K. Hoshino

Kyushu University, Hukuoka, Fukuoka, Japan

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Publications (58)117.28 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Transmission electron microscope (TEM) observation was performed to analyze microstructures in a (110)-plane GaN thin films grown by metal-organic vapor-phase epitaxy (MOVPE) on a r (102)-plane sapphire substrate Special attention was paid to an influence of small off-angle of the substrate plane to morphology of defects in the thin films. From the TEM observation, the following results were drawn. (1) The crystallographic orientation relationship between GaN and sapphire substrate is (110)[0001][100]GaN // (102)[101][110]sapphire. The direction of +c -polarity coincides with that reported previously. (2) The pits on the surface are formed on the grain boundaries of GaN. (3) The density of pits is related with the density of nucleation of GaN-islands on the substrate. The increase in density of pits with the off-angle can be explained by the increase of nucleation sites provided by atomic steps on the substrate. (4) The side-wall planes of pits and voids are considered to be closed to ±(0001), ±(114), and (112). (5) The formation of pits and voids are attributable to the trend that such inclining planes as (112) and (114) are stable compared with +c (0001). A possible technique for reduction of defects is also discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2009; 6(S2):S494 - S497.
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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) 01/2009; 6(S2):S684 - S686.
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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) 09/2008; 6(1):42 - 45.
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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) 06/2008; 5(9):3060 - 3062.
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    ABSTRACT: The high-efficiency GaN-based light emitting diodes (LEDs) with improved light extraction efficiency (LEE) using the needle-shape indium tin oxide (ITO) p-contact was successfully demonstrated. The needle-shape ITO p-contact was naturally grown by using electron-beam evaporation method under the precisely controlled condition. The structure of ITO p-contact varied sensitively from the planar-shape to the needle-shape with decreasing the deposition temperature and the partial oxygen pressure in the vacuum chamber. We fabricated the p-side-up GaN/sapphire LEDs with the needleshape ITO p-contact and those with the planar-shape ITO p-contact using the same LED wafer (peak wavelength: 405 nm). The external quantum efficiency (EQE) of the needle-shape ITO-LEDs is 1.5 times larger than that of the planar-shape ITO-LEDs (at a forward current of 20 mA). This dramatic increase is attributed to the dramatic increasing of the LEE of the needle-shape ITO-LEDs. These results show that the optimizing shape of ITO p-contact is the key technology to increase the EQE and the LEE of ITO-LEDs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2008; 5(6):2083-2085.
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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.
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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) 03/2008; 5(6):2114 - 2116.
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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) 03/2008; 245(5):878 - 880. · 1.61 Impact Factor
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    ABSTRACT: We investigated the effect of the misorientation angle of an r-plane sapphire substrate on a-plane GaN grown by metalorganic vapor phase epitaxy. The misorientation angle was changed systematically in the direction of the [0001] c-axis or [\bar{1}100] m-axis (denoted theta 1) and in the direction of the [11\bar{2}0] a-axis (denoted theta 2). Results show that the surface morphology and crystalline quality are very sensitive to theta 1 misorientation angle. We successfully grew an a-plane GaN layer with a pit-free surface by optimizing the misorientation angle of the r-plane sapphire substrate. We found that the r-plane sapphire substrate with a theta 1 misorientation angle between -0.53 and -0.28° is very effective for growing a-plane GaN with a pit-free surface. Moreover, a theta 1 misoriention angle between -0.53 and -0.28° improves crystalline quality in the GaN c-axis direction, but causes a slight increase in tilt mosaicity in the GaN m-axis direction. In contrast, a theta 2 misorientation angle between -0.55 and +0.52° produces no differences in the surface morphology and crystalline quality of a-plane GaN.
    Japanese Journal of Applied Physics 01/2008; 47:119-123. · 1.06 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) 05/2007; 4(7):2752 - 2755.
  • Masahiro Araki, Katsuyuki Hoshino, Kazuyuki Tadatomo
