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427 results on '"Hosoi, Takuji"'

1. Density functional theory study on effect of NO annealing for SiC(0001) surface with atomic-scale steps

Author

Uemoto, Mitsuharu, Funaki, Nahoto, Yokota, Kazuma, Hosoi, Takuji, and Ono, Tomoya

Subjects
Condensed Matter - Materials Science
Abstract

Density functional theory calculations for the electronic structures of the 4H-SiC(0001)/SiO$_2$ interface with atomic-scale steps are carried out to investigate the effect of NO annealing. The characteristic behavior of the conduction band edge states of SiC is strongly affected over a wide area of the interface by the Coulomb interaction of the O atoms in the SiO$_2$ region as well as the step structure of the interface, resulting in the discontinuity of the inversion layers at the step edges under the gate bias. The spatially discontinued band only allows the very limited conduction paths in the inversion layer, leading to the significantly decreased mobile carrier density. It is found that the Coulomb interaction of the O atoms is screened and the inversion layers become continuous when the nitrided layers are inserted at the interface by NO annealing. This result is in good agreement with experimental findings that the improvement of the performance of SiC metal-oxide-semiconductor field-effect-transistors by NO annealing is attributed to an increase in the mobile electron density rather than an increase in the mobility of electrons in the inversion layer., Comment: 12 pages

Published
2023
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4. First-Principles Study for Evidence of Low Interface Defect Density at Ge/GeO$_2$ Interfaces

Author

Saito, Shoichiro, Hosoi, Takuji, Watanabe, Heiji, and Ono, Tomoya

Subjects
Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract

We present the evidence of the low defect density at Ge/GeO$_2$ interfaces in terms of first-principles total energy calculations. The energy advantages of the atom emission from the Ge/GeO$_2$ interface to release the stress due to the lattice mismatch are compared with those from the Si/SiO$_2$ interface. The energy advantages of the Ge/GeO$_2$ are found to be smaller than those of the Si/SiO$_2$ because of the high flexibility of the bonding networks in GeO$_2$. Thus, the suppression of the Ge-atom emission during the oxidation process leads to the improved electrical properties of the Ge/GeO$_2$ interfaces.

Published
2009
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5. Fabrication and Luminescence Characterization of Ge Wires with Uniaxial Tensile Strains Applied using Internal Stresses in Deposited Metal Thin Films

Author

1000090252600, Shimura, Takayoshi, Tanaka, Shogo, 1000090452466, Hosoi, Takuji, 1000090379115, Watanabe, Heiji, 1000090252600, Shimura, Takayoshi, Tanaka, Shogo, 1000090452466, Hosoi, Takuji, 1000090379115, and Watanabe, Heiji

Abstract

This version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s11664-023-10309-w., We examined the fabrication process of uniaxial tensile-strained Ge wires in micro-bridge structures by utilizing the internal stresses in deposited metal thin films. This method enables strain control by adjusting film-deposition conditions, which is advantageous over previous methods that utilize internal stresses unintentionally applied to Ge-on-insulator substrates. We evaluated the internal stresses in W films formed by sputtering deposition methods. Tensile and compressive stresses were determined based on the Ar gas pressure during the deposition process. We applied tensile strain to Ge wires using 100-nm-thick W films, each with a tensile stress of 890 MPa, deposited in 1.5-Pa Ar gas. We confirmed that strains of up to 1.62% can be achieved and controlled by tuning the structural parameters of the bridge structure with the Ge wires. Photoluminescence peaks shifted to lower energies with increasing strain, in good agreement with theoretical predictions. We also used strained Ge wires to fabricate light-emitting diodes that exhibited clear electroluminescence peaks indicative of band structural modulation in the Ge wires.

