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Tsuyoshi Yoshitake Last modified date:2018.06.23



Graduate School
Undergraduate School
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E-Mail
Homepage
http://yoshitake.private.coocan.jp/univ_lab/index-e.htm
Quantum Materials Physics Research division, Department of Engineering Sciences for Electronics and Materials, Kyushu University .
Academic Degree
Dr. Eng.
Field of Specialization
Applied Physics, Thin Solid Film, Solid State Physics
Outline Activities
● Research
We make a study of an ecologically friendly new material, which is rich-abundant and is made from non-toxic elements, for an electric device. For example, they are diamond which is a high-pressure and high-temperature phase, diamond-like carbon which is a non-equilibrium phase, beta iron disilicide which is a candidate semiconductor for an opt-electric device and the others. We fabricate them by the film preparation method using a laser and a plasma technology. In addition, we develop the film preparation system in cooperation with some small and medium enterprises. The detail subjects of the study are as follows.
【Low temperature growth of diamond films by pulsed laser deposition】
【Fabrication of hydrogen-free diamond-like carbon films by physical vapor depositions and their application for coating】
【Research concerning ecologically friendly semiconductors and their application for electric devices】
【Research in a semiconductor / ferromagnetic metal superlattice】
【Research in a new cathode material for a lithium ion battery】
【Development of the innovative film preparation system】

● Education
I belong to Department of Engineering Sciences for Electronics and Materials. My additional affiliation for graduate school education is Department of Applied Science for Electronics and Materials. Besides, I contribute to the undergraduate school education and have the following classes: “Lecture on mechanics and practice”, “Elemental experiment on physics” and “Soft energy for sustainability”.

● Social activities
I contribute to the study group of The Japan Society of Applied Physics as a manager and contribute to Kyushu Chapter of The Japan Society of Applied Physics as an administrator.
In Kyushu University, I hold a additional post as a technical advisor of Kyushu TLO Company, Limited. In the year 2003, I had lectures in an open class and a seminar of the graduate school.
I have a lecture of the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University.
Research
Research Interests
  • Fabrication of new spintronics devises based on ferromagnetic Fe3Si/semiconducting FeSi2 heterostructural artificial lattices using nanofabrication techniques
    keyword : Fe-Si, spintronics, CPP, lithography
    2011.04【Research in a semiconductor / ferromagnetic metal superlattice】 There have been few studies for the hetero-structure, such as the ferromagnetic metal /semiconductor multi-layered film, because the fabrication is extremely difficult. However, this hetero-structure has a possibility that the anti-ferromagnetic and ferromagnetic coupling among the ferromagnetic layers can be switched through the intermediary of the semiconducting layers, whose electrical band structure can be changed by the heat and photons. Fe-Si system has both the semiconducting phases such as beta-FeSi2, amorphous FeSi2 and FeSi, and the ferromagnetic ones such as Fe3Si and Fe、and expected as a new candidate for spintronic. We fabricate the Fe3Si or Fe / nanocrystalline (NC) FeSi2 multi-layered films, and study a new physical properties at optical, electrical and magnetic points of view..
  • Applications of ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCDa/-C:H) films to phtodiodes including solar cells
    keyword : ultrananocrystalline diamond, UNCD, photodiodes, photoviltaics, solar cells
    2011.04【Low temperature growth of diamond and nanocrystalline diamond films by pulsed laser deposition】Diamond has many excellent properties such as the highest hardness, high chemical inertness, low friction coefficient and high optical transparency and thus it is expected for a variety of applications. In addition, it overcomes ecological and resources problems. Nanocrystalline diamond is also expected as a candidate for coating and heat sink, because it is easy to be grown and it has a smooth surface like DLC, and because it is stable for temperature and has high heat conductivity similarly to diamond. In this study, we attempt to grow them at a low substrate temperature by pulsed laser deposition in order to realize the application for a heat sink coating and an electric device..
  • Fabrication of cubic β-AlN films and evaluations of their physical properties
    keyword : cubic AlN, cubic, physical vapor deposition
    2005.04.
  • Study on ultrananocrystalline diamond films prepared by a coaxial arc plasma gun and their applications to hard coating and photovoltaics
    keyword : ultrananocrystaloine diamond, coaxial arc plasma gun, hard coating, photovoltaics
    2005.04.
  • Farbrication of ultrananocrystalline diamond films by pulsed laser deposition
    keyword : ultrananocrystalline diamond, UNCD. pulsed laser deposition, PLD
    2000.04~2006.03【Low temperature growth of diamond and nanocrystalline diamond films by pulsed laser deposition】Diamond has many excellent properties such as the highest hardness, high chemical inertness, low friction coefficient and high optical transparency and thus it is expected for a variety of applications. In addition, it overcomes ecological and resources problems. Nanocrystalline diamond is also expected as a candidate for coating and heat sink, because it is easy to be grown and it has a smooth surface like DLC, and because it is stable for temperature and has high heat conductivity similarly to diamond. In this study, we attempt to grow them at a low substrate temperature by pulsed laser deposition in order to realize the application for a heat sink coating and an electric device..
  • Applications of iron disilicides to photovoltaics and NIR sensors
    keyword : beta iron disilicide, nanocrystalline iron disilicide, sputterng
    1999.04【Research concerning ecologically friendly semiconductors and their application for electric devices】 Nowadays, it is necessary for the materials tractable for the industrial application to have not only excellent material properties but also favorable ecological properties such as non-toxicity, abundance, and recyclability. Semiconducting beta-FeSi2 has excellent properties such as a direct optical band gap of 0.8-0.85 eV, a large optical absorption coefficient, good physical-chemical stability at high temperature and high resistance to the oxidation, and the possibility of growing epitaxially on Si substrates. In addition to these material properties, it overcomes ecological and resources problems because of its nontoxicity and the rich deposits that are present on earth. So it is expected to be a useful promising material for solar cells with theoretical efficiencies from 16 to 23 % in the future. In addition, recently it was reported that amorphous forms of iron disilicide also indicated semiconducting properties. It is very attractive at both the physical and engineering points of view because it can be grown easily on various kinds of substrate at room temperature. In this study, we fabricated thin films both by pulsed laser deposition (PLD) and by facing target DC sputtering (FTDCS) which was advantageous for the engineering applications, for the purpose of applying for the electric device such as a solar sell..
  • Fabrication of semiconductor/ferromagnetic metal atrificial lattices and study on their new physical phenomena based on spin-dependent conduction
    keyword : heterostructure, semiconductor, ferromagnetic, interlayer coupling, artificial lattices
    2001.04~2011.03【Research in a semiconductor / ferromagnetic metal superlattice】 There have been few studies for the hetero-structure, such as the ferromagnetic metal /semiconductor multi-layered film, because the fabrication is extremely difficult. However, this hetero-structure has a possibility that the anti-ferromagnetic and ferromagnetic coupling among the ferromagnetic layers can be switched through the intermediary of the semiconducting layers, whose electrical band structure can be changed by the heat and photons. Fe-Si system has both the semiconducting phases such as beta-FeSi2, amorphous FeSi2 and FeSi, and the ferromagnetic ones such as Fe3Si and Fe、and expected as a new candidate for spintronic. We fabricate the Fe3Si or Fe / nanocrystalline (NC) FeSi2 multi-layered films, and study a new physical properties at optical, electrical and magnetic points of view..
