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A01 group

A01-1 Creation of Singularity Structures by Time-Domain Control under Nonequilibrium Conditions

  • Principal Investigator / Hiroshi Fujioka (The University of Tokyo / Professor)
  • Co-Investigator / Yuki Tokumoto (The University of Tokyo / Lecturer)

Accuracy of film composition control remains rather low at around one atomic layer (~1 second) The current accuracy of film composition control remains rather low at around one atomic layer (~1 s). This is because the supply of raw materials is conventionally controlled using mechanical apparatus such as a rotary motion shutter. We have developed a new crystal growth technique named “pulsed excitation deposition.” This uses electric pulses to control the supply sequence of the excited elements to the thin-film surface and has a precision of one 10 millionth of an atomic layer (~100 ns). Our novel method can be used to fabricate a range of singularity structures in single crystals under computer control. Based on the results of a microstructural analysis, we will attempt to improve the fabrication of singularity structures.

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A01-2 Creation of singularity structure by top-down method based on equilibrium condition

  • Principal Investigator / Hideto Miyake (Mie University / Professor)
  • Co-Investigator / Tsutomu Araki (Ritsumeikan University / Professor)
  • Co-Investigator / Reina Miyagawa (Nagoya Institute of Technology / Assistant Professor)

The technological development of the control of the generation of stress or threading dislocations will be carried out by a top-down method using singular structures under an equilibrium condition.
(Mie University) The effects of singularity structures, such as substrate texture, thermal annealing, and selective-area growth for the epitaxial growth of nitride semiconductors (GaN, AlN, AlGaN) will be estimated for samples fabricated by MOVPE and HVPE. Specific technologies, such as void (three-dimensional singularity structure) formation, quantum wire (one-dimensional singularity structure) fabrication and exotic atoms (zero-dimensional singularity) incorporation will be used.
(Ritsumeikan University) The control of the stress or threading dislocations by MBE with nitrogen radicals from RF plasma will be developed for forming a singularity structure at the substrate surface or in the epitaxial layer. For example, nanoscale substrate textures produced using RF plasma or a singularity interface, such as graphene, will be investigated.
(Nagoya Institute of Technology) The periodic singularity structures of the nanoscale will be formed using a femtosecond laser, and growth of the nitride semiconductors by MOVPE, HVPE, and MBE is investigated on the structures.

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A01-3 Creation of a multi-dimensional and scale singularity structure in crystals and understanding of its mechanism

  • Principal Investigator / Satoshi Kamiyama (Meijo University / Professor)
  • Co-Investigator / Tetsuya Takeuchi (Meijo University / Professor)
  • Co-Investigator / Motoaki Iwaya (Meijo University / Associate Professor)
  • Co-Investigator / Yoshio Honda (Nagoya University / Associate Professor)

In this project group, high-crystalline quality AlGaN using low-temperature deposited AlN interlayer and grooved substrate (substrate with singularity structure), high-crystalline GaInN using nano-size singularity structure, and Sb doped crystals (singularity atoms) have been realized. These intentional and control the multi-dimensional and scale singularity structure in crystals have realized the many novel devices such as world’s shortest wavelength semiconductor UV lasers, high efficiency, power UV-LEDs, and high sensitivity photosensors, and nitride-based solar cells. For further development and improvement of its novel devices, it is essential for creation of a new multi-dimensional and scale singularity structure in crystals and understanding of its mechanism.
In this project, we study the growth mechanism in the multi-dimensional and multi-scale singularity structure in crystals characterized by in situ X-ray and multi-wavelength laser beam. In addition, we invent a new singularity structure in crystal on the basis of this understanding. And, we develop the singularity structure in crystals as a new academic frontiers

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A01-4 Bottom up creation of singularities by utilization of equilibrium and non-equilibrium crystal growth from vapor phase

