Details of a Researcher - Ota, Yasutomo

Papers - Ota, Yasutomo

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Electro-mechanical control of Q factor in photonic crystal nanobeam cavity

R Ohta, Y Ota, H Takagi, N Kumagai, K Tanabe, S Ishida, S Iwamoto, ...

SSDM 2013 2012

Research paper (scientific journal), Joint Work, Accepted

Formation of a single In (Ga) As/GaAs quantum dot embedded in a site-controlled GaAs nanowire by metalorganic chemical vapor deposition for application to single photon sources

J Tatebayashi, Y Ota, D Karunathillake, S Ishida, M Nishioka, S Iwamoto, ...

MRS Online Proceedings Library 1439 (1), 115-119 (Materials Research Society Symposium Proceedings) 1439 115 - 119 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 0272-9172

We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μe V are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs. © 2012 Materials Research Society.

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Site-controlled formation of InAs/GaAs quantum-dot-in-nanowires for single photon emitters

J Tatebayashi, Y Ota, S Ishida, M Nishioka, S Iwamoto, Y Arakawa

Applied Physics Letters 100 (26), 263101 (AMER INST PHYSICS) 100 ( 26 ) 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We report the demonstration of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition. InAs/GaAs quantum-dot-innanowires (QD-in-NWs) with various InAs thicknesses are realized on patterned GaAs(111) B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10K from single QD-in-NWs with the narrowest exciton linewidth of 87 mu eV are observed. Light emission from the single QD-in-NW shows photon antibunching, along with biexciton-exciton cascaded emission process, which evidences single photon emission from high-quality QD-in-NWs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731208]

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Optical properties of site-controlled InGaAs quantum dots embedded in GaAs nanowires by selective metalorganic chemical vapor deposition

J Tatebayashi, Y Ota, S Ishida, M Nishioka, S Iwamoto, Y Arakawa

Japanese Journal of Applied Physics 51 (11S), 11PE13 (JAPAN SOC APPLIED PHYSICS) 51 ( 11 ) 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 0021-4922

We report the optical properties of site-controlled InGaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) grown by selective metalorganic chemical vapor deposition (MOCVD). InGaAs/GaAs QD-in-NWs with various QD heights and In compositions are realized on patterned GaAs(111) B substrates in the form of InGaAs/GaAs heterostructures, and identified by structural analyses using scanning transmission electron microscopy, photoluminescence (PL) characterization, and numerical analyses of the band structure using a single-band effective mass approximation. Room temperature (RT) light emission is observed at 1.03 mu m from InGaAs/GaAs QD-in-NWs which is indicative of the formation of high-quality InGaAs QD-in-NWs. Sharp emission peaks from exciton and biexciton of single In(Ga) As QD-in-NWs are observed by using mu-PL characterization at 10 K. (C) 2012 The Japan Society of Applied Physics

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Nanocavity-enhanced optical Stark shift in a single quantum dot under extremely low excitation power

H Takagi, Y Ota, N Kumagai, S Ishida, S Iwamoto, Y Arakawa

2012 Conference on Lasers and Electro-Optics (CLEO), 1-2 (IEEE) 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 2160-9020

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Intra-cavity frequency doubling in photonic crystal nanocavity quantum dot lasers

Y Ota, K Watanabe, S Iwamoto, Y Arakawa

IEEE Photonics Conference 2012, 610-611 (IEEE) 610 - 611 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 2374-0140

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High Q H1 photonic crystal nanocavities with efficient vertical emission

H Takagi, Y Ota, N Kumagai, S Ishida, S Iwamoto, Y Arakawa

Optics express 20 (27), 28292-28300 (OPTICAL SOC AMER) 20 ( 27 ) 28292 - 28300 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 1094-4087

We report on newly-designed H1-type photonic crystal (PhC) nanocavities that simultaneously exhibit high Q factors, small mode volumes, and high external coupling efficiencies (eta perpendicular to) of light radiated above the PhC membrane. Dipole modes of the H1 PhC nanocavities, which are doubly-degenerate and orthogonally-polarized in theory, are investigated both by numerical calculations and experiments. Through modifying the sizes and positions of the air-holes near to the defect cavity, a Q factor of 62,000 is achieved, accompanied with an improved eta perpendicular to of 0.38 (assuming an objective lens with a numerical aperture of 0.65). A further increase of.. to more than 0.60 is observed at the expense of slight degradation of Q factor (down to 50,000). We further experimentally confirm the increase of both Q and eta perpendicular to, using micro-photoluminescence measurements, and demonstrate high Q factors up to 25,000: the highest value ever reported for dipole modes in H1 PhC nanocavities. (C) 2012 Optical Society of America

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High guided mode–cavity mode coupling for an efficient extraction of spontaneous emission of a single quantum dot embedded in a photonic crystal nanobeam cavity

A Enderlin, Y Ota, R Ohta, N Kumagai, S Ishida, S Iwamoto, Y Arakawa

Physical Review B 86 (7), 075314 2012

Research paper (scientific journal), Joint Work, Accepted

Wavelength Tunable Quantum Dot Single-Photon Source with a Side Gate

T Nakaoka, Y Tamura, T Miyazawa, K Watanabe, Y Ota, S Iwamoto, ...

