Next-generation semiconductors: one way to wide, one way to narrow

Source: The content is reprinted from the official account " China Electronics News " by Semiconductor Industry Observer (ID: icbank) , author: Zhang Xinyi , thank you.

As the third-generation semiconductors represented by gallium nitride and silicon carbide enter the industrialization stage, the discussion on the new generation of semiconductor materials has entered the public eye. Antimonide, which is heading towards industrialization, as well as gallium oxide, diamond, and aluminum gallium nitride, which are highly concerned at home and abroad, are all regarded as important directions for the new generation of semiconductor materials. In terms of band gap width, antimonide is a narrowband semiconductor, while gallium oxide, diamond, and aluminum nitride are ultra-wide bandgap semiconductors. Will the new generation of semiconductor materials go all the way to wider or narrower?

The width of the bandgap determines the difficulty of electron transition and is one of the determining factors of the conductivity of semiconductors. The wider the bandgap, the closer the semiconductor material is to an insulator and the stronger the device stability. Therefore, ultra-wide bandgap semiconductors can be used in special environments such as high temperature, high power, high frequency and high radiation resistance.

"The operating temperature range of silicon devices is relatively limited, while ultra-wide bandgap semiconductors can be said to be 'the sky and the earth' and have a very wide range of adaptability." Yan Jianchang, a researcher at the Institute of Semiconductors, Chinese Academy of Sciences, told a reporter from China Electronics News.

In the field of optoelectronics, ultra-wide bandgap semiconductors have broad application space in ultraviolet light emission and ultraviolet detection. Ultraviolet light-emitting diodes and ultraviolet laser diodes based on ultra-wide bandgap semiconductors such as aluminum gallium nitride are used in medical and health fields such as sterilization and disinfection. Ultraviolet rays of specific wavelengths can help the human body supplement calcium. In industry, ultra-wide bandgap can be used to manufacture high-power ultraviolet light sources.

Among ultra-wide bandgap semiconductors, aluminum gallium nitride (an alloy material of aluminum nitride and gallium nitride), gallium oxide, and diamond are the more representative directions.

Unlike materials with relatively fixed bandgap widths such as gallium oxide and diamond, the bandgap width of aluminum gallium nitride can be adjusted within a certain range, making it a flexible semiconductor material.

"By adjusting the aluminum composition, aluminum gallium nitride can achieve different bandgap widths, ranging from 3.4 eV for gallium nitride to 6 eV for aluminum nitride. Through the appropriate ratio, a specific bandgap width can be obtained to emit ultraviolet rays of the corresponding wavelength, which is an interesting and useful property." Yan Jianchang said.

In terms of preparation technology, aluminum gallium nitride has already accumulated a certain amount of experience.

"The mainstream method for epitaxial preparation of gallium nitride and aluminum nitride is MOCVD (metal organic chemical vapor deposition), and the industry has accumulated two to three decades of experience in processes, equipment and other aspects. As an alloy material of gallium nitride and aluminum nitride, aluminum gallium nitride has many similarities with the two in epitaxial preparation. Industrialization has already started, and it is expected that in the next 3-5 years, it will be able to reach the level of large-scale mass production." Yan Jianchang pointed out to reporters.

Gallium oxide has higher energy conversion efficiency than wide bandgap semiconductors. At present, the preparation level of gallium oxide materials has made rapid progress, but there is still a lot of work to be done in epitaxy and devices.

"The bandgap of gallium oxide is wider than that of gallium nitride, silicon carbide, etc., so the power can be higher and it is more energy-efficient. The preparation conditions of gallium oxide are relatively harsh. Currently, epitaxial materials are mainly small in size of 2-3 inches, and there is still a long way to go for mass production and application." Associate Professor Guo Hui of Xidian University told a reporter from China Electronics News.

Yan Jianchang pointed out that insufficient heat dissipation capacity is a drawback of gallium oxide. How to circumvent this drawback and give full play to its advantages in power devices is a development direction worthy of attention.

Diamond is regarded as the "ultimate semiconductor" material, with the characteristics of ultra-wide bandgap, high thermal conductivity and high hardness. However, due to its highest hardness, it is also the most difficult to achieve semiconductor-level high purity, and there is still a long way to go before productization and industrialization.

"It is difficult to prepare and dope diamond at the semiconductor level, but we can use diamond-like materials or diamond particles to improve the heat dissipation of semiconductor devices and bring out the advantages and strengths of diamond itself," said Yan Jianchang.

In contrast to ultra-wide bandgap semiconductors, narrow bandgap semiconductors such as antimonide have the characteristics of high mobility and strong conductivity, and their application areas are also concentrated in the infrared, which is exactly distributed at the two ends of the spectrum with the ultraviolet light used for ultra-wide bandgap applications. It can be said that ultra-wide bandgap and narrow bandgap semiconductors have expanded the scope of human use of the spectrum.

