Impact of post-nitridation annealing in CO ambient on threshold voltage stability in 4H-SiC metal-oxide-semiconductor field-effect transistors

Hosoi, Takuji*; Osako, Momoe*; Moges, K.*; Ito, Koji*; Kimoto, Tsunenobu*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Express, 15(6), p.061003_1 - 061003_5, 2022/06

https://doi.org/10.35848/1882-0786/ac6f42

The combination of NO annealing and subsequent post-nitridation annealing (PNA) in CO ambient for SiO/SiC structures has been demonstrated to be effective in obtaining both high channel mobility and superior threshold voltage stability in SiC-based metal-oxide-semiconductor field-effect transistors (MOSFETs). N atoms on the SiO side of the SiO/SiC interface incorporated by NO annealing, which are plausible cause of charge trapping sites, could be selectively removed by CO-PNA at 1300C without oxidizing the SiC. CO-PNA was also effective in compensating oxygen vacancies in SiO, resulting high immunity against both positive and negative bias-temperature stresses.

High reactivity of HO vapor on GaN surfaces

Sumiya, Masatomo*; Sumita, Masato*; Tsuda, Yasutaka; Sakamoto, Tetsuya; Sang, L.*; Harada, Yoshitomo*; Yoshigoe, Akitaka

Science and Technology of Advanced Materials, 23(1), p.189 - 198, 2022/00

https://doi.org/10.1080/14686996.2022.2052180

GaN is an attracting material for power-electronic devices. Understanding the oxidation at GaN surface is important for improving metal-oxide-semiconductor (MOS) devices. In this study, the oxidation at GaN surfaces depending on the GaN crystal planes (+c, -c, and m-plane) was investigated by real time XPS and DFT-MD simulation. We found that HO vapor has the highest reactivity due to the spin interaction between HO and GaN surfaces. The bond length between the Ga and N on the -c GaN surface was increased by OH attacking the back side of three-fold Ga atom. The chemisorption on the m-plane was dominant. The intense reactions of oxidation and AlGaN formation for p-GaN were observed at the interface of the AlO layer deposited by ALD using HO vapor. This study suggests that an oxidant gas other than HO and O should be used to avoid unintentional oxidation during AlGaN atomi layer deposition.

Biodegradability of disulfide-organosilica nanoparticles evaluated by soft X-ray photoelectron spectroscopy; Cancer therapy implications

Mekaru, Harutaka*; Yoshigoe, Akitaka; Nakamura, Michihiro*; Doura, Tomohiro*; Tamanoi, Fuyuhiko*

ACS Applied Nano Materials (Internet), 2(1), p.479 - 488, 2019/01

https://doi.org/10.1021/acsanm.8b02023

Organosilica nanoparticles are attractive for use as drug delivery systems for cancer therapy. Ideally, the nanoparticles need to degrade in the body after drug delivery to minimize their risk. However, the biodegradation of organosilica nanoparticles has not been thoroughly investigated. In this study, we used X-ray photoelectron spectroscopy and field-emission scanning electron microscopy to investigate the degradation of organosilica nanoparticles by glutathione, a peptide found in cells. Our results indirectly indicate that glutathione is able to reduce the disulfide bonds present in the network of one type of the nanoparticles, promoting dissociation of these nanoparticles. The dissociated nanoparticles form large maple leaf-shaped structures under certain conditions. We consider the formation mechanism of these symmetrical structures.

Implementation of atomic layer deposition-based AlON gate dielectrics in AlGaN/GaN MOS structure and its physical and electrical properties

Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

Japanese Journal of Applied Physics, 57(6S3), p.06KA02_1 - 06KA02_7, 2018/06

https://doi.org/10.7567/JJAP.57.06KA02

We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.

Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

Japanese Journal of Applied Physics, 57(6S3), p.06KA07_1 - 06KA07_6, 2018/06

https://doi.org/10.7567/JJAP.57.06KA07

Thermal oxidation of AlGaN surface and its impact on the electrical properties of AlGaN/GaN MOS capacitors were investigated by means of synchrotron radiation photoelectron spectroscopy (SR-PES), atomic force microscopy (AFM) and C-V measurements. SR-PES analysis revealed that the AlGaN surface is oxidized even at low temperature of 400C, in contrast to no oxide formation on GaN surface. However, since no noticeable change in the surface morphology was observed at temperatures up to 800C, it can be concluded that an ultrathin oxide overlayer is formed on the AlGaN surface. On the other hand, for the oxidation treatments above 850C, the formation of small oxide grains was observed over the entire area of the AlGaN surface, and the growth of oxide grains significantly degraded the surface morphology. Therefore, the AlGaN/GaN MOS capacitors were fabricated on the AlGaN surface oxidized at moderate temperatures up to 800C. While we have confirmed that relatively good interface properties are obtained for direct AlON deposition without oxidation treatment, it was found that the oxidation treatment at 400C leads to further improvement of interface properties and reduction of C-V hysteresis.

Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

Yoshigoe, Akitaka; Shiwaku, Hideaki; Kobayashi, Toru; Shimoyama, Iwao; Matsumura, Daiju; Tsuji, Takuya; Nishihata, Yasuo; Kogure, Toshihiro*; Okochi, Takuo*; Yasui, Akira*; et al.

Applied Physics Letters, 112(2), p.021603_1 - 021603_5, 2018/01

https://doi.org/10.1063/1.5005799

A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, Fe) without charging issues. We found that Cs atoms were likely to be adsorbed evenly over the entire particle. Spatially-resolved X-ray absorption spectra (XAS) of the Cs M-edge region showed Cs to be present in a monocation state (Cs). Further pinpoint XAS measurements were also performed at the Fe L-edge to determine the chemical valence of the Fe atoms. Our results demonstrate the utility of SR-PEEM as a tool for spatially-resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

Characterization of surface carbon films on weathered Japanese roof tiles by soft X-ray spectroscopy

Muramatsu, Yasuji; Yamashita, Michiru*; Motoyama, Muneyuki*; Hirose, Mika*; Denlinger, J. D.*; Gullikson, E. M.*; Perera, R. C. C.*

X-Ray Spectrometry, 34(6), p.509 - 513, 2005/11

https://doi.org/10.1002/xrs.865

Surface carbon films on the weathered Japanese roof tiles were characterized by soft X-ray spectroscopy. From the X-ray absorption measurements, it was confirmed that the surface carbon films were oxidized by weathering. On the ohterhand, from the X-ray emission measurements, it can be confirmed that the degree of the orientation was kept in the inner carbon films.

Chemical analysis of carbon films on Japanese smoked roof tile "Ibushi Kawara" by soft X-ray spectroscopy using synchrotron radiation

Muramatsu, Yasuji

Rigaku Janaru, 36(1), p.35 - 42, 2005/04

https://ci.nii.ac.jp/naid/40006801121

Microstructure and weathering effects of carbon films on the Japanese smoked roof tile "Ibushi-Kawara" were investigated by soft X-ray spectroscopy using synchrotron radiation. The take-off/incident-angle dependence on the X-ray emission/absorption spectra of Kawara shows that the carbon-black-like sp2 carbon atoms partially form a layer structure oriented parallel to the basal clay plane, and that the degree of orientation of the carbon films is estimated to be 50% that of highly oriented pyrolytic graphite (HOPG). X-ray absorption measurements revealed that weathering oxidizes the carbon films and partial carboxy chemical bonding occurs.

Aqueous solutions of uranium(VI) as studied by time-resolved emission spectroscopy; A Round-robin test

Billard, I.*; Ansoborlo, E.*; Apperson, K.*; Arpigny, S.*; Azenha, M.-E.*; Birch, D.*; Bros, P.*; Burrows, H. D.*; Choppin, G. R.*; Couston, L.*; et al.

Applied Spectroscopy, 57(8), p.1027 - 1038, 2003/08

https://doi.org/10.1366/000370203322259002

no abstracts in English

Measurement of neodymium(III) and samarium(III) by spectrophotometer and laser-induced photoacoustic spectroscopic system: A Preliminary study for speciation of aqueous Np(IV) species.

Kitamura, Akira;

JNC TN8400 2001-009, 54 Pages, 2001/01

JNC-TN8400-2001-009.pdf:1.3MB

Spectroscopic measurements of neodymium(III) and samarium(III) were carried out by spectrophotometer and laser-induced photoacoustic spectroscopic (LPAS) system for the investigation of the detection limit of both systems. The absorption spectra and photoacoustic spectra of Nd and Sm were obtained with varying the concentration of the ions from 210 to 210 moldm. The absorption spectrum of Nd was also determined by a special spectrophotometer, of which the measurement cell was set in a glove box filled with inert nitrogen gas. For the comparison with these photoacoustic and absorption spectra, the absorption spectra of Nd and Sm were determined by an usual spectrophotometer with the light-path lengths of 1 cm and 10 cm. The detection limit of the photoacoustic measurement was reported much lower than that of absorbance measurement by several researchers. However, the present study was concluded that the detection limit of photoacoustic measurement with the present LPAS system was similar to that of absorbance measurement with the light-path length of 10 cm. The detection limits of neptunium(IV,V) were estimated and the possibility of the speciation of neptunium(IV) was discussed from the results of the present study.