Faculty Profiles - HARADA Shunta

Papers - HARADA Shunta

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Direct observation of stacking fault shrinkage in 4H-SiC at high temperatures by in-situ X-ray topography using monochromatic synchrotron radiation

Fujie Fumihiro, Harada Shunta, Koizumi Haruhiko, Murayama Kenta, Hanada Kenji, Tagawa Miho, Ujihara Toru

APPLIED PHYSICS LETTERS Vol. 113 ( 1 ) 2018.7

Development of angle-resolved spectroscopy system of electrons emitted from a surface with negative electron affinity state

Ichihashi Fumiaki, Dong Xinyu, Inoue Akito, Kawaguchi Takahiko, Kuwahara Makoto, Ito Takahiro, Harada Shunta, Tagawa Miho, Ujihara Toru

REVIEW OF SCIENTIFIC INSTRUMENTS Vol. 89 ( 7 ) 2018.7

Detection of edge component of threading dislocations in GaN by Raman spectroscopy

Nobuhiko Kokubo, Yosuke Tsunooka, Fumihiro Fujie, Junji Ohara, Kazukuni Hara, Shoichi Onda, Hisashi Yamada, Mitsuaki Shimizu, Shunta Harada, Miho Tagawa, Toru Ujihara

Applied Physics Express Vol. 11 ( 6 ) 2018.6

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

We succeeded in measuring the density and direction of the edge component of threading dislocations (TDs) in c-plane (0001) GaN by micro- Raman spectroscopy mapping. In the micro-Raman spectroscopy mapping of the E2 H peak shift between 567.85 and 567.75 cm-1, six different contrast images are observed toward directions of h1-100i. By comparing X-ray topography and etch pit images, the E2 H peak shift is observed where the edge component of TDs exists. In contrast, the E2 H peak is not observed where the screw component of TDs exists.

DOI： 10.7567/APEX.11.061002

Web of Science

Scopus

Dislocation behavior in bulk crystals grown by TSSG method

Kazuaki Seki, Kazuhiko Kusunoki, Yutaka Kishida, Hiroshi Kaido, Koji Moriguchi, Motohisa Kado, Hironori Daikoku, Takayuki Shirai, Mitsutoshi Akita, Akinori Seki, Hiroaki Saito, Shunta Harada, Toru Ujihara

Materials Science Forum Vol. 924 page： 39 - 42 2018

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

The dislocation behavior during bulk crystal growth on the 4H-SiC (000-1) C-face using the solution method was investigated. A 2 inch wafer with a 4 degree off angle was fabricated from a bulk crystal grown by the TSSG method, and the dislocations in the crystal were evaluated using synchrotron X-ray topography and TEM observation. From the topograph images, it was found that the TSD density remarkably decreased as the growth progressed. Furthermore, the TEM observation suggested that TSD decreases as the threading dislocations convert to in-plane defects toward the center of the crystal. Conventionally, it was considered that conversion of threading dislocations hardly occurs in solution growth on the C-face. However, it is thought that this phenomenon was not observable because the conversion efficiency is remarkably low. We speculate that dislocations may be converted by suddenly making macrosteps during bulk growth.

DOI： 10.4028/www.scientific.net/MSF.924.39

Scopus

Suppression of polytype transformation with extremely low-dislocation-density 4H-SiC crystal in two-step solution method

Kenta Murayama, Shunta Harada, Fumihiro Fujie, Xin Bo Liu, Ryota Murai, Can Zhu, Kenji Hanada, Miho Tagawa, Toru Ujihara

Materials Science Forum Vol. 924 page： 60 - 63 2018

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

We achieved the growth of extremely-high quality SiC crystal with two-step solution method with specially-designed seed crystals. The two-step growth consists of 1st step growth on Si-face for the reduction of threading dislocations and 2nd step growth on C-face for the reduction of basal plane dislocations and thickening. In this method, we can make the dislocation density extremely low, while the polytype easily changes during growth due to the absence of spiral hillocks originating from threading screw dislocation (TSD). In this study, we prepared specially designed seed crystals for both 1st and 2nd growth steps to provide steps continuously. In the seeds, a few TSDs exist at the upper-side of the step structure. Consequently, we demonstrated the suppression of the polytype transformation during the C-face growth with extremely low-dislocation-density crystal. Accordingly, we successfully obtained extremely low-dislocation density 4H-SiC with TSD, TED and BPD density of 11, 385 and 28 cm-2.

