博士論文概要

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Graduate School of Advanced Science and Engineering Waseda University

博士論文概要

Doctoral Thesis Synopsis

論文題目

Thesis Theme

Electron device applications of low-dimensional conductive carbon materials

低次元導電性炭素材料の電子デバイス応用

申請者

Masafumi INABA

稲葉優文

Department of Nanoscience and Nanoengineering, Research on Nanodevices

December, 2016

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No. 1

Low dimensional materials have unique quantum properties. Enormous numbers of studies have been reported about low dimensional materials. Carbon nanomaterials also have these low dimensional properties, and are the expected candidates for applying these quantum properties. The boundaries of low dimensional materials, such as the interface properties, and the interphase transition, also have the uniqueness and make us interested in. It is important to investigate the interfaces, especially electrical contact, of low dimensional carbon to other materials with 1-3 dimensions, the interface phase transition, and the conduction near interface to other materials.

Carbon nanotubes (CNTs) are known as a one dimensional material and have high electrical properties. A CNT has a structure of graphene sheet cylinder, and has no periodical edge except for cap region, which brings no electrical carrier backscattering. CNTs have chiralities, which determine the electric properties, that is, semiconducting or metallic. Although CNTs have the potential to withstand a very high current of up to ~10⁹ Acm^-2, in most cases, CNTs are used in applications with low conductivity, such as CNT electrodes for biosensing, supercapacitors, and thin-film transistors. For applying their excellent electrical properties in highly conductive devices such as power diodes and transistors, a dense forest of vertically aligned CNTs is advantageous because of its high CNT orientation and high density.

If almost all CNTs have semiconducting properties, extremely high density FET array can be realized.

But in reality, the mass CNTs, for example CNT forest, have distribution of its structure, and consists of both metallic and semiconducting CNTs. It is important to investigate its internal properties to use the excellent properties of CNTs.

Two dimensional carrier gas layer has been widely used in silicon metal-oxide-semiconductor filed-effect transistors (MOSFETs). Hydrogen-terminated (C-H) diamond surface also induces two dimensional hole gas layer (2DHG), which is due to surface dipole of C-H bond. Because C-H bond have a slight deviation of charge, H-terminated surface charges positively, and negative adsorbates in atmosphere or negative charges gate dielectric bend up the surface band, which induces 2DHG.

Fortunately, C-H diamond surface have no interfering surface potential and well-modulated. This p-type conductive layer on diamond has potential applications for power MOSFETs, and ion-sensitive sensors.

Because 2DHG on C-H diamond induces everywhere if the diamond is nearly intrinsic, and negative charges are placed on the surface, this will be induced on diamond side-walls. Although AlGaN/GaN high electron mobility transistors utilize two dimensional electron gas layer (2DEG) which is induced by spontaneous- and piezo- polarization of the interface of AlGaN and GaN, it cannot be induced on the side-walls due to the difference of plane direction.

In this thesis, electrical properties and electron devices using low dimensional carbon materials in longitudinal direction were investigated. For both CNTs and C-H diamond, longitudinal conduction properties have not been investigated, in spite of its necessity. In particular, properties of electrical contact of CNTs have some report for single CNT, but not investigated for the system of large number of CNTs.

CNTs formed on silicon carbide (SiC) is close-packed and vertically aligned CNT forest with zig-zag chiralities, and suitable for investigating contact properties. Firstly, CNT/SiC contact properties were

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investigated from a viewpoint of Schottky barrier. Secondly, CNT/CNT contact conductivity was investigated using not isolated CNTs but packed CNT forest. Thirdly, to investigate mass CNT system, the individual contact properties are investigated. Applying the contact resistivity to ordinal CNT forest, which is formed by remote plasma enhanced chemical vapor deposition in our case, we can investigate the internal electric properties. Forth, aligned sp² carbon was formed on (001) diamond using hot implantation and post annealing for the application of electrical contact to n-type diamond. Finally, we fabricated hydrogen terminated diamond metal-oxide-semiconductor field-effect transistors whose channel consists of two dimensional hole gas.

The chapter 1 overviews this thesis from the viewpoint of low dimensional carbon materials.

