Faculty Profiles - HARADA Shunta

Papers - HARADA Shunta

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Polytype Control in SiC Crystal Growth : Kinetic Polytype Control in 3C-SiC Solution Growth(<Special Issue>Formation and Crystal Growth of Metastable Phases)

Seki Kazuaki, Harada Shunta, Ujihara Toru

Journal of the Japanese Association for Crystal Growth Vol. 40 ( 4 ) page： 253 - 260 2014

Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

Silicon carbide forms polytypes due to different stacking arrangements of Si and C. For the use of semiconductor materials, it is necessary to fabricate a single polytype material. In this paper, firstly, determination factors of polytypes are introduced from both experimental and theoretical viewpoints, and the difficulty of the polytype control based on thermal stability is shown. Next, the actual control techniques in sublimation growth method and CVD method are shown to be based on the concept that the polytype sequence of seed crystal continues to the grown crystal. Finally, we propose the kinetic polytype control method based on the growth speed difference among polytypes in SiC solution growth.

DOI： 10.19009/jjacg.40.4_253

Achiral Metastable Crystals of Sodium Chlorate Forming Prior to Chiral Crystals in Solution Growth

Hiromasa Niinomi, Tomoya Yamazaki, Shunta Harada, Toru Ujihara, Hitoshi Miura, Yuki Kimura, Takahiro Kuribayashi, Makio Uwaha, Katsuo Tsukamoto

CRYSTAL GROWTH & DESIGN Vol. 13 ( 12 ) page： 5188 - 5192 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P2(1)/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 angstrom, b = 5.26 angstrom, c = 6.70 angstrom, beta = 109.71 degrees) revealed that the achiral phase should be identical to Phase III (a = 8.78 angstrom, b = 5.17 angstrom, c = 6.83 angstrom, beta = 110 degrees), which is a high-temperature phase from a melt growth of NaClO3. We advocate further assessment of the achiral crystal and a new pathway for the formation of chiral crystals via crystalline phase transition from achiral Phase III.

DOI： 10.1021/cg401324f

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SiC 結晶成長における多形制御～速度論的多形制御法の提案（3C-SiC 溶液成長を例に）～

関和明、原田俊太、宇治原　徹

日本結晶成長学会誌, Vol. 40 ( 4 ) page： 253 2013.12

SiC 結晶成長における多形制御～速度論的多形制御法の提案（3C-SiC 溶液成長を例に）～

関和明, 原田俊太, 宇治原徹

日本結晶成長学会誌, Vol. 40 ( 4 ) page： 253 2013.12

Direct Growth of AlN Single Crystal on Sapphire by Solution Growth Method

Hiroaki Matsubara, Kohei Mizuno, Yukihisa Takeuchi, Shunta Harada, Yasuo Kitou, Eiichi Okuno, Toru Ujihara

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 52 ( 8 ) page： 08JE17 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

AlN was directly grown on a sapphire substrate by the solution growth method with the Cu-Si-Al-Ti solvent under a nitrogen gas flow. X-ray diffraction measurements revealed that the grown AlN was single crystal. The AlN layer was epitaxially formed on the sapphire substrate with the orientation relationships: (0001)(AlN) parallel to (0001)(sapphire) and [(1) over bar 100](AlN) parallel to [<(1over bar>120](sapphire). The full widths at half maximum (FWHMs) of X-ray rocking curves for tilt and twist components were 414 and 2031 arcsec, respectively. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.08JE17

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Influence of solution flow on step bunching in solution growth of SiC crystals

Can Zhu, Shunta Harada, Kazuaki Seki, Huayu Zhang, Hiromasa Niinomi, Miho Tagawa, Toru Ujihara

Crystal Growth and Design Vol. 13 ( 8 ) page： 3691 - 3696 2013.8

Language：English Publishing type：Research paper (scientific journal)

