Published Papers - OZAKI Nobuhiko

Strain Balancing of Metal-Organic Vapour Phase Epitaxy InAs/GaAs Quantum Dot Lasers

Timothy S. Roberts, Benjamin J. Stevens, Edmund Clarke, Ian Tooley, Jonathan Orchard, Ian Farrer, David T. D. Childs, Nasser Babazadeh, Nobuhiko Ozaki, David Mowbray, Richard A. Hogg

IEEE Journal of Selected Topics in Quantum Electronics ( Institute of Electrical and Electronics Engineers (IEEE) )  23 ( 6 ) 1901208 1-8   2017.05  [Refereed]

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Ultra-small near-infrared multi-wavelength light source using a heterojunction photonic crystal waveguide and self-assembled InAs quantum dots

Sho Uchida, Nobuhiko Ozaki, Teruyuki Nakahama, Hisaya Oda, Naoki Ikeda, Yoshimasa Sugimoto （Part： Corresponding author )

Japanese Journal of Applied Physics ( IOP Publishing )  56 ( 5 ) 050303 1-4   2017.05  [Refereed]

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Gallium nitride light sources for optical coherence tomography

Graham R. Goldberg, Pavlo Ivanov, Nobuhiko Ozaki, David T. D. Childs, Kristian M. Groom, Kenneth L. Kennedy, Richard A. Hogg

SPIE Proceedings ( SPIE )  10104   101041X 1-7   2017.02  [Refereed]

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High-resolution and nondestructive profile measurement by spectral-domain optical coherence tomography with a visible broadband light source for optical-device fabrication

Tsuyoshi Nishi, Nobuhiko Ozaki, Yoichi Oikawa, Kunio Miyaji, Hirotaka Ohsato, Eiichiro Watanabe, Naoki Ikeda, Yoshimasa Sugimoto （Part： Corresponding author )

Japanese Journal of Applied Physics ( IOP Publishing )  55 ( 8S3 ) 08RE05 1-5   2016.08  [Refereed]

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Operation of an InAs quantum-dot embedded GaAs photonic crystal slab waveguide laser by using two-photon pumping for photonics integrated circuits

H. Oda, A. Yamanaka, N. Ozaki, N. Ikeda, Y. Sugimoto

AIP Advances ( AIP Publishing )  6 ( 6 ) 065215 1-6   2016.06  [Refereed]

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Emission wavelength variation of InAs quantum dots grown on GaAs using As2 molecules in molecular beam epitaxy

Yuma Hayashi, Nobuhiko Ozaki, Shunsuke Ohkouchi, Hirotaka Ohsato, Eiichiro Watanabe, Naoki Ikeda, Yoshimasa Sugimoto （Part： Corresponding author )

2016 Compound Semiconductor Week (CSW) [Includes 28th International Conference on Indium Phosphide & Related Materials (IPRM) & 43rd International Symposium on Compound Semiconductors (ISCS)] ( IEEE )    1 - 2   2016.06  [Refereed]

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Electrically Driven Near-Infrared Broadband Light Source with Gaussian-Like Spectral Shape Based on Multiple InAs Quantum Dots

Takuma YASUDA, Nobuhiko OZAKI, Hiroshi SHIBATA, Shunsuke OHKOUCHI, Naoki IKEDA, Hirotaka OHSATO, Eiichiro WATANABE, Yoshimasa SUGIMOTO, Richard A. HOGG （Part： Corresponding author )

IEICE Transactions on Electronics ( Institute of Electronics, Information and Communications Engineers (IEICE) )  E99.C ( 3 ) 381 - 384   2016.03  [Refereed]

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Superluminescent diode with a broadband gain based on self-assembled InAs quantum dots and segmented contacts for an optical coherence tomography light source

Nobuhiko Ozaki, David T. D. Childs, Jayanta Sarma, Timothy S. Roberts, Takuma Yasuda, Hiroshi Shibata, Hirotaka Ohsato, Eiichiro Watanabe, Naoki Ikeda, Yoshimasa Sugimoto, Richard A. Hogg （Part： Lead author,　Corresponding author )

Journal of Applied Physics ( AIP Publishing )  119 ( 8 ) 083107 1-7   2016.02  [Refereed]

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Gallium Nitride Super-Luminescent Light Emitting Diodes for Optical Coherence Tomography Applications

Graham R. Goldberg, Pavlo Ivanov, Nobuhiko Ozaki, David T. D. Childs, Kristian M. Groom, Kenneth L. Kennedy, Richard A. Hogg

2016 INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC) ( IEEE )    2016  [Refereed]

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The role of biasing of absorber sections in multi-contact GaN similar to 400nm SLEDs is discussed. We go on to assess such devices for OCT applications. Analysis of the SLED emission spectrum allows an axial resolution of 6.0 mu m to be deduced in OCT applications.

