Updated on 2021/11/30

写真a

 
CHOKAWA Kenta
 
Organization
Institute of Materials and Systems for Sustainability Center for Integrated Research of Future Electronics Multiphysics Simulation Section Designated assistant professor
Title
Designated assistant professor

Degree 1

  1. 博士 (工学) ( 2019.3   名古屋大学 ) 

 

Papers 4

  1. First-principles and thermodynamic analysis for gas phase reactions and structures of the SiC(0001) surface under conventional CVD and Halide CVD environments

    Chokawa Kenta, Daigo Yoshiaki, Mizushima Ichiro, Yoda Takashi, Shiraishi Kenji

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 60 ( 8 )   2021.8

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    Language:Japanese   Publisher:Japanese Journal of Applied Physics  

    The halide chemical vapor deposition (HCVD) technique has been improved to realize the defect-free 4H-SiC epitaxial layers. Although it is possible to obtain the 4H-SiC epitaxial layers by both HCVD and conventional CVD techniques, it has not been clarified what effects halide gases have on the growth mechanisms, especially for the surface reactions. We have performed the first-principles calculations and thermodynamics analysis to reveal the gas phase reactions and surface structures under the conventional CVD and HCVD environments. The silicon clusters and Si2C gases are the main products under the conventional CVD environments, while it changes to the SiCl2 gas under the HCVD environments. Moreover, we have clarified that the adsorption of Si gases onto the surface is suppressed under the HCVD environments. These results indicate that the introduction of halide gas can suppress the clustering of silicon both in the gas phase and on the surface.

    DOI: 10.35848/1347-4065/ac1127

    Web of Science

    Scopus

  2. Defect-free interface between amorphous (Al2O3)(1-x)(SiO2)(x) and GaN(0001) revealed by first-principles simulated annealing technique

    Chokawa Kenta, Shiraishi Kenji, Oshiyama Atsushi

    APPLIED PHYSICS LETTERS   Vol. 119 ( 1 )   2021.7

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    Language:Japanese   Publisher:Applied Physics Letters  

    We report first-principles molecular dynamics (MD) simulations that unveil the interface structures of amorphous mixed oxide (Al2O3)1−x(SiO2)x and GaN polar surfaces. The MD allows us to perform the melt and quench (simulated annealing) simulations to forge distinct amorphous samples. We find that the dangling bonds are completely absent at all the obtained interfaces. This annihilation is due to the diffusion of appropriate species, O for (Al2O3)1−x(SiO2)x/GaN(0001) and Al and Si for (Al2O3)1−x(SiO2)x/GaN(0001¯), from the amorphous to the interface and the subsequent formation of strong bonds with both ionicity and covalency at the interface. This absence of the dangling bond indicates the superiority of (Al2O3)1−x(SiO2)x films to Al2O3 or SiO2 as a gate oxide for the GaN-metal-oxide-semiconductor field effect transistor.

    DOI: 10.1063/5.0047088

    Web of Science

    Scopus

  3. Theoretical study on the effect of H-2 and NH3 on trimethylgallium decomposition process in GaN MOVPE

    Sakakibara Soma, Chokawa Kenta, Araidai Masaaki, Kusaba Akira, Kangawa Yoshihiro, Shiraishi Kenji

    JAPANESE JOURNAL OF APPLIED PHYSICS   Vol. 60 ( 4 )   2021.4

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    Language:Japanese   Publisher:Japanese Journal of Applied Physics  

    We investigate the decomposition process of trimethylgallium (TMGa) during GaN metal organic vapor phase epitaxy in detail by using ab inito calculations. We analyze the decomposition rate of TMGa by estimating Gibbs energy of activation including H2 as well as NH3 effects. Our obtained main reaction pathway of TMGa decomposition is as follows: Ga(CH3)3 + 3H2 + NH3 → Ga(CH3)2NH2 + 3H2 + CH4 → Ga(CH3)2H + 2H2 + NH3 +CH4 → GaCH3HNH2 + 2H2 + 2CH4 → GaCH3H2 + H2 + NH3 + 2CH4 → GaH2NH2 + H2 + 3CH4 → GaH3 + NH3 + 3CH4. Our proposed TMGa decomposition pathway can represent the actual epitaxial growth phenomenon by considering neither polymerization reactions nor radical reactions, which are now widely adopted in fluid simulations of crystal growth. Moreover, our proposed pathway is in good agreement with the experiments.

    DOI: 10.35848/1347-4065/abf089

    Web of Science

    Scopus

  4. Investigation of Negative Charge Storage Mechanism in the Potassium Ion Electret by First-Principle Calculations

    Nakanishi Toru, Miyajima Takeshi, Chokawa Kenta, Araidai Masaaki, Sugiyama Tatsuhiko, Hashiguchi Gen, Shiraishi Kenji

    IEEJ Transactions on Sensors and Micromachines   Vol. 141 ( 8 ) page: 292 - 298   2021

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    Language:Japanese   Publisher:The Institute of Electrical Engineers of Japan  

    <p>A potassium-ion electret, which is a key element of vibration-powered microelectromechanical generators, is a material that permanently stores negative charge. However, the charge storing mechanism of a potassium-ion electret is still unclear. In this study, we theoretically study the atomic and electronic structures of amorphous SiO<sub>2</sub> with and without potassium atoms using first-principles molecular-dynamics calculations. As a result of calculations, we confirmed the existence of a fivefold-coordinated Si atom with five Si-O bonds as a characteristic local structure in a-SiO<sub>2</sub> with potassium atoms, which is negatively charged. This result indicates that the fivefold-coordinated Si structure is the physical origin of the negative charge observed in potassium-ion electret. Furthermore, we show the guidelines for the experimental observation of the fivefold-coordinated structure and the fabrication of high-reliability potassium-ion electret.</p>

    DOI: 10.1541/ieejsmas.141.292

    Scopus

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