S. Komiyama

The University of Tokyo, Tōkyō, Japan

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Publications (218)489.02 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-highly-sensitive far-infrared detectors are developed for potential application to astronomy. The detectors exploit a novel mechanism called Charge Sensitive Infrared Phototransistors (CSIPs), in which an upper quantum well (QW) in GaAs/AlGaAs double QW structures is positively charged up by photo-excitation via inter-subband transition. This causes the conductance of the lower QW channel to increase. The device is effectively a phototransistor, in which the upper QW serves as a photo-sensitive gate to the source-drain channel provided by the lower QW. Resultant extraordinary high photoconductive gain makes CSIPs so sensitive as to detect single photons. CSIPs are well established in the mid-infrared (λ = 12-20 \upmu m), achieving noise equivalent power around 1.9 × 10^{-19} W/Hz^{1/2} with a quantum efficiency of 7 %. CSIPs have been demonstrated to work in longer wavelengths up to 45 \upmu m, but the sensitivity was not as high as in the shorter wavelengths, probably due to lower quantum efficiency. Reported here is a remarkable improvement in the performance of longer wavelength CSIPs (45 \upmu m), achieved primarily by optimizing the doping concentration in the upper QW. This work indicates that longer wavelength CSIPs are promising detectors for the astronomical application.
    Journal of Low Temperature Physics 01/2014; 176(3-4). DOI:10.1007/s10909-014-1140-6 · 1.04 Impact Factor
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    ABSTRACT: A plasmonic coupler, which consists of periodic metal gratings and a tapered waveguide, is integrated to a charge-sensitive infrared phototransistor (CSIP) for 45 µm wavelength radiation. The period and height of the gratings are about 42 µm and 4 µm, respectively. The gratings convert normally incident radiation into a surface wave, which is converged to the active region of the CSIP through the tapered waveguide. Both rise rate and signal amplitude become larger, due to the presence of the plasmonic coupler.
    Journal of Physics D Applied Physics 04/2013; 46(16):165107. DOI:10.1088/0022-3727/46/16/165107 · 2.52 Impact Factor
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    ABSTRACT: Semiconductor charge-sensitive infrared phototransistors (CSIPs) based on quantum wells are described. They are the only detectors that are able to count single photons in the terahertz region at present. In terms of the noise equivalent power (NEP), the detectors show experimental values of 7 × 10−20 W/Hz1/2, while theoretically expected values are even much lower. These NEP values are by several orders of magnitude lower than any other state-of-the-art highly sensitive detectors. In addition to the outstanding sensitivity, the detectors are featured by strong advantage of huge current responsivity (>1 × 105 A/W) and low output impedance (<10 kΩ). This excellent performance in the above has been obtained for λ = 12–28 μm. By introducing a modified scheme of detection (called “lateral-escape”) along with an improved coupler structure (bowtie antenna), we have achieved similar excellent performance for 45 μm. The CSIP provides extremely promising detectors for a variety of applications covering a wide spectral range of 12–100 μm.
    Journal of Applied Physics 03/2013; 113(13). DOI:10.1063/1.4795517 · 2.19 Impact Factor
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    ABSTRACT: Here we combined experiments and theory to study the optical properties of a plasmonic cavity consisting of a perforated metal film and a flat metal sheet separated by a semiconductor spacer. Three different types of optical modes are clearly identified-the propagating and localized surface plasmons on the perforated metal film and the Fabry-Perot modes inside the cavity. Interactions among them lead to a series of hybridized eigenmodes exhibiting excellent spectral tunability and spatially distinct field distributions, making the system particularly suitable for multicolor infrared light detections. As an example, we design a two-color detector protocol with calculated photon absorption efficiencies enhanced by more than 20 times at both colors, reaching ~42.8% at f<sub>1</sub> = 20.0THz (15μm in wavelength) and ~46.2% at f<sub>2</sub> = 29.5THz (~10.2μm) for a 1μm total thickness of sandwiched quantum wells.
    Optics Express 01/2013; 21(1):295-304. DOI:10.1364/OE.21.000295 · 3.53 Impact Factor
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    ABSTRACT: For charge-sensitive infrared phototransistors (CSIP), it is observed that “conductance decrease,” which is contrary to the standard “conductance increase” photon response, can also happen after absorbing infrared light. By experimental modeling the charge-up detection mechanism of CSIP via a capacitive way, we clarify that “conductance decrease” should be attributed to the significantly reduced low quantum well electron mobility after the photon-charging process, rather than a reversed electron transfer. This experimental result clearly indicates that photon-induced charges are able to modify the electron mobility in those “charge-sensitive sensor” types of semiconductor quantum single-photon detectors.
