Taiichi Otsuji - Academia.edu (original) (raw)
Papers by Taiichi Otsuji
Previous studies have shown that optical and/or injection pumping of graphene can enable negative... more Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) [5]. In this work, we experimentally observe amplified spontaneous broadband THz emission from 1 to 7.6 THz at 100K by carrier-injection in a population-inverted DFB-DG-GFET, demonstrating the birth of a new type of THz light-emitting diodes.
Journal of Physics D, Dec 5, 2019
We report on the design, evaluation and fabrication of the sub-terahertz (sub-THz) detector using... more We report on the design, evaluation and fabrication of the sub-terahertz (sub-THz) detector using a GaAs gated field-effect transistor with a buried quasi-two-dimensional electron gas created by the self-assembled Sn-nanothreads (Sn-NTs) embedded into the GaAs channel. This GaAs-Sn-NTs detector efficiently detects a sub- THz radiation at cryogenic and room temperatures (CT and RT respectively). Two possible detection mechanisms are the bolometric mechanism due to electron heating by the sub-THz radiation and the mechanism related to the rectification of the decayed plasmonic oscillations. We developed a classical self-consistent device model of the bolometric detection involving the Poisson equation and the electron density of states and estimated responsivity and noise-equivalent power of the detector. The measured I-V characteristics and the photoresponse to the incident sub-THz radiation at CT and RT are in reasonable agreement with our model. The detector demonstrates a better performance than semiconductor-based hot-electron bolometers and quantum-well/dot IR and THz photodetectors.
We experimentally observe the fast relaxation and relatively slow recombination dynamics of photo... more We experimentally observe the fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an epitaxial graphene-on-Si heterostructure under pumping with a 1550-nm, 80-fs pulsed fiber laser beam and probing with the corresponding terahertz (THz) beam generated by and synchronized with the pumping laser. The time-resolved electric-field intensity originating from the coherent terahertz photon emission is electro-optically sampled in totalreflection geometry. The Fourier spectrum from 1.8 to 5.2 THz agrees well the pumping photon spectrum. This result is attributed to amplified emission of THz radiation from the graphene sample stimulated by the THz probe beam, and provides evidence for the occurrence of negative dynamic conductivity in the terahertz spectral range.
Bulletin of the American Physical Society, Mar 19, 2010
Electronic and optoelectronic properties of the graphenebackgate transistor are presented. Our tr... more Electronic and optoelectronic properties of the graphenebackgate transistor are presented. Our transistor was fabricated on graphene film heteroepitaxially formed by the thermal decomposition on the surface of 3C-SiC grown on a Si substrate by organo-silane gas source molecular beam epitaxy. The film consists of a few graphene layers. Although some gate leakage current is observed, the experimental results show that our device works as an n-type transistor as well as an infrared photovoltaic transistor. The graphene channel saturated current is on the order of mA/mm. The estimated effective mobility has its maximum over 6000 cm 2 /(Vs). The photo-responsivity can be achieved up to mA/W. The backgate voltage tuning spectral characteristic is also observed. Heteroepitaxial graphene is a promising material for post-Si CMOS applications.
Nano- i mikrosistemnaâ tehnika, May 29, 2017
Nanophotonics, Feb 2, 2022
This paper reviews recent advances in the research and development of graphene-based plasmonic me... more 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-cellbattery 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.
Journal of Physics: Conference Series
We report on experimental and theoretical studies of nanoscale gate-lengths strained Silicon MODF... more We report on experimental and theoretical studies of nanoscale gate-lengths strained Silicon MODFETs as room temperature non resonant detectors. Devices were excited at room temperature by an electronic source at 150 and 300 GHz to characterize their sub-THz response. The maximum of the photovoltaic response was obtained when the FET gate was biased at a value close to the threshold voltage. Simulations based on a bi-dimensional hydrodynamic model for the charge transport coupled to a Poisson equation solver were performed by using Synopsys TCAD. A charge boundary condition for the floating drain contact was implemented to obtain the photovoltaic response. Results from numerical simulations are in agreement with experimental ones. To understand the coupling between terahertz radiation and devices, the devices were rotated at different angles under excitation at both sub-terahertz frequencies and their response measured. Both NEP (Noise Equivalent Power) and Responsivity were calculated from measurements. To demonstrate their utility, devices were used as sensors in a terahertz imaging system for inspection of hidden objects at both frequencies. Figure 4. Visible image (left) and terahertz ones (right) at 150/300 GHz obtained at room temperature with Device 3 with Lg = 500 nm.
