K. Hoshino

The University of Tokyo, Tōkyō, Japan

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Publications (95)100.01 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose that electrochemical cells based on bacteri- oRhodopsin (bR), a photosensitive protein, generate electric charges under illuminated light and that a suitable signal detection apparatus for this cell type is a charge amplifier. By using charge amplifiers, we observed bR-photocell electric charges that were proportional to the in- tensity of incident light, which ranged from 0 to 8mW/cm2. Then, the 4 × 4 micro-patterned bR photosensor array was connected to charge amplifiers to form an image sensor system. Static and moving images were detected with the constructed image sensor system.
    IEICE Electronics Express 04/2011; 8(7):505-511. DOI:10.1587/elex.8.505 · 0.32 Impact Factor
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    ABSTRACT: This letter reports on the micro-patterning of the photosensitive protein of bacterioRhodopsin (bR) geared toward bioelectronics-based image sensors. bR proteins are denatured by existing micro-fabrication processes, including destructive high-temperature (> 100 degrees C) heating and organic solvent cleansing. In our process, the desired area of the electrode for immobilizing bR is defined by a hydrophobic polymer that repels bR. After micro-fabrication, bR is selectively formed on the defined areas using electrophoretic deposition. A 5-mu m patterning resolution was achieved. An 8 x 8 photosensor array was fabricated, and its output electric charge was detected.
    IEICE Electronics Express 06/2010; 7(11):779-784. DOI:10.1587/elex.7.779 · 0.32 Impact Factor
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    ABSTRACT: Spatial imaging of spectrally-resolved four-wave mixing (SR FWM) was performed on a GaN film grown on c -sapphire substrate. The image obtained from the exciton resonances at zero time delay clearly showed some highly localized reductions in their intensities whose spatial profiles can be mapped out with a spatial resolution of ∼20 m. The image obtained from the evaluation of the quantum beats indicates these reductions correspond to the phase changes between two exciton transitions, reflecting the spatial properties of exciton-exciton interactions. The line-localization suggests a contribution of line-defect to the anomalous interactions (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 06/2009; 6(S2):S684 - S686. DOI:10.1002/pssc.200880771
  • T. Ishiguro · Y. Toda · S. Adachi · K. Tadatomo · K. Hoshino
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    ABSTRACT: Dephasing dynamics of exciton fine structure (EFS) caused by long and short range exchange interactions in GaN was investigated by using a four-wave-mixing (FWM) spectroscopy. The type of exchange interactions was selected by samples (uniaxially strained c -plane GaN films and a thick bulk GaN) and their geometries in optical excitation. Since each component of EFS is highly polarized, the polarization-dependent FWM spectra successfully resolve the dephasing dynamics in the individual EFS resonances. The results show a difference in dephasing time, suggesting a contribution of anisotropic exchange interaction (AEI). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2009; 6(1):42 - 45. DOI:10.1002/pssc.200879833
  • K. Hoshino · T. Murata · M. Araki · K. Tadatomo
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    ABSTRACT: We have successfully obtained high-quality GaN films directly on thick SiO2 patterned sapphire substrates by utilizing modified facet-controlled epitaxial lateral overgrowth (FACELO). GaN films were grown by metalorganic vapour phase epitaxy on the stripe patterned substrates with the SiO2 thickness of 1.2 μm. The threading dislocation density reached a value as low as 5 × 107 cm–2. We have also fabricated Light emitting diodes (LEDs). The output power and external quantum efficiency of the LED operated at 20 mA were 20.74 mW and 37.1%, respectively. This is due to not only the reduced dislocation density but also the improved light extraction efficiency because of the light scattering at the patterned GaN/thick-SiO2-masks interface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 07/2008; 5(9):3060 - 3062. DOI:10.1002/pssc.200779290
  • A. Nakamura · N. Yanagita · T. Murata · K. Hoshino · K. Tadatomo