Japanese Journal of Applied Physics 51 (2S), 02BJ05 (JAPAN SOC APPLIED PHYSICS) 51 ( 2 ) 2012

Research paper (scientific journal), Joint Work, Accepted, ISSN 0021-4922

We demonstrate photon antibunching from a wavelength controlled quantum dot single-photon source with a side gate. The photoluminescence peaks from the quantum dots embedded in the side-gate structure are clearly identified as a neutral exciton and a neutral biexciton by the studies of excitation-power dependence, polarization dependence, and photon correlation. The neutral exciton energy is controlled by the side gate via the quantum confined Stark effect. Measurement of the second-order autocorrelation function indicates g((2))(0) = 0.07 at 0 V, 0.14 at 0.8 V, and 0.24 at 0.9 V. The results show g((2))(0)s are below the 0.5 limit necessary for classification as a single photon source even under applied gate voltage. We also show a biexciton-exciton cascade which can be used to create entangled photon pairs. (C) 2012 The Japan Society of Applied Physics

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Effects of growth temperature of partial GaAs cap on InAs quantum dots in In‐flush process for single dot spectroscopy

N Kumagai, S Ohkouchi, M Shirane, Y Igarashi, M Nomura, Y Ota, ...

physica status solidi c 8 (2), 248-250 2011

Research paper (scientific journal), Joint Work, Accepted

Effects of growth temperature of partial GaAs cap on InAs quantum dots in In-flush process for single dot spectroscopy

Naoto Kumagai, Shunsuke Ohkouchi, Masayuki Shirane, Yuichi Igarashi, Masahiro Nomura, Yasutomo Ota, Shinichi Yorozu, Satoshi Iwamoto, Yasuhiko Arakawa

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 (WILEY-V C H VERLAG GMBH) 8 ( 2 ) 2011

Research paper (scientific journal), Joint Work, Accepted, ISSN 1862-6351

We have investigated effects of growth temperature of partial GaAs cap (T-cap) on InAs quantum dots (QDs) in indium-flush (In-flush) process with atomic force microscopy (AFM) and micro photoluminescence (mu-PL) measurements. T-cap in In-flush process are varied from 385 degrees C to 485 degrees C as an experimental parameter. In order to investigate the effects of T-cap on structural property of single InAs QD, shape of QD in initial capping process are characterized by AFM measurements in air at room temperature. While isotropic shape of QDs is kept in low T-cap conditions below about 440 degrees C, in-plane anisotropy of initial shape of QDs are increased with increasing of T-cap due to elongation to the [1 (1) over bar 0] direction. mu-PL measurements are performed at 7K for the investigation of the effects of T-cap on optical property in single InAs QDs. In low T-cap conditions from 410 degrees C to 435 degrees C, distinct emissions from excitonic states in single QDs are observed. In the same T-cap range, the AFM result shows that isotropic shape of QDs is kept. On the other hand, in high T-cap conditions above about 440 degrees C, indefinite peaks and broad emissions appear remarkably. Excitonic emissions which are observed in low T-cap range are hardly observed in this high T-cap range. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Competing influence of an in-plane electric field on the Stark shifts in a semiconductor quantum dot

T Nakaoka, Y Tamura, T Saito, T Miyazawa, K Watanabe, Y Ota, ...

Applied Physics Letters 99 (18), 181109 99 ( 18 ) 2011

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We report on the fabrication of a side-gate structure which enables a purely lateral electric field to be applied onto a self-assembled quantum dot. The lateral field produces an unconventional M'-shaped exciton energy shift-a blueshift followed by a redshift. The unconventional energy shift is reproduced by calculation. The calculation shows that only the positively charged exciton shows the unconventional shift. The origin is attributed to the field-induced hole-concentration in the bottom-corner of the dot, which strongly enhances the repulsive direct Coulomb interaction and reduces the exciton binding energy. © 2011 American Institute of Physics.

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New method to isolate and distribute photoluminescence emissions from InAs quantum dots over a wide-wavelength range

S Ohkouchi, N Kumagai, M Shirane, Y Igarashi, M Nomura, Y Ota, ...

Journal of crystal growth 323 (1), 250-253 (ELSEVIER SCIENCE BV) 323 ( 1 ) 250 - 253 2011

Research paper (scientific journal), Joint Work, Accepted, ISSN 0022-0248

We propose a new method to isolate and distribute the photoluminescence emission wavelengths of InAs quantum dots (QDs) over a wide-wavelength range by the growth of the partial GaAs capping layer at low temperature and annealing processes. When the partial capping layer was grown at 485 degrees C, the emission wavelengths of the QDs were distributed within a small range around the mean wavelength. On the other hand, when the partial capping layer was grown at a lower temperature of 423 degrees C, the emission wavelengths of the individual QDs were isolated and distributed over a wide range. Thus fabricated QDs are effective for the QD based devices such as single photon sources. (C) 2010 Elsevier B.V. All rights reserved.

