研究者詳細 - 原田　俊太

Advances in defect characterization techniques using polarized light observation in SiC wafers for power devices 招待有り査読有り Open Access

Harada, S; Murayama, K

JOURNAL OF CRYSTAL GROWTH 650 巻 2025年1月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Crystal Growth

This short review provides an overview of advancements in the characterization of defects in silicon carbide (SiC) wafers using polarized light observation. SiC, which has a wide bandgap and excellent thermal and electrical properties, is widely used in power devices. However, various defects such as threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD) can significantly affect device performance and reliability. Polarized light observation offers a nondestructive method for visualizing these defects and analyzing the stress fields induced within the SiC crystal structure. This paper summarizes recent developments in this technique, including the application of analyzer rotation to enhance the contrast in defect visualization. Furthermore, the development of automated systems for rapid wafer evaluation is discussed, highlighting the role of polarized light observation in improving quality control and production efficiency in SiC power device manufacturing.

DOI： 10.1016/j.jcrysgro.2024.127982

Observation of point defect and carrier lifetime distributions in hydrogen or helium ion implanted SiC PiN diodes for suppression of bipolar degradation 査読有り

Kato, M; Li, T; Sakane, H; Harada, S

JAPANESE JOURNAL OF APPLIED PHYSICS 64 巻 ( 1 ) 2025年1月

偏光観察によるパワーデバイスSiC基板の結晶欠陥可視化招待有り査読有り

原田俊太, 村山健太

まてりあ 63 巻 ( 10 ) 頁： 687 - 694 2024年10月

The effects of polyethylene glycol on the nucleation and growth of DNA-functionalized gold nanoparticles crystals 招待有り査読有り

Shoko Kojima, Lidong Zhang, Chandan Kumar, Hayato Sumi, Norobu Ohta, Hiroshi Sekiguchi, Kentaro Tsuzuki, Shunta Harada, Toru Ujihara, Katsuo Tsukamoto, Miho Tagawa

Journal of Crystal Growth 640 巻頁： 127740 2024年8月

Suppression of stacking-fault expansion in 4H-SiC diodes by helium implantation 査読有り Open Access

Li, T; Sakane, H; Harada, S; Kato, M

APPLIED PHYSICS EXPRESS 17 巻 ( 8 ) 2024年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Bipolar degradation is a critical problem in Silicon carbide devices, caused by the expansion of single Shockley stacking faults (1SSFs) from basal plane dislocations. This paper presents the effects of helium implantation on the suppression of 1SSFs expansion. The fabricated PiN diodes were analyzed using current-voltage characteristics and electroluminescence imaging. The results show that helium implantation can effectively suppress 1SSFs expansion without significantly degrading diode performance. We consider that this suppression is due to the pinning of dislocations by point defects introduced during helium implantation, and the reduction of carrier lifetime may also play a role in suppressing 1SSFs expansion.

DOI： 10.35848/1882-0786/ad6be5

Modulated crystallographic shear structure in titanium-chromium oxides: their structure and phonon-transport properties 査読有り

スペクトル超解像解析によるX線光電子分光測定時間の短縮招待有り査読有り

原田俊太

Isotope News 794 巻頁： 7 - 10 2024年8月

Harada, S; Hattori, T; Inden, M; Sugimoto, S; Ito, M; Tagawa, M; Ujihara, T

JOURNAL OF APPLIED CRYSTALLOGRAPHY 57 巻 ( Pt 4 ) 頁： 1212 - 1216 2024年8月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Crystallography

Advancements in phonon engineering have propelled the study of heat conduction within nanostructures, focusing on the wave nature of phonons for thermal conductivity manipulation. This work investigates the annealing-induced structural transformation of titanium-chromium oxide crystals, highlighting a role in modulating thermal conductivity through the regularization of crystallographic shear (CS) plane spacing. Utilizing high-angle annular dark-field scanning transmission electron microscopy and selected-area electron diffraction, a transformation from disordered to ordered arrangements of CS planes was observed through annealing at high temperatures. The thermal conductivity increased following annealing. The variability observed in the spacing of CS planes before annealing implies that phonon Anderson localization might play a role in the changes in thermal conductivity.

DOI： 10.1107/S1600576724006381

熱輸送のスペクトル酸化チタン自然超格子結晶の構造と熱輸送特性招待有り査読有り

原田俊太

伝熱 63 巻頁： 40 - 45 2024年7月

Effects of proton implantation into 4H-SiC substrate: Stacking faults in epilayer on the substrate 招待有り査読有り

Kato, M; Watanabe, O; Harada, S; Sakane, H

MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING 175 巻頁： 108264 - 108264 2024年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science in Semiconductor Processing

This study explored proton implantation into 4H-SiC substrates to suppress the expansion of single Shockley stacking faults (SSSFs), which is a source of bipolar degradation in 4H-SiC devices. While previous research has demonstrated the effectiveness of proton implantation in epitaxial layers, concerns about defect generation have persisted. Therefore, we implanted protons into 4H-SiC substrates, followed by epitaxial growth. Then, we fabricate PiN diodes using the epitaxial layer aiming to reduce SSSF expansion and enhance PiN diode reliability. The results indicate that proton implantation has no significant suppression effects on the SSSF expansion, coupled with the undesired induction of double Shockley stacking faults. Thus, proton implantation into the substrates does not enhance the reliability of 4H-SiC devices, emphasizing the need for further investigations into suppression mechanisms.

DOI： 10.1016/j.mssp.2024.108264

混合ガウスモデルと強化学習を用いたFZ結晶成長の自動制御招待有り査読有り

原田俊太, 土佐祐介, 大前遼, 松本遼平, 炭谷翔悟

日本結晶成長学会誌 51 巻 ( 1 ) 頁： 4 2024年4月

Analysis of Macrostep Interaction via Carbon Diffusion Field in SiC Solution Growth 査読有り

Nakanishi, Y; Kutsukake, K; Dang, YF; Harada, S; Tagawa, M; Ujihara, T

JOURNAL OF CRYSTAL GROWTH 631 巻頁： 127609 - 127609 2024年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Crystal Growth

In the top-seeded solution growth (TSSG) method for SiC, control of macrostep development is crucial for improving the crystal quality. Dislocation conversion phenomena caused by macrosteps with a certain height on the crystal surface can reduce the dislocation density, while over-developed macrosteps bring macroscopic defects such as solvent inclusions. It is experimentally reported that solution flow direction to the step movement has a substantial impact on the macrostep development: parallel solution flow promotes and anti-parallel solution flow suppresses the increase of macrostep height. Our hypothesis is that this macrostep development is governed by the interaction between the macrosteps not by the instability of the density of the atomical steps. In this study, we constructed a computational fluid dynamic model of the boundary layer around macrosteps on the crystal surface, incorporating the solution flow on the boundary layer and consumption of the carbon solute by the macrostep movement quantitatively. The computational simulation reveals that the macrostep with position shift from the center of the adjacent macrosteps moves to the direction of the nearer macrostep under the parallel flow and moves to the farther macrostep under the antiparallel flow. These macrostep movements result in the bunching and debunching of the macrosteps. The mechanisms of macrostep movements demonstrated in this study will be useful for the precise control of macrostep height aiming to the reduction of the dislocation density during SiC solution growth.

DOI： 10.1016/j.jcrysgro.2024.127609

Accelerating X-ray photoemission spectroscopy measurements using Bayesian super-resolution 査読有り Open Access

Harada, S; Tsujimori, K; Nomoto, T; Ito, T

JAPANESE JOURNAL OF APPLIED PHYSICS 63 巻 ( 4 ) 2024年4月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

This study applies Bayesian super-resolution to X-ray photoelectron spectroscopy (XPS), achieving up to a 20-fold reduction in measurement time while preserving data quality. Traditional XPS, crucial for surface analysis, typically requires extensive measurement durations. Our methodology significantly accelerates the process, as demonstrated with glass and Polytetrafluoroethylene samples, where we reduced measurement times by up to 1/20th without compromising spectral accuracy. This approach decreases noise levels and retains spectral integrity, offering a highly efficient solution for XPS. This innovation is particularly valuable in material science, enabling rapid, reliable surface analysis.

DOI： 10.35848/1347-4065/ad3140

Effects of proton implantation for expansion of basal plane dislocations in SiC toward suppression of bipolar degradation: review and perspective 査読有り

Kato, M; Harada, S; Sakane, H

JAPANESE JOURNAL OF APPLIED PHYSICS 63 巻 ( 2 ) 頁： 020804 - 020804 2024年2月

Effect of Solution Components on Solvent Inclusion in SiC Solution Growth 査読有り

Zhou, HQ; Miura, H; Fukami, Y; Dang, YF; Kutsukake, K; Harada, S; Tagawa, M; Ujihara, T

CRYSTAL GROWTH & DESIGN 24 巻 ( 4 ) 頁： 1806 - 1817 2024年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

In the solution growth method of silicon carbide, cellular structures and solvent inclusions are fatal defects. This study investigates the mechanism of how cosolvent chromium and additive aluminum influence the formation of cellular structures and inclusions via numerical simulations based on a phase field model. The simulation results indicate that introducing chromium into the solution increases the growth rate of the SiC crystals. The uneven distribution of chromium components near the macrostep edge is prone to trigger constitutional supersaturation, ultimately leading to cellular structures and inclusions. Constitutional supersaturation is more pronounced in solutions with a higher viscosity. Additionally, a small amount of additive aluminum increases the interfacial energy, enhancing the step stability by raising the potential barrier for curved steps and moderating step slopes. Experimental results demonstrate that a solution containing 40% chromium can increase the growth rate by three times compared to a pure Si solution. The Si0.59-Cr0.4-Al0.01 solution emerges as a promising candidate, maintaining a high growth rate while preserving step stability and effectively suppressing the development of cellular structures and inclusions.

DOI： 10.1021/acs.cgd.3c01476

DNA修飾ナノ粒子の結晶化とX線小角散乱による構造解析

田川美穂, 張力東, 小島憧子, 鷲見隼人, 横森真麻, 太田昇, 関口博史, 原田俊太, 宇治原徹

日本結晶学会誌 65 巻 ( Supplement ) 頁： s19 - s19 2023年10月

Non-destructive identification of edge-component burgers vector of threading dislocations in SiC wafers by birefringence imaging 査読有り

Harada, S; Matsubara, Y; Murayama, K

DIAMOND AND RELATED MATERIALS 138 巻 2023年10月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Diamond and Related Materials

Non-destructive characterization of crystalline defects in SiC wafers is important for manufacturing high-performance SiC power devices with high productivity. The present study shows that the edge component of the Burgers vector can be identified by birefringence imaging under conditions deviating slightly from the crossed-Nicols condition and by calculation of the in-plane shear stress distribution. It is also found that the combination of birefringence observation and X-ray topography allows the discrimination of the family of threading screw dislocations. The present results will further the understanding of the relationship between defect structure and the properties of SiC power devices.