Optical characterization of In-flushed InAs/GaAs quantum dots emitting a broadband spectrum with multiple peaks at ~1 μm

Shigehiro Kitamura, Masaya Senshu, Toshio Katsuyama, Yuji Hino, Nobuhiko Ozaki, Shunsuke Ohkouchi, Yoshimasa Sugimoto, Richard A Hogg （Part： Corresponding author )

Nanoscale Research Letters ( Springer Science and Business Media LLC )  10   231 1-6   2015.05  [Refereed]

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Abstract

We investigated optical properties of In-flushed InAs quantum dots (QDs) grown on a GaAs substrate by molecular beam epitaxy. By using the In-flush technique for setting the height of self-assembled InAs QDs, we have tuned the emission wavelength of InAs QDs to the ~1 μm regime, which can be utilized as a non-invasive and deeply penetrative probe for biological and medical imaging systems. The controlled emission exhibited a broadband spectrum comprising multiple peaks with an interval of approximately 30 meV. We examined the origin of the multiple peaks using spectral and time-resolved photoluminescence, and concluded that it is attributed to monolayer step fluctuations in the height of the In-flushed QDs. This feature can be advantageous for realizing a broadband light source centered at the ~1 μm regime, which is especially suitable for the non-invasive cross-sectional biological and medical imaging system known as optical coherence tomography.

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Imaging of spectral-domain optical coherence tomography using a superluminescent diode based on InAs quantum dots emitting broadband spectrum with Gaussian-like shape

Hiroshi Shibata, Nobuhiko Ozaki, Takuma Yasuda, Shunsuke Ohkouchi, Naoki Ikeda, Hirotaka Ohsato, Eiichiro Watanabe, Yoshimasa Sugimoto, Kenji Furuki, Kunio Miyaji, Richard A. Hogg （Part： Corresponding author )

Japanese Journal of Applied Physics ( IOP Publishing )  54 ( 4S ) 04DG07 1-5   2015.04  [Refereed]

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Spectral and temporal photoluminescence behavior of colloidal PbS quantum dots

S. Kitamura, M. Senshu, H. Tokushige, T. Katsuyama, N. Ozaki, I. Tanaka, Y. Sugimoto

Superlattices and Microstructures ( Elsevier BV )  79   123 - 134   2015.03  [Refereed]

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SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY WITH A WHITE LIGHT DEVELOPED FOR OPTICAL DEVICE FABRICATION

T. Nishi, N. Ozaki, H. Ohsato, E. Watanabe, N. Ikeda, Y. Sugimoto （Part： Corresponding author )

2015 20TH MICROOPTICS CONFERENCE (MOC) ( IEEE )    180 - 181   2015  [Refereed]

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We developed a spectral-domain optical coherence tomography (SD-OCT) with a white light source for high-resolution, non-destructive profile imaging. By using a 625-nm-centered white light (260 nm bandwidth), 0.69 mu m of axial resolution was achieved. This resolution is suitable for the inspection of thin photoresists (e.g., 1-2 mu m) coated semiconductor wafers, which are used for optical device fabrication.

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Integration of Emission-Wavelength-Controlled InAs Quantum Dots for Ultra-Broadband Near-Infrared Light Source

Nobuhiko Ozaki, Koichi Takeuchi, Yuji Hino, Yohei Nakatani, Takuma Yasuda, Shunsuke Ohkouchi, Eiichiro Watanabe, Hirotaka Ohsato, Naoki Ikeda, Yoshimasa Sugimoto, Edmund Clarke, Richard A. Hogg （Part： Lead author,　Corresponding author )

Nanomaterials and Nanotechnology ( SAGE Publications )  4   26 1-17   2014.09  [Refereed]  [Invited]

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Near-infrared (NIR) light sources are widely utilized in biological and medical imaging systems owing to their long penetration depth in living tissues. In a recently developed biomedical non-invasive cross-sectional imaging system, called optical coherence tomography (OCT), a broadband spectrum is also required, because OCT is based on low coherence interferometry. To meet these operational requirements, we have developed a NIR broadband light source by integrating self-assembled InAs quantum dots (QDs) grown on a GaAs substrate (InAs/GaAs QDs) with different emission wavelengths. In this review, we introduce the developed light sources and QD growth techniques that are used to control the emission wavelength for broadband emission spectra with center wavelengths of 1.05 and 1.3 μm. Although the strain-induced Stranski-Krastanov (S-K) mode-grown InAs/GaAs QDs normally emit light at a wavelength of around 1.2 μm, the central emission wavelength can be controlled to be between 0.9–1.4 μm by the use of an In-flush technique, the insertion of a strain-reducing layer (SRL) and bi-layer QD growth techniques. These techniques are useful for applying InAs/GaAs QDs as NIR broadband light sources and are especially suitable for our proposed spectral-shape-controllable broadband NIR light source. The potential of this light source for improving the performance of OCT systems is discussed.

