Abstract-Negative terahertz conductivity at vertical carrier injection in a black-Arsenic-Phosphorus-Graphene heterostructure integrated with a light-emitting diode

Victor Ryzhii, Maxim Ryzhii, Taiichi Otsuji, Valery E. Karasik, Vladimir G. Leiman, Vladimir Mitin, Michael S.Shur

https://arxiv.org/abs/1901.10755

We propose and analyze the heterostructure comprising a black-arsenic-phosphorus layer (b-As1−xPxL) and a graphene layer (GL) integrated with a light-emitting diode (LED). The integrated b-As1−xPxL-GL-LED heterostructure can serve as an active part of the terahertz (THz) laser using the interband radiative transitions in the GL. The feasibility of the proposed concept is enabled by the combination of relatively narrow energy gap in the b-As1−xPxL and the proper band alignment with the GL. The operation of the device in question is associated with the generation of the electron-hole pairs by the LED emitted near-infrared radiation in the b-As1−xPxL, cooling of the photogenerated electrons and holes in this layer, and their injection into the GL. Since the minimum b-As1−xPL energy gap is smaller than the energy of optical phonons in the GL, , the injection into the GL can lead to a relatively weak heating of the two-dimensional electron-hole plasma (2D-EHP) in the GL. At the temperatures somewhat lower than the room temperature, the injection can cool the 2D-EHP. This is beneficial for the interband population inversion in the GL, reinforcement of its negative dynamic conductivity, %in the THz range and the realization of the optical and plasmonic modes lasing supporting the new types of the THz radiation sources.

Abstract-Negative and positive terahertz and infrared photoconductivity in uncooled graphene

Victor Ryzhii, Dmitry S. Ponomarev, Maxim Ryzhii, Vladimir Mitin, Michael S. Shur, and Taiichi Otsuji

Fig. 1 Upper panel: the normalized carrier temperature variation (T − T0)/T0 (dashed lines) for different values of the parameter b (upper panel) and τ0 = 1 ps and the quasi-Fermi energy μ/T (solid line) for b = 0.1 and τ0 = 1 ps. Lower panel: the normalized carrier temperature variation (T − T0)/T0 (dashed line) for b = 0.1 and τ0 = 1 ps and the quasi-Fermi energy μ/T (solid lines) for b = 1 and different τ0.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-2-585

We develop the model for the terahertz (THz) and infrared (IR) photoconductivity of graphene layers (GLs) at room temperature. The model accounts for the linear GL energy spectrum and the features of the energy relaxation and generation-recombination mechanisms inherent at room temperature, namely, the optical phonon absorption and emission and the Auger interband processes. Using the developed model, we calculate the spectral dependences of the THz and IR photoconductivity of the GLs. We show that the GL photoconductivity can change sign depending on the photon frequency, the GL doping and the dominant mechanism of the carrier momentum relaxation. We also evaluate the responsivity of the THz and IR photodetectors using the GL photoconductivity. The obtained results along with the relevant experimental data might reveal the microscopic processes in GLs, and the developed model could be used for the optimization of the GL-based photodetectors.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Electrical modulation of terahertz radiation using graphene-phosphorene heterostructures

Victor Ryzhii, Taiichi Otsuji, Maxim Ryzhii, Dmitry Sergeevich Ponomarev, Valerij Karasik, Vladimir Leiman, Vladimir Mitin,  Michael Shur,

http://iopscience.iop.org/article/10.1088/1361-6641/aae9b2

We analyze the electrical modulation of the terahertz (THz) radiation associated with the carrier heating in the graphene-phosphorene (GP) heterostuctures. The heating of the carriers leads to the transfer of a significant fraction 
 of the light carriers in the G-layer to the P-layer with a relatively large carrier effective mass.
 This might result in a dramatic decrease in the conductivity of the GP-channel
 that could be used to modulate
 the incident THz radiation. We demonstrate that the depth of the THz radiation modulation can be large in relatively wide range of the modulation frequencies.

