JSPS KAKENHI Grant-in-Aid for Sci. Rsch. (S) Creation of 2D-Atomically-Thin-Layered Heterojunctions and their Applications to Novel Terahertz Photonic Devices

[Purpose and Background of the Research]
Terahertz (THz) is an unexplored electromagnetic frequency band in which conventional electronic and photonic devices cannot operate well due to the substantial physical limitations originating from the transit time delays and/or phonon decoherence. In such a situation, graphene, a carbon atomic monolayer sheet, has attracted attention thanks to its extremely high carrier transport properties of relativistic Dirac Fermions. Recently, study on atomically thin van der Waals (vdW) heterostructures consisting of graphene, h-BN, and/or transition-metal dichalcogenide (TMD) like MoS2 has been emerging. We theoretically found that a gated double-graphene-layered (G-DGL) heterostructure can mediate THz photon- and plasmon-assisted resonant tunneling between the GLs, enabling various functionalities in the THz domain with extremely higher quantum efficiencies by orders than ever. The key to make them in practical engineering is to develop the continuous hetero-epitaxial growth (C-H-Epi-G) technology.

This research project proposal has been accepted as a 5-year-term new theme of 2016 JSPS KAKENHI, Grant-in-Aid for Scientific Research (S), and is aimed to create the C-H-Epi-G technology for the 2D vdW heterojunction systems, and to devise highly efficient various THz functional devices by exploiting unprecedented physical phenomena exhibited among their complex quantum systems governed by electrons, photons, plasmons, as well as phonons (Fig. 1).

Fig.1

Fig. 1 Nonlinear complex quantum phenomena in G-DGL vdW heterojunctions and their applications to THz functional devices.

[Research Methods]
First, the G-DGL structure consisting of the DGL core shell and the external gate is created as the platform of device implementation. Second, the photon-assisted and plasmon-assisted resonant tunneling are introduced into the G-DGL as the physical operation mechanisms to manifest the advantage of the performances of THz amplification, oscillation, detection, and nonlinear wave control over the existing technologies. Third, the double resonance of the graphene plasmons and the tunneling is introduced as an advanced physical operation mechanism to obtain further improved performances of these functionalities (Fig. 2).

Fig.2

Fig. 2 Photon- and plasmon-assisted resonant tunneling in the G-DGLs for THz emit ters. Its atomically scaled bird' s view image (left) and a corresponding band diagram (right). By emitting photons whose energy is equal to the band offset Δ, all the excess electrons in the n-type GL can resonantly tunnel to the p-type GL throughout the h-BN tunnel barrier layer.

[Research Organization]
To conduct this cutting-edge research project we organize a nicest team in collaboration among the author's group at RIEC, Tohoku Univ. (PI and two Co-Pls, device modeling, process, and experiments), Assoc. Prof. H. Fukidome's group at RIEC, Tohoku Univ. (Co-PI, growth and characterization of high quality epitaxial graphene), Assoc. Prof. M. Ryzhii's group at Univ. Aizu (Co-PI, device modeling), and Dr. S. Suzuki's group at NTT Basic Research Laboratory (Co-PI, C-H-Epi-G of h-BN and TMDs with graphene). Young researchers and graduate students as well as international partners are also involved in the research as important supporting members in this project (Fig. 3).

Fig.3

Fig. 3 Research organization. PD: PosDoc researcher, DC: Doctor Course student, and MC: Master Course student.

[Expected Research Achievements and Scientific Significance]
Introduction of unprecedented physical mechanisms of complex quantum systems in the G-DGL is unique and has a great merit and impact to enable ultra-highly efficient THz functionalities. If successful this study, 100-Gbit/s-class ultra-fast THz wireless communications, such as Transfer-Jet that can transfer ultra-highcapacity media instantly, is expected to bring industrial revolution to the future of ubiquitous ICT societies

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