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Alcohol additive effect in hydrogen generation from water with carbon by photochemical reaction

Kosuke Maeda, Nobuhiko Ozaki, Ikuko Akimoto

Japanese Journal of Applied Physics ( IOP Publishing )  53 ( 5S1 ) 05FZ03 - 05FZ03   2014.03  [Refereed]

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Near-infrared superluminescent diode using stacked self-assembled InAs quantum dots with controlled emission wavelengths

Nobuhiko Ozaki, Takuma Yasuda, Shunsuke Ohkouchi, Eiichiro Watanabe, Naoki Ikeda, Yoshimasa Sugimoto, Richard A. Hogg （Part： Lead author,　Corresponding author )

Japanese Journal of Applied Physics ( IOP Publishing )  53 ( 4S ) 04EG10 - 04EG10   2014.02  [Refereed]

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Growth and Optical Characterizations of InAs-QDs Emitting at 1μm with a Broadband Spectrum for a Light Source for Biomedical Optical Coherence Tomography

Nobuhiko OZAKI, Yuji HINO, Shunsuke OHKOUCHI, Naoki IKEDA, Yoshimasa SUGIMOTO （Part： Lead author,　Corresponding author )

Journal of the Society of Materials Science, Japan ( Society of Materials Science, Japan )  62 ( 11 ) 679 - 682   2013.11  [Refereed]

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Broadband emission centered at ~1 µm with a Gaussian-like spectrum by stacking In-flushed QD layers

Nobuhiko Ozaki, Yuji Hino, Shunsuke Ohkouchi, Naoki Ikeda, Yoshimasa Sugimoto （Part： Lead author,　Corresponding author )

Physica Status Solidi C: Current Topics in Solid State Physics ( WILEY-V C H VERLAG GMBH )  10 ( 11 ) 1361 - 1364   2013.10  [Refereed]

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We have grown a stack of In-flushed InAs quantum dot (QD) layers to realize a broadband emission centered at similar to 1 mu m with a Gaussian-like spectrum as a light source for optical coherence tomography (OCT). The In-flush process, which enables control of the height of the QD, was optimized to control the emission wavelength and intensity of self-assembled InAs/GaAs QDs. A partial capping layer of GaAs was deposited on as-grown InAs/GaAs QDs with various thicknesses (d(cap)), and a rapid annealing of the sample was executed with the proper annealing temperature. By optimizing d(cap) and the annealing temperature for each QD layer, a broadband Gaussian-like spectrum with a 102-nm-bandwidth was obtained. The coherence function of the emission spectrum exhibits a 4.5-mu m axial resolution for OCT images without distinct side lobes. These results demonstrate the effectiveness of the In-flushed QDs as a light source to obtain high-quality OCT images.

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Hydrogen generation by laser irradiation of carbon powder in water

Ikuko Akimoto, Kousuke Maeda, Nobuhiko Ozaki

Journal of Physical Chemistry C ( American Chemical Society ({ACS}) )  117 ( 36 ) 18281 - 18285   2013.09  [Refereed]

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We report the photochemical activity of carbon powder in the generation of hydrogen from water by laser irradiation, without any electrodes and photocatalysts. The gas was obtained by laser irradiation in the VIS-NIR range and was dependent nonlinearly on the laser power density. From a gas component analysis and a repeated irradiation experiment, it was found that the carbon powder was oxidized and acted as a sacrificial reagent in the photochemical hydrogen generation. In addition, a highly carbonized charcoal, known as Bincho-tan, was found to effectively work for the hydrogen generation. © 2013 American Chemical Society.

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Extending emission wavelength of InAs/GaAs quantum dots beyond 1.3 mu m by using quantum dot bi-layer for broadband light source

N. Ozaki, Y. Nakatani, S. Ohkouchi, N. Ikeda, Y. Sugimoto, K. Asakawa, E. Clarke, R. A. Hogg （Part： Lead author,　Corresponding author )

Journal of Crystal Growth ( ELSEVIER SCIENCE BV )  378   553 - 557   2013.09  [Refereed]

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We have grown bi-layer InAs quantum dots (QDs) on GaAs substrates for extending the emission wavelength of InAs/GaAs QDs beyond 1.3 mu m. The QD bi-layer, which comprises two QDs layers (seed- and active-QDs) separated with a GaAs spacer layer of 10 nm in thickness, exhibits light emission from active-QDs with longer wavelength. An enlargement of the active-QDs occurred by optimizing several growth parameters: growth temperature of seed-QDs, amount of InAs supplied for seed- and active-QDs layers. These optimized parameters lowered the density of the seed-QDs strain spreading upward, which resulted in an enlargement of the active-QDs. We achieved a control of the extension of emission wavelength up to approximately 1.4 mu m from 1.2 mu m. These results indicate that the QD bi-layer can be applied to a broadband light source exhibiting an emission spectrum centered at 1.3 mu m with a bandwidth of 200 nm. (c) 2013 Elsevier B.V. All rights reserved.

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