DOI： 10.1016/j.diamond.2023.110192

Machine Learning for Semiconductor Process Simulation Described by Coupled Partial Differential Equations 査読有り

Sato, R; Kutsukake, K; Harada, S; Tagawa, M; Ujihara, T

ADVANCED THEORY AND SIMULATIONS 6 巻 ( 9 ) 2023年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Theory and Simulations

Technology computer-aided design (TCAD) simulation is an important tool for the development of semiconductor devices. Based on coupled partial differential equations (PDEs) for behaviors, TCAD can calculate objects such as impurities, point defects, and electronic carriers in semiconductors. However, over recent years semiconductor devices have become increasingly miniaturized and complicated, resulting in much longer calculation times for TCAD. Machine learning is one technology that may be used to overcome this simulation cost problem. In this study, a neural network architecture is proposed that considers the structure of the coupled PDEs. Features representing each concentration distribution of the calculation objects are extracted by convolution operations and their reaction is modeled by channel attention. The performance of the proposed architecture and of conventional neural network models is evaluated using a simulation dataset generated by 1D coupled PDEs that models the diffusion and reaction of vacancies and interstitial atoms. In addition, the advantage of the method is discussed through the analyses of error correlations of the two predictions and attention coefficients. The machine learning method developed in this study will be applicable to other physics described by coupled PDEs and is expected to speed up the computation of simulations in various fields.

DOI： 10.1002/adts.202300218

Numerical Modeling of the Cellular Structure Formation Process in SiC Solution Growth for Suppression of Solvent Inclusions 査読有り

Zhou, HQ; Miura, H; Dang, YF; Fukami, Y; Takemoto, H; Harada, S; Tagawa, M; Ujihara, T

CRYSTAL GROWTH & DESIGN 23 巻 ( 5 ) 頁： 3393 - 3401 2023年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

For the solution growth of silicon carbide, solvent inclusions are significant technological issues, and methods to suppress the formation of solvent inclusions are investigated in this study. Experimental observations show that solvent inclusions are formed behind the cellular structures. A phase field model is used to reproduce the formation process of cellular structures and solvent inclusions. Simulation results indicate that slight perturbations of the step front can convert into cellular structures in the case of insufficient supply of carbon, and the overdeveloped cellular structures consequently result in solvent inclusions. Accordingly, several schemes can be suggested by the simulation model to suppress the formation of cellular structures by enhancing the carbon supply. By increasing the carbon diffusion coefficient, cellular structures can be suppressed. Moreover, the step height and the solution flow direction also play an important role in suppressing the cellular structures. This study provides a comprehensive understanding of the formation process of cellular structures and solvent inclusions. A growth process with a high diffusion coefficient and opposite solution flow to the step flow direction was proposed to suppress the formation of cellular structures. The proposed numerical model could be applied in other solution crystal growth methods.

DOI： 10.1021/acs.cgd.2c01512

Development of High-Resolution Nuclear Emulsion Plates for Synchrotron X-Ray Topography Observation of Large-Size Semiconductor Wafers 査読有り Open Access

Harada, S; Nishigaki, T; Kitagawa, N; Ishiji, K; Hanada, K; Tanaka, A; Morishima, K

JOURNAL OF ELECTRONIC MATERIALS 52 巻 ( 5 ) 頁： 2951 - 2956 2023年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Electronic Materials

Characterization of defects in semiconductor wafers is essential for the development and improvement of semiconductor devices, especially power devices. X-ray topography (XRT) using synchrotron radiation is a powerful methods used for defect characterization. To achieve detailed characterization of large-size semiconductor wafers by synchrotron XRT, we have developed nuclear emulsion plates reaching a high-resolution and wide dynamic range. We have shown that higher-resolution XRT images could be obtained using emulsions with smaller iodobromide crystals, and demonstrated clear observation of threading edge dislocations in a SiC epitaxial layer having small contrast. Furthermore, we demonstrated XRT image acquisition for almost all of a 150-mm SiC wafer with one plate. Our development will contribute to advances in electronic materials, especially in the field of power electronics, in which defect characterization is important for improving the performance and yield of devices.

DOI： 10.1007/s11664-023-10270-8

Thermal conduction in titanium-chromium oxide natural superlattices with an ordered arrangement of nearly pristine interfaces 査読有り

Sugimoto, S; Kim, G; Takeuchi, T; Tagawa, M; Ujihara, T; Harada, S

JOURNAL OF ALLOYS AND COMPOUNDS 934 巻頁： 167915 2023年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Alloys and Compounds

Thermal conduction was investigated in titanium-chromium oxide natural superlattices with an ordered arrangement of crystallographic shear planes, which were nearly pristine interfaces for thermal phonons. Thermal conductivity exhibited a clear maximum value at around 50 K, which indicates interface roughness as small as 20 pm based on the calculation of thermal conductivity by a modified Debye-Callaway model. With an ordered arrangement of nearly pristine interfaces at nanoscale, the wave contribution to phonon transport was estimated to be predominant at lower temperatures (less than 100 K) and as much as 30 % even at room temperature. We found that the interface roughness greatly influences the thermal conduction in natural superlattice systems, which may lead to variations in the reported value of thermal conductivity. We have demonstrated that the wave contribution of thermal conductivity become apparent in bulk crystal having nano scale periodic structure with pristine interfaces.

DOI： 10.1016/j.jallcom.2022.167915

Suppression of partial dislocation glide motion during contraction of stacking faults in SiC epitaxial layers by hydrogen ion implantation 査読有り Open Access

Harada, S; Sakane, H; Mii, T; Kato, M

APPLIED PHYSICS EXPRESS 16 巻 ( 2 ) 頁： 021001 2023年2月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Bipolar degradation in SiC bipolar devices, in which stacking faults (SFs) expand to accommodate the movement of partial dislocations during forward bias application, is one of the critical problems impeding the widespread implementation of SiC power devices. Here we clearly demonstrate that the movement of partial dislocations can be suppressed by proton implantation, which has good compatibility with semiconductor processing, through investigation of the contraction behavior of SFs in SiC epitaxial layers subjected to proton implantation.

DOI： 10.35848/1882-0786/acb585

Modeling-Based Design of the Control Pattern for Uniform Macrostep Morphology in Solution Growth of SiC 査読有り

Dang, YF; Liu, XB; Zhu, C; Fukami, Y; Ma, SY; Zhou, HQ; Liu, X; Kutsukake, K; Harada, S; Ujihara, T

CRYSTAL GROWTH & DESIGN 23 巻 ( 2 ) 頁： 1023 - 1032 2023年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

In the solution growth of the SiC crystal, macrosteps with sufficient height on an off-axis substrate are required to reduce defects and achieve a high-quality grown layer. However, over-developed macrosteps can induce new defects and adversely affect the crystal quality. To better understand and control the behavior of macrosteps corresponding to the control parameters of the growth system, a simulation method that consists of a global two-dimensional computational fluid dynamic (CFD) model, a local three-dimensional CFD model near the growth front, and a kinetics model that describes the movement of macrosteps on the crystal surface is proposed. The simulation method is first applied to investigate the effect of the crystal rotation speed on macrostep morphology. Although the results indicate that a higher crystal rotation speed results in less step bunching, constantly rotating the crystal in one direction is demonstrated to be incapable of yielding a uniform macrostep distribution on the whole surface. Accordingly, a sophisticated control pattern is designed by periodically switching the flow direction underneath the crystal surface, where the proposed simulation method is critical to determine detailed control-parameter values. When the control pattern suggested by the simulation is used, a grown crystal with a uniform macrostep morphology and ideal step height on the whole surface is obtained in the practical experiment.

DOI： 10.1021/acs.cgd.2c01194

Analysis of carrier lifetime in a drift layer of 1.2-kV class 4H-SiC devices toward complete suppression of bipolar degradation 査読有り

Mii, T; Sakane, H; Harada, S; Kato, M

MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING 153 巻頁： 107126 2023年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science in Semiconductor Processing

We analyzed the carrier lifetime in a drift layer of 1.2 kV-class SiC p-n diodes to suppress bipolar degradation. According to the device simulation results, the required carrier lifetime in the drift layer was estimated to be shorter than 10 ns with a current density of 300 A/cm2 if the threshold hole density for the expansion of the stacking fault at the interface of the drift layer and substrate was 2 × 1016 cm−3. Numerical analysis revealed that to ensure a carrier lifetime shorter than 10 ns, the 1/e2 lifetime obtained by microwave photoconductivity decay (μ-PCD) measurements should be shorter than 7.2 ns. Experimental μ-PCD measurements showed that 1/e2 lifetimes obtained from the as-received epiwafer were much longer than 7.2 ns, and even after H+ implantation, high-temperature annealing, or electron irradiation, 1/e2 lifetimes were still long. Therefore, carrier lifetime control in the drift layer is not sufficient to suppress bipolar degradation, and a combination of carrier lifetime control with other methods is necessary for the fabrication of 1.2 kV-class SiC p-n diodes for the complete suppression of bipolar degradation at a current capacity of 300 A/cm2.

DOI： 10.1016/j.mssp.2022.107126

Prediction of operating dynamics in floating-zone crystal growth using Gaussian mixture model 査読有り

Omae, R; Sumitani, S; Tosa, Y; Harada, S

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS-METHODS 2 巻 ( 1 ) 頁： 294 - 301 2022年12月

非弾性Ｘ線散乱によるルチル型酸化チタンのフォノン分散測定査読有り

原田俊太, 小坂直輝, 筒井智嗣, 田中克志, 田川美穂, 宇治原徹

SPring-8/SACLA利用研究成果集 10 巻 ( 6 ) 頁： 521 - 523 2022年12月

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益財団法人高輝度光科学研究センター

ルチル型酸化チタンにおいて酸素欠損が生じると、酸素欠損を含む面欠陥が周期的に配列するシア構造と呼ばれる構造となることが知られている。このような面欠陥の周期配列によって生じる、フォノンの分散関係の変化を調べるために、本研究では比較のために、面欠陥の周期配列を含まないルチル型酸化チタンのフォノン分散を非弾性Ｘ線散乱によって測定した。(121)方向に沿ったフォノン分散測定の結果、40 meV 以下のエネルギー領域において３つのフォノンモードを観測することができた。

DOI： 10.18957/rr.10.6.521

Suppression of stacking-fault expansion in 4H-SiC PiN diodes using proton implantation to solve bipolar degradation 査読有り Open Access

Kato, M; Watanabe, O; Mii, T; Sakane, H; Harada, S

SCIENTIFIC REPORTS 12 巻 ( 1 ) 頁： 18790 2022年11月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

4H-SiC has been commercialized as a material for power semiconductor devices. However, the long-term reliability of 4H-SiC devices is a barrier to their widespread application, and the most important reliability issue in 4H-SiC devices is bipolar degradation. This degradation is caused by the expansion of single Shockley stacking-faults (1SSFs) from basal plane dislocations in the 4H-SiC crystal. Here, we present a method for suppressing the 1SSF expansion by proton implantation on a 4H-SiC epitaxial wafer. PiN diodes fabricated on a proton-implanted wafer show current–voltage characteristics similar to those of PiN diodes without proton implantation. In contrast, the expansion of 1SSFs is effectively suppressed in PiN diodes with proton implantation. Therefore, proton implantation into 4H-SiC epitaxial wafers is an effective method for suppressing bipolar degradation in 4H-SiC power-semiconductor devices while maintaining device performance. This result contributes to the development of highly reliable 4H-SiC devices.

