Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Applied Physics Express, 15(7), p.076001_1 - 076001_4, 2022/07
We discuss the energy dissipation of short-lived -positronium (-Ps) in polymers and silica glass. The parameter characterizing the Doppler broadening of -Ps annihilation is determined from the previously reported systematic data of positron annihilation age momentum correlation for various polymers and silica glass. A comparison of the parameter with that expected for thermalized -Ps trapped in a free volume reveals that -Ps is not thermalized and possesses excess energy in fluorinated polymers and silica glass, indicating that it is difficult for Ps to lose energy in substances containing heavy elements such as fluorine and silicon.
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
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.
Nakanuma, Takato*; Kobayashi, Takuma*; Hosoi, Takuji*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*
Applied Physics Express, 15(4), p.041002_1 - 041002_4, 2022/04
The leakage current and flat-band voltage (VFB) instability of NO-nitrided SiC (110) (a-face) MOS devices were systematically investigated. Although NO nitridation is effective in improving the interface properties, we found that it reduces the onset field of Fowler-Nordheim (F-N) current by about 1 MVcm, leading to pronounced leakage current. Synchrotron X-ray photoelectron spectroscopy revealed that the nitridation reduces the conduction band offset at the SiO/SiC interface, corroborating the above finding. Furthermore, systematical positive and negative bias stress tests clearly indicated the VFB instability of nitrided a-face MOS devices against electron and hole injection.
Mori, Michiyasu; Maekawa, Sadamichi
Applied Physics Express, 14(10), p.103001_1 - 103001_4, 2021/10
Chudo, Hiroyuki; Matsuo, Mamoru*; Harii, Kazuya*; Maekawa, Sadamichi*; Saito, Eiji
Applied Physics Express, 13(10), p.109102_1 - 109102_2, 2020/10
no abstracts in English
Daimon, Shunsuke*; Uchida, Kenichi*; Ujiie, Naomi*; Hattori, Yasuyuki*; Tsuboi, Rei*; Saito, Eiji
Applied Physics Express, 13(10), p.103001_1 - 103001_4, 2020/10
Fujimori, Kosuke*; Kitaura, Mamoru*; Taira, Yoshitaka*; Fujimoto, Masaki*; Zen, H.*; Watanabe, Shinta*; Kamada, Kei*; Okano, Yasuaki*; Kato, Masahiro*; Hosaka, Masahito*; et al.
Applied Physics Express, 13(8), p.085505_1 - 085505_4, 2020/08
To clarify the existence of cation vacancies in Ce-doped GdAlGaO (Ce:GAGG) scintillators, we performed gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS). GiPAL spectra of GAGG and Ce:GAGG comprised two exponential decay components, which were assigned to positron annihilation at bulk and defect states. By an analogy with Ce:YAlO, the defect-related component was attributed to Al/Ga-O divacancy complexes. This component was weaker for Ce, Mg:GAGG, which correlated with the suppression of shallow electron traps responsible for phosphorescence. Oxygen vacancies were charge compensators for Al/Ga vacancies. The lifetime of the defect-related component was significantly changed by Mg co-doping. This was understood by considering aggregates of Mg ions at Al/Ga sites with oxygen vacancies, which resulted in the formation of vacancy clusters.
Yamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Hisashi*; Takahashi, Tokio*; Shimizu, Mitsuaki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*
Applied Physics Express, 11(1), p.015701_1 - 015701_4, 2018/01
A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed on the basis of systematic physical and electrical characterizations. Chemical vapor deposition of SiO films directly onto GaN substrates forming Ga-oxide interlayers was used to fabricate SiO/GaO/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state density below 10cmeV were obtained by post-deposition annealing, Ga diffusion into overlying SiO layers severely degraded the insulating property and dielectric breakdown characteristics of the MOS devices. However, this problem was found to be solved by employing rapid thermal processing, leading to superior performance of the GaN-MOS devices in terms of interface quality, insulating property and gate dielectric reliability.
Hioki, Tomosato*; Iguchi, Ryo*; Qiu, Z.*; Hou, D.*; Uchida, Kenichi*; Saito, Eiji
Applied Physics Express, 10(7), p.073002_1 - 073002_4, 2017/06
Takamizawa, Hisashi; Shimizu, Yasuo*; Inoue, Koji*; Nozawa, Yasuko*; Toyama, Takeshi*; Yano, Fumiko*; Inoue, Masao*; Nishida, Akio*; Nagai, Yasuyoshi*
Applied Physics Express, 9(10), p.106601_1 - 106601_4, 2016/10
Asahara, Ryohei*; Nozaki, Mikito*; Yamada, Takahiro*; Ito, Joyo*; Nakazawa, Satoshi*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Applied Physics Express, 9(10), p.101002_1 - 101002_4, 2016/10
The superior physical and electrical properties of AlON gate dielectrics on AlGaN/GaN substrates in terms of thermal stability, reliability, and interface quality were demonstrated by direct AlON deposition and subsequent annealing. Nitrogen incorporation into alumina was proven to be beneficial both for suppressing intermixing at the insulator/AlGaN interface and reducing the number of electrical defects in AlO films. Consequently, we achieved high-quality AlON/AlGaN/GaN metal-oxide-semiconductor capacitors with improved stability against charge injection and a reduced interface state density as low as 1.210 cmeV. The impact of nitrogen incorporation into the insulator was discussed on the basis of experimental findings.
