Since the transistor was invented at Bell Laboratories in 1947 and the concept of the integrated circuit was presented by Jack Kilby of TI in 1958, devices using silicon semiconductors have been developed with tremendous drive. Today, ultrastructural, highly dense, and high-functional ULSI devices have become a reality. Accordingly, novel, three-dimensional devices that aim at multiple functions and high performance have been proposed, and novel materials have come into existence. As Artificial Intelligence (AI) has drawn increasing attention, the concept of “Singularity,” or singular technical point, has become a focus of great attention. Singularity is a prediction put forth by American futurist Ray Kurzweil, who said, “Singularity will come in 2045, when the speed of the evolution of technology will become infinite and Artificial Intelligence will exceed human intelligence.” This prediction is said to have its roots in “Moore’s law,” formulated by Intel founder Gordon Moore, which states that “the degree of integration of transistors doubles every year and a half.” The deep learning and self-learning functions of computers can be mentioned as significant driving factors behind the dramatic development of AI studies. The processing capacity of AI has increased exponentially owing to the evolution and combination of various technologies, and the speed of development of technology now far exceeds the biological limits of humankind. As a result, it is inevitable that “Singularity” will come to pass, and the technologies behind semiconductor devices contributing to the arrival of Singularity are expected to develop much further.

In the process of such semiconductor development, silicon carbide (SiC), among other materials, came to be expected as the next-generation semiconductor in the 1950s, but it could not succeed significantly as a practical device. SiC also attracted attention as the material used in green and red light-emitting elements. In the 1990s, SiC came into the spotlight, along with gallium nitride (GaN) crystal and other materials, by being put into practical use as the material used in blue light-emitting diodes. Today, as the silicon (Si) as power devices have already approached the physical limits of the material, next-generation devices focus on semiconductor substrates such as SiC and GaN, which have performance indexes tens to thousands of times higher than the Si semiconductor. Especially, high-power devices and high-frequency devices have attracted special attention, because the use of semiconductor devices in the automotive and other fields has increased dramatically. Furthermore, the single-crystal substrate of semiconducting diamond is considered to be the ultimate semiconductor device, so this topic has been vigorously researched.

The above-mentioned next-generation devices are called green devices because they could reduce power consumption and carbon dioxide emissions tremendously, leading to the realization of a low-carbon and energy-saving society. Such devices are utilized not only as high-power semiconductors and light-emitting semiconductors but also as various sensors, including gas sensors and UV sensors, as well as MEMS devices. Further application of such devices is expected in the future.

To actually produce the high-performance and multifunctional green devices, it will be necessary to establish the technologies for device integration and the manufacturing process. An example would be the process of growing crystals that are larger in diameter and higher in quality. The substrate materials applied in such technologies, including SiC, GaN, and diamond, are known as ultra-hard-to-process materials: their extreme mechanical and chemical stability makes the general manufacturing process much more difficult. A breakthrough is needed to solve this problem. Many challenges must be overcome systematically to produce a high-performance green device, as the device to which such crystalline materials are applied will reduce power consumption and carbon dioxide emissions extremely effectively.

This special issue focuses on manufacturing processes, including the planarization processing of every kind of hard-to-process crystal substrate, involved in producing green devices, sensors, etc. And the paper on the various applications of the device are published in this issue. This issue is expected to contribute to the establishment of a process for manufacturing green devices, which is an essential industrial strategy, as well as to future intensive studies in this field.