DOI： 10.1038/s41598-022-23691-y

Optimization of Flow Distribution by Topological Description and Machine Learning in Solution Growth of SiC 査読有り

Isono, M; Harada, S; Kutsukake, K; Yokoyama, T; Tagawa, M; Ujihara, T

ADVANCED THEORY AND SIMULATIONS 5 巻 ( 9 ) 頁： 2200302 2022年9月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Theory and Simulations

The macroscopic distribution of fluid flows, which affect the quality of final products for various kinds of materials, is often difficult to describe in mathematical formulae and hinders the implementation of empirical knowledge in scaling up. In the present study, the characteristics of the flow distribution in silicon carbide (SiC) solution growth are described by using the position of the saddle point and the solution growth conditions are optimized by computational fluid dynamics simulation, machine learning, and a genetic algorithm. As a result, the candidates of the optimal condition for the solution growth of 6-in. SiC crystals are successfully obtained from the empirical knowledge gained from 3-in. crystal growth, by adding the topological description to the objective function. The present design of the objective function using the topological description can possibly be applied to other crystal growth or materials processing problems and to overcome scale-up difficulties, which can facilitate the rapid development of functional materials such as SiC wafers for power device applications.

DOI： 10.1002/adts.202200302

A Transfer Learning-Based Method for Facilitating the Prediction of Unsteady Crystal Growth 査読有り

Dang, YF; Kutsukake, K; Liu, X; Inoue, Y; Liu, XB; Seki, S; Zhu, C; Harada, S; Tagawa, M; Ujihara, T

ADVANCED THEORY AND SIMULATIONS 5 巻 ( 9 ) 頁： 2200204 2022年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Theory and Simulations

Real-time prediction and dynamic control systems that can adapt to an unsteady environment are necessary for material fabrication processes, especially crystal growth. Recent studies have demonstrated the effectiveness of machine learning in predicting an unsteady crystal growth process, but its wider application is hindered by the large amount of training data required for sufficient accuracy. To address this problem, this study investigates the capability of transfer learning to predict geometric evolution in an unsteady silicon carbide (SiC) solution growth system based on a small amount of data. The performance of transferred models is discussed regarding the effect of the transfer learning method, training data amount, and time step length. The transfer learning strategy yields the same accuracy as that of training from scratch but requires only 20% of the training data. The accuracy is stably inherited through successive time steps, which demonstrates the effectiveness of transfer learning in reducing the required amount of training data for predicting evolution in an unsteady crystal growth process. Moreover, the transferred models trained with relatively more data (no more than 100%) further improve the accuracy inherited from the source model through multiple time steps, which broadens the application scope of transfer learning.

DOI： 10.1002/adts.202200204

Designing a High-Crystallinity Nano-Gapped Particle Superlattice via DNA-Guided Colloidal Crystallization and Dehydration 査読有り

Suppression of stacking fault expansion in a 4H-SiC epitaxial layer by proton irradiation 査読有り Open Access

Harada, S; Mii, T; Sakane, H; Kato, M

SCIENTIFIC REPORTS 12 巻 ( 1 ) 頁： 13542 2022年8月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

SiC bipolar degradation, which is caused by stacking fault expansion from basal plane dislocations in a SiC epitaxial layer or near the interface between the epitaxial layer and the substrate, is one of the critical problems inhibiting widespread usage of high-voltage SiC bipolar devices. In the present study, we investigated the stacking fault expansion behavior under UV illumination in a 4H-SiC epitaxial layer subjected to proton irradiation. X-ray topography observations revealed that proton irradiation suppressed stacking fault expansion. Excess carrier lifetime measurements showed that stacking fault expansion was suppressed in 4H-SiC epitaxial layers with proton irradiation at a fluence of 1 × 1011 cm−2 without evident reduction of the excess carrier lifetime. Furthermore, stacking fault expansion was also suppressed even after high-temperature annealing to recover the excess carrier lifetime. These results implied that passivation of dislocation cores by protons hinders recombination-enhanced dislocation glide motion under UV illumination.

DOI： 10.1038/s41598-022-17060-y

Observation of in-plane shear stress fields in off-axis SiC waters by birefringence imaging 査読有り Open Access

Harada, S; Murayama, K

JOURNAL OF APPLIED CRYSTALLOGRAPHY 55 巻頁： 1029 - 1032 2022年8月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Crystallography

For the nondestructive characterization of SiC wafers for power device application, birefringence imaging is one of the promising methods. In the present study, it is demonstrated that birefringence image contrast variation in off-axis SiC wafers corresponds to the in-plane shear stress under conditions slightly deviating from crossed Nicols according to both theoretical consideration and experimental observation. The current results indicate that the characterization of defects in SiC wafers is possible to achieve by birefringence imaging.

DOI： 10.1107/S1600576722006483

Sumi, H; Ohta, N; Sekiguchi, H; Harada, S; Ujihara, T; Tsukamoto, K; Tagawa, M

CRYSTAL GROWTH & DESIGN 22 巻 ( 6 ) 頁： 3708 - 3718 2022年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

For the emergence of quantum effects such as plasmonic enhancement, we successfully assembled high-crystallinity nano-gapped particle superlattices composed of sub-10 nm nanoparticles into the solid state through the self-assembly of DNA-programmed nanoparticles (DNA-NPs) in solution followed by dynamic isotropic contraction during dehydration. By this method of isotropic contraction, the crystal symmetry of the self-assembled DNA-NP superlattice in solution was inherited into a dehydrated and contracted one. The optimal isotropic contraction during dehydration was achieved by minimizing the g-factor, which is the index value of the degree of crystallinity. The g-factor was calculated using small-angle X-ray scattering and scanning electron microscopy data for self-assembled DNA-NP superlattices before and after dehydration. The experimental success was driven by our theoretical prediction based on the geometrical calculation regarding the spatial restriction of the nearest-neighbor particle arrangement in a three-dimensional crystal lattice, which was quantified as the particle volume fraction in the lattice, φ. By reducing the nanogap to less than 4 nm through DNA-programmed sub-10 nm nanoparticle crystallization, nanofabrication on a scale exhibiting quantum effects in a bottom-up manner would be feasible.

DOI： 10.1021/acs.cgd.2c00075

Identification of a novel large duplication (exon2_6dup): copy number variation in the LDLR gene in a large family with familial hypercholesterolemia by whole-genome sequencing

「スペクトル超解像」による分光分析の高精度化招待有り

原田俊太

OplusE 44 巻 ( 3 ) 頁： 217 - 217 2022年5月

品質管理へのAI活用の現状と展望—外観検査・棚卸しの自動化を例に招待有り査読有り

炭谷翔悟、西田陽良、原田俊太

システム／制御／情報 66 巻 ( 5 ) 頁： 161 - 167 2022年5月

Hori, M; Takahashi, A; Hosoda, K; Harada-Shiba, M

JOURNAL OF CLINICAL LIPIDOLOGY 16 巻 ( 2 ) 頁： 167 - 172 2022年3月

Crossover from incoherent to coherent thermal conduction in bulk titanium oxide natural superlattices 査読有り

Harada Shunta, Kosaka Naoki, Yagi Takashi, Sugimoto Shunya, Tagawa Miho, Ujihara Toru

SCRIPTA MATERIALIA 208 巻 2022年2月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scripta Materialia

We have investigated thermal conduction in bulk titanium oxide natural superlattices with crystallographic shear (CS) structures, in which dense planar faults are introduced with different periodicities, prepared by reductive annealing of rutile TiO2 and crystal growth by the floating zone method. High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) revealed that (132)rutile and (121)rutile CS planes with interspacings of 2.7 and 1.0 nm were introduced in the mother rutile structure. Time-domain thermoreflectance (TDTR) revealed that the thermal conductivity decreased by the introduction of CS planes, but that the decrease is not monotonic with increasing density of CS planes. Calculation of the thermal conductivity and the mean free path for phonons revealed that a crossover from incoherent to coherent thermal conduction took place, and coherent interfaces with nanoscale periodicity were formed as thermodynamically stable phases in bulk titanium oxide natural superlattices.

DOI： 10.1016/j.scriptamat.2021.114326

Numerical investigation of solute evaporation in crystal growth from solution: A case study of SiC growth by TSSG method 査読有り

Dang Y., Zhu C., Liu X., Yu W., Liu X., Suzuki K., Furusho T., Harada S., Tagawa M., Ujihara T.

Journal of Crystal Growth 579 巻頁： 126448 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Crystal Growth

Evaporation of the volatile solute from the liquid phase is a common problem for the crystal grown from solution, especially for the growth under high temperature. In the present study, a numerical model was constructed to quantitatively investigate the evaporation process in crystal growth. This model was applied in top-seeded solution growth (TSSG) of SiC crystal to simulate the transport of aluminum (Al), which is important for crystal surface morphology but easy to vaporize. The transport path of Al in the growth system was determined by analyzing the possible reactions on different boundaries. Accordingly, an improved structure was proposed to suppress the evaporation loss of Al during long-term growth, and was compared with the original case both numerically and experimentally. The simulation results showed that the improved structure could effectively decrease the Al loss by over 70%, and meanwhile had almost no influence on the thermal and flow environment in the solution. For the experimental results, the improved case presented much lower spontaneous nucleation possibilities and higher step height on the crystal surface, which matched well with the features of high Al addition in literatures. Therefore, the improved structure proposed in the present study was proven to be effective to enhance the composition stability of solution during long-term SiC solution growth, and this numerical method could be applied in the growth of other crystals facing the similar problem.

DOI： 10.1016/j.jcrysgro.2021.126448

Application of Bayesian Super-Resolution to Spectroscopic Data for Precise Characterization of Spectral Peak Shape 査読有り Open Access

Tsujimori, K; Hirotani, J; Harada, S

JOURNAL OF ELECTRONIC MATERIALS 51 巻 ( 2 ) 頁： 712 - 717 2022年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Electronic Materials

The number of data points of digitally recorded spectra have been limited by the number of multichannel detectors employed, which sometimes impedes the precise characterization of spectral peak shape. Here we describe a methodology to increase the number of data points as well as the signal-to-noise (S/N) ratio by applying Bayesian super-resolution in the analysis of spectroscopic data. In our present method, first, the hyperparameters for the Bayesian super-resolution are determined by a virtual experiment imitating actual experimental data, and the precision of the super-resolution reconstruction is confirmed by the calculation of errors from the ideal values. For validation of the super-resolution reconstruction of spectroscopic data, we applied this method to the analysis of Raman spectra. From 200 Raman spectra of a reference Si substrate with a data interval of about 0.8 cm−1, super-resolution reconstruction with a data interval of 0.01 cm−1 was successfully achieved with the promised precision. From the super-resolution spectrum, the Raman scattering peak of the reference Si substrate was estimated as 520.55 (+0.12, −0.09) cm−1, which is comparable to the precisely determined value reported in previous works. The present methodology can be applied to various kinds of spectroscopic analysis, leading to increased precision in the analysis of spectroscopic data and the ability to detect slight differences in spectral peak positions and shapes.

