Research
Wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have garnered attention as materials for blue LEDs, driving advancements in material research. The memory of Professors Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura receiving the Nobel Prize in Physics in 2014 for their contributions in this field is still fresh in our memories.
Wide-bandgap semiconductors possess intriguing material properties, including high insulation breakdown fields and high saturation drift velocities, making them highly appealing for electronic device applications. Leveraging these characteristics, applications have progressed in areas such as power conversion devices (power devices) and high-frequency amplifying transistors used in portable base stations (5G communication).
In order to realize a sustainable energy society, it is essential to establish the fundamental principles for the realization of wide-bandgap semiconductor devices. Particularly crucial is the exploration of unique physical phenomena at high electric fields and ultra-high temperatures, which were previously unimaginable with conventional semiconductors like silicon (Si).
For example, elucidating the collision ionization coefficient, a material property that determines insulation breakdown, reveals characteristics vastly different from traditional semiconductors. It exhibits interesting properties such as significant differences between electrons and holes (larger for holes) and substantial crystalline orientation dependence. However, much remains unknown, and continuous research is imperative for deeper understanding.
Our laboratory aims to elucidate the high-electric-field properties of wide-bandgap semiconductors. We have various research themes, and we are flexible in tailoring topics according to individual students' interests. Some ongoing specific research themes include:
・Precise evaluation of metal/wide-bandgap semiconductor Schottky interface properties
・Measurement of high-electric-field drift velocity in wide-bandgap semiconductors
・Understanding and modeling the carrier transport characteristics of two-dimensional electrons in nitride semiconductor heterojunctions
・Prototyping innovative transistors using novel nitride semiconductor heterojunctions
Based on unique ideas, we thoroughly discuss the most suitable device structures for accurately and precisely measuring these properties. We engage in in-depth discussions, often involving numerical calculations and simulations within the group or in collaboration with external researchers. Subsequently, utilizing the shared facilities at the University of Tokyo, such as the Takeda Advanced Clean Room, we fabricate our devices and conduct measurements and analyses.
Facing previously unexplored natural phenomena, the process is challenging, but the moment when we obtain results according to our design (or encounter entirely unexpected new phenomena) is genuinely exhilarating. Presenting these findings objectively and scientifically in papers and conferences is another rewarding moment that validates our daily efforts.
Research is undoubtedly demanding, but I sincerely hope that students can experience the profound joy of accomplishment and overcoming challenges. We are open to inquiries about laboratory visits, so please feel free to contact us anytime! (Email: tmaeda"at"g.ecc.u-tokyo.ac.jp)