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Affiliation |
Engineering educational research section Department of Engineering |
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External Link |
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IKARI Tetsuo
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Research Areas 【 display / non-display 】
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Manufacturing Technology (Mechanical Engineering, Electrical and Electronic Engineering, Chemical Engineering) / Electric and electronic materials
Papers 【 display / non-display 】
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Effectiveness of AlGaAs barrier layers as a redistribution channel of photoexcited carriers on anomalous temperature dependence of photoluminescence properties of GaAs quantum dots Reviewed
Yudai Miyauchi,1,a) Tetsuo Ikari,1 Takaaki Mano,2 Takeshi Noda,3 and Atsuhiko Fukuyama1
Journal of Applied Physics 128 055701 2020.6
Language：English Publishing type：Research paper (scientific journal)
Photoluminescence (PL) measurements at a wide temperature range, up to room temperature, for high-quality and high-density
GaAs/AlGaAs quantum dots (QDs) fabricated by droplet epitaxy were carried out to investigate the anomalous temperature dependence of
the PL peak energy from the QD ensemble. In addition to a reported redshift that deviated from the so-called Varshni's curve of the PL
peak energy in the low temperature region, a new blueshift was observed above 200 K. We analyzed the experimental results using a steadystate
rate equation model and observed a good agreement. The distribution of the QD sizes and the presence of the AlGaAs barrier layer as
a carrier coupling channel were considered in this model. This means that the wetting layer proposed thus far is not a necessary condition
for explaining the anomalous temperature behavior of the PL properties. In addition, it was found that the anomalous temperature behavior
was smeared out by the insertion of a GaAs height adjustment layer in order to homogenize the apparent QD size. We found that sufficient
control of the QD size is a necessary factor for high temperature stability of QD devices.DOI： 10.1063./5.0011571
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Effect of concentrated sunlight illumination on mobility and concentrator solar cell efficiency Reviewed
Tomoki Harada1*, Naoya Miyashita2 , Tetsuo Ikari1 , and Atsuhiko Fukuyama1
Japanese Journal of Applied Physics 59 071002 2020.6
Language：English Publishing type：Research paper (scientific journal)
The Hall measurements of n- and p-type Si and GaAs samples were carried out under concentrated sunlight illumination to discuss the effect of
illumination on mobility. We found that the carrier mobilities estimated from the experimental results decreased as the illumination increased. In
addition, we deduced that the lattice scattering and sample deterioration do not decrease the mobility. We then concluded that the decrease in
mobility is one of the reasons for the reduction in conversion efficiency of the concentrator solar cells. -
Decreasing of the thermal conductivity of Si nanopillar/SiGe composite films investigated by using a piezoelectric photothermal spectroscopy Reviewed
Tomoki Harada1, Tsubasa Aki1, Daisuke Ohori2, Seiji Samukawa2,3, Tetsuo Ikari1 and Atsuhiko Fukuyama1
Japanese Journal of Applied Physics 59 SKKA08 2020.4
Language：English Publishing type：Research paper (scientific journal)
To investigate the decrease of thermal conductivity ($\kappa $) of nanoscale Si materials, we conducted the piezoelectric photothermal (PPT) method for the highly periodic Si nanopillar arrays embedded in Si0.7Ge0.3. The PPT is an electrode free method that can measure a heat propagation in the parallel to the nanopillars direction. A distinctive dip was observed in the frequency-dependent PPT signal intensity. By focusing the dip frequency, $\kappa $ was estimated from the comparison with the model analysis based on the one-dimensional multilayer thermal diffusion equation. The estimated $\kappa $ was 0.19 ± 0.07 W m–1 K, in the parallel to the nanopillars direction. Since the considerable decrease of $\kappa $ was confirmed from the non-radiative recombination point of view, we found the present non-destructive PPT method is very useful to estimate $\kappa $ in the nanostructured devices for the thermoelectric application.
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Tsubasa Nakamura1*, Atsuhiko Fukuyama1, Masakazu Sugiyama2, and Tetsuo Ikari1
58 112001 - 112011 2019.10
Language：English Publishing type：Research paper (scientific journal)
We investigated the carrier non-radiative relaxation process of InGaAs/GaAsP superlattice (SL) solar cells with different barrier thicknesses by
combining piezoelectric photothermal (PPT) and surface photovoltage (SPV) measurements. The former technique detected heat generated by
non-radiative relaxation and the latter detected the surface potential change induced by the carrier accumulation. Although the mechanisms of
these measurements were different, corresponding signals of the transition between the quantum levels were observed in both spectra. The SPV
signal intensities were independent of the barrier thicknesses. The carrier tunneling process functioned poorly under open-circuit conditions.