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    ABSTRACT: We have investigated a direct growth of non-polar a-plane GaN on r-plane sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). We found that high-density nucleation of GaN islands was grown on r-plane sapphire substrate at an initial stage of high temperature growth without a buffer layer, which resulted in a flat surface of the a-plane GaN. We also studied an effect of growth conditions on surface morphologies and the growth features of the a-plane GaN. The results showed that inverse-triangular pits surrounded with facets were formed at a relatively high V/III ratio, and the lateral growth rate along the c-axis direction was enhanced at a relatively low V/III ratio. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2007; 4(7):2540 - 2543.
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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. · 1.69 Impact Factor
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    ABSTRACT: Fundamentally secure quantum cryptography has still not seen widespread application owing to the difficulty of generating single photons on demand. Semiconductor quantum-dot structures have recently shown great promise as practical single-photon sources, and devices with integrated optical cavities and electrical-carrier injection have already been demonstrated. However, a significant obstacle for the application of commonly used III-V quantum dots to quantum-information-processing schemes is the requirement of liquid-helium cryogenic temperatures. Epitaxially grown gallium nitride quantum dots embedded in aluminium nitride have the potential for operation at much higher temperatures. Here, we report triggered single-photon emission from gallium nitride quantum dots at temperatures up to 200 K, a temperature easily reachable with thermo-electric cooling. Gallium nitride quantum dots also open a new wavelength region in the blue and near-ultraviolet portions of the spectrum for single-photon sources.
    Nature Material 12/2006; 5(11):887-92. · 36.43 Impact Factor
  • Source
    Nat Mater. 11/2006; 5:887--892.
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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. · 1.61 Impact Factor
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    ABSTRACT: Exciton fine structures induced by the uniaxial strain have been revealed in gallium nitride grown on an a -plane sapphire substrate by using the spectrally-resolved four-wave mixing technique. Sensitivity on the exciton polarization is enhanced by the nonlinearities of the four wave mixing signals, and therefore the safety alternative tool for mapping of the uniaxial strain field and the resultant anisotropic exchange can be offered. Such a nonlinear spectroscopic measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2006; 3(6):1595 - 1598.
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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.
    physica status solidi (c) 01/2006; 3(6):2246-2249.
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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 01/2006; 88. · 3.52 Impact Factor
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    ABSTRACT: We present measurements of the second-order coherence function on emission from single GaN quantum dots. A large degree of photon antibunching is observed, demonstrating single-photon source operating at a record-short wavelength of 357 nm.
    Quantum Electronics and Laser Science Conference, 2005. QELS '05; 06/2005
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    ABSTRACT: We report single dot spectroscopy of hexagonal GaN/AlN self-assembled quantum dots grown by metal organic chemical vapor deposition. Through the reduction of the number of quantum dots using sub-micron mesa structures, we have obtained isolated photoluminescence peaks emitted by individual quantum dots. We have found that the biexciton inside a quantum dot has a negative binding energy. This negative biexciton binding energy is attributed to the effects of strong built-in electric field.

Publication Stats

525 Citations
117.28 Total Impact Points


  • 2009
    • Kyushu University
      Hukuoka, Fukuoka, Japan
  • 2007–2009
    • Yamaguchi University
      • • Faculty of Engineering
      • • Graduate School of Science and Engineering
      Yamaguti, Yamaguchi, Japan
  • 2007–2008
    • Hokkaido University
      • Division of Applied Physics
      Sapporo-shi, Hokkaido, Japan
  • 2000–2006
    • The University of Tokyo
      • • Institute of Industrial Science
      • • Research Center for Advanced Science and Technology
      Tokyo, Tokyo-to, Japan
  • 2003
    • Nanjing University
      • Department of Physics
      Nanjing, Jiangsu Sheng, China
  • 1995–1998
    • Saitama University
      • Department of Functional Material Science
      Saitama, Saitama, Japan