DOI： 10.4028/www.scientific.net/MSF.924.60

Scopus

Temperature dependence of carrier relaxation time in gallium phosphide evaluated by photoemission measurements

Fumiaki Ichihashi, Takahiko Kawaguchi, Xinyu Dong, Makoto Kuwahara, Takahiro Ito, Shunta Harada, Miho Tagawa, Toru Ujihara

AIP ADVANCES Vol. 7 ( 11 ) 2017.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

For understanding of carrier behavior in semiconductors, it is important to measure the carrier relaxation time. In the present study, the relaxation times of inter-valley transition from the valley to the X valley in GaP were evaluated by near-band-gap photoemission spectroscopy of electrons emitted from a surface with a negative electron affinity state. In the energy distribution curves, two peaks, which originate from the electron population accumulated in the valley and the X valley, were observed. From the temperature dependence of the energy of these two peaks, we could successfully evaluate the temperature dependence of the energies of the valley and the X valley. Furthermore, the relaxation times of the inter-valley transition from the valley to the X valley were estimated from the ratio of the electron concentration of the valley and the X valley. The values of the relaxation time are good agreement with the previous studies. These results indicate that the near-band-gap photoemission spectroscopy can directly investigate conduction electrons and also evaluate the carrier dynamics in semiconductor. (C) 2017 Author(s).

DOI： 10.1063/1.4997800

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Scopus

Optimization of crystallization conditions of SiC crystal with machine learning

Murai Ryota, Hatasa Goki, Tunooka Yosuke, Lin Hung, Murayama Kenta, Zhu Can, Harada Shunta, Tagawa Miho, Ujihara Toru

JSAP Annual Meetings Extended Abstracts Vol. 2017.2 ( 0 ) page： 3506 - 3506 2017.8

Investigation of high-temperature annealing process of sputtered AlN films

Xiao Shiyu, Liu Yikang, Suzuki Ryoya, Miyake Hideto, Hiramatsu Kazumasa, Harada Shunta, Ujihara Toru

JSAP Annual Meetings Extended Abstracts Vol. 2017.2 ( 0 ) page： 3378 - 3378 2017.8

Morphology of AlN whiskers grown by reacting N-2 gas and Al vapor

M. Matsumoto, H. Saitou, Y. Takeuchi, S. Harada, M. Tagawa, T. Ujihara

JOURNAL OF CRYSTAL GROWTH Vol. 468 page： 576 - 580 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We have investigated the morphology of AlN whiskers on a polycrystalline AlN substrate by using Fe-Al alloy melts under the different synthesis conditions. Formation density of the AlN whiskers increases and the diameter of the whisker decreases with increasing Al content of the Fe-Al alloy melt. Most of the AlN whiskers were zigzag shape with the hexagonal cross section. The longitudinal direction was the [0001] direction. The facet with the zigzag shape was the {1101} or {1101} pyramidal plane and the period of the zigzag facet was almost constant. The average diameter of the whiskers and the period of the zigzag facet decrease with increasing Al content. At the initial stage of the whisker formation, the island of AlN formed on the AlN substrate and the pyramidal facet grows via step-flow growth. From the observation, we discussed the possible mechanism for the formation of the zigzag-shape AlN whiskers.

DOI： 10.1016/j.jcrysgro.2016.11.127

Web of Science

Scopus

Two-step SiC solution growth for dislocation reduction

K. Murayama, T. Hori, S. Harada, S. Xiao, M. Tagawa, T. Ujihara

Journal of Crystal Growth Vol. 468 page： 874 - 878 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier B.V.

We propose a two-step silicon carbide (SiC) solution growth method for dislocation reduction to produce the high-quality silicon carbide SiC crystals. The two-step growth consists of the growth on a Si face and a C face. Firstly, seed crystal with low threading dislocation density was prepared by the growth on a Si face utilizing the threading dislocation conversion. Secondly, the growth on the C face was conducted on the prepared seed crystal with low threading dislocation density to reduce the density of basal plane dislocations and keep smooth growth surface. We demonstrate that the two-step growth leads to the reduction of the density for all types of dislocations by two orders of magnitude compared to the initial density of the seed crystal.

DOI： 10.1016/j.jcrysgro.2016.11.100

Web of Science

Scopus

Phase transition process in DDAB supported lipid bilayer

Takumi Isogai, Sakiko Nakada, Naoya Yoshida, Hayato Sumi, Ryugo Tero, Shunta Harada, Toru Ujihara, Miho Tagawa

JOURNAL OF CRYSTAL GROWTH Vol. 468 page： 88 - 92 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We report the results of microscope measurements examining the phase transition process of a cationic lipid, Dimethyldioctadecylammonium bromide (DDAB) supported lipid bilayer (SLB). Due to lateral fluidity and strong electrostatic interaction with DNA, SLB serves as a fluid substrate for assembling 2D lattices of DNA functionalized nanoparticles (DNA-NPs): lipid molecules work as carriers for transporting DNA-NPs. By fluorescence microscopy and atomic force microscopy (AFM), two types of phase transitions, which correspond to liquid crystalline-gel and liquid crystalline-interdigitated gel (L beta I) ones, were observed in DDAB SLB during cooling. In thermal equilibrium at room temperature both gel and L beta I phases have enough adsorbed amounts of DNA-NPs which indicate that both domains have enough surface charge densities for adsorbing DNA-NPs, however, during phase transition DNA-NPs preferably distributed into L beta I phase.