Nozaki, Mikito*; Ito, Joyo*; Asahara, Ryohei*; Nakazawa, Satoshi*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*
Applied Physics Express, 9(10), p.105801_1 - 105801_4, 2016/10
Interface reactions between Ti-based electrodes and n-type GaN epilayers were investigated by synchrotron radiation X-ray photoelectron spectroscopy. Metallic Ga and thin TiN alloys were formed at the interface by subsequently depositing Al capping layers on ultrathin Ti layers even at room temperature. By comparing results from stacked Ti/Al and single Ti electrodes, the essential role of Al capping layers serving as an oxygen-scavenging element to produce reactive Ti underlayers was demonstrated. Further growth of the metallic interlayer during annealing was observed. A strategy for achieving low-resistance ohmic contacts to n-GaN with low-thermal-budget processing is discussed.
Qiu, Z.*; Hou, D.*; Kikkawa, Takashi*; Uchida, Kenichi*; Saito, Eiji
Applied Physics Express, 8(8), p.083001_1 - 083001_3, 2015/08
Haku, Satoshi*; Tashiro, Takaharu*; Nakayama, Hiroyasu*; Ieda, Junichi; Entani, Shiro; Sakai, Seiji; Ando, Kazuya*
Applied Physics Express, 8(7), p.073009_1 - 073009_3, 2015/07
We found that the spin pumping in a NiFe/Pt bilayer is strongly suppressed by inserting single-layer graphene (SLG) at the interface. The spin pumping in the NiFe/Pt bilayer enhances the magnetization damping of the ferromagnetic layer, which is quantified from microwave frequency dependence of ferromagnetic resonance linewidth. We show that the enhancement of the magnetization damping due to the spin pumping disappears in a NiFe/SLG/Pt trilayer. This result indicates that the spin pumping is blocked by the atomic monolayer, demonstrating the crucial role of the interfacial short-range spin-exchange coupling in the spin pumping in metallic systems.
Okada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Yamada, Yoichi*; Sasaki, Masahiro*
Applied Physics Express, 8(2), p.025701_1 - 025701_4, 2015/02
We studied the surface oxidation on a Ge(111)-c(28) surface at room temperature using supersonic oxygen beams as a function of the translational energy of the incident oxygen molecules ranging from 26 meV to 2.3 eV. In situ synchrotron photoemission spectroscopy performed during the oxidation revealed that the surface oxidation terminated with the formation of a sub-monolayer oxide of at most 0.52 ML, for all the beam energies examined. In addition, the oxidation state of the surface oxides was found to depend on the translational energy. These results demonstrate the precise chemical control of the ultrathin surface oxides of Ge(111)-c(28).
Yoshida, Kensuke*; Fujioka, Shinsuke*; Higashiguchi, Takeshi*; Ugomori, Teruyuki*; Tanaka, Nozomi*; Ohashi, Hayato*; Kawasaki, Masato*; Suzuki, Yuhei*; Suzuki, Chihiro*; Tomita, Kentaro*; et al.
Applied Physics Express, 7(8), p.086202_1 - 086202_4, 2014/08
We demonstrate high conversion efficiency for extreme ultraviolet (EUV) emission at 6.5-6.7 nm from multiple laser beam-produced one-dimensional spherical plasmas. Multiply charged-state ions produce strong resonance emission lines, which combine to yield intense unresolved transition arrays in Gd, Tb, and Mo. The maximum in-band EUV conversion efficiency was observed to be 0.8%, which is one of the highest values ever reported due to the reduction of plasma expansion loss.
Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Ieda, Junichi; Haruki, Rie*; Okayasu, Satoru; Maekawa, Sadamichi; Yasuoka, Hiroshi; Saito, Eiji
Applied Physics Express, 7(6), p.063004_1 - 063004_4, 2014/06
A magnetic field is predicted to emerge on a particle in a rotating body even if the body is electrically neutral. This emergent field is called a Barnett field. We show that nuclear magnetic resonance (NMR) enables direct measurement of the Barnett field in solids. We rotated both a sample and an NMR coil synchronously at high speed and found an NMR shift whose sing reflects that of the nuclear magnetic moments. This result provides direct evidence of the Barnett field. The use of NMR for Barnett field measurement enables the unknown signs of nuclear magnetic moments in solids to be determined.
Fukaya, Yuki; Maekawa, Masaki; Kawasuso, Atsuo; Mochizuki, Izumi*; Wada, Ken*; Shidara, Tetsuo*; Ichimiya, Ayahiko*; Hyodo, Toshio*
Applied Physics Express, 7(5), p.056601_1 - 056601_4, 2014/05
no abstracts in English
Oyama, Tomoko; Nakamura, Hirotaka*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
Applied Physics Express, 7(3), p.036501_1 - 036501_3, 2014/03
A chlorinated polymer ZEP is a main-chain scission type (positive-tone) high-sensitivity resist. However, we found that ZEP changes to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100 kV electron beam as a dual-tone are evaluated with various developers. Owing to different solvation strengths, the resist sensitivity varied with different developers in the positive-tone region. On the other hand, it was found that the threshold dose for the positive-negative inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, we found that the amount of chlorine atoms and terminal double bonds generated by chain scission determines the threshold of the P-N inversion. This result provides important information for possible ZEP applications such as a dual-tone resist.
Iguchi, Ryo*; Sato, Koji*; Hirobe, Daichi*; Daimon, Shunsuke*; Saito, Eiji
Applied Physics Express, 7(1), p.013003_1 - 013003_4, 2014/01
We investigate a dc rectification effect of magnetization dynamics based on spin Hall magnetoresistance (SMR) in an insulating magnet/metal system on spin pumping measurements. We theoretically find that the rectification effect by SMR has different in-plane magnetization angle dependence from that of the inverse spin Hall effect on the spin pumping. The negligible contribution from the rectification effect is experimentally confirmed in a cavity measurement.