  • Fabrication of diamond-like carbon films by pulsed laser deposition
    keyword : DLC, PLD
    1996.04~2003.03【Fabrication of hydrogen-free diamond-like carbon films by physical vapor depositions and their application for coating】 Diamond-like carbon (DLC) have been adapted for coating on a metal mold, a tool and a machine part, because it has a high hardness, a low friction coefficient, a high adhesion and so on. DLC containing hydrogen has been mainly fabricated by a chemical vapor deposition method and have been applied for various industries as mentioned above. Hydrogen-free DLC prepared by physical vapor deposition methods has received much attention in recent years, because the deposited films have more excellent properties than those prepared by CVD. In general, hydrogen-free DLC is prepared by sputtering now. In this study, in order to grow a hydrogen-free DLC film having more excellent properties, we adapt a pulsed laser deposition method using a graphite target..
Current and Past Project
  • Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films, which are comprised of diamond crystallites with diameter of less than 10 nm embedded in an a-C:H matrix, possess large optical absorption coefficients in the visible range due to a large number of grain boundaries. Here, the grain boundaries exactly means that the interfaces between UNCD crystallites and those between UNCD and an a-C:H matrix. We have confirmed evident photoconduction corresponding to the large optical absorption. In this work, we are committed to apply this photoconduction to photovoltaics.
Academic Activities
Books
1. Mahmoud Shaban and Tsuyoshi Yoshitake, n-Type β-FeSi2/p-type Si near-infrared photodiodes prepared by facing-targets direct-current sputtering, InTech Open Access Publisher, in Advances in Photodiodes (InTech, 2010) Chap. 1., 2010.12.
Papers
1. Satoshi Takeichi, Takashi Nishiyama, Mitsuru Tabara, Shuichi Kawawaki, Masamichi Kohno, Koji Takahashi, Tsuyoshi Yoshitake, Hydrogenation effects on thermal conductivity of ultrananocrystalline diamond/amorphous carbon com-posite films prepared by coaxial arc plasma deposition, Appl. Phys. Express, https://doi.org/10.7567/APEX.11.065101, Vol. 11, No. 6 (2018) 065101, 2018.06.
2. Abdelrahman Zkria, Tsuyoshi Yoshitake, Temperature-dependent current-voltage characteristics and ultraviolet light detection of heterojunction diodes comprising n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films and p-type silicon substrates, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.7567/JJAP.56.07KD04, 56, 7, 2017.07, Heterojunction diodes comprising poorly (1 at. %) nitrogen-doped n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and p-type Si substrates were prepared in nitrogen and hydrogen mixed gas atmosphere by coaxial arc plasma deposition. Dark current density-voltage (J-V) characteristics were studied in the temperature range of 200-400 K, in order to investigate the current transport mechanism through the fabricated heterojunctions. The temperature dependence of the ideality factor and reverse saturation current reveals that carrier transport predominantly occurs in the generation-recombination mechanism and, at low temperatures, it accompanies tunneling via weak traps. The heterojunctions surely exhibited photodetection for 254nm ultraviolet light illumination. It is expected that photocarriers will be generated at UNCD grains and transported through an a-C:H matrix..
3. Takanori Hanada, Shinya Ohmagari, Abdelrahman Zkria, Nathaporn Promros, Tsuyoshi Yoshitake, Photodetection Characteristics of Heterojunctions Comprising p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films and n-Type Si Substrates at Low Temperatures, Journal of Nanoelectronics and Nanotechnology, DOI: https://doi.org/10.1166/jnn.2017.14104, Vol. 17, No. 5, pp. 3348-3351, 2017.05.
4. Abdelrahman Zkria, Hiroki Gima, Tsuyoshi Yoshitake, Application of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films for ultraviolet detection, Appl. Phys. A, DOI 10.1007/s00339-017-0798-4, Vol. 123, issue 581, 167 (6 pages), 2017.02.
5. Hiroki Gima, Abdelrahman Zkria, Yuki Katamune, Ryota Ohtani, Satoshi Koizumi, Tsuyoshi Yoshitake, Chemical bonding structural analysis of nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition, Applied Physics Express, 10.7567/APEX.10.015801, 10, 1, 2017.01, Nitrogen-doped ultra-nanocrystalline diamond/hydrogenated amorphous carbon composite films prepared in hydrogen and nitrogen mixed-gas atmospheres by coaxial arc plasma deposition with graphite targets were studied electrically and chemical-bonding-structurally. The electrical conductivity was increased by nitrogen doping, accompanied by the production of n-type conduction. From X-ray photoemission, near-edge X-ray absorption fine-structure, hydrogen forward-scattering, and Fourier transform infrared spectral results, it is expected that hydrogen atoms that terminate diamond grain boundaries will be partially replaced by nitrogen atoms and, consequently, φ C-N and C=N bonds that easily generate free electrons will be formed at grain boundaries..
6. Abdelrahman Zkria, Mahmoud Shaban, Takanori Hanada, Nathaporn Promros, Tsuyoshi Yoshitake, Current transport mechanisms in n-type ultrananocrystalline diamond/p-type Si heterojunctions, Journal of Nanoscience and Nanotechnology, 10.1166/jnn.2016.13663, 16, 12, 12749-12753, 2016.12, Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited on p-type Si substrates by coaxial arc plasma deposition. The deposited films possessed n-type conduction, and evidently formed pn heterojunctions with p-type Si substrates. The heterojunction devices showed typical rectification properties similar to those observed for conventional abrupt pn heterojunctions. The conduction mechanisms that govern current transport in these devices were analyzed using dark current-voltage measurements in the temperature range from 300 K to 80 K. The results revealed that a trap-assisted multi-step tunneling process is a dominant mechanism at lower temperatures and low forward bias. At least two defect levels with activation energies of 42 and 24 meV appear to activate this process. At moderate forward bias, the current followed a power-law dependence, attributable to a space-charge-limited current. This junction behavior might be owing to a large number of grain boundaries in the UNCD/a-C:H film that provide active centers for carrier recombination-tunneling processes at the junction interface..
7. Abdelrahman Zkria, Yuki Katamune, Tsuyoshi Yoshitake, Effects of Nitrogen doping on the electrical conductivity and optical absorption of ultrananocrystalline diamond/hydrogenated amorphous carbon films prepared by coaxial arc plasma dep, Jpn. J. Appl. Phys., http://doi.org/10.7567/JJAP.55.07LE01, Vol. 55, No. 7S2 (2016) 07LE01, 2016.07.
8. Nathaporn Promros, Ryuji Baba, Motoki Takahara, Tarek M. Mostafa, Phongsaphak Sittimart, Mahmoud Shaban, Tsuyoshi Yoshitake, Epitaxial Growth of beta-FeSi2 Thin Films on Si(111) Substrates by Radio Frequency Magnetron Sputtering and Their Application to Near-Infrared Photodetection, Jpn. J. Appl. Phys., http://doi.org/10.7567/JJAP.55.06HC03, Vol. 55, No. 6S2, 06HC03, 2016.06.
9. Hiroshi Naragino, Mohamed Egiza, Aki Tominaga, Kouki Murasawa, Hidenobu Gonda, Masatoshi Sakurai, Tsuyoshi Yoshitake, Room-temperature hard coating of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films on tungsten carbide by coaxial arc plasma deposition, Jpn. J. Appl. Phys. (Rapid Communication), http://doi.org/10.7567/JJAP.55.030302, Vol. 55, No. 3, 030302., 2016.01.
10. Takeshi Hara, Kenji Hanada, Tsuyoshi Yoshitake, Detection Methods of Diamond Diffraction Peaks in Ultrananocrystalline diamond?Amorphous Carbon Composite Films by X-ray Diffraction Measurement with Semiconductor Counter Detector, Jpn. J. Appl. Phys, to be published, 2015.11.
