【Expert Interview】Zhang Hui, Founder of Gallen Semiconductor: Let Gallium(III) oxide Semiconductor Materials Move from Laboratory to Industrialization

Entrepreneur coming out of the State Key Laboratory

      The State Key Laboratory of Silicon Materials in Zhejiang University has a long history. It was approved by the former State Planning Commission in 1985 and officially opened to the outside world in 1988. It is one of the earliest State Key Laboratories in China.

      This laboratory has produced a number of scientific and technological transformation achievements, and incubated a number of listed enterprises, such as Zhejiang Jin Ruihong, the head enterprise of microelectronics silicon single crystal in China, and Changzhou Shichuang Energy in the photovoltaic industry. All have laboratory transformation technology, and many of the students have become the backbone of well-known enterprises...

      In the strong entrepreneurial atmosphere, Zhang Hui, with dreams, also started his own entrepreneurial journey.

      Adhering to the concept of Academician Que Duanlin, founder of the State Key Laboratory of Silicon Materials, Academician Yang Deren, then director of the State Key Office, has been advocating the mode of "Industry-University-Research" to promote scientific research to serve the national economic construction. In 2018, under the arrangement and direct guidance of Academician Yang Deren, Zhang Hui and Dr. Xia Ning started the research and development and industrialization of gallium oxide materials together in the laboratory. At that time, Zhang Hui held a belief: the research and development of gallium oxide materials must not stay in the laboratory, it must go out to achieve industrialization.

      In Zhang’s view, among wide band gap semiconductor materials, other materials such as gallium nitride, silicon carbide, aluminum nitride, diamond, is mainly achieved by the gas phase method at present,while gallium oxide is the only wide band gap semiconductor material that can be prepared by melt method at atmospheric pressure. That is, a single crystal form from the melt (liquid phase) by solidification. Such methods have achieved great success in the preparation of silicon crystals When the gallium oxide substrate material is considered as the bottleneck of the whole industrial chain, Zhang Hui and his team realized that only by improving the growth rate of materials, reducing the cost and improving the crystal quality, can the industrialization of gallium oxide be truly promoted.

      Around 2020, through unremitting efforts and research, we finally successfully grew small-diameter gallium oxide crystals in the laboratory, and mastered the preliminary growth technology. At this time, the establishment of Hangzhou International Science and Technology Innovation Center of Zhejiang University brought new opportunities to the project. As a research and development project supported by Hangzhou International Science and Technology Innovation Center, thanks to the flexible scientific research system of the center, it has not only made further breakthroughs in technology, successfully grown 2-inch gallium oxide single crystal, and realized the small test of gallium oxide single crystal materials. Moreover, with the support of the center, we successfully incubated Gallium Ren Semiconductor Company and started the industrialization of gallium oxide semiconductor materials.

Low cost illuminates the way of industrial scale

      In the impression of colleagues of Garensemi, Zhang Hui is a complete a technologist, paving a way with excellent technology. And Zhang Hui himself knows that technology is very different in the laboratory from the industry.

      Zhang Hui told reporter from the Science and Technology Innovation Board Daily, if we intend to realize the industrialization, low production costs is necessary in addition to the good performance of the material itself. “Now, silicon carbide materials are still very expensive, and the price of silicon carbide power devices is several times higher than that of silicon-based devices. As the fourth generation of semiconductor materials, the competition focus of gallium oxide and silicon carbide is low cost.”

      Zhang Hui is very well aware of the development and iteration of the gallium oxide industry. He said, " Japan and other western countries  adopt the edge-defined film-fed growth(EFG) method to prepare gallium oxide material, but this method requires a lot of metal iridium to make the crucible. Usually a 4-inch crucible for gallium oxide material preparation requires at least 5 Kg iridium; Iridium is a precious metal. Its price is high, resulting in high costs for preparing gallium oxide. At the same time, the technical of EFG method may lead to intellectual property disputes.”

      Taking these into consideration, since his business started in 2018, Zhang Hui was wondering whether he could find a technical route that could significantly reduce the cost of gallium oxide preparation and have his own intellectual property rights.

      Recalling the process of research and development, Zhang Hui said that during the three years of research and iteration, the team has made a lot of attempts of new methods on gallium oxide materials; and till now, Garensemi has completely mastered a new set of core technology with fully independent intellectual property rights, namely casting method, which  came from a chance opportunity.