    IEEE Journal of Selected Topics in Quantum Electronics 01/2013; 19(1):8500406-8500406. DOI:10.1109/JSTQE.2012.2191767 · 3.47 Impact Factor
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    ABSTRACT: Charge sensitive infrared photo transistors (CSIPs) made in GaAs/AlGaAs bilayer two-dimensional electron systems (2DESs) serve as sensitive photodetectors in the mid- and long-wavelength infrared regions. A new design of CSIP is proposed to expand the wavelength range to longer wavelengths (λ > 36 μm). Remarkably improved detector performance is demonstrated for λ ≈ 39 μm. In CSIPs electrons are photo-excited in a floating gate (FG) served by an isolated region of upper layer 2DESs. In the new design (i) a bow-tie antenna couples incident radiation to an FG far smaller in size (2-3 μm) than the wavelength and (ii) excited electrons 'laterally' escape from the FG via tunneling through a barrier formed by biased metal cross gates. The charge state of the FG is sensed by a source-drain channel in the lower layer of the 2DES. The sensitivity and the quantum efficiency have been greatly improved, indicating that CSIPs are promising detectors in an expanded wavelength range exceeding 36 μm.
    Nanotechnology 12/2012; 24(2):025205. DOI:10.1088/0957-4484/24/2/025205 · 3.67 Impact Factor
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    ABSTRACT: We have recently developed a THz near-field microscope with an ultrahighly sensitive detector, CSIP (charge-sensitive infrared phototransistor). The microscope probes spontaneous evanescent field on samples derived from local phenomena and the signal origin from metals was previously revealed to be thermal charge/current fluctuations. The intensity of passive near-field signal is very well consistent with Bose-Einstein distribution, which corresponds to the sample temperature. In this study, we demonstrate nano-thermometry with the microscope by monitoring passive near-field signals on a biased NiCr pattern. The obtained signals correspond to the local temperature and the result shows that the inner side of the line curve is much brighter than outer side. It can be easily interpreted by Kirchhoff’s law. The spatial resolution is 60 nm, which cannot be experimentally achieved by any other optical thermometry. This demonstration strongly suggests that our microscope is very well suited for real-time temperature mapping of complicated circuit patterns, and others like bio-samples.
    Key Engineering Materials 11/2012; 523-524:821-825. DOI:10.4028/www.scientific.net/KEM.523-524.821 · 0.19 Impact Factor
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    ABSTRACT: Projection type photo lithography and electroplating techniques were applied to fabricate a plasmonic coupler, and to integrate the coupler on top of a photo detector for terahertz frequency. The coupler is a metallic disk with a sub-wavelength aperture surrounded by concentric gratings. The period and height of the gratings are about 200 μm and 20 μm, respectively. The photo detector is 2-dimensional electron gas in perpendicular magnetic field. The photo signal is change of longitudinal resistance, due to cyclotron absorption of photons. Enhancement of photo signal, due to presence of the plasmonic coupler, was observed.
    Applied Physics Letters 08/2012; 101(9). DOI:10.1063/1.4748581 · 3.52 Impact Factor
  • Ting-Ting Kang, Takeji Ueda, Susumu Komiyama
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    ABSTRACT: For an infrared photon detector, such as charge-sensitive infrared phototransistors (CSIPs), we propose and use a capacitive charging method to study some failure mechanisms that disable the photon response of CSIPs. Two failure mechanisms are highlighted, namely interquantum well (QW) leakage and low tunneling probability for intersubband-transition-excited electrons. A correlation between the Al content in the inter-QW AlGaAs barrier and the failure mechanism type are discussed. On the other hand, the previously unexplained puzzle that the success of photon response is only weakly dependent on the QW electron mobility that is attributed to an imperfect inter-QW barrier.
    IEEE Transactions on Electron Devices 08/2012; 59(8):2129-2135. DOI:10.1109/TED.2012.2199992 · 2.36 Impact Factor
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    T. Nakajima, Kuan-Ting Lin, S. Komiyama
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    ABSTRACT: Electrical control and detection of spin precession are experimentally demonstrated by using spin-resolved edge states in the integer quantum Hall regime. Spin precession is triggered at a corner of a biased metal gate, where electron orbital motion makes a sharp turn leading to a nonadiabatic change in the effective magnetic field via spin-orbit interaction. The phase of precession is controlled by the group velocity of edge-state electrons tuned by gate bias voltage: A spin-FET device is thus realized by all-electrical means, without invoking ferromagnetic material. The effect is also interpreted in terms of a Mach-Zehnder-type spin interferometer.
