Publications
ResearcherID : C-5956-2008 (TY, h-index: 24) , AAZ-8749-2021 (RK, h-index: 11)
Google Scholar : TY (h-index: 34), RK (h-index: 11)
2019
Takashi Yatsui
Recent improvement of silicon absorption in opto-electric devices Journal Article
In: Opto-Electronic Advances, vol. 2, no. 10, pp. 190023, 2019, (review article, selected as cover story).
Abstract | Links | BibTeX | Tags: Direct wave-vector excitation, First, First principle calculation, Indirect band gap, Near-field effect, Plasmon, Review, Si
@article{OEA_RefItem:1,
title = {Recent improvement of silicon absorption in opto-electric devices},
author = {Takashi Yatsui},
doi = {10.29026/oea.2019.190023},
year = {2019},
date = {2019-10-01},
urldate = {2019-10-01},
journal = {Opto-Electronic Advances},
volume = {2},
number = {10},
pages = {190023},
publisher = {OEA},
abstract = {Silicon dominates the contemporary electronic industry. However, being an indirect band-gap material, it is a poor absorber of light, which decreases the efficiency of Si-based photodetectors and photovoltaic devices. This review highlights recent studies performed towards improving the optical absorption of Si. A summary of recent theoretical approaches based on the first principle calculation has been provided. It is followed by an overview of recent experimental approaches including scattering, plasmon, hot electron, and near-field effects. The article concludes with a perspective on the future research direction of Si-based photodetectors and photovoltaic devices.},
note = {review article, selected as cover story},
keywords = {Direct wave-vector excitation, First, First principle calculation, Indirect band gap, Near-field effect, Plasmon, Review, Si},
pubstate = {published},
tppubtype = {article}
}
Silicon dominates the contemporary electronic industry. However, being an indirect band-gap material, it is a poor absorber of light, which decreases the efficiency of Si-based photodetectors and photovoltaic devices. This review highlights recent studies performed towards improving the optical absorption of Si. A summary of recent theoretical approaches based on the first principle calculation has been provided. It is followed by an overview of recent experimental approaches including scattering, plasmon, hot electron, and near-field effects. The article concludes with a perspective on the future research direction of Si-based photodetectors and photovoltaic devices.
Takashi Yatsui, Syunsuke Okada, Tatsuya Takemori, Takumi Sato, Kota Saichi, Tatsuro Ogamoto, Shohei Chiashi, Shigeo Maruyama, Masashi Noda, Kazuhiro Yabana, Kenji Iida, Katsuyuki Nobusada
Enhanced photo-sensitivity in a Si photodetector using a near-field assisted excitation Journal Article
In: Communications Physics, vol. 2, pp. 62, 2019.
Abstract | Links | BibTeX | Tags: Direct wave-vector excitation, First, Selected, Si photodetector
@article{yatsui2019Si,
title = {Enhanced photo-sensitivity in a Si photodetector using a near-field assisted excitation},
author = {Takashi Yatsui and Syunsuke Okada and Tatsuya Takemori and Takumi Sato and Kota Saichi and Tatsuro Ogamoto and Shohei Chiashi and Shigeo Maruyama and Masashi Noda and Kazuhiro Yabana and Kenji Iida and Katsuyuki Nobusada},
doi = {10.1038/s42005-019-0173-1},
year = {2019},
date = {2019-06-01},
journal = {Communications Physics},
volume = {2},
pages = {62},
publisher = {Springer Nature},
abstract = {Silicon is an indispensable material in electric device technology. However, Si is an indirect bandgap material; therefore, its excitation efficiency, which requires phonon assistance, is low under propagating far-field light. To improve the excitation efficiency, herein we performed optical near-field excitation, which is confined in a nano-scale, where the interband transitions between different wave numbers are excited according to the uncertainty principle; thus, optical near-field can directly excite the carrier in the indirect bandgap. To evaluate the effect of optical near-field confined in a nano-scale, we fabricate the lateral Si p-n junction with Au nanoparticles as sources to generate the field confinement. We observed a 47.0 % increase in the photo-sensitivity rate. In addition, by using the thin lateral p-n junction, which eliminates the far-field excitation, we confirmed a 42.3 % increase in the photo-sensitivity rate.},