DOI： 10.1007/s11664-021-09326-4

Solvent design aiming at solution property induced surface stability: A case study using SiC solution growth 査読有り

Liu, XB; Dang, YF; Suzuki, K; Zhu, C; Yu, WC; Harada, S; Tagawa, M; Ujihara, T

JOURNAL OF CRYSTAL GROWTH 578 巻頁： 126425 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Crystal Growth

For solution growth of silicon carbide, it is significant to understanding the evolutionary mechanism of step bunching. This study infers that solute's incorporation into steps and transport together determines step bunching progress. The occurrence of step bunching is due to the depletion of solute in the region with high step density, caused by a high step kinetic coefficient. On the other hand, by promoting the transport of the solute in the solution, the step speed becomes uniform, thereby the step bunching can be prevented. Furthermore, we proposed a non-dimensional Damköhler number for crystal growth in step-flow mode. It correlates incorporation rates with bulk diffusion rates and can build a phase map of growth rates and step bunching stability. Several solvents are located in the phase map, demonstrating the possible usage of the phase map as a pointer for solvent designing.

DOI： 10.1016/j.jcrysgro.2021.126425

Automatic Detection of Basal Plane Dislocations in a 150-mm SiC Epitaxial Wafer by Photoluminescence Imaging and Template-matching Algorithm 査読有り

Harada, S; Tsujimori, K; Matsushita, Y

JOURNAL OF ELECTRONIC MATERIALS 51 巻 ( 1 ) 頁： 243 - 248 2022年1月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Electronic Materials

In this study, an algorithm was constructed for the automatic detection of basal plane dislocations (BPDs) propagating in SiC epitaxial layers in photoluminescence images, and its performance was evaluated. The BPDs are the origin of the degradation of SiC bipolar devices caused by the expansion of stacking faults. The present automatic detection algorithm, based on the template-matching method, was confirmed to have high accuracy and precision, and we succeeded in visualizing the BPD density in 150-mm SiC epitaxial wafers. We confirmed that the template-matching method is applicable for the detection of crystalline defects with geometrically fixed shapes such as BPDs in SiC epitaxial layers.

DOI： 10.1007/s11664-021-09284-x

Polarized light observation of semiconductor wafers for power devices

High fracture toughness AlN achieved by addition of AlN whiskers and tape-casting 査読有り Open Access

Shimizu, H; Kondo, N; Shimamura, A; Hotta, M; Harada, S; Ujihara, T; Ohnishi, Y

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 130 巻 ( 1 ) 頁： 195 - 198 2022年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Aluminum nitride (AlN) possesses excellent thermal conductivity and electrical resistivity, which makes it an ideal candidate for high-power, high-speed integrated circuit substrates. Its low fracture toughness requires the manufacturing of thicker substrates. However, this leads to degraded heat dissipation performance. Herein, we investigated a new strategy, combining the addition of AlN whiskers and tape-casting, to overcome the low fracture toughness disadvantage. The sintered AlN with AlN whiskers addition induced the formation of a highly anisotropic microstructure with aligned rod-like grains, effectively enhancing the fracture toughness to 6.7MPam1/2, while maintaining thermal conductivity but degrading strength.

DOI： 10.2109/jcersj2.21143

Murayama K., Mizutani S., Mizutani Y., Harada S.

2022 IEEE International Meeting for Future of Electron Devices, Kansai, IMFEDK 2022 2022年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：2022 IEEE International Meeting for Future of Electron Devices, Kansai, IMFEDK 2022

Polarized light observation is one of the promising methods for the non-destructive characterization of semiconductor wafers for power devices. We have visualized the distribution of defects in SiC wafers by birefringence imaging.

DOI： 10.1109/IMFEDK56875.2022.9975432

Association between Achilles Tendon Softness and Atherosclerotic Cardiovascular Disease in Patients with Familial Hypercholesterolemia

シミュレーションに基づく結晶成長プロセスインフォマティクス

沓掛健太朗, 角岡洋介, 郁万成, 黨一帆, 原田俊太, 宇治原徹

日本結晶成長学会誌 49 巻 ( 1 ) 頁： n/a 2022年

Michikura, M; Ogura, M; Hori, M; Matsuki, K; Makino, H; Hosoda, K; Harada-Shiba, M

JOURNAL OF ATHEROSCLEROSIS AND THROMBOSIS 29 巻 ( 11 ) 頁： 1603 - 1612 2022年

Immobilization of partial dislocations bounding double Shockley stacking faults in 4H-SiC observed by in situ synchrotron X-ray topography 査読有り

Fujie, F; Harada, S; Suo, H; Raghothamachar, B; Dudley, M; Hanada, K; Koizumi, H; Kato, T; Tagawa, M; Ujihara, T

MATERIALIA 20 巻頁： 101246 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materialia

The expansion of double Shockley stacking faults (DSFs) in an n-type 4H-SiC substrate with a nitrogen concentration of 3.9 × 1019 cm−3 was investigated using in situ synchrotron X-ray topography. DSF expansion was observed to be suppressed and immobilized above 1590 K, along with the partial dislocation (PD) shape being changed from a straight to zig-zag configuration. For a different heating process (higher heating rate), the PDs could continue to expand, even above 1590 K. Ex situ topography experiments revealed that the DSFs close to the specimen surface expanded widely, although those expanding toward the specimen interior became immobile. One possible mechanism for this immobilization was proposed, where the core structural changes from a Si-core to the C-core by non-conservative motion induced by the interaction between the PDs and point defects (C interstitials).

DOI： 10.1016/j.mtla.2021.101246

Surface relaxation and photoelectric absorption effects on synchrotron X-ray topographic images of dislocations lying on the basal plane in off-axis 4H-SiC crystals 査読有り Open Access

Ailihumaer, T; Peng, HY; Fujie, F; Raghothamachar, B; Dudley, M; Harada, S; Ujihara, T

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS 271 巻頁： 115281 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering: B

A more sophisticated simulation model is developed based on the principle of ray-tracing to simulate the grazing-incidence synchrotron X-ray topographic contrast of dislocations lying on the basal plane including basal plane dislocations and deflected threading screw and mixed dislocations in off-axis 4H-SiC crystals. The model incorporates effects of surface relaxation as well as the photoelectric absorption to predict dislocation contrast. Compared to conventional ray-tracing images, surface relaxation effects dominate dislocation contrast for diffraction near the crystal surface. The simulated dislocation contrast gradually weakens with increasing depth of the diffracted beam position within the crystal due to photoelectric absorption. The distinctive features of the net simulated dislocation images obtained by aggregating through the effective penetration depth correlate well with contrast features observed on the experimental topographic images. Depth analysis reveals that in some cases the diffracted X-rays from regions below the dislocation can contribute additional contrast features previously not considered.

DOI： 10.1016/j.mseb.2021.115281

混合ガウスモデルを用いた浮遊帯域溶融法における融液状態のダイナミクス推定

大前遼, 炭谷翔悟, 土佐祐介, 原田俊太

応用物理学会学術講演会講演予稿集 2021.2 巻 ( 0 ) 頁： 3410 - 3410 2021年8月

Two-Step Nanoparticle Crystallization via DNA-Guided Self-Assembly and the Nonequilibrium Dehydration Process 査読有り Open Access

Sumi, H; Ohta, N; Sekiguchi, H; Harada, S; Ujihara, T; Tsukamoto, K; Tagawa, M

CRYSTAL GROWTH & DESIGN 21 巻 ( 8 ) 頁： 4506 - 4515 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystal Growth and Design

DNA strands are powerful tools as ligand molecules that bind nanoparticles to each other via programmable self-assembly for colloidal crystallization. We found that hydrated DNA-functionalized nanoparticle (DNA-NP) superlattices with a properly controlled volume fraction and spatial arrangement of nanoparticles successfully maintained their crystallinity even after dehydration, which involves drastic contraction. A detailed study of the structural changes was performed for the self-assembled DNA-NP sample using small-angle X-ray scattering (SAXS) after dehydration. Then, an optimal volume fraction of nanoparticles in the superlattice, φ, which minimized the level of distortion of the dehydrated superlattice, was found for each bcc and fcc structure. By acquiring clear SAXS diffraction patterns showing crystal symmetries for dehydrated DNA-NP superlattices, their lattice distortion was evaluated using our analysis technique, which is based on Hosemann's paracrystalline theory and involves SAXS and scanning electron microscopy data. Geometrical calculations substantiated the ease of movement of a nanoparticle under the influence of repulsions from adjacent particles that mainly affect the dehydration stability. These results suggest that it is possible to design the crystal structure of solid nanoparticle superlattices via DNA-guided nanoparticle assembly under a near-equilibrium state in solution as the first step, followed by dehydration under nonequilibrium conditions as the second step.

DOI： 10.1021/acs.cgd.1c00398

Y Local Atomic Structures for Tunable Ordered Arrangements of Crystallographic Shear Planes in Titanium-Chromium Oxide Natural Superlattices 査読有り

Harada Shunta, Sugimoto Shunya, Kosaka Naoki, Tagawa Miho, Ujihara Toru

JOURNAL OF PHYSICAL CHEMISTRY C 125 巻 ( 28 ) 頁： 15730 - 15736 2021年7月

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

The atomic structure of titanium-chromium oxide natural superlattices with different compositions having an ordered arrangement of crystallographic shear (CS) planes was investigated by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and electron diffraction, using polycrystalline ceramics prepared by arc-melting and heat treatment. Analysis of the electron diffraction patterns revealed that not only the interspacing but also the direction of planar faults changed depending on the chromium concentration. HAADF-STEM observations showed that the atomic arrangements of CS planes deviating from (121)rutile are random arrangements of (121)rutile CS planes and (011)rutile antiphase boundaries. Using a random walk model and by calculating the specularity parameter, we found that the CS planes in titanium-chromium oxides behave as coherent interfaces for phonons based on the estimation of interface roughness.