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    ABSTRACT: We have systematically investigated the influence of sapphire substrate misorientation on the structural and optical properties of GaN-based LEDs grown by MOVPE. The LED properties were found to be very sensitive to the misorientation. We grew five samples of LEDs on sapphire substrates with various misorientation angles (0.02∼1.0°). The EL intensity increased when misorientation angles increased to 0.25°. The intensity, however, decreased dramatically when misorientation angles exceeded 0.25°. We also grew the samples of each layer of the LEDs, viz., GaN, InGaN, InGaN/GaN MQWs, and p-GaN layer. CL and PL analyses showed that the crystalline quality of InGaN (MQWs) layer became lower while that of GaN layer improved as misorientation angles increased. In addition, the increased misorientation caused the decreased indium composition and the indium compositional fluctuation. Moreover, the hole (carriers) concentration of p-GaN layer decreased with increasing misorientation angles. As these results, the misorientation angle of around 0.25° is suitable for the LEDs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2008; 5(6):2007-2009. DOI:10.1002/pssc.200778681
  • T. Ishiguro · Y. Toda · S. Adachi · K. Hoshino · Y. Arakawa
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    ABSTRACT: Dephasing dynamics of excitons in a GaN film grown on a -plane sapphire were studied by using the spectrallyresolved four-wave-mixing (SR-FWM) spectroscopy. Due to the anisotropic exchange interaction originates from the anisotropic strain field of the substrate, the degenerate exciton states with the total angular moment ± 1 mix and split into their fine structures. Since each component of the exciton fine structure (EFS) is highly polarized, the polarization-dependent SR-FWM spectra successfully resolve the dephasing dynamics in the individual EFS resonances. The result of each EFS shows a significantly different dephasing time, suggesting that the anisotropic dephasing contribution occurs in each EFS. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2008; 5(6):2114 - 2116. DOI:10.1002/pssc.200778466
  • Y. Toda · T. Ishiguro · S. Adachi · K. Hoshino · K. Tadatomo
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    ABSTRACT: We have previously demonstrated that a spectrally-resolved four-wave mixing highlights the anisotropically polarized excitons in the uniaxially strained GaN films [1], where the enhancement of sensitivity for an uniaxial strain was achieved by nonlinear response of the exciton polarization. In this work, we have applied this technique to the GaN films on various substrates including isotropic ones, and have examined the sensitivity of the technique. The results show distinct polarizations and energy variations originating from the uniaxial strain, the magnitude of which depends on the sample and its position. The minimum changes of the polarized FWM intensity and exchange energy splittings correspond to a uniaxial strain of 5.0 × 10–5, which currently gives a lower resolution limit of this technique. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (b) 05/2008; 245(5):878 - 880. DOI:10.1002/pssb.200778435 · 1.49 Impact Factor
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    ABSTRACT: We developed a tunable wedge prism by electrowetting actuation. Our prism can shift the field of view to the left or to the right and is useful for small cameras and endoscopes because its field of view can be changed without the need for large instruments. It consists of two plates that face each other, and a liquid is sandwiched between them. The liquid and plates form a wedge when the angle between the plates is changed. We used electrowetting to change the angle between the plates. The wedge prism is small because the liquid driven by electrowetting works as a prism. In addition, the prism produces a clear field of view because its optical flatness is determined by the flatness of the plates.
    Journal of Microelectromechanical Systems 01/2008; 16(6-16):1537 - 1542. DOI:10.1109/JMEMS.2007.906074 · 1.75 Impact Factor
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    ABSTRACT: Quantum beats in the time-resolved four-wave mixing (FWM) signals arising from GaN excitons are observed. Two different types of beats are investigated: beats between the A-exciton (XA) and B-exciton (XB) states; beats between the XA and A-biexciton ((XXA)) states. The former exhibits oscillations along all directions in the delay- (τ ) and real-time (t) plane while the latter exhibits no beat in the direction parallel to the diagonal axis (τ = t). The results are well reproduced by a model calculation, showing good homogeneity of the sample.
    physica status solidi (c) 06/2007; 4(7):2752 - 2755. DOI:10.1002/pssc.200674703
  • A. Nakai · K. Hoshino · K. Matsumoto · I. Shimoyama
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    ABSTRACT: This paper reports a double-sided scanning micromirror array for an autostereoscopic display. Double-sided micromirrors actuated by both external magnetic force and Lorentz force were designed and fabricated using MEMS technology, and some characteristics of a micromirror were measured. A micromirror array, two pinhole arrays, microlenses, and an LED matrix were assembled into a prototype autostereoscopic display, and the relation between the view angle and the light intensity was measured under some conditions. The light intensity distribution of this prototype demonstrated the feasibility of using double-sided micromirror arrays to make autostereoscopic displays.