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    ABSTRACT: We study the operation of a system where quantum dot (QD) and point contact (PC) defined in a two-dimensional electron gas of a high-mobility GaAs/AlGaAs heterostructure are capacitively coupled to each other and to metallic single electron transistor (SET). The charge state of the quantum dot can be probed by the point contact or single electron transistor. These can be used for sensitive detection of terahertz radiation. In this work, we explore an electrostatic model of the system. From the model, we determine the sensitivity of the point contact and the single electron transistor to the charge excitation of the quantum dot. Nearly periodic oscillations of the point contact conductance are observed in the vicinity of pinch-off voltage. They can be attributed to Coulomb blockade effect in a quasi-1D channel because of unintentional formation of small quantum dot. The latter can be a result of fluctuations in GaAs quantum well thickness.
    Journal of Applied Physics 07/2012; 112(1). DOI:10.1063/1.4736419 · 2.19 Impact Factor
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    ABSTRACT: We investigate the dynamic properties of the breakdown of integer quantum Hall states (QHSs). The critical field of QHS breakdown that occurs at a filling factor of ν∼2 is found to depend on the scan rate of the applied Hall field EH and to fluctuate stochastically; in contrast, a smooth breakdown is observed at ν∼4. The histogram of the critical values of EH can be used to derive the escape and relaxation time, ranging from a few seconds to 10 μs between the low-dissipation QHS and the dissipation state. The increase of the escape rate between the low-dissipative QHS and the dissipative state is accompanied by a decrease of the relaxation rate and vice versa, indicating the bistable nature of the breakdown phenomena. The observed results agree well with the calculated results based on the basis of the bootstrap electron heating model. We conclude that the dynamic behaviors of QHS breakdown are governed by the transition probability that resides in the thermal bistable regime between the QHS and the dissipation states.
    Physical review. B, Condensed matter 06/2012; 85(24). DOI:10.1103/PhysRevB.85.245315 · 3.66 Impact Factor
  • Takeji Ueda, Naomi Nagai, Susumu Komiyama
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    ABSTRACT: Charge sensitive infrared phototransistors (CSIPs), ultrasensitive detectors in the wavelength range of 10--50 μm, are fabricated in GaAs/AlGaAs superlattice structures. The superlattice structures consist of alternately grown 2-nm-thick Al0.3Ga0.7As tunnel barriers and thickness-modulated GaAs layers from 2 to 10 nm. The tilted miniband formed in a superlattice structure serves as a potential slope similar to formally used compositionally graded barriers. The utilization of the superlattice in a CSIP is expected to give advantages of easier design, less impurities, and better repeatability in crystal growth, and therefore provides more reliable device performance. The novel structure paves the way for the future mass production of CSIPs.
    Japanese Journal of Applied Physics 05/2012; 51(5):0206-. DOI:10.1143/JJAP.51.050206 · 1.06 Impact Factor
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    Takeji Ueda, Susumu Komiyama
    Photodetectors, 03/2012; , ISBN: 978-953-51-0358-5
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    ABSTRACT: Microscopy of electron spin states in edge channels are performed by using nuclear spin polarization as a sensitive local probe in the integer quantum Hall regime of the filling factor νbulk = 2. The nuclear polarization situated within the compressible region of 1<ν<2 is found to exhibit anomalous enhancement of the relaxation rate. The relaxation rate is crucially influenced by the magnetic field strength as well as the softness of the gate-controlled confinement potential, suggesting that the ground state of the edge channels is the spin-textured state.
    12/2011; DOI:10.1063/1.3666526
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    Kenji Ikushima, Susumu Komiyama
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    ABSTRACT: Photon emission caused by quantum electron transport has been found in the quantum Hall effect regime through photon-counting THz microscopy. The imaging reveals that Landau-level emission occurs at the confluence of unequally occupied edge channels in the quantum Hall effect plateau (filling factor ν=4) when a potential barrier across the Hall bar is introduced. It is also found that the confluence at the lower-potential sample boundary (with positive Hall voltage) emits more photons than that at the higher-potential one. Since electrons and holes are injected via phase-coherent conducting channels, this photon emission phenomenon will provide a new platform for studying the interplay between quantum electron transport and quantum optics.