Conversely, the PPT signal intensities increased with decreasing barrier thickness. We experimentally demonstrated that the non-radiative
relaxation component increased as the barrier thicknesses decreased owing to the lattice relaxation at interfaces between the quantum well and
barrier layers. We concluded that the non-radiative relaxation process in the SL structure must be directly evaluated to improve the solar cell
performance. © 2019 The Japan Society of Applied Physics -
Tsubasa Nakamura , Atsuhiko Fukuyama, Masakazu Sugiyama and Tetsuo Ikari
Journal of Physics D: Applied Physics 52 045104 2018.11
Language：English Publishing type：Research paper (scientific journal)
We discuss the effect of interlayer insertion into the light absorption region of a carrier escape process for superlattice (SL) solar cells determined by the temperature dependence of photoluminescence (PL) signals. 20-period SL solar cells, with and without interlayers, were prepared. The temperature dependence of the integrated PL intensities due to the transition between quantum levels is well explained by the carrier relaxation models consisting of four processes: radiative and nonradiative recombinations in the SL, thermionic emission to the barrier, and tunnelling after thermal excitation from the lower to the upper levels. We observed that the activation energy for the carrier thermal escaping the quantum well was significantly reduced by the insertion of an interlayer. Moreover, the carrier thermal escaping was also found to be dominant in all processes at 300 K from the calculation of the relevant lifetimes. These results indicate that the insertion of an interlayer results in SL solar cells with a higher efficiency than conventional solar cells.
DOI： 10.1088/1361-6463
Books 【 display / non-display 】
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薄膜シリコン系太陽電池の最新技術
碇 哲雄、福山敦彦（ Role： Joint author）
シーエムシー出版、2009年7月、pp.107-117 2009.7
Language：Japanese Book type：Scholarly book
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Progress of Photothermal and Photoacoustic Science and Technology - Semiconductors and elecronic materials
Tetsuo IKARI and Atsuhiiko FUKUYAMA（ Role： Joint author）
SPIE Press 2000.1
Language：English Book type：Scholarly book
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Photoacoustic and Photothermal Phenomena in Semiconductors
T. Ikari, Y. Koga and S. Shigetomi（ Role： Joint author）
North Holland 1987.1
Language：English Book type：Scholarly book
MISC 【 display / non-display 】
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世界初、酸化亜鉛で透明導電膜の大型化に成功
山本哲也、碇 哲雄、他6名
月刊ディスプレー 2004年6月 p.70-74 2006.6
Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media) Publisher：月刊ディスプレー？？
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圧電素子光熱分光法による微結晶シリコン薄膜の光吸収スペクトル
碇 哲雄、境健太郎、福山敦彦
超音波TECHNO 2004年9-10月号、p.75 2004.9
Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media) Publisher：超音波工業社
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反応性プラズマ蒸着法によるGa添加酸化亜鉛透明導電膜
山本哲也、碇 哲雄、他8名
機能材料 2004年9月 p.44-54 2004.9
Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media) Publisher：機能材料？
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圧電素子光熱分光法による半導体薄膜の評価
碇 哲雄、福山敦彦
日本光学会会誌、2005年2月 2004.2
Language：Japanese Publishing type：Research paper, summary (national, other academic conference) Publisher：日本光学会
Presentations 【 display / non-display 】
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Effects of N precursor duration on opt-electrical properties of GaAsN films grown by atomic layer epitaxy International conference
H. Suzuki, W. Ding, T. Yamaguchi, T. Haraguchi, S. Goto, Y. Yokoyama, K. Maeda, A. Fukuyama, and T. Ikari
23th Photovoltaic Science and Engineering Conference (PVSEC-23), Oct. 28 - Nov. 01, Taipei, Taiwan (2013). (Taipei, Taiwan) 23th Photovoltaic Science and Engineering Conference (PVSEC-23)
Event date： 2013.10.28 - 2013.11.1
Language：English Presentation type：Poster presentation
