Curriculum Vitaes

Rie Togashi

  (富樫 理恵)

Profile Information

Affiliation
Associate Professor, Faculty of Science and Technology, Department of Engineering and Applied Sciences, Sophia University
Degree
博士(工学)(東京農工大学)

Researcher number
50444112
J-GLOBAL ID
201801000291501271
researchmap Member ID
7000023348

2006-2018、 国立大学法人東京農工大学大学院工学研究院、III族窒化物半導体、III族酸化物半導体結晶に関するエピタキシャル成長および理論解析について研究
2018-現在 上智大学理工学部機能創造理工学科、III族窒化物半導体、III族酸化物半導体結晶に関する結晶成長、デバイス応用、理論解析について研究

(研究テーマ)
III族酸化物半導体結晶成長
前駆体二段階生成HVPE法によるInN成長
III族窒化物半導体成長


Papers

 62
  • Hiroto Sekiguchi, Hayato Katagiri, Kota Hoshino, Rie Togashi, Katsumi Kishino
    Japanese Journal of Applied Physics, 64(2) 028004-028004, Feb 1, 2025  Peer-reviewed
    Abstract The integration of red-green-blue (RGB) light sources is essential for the development of high-resolution micro-light-emitting diode (micro-LED) displays. In this study, we propose a color-tunable device based on self-assembled InGaN-based nanocolumn LEDs without a patterning process. The nanocolumn LEDs exhibited a color shift from red to orange-yellow, pale green, and further to blue as the driving voltage increased. Micro-electroluminescence measurements revealed that a small wavelength shift was observed within individual nanocolumn regions. Instead, emission spots sequentially turned on, transitioning from red to blue (660-435 nm), elucidating the mechanism of color tuning. Combined with pulse-width-modulation driving, these findings open the pathway for the realization of novel monolithic RGB-LED devices.
  • Takayoshi Oshima, Rie Togashi, Yuichi Oshima
    Science and Technology of Advanced Materials, 25(1) 2378683, Jul 29, 2024  Peer-reviewed
  • Kota Hoshino, Rie Togashi, Katsumi Kishino
    physica status solidi (b), 2400064-1-2400064-8, Apr 25, 2024  Peer-reviewed
    Herein, triangular‐lattice nanopillar templates are fabricated on sputter‐deposited AlN/Si (111) substrates. Nanotemplate selective‐area growth via radiofrequency‐plasma‐assisted molecular beam epitaxy is employed to grow GaN nanocolumns on the nanopillars. Well‐ordered uniform GaN nanocolumn arrays are obtained by inserting a migration‐enhanced‐epitaxy grown AlN/AlGaN buffer layer, thereby aligning the polarity of GaN to Ga‐polar. Subsequently, bulk InGaN active layers are grown on top of the GaN nanocolumns with increasing growth time (tg = 10–20 min). In the initial stage of growth (tg = 10 min), low‐In‐content InGaN grows on the edges of the six‐sided pyramidal top of the GaN nanocolumns. As the growth progresses, low‐In‐composition InGaN fills the sides between InGaN on the edges, while high‐In‐composition InGaN rapidly grows on the top of the c‐plane nanocolumns. High‐angle annular dark‐field scanning transmission electron microscopy reveals the formation of an InGaN core, covered with a low‐In‐composition InGaN shell, on the top of the nanocolumns. At tg = 20 min, the photoluminescence spectrum exhibits a peak at 669 nm with a full width at half maximum value of 51.7 nm. Thus, the proposed method is suitable for growing red‐light‐emitting well‐ordered InGaN/GaN nanocolumn arrays on Si.
  • Hiroyuki Shimada, Hironobu Kariyazono, Yohei Nakagawa, Shinji Terao, Kentaro Takayanagi, Koichiro Akasaka, Shunsuke Ishizawa, Koichi Morozumi, Tsutomu Asakawa, Rie Togashi, Katsumi Kishino
    Japanese Journal of Applied Physics, 63(2) 02SP67-02SP67, Jan 23, 2024  Peer-reviewed
    Abstract In this paper, we report achieving extremely high-density packing in high-voltage vertical gallium nitride (GaN) nanocolumn Schottky barrier diodes (NC-SBDs) through the adoption of a bottom-up process. The NC-SBDs were formed via epitaxial growth using Titanium-mask selective area growth (Ti-SAG) by rf-plasma-assisted MBE (rf-MBE), realizing a packing density equivalent to exceeding 10 million columns/mm2. Our fabricated NC-SBDs with a period of 300 nm, a diameter of 250 nm, and a drift length of 1.3 μm demonstrated a breakdown voltage (BV) of 260 V with an on-resistance of 2.0 mΩcm2, yielding an excellent figure of merit of 33.8 MW/cm2 for nanocolumn-based high-voltage devices. We also discuss dielectric reduced surface field effect and impurities within the nanocolumns as potential factors contributing to the achievement of higher BV devices.
  • Tomohiro Yamaguchi, Yasushi Nanishi, Takuo Sasaki, Masamitu Takahasi, Takeyoshi Onuma, Tohru Honda, Rie Togashi, Katsumi Kishino
    Journal of the Japanese Association for Crystal Growth, 51(2) 51-2-06, 2024  Peer-reviewedInvited

Misc.

 77

Presentations

 394

Research Projects

 16