    Sensors and Actuators A Physical 03/2007; 135(1-135):80-85. DOI:10.1016/j.sna.2006.07.036 · 1.90 Impact Factor
  • S. Srisomrun · Y. Mita · K. Hoshino · M. Sugiyama · T. Shibata
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    ABSTRACT: This paper presents the fabrication for transferring an SOI LSI chip to organic flexible material like PDMS (poly-dimethyl-siloxane). The test chip has 60 nm- thick active layer, 200 nm BOX (buried oxide) layer and 9 mum 5-layer metals of 0.15 mum technology. The fabrication also included the process of building electrode contacts by etching through buried oxide (BOX) layer to metal layer. The SOI chip with original thickness of 500 mum was embedded in PDMS and thinned to less than 10 mum thick. The structure of active layer, contacts and other interconnection patterns of SOI chip are seen through, because silicon oxide as insulator is transparent. In addition, this silicon on PDMS devices are bendable because they were extremely thin and placed on flexible PDMS. Transistor characteristics were measured, showing slight decrease in S-factor but increase in maximum current after process, and slight decrease after bending.
    Micro Electro Mechanical Systems, 2007. MEMS. IEEE 20th International Conference on; 02/2007
  • K. Hoshino · N. Yanagita · M. Araki · K. Tadatomo
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    ABSTRACT: We have investigated the correlation between the formation of single-crystal GaN islands in low-temperature (LT)-GaN buffer layer and the crystalline quality of subsequently grown high-temperature (HT)-GaN layer. X-ray diffraction (XRD) analysis showed that the LT-GaN layer was partially crystallized even without an annealing process. The annealing process transformed the nanometer-sized LT-GaN grains into the larger-sized islands whose size and density could be controlled by changing the growth temperature of LT-GaN layer. Atomic force microscopy (AFM) and XRD analyses indicated that the crystalline quality of HT-GaN layer depended strongly on the size and density of the islands in the LT-GaN layer. The full-width at half-maximum (FWHM) values of XRD rocking curves of GaN(0002) and (101¯2) reflections were 198 and 232arcsec, respectively, when the LT-GaN layer was grown at 475°C.
    Journal of Crystal Growth 01/2007; 298:232-234. DOI:10.1016/j.jcrysgro.2006.10.189 · 1.70 Impact Factor
  • M. J. Wang · B. Shen · Y. Wang · S. Huang · Z. J. Yang · K. Xu · GY Zhang · K. Hoshino · Y. Arakawa
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    ABSTRACT: The influence of the polarization effects on the energy band structures and electrical properties of GaN-based heterostructures has been investigated by means of capacitance-voltage (C-V) measurements of GaN/Al0.22Ga0.78N/GaN based metal-insulator-semiconductor (MIS) structures at various frequencies and temperatures. C-V profile shows a distinctive hump at about -10 V in the MIS structures, indicating the formation of the inversion mode in the MIS structures. It is thought that the inversion is due to the hole accumulation in the hole well formed at the top GaN/Al0.22Ga0.78N heterointerface induced by the strong polarization-induced electric fields. The theoretical calculation of the band structure of GaN/AlxGa1-xN/GaN heterostructure confirms the physical model for the inversion behaviors.
    Applied Physics Letters 06/2006; 88(24). DOI:10.1063/1.2213964 · 3.30 Impact Factor
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    ABSTRACT: The relationship between the magnetic field and the effective mass m* of the two-dimensional electron gas in the triangular quantum well at the heterointerface of modulation-doped Al0.15Ga0.85N/GaN heterostructures is investigated by means of temperature-dependent Shubnikov-de Haas measurements at low temperatures and high magnetic fields. The values of the m* have strong dependence on the magnetic field, which is thought to be attributed to conduction-band nonparabolicity of GaN. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    physica status solidi (c) 06/2006; 3(6):2246-2249. DOI:10.1002/pssc.200565200
  • T. Ishiguro · Y. Toda · S. Adachi · T. Mukai · K. Hoshino · Y. Arakawa
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    ABSTRACT: We have carried out time-integrated and spectrally-resolved four-wave mixing (FWM) measurements to study the effects of built-in strain within GaN films on their exciton structures and on their coherent dynamics. Precise values for exciton energies, linewidths, and oscillation periods of quantum beats were presented. Remarkable phase shifts of the quantum beats were observed in the GaN films on a-sapphire, suggesting the exciton–exciton interaction caused by the reduction of the crystal symmetry. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (b) 06/2006; 243(7):1560 - 1563. DOI:10.1002/pssb.200565167 · 1.49 Impact Factor
  • K Hoshino · K Yamada · K Matsumoto · I Shimoyama
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    ABSTRACT: A MEMS-compatible, simple fabrication technique for a nano-sized light source was developed, and its characteristics were investigated. This technique is a combination of top-down electrode fabrication and bottom-up nanoparticle trapping. As regards this technique, nanoparticles (CdSe/ZnS core-shell nanoparticles) in a solvent were electrostatically trapped in a nanometer-sized gap between two electrodes formed on a p-type silicon on an insulator (SOI) wafer. The width of the nanogap, which was created by electron-beam lithography, was 200 nm. The trapped nanoparticles maintained a bridged form between the electrodes even after the solvent evaporated. Electroluminescence from the nanoparticles in the gap was observed when a voltage was applied to the electrodes. We measured an optical spectrum of the emission to find a peak which corresponds to the bandgap of the nanoparticles. A micro-photoluminescence measurement using a 405 nm laser suggested that the rest of the electrically induced emission was the black body emission of the locally heated nanoparticles. SEM observation showed that the emission area was small, i.e., 60 000 nm2. The nano light source fabricated by our new method is useful for integration with other devices owing to the simplicity of the fabrication method.