In chapter 2, ohmic contact properties of CNT/ SiC interface was observed. Because CNTs on SiC atomically connects to SiC substrate, CNT have the potential to be an ohmic contact material, where Schottky barrier height in CNT/SiC interface is low. To extract Schottky barrier height, contact resistivity was calculated using transfer length method by varying dopant density in SiC substrates. We limited the conduction area by adopting the focused ion beam fabrication technique and contact resistivity was extracted by changing the conduct area. The contact resistivity with the SiC dopant density of 3×10¹⁸ cm^-

3 was ~10^-4 Ωcm². The corresponding Schottky barrier height was 0.4–0.45 eV, which is comparably low to nickel silicide (NiSix). NiSix is the widely used contacting material for SiC. Because the Schottky barrier height of CNT/SiC is reported to ~1.4 eV from the x-ray photo spectroscopy, this value is 1 eV smaller. This difference comes from the edge termination of CNT/SiC interface. In case hydrogen atoms terminates the edges of CNT and SiC, the band bends and the barrier decreases. Considering the high thermal conductivity of CNTs, CNT forest on SiC have high potential to be a heat dissipative ohmic contact materials for SiC.

In chapter 3, CNT/CNT contact conductivity of CNT forest on SiC was evaluated. Because CNT forest on SiC is densely packed, CNTs are contact to each other. From the relationship between sheet conductivity of CNT forest and CNT forest height, or thickness, the CNT cap region have conduction with a sheet conduction of approximately 7 mS/sq. and the conductivity of dense CNT forest in in-plane direction was ~50 S/cm, which is 2–3 times lower than that of CNT yarn, whose conducting is in CNT on-axis direction. By assuming the ideal CNT forest, CNTs are faceted like hexagons. Then CNT contact area can be calculated and the contact conductivity of CNT/CNT interface was ~10⁸ S/cm². This value can be explained as tunneling contact conductivity of electron clouds of CNT walls. We compared the contact conductivity of a reported CNT dispersed film, where CNTs contact to each other like X-shape and Y-shape. By assuming the CNT contact width, the contact length for Y-shape contact was evaluated to be in the order of 100 nm.

In chapter 4, two types of electric double layer (EDL) FETs using long CNT forest channel was fabricated and evaluated. Some mm-long CNT forest wall was synthesized on silicon substrate from the Al/Fe/Al sandwich catalyst by remote plasma chemical vapor deposition. The CNT wall was laid on glass plate and source and drain electrodes was formed in two ways. One is that the axis of CNTs is parallel to

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No. 3

current conduction and the other is vertical. For the former device, very large current of over 1A was controlled for the first time in carbon nanotube FETs. For the latter devices, the on/off ratio was ~10 regardless of no metallic/semiconducting separation of CNTs. For the latter device, the conductance was

~0.03 S, which was lower than the former vertical type CNT FETs. By modeling the CNT forest, the CNT resistivity at on-state corresponds to the total contact resistance between CNT bundles, and that at off-state mainly corresponds to the total resistivity of CNT transfer at off-state. Using the CNT/CNT contact resistivity obtained from chapter 3, the off-state resistivity of a CNT was calculated to ~10¹² Ωcm, which is 3–4 times higher than the on-state resistivity in vertical type CNT FETs. This value is consistent to the calculated resistivity of a semiconductor with small bandgap. In addition, the on-state resistance of a CNT in transfer region may correspond to the quantum resistance, which indicates the carriers have ballistic transport property.

In chapter 5, a vertical edge graphite layer (VEG) was fabricated on a diamond (001) substrate after high-dose ion implantation and high temperature annealing. The Al ions were implanted into the diamond (001) surface at 773 K (500°C), followed by high-temperature rapid thermal annealing (RTA) at 1973 K (1700°C). The graphite edges were vertically oriented, but each domain was randomly rotated in the in-plane direction, which was confirmed via multiple cross-sectional TEM images obtained from different directions rotated 2, 5, 10, and 15° around the [001] axis. The Raman spectra of the VEG exhibited a broad peak at 1440 cm⁻¹, while no significant peaks were observed in the photoluminescence spectra. The initial sp² structure state of the VEG was nucleated in early stage of high-temperature RTA and surface diamond was subsequently reconstructed, which was confirmed using stopping-and-range- of-ions-in-matter calculations and Rutherford backscattering/channeling measurements. This VEG structure may be useful for ohmic contact with diamond electrical devices.

In chapter 6, C-H diamond MOSFETs with vertical 2DHG channel was fabricated. A 2DHG layer is ubiquitously formed on the C-H diamond surface covered by atomic-layer-deposited-Al2O3. Using Al2O3 as a gate oxide, C-H diamond metal oxide semiconductor field-effect transistors (MOSFETs) operate in a trench gate structure where the diamond side-wall acts as a channel. MOSFETs with a side-wall channel exhibit equivalent performance to the lateral C-H diamond MOSFET without a side-wall channel. Here, a vertical-type MOSFET with a drain on the bottom is demonstrated in diamond with channel current modulation by the gate and pinch off. This is the first report of vertical type diamond MOSFETs. In IDS-VDS characteristics, there is voltage onset of -40 V. This is because the barrier at the trench bottom. To conduct current, carrier have to pass through the undoped diamond layer at trench bottom. Because the 2DHG layer is p-type, undoped layer becomes a high barrier for hole. To confirm this barrier, we measured IDS-VDS characteristics at high temperature of 400 °C, and the onset decreased to -20 V.