11. Yūki Katamune, Satoshi Takeichi, Shinya Ohmagari, Tsuyoshi Yoshitake, Hydrogenation effects on carrier transport in boron-doped ultrananocrystalline diamond/amorphous carbon films prepared by coaxial arc plasma deposition, J. Vac. Sci. Tech. A, http://dx.doi.org/10.1116/1.4931062, Vol. 6, Issue 6 (2015) 061514., 2015.09, [URL].
12. Abdelrahman Zkria, Hiroki Gima, Mahmoud Shaban, Tsuyoshi Yoshitake, Electrical Characteristics of Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition
, Appl. Phys. Express, doi:10.7567/APEX.8.095101, Vol. 8, No. 9 (2015) 095101, 2015.09, Nitrogen-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were synthesized in
nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition. The temperature dependence of electrical resistivity implies that
carriers are transported in hopping conduction. Heterojunctions comprising 3 at.% nitrogen-doped films and p-Si substrates exhibited a typical
rectifying action. The expansion of a depletion region into the film side was confirmed from the capacitance–voltage characteristics, and the built-in
potential and carrier concentration were estimated to be 0.51 eV and 7.5 ' 1016cm%3, respectively. It was experimentally demonstrated that
nitrogen-doped UNCD/a-C:H is applicable as an n-type semiconductor..
13. Hiroshi Naragino, Aki Tominaga, Kenji Hanada, Tsuyoshi Yoshitake, A synthesis method of ultrananocrystalline diamond in powder employing a coaxial arc plasma gun, Appl. Phys. Express, doi:10.7567/APEX.8.075101, Vol. 8, No. 7 (2015) 075101., 2015.07, A new method that enables us to synthesize ultrananocrystalline diamond (UNCD) in powder is proposed. Highly energetic carbon species ejected
from a graphite cathode of a coaxial arc plasma gun were provided on a quartz plate at a high density by repeated arc discharge in a compact
vacuum chamber, and resultant films automatically peeled from the plate were aggregated and powdered. The grain size was easily controlled
from 2.4 to 15.0nm by changing the arc discharge energy. It was experimentally demonstrated that the proposed method is a new and promising
method that enables us to synthesize UNCD in powder easily and controllably..
14. Tomohiro Yoshida, Yūtaro Ueda, Takeshi Daio, Aki Tominaga, Toshihiro Okajima, Tsuyoshi Yoshitake, Heteroepitaxial growth of b-AlN films on sapphire (0001) in nitrogen atmospheres by pulse laser deposition, Jpn. J. Appl. Phys., doi:10.7567/JJAP.54.06FJ05, Vol. 54, No. 6S1, 06FJ05., 2015.06.
15. Kenji Hanada, Tomohiro Yoshida, You Nakagawa, Hiroki Gima, Aki Tominaga, Masaaki Hirakawa, Yoshiaki Agawa, Takeharu Sugiyama, Tsuyoshi Yoshitake, Hardness and modulus of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by coaxial arc plasma deposition, Appl. Phys. A, doi: 10.1007/s00339-014-8949-3, Vol. 119, Issue 1, pp 205-210.
, 2015.02.
16. Tomohiro Yoshida, Kenji Hanada, Hiroki Gima, Ryota Ohtani, Kazushi Sumitani, Hiroyuki Setoyama, Aki Tominaga, Tsuyoshi Yoshitake, Influences of repetition rate of arc discharges on hardness and modules of ultrananocrystalline diamond films prepared by coaxial arc plasma deposition, Mater. Res. Express, doi: 10.1088/2053-1591/2/1/015021, Vol. 2, No.1 (2015) 015021., 2015.01.
17. Shinya Ohmagari, Takanori Hanada, Yūki Katamune, Sausan Al-Riyami, Tsuyoshi Yoshitake, Carrier Transport and Photodetection in Heterojunction Photodiodes Comprising n-Type Silicon and p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films, Jpn. J. Appl. Phys. , 10.7567/JJAP.53.050307, Vol. 53, No. 5, 050307, 2014.05.
18. Ken-ichiro Sakai, Yuta Noda, takeshi Daio, Daiki Tsumagari, Aki Tominaga, Kaoru Takeda, Tsuyoshi Yoshitake, Current-induced Magnetization Switching at Low Current Densities in CPP Structural Fe3Si/FeSi2 Artificial Lattices, Jpn. J. Appl. Phys. , 10.7567/JJAP.53.02BC15, Vol. 53, Issue 2S, 02BC15, 2014.02.
19. Ken-ichiro Sakai, Yuta Noda, Daiki Tsumagari, Hiroyuki Deguchi, Kaoru Takeda, Tsuyoshi Yoshitake, Temperature-Dependent Interlayer coupling in Fe3Si/FeSi2 artificial lattices, Phys. Status Solidi A, 10.1002/pssa.201330116, Vol. 211, No. 2, 323-328, 2014.02.
20. Sausan Al-Riyami, Hiroki Gima, Hiroshi Akamine, Tsuyoshi Yoshitake, Chemical Bonding of Nitrogenated Ultrananocrystalline Diamond Films Deposited on Titanium Substrates by Pulsed Laser Deposition, ECS J. Solid State Sci. Technol., 10.1149/2.016311jss, Vol. 2, issue 11 (2013) M33-38, 2013.11.
21. Yutaro Ueda, Takeshi Daio, Tomohiro Yoshida, Aki Tominaga, Toshihiro Okajima, Tsuyoshi Yoshitake, Crystalline-Structural Evaluations of Cubic AlN Thin Films Heteroepitaxially Grown on Sapphire(0001) by Pulsed Laser Deposition , Jpn. J. Appl. Phys., 10.7567/JJAP.52.08JE03, Vol. 52, No. 8 (2013) 08JE03., 2013.06, [URL], Cubic β-AlN thin films with different thicknesses were grown on sapphire (0001) in nitrogen atmosphere by pulsed laser deposition with sintered AlN targets, and their film structures were evaluated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found that β-AlN layers with a lattice constant of 7.89 Å are epitaxially grown on sapphire (0001) with a relationship of βAlN(111)[111]∥Al2O3(0001)[1100] at film thicknesses of less than 20 nm, and at larger thicknesses, polycrystalline β-AlN grains are grown on the epitaxial β-AlN layers in the Stranski–Krastanov (SK) mode. .
22. Sausan Al-Riyami, Hiroki Gima, Tsuyoshi Yoshitake, Effects of Hydrogen and Nitrogen Atmospheres on Growth of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films by Reactive Pulsed Laser Deposition, Jpn. J. Appl. Phys., 10.7567/JJAP.52.06GG06, Vol. 52, No. 6 (2013) 06GG06., 2013.06, [URL], The growth of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films was realized by pulsed laser deposition with a graphite target in a nitrogen atmosphere totally excluding hydrogen. The existence of 7 nm diamond grains was confirmed by X-ray diffraction. Nitrogen incorporation into the films was confirmed by X-ray photoemission and near-edge X-ray absorption structure spectroscopies, and the nitrogenation produced n-type conduction with an electrical conductivity of 0.2 Ω-1· cm-1 at 300 K. The results of study proved that nitrogen acts as a reactive gas for the formation of diamond grains, similarly to hydrogen. .