Published
2023

6. Probing the surface potential of SiO2/4H-SiC(0001) by terahertz emission spectroscopy.

Author

Nakanishi, Hidetoshi, Nishimura, Tatsuhiko, Kawayama, Iwao, Tonouchi, Masayoshi, Hosoi, Takuji, Shimura, Takayoshi, and Watanabe, Heiji

Subjects
EMISSION spectroscopy, SURFACE potential, CAPACITANCE-voltage characteristics, ELECTRIC fields, FEMTOSECOND pulses, TERAHERTZ spectroscopy
Abstract

Terahertz (THz) emission spectroscopy (TES) was used to evaluate the properties of interfaces between thermally grown oxides and 4H-SiC(0001) substrates. Metal–oxide–semiconductor (MOS) structures with transparent electrodes were irradiated with a femtosecond laser pulse and the emitted THz signal was measured by changing the applied gate voltage. The amplitude of the THz pulse signal is dependent on the electric field, namely, band bending near the SiO2/SiC interfaces, and thus contains information on the change in the surface potential of the SiC MOS structures. We compared the peak THz amplitude (ETHz) and gate voltage (Vg) curves taken from SiC MOS structures with different interface qualities and observed a steep ETHz–Vg curve for a high-quality SiO2/SiC interface as compared with the curve for a structure with a higher interface state density. We also compared the ETHz–Vg and capacitance–voltage characteristics of SiC MOS capacitors and investigated the mechanism of THz emission from the SiC MOS structures to validate the ability of the TES technique for characterizing SiO2/SiC interfaces. [ABSTRACT FROM AUTHOR]

Published
2021
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8. Voids and vacancy-type defects in SiO2/GaN structures probed by monoenergetic positron beams.

Author

Uedono, Akira, Ueno, Wataru, Yamada, Takahiro, Hosoi, Takuji, Egger, Werner, Koschine, Tönjes, Hugenschmidt, Christoph, Dickmann, Marcel, and Watanabe, Heiji

Subjects
POSITRON annihilation, POSITRON beams, PLASMA-enhanced chemical vapor deposition
Abstract

Voids in SiO2 films deposited on GaN were probed by using monoenergetic positron beams. The films were fabricated on GaN substrates by using plasma-enhanced chemical vapor deposition. The size and density of the voids in the films increased up to an annealing temperature of 800 °C and then decreased at 1000 °C. The observed annealing behaviors of the voids were attributed to the desorption of impurities incorporated during the deposition process and the shrinkage of the Si–O matrix by high-temperature annealing. Vacancy-type defects were introduced into the GaN substrate after 1000 °C annealing in O2 atmosphere due to the diffusion of Ga from the substrate to the SiO2 film. No out-diffusion of Ga into the SiO2 film was observed for the annealing in N2 atmosphere. Thus, the observed out-diffusion of Ga was attributed to the enhanced oxidation of GaN during the annealing in O2 atmosphere. The diffusion of positrons implanted into the GaN substrate toward the SiO2 film was suppressed by annealing, suggesting a decrease in the negative charges in the SiO2 film or near the SiO2/GaN interface. [ABSTRACT FROM AUTHOR]

Published
2020
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31. Electrical properties and energy band alignment of SiO2/GaN metal-oxide-semiconductor structures fabricated on N-polar GaN(0001¯) substrates.

Author

Mizobata, Hidetoshi, Tomigahara, Kazuki, Nozaki, Mikito, Kobayashi, Takuma, Yoshigoe, Akitaka, Hosoi, Takuji, Shimura, Takayoshi, and Watanabe, Heiji

Subjects
METAL oxide semiconductor capacitors, ENERGY bands, METAL oxide semiconductor field-effect transistors, ELECTRICAL energy, GALLIUM nitride, X-ray photoelectron spectroscopy, CONDUCTION bands
Abstract

The interface properties and energy band alignment of SiO2/GaN metal-oxide-semiconductor (MOS) structures fabricated on N-polar GaN(000 1 ¯ ) substrates were investigated by electrical measurements and synchrotron-radiation x-ray photoelectron spectroscopy. They were then compared with those of SiO2/GaN MOS structures on Ga-polar GaN(0001). Although the SiO2/GaN(000 1 ¯ ) structure was found to be more thermally unstable than that on the GaN(0001) substrate, excellent electrical properties were obtained for the SiO2/GaN(000 1 ¯ ) structure by optimizing conditions for post-deposition annealing. However, the conduction band offset for SiO2/GaN(000 1 ¯ ) was smaller than that for SiO2/GaN(0001), leading to increased gate leakage current. Therefore, caution is needed when using N-polar GaN(000 1 ¯ ) substrates for MOS device fabrication. [ABSTRACT FROM AUTHOR]

Published
2022
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33. Comprehensive physical and electrical characterizations of NO nitrided SiO2/4H-SiC(112̄0) interfaces.