Finally, I conclude this thesis in chapter 7.

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No.1

早稲田大学博士（工学）学位申請研究業績書

氏名稲葉優文印

（2017年2月現在）

種類別題名、発表・発行掲載誌名、発表・発行年月、連名者（申請者含む）

○Paper

Paper

○Proceedi ng

Patent

1. M. Inaba, T. Muta M. Kobayashi, T. Saito, M. Shibata, D. Matsumura, T. Kudo, A. Hiraiwa and H. Kawarada, "Hydrogen-terminated diamond vertical-type metal oxide semiconductor field-effect transistors with a trench gate", Appl. Phys. Lett. 109, 033503/1-4 (18 July 2016).

(DOI:10.1063/1.4958889)

2. M. Inaba, C.-Y. Lee, K. Suzuki, M. Shibuya, M.Myodo, Y. Hirano, W. Norimatsu, M.

Kusunoki, H.Kawarada, “Contact Conductivity of Uncapped Carbon Nanotubes Formed by Silicon Carbide Decomposition”, Journal of Physical Chemistry C, 120 (11), 6232–6238(27 February 2016)(DOI:10.1021/acs.jpcc.5b11815)

3. M. Inaba, K. Suzuki, M. Shibuya, C.-Y. Lee, Y. Masuda, N. Tomatsu, W. Norimatsu, A.

Hiraiwa, M. Kusunoki, H. Kawarada, "Very low Schottky barrier height at carbon nanotube and silicon carbide interface", Applied Physics Letters 106, 123501/1-5 (23 March 2015) (DOI:10.1063/1.4916248)

4. M. Myodo, M. Inaba, K. Ohara, R. Kato, M. Kobayashi, Y. Hirano, K. Suzuki, H. Kawarada,

“Large-current-controllable carbon nanotube field-effect transistor in electrolyte solution”, Applied Physics Letters 106, 213503/1-4 (27 May 2015)(DOI: 10.1063/1.4921454)

5. Y. Shintani, S. Ibori, K. Igarashi, T. Naramura, M. Inaba, H. Kawarada, "Polycrystalline boron- doped diamond with an oxygen-terminated surface channel as an electrolyte-solution-gate field-effect transistor for pH sensing", Electrochimica Acta, 212, 10-15 (10 Sept.2016) (DOI:10.1016/j.electacta.2016.06.104)

6. Y. Kitabayashi, T. Kudo, H. Tsuboi, T. Yamada, D. Xu, M. Shibata, D. Matsumura, Y.

Hayashi, Mohd Syamsul, M. Inaba, A. Hiraiwa and H. Kawarada, “Normally-off C- H Diamond MOSFETs with Partial C-O Channel Achieving 2-kV Breakdown Voltage”, IEEE Electron Device Letters, accepted.

7. H. Yamano, S. Kawai, K. Kato, T. Kageura, M. Inaba, T. Okada, I. Higashimata, M.

Haruyama,T. Tanii, K. Yamada, S. Onoda, W. Kada, O. Hanaizumi, T. Teraji, J. Isoya and H. Kawarada, “Coherence Properties and Charge Stability of Shallow Implanted Nitrogen Vacancy Centers in ¹²C enriched Diamond”, Japanese Journal of Applied Physics, accepted.

8. H. Kawarada, T. Yamada, D. Xu, H. Tsuboi, Y. Kitabayashi, D. Matsumura, M. Shibata, T.

Kudo, M. Inaba, and A. Hiraiwa, " Durability-enhanced two-dimensional hole gas of C-H diamond surface for complementary power inverter applications”, Scientific Reports, accepted.

9. M. Inaba, A. Seki, K. Sato, T. Kushida, T. Kageura, H. Yamano, A. Hiraiwa, H. Kawarada,

“Vertical Edge Graphite Layer on Diamond (001) after High-Dose Ion Implantation and High Temperature Annealing”, submitted.

10. M. Inaba, K. Suzuki, Y. Hirano, W. Norimatsu, M. Kusunoki, H. Kawarada, “Ohmic contact for silicon carbide by carbon nanotubes”, Materials Science Forum, 858, 561-564, (May 2016).