23. Yuki Katamune, Shinya Ohmagari, Sausan Al-Riyami, Seishi Takagi, Mahmoud Shaban, Tsuyoshi Yoshitake, Heterojunction Diodes Comprising p-Type Ultrananocrystalline Diamond Films Prepared by Coaxial Arc Plasma Deposition and n-Type Silicon Substrates , Jpn. J. Appl. Phys., 10.7567/JJAP.52.065801, Vol. 52, No. 6 (2013) 065801., 2013.06, [URL], Heterojunction diodes, which comprise boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by coaxial arc plasma deposition and n-type Si substrates, were electrically studied. The current–voltage characteristics showed a typical rectification action. An ideality factor of 3.7 in the forward-current implies that carrier transport is accompanied by some processes such as tunneling in addition to the generation–recombination process. From the capacitance–voltage measurements, the built-in potential was estimated to be approximately 0.6 eV, which is in agreement with that in a band diagram prepared on the assumption that carriers are transported in an a-C:H matrix in UNCD/a-C:H. Photodetection for 254 nm monochromatic light, which is predominantly attributable to photocurrents generated in UNCD grains, was evidently confirmed in heterojunctions. Since dangling bonds are detectable by electron spin resonance spectroscopy, their control might be an important key for improving the rectifying action and photodetection performance. .
24. Nathaporn Promros, Li Chen, Tsuyoshi Yoshitake, Evaluation of n-Type Nanocrystalline FeSi2/p-Type Si Heterojunctions Prepared by Pulsed Laser Deposition as Near-Infrared Photodetectors, J. Nanosci. Nanotechnol. , 10.1166/jnn.2013.7311, Vol. 13, No. 5 (2013) pp. 3577–3581., 2013.05, n-Type nanocrystalline (NC) FeSi2/p-type Si heterojunctions, which were prepared by pulsed laser deposition, were evaluated as a near infrared photodiode. The built-in potential was estimated to be approximately 1.1 eV from the capacitance–voltage measurement. These junctions showed a rectifying behavior accompanied by a large leakage current. The near infrared light detection performance was evaluated using a 1.33 m laser in the temperature range of 77–300 K. At a reverse bias of −5 V, the detectivity was 55×107 cm Hz1/2 W−1 at 300 K and it was dramatically enhanced to be 80×1010 cm Hz1/2 W−1 at 77 K. It was demonstrated that NC-FeSi2 is a new potential material applicable to NIR photodetectors operating at low temperatures..
25. Shotra Izumi, Mahmoud Shaban, Nathaporn Promros, Keita Nomoto, Tsuyoshi Yoshitake, Near-Infrared Photodetection of beta-FeSi2/Si Heterojunction Photodiodes at Low Temperatures
, Appl. Phys. Lett., http://dx.doi.org/10.1063/1.4789391, Appl. Phys. Lett. Vol. 102, Issue 3 (2013) 032107, 2013.02, n-type b-FeSi2/p-type Si heterojunction photodiodes were fabricated by facing-targets direct-current
sputtering, and their near-infrared photodetection properties were studied in the temperature range of
50–300 K. At 300K, devices biased at 5V exhibited a current responsivity of 16.6mA/W. The
measured specific detectivity was remarkably improved from 3.5109 to 1.41011 cmHz1/2/W as
the devices were cooled from 300K down to 50 K. This improvement is mainly attributable to
distinguished suppression in heterojunction leakage current at low temperatures. The obtained results
indicate that b-FeSi2/Si heterojunctions offer high potential to be employed as near-infrared
photodetectors that are compatible with the current Si technology. V.
26. E. Garratt, S. AlFaify, Tsuyoshi Yoshitake, Yuki Katamune, M. Bowden, M. Nandasiri, M. Ghantasala, D. C. Mancini, S. Thevuthasan, A. Kayani, Effect of chromium underlayer on the properties of nano-crystalline diamond films, Appl. Phys. Lett., http://dx.doi.org/10.1063/1.4774086, No. 102, Issue 1 (2012) 011913., 2013.01, [URL], This paper investigated the effect of chromium underlayer on the structure, microstructure, and composition of the nano-crystalline diamond films. Nano-crystalline diamond thin films were deposited at high temperature in microwave-induced plasma diluted with nitrogen, on single crystal silicon substrate with a thin film of chromium as an underlayer. Characterization of the film was implemented using non-Rutherford backscattering spectrometry, Raman spectroscopy, near-edge x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy. Nanoindentation studies showed that the films deposited on chromium underlayer have higher hardness values compared to those deposited on silicon without an underlayer. Diamond and graphitic phases of the films evaluated by x-ray and optical spectroscopic analyses determined consistency between the sp2 and sp3 phases of carbon in chromium sample to that of diamond grown on silicon. Diffusion of chromium was observed using ion beam analysis which was correlated with the formation of chromium complexes by x-ray diffraction..
27. Nathaporn Promros, Kyohei Yamashita, Ryuhei Iwasaki, Tsuyoshi Yoshitake, Effects of Hydrogen Passivation on Near-Infrared Photodetection of n-Type -FeSi2/p-Type Si Heterojunction Photodiodes, Jpn. J. Appl. Phys. , http://dx.doi.org/10.1143/JJAP.51.108006, Vol. 51, No. 10 (2012) 108006., 2012.10, Hydrogen passivation was applied to the initial epitaxial growth of n-type -FeSi2 thin films on p-type Si(111) substrates. Such passivation was applied at different gas inflow H2/Ar ratios ranging from 0 to 1.0. The photodetection performance of the photodiode fabricated at the optimum ratio of 0.2 was markedly improved as compared with those of the other samples. The quantum efficiency and detectivity were 2.08% and 5:40 109 cmHz1=2W1, respectively. The enhanced photodetective performance should be mainly because dangling bonds that act as trap centers for photocarriers are effectively inactivated by the passivation..
28. , [URL].
29. Nathaporn Promros, Kyohei Yamashita, Shota Izumi, Ryu¯hei Iwasaki, Mahmoud Shaban, Tsuyoshi Yoshitake, Near-Infrared Photodetection of n-Type β-FeSi2/intrinsic Si/p-Type Si Heterojunctions at low temperatures, Jpn. J. Appl. Phys. , http://dx.doi.org/10.1143/JJAP.51.09MF02, Vol. 51, No. 9 (2012) 09MF02., 2012.09.
30. Shinya Ohmagari, Tsuyoshi Yoshitake, p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed Laser Deposition and Their Application to Photodetectors, Jpn. J. Appl. Phys., http://dx.doi.org/10.1143/JJAP.51.090123, Vol. 51, No. 9, (2012) 090123 (Selected Topics in Applied Physics), 2012.07.
31. Yuki Katamune, Shinya Ohmagari, Tsuyoshi Yoshitake, Boron-Induced Dramatically Enhanced Growth of Diamond Grains in Nanocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films deposition by Coaxial Arc Plasma Deposition, Jpn. J. Appl. Phys., 10.1143/JJAP.51.078003, Vol. 51, No. 7 (2012) 078003., 2012.07, [URL], Boron-doped nanocrystalline diamond/hydrogenated amorphous carbon composite films were prepared by coaxial arc plasma deposition. The X-ray diffraction measurement exhibited that the diamond grain size is remarkably increased from 2 nm (undoped films) to 82 nm and the lattices of the grains are dilated accompanied by the incorporation of boron atoms into the lattices. The near-edge X-ray absorption fine-structure showed a weak exciton peak of diamond due to the enlarged grains. The enhanced growth mechanism is discussed on the basis of a defect-induced diamond growth model. .
