Yuki Kurita

Ultrahigh sensitive sub-terahertz detection by InP-based asymmetric dual-grating-gate high-electron-mobility transistors and their broadband characteristics

We report on room-temperature plasmonic detection of sub-terahertz radiation by InAlAs/InGaAs/InP high electron mobility transistors with an asymmetric dual-grating-gate structure. Maximum responsivities of 22.7 kV/W at 200 GHz and 21.5 kV/W at 292 GHz were achieved under unbiased drain-to-source condition. The minimum noise equivalent power was estimated to be 0.48 pW/Hz0.5 at 200 GHz at room temperature, which is the record-breaking value ever reported for plasmonic THz detectors. Frequency dependence of the responsivity in the frequency range of 0.2–2 THz is in good agreement with the theory.

Threshold of terahertz population inversion and negative dynamic conductivity in graphene under pulse photoexcitation

We present a theoretical study of population inversion and negative dynamic conductivity in intrinsic graphene in the terahertz (THz) frequency range upon pulse photoexcitation at near-/mid-infrared wavelengths. The threshold pulse fluence required for population inversion and negative dynamic conductivity can be orders of magnitude lower when the pulse photon energy is lower, because of the inverse proportionality of the photoexcited carrier concentration to the pulse photon energy and because of the weaker carrier heating. We also investigate the dependence of dynamic conductivity on momentum relaxation time. Negative dynamic conductivity takes place either in high- or low-quality graphene, where Drude absorption by carriers in the THz frequency is weak.

Plasmonic terahertz monochromatic coherent emission from an asymmetric chirped dual-grating-gate InP-HEMT with a photonic vertical cavity

We designed and fabricated InP-based high electron mobility transistors featuring an asymmetric chirped dual-grating-gate structure with a resonant-enhanced photonic vertical cavity. The device structure greatly enhances the Doppler-effect-driven plasma instability, resulting in intense monochromatic superradiant terahertz emission at 3.55 THz at 140K for the first time.

Extremely-high sensitive terahertz detector based on dual-grating gate InP-HEMTs

We report on an extremely-high sensitive terahertz (THz) detector based on our original asymmetric dual-grating gate high electron mobility transistors (A-DGG HEMTs) designed and fabricated using InAlAs/InGaAs/InP material systems. The obtained responsivity is 22.7 kV/W at 200 GHz. To the best of our knowledge, this value is the record responsivity ever reported for this frequency range at room temperature.