Abstract-Current-injection terahertz lasing in a distributed-feedback dual-gate graphene-channel transistor

G. Tamamushi,  T. Watanabe,  J. Mitsushio,  A. A. Dubinov,  A. Satou, T. Suemitsu,  M. Ryzhii,  V. Ryzhii,  T. Otsuji

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10111/1011126/Current-injection-terahertz-lasing-in-a-distributed-feedback-dual-gate/10.1117/12.2249983.pdf?SSO=1

This paper reviews recent advancement on the research toward graphene-based terahertz (THz) lasers. Optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the THz spectral range, which may lead to new types of THz lasers. A forward-biased graphene structure with a lateral p-i-n junction was implemented in a distributed-feedback (DFB) dual-gate graphene-channel FET and observed a single mode emission at 5.2 THz at 100K. The observed spectral linewidth fairly agrees with the modal gain analysis based on DFB-Fabry-Perrot hybrid-cavitymode modeling. Although the results obtained are still preliminary level, the observed emission could be interpreted as THz lasing in population-inverted graphene by carrier-injection.

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Abstract-Graphene vertical hot-electron terahertz detectors

V. Ryzhii^1,2,a), A. Satou¹, T. Otsuji¹, M. Ryzhii³, V. Mitin⁴ and M. S. Shur⁵
http://scitation.aip.org/content/aip/journal/jap/116/11/10.1063/1.4895738
1 Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577, Japan
2 Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University and Institute of Ultra High Frequency Semiconductor Electronics, Russian Academy of Sciences, Moscow 111005, Russia
3 Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu 965-8580, Japan
4 Department of Electrical Engineering, University at Buffalo, Buffalo, New York 1460-1920, USA
5 Departments of Electrical, Electronics, and Systems Engineering and Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA
a) Electronic mail: v-ryzhii@riec.tohoku.ac.jp
J. Appl. Phys. 116, 114504 (2014); http://dx.doi.org/10.1063/1.4895738

We propose and analyze the concept of the vertical hot-electron terahertz (THz) graphene-layerdetectors (GLDs) based on the double-GL and multiple-GL structures with the barrier layers made of materials with a moderate conduction band off-set (such as tungsten disulfide and related materials). The operation of these detectors is enabled by the thermionic emissions from the GLs enhanced by the electrons heated by incoming THz radiation. Hence, thesedetectors are the hot-electron bolometric detectors. The electron heating is primarily associated with the intraband absorption (the Drude absorption). In the frame of the developed model, we calculate the responsivity and detectivity as functions of the photon energy, GL doping, and the applied voltage for the GLDs with different number of GLs. The detectors based on the cascade multiple-GL structures can exhibit a substantial photoelectric gain resulting in the elevated responsivity and detectivity. The advantages of the THz detectors under consideration are associated with their high sensitivity to the normal incident radiation and efficient operation at room temperature at the low end of the THz frequency range. Such GLDs with a metal grating, supporting the excitation of plasma oscillations in the GL-structures by the incident THz radiation, can exhibit a strong resonant response at the frequencies of several THz (in the range, where the operation of the conventional detectors based on A3B5 materials, in particular, THz quantum-well detectors, is hindered due to a strong optical phonon radiation absorption in such materials). We also evaluate the characteristics of GLDs in the mid- and far-infrared ranges where the electron heating is due to the interband absorption in GLs.

Abstract-Graphene vertical hot-electron terahertz detectors

V. Ryzhii, A. Satou, T. Otsuji, M.Ryzhii, V. Mitin, M.S. Shur

http://arxiv-web3.library.cornell.edu/abs/1409.0616

We propose and analyze the concept of the vertical hot-electron terahertz (THz) graphene-layer detectors (GLDs) based on the double-GL and multiple-GL structures with the barrier layers made of materials with a moderate conduction band off-set (such as tungsten disulfide and related materials). The operation of these detectors is enabled by the thermionic emissions from the GLs enhanced by the electrons heated by incoming THz radiation. The electron heating is primarily associated with the intraband absorption (the Drude absorption). We calculate the responsivity and detectivity as functions of the photon energy, GL doping, and the applied voltage for the GL detectors (GLDs) with different number of GLs. The detectors based on the cascade multiple-GL structures can exhibit a substantial photoelectric gain resulting in the elevated responsivity and detectivity. The advantages of the THz detectors under consideration are associated with their high sensitivity to the normal incident radiation and efficient operation at room temperature at the low end of the THz frequency range. Such GLDs with a metal grating, supporting the excitation of plasma oscillations in the GL-structures by the incident THz radiation, can exhibit a strong resonant response at the frequencies of several THz (in the range, where the operation of the conventional detectors based on A3B5 materials, in particular THz quantum-well detectors, is hindered due to a strong optical phonon radiation absorption in such materials).