32. Yuki Katamune, Shinya Ohmagari, Itsuroh Suzuki, Tsuyoshi Yoshitake, Effects of Aluminum Incorporation on Diamond Grain Growth in Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Coaxial Arc Plasma Deposition, Jpn. J. Appl. Phys., 10.1143/JJAP.51.068002, Vol. 51, No. 6 (2012) 068002., 2012.06, [URL], Al-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were prepared by coaxial arc plasma deposition with an Al-blended graphite target. The grain size estimated from X-ray diffraction peaks was 27 nm; this value is an order of magnitude larger than that of unincorporated films. The appearance of diamond-200 and 222 peaks, which generally disappear due to the extinction rule of diffraction, and the dilation of lattice, implied the incorporation of Al atoms into the lattices. The near-edge X-ray absorption fine-structure showed a sharp exciton peak due to diamond, which is attributed to the enlarged grains. .
33. Shinya Ohmagari, Tsuyoshi Yoshitake, Deep-Ultraviolet Light Detection of p-Type Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films, Appl. Phys. Express, 10.1143/APEX.5.065202, Vol. 5, No. 6 (2012) 065202., 2012.06, [URL], Deep-ultraviolet (DUV) light detection of p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by pulsed laser deposition was investigated. The photocurrent spectra revealed that the UNCD/a-C:H films possess strong responses in the wavelength range between 210 and 280 nm, which might originate from UNCD grains. The heterojunction photodiodes comprised of p-type UNCD/a-C:H and n-type Si exhibited an obvious photovoltaic action for 254 nm DUV light illumination. The external quantum efficiency and responsivity of the photodiodes were estimated to be 71% and 130 mA/W, respectively. It was proved that UNCD/a-C:H is a new promising material applicable to DUV photodetectors..
34. Shinya Ohmagari, Yūki Katamune, Hikaru Ichinose, and Tsuyoshi Yoshitake, "Enhanced growth of diamond grains in ultrananocrystalline diamond/hydrogenated amorphous carbon composite films by pulsed laser deposition with boron-blended graphite targets", Jpn. J. Appl. Phys., 10.1143/JJAP.50.035101, Vol. 51, No. 2 (2012) 025503., 2012.02, [URL], Heterojunction diodes comprised of p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) and n-type Si, wherein 3 at. % boron-doped UNCD/a-C:H films were deposited on Si substrates by pulsed laser deposition, were electrically studied. The current–voltage (I–V) characteristics showed the typical rectification action with a leakage current density of 4.7 ×10-5 A/cm2 at a reverse voltage of -1 V. The carrier transport is expected to be in generation–recombination process accompanied by tunneling at low forward voltages of 0.1–0.5 V, and to be predominantly in tunneling at 0.5–1.0 V, from ideality factors estimated from the forward I–V curve. Grain boundaries in the UNCD/a-C:H film might act as centers for tunneling. From the capacitance–voltage measurement, the build-in potential of the heterojunction and an active carrier concentration in the p-type UNCD/a-C:H film were estimated to be 0.6 eV and 1.4 ×1017 cm-3, respectively. .
35. Ken-ichiro Sakai, Takayuki Sonoda, Shin-ichi Hirakawa, Kaoru Takeda, and Tsuyoshi Yoshitake, Current-Induced Magnetization Switching in Fe3Si/FeSi2 Artificial Lattices, Jpn. J. Appl. Phys., 10.1143/JJAP.50.08JD06, Vol. 51, No. 2 (2012) 028004., 2012.02, [URL], Fe3Si/FeSi2/Fe3Si trilayered films were grown on Si(111) substrates at a substrate temperature of 300 °C by facing-targets direct-current sputtering, and current-induced magnetization switching in current-perpendicular-to-plane geometry was studied for the films wherein an antiferromagnetic interlayer coupling perpendicular to the plane was probably formed at room temperature. The appearance of a hysteresis loop in the electrical resistance–injection current curve well coincided with that of a hysteresis loop in the magnetization curve perpendicular to the plane. In addition, the hysteresis loop in the electrical resistance–injection current curve disappeared under large magnetic fields. The origin of the change in the electrical resistance for the injection current might be the change in the interlayer coupling. .
36. Nathaporn Promros, Kyohei Yamashita, Chen Li, Kenji Kawai, Mahmoud Shaban, Toshihiro Okajima, and Tsuyoshi Yoshitake, n-Type Nanocrystalline FeSi2/intrinsic Si/p-Type Si Heterojunction Photodiodes fabricated by Facing-Targets Direct-Current Sputtering, Jpn. J. Appl. Phys., 10.1143/JJAP.51.021301, Vol. 51, No. 2 (2012) 021301., 2012.01, [URL], n-Type nanocrystalline (NC) FeSi2/intrinsic (i) Si/p-type Si heterojunctions, which were prepared by facing-target direct current sputtering, were evaluated as near-infrared photodiodes, and the effects of thin i-Si layer insertion on diode performance were studied. Their junction capacitance and reverse leakage current were clearly reduced compared with those of n-type NC-FeSi2/p-type Si heterojunctions. The capacitance–voltage curve implied that the effects of interface states is relatively suppressed by i-Si insertion. The near-infrared light detection performance was investigated using a 1.33 µm laser in the temperature range of 77–300 K. The detectivities at 300 and 77 K were 1.9 ×108 and 3.0 ×1011 cm Hz1/2 W-1, respectively, at a negative bias of -5 V, which were markedly improved compared with that of p–n heterojunctions. This might be because the formation of interface states that act as trap centers for photocarriers is suppressed. .
37. Shin-ichi Hirakawa, Takayuki Sonoda, Ken-ichiro Sakai, Kaoru Takeda1, and Tsuyoshi Yoshitake, Temperature-Dependent Current-Induced Magnetization Switching in Fe3Si/FeSi2/Fe3Si trilayered films, Jpn. J. Appl. Phys., 10.1143/JJAP.50.08JD06, Vol. 50, No. 8 (2011) 08JD06., 2011.08, [URL], Fe3Si/FeSi2/Fe3Si trilayered films were grown on Si(111) substrates at a substrate temperature of 300 °C by facing-targets direct-current sputtering, and current-induced magnetization switching in current-perpendicular-to-plane geometry was studied for the films wherein an antiferromagnetic interlayer coupling perpendicular to the plane was probably formed at room temperature. The appearance of a hysteresis loop in the electrical resistance–injection current curve well coincided with that of a hysteresis loop in the magnetization curve perpendicular to the plane. In addition, the hysteresis loop in the electrical resistance–injection current curve disappeared under large magnetic fields. The origin of the change in the electrical resistance for the injection current might be the change in the interlayer coupling. .
38. Sausan Al-Riyami, Shinya Ohmagari, and Tsuyoshi Yoshitake, Near-Edge X-ray Absorption Fine-Structure Spectroscopic Study on Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed Laser Deposition, Jpn. J. Appl. Phys., 10.1143/JJAP.50.08JD05, Vol. 50, No. 8 (2011) 08JD05., 2011.08, [URL], Nitrogen-doped ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films, which possessed n-type conduction with enhanced electrical conductivity, were prepared by pulsed laser deposition. The film doped with a nitrogen content of 7.9 at. % possessed enhanced electrical conductivity of 18 Ω-1·cm-1 at 300 K. The near-edge X-ray absorption fine-structure (NEXAFS) measurement indicated the appearance of additional peaks due to π* C=N, σ* C=N, and σ* C–N bonds compared with the spectra of undoped films. The sp2 bonding fraction estimated from the NEXAFS spectra increased with the nitrogen content. The enhanced electrical conductivity is probably due to the formation of additional π* and σ* states and the enhancement in the sp2 bonding fraction. .
