Faculty Profiles - HARADA Shunta

Papers - HARADA Shunta

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Suppression of stacking-fault expansion in 4H-SiC PiN diodes using proton implantation to solve bipolar degradation Reviewed

Masashi Kato, Ohga Watanabe, Toshiki Mii, Hitoshi Sakane, Shunta Harada

Scientific Reports Vol. 12 ( 1 ) page： 18790 2022.11

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

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 Reviewed

Masaru Isono, Shunta Harada, Kentaro Kutsukake, Tomoo Yokoyama, Miho Tagawa, Toru Ujihara

Advanced Theory and Simulations Vol. 5 ( 9 ) page： 2200302 2022.9

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal)

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 Reviewed

Yifan Dang, Kentaro Kutsukake, Xin Liu, Yoshiki Inoue, Xinbo Liu, Shota Seki, Can Zhu, Shunta Harada, Miho Tagawa, Toru Ujihara

Advanced Theory and Simulations Vol. 5 ( 9 ) page： 2200204 2022.9

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

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 Reviewed

Shunta Harada, Toshiki Mii, Hitoshi Sakane, Masashi Kato

Scientific Reports Vol. 12 ( 1 ) page： 13542 2022.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

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 wafers by birefringence imaging Reviewed

Shunta Harada, Kenta Murayama

Journal of Applied Crystallography Vol. 55 page： 1029 - 1032 2022.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

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 Reviewed

Hayato Sumi, Noboru Ohta, Hiroshi Sekiguchi, Shunta Harada, Toru Ujihara, Katsuo Tsukamoto, Miho Tagawa

Crystal Growth & Design Vol. 22 ( 6 ) page： 3708 - 3718 2022.6

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

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 Invited

原田俊太

OplusE Vol. 44 ( 3 ) page： 217 - 217 2022.5

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 Invited Reviewed

炭谷翔悟、西田陽良、原田俊太

システム／制御／情報 Vol. 66 ( 5 ) page： 161 - 167 2022.5

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 Vol. 16 ( 2 ) page： 167 - 172 2022.3

Crossover from incoherent to coherent thermal conduction in bulk titanium oxide natural superlattices Reviewed

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

Scripta Materialia Vol. 208 2022.2

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

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 Reviewed

Yifan Dang, Can Zhu, Xin Liu, Wancheng Yu, Xinbo Liu, Koki Suzuki, Tomoaki Furusho, Shunta Harada, Miho Tagawa, Toru Ujihara

Journal of Crystal Growth Vol. 579 page： 126448 2022.2

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

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 Reviewed

Kota Tsujimori, Jun Hirotani, Shunta Harada

JOURNAL OF ELECTRONIC MATERIALS Vol. 51 ( 2 ) page： 712 - 717 2022.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

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 Reviewed

Xinbo Liu, Yifan Dang, Koki Suzuki, Can Zhu, Wancheng Yu, Shunta Harada, Miho Tagawa, Toru Ujihara

JOURNAL OF CRYSTAL GROWTH Vol. 578 page： 126425 2022.1

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

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 Damko center dot hler 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 Reviewed

Shunta Harada, Kota Tsujimori, Yosuke Matsushita

JOURNAL OF ELECTRONIC MATERIALS Vol. 51 ( 1 ) page： 243 - 248 2022.1

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

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

High fracture toughness AlN achieved by addition of AlN whiskers and tape-casting Reviewed

Hiroki Shimizu, Naoki Kondo, Akihiro Shimamura, Mikinori Hotta, Shunta Harada, Toru Ujihara, Yoshihiro Ohnishi

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 130 ( 1 ) page： 195 - 198 2022.1

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

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 6.7 MPa m1/2, while maintaining thermal conductivity but degrading strength. (c) 2022 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.21143

Polarized light observation of semiconductor wafers for power devices

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

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

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

Process informatics using simulation data for crystal growth

Kutsukake Kentaro, Tsunooka Yosuke, Wancheng Yu, Dang Yifan, Harada Shunta, Ujihara Toru

Journal of the Japanese Association for Crystal Growth Vol. 49 ( 1 ) page： n/a 2022

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

<p> In this paper, machine learning and optimization based on simulation data of crystal growth are discussed from the viewpoint of informatics application, introducing our application to solution growth of SiC crystal. First, general aspects of crystal growth process simulation and its informatics applications are described. Next, after an overview of the solution growth of SiC crystal, the process optimization of solution growth of SiC crystal using machine learning is described, including the prediction model of temperature and flow of the solution in the crucible, the optimization of geometry conditions, and the optimization of process conditions corresponding to time evolution. Next, application to other materials is described. Finally, this paper is summarized with future prospects.</p>

DOI： 10.19009/jjacg.49-1-06

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

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

JOURNAL OF ATHEROSCLEROSIS AND THROMBOSIS Vol. 29 ( 11 ) page： 1603 - 1612 2022

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

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

MATERIALIA Vol. 20 page： 101246 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The expansion of double Shockley stacking faults (DSFs) in an n-type 4H-SiC substrate with a nitrogen concentration of 3.9 x 10(19) 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 Reviewed

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

Materials Science and Engineering B: Solid-State Materials for Advanced Technology Vol. 271 page： 115281 2021.9

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

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

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