【Expert Interview】Professor Zhang Jincheng, Xidian University: Create a good ecology of industry-university-research cooperation to promote the high-quality development of gallium oxide semiconductors

      In 2023, the Asian Gallium Oxide Alliance (hereinafter referred to as"AGOA") expanded a new channel, —— Expert Interviews. It is provided by the governing units, member units and expert committee within the Alliance to explain their different opinions on the field of gallium oxide, leading us to know, understand, and explore the world of gallium oxide.

      This time, we have the honor to interview Professor Zhang Jincheng of Xidian University, director of the Technical Expert Committee of the Alliance, to share his unique views on gallium oxide as a material.

Guest Introduction

      Zhang Jincheng, Vice President of Xi'an University of Electronic Science and Technology,  a Professor of 2^nd class, the Winner of Science and Technology Innovation Award of He Liang He Li Foundation, the Winner of National Natural Science Fund for Distinguished Young Scholars, and Distinguished Professor of Changjiang Scholars of the Ministry of Education. He is a member of the sixth and seventh sessions of the Space Electronics Branch of the Chinese Electronics Society, a member of the Semiconductor Physics Committee of the Chinese Physical Society. He used to be the former chairman of the Electronic Devices Branch of international academic conferences such as ICNS (International Nitride Semiconductor Conference) and DRIP (International Defect Identification and Detection Conference), and he used to be the vice director of the Organizing Committee of the National Semiconductor Physics Academic Conference. He has been engaged in the research of wide band-gap semiconductor gallium nitride, ultra wide band-gap semiconductor gallium oxide and diamond for a long time, and has made a series of important innovative achievements in low defect epitaxial materials and new heterostructures, high-power RF devices and circuits, high-voltage power electronic devices, etc. His achievements have been successfully applied to Beidou navigation satellite, 5G communication base station and other major national projects, and his representative achievements have been included in the "13th Five Year" National Science and Technology Achievement Exhibition. He won two second prizes of the National Technological Invention Award, separately as the First and the Second Individual to accomplish, and seven first prizes of provincial and ministerial science and technology awards. He has published more than 200 high-level academic papers, three monographs, more than 100 invention patents, and he has been invited more than 50 times to give reports at domestic and foreign academic conferences.

AGOA：Which fields of applications do you think gallium oxide, as an ultra-wide band gap semiconductor material, with its advantages, would be most likely applied in the future?

      Gallium oxide has the characteristics of ultra-wide forbidden band width (4.9~5.3eV), ultra-high breakdown field strength (~8MV / cm), high electron saturation drift rate (2 x10⁷ cm/s), excellent thermal stability and so on, which significantly outperformed the wide-band semiconductors SiC and GaN. At the same time, gallium oxide is one of the few wide band and ultra-wide band gap semiconductor materials that can be  prepared at low cost via "FZ (floating zone)" and "EFG (edge-definedfilm-fed growth)" solution growth method of. Therefore, gallium oxide, which has both ultra-high performance and low cost potential, has been widely concerned and highly expected by academia and industry.

      Gallium oxide has a good application prospect in high efficiency high voltage power devices, high power radio frequency devices, deep ultraviolet detectors, irradiation and other functional devices applied in extreme conditions. It is expected to develop miniaturized, efficient and cost-effective super power diodes and transistors in short time.

AGOA：What do you think are the research difficulties of gallium oxide materials at present?

      There are still many key challenges and difficulties for gallium oxide materials and devices. One is the low cost, high quality, large size of gallium oxide single crystal growth; Second, high-speed, low-defect gallium oxide epitaxial growth; Third, the material defect identification, inhibition and its influence mechanism; Third, the material defect identification, inhibition and its influence mechanism; Fifth, the device heat dissipation and self-heating caused by low thermal conductivity; Sixth, the key processes and structures suitable for gallium oxide devices to play high performance devices, such as gate oxide layer, surface passivation, high voltage terminal, low resistance ohm contact, electric field control structure, etc.

AGOA：Could you please brief us on the current research progress of gallium oxide materials and the possible future research directions?

      At present, one of the main research directions of the National Key Laboratory of Wide Band Semiconductor and the National Engineering Research Center based on Xidian University is gallium oxide ultra-wide band gap semiconductor materials and devices. Under the leadership of Academician Hao Yue, we adhere to the research tradition of the integrated layout of equipment, material and device. We developed domestic gallium oxide epitaxial MOCVD equipment, Mix-CVD equipment and its high-performance epitaxial materials. The performance of N-type doped gallium oxide epitaxial materials with high concentration and high mobility is in the international advanced level. Developed a series of high-voltage gallium oxide power diodes, power transistors and radio frequency transistors, and the device performance has always maintained the international leading level in recent years. Among them, Various new terminal structures such as ion injection, junction and PN heterojunction and 3 kV, 6 kV, 8 kV and 10 kV high voltage diode are highly concerned by international counterparts. At the same time, focusing on the gallium oxide heat dissipation problem, we have developed silicon carbide and gallium oxide transistors on the diamond substrate, which provides a solution for the lateral device heat dissipation. In the future, Xidian's gallium oxide research will continue to focus on large-size and high-quality gallium oxide epitaxial equipment and epitaxial growth, high-voltage power devices and high-power RF devices and other cutting-edge technology research. Meanwhile, we will continue to cooperate with enterprises to promote the engineering and industrialization of gallium oxide materials and devices.