39. Al-Riyami Sausan, Shinya Ohmagari, and Tsuyoshi Yoshitake, Fourier Transform Infrared Spectroscopic Study of Nitrogen-Doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed laser Deposition, Diamond Relat. Mater., Vol. 20 (2011) pp. 1072-1075., 2011.06.
40. Shinya Ohmagari, Sausan Al-Riyami, and Tsuyoshi Yoshitake, p-Type ultrananocrystalline diamond/hydrogenated amorphous carbon composite/n-type Si heterojunction diodes fabricated by pulsed laser deposition, Jpn. J. Appl. Phys. , 10.1143/JJAP.49.031302, Vol. 50, No. 3, 035101., 2011.03, [URL], p-Type ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films were fabricated by pulsed laser deposition using boron-doped graphite targets. Thermal analysis confirmed the occurrence of p-type conduction. The electrical conductivity increased with the doped amount of boron. An activation energy estimated from the Arrhenius plot was approximately 0.1 eV. Near-edge X-ray absorption fine structure spectra revealed that the σ*C–H peak weakened and the σ*C–B peak strengthened with an increase in the doped amount of boron. Fourier transform infrared spectroscopy showed that the sp3 C–H peak weakened with the doped amount of boron. These probably indicate that the hydrogen atoms that terminate the dangling bonds of UNCD crystallites are partially replaced with boron atoms. .
41. Kenji Hanada, Tomohiro Yoshida, You Nakagawa, and Tsuyoshi Yoshitake, Formation of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films in Vacuum by Using A Coaxial Arc Plasma Gun, Jpn. J. Appl. Phys., 10.1143/JJAP.49.125503, Vol. 49, No. 12 (2010) 125503., 2010.12, [URL], Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite films were grown in vacuum using a coaxial arc plasma gun. From the X-ray diffraction measurement, the UNCD crystallite size was estimated to be 1.6 nm. This size is dramatically reduced from that (2.3 nm) of UNCD/hydrogenated amorphous carbon (a-C:H) composite films grown in a hydrogen atmosphere. The sp3/(sp3 + sp2) value, which was estimated from the X-ray photoemission spectrum, was also reduced to be 41%. A reason for it might be the reduction in the UNCD crystallite size. From the near-edge X-ray absorption fine-structure (NEXAFS) spectrum, it was found that the π*C=C and π*C≡C bonds are preferentially formed instead of the σ*C–H bonds in the UNCD/a-C:H films. Since the extremely small UNCD crystallites (1.6 nm) correspond to the nuclei of diamond, we consider that UNCD crystallite formation should be due predominantly to nucleation. The supersaturated condition required for nucleation is expected to be realized in the deposition using the coaxial arc plasma gun. .
42. Mahmoud Shaban, Kenji Kawai, Nathaporn Promros, and Tsuyoshi Yoshitake, n-Type Nanocrystalline-FeSi2/p-Type Si Heterojunction Photodiodes Prepared at Room Temperature, IEEE Electron Device Lett., Vol. 31, No. 12, pp. 1428-1430., 2010.12.
43. Sausan Al-Riyami, Shinya Ohmagari, and Tsuyoshi Yoshitake, Electrical Properties and Chemical Bonding Structures of Nitrogen-doped Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Pulsed Laser Deposition, Appl. Phys. Express, 10.1143/APEX.3.115102, Vol. 3, No. 11 (2010) 115102., 2010.11, [URL], Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited by pulsed laser
deposition. The film doped with a nitrogen content of 7.9 at.% possessed n-type conduction with an electrical conductivity of 181cm1 at
300 K. A heterojunction with p-type Si exhibited typical rectifying action. The UNCD grain size was estimated to be 2.5nm from X-ray diffraction
measurement. Near-edge X-ray absorption fine-structure and Fourier transform infrared spectroscopies revealed the preferential formations of
C¼N and C–N bonds and an enhanced amount of sp2 bonds in the films..
44. Kenji Hanada, Tsuyoshi Yoshitake, Takashi Nishiyama, and Kunihito Nagayama, Time-Resolved Spectroscopic Observation of Deposition Processes of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films by Using a Coaxial Arc Plasma Gun, Jpn. J. Appl. Phys., 10.1143/JJAP.49.08JF09, Vol. 49, No. 8 (2010) 08JF09., 2010.08, [URL].
45. Kenji Hanada, Takashi Nishiyama, Tsuyoshi Yoshitake, and Kunihito Nagayama, Optical Emission Spectroscopic of Deposition Process of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films by Using a Coaxial Arc Plasma Gun, Diamond Relat. Mater., in press, 2010.05.
46. Kazushi Sumitani, Ryota Ohtani, Tomohiro Yoshida, You Nakagawa, Satoshi Mohri, Tsuyoshi Yoshitake, Influences of repetition rate of laser pulses on growth of crystalline AlN films on sapphire(0001) substrates by pulsed laser deposition, Diamond Relat. Mater., Vol. 19 (2010) pp. 618-620., 2010.04.
47. Sausan Al-Riyami, Shinya Ohmagari, and Tsuyoshi Yoshitake, X-ray Photoemission Spectroscopy of Nitrogen-Doped UNCD /a-C:H Films Prepared by Pulse Laser Deposition, Diamond Relat. Mater., 10.1016/j.diamond.2010.01.023, Vol. 19 (2010) pp. 510-513., 2010.04.
48. Shinya Ohmagari, Tsuyoshi Yoshitake, Akira Nagano, Ryota Ohtani, Hiroyuki Setoyama, Eiichi Kobayashi, and Kunihito Nagayama, X-ray photoemission spectroscopy study of ultrananocrystalline diamond/hydrogenated amorphous carbon films prepared by pulsed laser deposition, Diamond Relat. Mater., in press, 2010.04.
49. Shinya Ohmagari, Tsuyoshi Yoshitake , Akira Nagano, Ryota Ohtani, Hiroyuki Setoyama, Eiichi Kobayashi, Takeshi Hara, and Kunihito Nagayama, Formation of p-Type Semiconducting Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films by Boron Doping, Jpn. J. Appl. Phys., 10.1143/JJAP.49.031302, Vol. 49, No. 3 (2010) 031302, 2010.03, [URL].
50. Kazushi Sumitani , Ryota Ohtani, Tomohiro Yoshida, You Nakagawa, Satoshi Mohri, and Tsuyoshi Yoshitake, Synchrotron X-ray Diffraction Study of Single-Phase β-AlN Thin Film Heteroepitaxially Grown on a Sapphire(0001) Substrate by Pulsed Laser Deposition, Jpn. J. Appl. Phys. , Vol. 49, No. 2 (2010) 020212., 2010.02.
51. Tsuyoshi Yoshitake, You Nakagawa, Akira Nagano, Ryota Ohtani, Hiroyuki Setoyama, Eiichi Kobayashi, Kazushi Sumitani, Yoshiaki Agawa, and Kunihito Nagayama, Structural and physical characteristics of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films deposited using a coaxial arc-plasma gun, Jpn. J. Appl. Phys., 10.1143/JJAP.49.015503, Vol. 49, No. 1, 015503, 2010.01, [URL].
52. Mahmoud Shaban, Shota Izumi, Keita Nomoto, and Tsuyoshi Yoshitake, "n-Type β-FeSi2/intrinsic-Si/p-type Si heterojunction photodiodes for near-infrared light detection at room temperature", Appl. Phys. Lett., 10.1063/1.3250171 , Vol.95 (2009) 162102., 2009.10, [URL].