Abstract-Terahertz-wave generation using graphene: Toward new types of terahertz lasers

Taiichi Otsuji, Stephane Boubanga Tombet, Akira Satou, Maxim Ryzhii, Victor Ryzhii

https://ieeexplore.ieee.org/document/6516886/

This paper reviews recent advances in terahertz-wave generation in graphene toward the creation of new types of terahertz lasers. First, fundamental basis of the optoelectronic properties of graphene is introduced. Second, nonequilibrium carrier relaxation and recombination dynamics in optically or electrically pumped graphene are described to introduce a possibility of negative dynamic conductivity in a wide terahertz range. Third, recent theoretical advances toward the creation of current-injection graphene terahertz lasers are described. Fourth, unique terahertz dynamics of the 2-D plasmons in graphene are described. Finally, the advantages of graphene materials and devices for terahertz-wave generation are summarized.

Abstract-Nonlinear response of infrared photodetectors based on van der Waals heterostructures with graphene layers

Victor Ryzhii, Maxim Ryzhii, Dmitry Svintsov, Vladimir Leiman, Vladimir Mitin, Michael S. Shur, and Taiichi Otsuji

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-5-5536&origin=search

We report on the device model for the infrared photodetectors based on the van der Waals (vdW) heterostructures with the radiation absorbing graphene layers (GLs). These devices rely on the electron interband photoexcitation from the valence band of the GLs to the continuum states in the conduction band of the inter-GL barrier layers. We calculate the photocurrent and the GL infrared photodetector (GLIP) responsivity at weak and strong intensities of the incident radiation and conclude that the GLIPs can surpass or compete with the existing infrared and terahertz photodetectors. The obtained results can be useful for the GLIP design and optimization.

© 2017 Optical Society of America

Abstract-Terahertz LED based on current injection dual-gate graphene-channel field effect transistors

 Deepika Yadav, Youssef Tobah,  Kenta Sugawara,  Junki Mitsushio,   Gen Tamamushi,  Takayuki Watanabe, Alexander A. Dubinov,  Maxim Ryzhii,  Victor Ryzhii,  Taiichi Otsuji

http://ieeexplore.ieee.org/document/7999519/

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.

Abstract-Broadband Terahertz-Light Emission by Current-Injection Distributed-Feedback Dual-Gate Graphene-Channel Field-Effect Transistor

Deepika Yadav, Youssef Tobah, Gen Tamamushi, Junki Mitsushio, Takayuki Watanabe, Alexander Dubinov, Maxim Ryzhii, Victor Ryzhii, and Taiichi Otsuji

https://www.osapublishing.org/abstract.cfm?uri=CLEO_AT-2017-AM2B.7

Observed spontaneous THz emission(1-7.6THz) at 100K by current injection in distributed-feedback dual-gate graphene transistor. We saw nonlinear threshold-like behavior w.r.t the current-injection level. Precise DFB cavity design is expected to transcend spontaneous emission to stimulated emission.

© 2017 OSA

Abstract-Challenges to create graphene terahertz lasers

Taiichi Otsuji1, Akira Satou1, Maxim Ryzhii2, Vyachaslav Popov3, Vladimir Mitin4 and Victor Ryzhii1

otsuji@riec.tohoku.ac.jp

1 Research Institute of Electrical Communication, Tohoku University, Japan
2 Computational Nano-Electronics Laboratoty, University of Aizu, Japan
3 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), RAS, Russia
4 Department of Electrical Engineering, University at Buffalo, SUNY, USA
http://iopscience.iop.org/1742-6596/486/1/012007;jsessionid=590E7E5B537BB812B7FF197D7794D0D8.c2

The gapless, linear energy spectrum of graphene can lead to population inversion and negative dynamic conductivity in the terahertz range when graphene is optically or electrically pumped, which makes it possible to create a new type of graphene terahertz lasers. This paper reviews recent advances in scientific challenges to create graphene-based terahertz lasers.

Abstract-Double-graphene-layer terahertz laser: concept, characteristics, and comparison

My note: The entire article can be read for free online, at the posted link.

Victor Ryzhii, Alexander A. Dubinov, Taiichi Otsuji, Vladimir Ya. Aleshkin, Maxim Ryzhii, and Michael Shur  »View Author Affiliations
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-21-25-31567&id=276087

We propose and analyze the concept of injection terahertz (THz) lasers based on double-graphene-layer (double-GL) structures utilizing the resonant radiative transitions between GLs. We calculate main characteristics of such double-GL lasers and compare them with the characteristics of the GL lasers with intra-GL interband transitions. We demonstrate that the double-GL THz lasers under consideration can operate in a wide range of THz frequencies and might exhibit advantages associated with the reduced Drude absorption, weaker temperature dependence, voltage tuning of the spectrum, and favorable injection conditions.