Dr. Akira Satou

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Academic Career Length

25Years (2002-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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6 July 2020 in Physical Review X

Journal Article

Room-Temperature Amplification of Terahertz Radiation by Grating-Gate Graphene Structures

Stephane Boubanga Tombet

We study terahertz (THz) radiation transmission through grating-gate graphene-based nanostructures. We report on room-temperature THz radiation amplification stimulated by current-driven plasmon excitation. Specifically, with an increase of the dc current under periodic charge density modulation, we observe a strong redshift of the resonant THz plasmon absorption, followed by a window of complete transparency to incoming radiation and subsequent amplification and blueshift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. Additionally, we present a simple model offering a phenomenological description of the observed THz amplification. This model shows that in the presence of a dc current the radiation-induced correction to dissipation is sensitive to the phase shift between oscillations of carrier density and drift velocity. And, with an increasing current, the dissipation becomes negative, leading to amplification. The experimental results of this work, as all obtained at room-temperature, pave the way toward the new 2D plasmon-based, voltage-tunable THz radiation amplifiers.

10 June 2016 in Physical Review B

Journal Article

Giant plasmon instability in a dual-grating-gate graphene field-effect transistor

Y. Koseki

V. Ryzhii

Taiichi Otsuji

Vyacheslav V. Popov

Akira Satou

We study the instability of plasmons in a dual-grating-gate graphene field-effect transistor induced by dc current injection using self-consistent simulations with the Boltzmann equation. With only acoustic-phonon-limited electron scattering, it is demonstrated that a total growth rate of the plasmon instability, with a terahertz/midinfrared range of the frequency, can exceed

4 \times 10^{12} s^{- 1}

at room temperature, which is an order of magnitude larger than in two-dimensional electron gases based on the usual semiconductors. By comparing the simulation results with existing theory, it is revealed that the giant total growth rate originates from a simultaneous occurrence of the so-called Dyakonov-Shur and Ryzhii-Satou-Shur instabilities.

1 December 2022 in APL Photonics

Journal Article

Fast and sensitive terahertz detection with a current-driven epitaxial-graphene asymmetric dual-grating-gate field-effect transistor structure

Koichi Tamura

Chao Tang

Daichi Ogiura

Kento Suwa

Hirokazu Fukidome

Akira Satou

We designed and fabricated an epitaxial-graphene-channel field-effect transistor (EG-FET) featuring an asymmetric dual-grating-gate (ADGG) structure working as a current-driven terahertz detector and experimentally demonstrated a 10 ps-order fast response time and a high responsivity of 0.3 mA/W to 0.95 Terahertz (THz) radiation incidence at room temperature. The ADGG and drain–source bias dependencies of the measured photoresponse showed a clear transition between plasmonic detection under periodic electron density modulation conditions with depleted regions and photothermoelectric (PTE) detection under entirely highly doped conditions without depleted regions. We identified the PTE detection that we observed as a new type of unipolar mechanism in which only electrons or holes contribute to rectifying THz radiation under current-driven conditions. These two detection mechanisms coexisted over a certain wide transcendent range of the applied bias voltages. The temporal photoresponses of the plasmonic and PTE detections were clearly shown to be comparably fast on the order of 10 ps, whereas the maximal photoresponsivity of the PTE detection was almost twice as high as that of the plasmonic detection under applied bias conditions. These results suggest that the ADGG-EG-FET THz detector will be promising for use in 6G- and 7G-class high-speed wireless communication systems.

31 October 2002 in Journal of Applied Physics

Journal Article

Plasma mechanism of terahertz photomixing in high-electron mobility transistor under interband photoexcitation

V. Ryzhii

I. Khmyrova

Akira Satou

P. O. Vaccaro

T. Aida

Michael Shur

We show that modulated near-infrared radiation can generate terahertz plasma oscillations in the channel of a high-electron mobility transistor. This effect is associated with a temporarily periodic injection of the electrons photoexcited by modulated near-infrared radiation into the transistor channel. The excitation of the plasma oscillations has the resonant character. It results in the pertinent excitation of the electric current in the external circuit that can be used for generation of terahertz electromagnetic radiation.