    Journal of Micromechanics and Microengineering 05/2006; 16(7):1285. DOI:10.1088/0960-1317/16/7/023 · 1.73 Impact Factor
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    ABSTRACT: We report on 30-μm-pitch organic light-emitting diode (OLED) stripes, whose cathode was patterned by lift-off method using a surface-unmodified silicon (Si) convex stamp. The OLED stripes consisted of ITO (120nm)–α-NPD (70nm)–Alq3 (70nm)–Al (30nm)–Au (approx. 1nm) layers on a glass wafer (12mm×12mm×0.5mm). A 0.7-μm-wide convex stamp was formed on an Si wafer by plasma etching in CF4, and it was pressed on the unpatterned Al–Au surface of the OLED cathode layers. The unwanted metal was removed because the additive top Au layer adhered to the Si stamp, resulting in a fine cathode pattern. Because the surface of the stamp does not need to be modified or covered by any other layers when it is pressed, this stamp is more suitable for repeated use than ones in previously proposed lift-off methods. The stamp endured use for patterning six times.We calculated the shearing stresses in the metal layers using the finite element method and estimated the optimal thickness of the metal and organic layers. The experimental results fit well with the estimation: layer thicknesses of 20–30nm for the metal layer and 100–150nm for the organic layer were optimal. Some areas near the metal-removed areas were damaged, suggesting that the stamping lift-off method is limited to pattern scales larger than several microns.
    Sensors and Actuators A Physical 04/2006; 128(2):339-343. DOI:10.1016/j.sna.2006.02.013 · 1.90 Impact Factor
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    ABSTRACT: A method is described for mechanically tuning the transmittance of two-dimensional photonic crystal slab reflectors. These reflectors have a triangular lattice of air holes in a silicon waveguide, and the crystals act as optical reflectors because of their photonic band gaps. The transmittance is tuned by inserting the tip of an atomic force microscopy cantilever into one of the air holes; the filled air hole transmits the incident light. Experiment demonstrated that this increases the transmittance 1.1 times, which agrees with calculations using finite difference time domain method. This method can thus be used to mechanically tune the PhC transmittance.
    Sensors and Actuators A Physical 03/2006; 128(1):197-201. DOI:10.1016/j.sna.2005.12.051 · 1.90 Impact Factor
  • Kentaro Noda · Kazunori Hoshino · Kiyoshi Matsumoto · Isao Shimoyama
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    ABSTRACT: In this paper, we propose a tactile sensor with standing piezoresistive cantilevers embedded in an elastic material. The sensor detects the shear stress applied on its surface. Each standing piezoresistive cantilever in the elastic material detects a certain axial component of applied shear stress. By arranging this standing piezoresistive cantilever in orthogonal directions, the directions and the magnitudes of applied shear stress is detected. The efficiency of this sensor was confirmed in the range of −5.0 to 5.0 kPa. We measured the 2.45 kPa shear stress applied to this sensor from several directions and confirmed that the sensor has a high accuracy for the shear stress detection.
    Sensors and Actuators A Physical 03/2006; 127(2-127):295-301. DOI:10.1016/j.sna.2005.09.023 · 1.90 Impact Factor

Publication Stats

679 Citations
100.01 Total Impact Points


  • 1998–2010
    • The University of Tokyo
      • • Department of Mechano-Informatics
      • • Research Center for Advanced Science and Technology
      • • Graduate School of Information Science and Technology
      Tōkyō, Japan
  • 2007–2009
    • Yamaguchi University
      • • Faculty of Engineering
      • • Graduate School of Science and Engineering
      Yamaguti, Yamaguchi, Japan
    • Hokkaido University
      • Division of Applied Physics
      Sapporo, Hokkaidō, Japan
  • 1995–2000
    • Saitama University
      • Department of Functional Material Science
      Saitama, Saitama, Japan