Abstract-Current-driven detection of terahertz radiation using a dual-grating-gate plasmonic detector

S. Boubanga-Tombet^1,a), Y. Tanimoto¹, A. Satou¹, T. Suemitsu¹, Y. Wang²,H. Minamide², H. Ito², D. V. Fateev^3,4, V. V. Popov^3,4 and T. Otsuji¹
 HIDE AFFILIATIONS
1 Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai 980-8577, Japan
2 RIKEN Sendai, 519-1399 Aramaki Aoba, Aoba-ku, Sendai 980-0845, Japan
3 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), 410019 Saratov, Russia
4 Saratov State University, 410012 Saratov, Russia
a) Author to whom correspondence should be addressed. Electronic mail: stephanealbon@hotmail.com
Appl. Phys. Lett. 104, 262104 (2014); http://dx.doi.org/10.1063/1.4886763

We report on the detection of terahertz radiation by an on-chip planar asymmetric plasmonicstructure in the frequency region above one terahertz. The detector is based on a field-effect transistor that has a dual grating gate structure with an asymmetric unit cell, which provides a geometrical asymmetry within the structure. Biasing the detector with a dc source-to-drain current in the linear region of the current-voltage characteristic introduces an additional asymmetry (electrical asymmetry) that enhances the detector responsivity by more than one order of magnitude (by a factor of 20) as compared with the unbiased case due to the cooperative effect of the geometrical and electrical asymmetries. In addition to the responsivity enhancement, we report a relatively low noise equivalent power and a peculiar non-monotonic dependence of the responsivity on the frequency, which results from the multi-plasmonic-cavity structure of the device.

Abstract-Damping of Terahertz Plasmons in Graphene Coupled with Surface Plasmons in Heavily-Doped Substrate

A. Satou, Y. Koseki, V. Ryzhii, V. Vyurkov, T. Otsuji

(Submitted on 15 Jan 2014)

http://arxiv.org/abs/1401.3396

Coupling of plasmons in graphene at terahertz (THz) frequencies with surface plasmons in a heavily-doped substrate is studied theoretically. We reveal that a huge scattering rate may completely damp out the plasmons, so that proper choices of material and geometrical parameters are essential to suppress the coupling effect and to obtain the minimum damping rate in graphene. Even with the doping concentration 10^{19} - 10^{20} cm^{-3} and the thickness of the dielectric layer between graphene and the substrate 100 nm, which are typical values in real graphene samples with a heavily-doped substrate, the increase in the damping rate is not negligible in comparison with the acoustic-phonon-limited damping rate. Dependence of the damping rate on wavenumber, thicknesses of graphene-to-substrate and gate-to-graphene separation, substrate doping concentration, and dielectric constants of surrounding materials are investigated. It is shown that the damping rate can be much reduced by the gate screening, which suppresses the field spread of the graphene plasmons into the substrate.

Abstract-Threshold of Terahertz Population Inversion and Negative Dynamic Conductivity in Graphene Under Pulse Photoexcitation

 http://arxiv.org/abs/1210.6704

We theoretically study the population inversion and negative dynamic conductivity in intrinsic graphene in the terahertz (THz) frequency range upon pulse photoexcitation with near-/mid-infrared wavelength. The threshold pulse energy required for the population inversion and negative dynamic conductivity can be orders-of-magnitude lower when the pulse photon energy is lower, due to the inverse proportionality of the photoexcited carrier concentration to the pulse photon energy and to the weaker carrier heating. We also investigate the dependence of the dynamic conductivity on the momentum relaxation time. The negative dynamic conductivity takes place either in high- or low-quality graphene, where the Drude absorption by carriers in the THz frequency is weak.

Abstract: Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

http://prb.aps.org/abstract/PRB/v85/i3/e035443

Received 5 April 2011; revised 11 November 2011; published 26 January 2012

We report, within a picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons and holes in an exfoliated graphene under infrared pulse excitation. We conduct time-domain spectroscopic studies using an optical pump and terahertz probe with an optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold-like behavior, testifying to the occurrence of the negative conductivity and the population inversion. The phase behavior of the measured terahertz electric field also shows clear Lorentzian-like normal dispersion around the gain peak, testifying to the amplification that can be attributed to stimulated emission of photocarriers in the inverted states. The emission spectra clearly narrow at a longer terahertz probe delay time, giving evidence that the quasi-Fermi energy moves closer to the equilibrium at this longer terahertz probe delay time.

©2012 American Physical Society

URL:

http://link.aps.org/doi/10.1103/PhysRevB.85.035443

DOI:

10.1103/PhysRevB.85.035443

PACS:

78.45.+h, 78.47.D-, 78.66.Tr, 78.70.-g

^*stephanealbon@hotmail.com

Abstract:Ultrafast carrier dynamics and terahertz emission in optically pumped graphene at room temperature

S. Boubanga-Tombet, S. Chan, A. Satou, V. Ryzhii, and T. Otsuji

http://prb.aps.org/accepted/B/8d071Y6cQf41b62629da6ff57cc914dfee7cb4880

We report within picosecond time scale, fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an exfoliated graphene under infrared pulse excitation. We conduct time domain spectroscopic studies using an optical pump/terahertz probe and optical probe technique and show that graphene sheet amplifies an incoming terahertz field. The graphene emission spectral dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion. The phase behavoir of the measured Terahertz electric field also show clear Lorentzian-like normal dispersion around the gain peak, testifying the occurrence of amplification that can be attributed to stimulated emission of photo-carriers in the inverted states. The emission spectra also show a clear narrowing at longer terahertz probe delay time giving a clear evidence of the quasi-fermi energy moving closer to the equilibrium at this longer terahertz probe delay time.