研究者詳細 - 原田　俊太

論文 - 原田　俊太

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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

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

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

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

「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

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

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

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