    Physical review. B, Condensed matter 10/2011; 84(15). DOI:10.1103/PhysRevB.84.155313 · 3.66 Impact Factor
  • Y Kajihara, K Kosaka, S Komiyama
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    ABSTRACT: Long wavelength infrared (LWIR) waves contain many important spectra of matters like molecular motions. Thus, probing spontaneous LWIR radiation without external illumination would reveal detailed mesoscopic phenomena that cannot be probed by any other measurement methods. Here we developed a scattering-type scanning near-field optical microscope (s-SNOM) and demonstrated passive near-field microscopy at 14.5 µm wavelength. Our s-SNOM consists of an atomic force microscope and a confocal microscope equipped with a highly sensitive LWIR detector, called a charge-sensitive infrared phototransistor (CSIP). In our s-SNOM, photons scattered by a tungsten probe are collected by an objective of the confocal LWIR microscope and are finally detected by the CSIP. To suppress the far-field background, we vertically modulated the probe and demodulated the signal with a lock-in amplifier. With the s-SNOM, a clear passive image of 3 µm pitch Au/SiC gratings was successfully obtained and the spatial resolution was estimated to be 60 nm (λ/240). The radiation from Au and GaAs was suggested to be due to thermally excited charge/current fluctuations and surface phonons, respectively. This s-SNOM has the potential to observe mesoscopic phenomena such as molecular motions, biomolecular protein interactions and semiconductor conditions in the future.
    Measurement Science and Technology 06/2011; 22(8):085102. DOI:10.1088/0957-0233/22/8/085102 · 1.35 Impact Factor
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    ABSTRACT: We discuss the interplay between surface plasmon polaritons (SPPs) and localized shape resonances (LSRs) in a plasmonic structure working as a photo-coupler for a GaAs quantum well photodetector. For a targeted electronic inter-subband transition inside the quantum well, maximum photon absorption is found by compromising two effects: the mode overlapping with incident light and the lifetime of the resonant photons. Under the optimal conditions, the LSR mediates the coupling between the incident light and plasmonic structure while the SPP provides long-lived resonance which is limited ultimately by metal loss. The present work provides insight to the design of plasmonic photo-couplers in semiconductor optoelectronic applications. KeywordsSurface plasmon polariton–Localized shape resonance–Extraordinary optical transmission–Inter-subband transition
    Plasmonics 06/2011; 6(2):319-325. DOI:10.1007/s11468-011-9207-6 · 2.74 Impact Factor
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    ABSTRACT: An electrically isolated quantum well (QW) island can be positively charged by incoming infrared photon, because its electrons absorb photon energy via intersubband transition and acquire enough energy to escape it. This process has been used in a double QW photon-detector. Here, we present the observation of so-called negative photon-response in such detector. Its origin is clarified to be an electron mobility reduction phenomenon resulted from the photon induced charges.
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    Yusuke Kajihara, Keishi Kosaka, Susumu Komiyama
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    ABSTRACT: Thermal radiation from samples of Au layers patterned on GaAs, SiO(2), and SiC at 300 K are studied with a scattering-type scanning near-field optical microscope (wavelength: ~14.5 μm), without applying external illumination. Clear near-field images are obtained with a spatial resolution of ~60 nm. All the near field signals derived from different demodulation procedures decrease rapidly with increasing probe height h with characteristic decay lengths of 40 ~60 nm. Near-field images are free from any signature of in-plane spatial interference. The findings are accounted for by theoretically expected surface evanescent waves, which are thermally excited in the close vicinity of material surfaces. Outside the near-field zone (1 μm < h), signals reappear and vary as a sinusoidal function of h, exhibiting a standing wave-like interference pattern. These far-field signals are ascribed to the effect of weak ambient radiation.
    Optics Express 04/2011; 19(8):7695-704. DOI:10.1364/OE.19.007695 · 3.53 Impact Factor

Publication Stats

3k Citations
489.02 Total Impact Points


  • 1985–2013
    • The University of Tokyo
      • • Department of Basic Medical Sciences
      • • Department of Applied Life Sciences
      Tōkyō, Japan
  • 2007
    • Royal Holloway, University of London
      Эгхем, England, United Kingdom
  • 2000
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 1990
    • Fujitsu Ltd.
      Kawasaki Si, Kanagawa, Japan