DOI： 10.1016/j.jcrysgro.2016.09.063

Web of Science

Scopus

Solvent design for high-purity SiC solution growth

"S. Harada, G. Hatasa, K. Murayama, T. Kato, M. Tagawa, T. Ujihara"

Mater. Sci. Forum Vol. 897 page： 32-35 2017.5

Formation of basal plane dislocations introduced by collision of macrosteps on growth surface during SiC solution growth

"T. Hori, K. Murayama, S. Harada, S. Xiao, M. Tagawa, T. Ujihara"

Mater. Sci. Forum Vol. 897 page： 28-31 2017.5

SiC solution growth on Si face with extremely low density of threading screw dislocations for suppression of polytype transformation

"K. Murayama, T. Hori, S. Harada, S. Xiao, M. Tagawa, T. Ujihara"

Mater. Sci. Forum Vol. 897 page： 24-27 2017.5

Crystal Orientation Dependence of Precipitate Structure of Electrodeposited Li Metal on Cu Current Collectors

K. Ishikawa, Y. Ito, S. Harada, M. Tagawa, T. Ujihara

Cryst. Growth Des. Vol. 17 ( 5 ) page： 2379 - 2385 2017.5

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

Dendritic growth at the Li anode during charging is caused by a morphological inhomogeneity of Li electrodeposition. In this study, we investigate the dependence of the morphology of Li electrodeposited on a polycrystalline Cu current collector on the Cu grain orientation both experimentally and by numerical analysis. The experimental results show that the Li precipitates that form on Cu grains that have close to (111) orientations are the smallest and the most uniform in size. Such a morphology is expected to be effective for the suppression of dendrite; growth. Numerical analysis indicates that the initial stage of electrodeposition plays an important role in determining morphological variation, and this is due to the crystal orientation dependence of the adatom concentration at equilibrium.

DOI： 10.1021/acs.cgd.6b01710

Web of Science

Scopus

Wulff polyhedral colloidal crystallization using DNA-nanoparticle superlattice precursors

Sumi Hayato, Isogai Takumi, Yoshida Naoya, Harada Shunta, Ujihara Toru, Tagawa Miho

JSAP Annual Meetings Extended Abstracts Vol. 2017.1 ( 0 ) page： 2741 - 2741 2017.3

Modification of the surface morphology of 4H-SiC by addition of Sn and Al in solution growth with SiCr solvents

Naoyoshi Komatsu, Takeshi Mitani, Yuichiro Hayashi, Tomohisa Kato, Shunta Harada, Toru Ujihara, Hajime Okumura

JOURNAL OF CRYSTAL GROWTH Vol. 458 page： 37 - 43 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

For solution growth of 4H-SiC with Si0.6-x-yCr0.4AlxSny solvents, the changes in surface morphology and polytype induced by the addition of Sn and Al to the Si0.6Cr0.4 solvent were investigated. Growth with Si0.6Cr0.4 solvents resulted in a rough surface covered with large macrosteps that were several micrometers high, and the polytype of the grown layer transformed to 6H and 15R-SiC. The surface roughening and polytype instability were suppressed when more than 2 at% Al was added to the SiCr0.4 solvent. We also found that the combined addition of both 2-4 at% Sn and 0.5-1 at% Al resulted in smooth surface morphology. We discussed the modification of the surface morphology of 4H-SiC caused by the additives in terms of the wetting properties of the solvents. Based on the results of experiments and thermodynamic calculations, the addition of both Sn and Al increased the liquid/solid interfacial energy. Because the two-dimensional nucleation energy increases with the interfacial energy, we conclude that smooth step flow growth of 4H-SiC was achieved by lowering the frequency of two-dimensional nucleation on the growth surface.

DOI： 10.1016/j.jcrysgro.2016.10.045

Web of Science

Scopus

Crystal Orientation Dependence of Precipitate Structure of Electrodeposited Li Metal on Cu Current Collectors

"K. Ishikawa, Y. Ito, S. Harada, M. Tagawa, T. Ujihara"

Cryst. Growth Des. Vol. 17 page： 2379-2385 2017

Phase transition process in DDAB supported lipid bilayer

"T. Isogai, S. Nakada, N. Yoshida, H. Sumi, R. Tero, S. Harada, T. Ujihara, M. Tagawa"

J. Cryst. Growth Vol. 468 page： 88-92 2017

Modification of the surface morphology of 4H-SiC by addition of Sn and Al in solution growth with SiCr solvents

"N. Komatsu, T. Mitani, Y Hayashi, T Kato, S. Harada, T. Ujihara, H. Okumura"

J. Cryst. Growth Vol. 458 page： 37-43 2017

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Papers - HARADA Shunta