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Strong coupling between a photonic crystal nanobeam cavity and a single quantum dot

R Ohta, Y Ota, M Nomura, N Kumagai, S Ishida, S Iwamoto, Y Arakawa

Applied Physics Letters 98 (17), 173104 (AMER INST PHYSICS) 98 ( 17 ) 2011

Research paper (scientific journal), Joint Work, Accepted, ISSN 0003-6951

We demonstrated the strong coupling between a one-dimensional photonic crystal nanobeam cavity and a single quantum dot (QD). Thanks to a high quality factor (similar to 25 000) with small mode volume [0.38 X (n/lambda)(3)] of the nanobeam cavity, an anticrossing behavior with a vacuum Rabi splitting of 226 mu eV was observed. The ratio of the QD-cavity coupling strength to the cavity decay rate, which is a figure of merit of quantum optical applications, is estimated to 2.1. This is the highest value among any QD-based cavity quantum electrodynamics systems reported so far. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3579535]

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Spontaneous two-photon emission from a single quantum dot

Y Ota, S Iwamoto, N Kumagai, Y Arakawa

Physical review letters 107 (23), 233602 (AMER PHYSICAL SOC) 107 ( 23 ) 233602 - 233602 2011

Research paper (scientific journal), Joint Work, Accepted, ISSN 0031-9007

Spontaneous two-photon emission from a solid-state single quantum emitter is observed. We investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high Q photonic crystal nanocavity. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity inspires the biexciton to simultaneously emit two photons into the mode, resulting in clear emission enhancement of the mode. Meanwhile, the suppression of other single photon emission from the biexciton was observed, as the two-photon emission process becomes faster than the others at the resonance.

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Observation of Purcell effect in a 3D photonic crystal nanocavity with a single quantum dot

A Tandaechanurat, Y Ota, N Kumagai, S Ishida, S Iwamoto, Y Arakawa

International Quantum Electronics Conference, J967 (Optics InfoBase Conference Papers) 10 - 11 2011

Research paper (scientific journal), Joint Work, Accepted

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Charged and neutral biexciton-exciton cascade in a single quantum dot within a photonic bandgap

M. Shirane, Y. Igarashi, Y. Ota, M. Nomura, N. Kumagai, S. Ohkouchi, A. Kirihara, S. Ishida, S. Iwamoto, S. Yorozu, Y. Arakawa

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES (ELSEVIER SCIENCE BV) 42 ( 10 ) 2563 - 2566 2010.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 1386-9477

We investigate the recombination dynamics of positively charged and neutral biexcitons and excitons in a single InAs/GaAs quantum dot (QD) within a two-dimensional (2D) photonic bandgap (PBG). The 20 PBG makes the exciton lifetime four times longer and enhances photon-extraction efficiency compared to those without the PBG. Photon cross-correlation measurements demonstrate the cascade emissions of both charged and neutral biexcitons-excitons from the same QD. In the charged case, a hole in the p-shell relaxes into the s-shell between the cascade, and the corresponding transition is confirmed based on the spin configuration. The long exciton lifetime with the PBG helps us to reveal the spin dynamics that did not clearly appear in intrinsic QDs. (C) 2010 Elsevier B.V. All rights reserved.

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Charged and neutral biexciton–exciton cascade in a single quantum dot within a photonic bandgap

M Shirane, Y Igarashi, Y Ota, M Nomura, N Kumagai, S Ohkouchi, ...

Physica E: Low-dimensional Systems and Nanostructures 42 (10), 2563-2566 2010

Research paper (scientific journal), Joint Work, Accepted

Laser oscillation in a strongly coupled single-quantum-dot–nanocavity system

M Nomura, N Kumagai, S Iwamoto, Y Ota, Y Arakawa

Nature Physics 6 (4), 279-283 (Springer Science and Business Media LLC) 6 ( 4 ) 279 - 283 2010

Research paper (scientific journal), Joint Work, Accepted, ISSN 1745-2473

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Suppression of indefinite peaks in InAs/GaAs quantum dot spectrum by low temperature capping in the indium-flush method

N Kumagai, S Ohkouchi, S Nakagawa, M Nomura, Y Ota, M Shirane, ...

Physica E: Low-dimensional Systems and Nanostructures 42 (10), 2753-2756 (ELSEVIER SCIENCE BV) 42 ( 10 ) 2753 - 2756 2010

Research paper (scientific journal), Joint Work, Accepted, ISSN 1386-9477

We have investigated effects of growth temperature of thin GaAs capping layer in the initial stage of indium-flush process using atomic force microscopy and microscopic photoluminescence (mu-PL) methods. The shape of capped InAs quantum dot (QD) and its mu-PL properties are sensitive to the growth temperature of thin GaAs capping layer. In the case of the high temperature cap, the QD shape in initial capping stage is elongated along the [1 1 -0] direction, and mu-PL spectrum shows several peaks accompanied with indefinite peaks. On the other hand, the low temperature case, the QD shape is kept in isotropic and mu-PL spectrum shows distinctive emissions from excitonic states of the QD with suppressed indefinite peaks. These results indicate that the low temperature capping is effective to keep an isotropic shape of QD and suppress indefinite peaks. (C) 2009 Elsevier B.V. All rights reserved.

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