(DOI:10.4028/www.scientific.net/MSF.858.561)

11. 出願日：平成27年 9月14日出願番号：特願2015-180891

発明の名称：グラファイト積層ダイヤモンド基板及びその製造方法、並びに半導体装置及びその製造方法

12. 出願日：平成27年 8月27日出願番号：特願2015-168227

発明の名称：ダイヤモンド電界効果トランジスタ及びその製造方法

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No.2

早稲田大学博士（工学）学位申請研究業績書

Patent

Presentation

13. 出願日：平成27年2月25日出願番号：特願2015-035152 発明の名称：電力素子 14. 出願日：平成27年 2月 3日

出願番号：特願2015-019080

発明の名称：ナノカーボン基材の製造方法およびナノカーボン基材 15. 出願日：平成25年 2月 1日

出願番号：特願2013-018374

発明の名称：電界効果トランジスタ 16. 出願日：平成25年 2月 1日

出願番号：特願2013-018375

発明の名称：キャリア輸送方向に対して直交する方向に CNT チャネルを有する電界効果トランジスタ

17. 出願日：平成25年 2月 1日出願番号：特願2013-018376

発明の名称：半導体装置に好適なカーボンナノチューブ束群を用いた半導体装置の製造方法、及び半導体装置

18. 稲葉優文, 五十嵐圭為, 楢村卓朗, 阿部修平, 柴田将暢, 新谷幸弘, 平岩篤, 川原田洋, ”ダイヤモンド電解質溶液ゲート FET のしきい値”,第 77回応用物理学会秋季学術講演会, 朱鷺メッセ, 2016年9月13日-16日（口頭）

19. M. Inaba, K. Igarashi, T. Naramura, S. Abe, M. Shibata, Y. Shintani, A. Hiraiwa, H. Kawarada,

"Threshold shift of diamond electrolyte-solution gate field-effect transistor by anodic

oxidation", 第51回フラーレン・ナノチューブ・グラフェン総合シンポジウム, かで

る2･7, 札幌市, 2016年9月6日-8日（口頭）

20. M. Inaba, T. Muta, M. Kobayashi, D. Matsumura, T. Saito, T. Kudo, A. Hiraiwa, H. Kawarada,

"Vertical Type Hydrogen Terminated Diamond MOSFETs", 第35回電子材料シンポジウム, ラフォーレ琵琶湖(滋賀), 2016年7月6-8日（ポスター・EMS賞）

21. 稲葉優文, 費文茜, 平野優, 鈴木和真, 川原田洋, ”ダイヤモンドへの高温アニールにより作製した垂直配向グラファイト”,第 63 回応用物理学会春季学術講演会, 東京工業大学, 2016年3月19日-22日（口頭）

22. M. Inaba, W. Fei, Y. Hirano, K. Suzuki, H. Kawarada, "Vertically oriented Graphite layer formed on hot-implanted diamond, (100) surface", 第50回フラーレン・ナノチューブ・

グラフェン総合シンポジウム, 東京大学, 2016年2月20日-22日（ポスター）

23. M. Inaba, K. Suzuki, Y. Hirano, W. Norimatsu, M. Kusunoki, H. Kawarada, "Schottky barrier height lowering at silicon carbide by carbon nanotubes", 16th International Conference on Silicon Carbide and Related Materials (ICSCRM2015), Giardini Naxos, Italy, Oct. 4-9, 2015.

(poster)

24. M. Inaba, H. Yamano, K. Kato, T. Kageura, M. Shibata, S. Onoda, T. Teraji, J. Isoya, T. Tanii, H. Kawarada, "Diamond surface fluorescence for device sensing", Diamond Quantum Sensing Workshop 2015, Takamatsu, Japan, Aug.5-7, 2015. (poster)

25. M. Inaba, K. Suzuki, M. Shibuya, C.-Y. Lee, Y. Masuda, N. Tomatsu, A.Hiraiwa, M. Kusunoki, H. Kawarada, "Low Schottky barrier height at carbon nanotube and silicon carbide interface for power electronic devices", NT15: The Sixteenth International Conference on the Science and Application of Nanotubes, Nagoya University, Nagoya, Japan, 29 June- 3 July, 2015.

