Taiichi Otsuji

Abstract Graphene is a one-atom-thick planar sheet of a honeycomb carbon crystal. Its gapless and linear energy spectra of electrons and holes lead to nontrivial features such as giant carrier mobility and broadband flat optical response. In this paper, recent advances in graphene-based devices in terahertz science and technology are reviewed. First, the fundamental basis of the optoelectronic properties of graphene is introduced. Second, synthesis and crystallographic characterization of graphe

We have observed the frequency dependence of the plasma resonant intensity in the terahertz range for a short gate-length InGaP∕InGaAs∕GaAs pseudomorphic high-electron-mobility transistor. The plasma resonance excitation was performed by means of interband photoexcitation using the difference-frequency component of a photomixed laser beam. Under sufficient density of two-dimensional (2D) conduction electrons (>1012cm−2) and a moderate modulation index (the ratio of the density of photoexc

The terahertz (THz) range is the next frontier of electronics and optoelectronics with potential applications ranging from imaging, space communications, computing, quality control, and homeland security to biotechnology and medicine. At THz frequencies, the electron inertia becomes important, providing delay between the applied voltage and electron velocity and current. When the electron collisions with impurities and lattice vibrations are infrequent, this delay leads to oscillations of the el

This paper reviews recent advances in graphene active plasmonics for terahertz (THz) device applications. Two-dimensional plasmons in graphene exhibit unique optoelectronic properties and mediate extraordinary light–matter interactions. It has been discovered theoretically that when the population of Dirac fermionic carriers in graphene are inverted by optical or electrical pumping, the excitation of graphene plasmons by the THz photons results in propagating surface plasmon polaritons with gian

Recent advances in emission and detection of terahertz radiation using two-dimensional (2D) electron systems in III–V semiconductors and graphene are described. First the 2D plasmon resonance is presented to demonstrate intense broadband terahertz emission and detection from InGaP/InGaAs/GaAs and InAlAs/InGaAs/InP material systems. The device structure is based on a high-electron mobility transistor and incorporates the author's original asymmetrically interdigitated dual-grating gates. Second t

A novel terahertz plasma-wave photomixer that can improve the conversion gain and terahertz radiation power is proposed and evaluated. The photomixer is based on a high-electron mobility transistor and incorporates doubly interdigitated grating strips for the gate electrodes that periodically localize the 2D plasmons in 100-nm regions with a micron-order interval. A vertical cavity structure is formed in between the top metal grating and a terahertz mirror placed at the backside. The device feat

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 or recombination dynamics in optically or electrically pumped graphene is described to introduce a possibility of negative dynamic conductivity in a wide terahertz range. Third, recent theoretical advances toward the creation of current-inject

This paper reviews recent advances in our original 2D-plasmon-resonant terahertz emitters. The structure is based on a high-electron-mobility transistor and featured with doubly interdigitated grating gates. The dual grating gates can alternately modulate the 2D electron densities to periodically distribute the plasmonic cavities along the channel, acting as an antenna. The device can emit broadband terahertz radiation even at room temperature from self-oscillating 2D plasmons under the DC-biase

A pulse-rate-tunable, highly extinctive, ultra-highspeed electrooptic pulse pattern generator has been developed. The optical short pulse generation is based on sinusoidal electrooptic phase modulation and linear chirp compensation using a dispersive medium. Filtering the nonlinear chirp components generated by sinusoidal phase modulation drastically improves the pulse extinction, and makes nearly background-free picosecond pulsation over a wide pulse-rate range even when the group delay dispers

We report on the first experimental observation of terahertz emission and detection in a double graphene layered (GL) heterostructure which comprises a thin hexagonal-boron nitride tunnel-barrier layer sandwiched between two separately contacted GLs. Inter-GL population inversion is induced by electrically biasing the structure. Resonant tunneling and negative differential resistance is expected when the two graphene band structures are perfectly aligned. However, in the case of small misalignme

Abstract A distributed feedback dual‐gate graphene‐channel field‐effect transistor (DFB‐DG‐GFET) was fabricated as a current‐injection terahertz (THz) light‐emitting laser transistor. We observed a broadband emission in a 1–7.6‐THz range with a maximum radiation power of ~10 μW as well as a single‐mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar

A grating-bicoupled plasmon-resonant terahertz emitter was fabricated using InGaP∕InGaAs∕GaAs heterostructure material systems. The device structure is based on a high-electron mobility transistor and incorporates doubly interdigitated grating gates that periodically localize the two-dimensional (2D) plasmon in 100nm regions with a submicron interval. Photoexcited electrons, injected to the 2D plasmon cavities, extensively promoted the plasmon instability, resulting in observation of emission of

This paper describes the design and performance of an 80-Gbit/s 2:1 selector-type multiplexer IC fabricated with InAlAs/InGaAs/InP HEMTs. By using a double-layer interconnection process with a low-dielectric insulator, microstrip lines were designed to make impedance-matched, high-speed intercell connection of critical signal paths. The record operating data rate was measured on a 3-in wafer. In spite of the bandwidth limitation on the measurement setup, clear eye patterns were successfully obse

This paper describes a novel dynamic flip-flop (FF) circuit that can operate 30% faster than conventional clocked inverter-type FFs. A new wideband clock buffer is introduced to cover the FF operation range. An 8- to 24-Gb/s decision circuit and a 9- to 26-GHz 1/2 frequency divider were developed utilizing production-level 0.2-/spl mu/m GaAs MESFET technology.

Terahertz (THz) wave detectors include Golay cells, bolometers, pyroelectric detectors, superconductor tunnel junction detectors (STJs), and Schottky-barrier diodes (SBDs). Of these, most (except STJs and SBDs) are of the thermoelectric type; they are highly sensitive, but the response speed is low. On the other hand, in SBDs operating at room temperature, the response is fast, but the sensitivity is rather low at high frequencies; this is due to the carrier transit-time effect. Therefore, a non