The control of step bunching by solution flow in 4H-SiC solution growth is proposed. We achieved the solution flow control with the specially designed top-seeded solution growth method as follows: by deviating a seed crystal from the center of a crucible and rotating the crucible in one direction, the solution flow direction was controlled to be parallel or antiparallel to the step-flow direction. After the growth, the widely spaced, accumulated macrosteps were observed and the surface of the grown crystal became rough under the parallel flow. On the other hand, the development of the macrosteps was suppressed under the antiparallel flow. As the growth proceeds, the surface roughness of the growth surface increases under the parallel flow, while the surface roughness decreases under the antiparallel flow. This fact suggests the solution flow control can be an effective method to suppress the step bunching during the solution growth of SiC single crystals. © 2013 American Chemical Society.

DOI： 10.1021/cg400706u

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Evolution of threading screw dislocation conversion during solution growth of 4H-SiC Reviewed

S. Harada, Y. Yamamoto, K. Seki, A. Horio, T. Mitsuhashi, M. Tagawa, T. Ujihara

APL Materials Vol. 1 ( 2 ) page： 022109 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：American Institute of Physics Inc.

Evolution of threading screw dislocation (TSD) conversion during the solution growth of 4H-SiC on a vicinal crystal of 4H-SiC(0001) was investigated by synchrotron X-ray topography. Selecting appropriate X-ray wavelength and g vector, we can change the penetration of X-ray, and the dislocation behaviors with the different depth were successfully observed. Evidently TSDs parallel to the c-axis having c-component Burgers vector were changed into defects on the (0001) basal planes with the same Burgers vector as the TSDs, propagating to the [11\\documentclass[12pt]{minimal}\\begin{document}$\\bar{2}$\\ end{document}2̄0] step-flow direction by advancing macrosteps during the solution growth. The TSD conversions stochastically took place during the growth. The conversion rate was almost uniform and finally almost all TSDs were converted to the basal plane defects. The conversion rate was low at the very early stage of the growth, which implies that the macrosteps were not formed at the initial stage of the solution growth. © 2013 Author(s).

DOI： 10.1063/1.4818357

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Solution growth of an ultra-high quality SiC crystal

UJIHARA Toru, HAKADA Shunta, YAMAMOTO Yuji, SEKI Kazuaki

Oyo Buturi Vol. 82 ( 4 ) page： 326 - 329 2013.4

Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Applied Physics

<p>The improvement of the substrate quality is important to apply SiC materials to high-performance power devices. A solution growth method is attracting attention as the technique for "ultra-high quality" crystal growth. In our research, it has been revealed that threading dislocations are converted to other defects in the basal planes and they are swept from the crystal during the growth process. Utilizing this conversion phenomenon, we have demonstrated ultra-high quality growth. Recently, reports of improvements in the crystal growth rate and the expansion of the crystal size have also been made using other groups. We have almost established the solution growth as a full-scale quality SiC bulk crystal growth technology.</p>

DOI： 10.11470/oubutsu.82.4_326

超高品質SiC溶液成長 Invited Reviewed

宇治原徹、原田俊太、山本祐治、関和明

応用物理 Vol. 82 page： 326-329 2013.4

SiC溶液成長の最近の展開

原田俊太、山本祐治、関和明、宇治原　徹

日本結晶成長学会誌, Vol. 40 page： 25 2013.4

SiC溶液成長の最近の展開

原田俊太, 山本祐治, 関和明, 宇治原徹

日本結晶成長学会誌, Vol. 40 page： 25 2013.4

超高品質SiC溶液成長 Invited Reviewed

宇治原徹, 原田俊太, 山本祐治, 関和明

応用物理 Vol. 82 page： 326-329 2013.4

Effect of Surface Polarity on the Conversion of Threading Dislocations in Solution Growth Reviewed