Conference on Lasers and Electro-Optics, 2022
IEICE technical report. Electron devices, Dec 1, 2006
Electromagnetics Academy, 2015
ITE Technical Report, 2016
2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2018
We experimentally demonstrate terahertz light amplification by instability-driven stimulated emis... more We experimentally demonstrate terahertz light amplification by instability-driven stimulated emission of graphene plasmon polaritons in an asymmetric dual-grating-gate transistor structure. D.C. channel current driven by the drain bias voltage induces plasmon instability, alternating the electromagnetic response from the resonant absorption to the resonant amplification (up to ~ 9 % gain) beyond the threshold drain bias voltage at room temperature.
Technical report of IEICE. SDM, 2009
The Japan Society of Applied Physics, 2017
We propose a novel technology for fabricating plasmonic photoconductive antennas (PCAs) based on ... more We propose a novel technology for fabricating plasmonic photoconductive antennas (PCAs) based on superlattice (SL) with increased height of the plasmonic gratings up to 100 nm. We passivate the surface of the SL by Si3N4, etch there windows and deposit Ti/Au antenna metallization. The plasmonic gratings are formed by electron-beam lithography with Ti/Au metallization followed by lift-off. Then an Al2O3 anti-reflection coating layer for reduction of the Fresnel reflection losses is used on the top of the plasmonic gratings, which also serves for maintaining its mechanical stability and providing the excitation of guided modes at the resonant wavelengths of the subwavelength slab waveguide formed by the metal gratings. Current-voltage measurements under femtosecond laser illumination reveal strong increase of the transient photocurrent generated by the fabricated plasmonic PCA which is 15 times higher than for conventional one (i.e. without the plasmonic gratings). The obtained terahe...
The Japan Society of Applied Physics, 2016
Previous studies have shown that optical and/or injection pumping of graphene can enable negative... more Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) [5]. In this work, we experimentally observe amplified spontaneous broadband THz emission from 1 to 7.6 THz at 100K by carrier-injection in a population-inverted DFB-DG-GFET, demonstrating the birth of a new type of THz light-emitting diodes.
Journal of Physics D, Dec 5, 2019
We report on the design, evaluation and fabrication of the sub-terahertz (sub-THz) detector using... more We report on the design, evaluation and fabrication of the sub-terahertz (sub-THz) detector using a GaAs gated field-effect transistor with a buried quasi-two-dimensional electron gas created by the self-assembled Sn-nanothreads (Sn-NTs) embedded into the GaAs channel. This GaAs-Sn-NTs detector efficiently detects a sub- THz radiation at cryogenic and room temperatures (CT and RT respectively). Two possible detection mechanisms are the bolometric mechanism due to electron heating by the sub-THz radiation and the mechanism related to the rectification of the decayed plasmonic oscillations. We developed a classical self-consistent device model of the bolometric detection involving the Poisson equation and the electron density of states and estimated responsivity and noise-equivalent power of the detector. The measured I-V characteristics and the photoresponse to the incident sub-THz radiation at CT and RT are in reasonable agreement with our model. The detector demonstrates a better performance than semiconductor-based hot-electron bolometers and quantum-well/dot IR and THz photodetectors.
We experimentally observe the fast relaxation and relatively slow recombination dynamics of photo... more We experimentally observe the fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an epitaxial graphene-on-Si heterostructure under pumping with a 1550-nm, 80-fs pulsed fiber laser beam and probing with the corresponding terahertz (THz) beam generated by and synchronized with the pumping laser. The time-resolved electric-field intensity originating from the coherent terahertz photon emission is electro-optically sampled in totalreflection geometry. The Fourier spectrum from 1.8 to 5.2 THz agrees well the pumping photon spectrum. This result is attributed to amplified emission of THz radiation from the graphene sample stimulated by the THz probe beam, and provides evidence for the occurrence of negative dynamic conductivity in the terahertz spectral range.
