B01 group

B01-1 Multiscale characterization of singularity structures and behaviors thereof

    Principal Investigator / Akira Sakai (Osaka University / Professor)
  • Co-Investigator / Yasuhiko Imai (Japan Synchrotron Radiation Research Institute / Associate Senior Scientist)

In situ Nanobeam X-ray Diffraction (nanoXRD) with 100-nm-scale spatial resolution and sub-nano-second time resolution enables a wide-range analysis of local strain and domain textures in semiconductor crystals and devices. In addition, an effective combination of nanoXRD and microscopy methods detecting microstructures and distribution of defects realizes multiscale structural characterization from nanometer to millimeter. In this project, we focus on the singularity structures and behaviors thereof mainly in nitride semiconductor crystals, such as nano-voids, dislocations,
polar/non-polar lattices influencing piezoelectric effects, etc. Being supplied with several singularity-structure-controlled materials and devices from other groups, we perform three-dimensional precise structural analysis and in situ dynamic characterization for them. By exploiting active functions of the singularity structures, we systematize extended crystallography as a new field of study and contribute to the innovation of next generation green electronics.

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B01-2 Study of dynamics of carrier trapping/scattering in singularity crystal structure by means of positron annihilation

  • Principal Investigator / Akira Uedono (University of Tsukuba / Professor)
  • Co-Investigator / Nagayasu Oshima (National Institute of Advanced Industrial Science and Technology / Senior Researcher)
  • Co-Investigator / Masatomo Sumiya (National Institute for Materials Science / Chief Researcher)
  • Co-Investigator / Shoji Ishibashi (National Institute of Advanced Industrial Science and Technology / Leader, Team)
  • Co-Investigator / Hironori Okumura (University of Tsukuba / Assistant Professor)

Positron annihilation is a non-destructive detection tool for vacancy-type defects or open spaces in materials (Figure A). Using this technique, one can study such singularity structures with high sensitivity, and determine their species, concentrations and depth distributions. The purpose of the present research as follows; (i) a study of carrier trapping/scattering phenomena and their optical reactions, and (ii) developments of the measurement system in order to use a positron as a probe of electric field (Figure B and C). Measurement systems equipped with positron beam, illumination system, electron beam, and bias applying electronics are installed at University of Tsukuba and National Institute of Advanced Industrial Science and Technology. We use the positron annihilation spectroscopy to study properties of the singularity structures from a view of material science, and propose guidelines for the fabrication of electric devices using such structures.

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B01-3 3D spectroscopic characterization of crystal singularities and application of defects based on phonon science

  • Principal Investigator / Yoshihiro Isitani (Chiba University / Professor)
  • Co-Investigator / Yuzo Shinozuka (Wakayama University / Professor)
  • Co-Investigator / Bei Ma (Chiba University / Research Associate)

In this study, we characterize various crystal singularities and its application to the control of electronic and radiative properties of wide bandgap semiconductors by observing the interactions between carriers and phonons.
(1) Nondestructive spatially resolved characterization of crystal singularities and their physical properties
 Characterization of structural properties such as strain, electronic states, and lattice vibration states in crystals of devices epitaxially grown on patterned substrates.
 3D images of strain and interaction potential fields of carriers and lattice vibrations, particularly in the vicinity of dislocations and point defects

Here, we pursue the sensitive detection of fields of strain and crystal defects by the enhancement of electric field of electromagnetic waves using antenna structures, and also characterize carrier and exciton dynamics in the fields possessing crystal singularities by resonant Raman measurements using two-wavelength laser beams. Numerical analysis of the dynamics including phonon processes under nonthermal condition is also conducted. We build a bridge across the issues of defects and device properties on the basis of these studies.
(2) Application of the physics of defects to the control of optical and electrical properties for devices
We investigate the improvement of carrier transport properties, radiative efficiency, and current extraction from multi-quantum well structures by controlling the localization and delocalization of phonons using crystal singularities and the resultant increase and decrease in the interaction between phonons and carriers.

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B01-17-1 Multiscale structure analysis of defects in nitride and oxide semiconductors

  • Principal Investigator / Takanori Kiguchi (Tohoku University / Associate Professor)

Lattice defects and residual strain inhibits the quality of the crystal growth and the electro-optical properties of nitrides and oxides semiconductors. Using the microscopy, our group attempt to elucidate the new insight concerning the structure, the morphology, the strain field, and the electronic state of the structural singularity such as defects in multiscale from 2D to 3D in order to improve and create the novel physical properties and devices.

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B01-17-2 Probing charges and polarizations induced by singularity structures with terahertz radiations

  • Principal Investigator / Iwao Kawayama (Osaka University / Associate Professor)

The purpose of this study is probing local charges, electric fields, polarizations and the change of chemical potentials induced by singularity structures, e. g. controlled defects and dislocations, hetero structures and composition-gradient areas, in semiconductors using terahertz emission imaging and spectroscopy. The amplitudes and the phases of the terahertz radiations induced by the illumination of femtosecond laser pulses reflect transient photocurrents and/or modulation of polarizations excited by the laser pulses. In this study, we systematically investigate the relation between various singularity structures in semiconductors and characteristics of terahertz radiations from their structures, and elucidate the generation mechanism of the terahertz radiations in cooperation with the researchers in the fields of crystal growth, device fabrication and optical measurement in this project. Based on the fundamental studies on the terahertz radiations, we will realize the selective and quantitative measurements of charges, electric fields and polarizations induced by singularity structures and demonstrate the validity of terahertz emission imaging and spectroscopy as novel probes to investigate local properties of semiconductor materials and devices.

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B01-17-3 Theoretical calculations on ion dynamics around singularities in oxides

  • Principal Investigator / Satoshi Watanabe (The University of Tokyo / Professor)

In our group, by combining first-principles calculations and machine-learning techniques (especially neural network), we develop simulation methods to analyze ion dynamics that have both reliability and computational efficiency. Specifically, we establish schemes to construct interatomic potentials that can be applicable to (1) multi-component materials with various structures (including amorphous) and compositional ratios, (2) systems under external electric fields, and (3) phonon calculations of systems with defects. Using the developed schemes/methods, we aim at clarifying ion dynamics behaviors around singularities in oxides and their effects on the performances of various devices such as resistive switches, fuel cells and secondary batteries.

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B01-17-4 Reconstruction of diffraction crystallography using advanced X-ray

  • Principal Investigator / Eiji Nishibori (University of Tsukuba / Professor)

The aim of the project is development of the fundamental analytical techniques for x-ray diffraction using 100nm-sized synchrotron radiation X-ray beam (Nanobeam X-ray Diffraction: nanoXRD). We mainly focus analytical technique to determine an atomic configuration with 0.001 nm accuracy. The accuracy is comparable to that of conventional X-ray crystallography. We use a general-purpose computing on graphics processing units (CPGPU) technique to accelerate our analytical method. X-ray diffraction from nanostructure with 100 million atoms can be calculated with reasonable time by GPGPU. We will determine the atomic scale structure of nanometer-sized device including strain and defect. We would like to do a reconstruction of diffraction crystallography for nanometer sized device and structure in the feature.

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