Author

Nakanuma, Takato, Iwakata, Yu, Watanabe, Arisa, Hosoi, Takuji, Kobayashi, Takuma, Sometani, Mitsuru, Okamoto, Mitsuo, Yoshigoe, Akitaka, Shimura, Takayoshi, and Watanabe, Heiji

Abstract

Nitridation of SiO2/4H-SiC(112̄0) interfaces with post-oxidation annealing in an NO ambient (NO-POA) and its impact on the electrical properties were investigated. Sub-nm-resolution nitrogen depth profiling at the interfaces was conducted by using a scanning X-ray photoelectron spectroscopy microprobe. The results showed that nitrogen atoms were incorporated just at the interface and that interface nitridation proceeded much faster than at SiO2/SiC(0001) interfaces, resulting in a 2.3 times higher nitrogen concentration. Electrical characterizations of metal-oxide-semiconductor capacitors were conducted through capacitance–voltage (C – V) measurements in the dark and under illumination with ultraviolet light to evaluate the interface defects near the conduction and valence band edges and those causing hysteresis and shifting of the C – V curves. While all of these defects were passivated with the progress of the interface nitridation, excessive nitridation resulted in degradation of the MOS capacitors. The optimal conditions for NO-POA are discussed on the basis of these experimental findings. [ABSTRACT FROM AUTHOR]

Published
2022
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34. Fixed-charge generation in SiO2/GaN MOS structures by forming gas annealing and its suppression by controlling Ga-oxide interlayer growth.

Author

Mizobata, Hidetoshi, Nozaki, Mikito, Kobayashi, Takuma, Hosoi, Takuji, Shimura, Takayoshi, and Watanabe, Heiji

Abstract

A recent study has shown that anomalous positive fixed charge is generated at SiO2/GaN interfaces by forming gas annealing (FGA). Here, we conducted systematic physical and electrical characterizations of GaN-based metal-oxide-semiconductor (MOS) structures to gain insight into the charge generation mechanism and to design optimal interface structures. A distinct correlation between the amount of FGA-induced fixed charge and interface oxide growth indicated the physical origins of the fixed charge to be defect formation driven by the reduction of the Ga-oxide (GaO x) interlayer. This finding implies that, although post-deposition annealing in oxygen compensates for oxygen deficiencies and FGA passivates defect in GaN MOS structures, excessive interlayer GaO x growth leads to instability in the subsequent FGA treatment. On the basis of this knowledge, SiO2/GaO x /GaN MOS devices with improved electrical properties were fabricated by precisely controlling the interfacial oxide growth while taking advantage of defect passivation with FGA. [ABSTRACT FROM AUTHOR]

Published
2022
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35. Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light

Author

Ngo, Nguyen Hoai, primary, Nguyen, Anh Quang, additional, Bufler, Fabian M., additional, Kamakura, Yoshinari, additional, Mutoh, Hideki, additional, Shimura, Takayoshi, additional, Hosoi, Takuji, additional, Watanabe, Heiji, additional, Matagne, Philippe, additional, Shimonomura, Kazuhiro, additional, Takehara, Kohsei, additional, Charbon, Edoardo, additional, and Etoh, Takeharu Goji, additional

Published
2020
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40. Comprehensive and systematic design of metal/high-k gate stack for high-performance and highly reliable SiC power MOSFET

Author

Hosoi, Takuji, primary, Azumo, Shuji, additional, Kashiwagi, Yusaku, additional, Hosaka, Shigetoshi, additional, Yamamoto, Kenji, additional, Aketa, Masatoshi, additional, Asahara, Hirokazu, additional, Nakamura, Takashi, additional, Kimoto, Tsunenobu, additional, Shimura, Takayoshi, additional, and Watanabe, Heiji, additional

Published
2020
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45. (Invited) Gate Stack Technologies for SiC Power MOSFETs

Author

Watanabe, Heiji, primary, Hosoi, Takuji, additional, Kirino, Takashi, additional, Uenishi, Yusuke, additional, Chanthaphan, Atthawut, additional, Ikeguchi, Daisuke, additional, Yoshigoe, Akitaka, additional, Teraoka, Yuden, additional, Mitani, Shuhei, additional, Nakano, Yuki, additional, Nakamura, Takashi, additional, and Shimura, Takayoshi, additional

Published
2019
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