53. Mahmoud Shaban, Keita Nomoto, Shota Izumi, and Tsuyoshi Yoshitake, "Characterization of near-infrared n-type β-FeSi2/p-type Si heterojunction photodiodes at room temperature", Appl. Phys. Lett., 10.1063/1.3151915 , 94 (2009) 222113., 2009.06, [URL].
54. Shinya Ohmagari, Tsuyoshi Yoshitake, Akira Nagano, Sausan AL-Riyama, Ryota Ohtani, Hiroyuki Setoyama, Eiichi Kobayashi and Kunihito Nagayama, "Near-edge X-ray absorption fine-structure of ultrananocrystalline diamond/amorphous carbon films prepared by pulsed laser deposition", J. Nanomater., in press, 2009.03.
55. Tsuyoshi YOSHITAKE , Akira NAGANO, Shinya OHMAGARI, Masaru ITAKURA, Noriyuki KUWANO, Ryota OHTANI, Hiroyuki SETOYAMA, Eiichi KOBAYASHI, and Kunihito NAGAYAMA, "Near-edge X-ray absorption fine-structure, X-ray photoemission, Fourier transfer infrared spectroscopies of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films"
, Jpn. J. Appl. Phys., 10.1143/JJAP.48.020222, Vol. 48, No. 2 (2009) 020222., 2009.02, [URL].
56. Kenji Hanada, Takashi Nishiyama, Tsuyoshi Yoshitake, and Kunihito Nagayama, "Time-resolved Observation of Deposition Process of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films in Pulsed Laser Deposition", J. Nanomater., 2009 (2009) 901241., 2009.01.
57. Satoshi MOHRI, Tsuyoshi YOSHITAKE, Takeshi HARA, and Kunihito NAGAYAMA, "Growth of metastable cubic AlN by reactive pulsed laser deposition", Diamond Rel. Mater., 17, pp. 1796-1799, 2008.08.
58. Mahmoud SHABAN, Haruhiko KONDO, Kazuhiro NAKASHIMA, and Tsuyoshi YOSHITAKE, "Electrical and Photovoltaic Properties of n-Type Nanocrystalline FeSi2/p-Type Si Heterojunctions Prepared by Facing Target Direct-current Sputtering at Room Temperature", Jpn. J. Appl. Phys, 10.1143/JJAP.47.5420, Vol. 47, No. 7, pp. 5420-5422., 2008.07, [URL].
59. Mahmoud SHABAN, Keita NOMOTO, Kazuhiro NAKASHIMA, and Tsuyoshi YOSHITAKE, "Low-temperature Annealing of n-type β-FeSi2/p-type Si Heterojunctions"
, Jpn. J. Appl. Phys, Vol. 47, No. 5, pp. 3444-3446., 2008.05.
60. Tsuyoshi YOSHITAKE , Satoshi MOHRI, Takeshi HARA, and Kunihito NAGAYAMA, "Growth of metastable β-AlN by pulsed laser deposition", Jpn. J. Appl. Phys, Vol. 47, No. 5, pp. 3600-3602, 2008.05.
61. Kaoru TAKEDA, Tsuyoshi YOSHITAKE , Yoshiki SAKAMOTO, Tetsuya OGAWA, Daisuke HARA, Masaru ITAKURA, Noriyuki KUWANO, Toshinori KAJIWARA, and Kunihito NAGAYAMA, "Enhanced interlayer coupling and magnetoresistance ratio in Fe3Si/FeSi2 superlattices", Appl. Phys. Express, Vol. 1, No. 2 (2008) 021302., 2008.02.
62. Mahmoud SHABAN, Kazuhiro NAKASHIMA, and Tsuyoshi YOSHITAKE, "Substrate Temperature Dependence of Photovoltaic Properties of β-FeSi2/Si Heterojunctions Prepared by Facing-target DC Sputtering"
, Jpn. J. Appl. Phys. Part 1, Vol. 46, No. 12, pp. 77087710, 2007.12.
63. Kaoru TAKEDA, Tsuyoshi YOSHITAKE, Dai NAKAGAUCHI, Tetsuya OGAWA, Daisuke HARA, Masaru ITAKURA, Noriyuki KUWANO, Yoshitsugu TOMOKIYO, Toshiyuki KAJIWARA, and Kunihito Nagayama, "Epitaxy in Fe3Si/FeSi2 superlattices prepared by facing target direct-current sputtering at room tempertaure", Jpn. J. Appl. Phys. Part 1, Vol. 46, No. 12, pp. 78467848., 2007.12.
64. Tsuyoshi YOSHITAKE, Akira NAGANO, Masaru ITAKURA, Noriyuki KUWANO, Takeshi HARA, and Kunihito NAGAYAMA, "Spectral absorption properties of ultrananocrystalline diamond/amorphous carbon composite thin films prepared by pulsed laser deposition", Jpn. J. Appl. Phys. Part 2, 10.1143/JJAP.46.L936, Vol.46, No.38, pp.L936 - L938, 2007.10, [URL].
65. Mahmoud SHABAN, Kazuhiro NAKASHIMA, Wataru YOKOYAMA, and Tsuyoshi YOSHITAKE, "Photovoltaic Properties of n-type β-FeSi2/p-type Si Heterojunctions", Jpn. J. Appl. Phys. Part2, 10.1143/JJAP.46.L667, Vol. 46, No.27, pp. L667-L669, 2007.07, [URL].
66. T. Yoshitake, T. Ogawa, D. Nakagauchi, D. Hara, M. Itakura, N. Kuwano, Y. Tomokiyo, K. Takeda, T. Kajiwara, M. Ohashi, G. Oomi and K. Nagayama, "Interlayer coupling in ferromagnetic epitaxial Fe3Si/FeSi2 superlattices", Appl. Phys. Lett., 10.1063/1.2410222 , 89, 253110, 2006.12, [URL].
67. T. Yoshitake, Y. Inokuchi, A. Yuri, and K. Nagayama, "Direct epitaxial growth of semiconducting beta-FeSi2 thin films by facing targets direct-current sputtering", Appl. Phys. Lett., 10.1063/1.2200153 , 88, 182104, 2006.06, [URL].
68. K. Takarabe, H. Doi, Y. Mori, K. Fukui, T. Yoshitake, K. Nagayama, "Enhanced optical absorption in nano crystalline FeSi2 and hydrogenation effect on its characteristic energy", Appl. Phys. Lett., 88, 061911, 2006.02.
69. T. Yoshitake, D. Nakagauchi, T. Ogawa, M. Itakura, N. Kuwano, Y. Tomokiyo, T. Kajiwara, and K. Nagayama, "Room-temperature epitaxial growth of ferromagnetic Fe3Si films on Si(111) by facing target direct-current sputtering", Appl. Phys. Lett., 10.1063/1.1978984, 86, 26, 86, 262505, 2005.09.
70. Tsuyoshi Yoshitake, Takeshi Hara, Tomohito Fukugawa, Ling yun Zhu, Masaru Itakura, Noriyuki Kuwano, Yoshitsugu Tomokiyo and Kunihito Nagayama, "Low-Temperature Growth of Nanocrystalline Diamond by Reactive Pulsed Laser Deposition under a Hydrogen Atmosphere", Jpn. J. Appl. Phys. Part2, 10.1143/JJAP.43.L240, 43, 2B, L240-L242, Vol. 43, pp. L 240–L 242, 2004.06.
71. T. Yoshitake, M. Yatabe, M. Itakura, N. Kuwano, Y. Tomokiyo, and K. Nagayama, "Semiconducting nanocrystalline iron disilicide thin films prepared by pulsed-laser ablation", Appl. Phys. Lett., 10.1063/1.1617374, 83, 15, 3057-3059, Vol. 83, 3057-3059., 2003.10.