DOI： 10.1021/acs.jpcc.1c04516

Adaptive process control for crystal growth using machine learning for high-speed prediction: application to SiC solution growth

Ordered Arrangement of Planar Faults with Picoscale Perfection in Titanium Oxide Natural Superlattices 査読有り

The Journal of Physical Chemistry C 125 巻 ( 20 ) 頁： 11175 - 11181 2021年5月

Design of automatic detection algorithm for dislocation contrasts in birefringence images of SiC wafers 査読有り

Kawata Akira, Murayama Kenta, Sumitani Shogo, Harada Shunta

JAPANESE JOURNAL OF APPLIED PHYSICS 60 巻 ( SB ) 2021年5月

Synchrotron X-ray topographic image contrast variation of screw-type basal plane dislocations located at different depths below the crystal surface in 4H-SiC 査読有り国際共著

Fujie Fumihiro, Peng Hongyu, Ailihumaer Tuerxun, Raghothamachar Balaji, Dudley Michael, Harada Shunta, Tagawa Miho, Ujihara Toru

ACTA MATERIALIA 208 巻 2021年4月

Geometrical design of a crystal growth system guided by a machine learning algorithm 査読有り

Wancheng Yu, Can Zhu, Wei Huang, Dang Yifan, Kentaro Kutsukake, Shunta Harada, Miho Tagawa, Toru Ujihara

CrystEngComm 23 巻 ( 14 ) 頁： 2695 - 2702 2021年4月

Dang Yifan, Zhu Can, Ikumi Motoki, Takaishi Masaki, Yu Wancheng, Huang Wei, Liu Xinbo, Kutsukake Kentaro, Harada Shunta, Tagawa Miho, Ujihara Toru

CrystEngComm 23 巻 ( 9 ) 頁： 1982 - 1990 2021年3月

Analysis of dislocation line tilt in GaN single crystal by Raman spectroscopy

Kokubo Nobuhiko, Tsunooka Yosuke, Inotsume Sho, Fujie Fumihiro, Onda Shoichi, Yamada Hisashi, Shimizu Mitsuaki, Harada Shunta, Tagawa Miho, Ujihara Toru

JAPANESE JOURNAL OF APPLIED PHYSICS 60 巻 ( SA ) 2021年1月

大口径SiCバルク結晶成長における主要技術とプロセス・インフォマティクスの活用

宇治原徹, 朱燦, 角岡洋介, 古庄智明, 鈴木皓己, 沓掛健太朗, 高石将輝, 郁万成, 黨一帆, 磯野優, 竹内一郎, 田川美穂, 原田俊太

日本結晶成長学会誌 48 巻 ( 3 ) 頁： n/a 2021年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶成長学会

We have been developing a SiC crystal growth technique using the solution method. As a result, we have achieved the growth of ultra-high quality crystals with extremely low dislocation density. The key to this is the reduction of dislocation density by utilizing the macro-step dislocation conversion phenomenon and the suppression of surface morphology roughness by controlling the flow in the solution. In order to put these technologies to practical use, we have developed a new machine learning technique for optimizing crystal growth conditions for large-diameter crystals. In this method, a model is constructed in the computer that reproduces the actual experiment quickly and accurately, and then hundreds of thousands or millions of trials are performed using the model to derive the experimental conditions with high efficiency. This means that optimization by surrogate models, which is one of the methods of process informatics, has been realized in crystal growth. By using these techniques, we were able to achieve 6-inch crystal growth in a very short time.

DOI： 10.19009/jjacg.48-3-04

Temperature dependence of double Shockley stacking fault behavior in nitrogen-doped 4H-SiC studied by in-situ synchrotron X-ray topography

Numerical investigation and optimization of time evolution in the solution during solution growth for SiC crystal

Dang Yifan, Zhu Can, Yu Wancheng, Huang Wei, Ikumi Motoki, Harada Shunta, Tagawa Miho, Ujihara Toru

JSAP Annual Meetings Extended Abstracts 2020.2 巻 ( 0 ) 頁： 2128 - 2128 2020年8月

Fujie Fumihiro, Harada Shunta, Hanada Kenji, Suo Hiromasa, Koizumi Haruhiko, Kato Tomohisa, Tagawa Miho, Ujihara Toru

ACTA MATERIALIA 194 巻頁： 387 - 393 2020年8月

Behavior of Threading Dislocations from GaN Substrate to Epitaxial Layer

Inotsume Sho, Kokubo Nobuhiko, Yamada Hisashi, Onda Shoichi, Kojima Jun, Ohara Junji, Harada Shunta, Tagawa Miho, Ujihara Toru

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 257 巻 ( 4 ) 2020年4月

Demonstration of Observation of Dislocations in GaN by Novel Birefringence Method

Tanaka Atsushi, Inotsume Syo, Harada Shunta, Hanada Kenji, Honda Yoshio, Ujihara Toru, Amano Hiroshi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 257 巻 ( 4 ) 2020年4月

機械学習を活用した SiC 高品質結晶成長条件のデザイン招待有り査読有り

原田俊太，林宏益，角岡洋介，朱燦，鳴海大翔，沓掛健太朗，宇治原徹

まてりあ 59 巻 ( 3 ) 頁： 145 - 152 2020年3月

Effect of Crystal Orientation of Cu Current Collectors on Cycling Stability of Li Metal Anodes

Ishikawa Kohei, Harada Shunta, Tagawa Miho, Ujihara Toru

ACS APPLIED MATERIALS & INTERFACES 12 巻 ( 8 ) 頁： 9341 - 9346 2020年2月

Application of C-face dislocation conversion to 2 inch SiC crystal growth on an off-axis seed crystal

Liu Xinbo, Zhu Can, Harada Shunta, Tagawa Miho, Ujihara Toru

CRYSTENGCOMM 21 巻 ( 47 ) 頁： 7260 - 7265 2019年12月

Nondestructive visualization of threading dislocations in GaN by micro raman mapping

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

JAPANESE JOURNAL OF APPLIED PHYSICS 58 巻 ( SC ) 2019年6月

SiC溶液成長による高品質化と機械学習の応用招待有り査読有り

原田俊太，朱燦，角岡洋介，沓掛健太朗，宇治原徹

14 巻 ( 1 ) 頁： 13 - 18 2019年6月

SiC溶液成長による高品質化と機械学習の応用招待有り査読有り

原田俊太, 朱燦, 角岡洋介, 沓掛健太朗, 宇治原徹

14 巻 ( 1 ) 頁： 13 - 18 2019年6月

Evaluation of basal plane dislocation behavior in the epitaxial layer on a 4H-SiC wafer fabricated by the solution growth method

Seki K.

Materials Science Forum 963 MSF 巻頁： 80 - 84 2019年

結晶成長学的見地による金属負極の析出形態と結晶方位の相関解明

石川晃平, 三橋貴仁, 伊藤靖仁, 竹内幸久, 原田俊太, 田川美穂, 宇治原徹

日本結晶成長学会誌 46 巻 ( 1 ) 頁： 136-140 2019年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶成長学会

Metal anodes are promising materials for rechargeable batteries because of the higher capacity. However, low cycle efficiency due to non-uniform deposition prevents them from realization. In this review, we report the crystal orientation dependence of the deposition shape of Li and Zn, which are known as attractive materials for anodes. The result shows that the both of Li and Zn morphology has crystal orientation dependence.

DOI： 10.19009/jjacg.46-1-08

機械学習を用いた結晶成長予測モデルの構築とその応用

宇治原徹, 角岡洋介, 畑佐豪記, 沓掛健太朗, 石黒祥生, 村山健太, 鳴海大翔, 原田俊太, 田川美穂

表面と真空 62 巻 ( 3 ) 頁： 136 - 140 2019年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本表面真空学会

The prediction model of the result of computed fluid dynamics simulation in SiC solution growth was constructed on neural network using machine learning. Utilizing the prediction model, we can optimize quickly crystal growth conditions. In addition, the real-time visualization system was also made using the prediction model.

DOI： 10.1380/vss.62.136

CiNii Books

Machine learning for SiC top-seeded solution growth - Prediction, optimization and visualization 査読有り

Toru Ujihara, Yosuke Tsunooka, Goki Hatasa, Can Zhu, Kentaro Kutsukake, Taka Narumi, Shunta Harada, Miho Tagawa

CS MANTECH 2019 - 2019 International Conference on Compound Semiconductor Manufacturing Technology, Digest of Papers 2019年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

© 2019 CS Mantech. All rights reserved. We are developing solution growth technique for high-quality SiC bulk crystal. In actual, we have achieved high-quality crystal with very-low-density of threading dislocations grown by controlling the surface morphology. In order to apply this technique to large-scale crystal growth, it is necessary to control supersaturation at growth surface, flow rate and flow direction of solvent in detail. However, there are many growth parameters which should be optimized. Simulation technique based on computational fluid dynamics (CFD) is often used. However, it is still difficult to optimize growth condition by utilizing simulation technique since the calculation speed of CFD simulation is not enough to optimize the growth conditions, exhaustively. In recent, informatics including machine learning is applied to various fields including materials science. In this study, we tried to apply machine learning to the analysis of the results of CFD. We could make the model to optimize the crystal growth parameters based on a neural network model. Using the model, the optimization time became 10000 times faster. This is just a trial of “Process Informatics”.

Machine learning for SiC top-seeded solution growth - Prediction, optimization and visualization

Ujihara T.

CS MANTECH 2019 - 2019 International Conference on Compound Semiconductor Manufacturing Technology, Digest of Papers 2019年

Improvement mechanism of sputtered AlN films by high-temperature annealing

Xiao Shiyu, Suzuki Ryoya, Miyake Hideto, Harada Shunta, Ujihara Toru

JOURNAL OF CRYSTAL GROWTH 502 巻頁： 41 - 44 2018年11月

High-speed prediction of computational fluid dynamics simulation in crystal growth

Tsunooka Yosuke, Kokubo Nobuhiko, Hatasa Goki, Harada Shunta, Tagawa Miho, Ujihara Toru

CRYSTENGCOMM 20 巻 ( 41 ) 頁： 6546 - 6550 2018年11月

Determination of edge-component Burgers vector of threading dislocations in GaN crystal by using Raman mapping

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

APPLIED PHYSICS EXPRESS 11 巻 ( 11 ) 2018年11月

Observation of carrier recombination in single Shockley stacking faults and at partial dislocations in 4H-SiC

Kato Masashi, Katahira Shinya, Ichikawa Yoshihito, Harada Shunta, Kimoto Tsunenobu

JOURNAL OF APPLIED PHYSICS 124 巻 ( 9 ) 2018年9月

GaN基板からエピタキシャル膜へ伝播する転位の分類と挙動の解明

井爪将, 小久保信彦, 山田永, 恩田正一, 大原淳士, 原田俊太, 田川美穂, 宇治原徹

応用物理学会学術講演会講演予稿集 2018.2 巻 ( 0 ) 頁： 3248 - 3248 2018年9月

In Situ Observation of Chiral Symmetry Breaking in NaClO3 Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring

Niinomi Hiromasa, Sugiyama Teruki, Tagawa Miho, Harada Shunta, Ujihara Tom, Uda Satoshi, Miyamoto Katsuhiko, Omatsu Takashige

CRYSTAL GROWTH & DESIGN 18 巻 ( 8 ) 頁： 4230 - 4239 2018年8月

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 113 巻 ( 1 ) 2018年7月

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 89 巻 ( 7 ) 2018年7月

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

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

APPLIED PHYSICS EXPRESS 11 巻 ( 6 ) 2018年6月

Dislocation behavior in bulk crystals grown by TSSG method

Seki K.

Materials Science Forum 924 巻頁： 39 - 42 2018年

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

Murayama K.

Materials Science Forum 924 巻頁： 60 - 63 2018年

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

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

AIP ADVANCES 7 巻 ( 11 ) 2017年11月

機械学習を用いたSiC結晶成長実験条件の最適化

村井良多, 畑佐豪記, 角岡洋介, 林宏益, 村山健太, 朱燦, 原田俊太, 田川美穂, 宇治原徹

応用物理学会学術講演会講演予稿集 2017.2 巻 ( 0 ) 頁： 3506 - 3506 2017年8月

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 2017.2 巻 ( 0 ) 頁： 3378 - 3378 2017年8月

Morphology of AlN whiskers grown by reacting N<inf>2</inf> gas and Al vapor

Matsumoto M.