  • Principal Investigator / Yoshinao Kumagai (Tokyo University of Agriculture and Technology / Professor)
  • Co-Investigator / Hisashi Murakami (Tokyo University of Agriculture and Technology / Associate Professor)
  • Co-Investigator / Tomohiro Yamaguchi (Kogakuin University / Associate Professor)
  • Co-Investigator / Keita Konishi (Tokyo University of Agriculture and Technology / Assistant Professor)

Growth of stable and metastable phases of group-III wide bandgap semiconducting sesquioxides (Al2O3, Ga2O3, and In2O3) and their alloys is investigated by halide vapor phase epitaxy (HVPE). Clarification of growth conditions for the meta-stable phase is tackled by both experimentally and theoretically, which will be important knowledge of growing phase-matching alloys having wide bandgaps of 3-9 eV. In addition, two-dimensional (2D) mixed layers of stable and metastable phases are utilized to control stresses and dislocations at the hetero-interfaces by subsequent growth under the condition suitable for stable phases. Analyses of grown layers are carried out in collaboration with groups B01 and B02, and possibility of the layers in future devices is discussed with group A02.

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A01-5 Computational materials design for hetero-bond manipulation

  • Principal Investigator / Tomonori Ito (Mie University / Professor)
  • Co-Investigator / Kazumasa Hiramatsu (Mie University / Professor)
  • Co-Investigator / Toru Akiyama (Mie University / Associate Professor)
  • Co-Investigator / Takahiro Kawamura (Mie University / Assistant Professor)
  • Co-Investigator / Yoshihiro Kangawa (Kyushu University / Professor)

Computational materials design for manipulating hetero-bond as an element of singularity-structure (hereafter “the element”) is performed using various computational methods incorporating growth conditions. Utilizing surface (two-dimensional defect) and nanostructures with large surface area as a field of singularity-structure fabrication (hereafter “the field”), Ito and Akiyama (Mie University) investigate stacking and compositional modualtions, and structural transformation due to hetero-bonds appearing on “the field” as functions of growth conditions such as temperature and bean-equivalent pressure. Kangawa (Kyushu University) and Kawamura (Mie University) study incorporation process of hetero-bond into “the field” such as interface (two-dimensional defect) and dislocation (one-dimensional defect) to predict compositional fluctuation and segregation at and across the surface and the interface for processed substrate (three-dimensional defect). In the calculation procedure, ab initio-based approach combining pseudopoetntial and quantum statistical chemistry is mainly employed in addition to Monte Carlo and molecular dynamics methods. Moreover, collaborating with real-time strain analysis by Hiramatsu (Mie University), the interaction between “the element” and “the field” is clarified in terms of hetero-bond species to establish the guiding-principles for singularity structure fabrication.

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A01-17-1 Nonlinear Optical Device Application of Polarity-Controlled Singular Structures in Nitride Semiconductors

  • Principal Investigator / Ryuji Katayama (Osaka University / Professor)

Recently the development for the deep ultraviolet light generation method via wavelength conversion, aside from the band-edge emission, are desired for the high-efficiency light sources. Also compact quantum light sources with high scalability and stability are needed for the quantum information field. These nonlinear optical devices can be realized by utilizing the strong second-order optical nonlinearity in nitride semiconductors originated from the braking of the inversion symmetry and fabricating the polarity-inverted structures in which the local c-axis orientation is intentionally modulated. In this work, the aim ie the realization of the deep-ultraviolet light sources along with the quantum entangled photon pairs sources pumped by the blue lasers, by further understanding the nature and control mechanism of singular structure named "polarity inversion" in nitride semiconductors, to find the way to the practical use of such microstructures.