Venue：Taipei, Taiwan
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Bandgap Gradient of Cu(In,Ga)Se2 Solar Cell Investigated by a Photothermal and a Photoluminescence Spectroscopies International conference
A.Fukuyama, T. Ikari, H. Hisamatsu and S. Yamaguchi, T. Yamaguchi
EU-PVSEC (European Photovoltaic conference) , Sep. 30-Oct. 4, 1AV.2.23, Paris, France (2013). (Paris, France) EU-PVSEC (European Photovoltaic conference)
Event date： 2013.9.30 - 2013.10.3
Language：English Presentation type：Poster presentation
Venue：Paris, France
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Non-radiative carrier recombination rate in multiple quantum well solar cells determined by using a photothermal and a surface photovoltage spectroscopies International conference
T. Ikari, A. Fukuyama, T. Aihara, M. Kojima, M. Sugiyama, and Y. Nakano
EU-PVSEC (European Photovoltaic conference) , Sep. 30-Oct. 4, 1AV.2.23, Paris, France (2013). (Paris, France) EU-PVSEC (European Photovoltaic conference)
Event date： 2013.9.30 - 2013.10.3
Language：English Presentation type：Poster presentation
Venue：Paris, France
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Estimation of Mini-band in Strain-Balanced InGaAs/GaAsP Quantum Well Solar Cells by Using a Piezoelectric Photothermal Method International conference
T. Aihara, Y. Yokoyama, M. Kojima, H. Suzuki, A. Fukuyama, Y. Wang, M. Sugiyama, Y. Nakano, and T. Ikari,
The 39th IEEE Photovoltaic Specialists Conference (IEEE-PVSC39), June 16-21, USA (2013). (Tampa, USA) The 39th IEEE Photovoltaic Specialists Conference (IEEE-PVSC39)
Event date： 2013.6.16 - 2013.6.21
Language：English Presentation type：Poster presentation
Venue：Tampa, USA
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Effect of Si-doping on the photoreflectance spectra of catalyst-free MBE-VLS grown GaAs nanowires on the (111)Si substrate International conference
A. Suzuki, A. Fukuyama, J-H. Paek, M. Yamaguchi, and T. Ikari
EMRS (European Materials Research Society Symposium), May. 27-31, H-VI-1 Strasbourg, France (2013). Oral. (Strasbourg, France) EMRS
Event date： 2013.5.27 - 2013.5.31
Language：English Presentation type：Poster presentation
Venue：Strasbourg, France
Grant-in-Aid for Scientific Research 【 display / non-display 】
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非発光電子遷移損失からみた半導体量子構造太陽電池における超格子構造の優位性
Grant number：18K04876 2018.04 - 2023.03
独立行政法人日本学術振興会 科学研究費補助金 基盤研究(C)
碇 哲雄、福山 敦彦
Authorship：Coinvestigator(s)
量子化された電子準位間遷移を活用する量子構造太陽電池は、高効率デバイスとして精力的に研究がなされている。しかし、光励起されたキャリアの非発光再結合遷移は、効率を大きく低下させる重要な因子であるにもかかわらずその直接的測定が難しく、遷移メカニズムが解明できていない。我々は、この非発光電子遷移をその時に発生する熱を圧電素子で検出する光熱変換分光法という実験手法を持っており、太陽電池構造中の「非発光遷移による損失」を抽出して測定できる。そこで、従来の光学的評価法に我々独自の実験手法を加えることで、「光によって生成されたキャリアの全ての緩和過程」をその温度依存性の実験より系統的に解明し、それによって、現在の主流である「量子井戸」と「量子ドット」の構造における非発光遷移による損失と量子構造作製の正確さとの二つの観点から比較検討することで前者の優位性を示す。後者は、非発光遷移による損失の知見なしにはできないものである。
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光熱変換技術を用いた結晶成長方向に組成の異なる半導体薄膜の光吸収スペクトル測定
Grant number：25390082 2013.04 - 2016.03
科学研究費補助金 基盤研究(C)
Authorship：Principal investigator
この研究では、高感度PPTS法（光熱変換分光法）を用いて光励起キャリアの非発光緩和過程を実験的に調べ、結晶成長方向（膜厚方向）に組成、即ちエネルギーギャップが変化する薄膜半導体光デバイス材料の光吸収スペクトルを厚さ方向の関数として測定解析する新しい実験手法を開発する。
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光熱変換技術を用いた結晶粒界などで光散乱の多い半導体薄膜の光吸収スペクトル
Grant number：22560024 2010.06 - 2013.03
科学研究費補助金 基盤研究(C)
Authorship：Principal investigator
この研究では、高感度PPTS法（光熱変換分光法）を用いて、発熱という間接手段を用い、大きな結晶粒界や組成変動をもつ薄膜半導体光デバイス材料の光吸収スペクトルを測定可能にする実験手法を確立する。 特に積層型太陽電池や光ファイバー用発光素子として期待されるGaInN等の組成を持つ半導体薄膜に関しては現在の試料は組成が制御できていない事もあり、測定した禁制帯幅のIn濃度依存性が理論曲線に乗らない（研究業績：2007年#5,6）。従って、更に組成を精密制御した試料を用いたPPTS測定実験によって正確な禁制帯幅を数値解析して決定し、結晶組成やその均一性が電子帯構造に及ぼす影響を解明する。また、特に光散乱の大きいZnO薄膜などに対しては、ナノロッド、ナノワイアに付いてPPTS測定を行い、表面、界面の面積が大きい量子構造の光吸収スペクトルを測定する。これによって、これまで公表して来た超薄膜と共に、ナノ構造材料一般に適用できる新しい光学的評価技術が確立される。
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光熱変換分光法による超薄膜半導体量子構造の光吸収スペクトル
Grant number：15560020 2003.04 - 2005.03
科学研究費補助金 基盤研究(C)
光熱変換分光法による超薄膜半導体量子構造の光吸収スペクトル