Journal of Crystal Growth 468 巻頁： 576 - 580 2017年6月

Two-step SiC solution growth for dislocation reduction

Murayama K.

Journal of Crystal Growth 468 巻頁： 874 - 878 2017年6月

Phase transition process in DDAB supported lipid bilayer

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

JOURNAL OF CRYSTAL GROWTH 468 巻頁： 88 - 92 2017年6月

Solvent design for high-purity SiC solution growth

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

Mater. Sci. Forum 897 巻頁： 32-35 2017年5月

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 897 巻頁： 28-31 2017年5月

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 897 巻頁： 24-27 2017年5月

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

Ishikawa Kohei, Ito Yasumasa, Harada Shunta, Tagawa Miho, Ujihara Toru

CRYSTAL GROWTH & DESIGN 17 巻 ( 5 ) 頁： 2379 - 2385 2017年5月

DNA修飾ナノ粒子超格子を前駆体としたウルフ多面体型コロイド結晶の形成

鷲見隼人, 磯貝卓巳, 吉田直矢, 原田俊太, 宇治原徹, 田川美穂

応用物理学会学術講演会講演予稿集 2017.1 巻 ( 0 ) 頁： 2741 - 2741 2017年3月

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

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

JOURNAL OF CRYSTAL GROWTH 458 巻頁： 37 - 43 2017年1月

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 458 巻頁： 37-43 2017年

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. 17 巻頁： 2379-2385 2017年

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 468 巻頁： 88-92 2017年

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

Hori T.

Materials Science Forum 897 巻頁： 28 - 31 2017年

Solvent design for high-purity SiC solution growth

Harada S.

Materials Science Forum 897 巻頁： 32 - 35 2017年

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

Murayama K.

Materials Science Forum 897 巻頁： 24 - 27 2017年

Plasmonic Heating-Assisted Laser-Induced Crystallization from a NaClO3 Unsaturated Mother Solution

"H. Niinomi, T. Sugiyama, M. Tagawa, M. Maruyama, T. Ujihara, T. Omatsu, Y. Mori"

Cryst. Growth Des. 2016年12月

Plasmonic Heating-Assisted Laser-Induced Crystallization from a NaClO3 Unsaturated Mother Solution

H. Niinomi, T. Sugiyama, M. Tagawa, M. Maruyama, T. Ujihara, T. Omatsu, Y. Mori

Cryst. Growth Des. 2016年12月

Analysis of the carbon transport near the growth interface with respect to the rotational speed of the seed crystal during top-seeded solution growth of SiC

Umezaki Tomonori, Koike Daiki, Harada Shunta, Ujihara Toru

JAPANESE JOURNAL OF APPLIED PHYSICS 55 巻 ( 12 ) 頁： 125601 2016年12月

Conversion Behavior of Threading Screw Dislocations on C Face with Different Surface Morphology During 4H-SiC Solution Growth

Xiao Shiyu, Harada Shunta, Murayama Kenta, Tagawa Miho, Ujihara Toru

CRYSTAL GROWTH & DESIGN 16 巻 ( 11 ) 頁： 6436 - 6439 2016年11月

Conversion behavior of threading screw dislocations on C face with different surface morphology during 4H-SiC solution growth

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

Cryst. Growth Des. 頁： 6436–6439 2016年10月

Conversion behavior of threading screw dislocations on C face with different surface morphology during 4H-SiC solution growth

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

Cryst. Growth Des. 頁： 6436–6439 2016年10月

Characterization of V-Shaped Defects Formed during the 4H-SiC Solution Growth by Transmission Electron Microscopy and X-ray Topography Analysis

Xiao Shiyu, Harada Shunta, Murayama Kenta, Ujihara Toni

CRYSTAL GROWTH & DESIGN 16 巻 ( 9 ) 頁： 5136 - 5140 2016年9月

Characterization of V-shaped defects formed during the 4H-SiC solution growth by transmission electron microscopy and X-ray topography analysis

"S. Xiao, S. Harada, K. Murayama, T. Ujihara"

Cryst. Growth Des. 16 巻 ( 9 ) 頁： 5136-5140 2016年7月

Enantioselective amplification on circularly polarized laser-induced chiral nucleation from a NaClO 3 solution containing Ag nanoparticles

"H. Niinomi, T. Sugiyama, M. Tagawa, K. Murayama, S. Harada, T. Ujihara"

CrystEngComm 18 巻 ( 39 ) 頁： 7441-7448 2016年7月

Characterization of V-shaped defects formed during the 4H-SiC solution growth by transmission electron microscopy and X-ray topography analysis

S. Xiao, S. Harada, K. Murayama, T. Ujihara

Cryst. Growth Des. 16 巻 ( 9 ) 頁： 5136-5140 2016年7月

Enantioselective amplification on circularly polarized laser-induced chiral nucleation from a NaClO 3 solution containing Ag nanoparticles

H. Niinomi, T. Sugiyama, M. Tagawa, K. Murayama, S. Harada, T. Ujihara

CrystEngComm 18 巻 ( 39 ) 頁： 7441-7448 2016年7月

Spatial Distribution of Carrier Concentration in 4H-SiC Crystal Grown by Solution Method 査読有り

Zhen Jiang Wang, Takahiko Kawaguchi, Kenta Murayama, Kenta Aoyagi, S. Harada, Miho Tagawa, Takenobu Sakai, Tomohisa Kato, Toru Ujihara

Materials Science Forum 858 巻頁： 57-60 2016年5月

High-Speed Solution Growth of Single Crystal AlN from Cr-Co-Al Solvent 査読有り

Shota Watanabe, Masashi Nagaya, Yukihisa Takeuchi, Kenta Aoyagi, S. Harada, Miho Tagawa, Toru Ujihara

Materials Science Forum 858 巻頁： 1210-1213 2016年5月

Effect of magnesium ion concentration on two-dimensional structure of DNA-functionalized nanoparticles on supported lipid bilayer 査読有り

Isogai Takumi, Akada Eri, Nakada Sakiko, Yoshida Naoya, Tero Ryugo, Harada Shunta, Ujihara Toru, Tagawa Miho

JAPANESE JOURNAL OF APPLIED PHYSICS 55 巻 ( 3 ) 頁： 03DF11 2016年3月

Polytype control by activity ratio of silicon to carbon during SiC solution growth using multicomponent solvents 査読有り

Horio Atsushi, Harada Shunta, Koike Daiki, Murayama Kenta, Aoyagi Kenta, Sakai Takenobu, Tagawa Miho, Ujihara Toru

JAPANESE JOURNAL OF APPLIED PHYSICS 55 巻 ( 1 ) 頁： 01AC01 2016年1月

Thin film growth of CaFe2As2 by molecular beam epitaxy 査読有り

Hatano T., Kawaguchi T., Fujimoto R., Nakamura I., Mori Y., Harada S., Ujihara T., Ikuta H.

SUPERCONDUCTOR SCIENCE & TECHNOLOGY 29 巻 ( 1 ) 頁： 015013 2016年1月

Polytype control by activity ratio of silicon to carbon during SiC solution growth using multicomponent solvents 査読有り

A. Horio, S. Harada, D. Koike, K. Murayama, K. Aoyagi, T. Sakai, M. Tagawa, T. Ujihara

Japanese Journal of Applied Physics 55 巻頁： 01AC01 2016年

Effect of magnesium ion concentration on two-dimensional structure of DNA-functionalized nanoparticles on supported lipid bilayer 査読有り

T.Isogai, E. Akada, S. Nakada, N. YOshida, R. Tero,S. Harada, T. Ujihara, M. Tagawa

Japanese Journal of Applied Physics 55 巻頁： 03DF11 2016年

Enantioselective amplification on circularly polarized laser-induced chiral nucleation from a NaClO3 solution containing Ag nanoparticles

"H. Niinomi, T. Sugiyama, M. Tagawa, M. Maruyama, S. Harada, T. Ujihara"

CrystEngComm 18 巻頁： 7441-7448 2016年

Analysis of the carbon transport near the growth interface with respect to the rotational speed of the seed crystal during top-seeded solution growth of SiC

"T. Umezaki, D. Koike, S. Harada, T. Ujihara"

Japanese Journal of Applied Physics 55 巻 ( 12 ) 頁： 125601 2016年

Two-step SiC solution growth for dislocation reduction

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

J. Cryst. Growth 2016年

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"

J. Cryst. Growth 2016年

Enantioselective amplification on circularly polarized laser-induced chiral nucleation from a NaClO3 solution containing Ag nanoparticles

Niinomi H., Sugiyama T., Tagawa M., Murayama K., Harada S., Ujihara T.

CRYSTENGCOMM 18 巻 ( 39 ) 頁： 7441 - 7448 2016年

半導体伝導帯構造を明らかにする可視光電子光電子分光法の提案

宇治原徹, 市橋史朗, 董キン宇, 井上明人, 川口昂彦, 桑原真人, 伊藤孝寛, 原田俊太, 田川美穂

表面科学学術講演会要旨集 36 巻 ( 0 ) 頁： 338 - 338 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本表面科学会

我々は負の電子親和力（NEA）状態を半導体表面に形成することで、伝導帯を伝導する電子を直接真空に取り出し分光する手法を開発した。本手法では、通常の光電子分光では評価が困難な伝導帯のバンド分散を明らかにすることができる。本講演では、この手法より高効率太陽電池の構造として期待されるナノ超格子構造によるミニバンドの評価を行った。また、これはまさに可視光照射時の半導体内の電子のオペランド評価と言える。

DOI： 10.14886/sssj2008.36.0_338

Measurement of energy distribution of conduction electrons in superlattice by visible-light photoemission spectroscopy

Spatial distribution of carrier concentration in 4H-SiC crystal grown by solution method 査読有り

Wang Z.J.

Materials Science Forum 858 巻頁： 57 - 60 2016年

High-speed solution growth of single crystal AlN from Cr-Co-Al solvent 査読有り

Watanabe S.

Materials Science Forum 858 巻頁： 1210 - 1213 2016年

Ichihashi F.

