Developing semiconductor materials to help create devices that are useful to society

Associate professor Rie Togashi from the Faculty of Science and Technology develops semiconductor crystals as new materials for use in optical and electronic devices. These crystals have various potential applications in semiconductor components including VR glasses and electric vehicles. She talks about crystals, the difficulty in making them, and the significance of practical application.

Optical and electronic devices are almost always used in everyday electrical equipment such as computers, mobile phones, traffic lights, and full-color displays. Optical devices record or transmit information, while electronic devices control the flow of electrons and charged particles. Semiconductor crystals are indispensable as materials for creating these devices.

A crystal refers to a solid where the atoms or molecules are arranged in a systematic order. It is possible to create a variety of electrical equipment from semiconductor crystals that are produced through artificial layering, such as by attaching electrodes to these crystals. I undertake research in crystal growth, which is the process for producing such crystals.

Seeking to achieve crystals that emit the primary colors of red, green, and blue

There are two main subjects in my research. One is nitride nanocolumn crystal, where indium gallium nitride (InGaN)—a nitride semiconductor that serves as the material for light emitting diodes (LEDs), which emit light when an electrical voltage is applied—is shaped into columnar crystal structures in the order of nanometers (one-millionth of a millimeter).

Such crystals have potential application as materials for small LEDs called micro-LEDs. I work with visiting professor Katsumi Kishino—a leading expert in nanocolumn research—from the Faculty of Science and Technology to conduct research on how to make these crystals emit the three primary colors of red, green, and blue brightly for long periods of time.

If we can achieve the emission of the three primary colors, it will be possible to create ultra-small projector TVs and glasses for VR devices using micro-LEDs. In our research, we create nitride nanocolumn crystals using a molecular beam epitaxy growth which generates a molecular beam from the component molecules under ultra-high vacuum, and supplies it to the underlying crystal substrate to grow a thin film that inherits the same crystalline information as the underlying substrate.

Currently, we are working to achieve light emission—the objective of our research—by changing the length and diameter of the nanocolumn crystals into various shapes.

Research on power semiconductor materials made solely from water and metals

Another subject of my research is known as gallium oxide semiconductor crystal, which is an oxide crystal that serves as material for power semiconductors. This research is being undertaken jointly with Tokyo University of Agriculture and Technology, Osaka University, and other partners.

As power semiconductors allow the flow of high currents at high voltages, they are used in applications such as electric vehicle systems, and currently, semiconductors made from silicon form the mainstream. It has been found that we can significantly limit electrical loss if we use gallium oxide crystals in place of silicon.

The gallium oxide semiconductor crystal that we are working on has the possibility of being made solely from water and metals. If achieved, I think it will be sought by society as an affordable and safe material.

From the time when I was a student, I was taught that the ties between people are important in research. There is a limit to the capabilities of an individual. I believe that pursuing research together with various researchers will lead to the early realization of results. I find my research interesting when crystals are formed according to the design. The fact that these crystals will also serve as materials for devices that are useful to society also gives me motivation.

My research goal going forward is to achieve practical application of these two crystals as early as possible. I also want students to have an interest in material research—including crystal growth—and research on semiconductors, and I hope to do so by conducting appealing classes that are easy to understand.

The book I recommend

“Madame Curie: A Biography”
by Eve Curie, Japanese translation by Mariko Kono, Hakusuisha

Blessed with the opportunity to be a visiting scholar at a graduate school in Sweden with a chance to visit a Polish research institute, I bought a biography of Madame Curie, who was born in Poland. As a female researcher myself, I was inspired by the book, which went into details about her research and how she balanced child raising with her work.

Rie Togashi

  • Associate Professor
    Department of Engineering and Applied Sciences
    Faculty of Science and Technology

Graduated from the Department of Applied Chemistry, Faculty of Engineering, Tokyo University of Agriculture and Technology, and received her Ph.D. in Engineering after completing the doctoral program of the Department of Applied Chemistry at the university’s Graduate School of Engineering. Took on several positions—such as academic affairs staff at the Graduate School of Engineering and assistant professor at the Institute of Engineering of Tokyo University of Agriculture and Technology; visiting scholar at the Department of Physics, Chemistry and Biology, Linköping University, Sweden; and assistant professor at the Department of Engineering and Applied Sciences, Faculty of Science and Technology, Sophia University—before assuming her current position in 2023.

Department of Engineering and Applied Sciences

Interviewed: October 2023

Sophia University

For Others, With Others