      "While preparing gallium oxide by vertical pulling method, we accidentally found the casting method, which is a new gallium oxide crystal growth method. There are many advantages of this method. First, it can greatly reduce the amount of iridium, which can reduce the cost by nearly 80%. Second, due to less exposed to the oxidizing environment, the loss of each crucible is reduced. This visible cost reduction greatly encouraged Zhang Hui and his team who work in the frontline research. Reducing the cost means that we can promote large-scale industrialization.

      In the interview, Zhang Hui also proudly told the reporter: " The casting method also has a significant industrialization advantage, which makes the technical route and process relatively simple, and the process short... these are conducive to the realization of automatic control. With the maturity of the process, the labor cost in production can be greatly reduced. Moreover, it is likely to achieve gallium oxide single crystal substrate with high quality and large size like silicon single crystal material. In order to achieve this goal, the stress problem in the crystal needs to be solved.”

      According to Zhang Hui's strategic plan, gallium oxide substrate of 2 inches, 4 inches, 6 inches and 8 inch ... are the goals to break through and achieve for Garensemi in the future.

Develop a large size substrate, wait for great leap

      Preparing substrate with large size and high quality have always been the direction of Zhang Hui and Garensemi research and development.

      According to Zhang Hui, the current technical path of using casting technology to prepare large-size gallium oxide crystals has been accessed, and the next step is to optimize the process.

      "During the research of the casting method, the team solved many problems to optimize the casting process, such as solid-liquid interface instability of gallium oxide, high-density dislocation of grain crystal heat impact, temperature gradient regulation and crystal cracking. After breaking through various technical problems in the growth and processing processes, high-quality gallium oxide single crystal substrate has been obtained. At the same time, the company has achieved more than 10 domestic authorized patents, and internationally, the patents are also being dealt with.”

      To go from small sizes such as 2 inches and 4 inches to the final 6-inch and 8-inch large size substrate, Zhang said, repeated studies in the process are needed to optimize the temperature gradient.

      "The biggest advantages of casting method is low cost, large output and simple process. Until then, academia and industry did not expect to prepare gallium oxide single crystal by casting method. However, the team successfully obtained high quality gallium oxide single crystal material through technological breakthrough, which proved that this is a feasible new technical route. If the temperature gradient of crystal growth can be further controlled in the future, a larger size of gallium oxide single crystal growth may be achieved.”

      These breakthroughs and development are closely linked with the  decades of experience in silicon crystal material research and development, achievements transformation by State Key Laboratory of Silicon Materials, and depend on technical team to have understanding of every growth technology, principle, process and equipment in the field of crystal growth, so as to achieve the analogy and develop a new growth method of gallium oxide.

      So far, Zhang Hui said, Garensemi has realized the pilot test of 2-inch gallium oxide substrate, in which the yield has been higher than that of silicon carbide, and the 4-inch product is about to achieve break through. "After the completion of the first round of angel finance, the recruitment of researchers has been increased. At present, the team has more than 30 people, most of whom are R & D personnel with doctor's and master's degrees. Their academic background ranges physics, chemistry, materials to semiconductor devices and other fields, forming an excellent team of interdisciplinary integration.

      From the perspective of the industrial chain, Zhang Hui said that the quality of upstream gallium oxide raw materials needs to be further improved, and now the purity of gallium oxide is basically five "9", which is considerably lower than electronic silicon raw materials, so there is very big upgrade space to improve its purity. "The purity of the material directly decides the performance and application of the device. For example, in the application of power grid, the device must work stably without any cut-off, otherwise it will bring disaster to the power grid. Therefore, in the research and development, the team also maintained close cooperation with several domestic upstream gallium oxide raw material enterprises to maintain the stability of the supply chain.”

      The core of midstream gallium oxide single crystal growth is equipment. Our casting equipment adheres to independent R & D, and the company has carried out research and development of epitaxial wafer, and will strive to provide high quality gallium oxide epitaxial wafer for device manufacturers. After the completion of the research and development of substrate and epitaxy, downstream applications will be further promoted, and gallium oxide devices are expected to be applied in national defense, state grid, new energy vehicles, rail transit, 5G communication and other important fields.

      Since the R & D team set up in 2018, to 2022 the company established to realize the industrialization and completed the Angle Financing, Zhang Hui and his team worked hard and made good results, step by step,from university teacher to practical entrepreneurship. After having a 2-inch gallium oxide single crystal product. Zhang Hui has confidence to develop a larger gallium oxide single crystal product with higher quality and lower cost. According to Zhang Hui's words, now we are waiting for the great leap of industrialization, let the light of dreams illuminate the way ahead.