2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015 2015年12月

Non-uniform electrodeposition of zinc on the (0001) plane

Mitsuhashi Takato, Ito Yasumasa, Takeuchi Yukihisa, Harada Shunta, Ujihara Toru

THIN SOLID FILMS 590 巻頁： 207 - 213 2015年9月

Effect of aluminum addition on the surface step morphology of 4H-SiC grown from Si-Cr-C solution

Mitani Takeshi, Komatsu Naoyoshi, Takahashi Tetsuo, Kato Tomohisa, Harada Shunta, Ujihara Toru, Matsumoto Yuji, Kurashige Kazuhisa, Okumura Hajime

JOURNAL OF CRYSTAL GROWTH 423 巻頁： 45 - 49 2015年8月

"Effect of aluminum addition on the surface step morphology of 4H-SiC grown from Si-Cr-C solution" 査読有り

Takeshi Mitani, Naoyoshi Komatsu, Tetsuo Takahashi, Tomohisa Kato, Shunta Harada, Toru Ujihara, Yuji Matsumoto, Kazuhisa Kurashige, Hajime Okumura

Journal of Crystal Growth 423 巻頁： 45–49 2015年8月

Non-uniform electrodeposition of zinc on the (0001) plane 査読有り

T. Mitsuhashi, Y. Ito, Y. Takeuchi, S. Harada,T. Ujihara

Thin Solid Films 590 巻頁： 207-213 2015年6月

Non-uniform electrodeposition of zinc on the (0001) plane 査読有り

T. Mitsuhashi, Y. Ito, Y. Takeuchi, S. Harada, T. Ujihara

Thin Solid Films 590 巻頁： 207-213 2015年6月

Dislocation conversion during sic solution growth for high-quality crystals 査読有り

Harada S.

Materials Science Forum 821-823 巻頁： 3 - 8 2015年

Control of interface shape by non-axisymmetric solution convection in top-seeded solution growth of SiC crystal 査読有り

Koike D.

Materials Science Forum 821-823 巻頁： 18 - 21 2015年

Improvement of surface morphology by solution flow control in solution growth of SiC on off-axis seeds 査読有り

Umezaki T.

Materials Science Forum 821-823 巻頁： 31 - 34 2015年

Research on solvent composition for different surface morphology on C face during 4H-SiC solution growth 査読有り

Xiao S.Y.

Materials Science Forum 821-823 巻頁： 39 - 42 2015年

3C-SiC crystal on sapphire by solution growth method 査読有り

Shibata K.

Materials Science Forum 821-823 巻頁： 185 - 188 2015年

Thin film growth of CaFe2As2 by molecular beam epitaxy 査読有り

T. Hatano, T. Kawaguchi, R. Fujimoto, I. Nakamura, Y. Mori, S. Harada, T. Ujihara and H. Ikuta

Superconductor Science and Technology 29 巻頁： 015013 2015年

Measurement of Energy Distribution of Conduction Electrons in Superlattice by Visible-Light Photoemission Spectroscopy

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

2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC) 2015年

Measurement of Energy Distribution of Conduction Electrons in Superlattice by Visible-Light Photoemission Spectroscopy 査読有り

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

2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC) 2015年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：IEEE

Visible-light photoemission spectroscopy (VPS) is a novel angle-resolved photoemission spectroscopy developed by us for measuring conduction electrons emitted from a surface with negative electron affinity state. In this study, InGaAs/GaAsP quantum well superlattice was analyzed by the VPS method with changing the excitation photon energy. By comparing with comparison of the energy distribution curves obtained by different excitation energy, the first and second conduction mini-band structures were directly clarified.

Different behavior of threading edge dislocation conversion during the solution growth of 4H-SiC depending on the Burgers vector

Dislocation Conversion during SiC Solution Growth for High-quality Crystals 査読有り

原田俊太

Materials Forum N/A 巻 2015年

Harada Shunta, Yamamoto Yuji, Seki Kazuaki, Horio Atsushi, Tagawa Miho, Ujihara Toru

ACTA MATERIALIA 81 巻頁： 284 - 290 2014年12月

Electrostatic acceleration of helicon plasma using a cusped magnetic field

Harada S., Baba T., Uchigashima A., Yokota S., Iwakawa A., Sasoh A., Yamazaki T., Shimizu H.

APPLIED PHYSICS LETTERS 105 巻 ( 19 ) 2014年11月

Forming two-dimensional structure of DNA-functionalized Au nanoparticles via lipid diffusion in supported lipid bilayers

Isogai Takumi, Piednoir Agnes, Akada Eri, Akahoshi Yuki, Tero Ryugo, Harada Shunta, Ujihara Toru, Tagawa Miho

JOURNAL OF CRYSTAL GROWTH 401 巻頁： 494 - 498 2014年9月

The investigation of step structure with different TSDs conversion behavior during 4H-SiC solution growth

Xiao Shiyu, Hara Natsumi, Harada Shunta, Ujihara Toru

JSAP Annual Meetings Extended Abstracts 2014.2 巻 ( 0 ) 頁： 3317 - 3317 2014年9月

Defect evolution in high-quality 4H-SiC grown by solution method

Harada, S; Tagawa, M; Ujihara, T

ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 70 巻頁： C1415 - C1415 2014年8月

Defect evolution in high-quality 4H-SiC grown by solution method

Harada S, Tagawa M, Ujihara T

ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES 70 巻頁： C1415 - C1415 2014年8月

Emergence and Amplification of Chirality via Achiral-Chiral Polymorphic Transformation in Sodium Chlorate Solution Growth

Niinomi Hiromasa, Miura Hitoshi, Kimura Yuki, Uwaha Makio, Katsuno Hiroyasu, Harada Shunta, Ujihara Toru, Tsukamoto Katsuo

CRYSTAL GROWTH & DESIGN 14 巻 ( 7 ) 頁： 3596 - 3602 2014年7月

Low-dislocation-density 4H-SiC crystal growth utilizing dislocation conversion during solution method 査読有り

Yamamoto Yuji, Harada Shunta, Seki Kazuaki, Horio Atsushi, Mitsuhashi Takato, Koike Daiki, Tagawa Miho, Ujihara Toru

APPLIED PHYSICS EXPRESS 7 巻 ( 6 ) 頁： 065501 2014年6月

Solubility measurement of a metastable achiral crystal of sodium chlorate in solution growth

Niinomi Hiromasa, Horio Atsushi, Harada Shunta, Ujihara Toru, Miura Hitoshi, Kimura Yuki, Tsukamoto Katsuo

JOURNAL OF CRYSTAL GROWTH 394 巻頁： 106 - 111 2014年5月

Nitrogen doping of 4H-SiC by the top-seeded solution growth technique using Si-Ti solvent

Kusunoki Kazuhiko, Kamei Kazuhito, Seki Kazuaki, Harada Shunta, Ujihara Toru

JOURNAL OF CRYSTAL GROWTH 392 巻頁： 60 - 65 2014年4月

Increase in the Growth Rate by Rotating the Seed Crystal at High Speed during the Solution Growth of SiC 査読有り

T. Umezaki, D. Koike, A. Horio, S. Harada, and T. Ujihara

Materials Science Forum 778-780 巻頁： 63-66 2014年1月

Surface Morphology and Threading Dislocation Conversion Behavior during Solution Growth of 4H-SiC Using Al-Si Solvent 査読有り

S. Harada, Y. Yamamoto, S. Xiao, M. Tagawa, and T. Ujihara

Materials Science Forum 778-780 巻頁： 67-70 2014年1月

"Direct measurement of conduction miniband structure in superlattice by visible-light photoemission spectroscopy"

F. Ichihashi, D. Shimura, K. Nishitani, T. Kawaguchi, M. Kuwahara, T. Ito, S. Harada, H. Katsuno, M. Tagawa, T.Ujihara

Photovoltaic Specialist Conference (PVSC), 2014 IEEE 40th , 8-13 June 2014 頁： 2882-2885 2014年

Different behavior of threading edge dislocation conversion during the solution growth of 4H-SiC depending on the Burgers vector 査読有り

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

Acta Materialia 81 巻頁： pp. 284-290 2014年

Direct Measurement of Conduction Miniband Structure in Superlattice by Visible-Light Photoemission Spectroscopy

Ichihashi Fumiaki, Shimura Daiki, Nishitani Kenji, Kawaguchi Takahiko, Kuwahara Makoto, Ito Takahiro, Harada Shunta, Katsuno Hiroyasu, Tagawa Miho, Ujihara Tofu

2014 IEEE 40TH PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC) 頁： 2882 - 2885 2014年

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)(<特集>準安定相の形成と結晶成長)

関和明, 原田俊太, 宇治原徹

日本結晶成長学会誌 40 巻 ( 4 ) 頁： 253 - 260 2014年

掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶成長学会

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

Direct measurement of conduction miniband structure in superlattice by visible-light photoemission spectroscopy

Ichihashi F.

2014 IEEE 40th Photovoltaic Specialist Conference, PVSC 2014 頁： 2882 - 2885 2014年

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

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

CRYSTAL GROWTH & DESIGN 13 巻 ( 12 ) 頁： 5188 - 5192 2013年12月

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, 40 巻 ( 4 ) 頁： 253 2013年12月

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, 40 巻 ( 4 ) 頁： 253 2013年12月

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

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

JAPANESE JOURNAL OF APPLIED PHYSICS 52 巻 ( 8 ) 頁： 08JE17 2013年8月

Evolution of threading screw dislocation conversion during solution growth of 4H-SiC 査読有り

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

APL MATERIALS 1 巻 ( 2 ) 頁： 022109 2013年8月

Influence of Solution Flow on Step Bunching in Solution Growth of SiC Crystals

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

CRYSTAL GROWTH & DESIGN 13 巻 ( 8 ) 頁： 3691 - 3696 2013年8月

超高品質SiC溶液成長

宇治原徹, 原田俊太, 山本祐治, 関和明

應用物理 82 巻 ( 4 ) 頁： 326 - 329 2013年4月

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人応用物理学会

パワーデバイス用材料として現在盛んに研究開発が行われているSiCにおいては，基板結晶の高品質化が極めて重要である．溶液成長法はそれを実現する手法として注目を集めつつある．我々はSiC溶液成長過程において，結晶に含まれる貫通転位が基底面内の転位やフランク型欠陥へ頻繁に変換することを見いだし，さらにこの現象を利用して多くの貫通転位を結晶外部に放出させることで，高品質結晶が実現されることを示してきた．最近では，ほかのグループから結晶成長速度の向上や結晶口径の拡大に関する報告もなされている．本格的な高品質バルク結晶成長技術として確立されるまで，あと少しのところにきている．

DOI： 10.11470/oubutsu.82.4_326

超高品質SiC溶液成長招待有り査読有り

宇治原徹、原田俊太、山本祐治、関和明

応用物理 82 巻頁： 326-329 2013年4月

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, 40 巻頁： 25 2013年4月

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, 40 巻頁： 25 2013年4月

超高品質SiC溶液成長招待有り査読有り

宇治原徹, 原田俊太, 山本祐治, 関和明

応用物理 82 巻頁： 326-329 2013年4月

Effect of Surface Polarity on the Conversion of Threading Dislocations in Solution Growth 査読有り

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

Materials Science Forum 740-742 巻頁： 15-18 2013年1月

Reduction of Threading Screw Dislocation Utilizing Defect Conversion during Solution Growth of 4H-SiC 査読有り

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

Materials Science Forum 740-742 巻頁： 189-192 2013年1月

Bulk 3C-SiC Crystal by Top Seeded Solution Growth Method 査読有り

K. Seki, S. Harada, T. Ujihara

Materials Science Forum 740-742 巻頁： 311-314 2013年1月

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) 頁： 288 - 291 2013年

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

Shimura D.

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

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

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) 頁： 306 - 310 2013年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：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.