Y. Yamamoto, S. Harada, K. Seki, A. Horio, T. Mitsuhashi, T. Ujihara

Materials Science Forum Vol. 740-742 page： 15-18 2013.1

Reduction of Threading Screw Dislocation Utilizing Defect Conversion during Solution Growth of 4H-SiC Reviewed

S. Harada, Y. Yamamoto, K. Seki, T. Ujihara

Materials Science Forum Vol. 740-742 page： 189-192 2013.1

Bulk 3C-SiC Crystal by Top Seeded Solution Growth Method Reviewed

K. Seki, S. Harada, T. Ujihara

Materials Science Forum Vol. 740-742 page： 311-314 2013.1

Electron Spectroscopy of Conduction Electrons Excited by Visible Light Utilizing NEA Surface

Ichihashi Fumiaki, Shimura Daiki, Nishitani Kenji, Kuwahara Makoto, Ito Takahiro, Harada Shunta, Tagawa Miho, Ujihara Toru

2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC) page： 288 - 291 2013

Electron spectroscopy of conduction electrons excited by visible light utilizing NEA surface Reviewed

Fumiaki Ichihashi, Daiki Shimura, Kenji Nishitani, Makoto Kuwahara, Takahiro Ito, Shunta Harada, Miho Tagawa, Toru Ujihara

Conference Record of the IEEE Photovoltaic Specialists Conference page： 288 - 291 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Electrical and Electronics Engineers Inc.

In this paper we propose an angle-resolved photoemission spectroscopy to observe the conduction electrons emitted from a surface of negative electron affinity state. In actual, we have measured conduction electrons in a GaAs bulk crystal and obtained the electron dispersion around Γ point. In addition, we could also observe hot electrons excited by the light which energy was much larger than band gap energy. These results suggest that the method we proposed is one of the most powerful tools for the evaluation method of the conduction band. © 2013 IEEE.

DOI： 10.1109/PVSC.2013.6744149

Scopus

Current Advances in SiC Solution Growth(<Special Issue>)Opening Up a New World of Crystal Growth on SiC)

Harada Shunta, Yamamoto Yuji, Seki Kazuaki, Ujihara Toru

Journal of the Japanese Association for Crystal Growth Vol. 40 ( 1 ) page： 25 - 32 2013

Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

Solution growth has a potential to achieve high quality bulk SiC growth. In this paper we review current advances in SiC solution growth specially focusing on the crystal quality. During the solution growth, threading dislocations tend to be converted to basal plane defects by the step-flow of macrosteps. This phenomenon implies that all dislocations can be excluded from the lateral face of the crystal in principle. Actually, high quality SiC crystal with very low threading dislocation density was obtained applying the dislocation conversion during the solution growth.

DOI： 10.19009/jjacg.40.1_25

Ultrahigh-resolution direct observation of mini-bands formed in InGaAs/AlGaAs superlattice

Shimura D.

Conference Record of the IEEE Photovoltaic Specialists Conference page： 306 - 310 2013

Ultrahigh-resolution direct observation of mini-bands formed in InGaAs/AlGaAs superlattice Reviewed

Daiki Shimura, Fumiaki Ichihashi, Kenji Nishitani, Shunta Harada, Makoto Kuwahara, Takahiro Ito, Masaharu Matsunami, Shin-ichi Kimura, Takenobu Sakai, Miho Tagawa, Toru Ujihara

2013 IEEE 39TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC) page： 306 - 310 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Mini-bands formed in superlattice structures are often used for an intermediate-band solar cell. In order to design an optimized structure, it is important to measure the mini-band dispersions which influence transport properties and solar-energy conversion efficiency. In this study, we directly observed the dispersions of mini-bands formed in InGaAs/AlGaAs quantum-well superlattices by angle-resolved photoemission spectroscopy with synchrotron radiation light. The short-period energy dispersions due to the mini-bands around the X-valley were clearly obtained. In addition, the effective mass coefficient of each mini-band could be individually evaluated.

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Papers - HARADA Shunta