particularly important. To select potential research directions with potential and advantages, we must not follow the trend."
From the perspective of competition, the good direction, other units at home and abroad will also be optimistic, and some unit funds and equipment conditions are better. In this regard, Zhang Guoyi pointed out that although there is a big gap between us and foreign countries in terms of capital and conditions, we should share the equipment, technology and research strength through cooperation with other relevant scientific research units or enterprises in China. A leading position in research.
“Last year, we established the Joint Research Center for Wide Band-Gap Semiconductors of Peking University, including the researchers of the University of Beijing University and the Institute of Microelectronics. The interdisciplinary cooperation thus formed has greatly accelerated the progress of our research. At the same time, we are actively engaged in international cooperation and exchanges with research units and personnel from countries such as the United States, Britain, Japan, and Korea. The young student team is also very hard-working and can quickly enter the role. At the technical level, we have Confidence keeps our leading position 1 
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Beida-wide forbidden semiconductor research center: targeting market applications for research
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