Bulletin of the American Physical Society, Mar 19, 2010
Electronic and optoelectronic properties of the graphenebackgate transistor are presented. Our tr... more Electronic and optoelectronic properties of the graphenebackgate transistor are presented. Our transistor was fabricated on graphene film heteroepitaxially formed by the thermal decomposition on the surface of 3C-SiC grown on a Si substrate by organo-silane gas source molecular beam epitaxy. The film consists of a few graphene layers. Although some gate leakage current is observed, the experimental results show that our device works as an n-type transistor as well as an infrared photovoltaic transistor. The graphene channel saturated current is on the order of mA/mm. The estimated effective mobility has its maximum over 6000 cm 2 /(Vs). The photo-responsivity can be achieved up to mA/W. The backgate voltage tuning spectral characteristic is also observed. Heteroepitaxial graphene is a promising material for post-Si CMOS applications.
Nano- i mikrosistemnaâ tehnika, May 29, 2017
Nanophotonics, Feb 2, 2022
This paper reviews recent advances in the research and development of graphene-based plasmonic me... more 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-cellbattery 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.
Journal of Physics: Conference Series
We report on experimental and theoretical studies of nanoscale gate-lengths strained Silicon MODF... more We report on experimental and theoretical studies of nanoscale gate-lengths strained Silicon MODFETs as room temperature non resonant detectors. Devices were excited at room temperature by an electronic source at 150 and 300 GHz to characterize their sub-THz response. The maximum of the photovoltaic response was obtained when the FET gate was biased at a value close to the threshold voltage. Simulations based on a bi-dimensional hydrodynamic model for the charge transport coupled to a Poisson equation solver were performed by using Synopsys TCAD. A charge boundary condition for the floating drain contact was implemented to obtain the photovoltaic response. Results from numerical simulations are in agreement with experimental ones. To understand the coupling between terahertz radiation and devices, the devices were rotated at different angles under excitation at both sub-terahertz frequencies and their response measured. Both NEP (Noise Equivalent Power) and Responsivity were calculated from measurements. To demonstrate their utility, devices were used as sensors in a terahertz imaging system for inspection of hidden objects at both frequencies. Figure 4. Visible image (left) and terahertz ones (right) at 150/300 GHz obtained at room temperature with Device 3 with Lg = 500 nm.
Conference on Lasers and Electro-Optics, 2022
IEICE technical report. Electron devices, Dec 1, 2006
Electromagnetics Academy, 2015
ITE Technical Report, 2016
2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2018
We experimentally demonstrate terahertz light amplification by instability-driven stimulated emis... more We experimentally demonstrate terahertz light amplification by instability-driven stimulated emission of graphene plasmon polaritons in an asymmetric dual-grating-gate transistor structure. D.C. channel current driven by the drain bias voltage induces plasmon instability, alternating the electromagnetic response from the resonant absorption to the resonant amplification (up to ~ 9 % gain) beyond the threshold drain bias voltage at room temperature.
Technical report of IEICE. SDM, 2009
The Japan Society of Applied Physics, 2017
We propose a novel technology for fabricating plasmonic photoconductive antennas (PCAs) based on ... more We propose a novel technology for fabricating plasmonic photoconductive antennas (PCAs) based on superlattice (SL) with increased height of the plasmonic gratings up to 100 nm. We passivate the surface of the SL by Si3N4, etch there windows and deposit Ti/Au antenna metallization. The plasmonic gratings are formed by electron-beam lithography with Ti/Au metallization followed by lift-off. Then an Al2O3 anti-reflection coating layer for reduction of the Fresnel reflection losses is used on the top of the plasmonic gratings, which also serves for maintaining its mechanical stability and providing the excitation of guided modes at the resonant wavelengths of the subwavelength slab waveguide formed by the metal gratings. Current-voltage measurements under femtosecond laser illumination reveal strong increase of the transient photocurrent generated by the fabricated plasmonic PCA which is 15 times higher than for conventional one (i.e. without the plasmonic gratings). The obtained terahe...
The Japan Society of Applied Physics, 2016