SiC溶液成長の最近の展開(<特集>SiCの現状と今後の展開)

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

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

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

原田俊太, 山本祐治, 関和明, 宇治原徹

日本結晶成長学会誌 40 巻 ( 1 ) 頁： 25 - 32 2013年

掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶成長学会

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

Electron spectroscopy of conduction electrons excited by visible light utilizing NEA surface 査読有り

Ichihashi F.

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

2SBA-03 DNAセルフアセンブリによるナノ粒子超構造制御(2SBA 反応場デザインによる生命現象の再構成-創って知る生物物理-,シンポジウム,日本生物物理学会第51回年会(2013年度))

田川美穂, 磯貝卓巳, 赤田英里, 原田俊太, 宇治原徹, ヤンガーケビン, ガングオレグ

生物物理 53 巻 ( 1 ) 頁： S92 2013年

Polytype-selective growth of SiC by supersaturation control in solution growth

Seki Kazuaki, Alexander, Kozawa Shigeta, Harada Shunta, Ujihara Toru, Takeda Yoshikazu

JOURNAL OF CRYSTAL GROWTH 360 巻 ( 1 ) 頁： 176 - 180 2012年12月

High-Efficiency Conversion of Threading Screw Dislocations in 4H-SiC by Solution Growth

Yamamoto Yuji, Harada Shunta, Seki Kazuaki

Applied physics express 5 巻 ( 11 ) 頁： "115501 - 1"-"115501-3" 2012年11月

High-Efficiency Conversion of Threading Screw Dislocations in 4H-SiC by Solution Growth 査読有り

Yamamoto Yuji, Harada Shunta, Seki Kazuaki, Horio Atsushi, Mitsuhashi Takato, Ujihara Toru

APPLIED PHYSICS EXPRESS 5 巻 ( 11 ) 頁： 115501 2012年11月

Polytype Transformation by Replication of Stacking Faults Formed by Two-Dimensional Nucleation on Spiral Steps during SiC Solution Growth 査読有り

Harada Shunta, Alexander, Seki Kazuaki, Yamamoto Yuji, Zhu Can, Yamamoto Yuta, Arai Shigeo, Yamasaki Jun, Tanaka Nobuo, Ujihara Toru

CRYSTAL GROWTH & DESIGN 12 巻 ( 6 ) 頁： 3209 - 3214 2012年6月

Stable Growth of 4H-SiC Single Polytype by Controlling the Surface Morphology Using a Temperature Gradient in Solution Growth 査読有り

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

Materials Science Forum 717-720 巻頁： 53-56 2012年5月

Anisotropy of Lattice Thermal Conduction in TiO2-x with High Density of Planar Defects by Atomistic Simulations

Y. Miyauchi, M. Tada, M. Yoshiya, S. Harada, K. Tanaka, H. Yasuda, H. Inui

AMTC Letters 3 巻頁： 242-243 2012年5月

Conversion Mechanism of Threading Screw Dislocation during SiC Solution Growth

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

Materials Science Forum 717-720 巻頁： 351-354 2012年5月

Anisotropy of Lattice Thermal Conduction in TiO2-x with High Density of Planar Defects by Atomistic Simulations

Y. Miyauchi, M. Tada, M. Yoshiya, S. Harada, K. Tanaka, H. Yasuda, H. Inui

AMTC Letters 3 巻頁： 242-243 2012年5月

CT-2-2 高品質SiC溶液成長(CT-2.ワイドギャップ半導体パワーデバイスの現状と展望,チュートリアルセッション,ソサイエティ企画)

宇治原徹, 原田俊太, 関和明, 山本祐治

電子情報通信学会総合大会講演論文集 2012 巻 ( 2 ) 頁： "SS - 19"-"SS-21" 2012年3月

CT-2-2 高品質SiC溶液成長(CT-2.ワイドギャップ半導体パワーデバイスの現状と展望,チュートリアルセッション,ソサイエティ企画)

宇治原徹, 原田俊太, 関和明, 山本祐治

電子情報通信学会総合大会講演論文集 2012 巻 ( 2 ) 頁： "SS - 19"-"SS-21" 2012年3月

Direct Observation of Vacancies and Local Thermal Vibration in Thermoelectric Rhenium Silicide 査読有り

Harada, S; Tanaka, K; Kishida, K; Okamoto, NL; Endo, N; Okunishi, E; Inui, H

APPLIED PHYSICS EXPRESS 5 巻 ( 3 ) 頁： 035203 2012年3月

Conversion Mechanism of Threading Screw Dislocation during SiC Solution Growth

Ujihara Toru, Kozawa Shigeta, Seki Kazuaki, Alexander, Yamamoto Yuji, Harada Shunta

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 717-720 巻頁： 351 - + 2012年

Stable Growth of 4H-SiC Single Polytype by Controlling the Surface Morphology Using a Temperature Gradient in Solution Growth 査読有り

Yamamoto Yuji, Seki Kazuaki, Kozawa Shigeta, Alexander, Harada Shunta, Ujihara Toru

SILICON CARBIDE AND RELATED MATERIALS 2011, PTS 1 AND 2 717-720 巻頁： 53 - 56 2012年

Acoustic Design Shape and Topology Sensitivity Formulations Based on Adjoint Method and BEM

Matsumoto, T; Yamada, T; Takahashi, T; Zheng, CJ; Harada, S

CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES 78 巻 ( 2 ) 頁： 77 - 94 2011年8月

Crystal structure refinement of ReSi1.75 with an ordered arrangement of silicon vacancies 査読有り

Shunta Harada, Hiroaki Hoshikawa, Kosuke Kuwabara, Katsushi Tanaka, Eiji Okunishi, Haruyuki Inui

PHILOSOPHICAL MAGAZINE 91 巻 ( 23 ) 頁： 3108 - 3127 2011年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

The crystal structure and microstructure of ReSi1.75 were investigated by synchrotron X-ray diffraction combined with scanning transmission electron microscopy. ReSi1.75 contains an ordered arrangement of vacancies in Si sites in the underlying tetragonal C11(b) lattice of the MoSi2-type and the crystal structure is monoclinic with the space group Cm. Atomic positions of Si atoms near vacancies are considerably displaced from the corresponding positions in the parent C11(b) structure, and they exhibit anomalously large local thermal vibration accompanied by large values of atomic displacement parameter. There are four differently-oriented domains with two of them being related to each other by the 90 degrees rotation about the c-axis of the underlying C11(b) lattice and the other two being their respective twins. The habit planes for domain boundaries observed experimentally are consistent with those predicted with ferroelastic theory.

DOI： 10.1080/14786435.2011.570278

Direct observation of an ordered arrangement of vacancies and large local thermal vibration in rhenium silicide by Cs-corrected STEM 査読有り

Shunta Harada', Katsushi Tanaka, Kyosuke Kishida, Norihiko L. Okamoto', Noriaki Endo, Eiji Okunishi, Haruyuki Inui

Materials Research Society Symposium Proceedings 1295 巻頁： 397 - 402 2011年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

The crystal structure of thermoelectric rhenium silicide with an ordered arrangement of vacancies is investigated by utilizing spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM) combined with synchrotron X-ray diffraction and conventional transmission electron microscopy. By STEM Cs corrected imaging, we can clearly observe Si vacancies in rhenium silicide, which is impossible without Cs correction. In addition, significantly reduced contrast levels are noted in STEM images for particular Si sites near vacancies. From the STEM image simulation, the reduced contrast levels are concluded to be due to anomalously large local thermal vibration of these Si atoms. The crystal structure of rhenium silicide can be successfully refined by the synchrotron X-ray diffraction starting with the deduced structure model from the STEM images and the occurrence of large local thermal vibration can be qualitatively confirmed. Furthermore, we confirm the validity of the refined crystal structure of rhenium silicide by comparing experimental images with simulated image generating with the refined crystal structure parameters. © 2011 Materials Research Society.

DOI： 10.1557/opl.2011.43

Al融液窒化法における高密度AlN形成メカニズム

水野恒平, 松原弘明, 竹内幸久, 原田俊太, 宇治原徹, 青木祐一, 小原公和

日本セラミックス協会年会・秋季シンポジウム講演予稿集 2011 巻 ( 0 ) 頁： 761 - 761 2011年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

AlNは高熱伝導絶縁体で、パワーデバイス用放熱基板として期待されている。我々は、焼結法に代わる手法として、Al融液と窒素からAlNを成長する融液窒化法に着目し、これまでに、Mg蒸気と窒素ガスを同時に外部から供給する手法で、完全にAl融液をAlNへと変換させることに成功している。しかし、得られたAlNには高密度な部分とポーラス部分が混在していた。そこで、高密度AlNの形成メカニズムを解明するために、原料をAl板に変更し、Mg蒸気の供給時間を制御して実験を行った。窒化は原料表面のみで生じており、Mg蒸気が融液表面の酸化膜と反応して、酸化膜が破れ、そこからAl融液が酸化膜上にしみ出し、しみ出した融液と窒素が反応し、AlNを生成するというメカニズムが示唆された。

DOI： 10.14853/pcersj.2011F.0.761.0

シア構造内包magneli相TiO2-xの原子レベル熱伝導機構解析

吉矢真人, 宮内洋平, 多田昌浩, 原田俊太, 田中克志, 安田秀幸, 乾晴行

日本セラミックス協会年会・秋季シンポジウム講演予稿集 2011 巻 ( 0 ) 頁： 759 - 759 2011年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

熱電材料としても注目される、ナノメートルオーダーの面間隔のシア構造を内包するTiO2-xの熱伝導機構の解析を摂動分子動力学法により行った。得られた熱伝導度は大きな方位依存性を示し、シア面垂直方向についてはシア面間隔の減少と共に熱伝導度減少が見られたが、面間隔が数Åの範囲では、シア面平行方向の熱伝導度の面間隔依存性は非常に小さなものでありほぼ一定であった。また直感に反して、シア面に垂直方向の熱伝導度がシア面平行方向の熱伝導度よりも低いことがわかった。これはシア面に沿った原子の配位環境の乱れに起因するものであると考えられる。

DOI： 10.14853/pcersj.2011F.0.759.0

Thermoelectric properties and crystallographic shear structures in titanium oxides of the Magneli phases 査読有り

Shunta Harada, Katsushi Tanaka, Haruyuki Inui

JOURNAL OF APPLIED PHYSICS 108 巻 ( 8 ) 2010年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

The thermoelectric properties of Magneli phase titanium oxides TinO2n-1 (n=2,3,...) have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO2-x (x=0.05, 0.10, 0.15, and 0.20) prepared by conventional hot-pressing are all identified to be one of the Magneli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficiency. Electrical conduction is n-type for all specimens and the carrier concentration increases with the increase in the oxygen deficiency. The values of lattice thermal conductivity, on the other hand, decrease with the increase in the oxygen deficiency, which can be attributed to phonon scattering at the crystallographic shear plane. The largest value of thermoelectric figure of merit Z, 1.6 X 10(-4) K-1 was obtained at 773 K for the hot-pressed specimen of TiO1.90. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3498801]

DOI： 10.1063/1.3498801