Pursuing the Ultimate: The Potential of Diamond as a Semiconductor Material
“If I am going to do something, I want to challenge myself with the most difficult and ultimate task.” The driving force behind Associate Professor Tsubasa Matsumoto’s research on diamond semiconductors is his desire to take on devices that no one has ever created before. His interest was sparked during his time at a technical college, when a sentence in a textbook caught his attention: “Diamond is a semiconductor material with ultimate physical properties.” The textbook described how diamond’s intrinsic characteristics—such as high thermal conductivity, excellent breakdown field—make it an ideal material for semiconductor applications. Until then, he had been engaged in research on silicon carbide (SiC) as a semiconductor substrate material. However, upon entering graduate school, he decided to join a laboratory dedicated to studying diamond as a semiconductor material. “Research is not about tracing what is already known, but about envisioning a world that no one has ever seen,” he says. For him, diamond semiconductors represented the first step toward that unseen world.
Diamond Semiconductor
To date, Dr. Matsumoto has been engaged in the development of a wide range of devices that apply diamond as a semiconductor material. Among his current research challenges, the development of a diamond-based MOSFET (metal–oxide–semiconductor field-effect transistor) stands out as a central focus. MOSFETs are essential semiconductor devices for power control and are expected to play a key role in the field of power electronics, which handles large amounts of electrical power in applications such as automobiles, high-speed rail systems, industrial facilities, and space equipment. Compared with conventional silicon-based devices, diamond exhibits superior performance, particularly under high-voltage and high-temperature conditions. One of the most significant advantages of diamond semiconductors is their potential to dramatically reduce “heat loss” that occurs during power conversion. If realized, this reduction would lead to substantial improvements in energy efficiency. For example, a 1 kW power supply—roughly equivalent to that used by an air conditioner—with a 1% heat loss would waste 10 W of energy as heat, enough to charge a single smartphone. At a power level of 10 kW, the same loss rate would result in 100 W of wasted energy, comparable to the power consumption of a laptop computer. This illustrates why minimizing heat loss is a critically important issue in power electronics. “By using diamond, we can suppress these losses and enable more efficient use of energy,” Dr. Matsumoto explains. In general, semiconductor devices are fabricated by combining n-type semiconductors, in which electrons act as charge carriers, with p-type semiconductors, where charge is carried by holes. In diamond semiconductors, however, achieving stable n-type conductivity is considered particularly challenging. Although research in this area is being pursued worldwide, no solution has yet reached a practical level of application. Dr. Matsumoto is currently working on the development of n-type diamond semiconductors and notes, “If this can be realized, the potential of diamond electronics will expand significantly.”
Taking on Challenges That No One Else Can
“Doing what no one else can do.” This principle consistently underpins Associate Professor Matsumoto’s research approach. He believes that unexpected experimental results often contain the seeds of the next discovery. In his interactions with students, he places particular emphasis on one-on-one dialogue, using these discussions to cultivate independent thinking and problem-solving skills. For Dr. Matsumoto, research is an intellectual endeavor that involves formulating questions, testing hypotheses, and, at times, transcending existing frameworks to create entirely new structures. It is through this cumulative process that his work has advanced toward the design of diamond semiconductor devices that do not yet exist anywhere in the world. Recently, he proposed a novel device architecture unlike any previously reported, which was subsequently adopted as a large-scale research project. Taking on difficult challenges has the power to shape the future. While approaches to the unknown inevitably involve setbacks and failures, the knowledge and experience gained in the process are passed on to the next generation of researchers. Dr. Matsumoto is committed to thinking alongside his students, engaging in open discussion, and creating new value without fear of failure. Guided by this conviction, he continues his daily research efforts with the aim of seeing diamond semiconductor technologies widely adopted in society.
(Science writer: Yuko MITERA, English translation:Md Abul Kalam SIDDIKE)
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