2 February 2022 in Nanophotonics

Journal Article

Graphene‐based plasmonic metamaterial for terahertz laser transistors

Taiichi Otsuji

Stephane Boubanga Tombet

+10

This paper reviews recent advances in the research and development of graphene‐based plasmonic metamaterials for terahertz (THz) laser transistors. The authors’ theoretical discovery on THz laser transistors in 2007 was realized as a distributed‐feedback dual‐gate graphene‐channel field‐effect transistor (DFB‐DG‐GFET) in 2018, demonstrating ∼0.1 µW single‐mode emission at 5.2 THz and ∼80 µW amplified spontaneous 1–7.6 THz emission at 100 K. To realize room‐temperature, dry‐cell‐battery operating intense THz lasing with fast direct modulation, various approaches based on graphene plasmonic metamaterials are investigated and introduced as real device implementations, including (i) replacement of the laser photonic cavity with plasmonic cavity enormously improving the THz photon field confinement with larger gain overlapping, (ii) introduction of THz amplification of stimulated emission via current‐driven graphene Dirac plasmons (GDPs), and (iii) controlling the parity and time‐reversal symmetry of GDPs enabling ultrafast direct gain‐switch modulation. Possible real device structures and design constraints are discussed and addressed toward coherent light sources applicable to future 6G‐ and 7G‐class THz wireless communication systems.

27 November 2013 in Optical Engineering

Journal Article

Emission and detection of terahertz radiation using two-dimensional plasmons in semiconductor nanoheterostructures for nondestructive evaluations

Taiichi Otsuji

Takayuki Watanabe

Stephane Albon Boubanga Tombet

Akira Satou

Victor Ryzhii

Wojciech Knap

The recent advances in emission and detection of terahertz radiation using two-dimensional (2-D) plasmons in semiconductor nanoheterostructures for nondestructive evaluations are reviewed. The 2-D plasmon resonance is introduced as the operation principle for broadband emission and detection of terahertz radiation. The device structure is based on a high-electron-mobility transistor and incorporates the authors’ original asymmetrically interdigitated dual-grating gates. Excellent THz emission and detection performances are experimentally demonstrated by using InAlAs/InGaAs/InP and/or InGaP/InGaAs/GaAs heterostructure material systems. Their applications to nondestructive material evaluation based on THz imaging are also presented.

About Me

Akira Satou received his B.S., M.S., and PhD computer science degrees from the University of Aizu, Japan, in 2003, 2005, and 2008, respectively. He was a research fellow of the Japan Society for the Promotion of Science (JSPS) in 2006 and 2007. He was an assistant lecturer at the University of Aizu, Japan, in 2008 and 2009. From 2010 to 2017, he was an assistant professor at the Research Institute of Electrical Communication, Tohoku University, Japan. He was promoted to an associate professor in 2017. His research activity is associated with theoretical study and computer simulation of carrier transport in semiconductor nanostructures, including heterostructure two-dimensional electron gas and graphene, for millimeter-wave/terahertz/photonics applications, as well as the implementation of such devices and measurement of their physical properties and performances. He is the author and co-author of 69 papers in refereed journals and 212 presentations at international conferences (including 21 talks to which he was invited). He received the Young Research Investigator Award in 2013 from the Miyagi Industrial and Science Foundation and the M. Ishida Foundation Special Research Award (M. Ishida Prize) in 2023. He is a senior member of the Institute of Electric and Electronics Engineers, a member of the Japan Society of Applied Physics, a member of the Institute of Electrical and Electronics Engineers, and a member of the American Physical Society.

Dr. Akira Satou

Dr. Akira Satou

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