keywords = {Direct wave-vector excitation, First, Selected, Si photodetector},
pubstate = {published},
tppubtype = {article}
}
Silicon is an indispensable material in electric device technology. However, Si is an indirect bandgap material; therefore, its excitation efficiency, which requires phonon assistance, is low under propagating far-field light. To improve the excitation efficiency, herein we performed optical near-field excitation, which is confined in a nano-scale, where the interband transitions between different wave numbers are excited according to the uncertainty principle; thus, optical near-field can directly excite the carrier in the indirect bandgap. To evaluate the effect of optical near-field confined in a nano-scale, we fabricate the lateral Si p-n junction with Au nanoparticles as sources to generate the field confinement. We observed a 47.0 % increase in the photo-sensitivity rate. In addition, by using the thin lateral p-n junction, which eliminates the far-field excitation, we confirmed a 42.3 % increase in the photo-sensitivity rate.
Masashi Noda, Kenji Iida, Maiku Yamaguchi, Takashi Yatsui, Katsuyuki Nobusada
Direct Wave-Vector Excitation in an Indirect-Band-Gap Semiconductor of Silicon with an Optical Near-field Journal Article
In: Phys. Rev. Applied, vol. 11, no. 4, pp. 044053, 2019.
Abstract | Links | BibTeX | Tags: Direct wave-vector excitation, Si
@article{PhysRevApplied.11.044053,
title = {Direct Wave-Vector Excitation in an Indirect-Band-Gap Semiconductor of Silicon with an Optical Near-field},
author = {Masashi Noda and Kenji Iida and Maiku Yamaguchi and Takashi Yatsui and Katsuyuki Nobusada},
doi = {10.1103/PhysRevApplied.11.044053},
year = {2019},
date = {2019-04-01},
journal = {Phys. Rev. Applied},
volume = {11},
number = {4},
pages = {044053},
publisher = {American Physical Society},
abstract = {In this work, our first-principles calculations reveal that direct wave-vector excitation (i.e., interband transitions between different wavenumbers without phonon assistance) can occur in the indirect-band-gap semiconductor silicon. The wave-vector excitation is successfully induced by irradiation of a silicon thin film with an optical near-field (ONF). As a result, the absorption-band-edge energy Eedge shifts to a lower photon energy of 1.6 eV for ONF excitation from Eedge of 2.1 eV for the conventional excitation by propagating far-field light. The direct wave-vector excitation is caused by the sufficiently large components of wave vectors inherent in the ONF, and thus does not require phonon assistance. For a realistic silicon system, it is clarified that the wave-vector excitations are determined by the energy difference between the valence and conduction bands and occur irrespective of the initial and final wave vectors.},
keywords = {Direct wave-vector excitation, Si},
pubstate = {published},
tppubtype = {article}
}
In this work, our first-principles calculations reveal that direct wave-vector excitation (i.e., interband transitions between different wavenumbers without phonon assistance) can occur in the indirect-band-gap semiconductor silicon. The wave-vector excitation is successfully induced by irradiation of a silicon thin film with an optical near-field (ONF). As a result, the absorption-band-edge energy Eedge shifts to a lower photon energy of 1.6 eV for ONF excitation from Eedge of 2.1 eV for the conventional excitation by propagating far-field light. The direct wave-vector excitation is caused by the sufficiently large components of wave vectors inherent in the ONF, and thus does not require phonon assistance. For a realistic silicon system, it is clarified that the wave-vector excitations are determined by the energy difference between the valence and conduction bands and occur irrespective of the initial and final wave vectors.