Takahide Yamaguchi is a Principal Researcher at the National Institute for Materials Science (NIMS). He also holds a concurrent position as a professor at the Institute of Pure and Applied Sciences, University of Tsukuba (University of Tsukuba-NIMS Joint Graduate School). He received his phD from the University of Tokyo in 2000. His research focuses on the development of electronic devices based on diamond.

In this presentation, I discuss our work on improving channel mobility in diamond field-effect transistors (FETs). Diamond, an ultrawide bandgap semiconductor with excellent thermal conductivity and radiation hardness, holds great promise for power electronics and applications in harsh environments. Although many studies have focused on diamond FETs with hydrogen-terminated surfaces, conventional devices often exhibit low mobility because Coulomb scattering centers are present just above the channel, a result of surface transfer doping that can occur either intentionally or unintentionally. To address this, we used transferred single-crystal hexagonal boron nitride (hBN) as the gate insulator instead of deposited amorphous oxides and fluorides, and avoided exposing the diamond surface to air [1]. This approach effectively suppresses transfer doping and improves the quality of the interface between the insulator and diamond. We achieved channel mobility of about 1000 cm²V⁻¹s⁻¹ at room temperature, which is exceptionally high for p-channel FETs based on wide bandgap semiconductors [2]. I also present related results, including a novel device isolation technique using nitrogen ion implantation to create cleaner channel interfaces [3].

1. Y. Sasama, T. Kageura, M. Imura, K. Watanabe, T. Taniguchi, T. Uchihashi and T. Yamaguchi, Nature Electronics 5, 37 (2022) DOI:10.1038/s41928-021-00689-4
2. Y. Sasama, T. Iwasaki, M. Imura, K. Watanabe, T. Taniguchi, T. Yamaguchi, Applied Physics Letters 127, 143502 (2025) DOI:10.1063/5.0272041
3. K. Hino, M. Monish, Y. Sasama, K. Sakamoto, T. Yamaguchi, Applied Physics Letters 128, 213503 (2026) DOI:10.1063/5.0323938