AGOA：From the perspective of device research demand, what aspects do you think need to improve and breakthrough in the supply of gallium oxide substrate and epitaxial materials?

      From the perspective of device research requirements, the conductive gallium oxide substrate first needs to improve the n-type doping concentration and mobility, so as to reduce the parasitic resistance and thermal production of gallium oxide power devices. Second, it is necessary to enlarge the size of gallium oxide single crystal substrate, and continuously reduce the substrate cost. Gallium oxide epitaxial materials need to further reduce the background electron concentration of the epitaxial layer to 10¹⁵ or even 10¹⁴ cm^-3 with the capacity of high-speed thickening epitaxial to provide support for gallium oxide devices to reach ultra-high-voltage indicators such as 10-100 kV, and constantly suppress the epitaxial layer defects and provide the material uniformity.

AGOA：In the process of gallium oxide from scientific research to industrialization, what aspects do we need to make great efforts to solve?

      Gallium oxide, from scientific research to industrialization, just like silicon, gallium arsenide, silicon carbide, gallium nitride and other semiconductor predecessors, needs a process of technology promotion and demand traction to develop continuously. In terms of technology promotion, the frontier and key technologies that have been broken through need to continuously improve the technology maturity, which is through the whole chain high-performance technology system from substrate, epitaxy to device, in order to achieve typical engineering devices such as diodes or transistors, turning the performance potential of gallium oxide into a usable practical advantage. In terms of demand trend, it is necessary to identify several demonstration scenarios for the first application practice, such as efficient power modules for consumer electronics or industrial electronics, high-voltage electric drives or electric propulsion modules for various high-end equipment. Gallium oxide industrialization could be driven and realized through advanced application demonstration.

      In terms of gallium oxide cost, material suppliers mainly are expected to provide high quality, large size and low defect substrate materials for industrialization, and further create the cost advantage of gallium oxide. At the same time, we should continue to develop a crystal growth mode more suitable for industrialization to meet the needs of industrialization. Larger epitaxial layer thickness and lower epitaxial layer concentration are needed and are expected to improve the consistency and uniformity of large size epitaxy to meet the demand of industrialization. In terms of devices, it is necessary to continuously develop and optimize the device structure and key process, and develop a process scheme suitable for mass production to ensure a stable yield. Meanwhile, the route and solution of the packaging process should also be considered. Therefore, industrialization should consider not the problem of a single link, but the cooperation of the upstream and downstream of the whole industrial chain. There will certainly be a lot of problems to solve in this process, so all the gallium researchers need to work together to overcome the difficulties.

AGOA：In the process of realizing gallium oxide industrialization, a large number of technical talents is needed. What are your suggestions in terms of talent training and reserve? Do you think the school-enterprise joint directional training is a good direction?

      The development of gallium oxide industry, like other industries, needs talents first, especially to cultivate high-level talents who master core technologies and can be entrusted with important posts. For gallium oxide, a frontier strategic field, whose future potential is huge, it is urgent to accelerate the training of a group of doctoral and master and other high-level talents.The current market demand shouldn’t be the only aspect that is considered. The development of talent training should goes ahead of the market demand, and reserve of talent should be for future demand. Talents need to get trained in major scientific research projects, in the real industrial environment. Therefore, the ministries and commissions of the nation need to increase the layout of major scientific research projects in the field of gallium oxide, which is not only crucial for the key technologies, but also for the training of high-level talents. Education, science and technology, talent integration system layout is required. School-enterprise joint directional training is necessary to improve the innovative practice ability of talents and the ability to solve complex engineering problems. In particular, it is an important means to jointly cultivate talents in the field of wide band semiconductor.

AGOA：Do you have any comments or suggestions on the work of the Alliance?

      China has a vast territory, and the innovation resources and industrial resources are relatively dispersed geographically. The Alliance can play a key role in how to gather the dispersed forces into a group and build an efficient and collaborative innovation ecology and industrial ecology. Therefore, we expect that the Alliance could play a greater role in aggregating research forces at home and abroad, and establish a coordination mechanism with relevant national scientific research platforms, industry associations and other institutions.