(poster)

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No.3

早稲田大学博士（工学）学位申請研究業績書

Presentation

26. M. Inaba, C. Lee , K. Suzuki , Y. Hirano , M. Shibuya , M. Myodo , W. Norimatsu , M.

Kusunoki , H. Kawarada, “In-plane conductivity of dense CNT forest formed on Silicon carbide and contact resistivity estimation of parallel adjacent CNT” 9th International Conference on New Diamond and Nano Carbons, Shizuoka, Japan, 24- 28 May 2015. (oral)

27. M. Inaba, Y. Hirano, M. Shibata, K. Suzuki, C. Lee, M. Myodo, A. Hiraiwa, W. Norimatsu, M.

Kusunoki, H. Kawarada, "Carbon nanotube synthesis by non-catalytic CVC from dense carbon nanotube forest", 9th International Conference on New Diamond and Nano Carbons, Shizuoka, Japan, 24- 28 May 2015. (poster)

28. 稲葉優文, 李智宇, 鈴木和真, 平野優, 費文茜, 乗松航, 楠美智子, 川原田洋,”カーボンナノチューブ間の接触抵抗”, 第 76 回応用物理学会秋季学術講演会、名古屋国際会議場(愛知)、2015年9月13日-16日（口頭）

29. M. Inaba, W. Norimatsu, M. Kusunoki, H. Kawarada, "Contact resistivity evaluation of parallel adjacent CNTs from in-plane conductivity of dense CNT forest on silicon carbide", 第49回フラーレン・ナノチューブ・グラフェン総合シンポジウム, 北九州国際会議場(福岡), 2015年9月7日-9日（口頭）

30. M. Inaba, K. Suzuki, Y. Hirano, W. Norimatsu, M. Kusunoki, H. Kawarada, "Electrical contact of carbon nanotube and silicon carbide interface", 第34回電子材料シンポジウム(The 34th Electronic Materials Symposium), ラフォーレ琵琶湖(滋賀), 2015年7月15日-17日（ポスター）

31. 稲葉優文, 李智宇, 鈴木和真, 渋谷恵, 明道三穂, 平野優, 乗松航, 楠美智子, 川原田洋, "SiC上カーボンナノチューブフォレストのパターニング形成のための

耐超高温ZnO/Cマスク", 第62回応用物理学会春季学術講演会, 東海大学湘南キャン

パス, 2015年3月（口頭）

32. M. Inaba, Chih-Yu Lee, K. Suzuki, Y. Hirano, M. Shibuya, M. Myodo, W. Norimatsu, M.

Kusunoki, H. Kawarada, “Electrical contact of parallel adjacent CNTs estimated from in-plane conductivity of dense CNT forest on silicon carbide”, 第48回フラーレン・ナノチューブ・

グラフェン総合シンポジウム, 東京大学, 2015年2月（ポスター）

33. M. Inaba, C.-Y. Lee, K. Suzuki, M. Shibuya, M. Myodo, A. Hiraiwa, W. Norimatsu, M.

Kusunoki, H. Kawarada "In-plane Conduction of Dense Carbon Nanotube Forest Formed on Silicon Carbide" NT14: The Fifteenth International Conference on the Science and Application of Nanotubes, University of Southern California, Los Angeles, CA, USA 2-6 June, 2014.

34. M. Inaba, C.-Yu Lee, K. Suzuki, M. Shibuya, M.Myodo, A. Hiraiwa, W. Norimatsu, M.

Kusunoki, H.Kawarada, "In-plane conductivity of dense carbon nanotube forest formed by silicon carbide surface decomposition method" IUMRS-ICA2014, International Union of Materials Research Societies, International Conference in Asia 2014(The 15th IUMRS- ICA ),Fukuoka,Japan,24-30 August 2014.

35. M. Inaba, C.-Yu Lee, K. Suzuki, M. Shibuya, A. Hiraiwa, Y. Masuda, W. Norimatsu, M.Kusunoki, H. Kawarada, "In-plane conductivity of dense carbon nanotube forest on semi- insulating silicon carbide" 第46回フラーレン・ナノチューブ・グラフェン総合シンポジウム,東京大学,2014年3月3日-5日

36. M. Inaba, C.-Y. Lee, K. Suzuki, M. Shibuya, Y. Hirano, M. Myodo, A. Hiraiwa, W.Norimatsu, M. Kusunoki, H. Kawarada, "Mask Patterning at Very High Temperature for Carbon Nanotube Forest on Silicon Carbide"第47回フラーレン・ナノチューブ・グラフェン総合シンポジウム、名古屋大学、2014年9月3日-5日

37. M. Inaba, M. Shibuya, Y. Masuda, A. Hiraiwa, M. Kusunoki, H. Kawarada,"Estimation of conduction at CNT/SiC interface of vertically aligned and high density CNT on SiC", NT13:

The Fourteenth International Conference on the Science and Application of Nanotubes, Espoo, Finland, Jun. 2013

博 士 論 文 概 要

Graduate School of Advanced Science and Engineering Waseda University