In Japanese !!
IEEE-EDS Japan Joint Chapter
IEEE-EDS Distinguished Lecturer Public Lecture of the Electron Devices Society
Creation of Semiconductor Plasmonic Functional Devices and Their Application tothe Next Generation Beyond 5G Terahertz Wireless Communications
Professor Taiichi Otsuji
RIEC: Research Institute of Electrical Communication
Tohoku University, Sendai 9808577, JapanAs we are required to change to a new normal society over the COVID-19 pandemic, the use cases ofsmartphones are diversifying to an extent far beyond our imagination, and people's demand for wirelesscommunication technology that enables "higher speed, higher capacity, and massive connections" continuesunabated. In this regard, research and development of the next generation Beyond 5G (B5G), i.e., 6G and 7G
are being actively conducted in order to cope with the increasing traffic volume in mobile communications.
However, there is the technological difficulties, called "THz gap," over the entire THz electromagnetic spectral
range due to the fundamental physical limits on both existing electronic and photonic technology. In such asituation, graphene has attracted considerable attention due to its massless and gapless energy spectrum. This
lecture reviews recent advances in the research for the creation of semiconductor plasmonic functional devices
and their application to the next generation beyond 5G terahertz (THz) wireless communications.
2D electronic and plasmonic THz devices based on graphene-based 2D materials, particularly highlighting theTHz sources and detectors. Carrier-injection pumping of graphene can enable negative-dynamic conductivity
in the THz range, which may lead to new types of THz lasers. The dual-gate graphene channel transistor (DGGFET) structure serves carrier population inversion in the lateral p-i-n junctions under complementary dualgate biased and forward drain biased conditions, promoting spontaneous incoherent THz light emission. Alaser cavity structure implemented in the active gain area can transcend the incoherent light emission to thesingle-mode lasing. We designed and fabricated the distributed feedback (DFB) DG-GFET. A teeth-brash-shaped
DG structure is introduced as the DFB cavity having the fundamental mode at 4.96 THz. Broadband ratherintense (~80 μW) amplified spontaneous emission from 1 to 8 THz and weak (~0.1 μW) single-mode lasing at
5.2 THz were observed at 100K in different samples. When the substrate-thickness dependent THz photon field
distribution could not meet the maximal available gain-overlapping condition, the DFB cavity cannot work
properly, resulting in broadband LED-like incoherent emission. To increase the operating temperature andlasing radiation intensity, further enhancement of the THz gain and the cavity Q factor are mandatory.
Plasmonic metasurface structures promoting the super-radiance and/or instabilities are promising for giantTHz gain enhancement.
In terms of THz detection, nonlinear nature of graphene plasmons enables drastic enhancement of detection
responsivity that can well outperform any existing room-temperature fast detectors. Recently weexperimentally demonstrated 100-Gbit/s-class fast and sensitive THz detection in an ADGG-GFET utilizing
current-driven plasmonic and photothermoelectric rectification mechanisms.
In the final part, we introduce the double-graphene-layered van der Waals heterostructures to mediate thephoton/plasmon assisted resonant tunneling working for highly efficient THz sources and detectors. Future
trends towards the smarter society based on the 6G and 7G THz wireless communications are also discussed.

When:
13:00 – 14:00 JST, October 31st, 2022.
Where:Zoom Online
Link:
To be emailed shortly for pre-registered attendees
Language:
Japanese (presentation) / English (slides)
Fee:Free of charge
Pre-Registration: Mandatory. To preregister, <Click here!> or ☞Contact:
Assoc. Prof. Tomoko Shimizu, Keio University
Email: t-kura@gipc.akita-u.ac.jp
Taiichi Otsuji is a professor at the Research Institute of Electrical Communication(RIEC), Tohoku University, Sendai, Japan. He received the B.S. and M.S. degrees
in electronic engineering from Kyushu Institute of Technology, Fukuoka, Japan, in
1982 and 1984, respectively, and the Dr. Eng. degree in electronic engineeringfrom Tokyo Institute of Technology, Tokyo, Japan in 1994. From 1984 to 1999 heworked for NTT Laboratories, Kanagawa, Japan. In 1999 he joined Kyushu
Institute of Technology as an associate professor, being a professor in 2002. He
joined RIEC, Tohoku University, in 2005. His current research interests include
terahertz electronic, photonic and plasmonic materials/devices and theirapplications. He has authored and co-authored 280 peer-reviewed journal papers and more than 600
conference proceedings including 200 invited presentations, and holds 11 Japanese and 7 US patents. He isthe recipient of the Outstanding Paper Award of the 1997 IEEE GaAs IC Symposium in 1998, Prizes for Scienceand Technology in Research Category, the Commendation for Sci-ence and Technology by the MEXT, Japan, in
2019, and the 59th Achievement Award of the IEICE (Institute of Electronics, Information, and Communication
Engineers), Japan, in 2022. He has served as an IEEE Electron Device Society Distinguished Lecturer since 2013.
He is a Fellow of the IEEE, OPTICA (former OSA), and JSAP (Japan Society of Applied Physics), a Senior Memberof the IEICE, and a member of the MRS (Materials Research Society) and SPIE (International Society for OpticalEngineering).