72. Tsuyoshi Yoshitake, Takashi Nishiyama and Kunihito Nagayama, "Homo-Growth of Diamond Single Phase Thin Films by Pulsed Laser Ablation of Graphite", Jpn. J. Appl. Phys. Part2, Vol.40, No.6A pp.L573 - L575., 2001.06.
73. Tsuyoshi Yoshitake, Gousuke Shiraishi, and Kunihito Nagayama, "Droplet-free thin films deposited by pulsed laser deposition using a mechanical filter", Jpn. J. Appl. Phys. Part1, Vol. 41, 836-837, 2001.02.
Presentations
1. Tsuyoshi Yoshitake, Eslam Abubakr, Hiroshi Ikenoue, Application of laser-induced doping in liquids containing dopants to diamond, OIST Diamond Workshop, 2017.10.
2. Tsuyoshi Yoshitake, Widely-variable electrical conductivity of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films prepared by PVD, 3rd French-Japanese Workshop on Diamond Power Devices, 2015.07.
3. Tsuyoshi Yoshitake, Preparation of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared by Physical Vapor Deposition and Their Application to Photodiodes and Hard Coating, Hasselt Diamond Workshop 2015 SBDD XX, 2015.02.
4. Tsuyoshi Yoshitake, Yuki Katamune, Takanori Hanada, Satoshi takeichi, Shinya Ohmagari, Application of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films to Photodiodes, Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014), 2014.12.
5. Tsuyoshi Yoshitake, Yuki Katamune, Takanori Hanada, Hiroki Gima, Abdelrahman M. Ahmed, Shinya Ohmagari, Sausan Al-Riyami, Kenji Hanada, Growth of UNCD/a-C:H composite films by PVD and their electrical conductivity control, Japan-France Workshop on Diamond Power Devices, 2014.10.
6. Tsuyoshi Yoshitake, Present state of research on photodiodes comprising iron disilicides and problems awaiting solution, International conference and summer school on advanced silicide technology 2014, 2014.07, Semiconducting iron disilicide is a new candidate applicable to near-infrared-wavelength photoelec-tronic devices [1-3], because it possesses features such as a direct optical band gap of 0.85 eV above an indirect gap (0.76 eV) and a large absorption coefficient, which is 10^5 cm1 at 1.0 eV[4]. Since beta-FeSi2 can be epitaxially grown on Si due to small lattice mismatches, a heterojunction diode comprising a beta-FeSi2 thin film and singlecrystalline Si substrate is a device that can be briefly formed by employing vapor deposition. For near-infrared light detection in the Si/beta-FeSi2 heterojunction diodes, near-infrared light transmitted through the front-side Si substrate can be absorbed in the depletion region of the back-side beta-FeSi2 thin film.
In our previous works, we have progresses researches on p-type Si/n-type beta-FeSi2 heterojunction diodes, totally from the epitaxially growth of beta-FeSi2 thin film on Si(111) by sputtering [5] to the evaluation of p-type Si/n-type beta-FeSi2 heterojunctions as photodetectors [6,7]. It was confirmed that beta-FeSi2 in the heterojunction evidently con-tributes to the photodetection of near-infrared light from the photoresponse spectrum of the heterojunction, as shown in Fig. 1. In addition, as shown in Fig.2, the heterojunction clearly exhibited current due to photogenerated carriers for 1.33 micrometer monochromatic light in the I-V curves in comparison with that in the dark. The detectivity at temperatures lower than 100 K reach approximately 2*10^11 cmHz^1/2 /W, which is comparable with that of existing near infrared photodiodes comprising PbS and InAs at the same temperature. However, the external quantum efficiency is less than 10 % [6,7].
In this presentation, the progress thus far of our research and recent problems that we are facing and should be solved for the next step will be introduced. A serious problem for p-type Si/n-type beta-FeSi2 heterojunctions is that a barrier due to a band offset appears in the valence band and it prevents from the flow of photogenerated carriers from the n-type beta-FeSi2 layer to the p-type Si layer. The opposite combination, namely n-type Si/p-type beta-FeSi2, is structurally ideal because of it has no barriers due to the band offset. In order to form p-type -FeSi2, the residual carrier density should be reduced for controlling the conduction type. Carbon doping, which might be effective for a reduction in the carrier density, will be introduced.

[1] D. Leong, M. Harry, K. J. Reeson, and K. P. Homewood, Nature (London) 387 (1997) 686.
[2] Y. Maeda, T. Akita, K. Umezawa, K. Miyake, M. Sagawa, SPIE Proc. 3419 (1998) 341916.
[3] T. Ootsuka, Y. Fudamoto, M. Osamura, T. Suemasu, Y. Makita, Y. Fukuzawa, and Y. Nakayama, Appl. Phys. Lett. 91 (2007) 142114.
[4] H. Udono, I. Kikuma, T. Okuno, Y. Matsumoto, and H. Tajima: Appl. Phys. Lett. 85 (2004) 1937.
[5] .M. Shaban, S. Izumi, K. Nomoto, and T. Yoshitake, Appl. Phys. Lett. 95 (2009) 162102.
[6] N. Promros, K. Yamashita, S. Izumi, R. Iwasaki, M. Shaban, and T. Yoshitake, Jpn. J. Appl. Phys. 51 (2012) 09MF02.
[7] S. Izumi, M. Shaban, N. Promros, K. Nomoto, and T. Yoshitake, Appl. Phys. Lett. 102 (2013) 032107..
7. Tsuyoshi Yoshitake, Ecologically Friendly Semiconductors: Iron Disilicides and Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon, IUMRS-International Conference on Electronic Materials (IUMRS-ICEM 2012), 2012.09.
Membership in Academic Society
  • Japan Society of Applied Physics
  • 学内
Awards
  • 学内
  • 学外
  • 学内
Educational
Educational Activities
【Graduate School】
The affiliation for graduate school education is Quantum Materials Physics Laboratory, Department of Applied Science for Electronics and Materials. I give two lectures every year as follows.
Advanced Topics of Quantum Materials Physics
Elemental Quantum Physics
In addition, I conrtibute to a lecture shared by deparment professors

【Undergraduate School】
I have two classes on elemental mechanics.
In addiiton, I join two shared lectures on renewable energy.
Social
Professional and Outreach Activities
【Academic society】
Chief accountant, Symposium on SAGA Light Sources, 2006

Accountant chairman, Symposium on Silicide Semiconductor and Related Materials, IUMRS-ICAM2003 (The 8th IUMRS International Conference on Advanced Materials).
Member of the organization committee, Symposium on High-Speed Photographing and Photonics 2003.

Member of the organization committee, Symposium on High-Speed Photographing and Photonics 2001.
Member of the executive committee, Summer School on Silicide Semiconductors and Related Materials (2001).

Member of the executive committee, UK-Japan Workshop on Kankyo-Semiconductors (2000).
Manager of the symposium, 2000 Spring JSAP Annual Meeting.
Member of the executive committee, 2000 Laser Society Annual meeting.

Member of the executive committee, The 1st Symposium on Kankyo-Semiconductors (1999).

Member of the executive committee, Symposium on Optics (1996).

【The others】
Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2006).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2005).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2004).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2003).
Technical advisor, Kyushu TLO Company, Limited (the year 2000-2003)
Lecturer, the university xtension(the 2003)

Lecturer, the 48th technical institute organized by KASTEC (2002).
Lecturer, KASTEC Seminar (2002).