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A01-17-2 Growth and characterization of polytypes in ultra-thin films of III-N compound semiconductors

  • Principal Investigator / Masamitu Takahasi (National Institutes for Quantum and Radiological Science and Technology / Group Leader)

The polarized surfaces of ionic compound semiconductors including III-N group semiconductors are intrinsically unstable due to the divergence of electrostatic energy. At the surface or in a thin layer of these compounds, therefore, crystal structures unseen in bulk materials are possibly formed thanks to a large degree of freedom in atomic arrangement and composition. Such structural singularity is expected to lead to new electronic and optoelectronic devices. To this end, the experimental and theoretical characterization of the structures specific to the surface or ultra-thin films is vitally important. In this project, we focus on the initial growth of III-N compound semiconductors to explore polytypes with exotic properties and reveal their growth mechanisms using in situ synchrotron techniques.

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A01-17-3 Development of heteroepitaxial growth technology of high quality crystals by stress relaxation using self-generated voids

  • Principal Investigator / Momoko Deura (The University of Tokyo / Assistant Professor)

In conventional crystal growth technologies, it is common to use high quality substrates without any defects or surface roughness. However, in this study, we aim to realize a heteroepitaxial growth technology of high quality crystals by relaxation of internal stress of epitaxial films using "voids", which are one of the singularity structures, just below the substrate surface. This technology will be analyzed and demonstrated by the heteroepitaxial growth of group-III nitride semiconductors on Si substrates. First, we fabricate the SiC thin films on Si substrates utilizing the surface carbonization technology with equilibrium reactions and realize "SiC/Si substrates with self-generated voids and flat surface" actively using voids spontaneously generated just below the SiC thin films (i.e., the SiC/Si interface). Next, nitride semiconductor films with high crystal quality will be grown on the substrates. Finally, we will clarify the material-independent universal findings about the correlation between internal stress and crystal quality of the epitaxial films by quantitative analyses.

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A01-17-4 Active control of stacking fault in SiC bulk crystal

  • Principal Investigator / Shunta Harada (Nagoya University / Lecturer)

Although stacking faults in silicon carbide (SiC) crystals are known to be expanded by carrier recombination, the mechanism has not been clarified. Considering based on the theory of dislocation, in order for the stacking fault to expand at room temperature, it is necessary that (1) the stacking fault energy decreases and becomes negative, and (2) the Peierls potential of the partial dislocation bordering the stacking fault decreases. In this study, we investigated in-situ observation of stacking defect extension during ultraviolet irradiation and measured lifetime in stacking faults, to construct a physical model for bridging dislocation theory and semiconductor physics, and realized active control of the stacking faults.

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A01-17-5 Creation of anomalous crystal structures by asymmetry strain gradient and order-disorder artificial lattices on functional oxides

  • Principal Investigator / Hitoshi Tabata (The University of Tokyo / Professor)

We would like to demonstrate new-type multiferroic materials based on various functionality and crystallographic tolerability related with flexsoelectrisity of metal oxides. Iron based oxides are chosen as target materials. Breaking of space inversion symmetry is introduced by a strain gradient at the interface of hetero-epitaxial thin films and single crystal substrates due to a lattice mismatch. It is expected that canted spin and space inversion symmetry breaking will give us new phenomena. Eventually, we would like to realize enhancement of spin-phonon combined magnon and multiferroinc properties induced by Dzyloshinski-Moriya interaction.

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A01-17-6 Singular structure and photocatalytic activity of calcium titanate fine crystals

  • Principal Investigator / Hisao Yoshida (Kyoto University / Professor)

Since photocatalysts are unique materials that can promote chemical reactions under photoirradiation, they can utilize the solar energy to produce more useful molecules of high chemical potential from stable molecules such as water and carbon dioxide. Recently, we found that calcium titanate fine crystals can efficiently promote decomposition of carbon dioxide to carbon monoxide and oxygen under UV light irradiation without using any special chemical reagent. On the other hand, we elucidated that metal cation doping to calcium titanate fine crystals made them be fine crystals of large or small size, depending on the loading ratio. In this study, we will try to clarify the relation between the singular structure created by the doping, such as the completeness/incompleteness of the crystal structure, the electron structure, and the surface structure, and their photocatalytic activity.

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