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Asymmetric-dual-grating-gate high-electron-mobility-transistors (ADGG-HEMTs) are expected for on-chip, sensitive, room-temperature operating, high-speed THz detectors. In this paper, we experimentally verify the high-speed response of an ADGG-HEMT by measuring its response to THz pulse generated from an injection-seeded THz-wave parametric generator (is-TPG). From the pulse response waveform of the...
We examine array configuration and silicon-lens integration of asymmetric-dual-grating-gate high-electron-mobility transistors (A-DGG HEMTs) as plasmonic terahertz detectors in order to enhance their external coupling efficiencies. We demonstrate 4-fold enhancement of the efficiency by an array of four series-connected detectors and 6-fold enhancement by the hyper-hemispherical silicon-lens integration...
We experimentally verify that the low external responsivity of nanostructured asymmetric-dual-grating-gate high-electron-mobility transistors (A-DGG HEMTs) as plasmonic terahertz detectors developed so far is attributed to their low external coupling efficiency. We separately demonstrate (1) 4-fold enhancement of the efficiency by an array of series-connected 4×1 detectors due to the increase in the...
After the Fukushima Dai-ichi nuclear accident, a need for assuring safety of fusion energy has grown in the Japanese (JA) fusion research community. DEMO safety research has been launched as a part of Broader Approach DEMO Design Activities (BA-DDA). This paper reports progress in the fusion DEMO safety research conducted under BA-DDA. Safety requirements and evaluation guidelines have been, first...
We report on room-temperature plasmonic detection of the thermal emission from a black body in the terahertz and mid-infrared domains by dual-grating-gate InAlAs/InGaAs/InP high electron mobility transistors (HEMTs). In such detectors, the asymmetric grating gate of a large area acts as an effective antenna that improves the performance in the two spectral domains.
We theoretically discovered and experimentally manifested that the carrier population inversion in graphene results in stimulating emission of plasmons with a giant gain, leading to superradiant terahertz lasing from a structured graphene.
We numerically study frequency dispersion and damping mechanisms of plas-mons in graphene transistor structures. We investigate the gate-voltage tunability of plasmon frequencies and the damping due to the carrier scattering with disorders and acoustic phonons.
Graphene, a monolayer carbon-atomic honeycomb lattice crystal, has attracted attention due to its peculiar carrier transport properties owing to the massless and gapless energy spectrum. Optical and/or injection pumping of graphene can exhibit negative-dynamic conductivity in the terahertz (THz) spectral range, which may bring new types of THz lasers. This paper reviews recent advances in terahertz...
We propose and analyze an electro-optical modulator based on a gated graphene structure and utilizing the electrically-controlled Pauli blocking. It is demonstrated that the resonant excitation of plasma oscillations can lead to a substantial enhancement of the modulation efficiency in the terahertz range of modulation frequencies.
We conduct time domain spectroscopy studies and shows that graphene sheet amplifies an incoming terahertz field. The graphene emission spectra dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion in the terahertz range, paving the way for a new class room temperature graphene based terahertz lasers.
We overview novel concepts of terahertz and infrared interband detectors and lasers based on single- and multiple-graphene layer structures and discuss the features of their operation and feasibility of realization.
The gapless and linear energy spectra of electrons and holes in graphene lead to nontrivial features such as negative dynamic conductivity in the terahertz spectral range. This paper reviews recent advances in theoretical and experimental study on terahertz light amplification by stimulated emission of radiation in optically pumped graphene.
We study nonequilibrium carriers (electrons and holes) in an intrinsic graphene at low temperatures under infrared optical pumping. We calculate the energy distributions of carriers using a quasi-classical kinetic equation. It is found that the nonequilibrium distributions are determined by an interplay between weak energy relaxation on acoustic phonons and generation-recombination processes as well...
We study plasma waves in a high-electron-mobility transistor (HEMT) structure by numerical simulation using the kinetic electron transport model. We find that the plasma waves in the gated section of the channel can damp even without the electron collisions with impurities and phonons. The damping is related to the thermal spread of the electron velocity. We also show that the ungated sections of...
We study the effect of side contacts on plasma oscillations in two-dimensional (2D) electron systems by numerical simulation. Our model is based on the kinetic electron transport equation and the self-consistent Poisson equation. We find that the contacts absorb the energy of plasma oscillations excited in the 2D electron channel and consequently this effect can be a dominant damping mechanism, surpassing...
We observed and characterized broadband terahertz emission from our original plasmon-resonant emitter structured by dual-grating gate high electron mobility transistors (HEMT's). The samples are fabricated in two structures: a standard single-heterostructure HEMT with metallic grating gates and a double-decked (DD) HEMT with semiconducting 2-dimensional electron gas (2DEG) grating gates. The mechanism...
The plasma waves in graphene- based heterostuctures can be used in novel devices for generation, frequency multiplication, and detection of terahertz radiation surpassing the devices made of A3B5 heterostructures. The dynamic AC conductivity in optically pumped graphene can be negative in a certain range (terahertz) of frequencies. This can lead to the self-excitation of terahertz plasma waves followed...
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