In the field of optoelectronics, antimonide material systems are expected to become the main material system for future infrared imaging systems. According to Niu Zhichuan, a professor at the Institute of Semiconductors of the Chinese Academy of Sciences, traditional infrared optoelectronic materials are difficult to manufacture for large arrays, dual-color, multi-color focal planes, and far-infrared focal planes due to bottlenecks such as insufficient uniformity, small substrate area, and extremely low yield.

"Antimonides have high performance, and their band gap regulation has a wider range of applications, lower costs, and larger manufacturing scales. Gallium antimonide-based semiconductor epitaxial material technology has grown into the mainstream of infrared optoelectronic device manufacturing," Niu Zhichuan told a reporter from China Electronics News.

In the field of microelectronics, antimonide semiconductors have ultra-high-speed mobility that exceeds that of the previous three generations of semiconductor systems, and have great potential in the development of ultra-low power consumption and ultra-high-speed microelectronic integrated circuit devices.

In the field of thermoelectric devices, various crystalline materials containing antimony elements have excellent thermoelectric and refrigeration effects. They have long been an important technical direction in the field of thermoelectric refrigeration devices and have broad application prospects.

In terms of preparation, the structural characteristics and preparation processes of antimonide narrow-bandgap semiconductors are similar or compatible with those of III-V system such as gallium arsenide and indium phosphide. Therefore, there are no obstacles to mass production technology. The preparation cost is mainly restricted by the single crystal substrate wafer area, epitaxial material mass production capacity, and process integration technology yield.

"As the demand for functional devices increases, the manufacturing of antimonide-based lasers and detectors has been fully verified in mass production. The manufacturing scale in various application fields of optoelectronic functions has gradually expanded and the conditions for mass production have been met," Niu Zhichuan pointed out.

The new generation of semiconductor materials is the cornerstone of industrial transformation. From the first generation of semiconductor materials represented by silicon, the second generation of semiconductor materials represented by gallium arsenide and indium phosphide, and the third generation of semiconductor materials represented by gallium nitride and silicon carbide, the working scope and application scenarios of semiconductor devices are constantly expanding, providing strong support for the development of the information society.

Advanced diagram of representative semiconductor materials

So, what elements should a new generation of semiconductor materials with real technological prospects have?

Niu Zhichuan said that when evaluating the development prospects of semiconductor materials, two indicators should be paid attention to.

First, whether a highly controllable mass production technology can be developed is a necessary prerequisite for judging whether new system materials have long-term development prospects. In the early stages of development for practical applications, it is necessary to evaluate the feasibility of large-scale production platforms, including large-scale manufacturing equipment, and to test the stability of product yield and device performance through small and medium-scale engineering tests.

The second is whether the technology iteration chain is complete, which is a necessary consideration for the success of marketization. The semiconductor technology iteration chain includes whether the relevant supporting conditions required for all technical links have reliable sources, the volatility of the market cycle, the cost-effectiveness of user demand for products, and the advantages and disadvantages of materials compared with competing products.

On the basis of having industrial prospects, how can we give full play to the properties of the materials themselves, transform them into the driving force of industrial development and release market value?

Yan Jianchang said that each material has its own advantages and limitations, and we should give full play to or tap into its favorable factors to maximize its strengths and avoid its weaknesses. The industry once believed that the defect density of gallium nitride materials was too high to be used for light emission, but some special mechanisms of gallium nitride can circumvent the problem of defect density and make up for the lack of purity based on its own advantages such as hardness and chemical stability, thus winning room for development.

"Whether it is aluminum gallium nitride, gallium oxide or diamond, there is still a lot of room for device and industrial development. The foundation of development depends on the material itself and the level of material preparation. We must achieve lower defect density and fully explore the advantages and potential of the material. This is the foundation for future ultra-wide bandgap technology and industrial development." Yan Jianchang said.

Guo Hui said that it takes time to increase the volume of new materials, and it is necessary to consider the overall benefits and find the market position.

"In the field of microelectronics, ultra-wide bandgap semiconductors are mainly used for power semiconductors. We must consider not only the preparation cost of the material itself and the cost of the power device itself, but also the cost of using the device in the system. We need to find market space and form market competitiveness through comprehensive benefits," said Guo Hui.

Niu Zhichuan said that on the basis of solid laboratory technology development and research, we must deeply understand the basic technical methods and paths for optimizing material properties, establish basic physical and chemical property data in all aspects, and form the best iterative model from design to device function realization. On this basis, we will build a pilot platform to focus on testing the technical processes, plans and specifications for achieving high-yield engineering manufacturing. In the future, we will add user customization requirements, gradually improve the mass production manufacturing technology of specific functions of the device, improve iteration efficiency, and deeply integrate with the market.