Mitsuhiro Hanabe

Terahertz plasma wave resonance of two-dimensional electrons in InGaP/InGaAs/GaAs high-electron-mobility transistors

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 photoexcited electrons to the initial density of the 2D electrons) we clearly observed the plasma-resonant peaks at 1.9 and 5.8THz corresponding to the fundamental and third-harmonic resonance at room temperature, which is in good agreement with theory.

A grating-bicoupled plasma-wave photomixer with resonant-cavity enhanced structure

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 features electronic tuning of plasmon characteristic frequencies, providing continuously-tunable operation below 1 THz to beyond 10 THz. Frequency-dependent finite-differential time-domain analysis demonstrates that the grating-bicoupled plasmonic structure acts as a broadband terahertz photomixer and antenna and that the vertical cavity structure effectively enhances the conversion gain and radiation power.

Grating-bicoupled plasmon-resonant terahertz emitter fabricated with GaAs-based heterostructure material systems

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 terahertz electromagnetic radiation at room temperature.

Room temperature generation of terahertz radiation from a grating-bicoupled plasmon-resonant emitter: Size effect

A doubly interdigitated grating gates structure was incorporated into a GaAs-based high-electron mobility transistor to configure a plasmon-resonant emitter. Two dimensional electrons are then periodically confined in 100nm regions. The devices exhibit a plasma-wave signature under 1.5μm cw laser illumination. Two devices with different geometries have been subjected to an impulsive laser at room temperature. The authors observed clear generation of terahertz radiation from both devices.

Modulation effects of photocarriers on the terahertz plasma-wave resonance in high-electron-mobility transistors under interband photoexcitation

Two-dimensional (2-D) electron plasma in a submicron channel of a high-electron mobility transistor (HEMT) is excited by interband photoexcitation, resulting in performing the photomixing function. The injected photoelectrons modulate the total 2-D electron density, affecting the plasma resonant properties. The modulation depth of the density of 2-D electrons by the photoelectrons deeply relates to the resonant intensity and fr. This effect was modeled analytically in the 2-D plasma hydrodynamic equation. In order to validate the analytical calculation, the plasma-wave resonance was experimentally observed for a 0.15-µm gate-length InGaP/InGaAs/GaAs pseudomorphic HEMT in the terahertz range. At the modulation depth of 30%, the resonance was clearly observed with a double peak (the peak at 1.9/5.8 THz corresponding to the fundamental/third harmonic resonance). The resonant frequencies slightly shifted downward and the intensity attenuated with decreasing the modulation depth. Observed resonant frequencies support the analytical calculation.

Threshold behavior of photoinduced plasmon-resonant self-oscillation in a new interdigitated grating gates device

The new doubly interdigitated grating gate high-electron-mobility transistor (HEMT) has been subjected at room temperature to a 1.5 µm cw laser beam. The observed photoresponse shows a threshold behavior as a function of drain-to-source bias for different gate voltages. The result was interpreted as a clear signature of the self-oscillation of plasma waves.

Structure-Sensitive Design for Wider Tunable Operation of Terahertz Plasmon-Resonant Photomixer

We performed numerical analyses on structure sensitive field emission properties of our proposing plasmon resonant photomixer (PRX) in the terahertz range. The photomixer incorporates doubly interdigitated grating strips for gate electrodes and a vertical resonator structure for realizing highly efficient terahertz emission even at room temperature. We investigated the dependence of total field emission properties of PRXs on their material and dimension parameters. Introduction of low-conductive gate electrodes and ac-coupled 2D periodic plasmon gratings with depleted connecting portions are effective for expanding its lower cutoff frequency. The cutoff frequency, which is around 1.0 THz in standard metal-gates configuration, is expanded to less than 500 GHz. The output intensity could also be amplified more than double. On the other hand, a shorter vertical cavity is effective for expanding its upper cutoff frequency, which is expanded close to vertical resonant frequency, while maintaining the lower cutoff frequency. The combination of these design rules can realize much broader bandwidth operation.

Novel Plasmon-Resonant Terahertz-Wave Emitter Using a Double-Decked HEMT Structure

A new plasmon-resonant THz-wave emitter is fabricated and characterized. The heterostructure of the device consists of double-decked high electron mobility transistor (HEMT) and the upper-deck HEMT works as a grating antenna to convert the non-radiative plasmonic wave in the lower-deck HEMT channel to radiative THz electromagnetic wave. This conversion can be done more efficiently than a metal grating antenna. The experimental observed clear evidence of the THz-wave emission from the double-decked HEMT device.

A Grating-Bicoupled Plasmon-Resonant Terahertz Emitter Fabricated with GaAs-Based Heterostructure Metamaterial Systems

A grating-bicoupled plasmon-resonant terahertz emitter was fabricated using GaAs-based heterostructure metamaterial systems. Photo-excited electrons, injected to the two-dimensional plasmon cavities, promoted the plasmon instability, resulting in the first observation of terahertz emission at room temperature.

A novel terahertz plasma-wave photomixer with resonant-cavity enhanced structure

Two-dimensional (2D) plasmon in a submicron transistor channel can make resonant oscillation in the terahertz range. We propose a novel terahertz plasma-wave photomixer that can improve the conversion gain and terahertz radiation power. The photomixer is based on a high-electron mobility transistor (HEMT) and incorporates doubly interdigitated grating strips for the gate electrodes that periodically localize the 2D plasmons in sub 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. FDTD simulation demonstrates that a newly-introduced vertical cavity structure effectively enhances the conversion gain and radiation power.