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| 1.
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Nakata, Shunji ; Maeda, Ryoji ; Kawae, Takeshi ; Morimoto, Akiharu ; Shimizu, Tatsuo
概要:
A thin-film structure comprising Al2O3/Al-rich Al2O3/SiO2 was fabricated on Si substrate. We used radio-frequency magnet
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ron co-sputtering with Al metal plates set on an Al2O3 target to fabricate the Al-rich Al2O 3 thin film, which is used as a charge storage layer for nonvolatile Al2O3 memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al2O3 is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 1018 cm-3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory. © 2011 Elsevier B.V. All rights reserved.
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| 2.
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Zhou, Jiang-Huai ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />We report on a detailed investigation of the spatial distribution of dangling b
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onds (DB's) in light-soaked hydrogenated amorphous silicon (a-Si:H) films. The results for light soaking at different light intensities (3 W/cm2 and 300 mW/cm2) show that the inverse power-law DB distribution, Nυ(x)=Cυx-α, holds regardless of the light soaking intensity. Here, Nυ(x) is the volume density of DB's at depth x measured from the surface, and Cυ and α(≈0.6) are constants. The nonuniform spatial distribution of DB's in light-soaked a-Si:H is thought to originate from a nonuniform distribution of photocarriers during light soaking rather than from an inhomogeneity of the material. The same annealing behavior of light-induced DB's was observed regardless of the thickness of the sample and regardless of whether the sample was light soaked from one side or from both sides. This result, together with the observation of identical spin characteristics, indicates that the light-induced DB's at various depths of a given a-Si:H sample are identical in nature. The surface DB density is found to be much less sensitive to light soaking than the bulk DB density and can be assumed unchanged if the light-soaking intensity is not much higher than 300 mW/cm2 and the light-soaking time is shorter than ∼10 h. We show that the conventional method of estimating the surface DB density is no longer appropriate for light-soaked a-Si:H, due to the highly nonuniform distribution of DB's in the material. The nonuniform distribution of DB's can lead to significant disagreements between different techniques in quantifying the Staebler-Wronski effect and should therefore be taken into account in studies of the SW effect.
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| 3.
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Morimoto, Akiharu ; Takezawa, Katsuhito ; Minamikawa, Toshiharu ; Yonezawa, Yasuto ; Shimizu, Tatsuo
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金沢大学工学部<br />The effect of ambient gas on the preparation of YBa2Cu3Ox (YBCO) high-Tc superconducting thin films by puls
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ed laser ablation was explored in gas mixtures of argon+oxygen, argon+nitrous oxide, and nitrous oxide+oxygen. These experiments revealed that a reducing environment for the preparation of YBCO films enhances the film growth with the high temperature phase (trilayered perovskite YBCO) rather than the low temperature phase (cubic YBCO). This phenomenon is explained in terms of thermodynamic phase diagram. The effect of nitrous oxide on the thermodynamic phase diagram is far smaller than that of oxygen by a factor of two to three orders of magnitude.
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| 4.
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Morimoto, Akiharu ; Shigeno, Hideki ; Morita, Shinya ; Yonezawa, Yasuto ; Shimizu, Tatsuo
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金沢大学工学部<br />The effect of ambient N2 gas on the preparation of Ti0.9Al0.1N (TAN) thin films for ferroelectric capacitor
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s by pulsed laser ablation (PLA) using ArF and KrF excimer lasers was explored. The TAN films were prepared on (100)Si substrates heated at 620°C in various N2 pressures ranging from vacuum to 130 Pa. The TAN crystal growth was found to be influenced by the content of unintentionally incorporated O which was found to be controlled by the introduction of N2 gas into the deposition chamber. The O content for films prepared by KrF was found to be smaller than that for films prepared by ArF. This was due to the smaller optical absorption cross-section of KrF excimer laser for residual O2 or H2O molecules in the chamber and/or the higher deposition rate. The TAN film prepared by KrF excimer laser was found to be nearly epitaxial Si with a cube-on-cube crystallographic orientation.
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| 5.
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Yonezawa, Yasuto ; Matsuda, Kazuko ; Morimoto, Akiharu ; Shimizu, Tatsuo
概要:
金沢大学工学部<br />Bi-iron garnet(BIG) firms were prepared using Bi-substituted Y-iron-garnet(Bi:YIG) template layer on platin
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ized Si. First, Bi:YIG template layer was prepared on the platinized (100)Si (Pt/Ti/Sio2/Si) by PLA deposition and successive rapid thermal annealing (RTA). Then Bi3Fe5O12 firm was grown on the template layer by PLA. The Bi3Fe5O12 firm deposited was found to have a garnet (BIG) phase by X-ray diffraction measurement. For the BIG firm, the saturated magnetization and the Faraday rotation were characterized and discussed.
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| 6.
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Nádaždy, V. ; Durń, R. ; Thurzo, I. ; Pinčík, E. ; Nishida, A. ; Shimizu, J. ; Kumeda, Minoru ; Shimizu, Tatsuo
概要:
金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />Results of charge deep-level transient spectroscopy (DLTS) and electron spin re
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sonance (ESR) measurements on undoped hydrogenated amorphous silicon (a-Si:H) clearly demonstrate that a group of gap states with a mean energy of 0.82 eV as observed in charge DLTS experiments for a-Si:H based metal/oxide/semiconductor structure is the same as the g=2.0055 ESR defect (the Dz component). This correlation provides a distinct marker for charge DLTS technique. We obtained a very good fit to spectra obtained on undoped a-Si:H in the annealed state whilst there is some discrepancy between the experimental and simulated spectra for the light-soaked state. The first quantitative comparison of defect pool model with gap states directly observed by charge DLTS offers not only additional data for more accurate identification of all the intrinsic and light-induced defects. This also renders distinct counter-evidence to recently published conjectures about the creation of another charged defect during early stage of Staebler-Wronski effect. By contrast, our presented results clearly argue for opposite process, i.e., decay of positively charged defect states Dh.
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| 7.
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Morimoto, Akiharu ; Maeda, Yoshimi ; Shimizu, Tatsuo ; Yonezawa, Yasuto ; Minamikawa, Toshiharu
概要:
金沢大学工学部<br />Yttrium iron garnet (YIG) films were grown by pulsed laser ablation (PLA) on (111) Gadolinium Gallium Garne
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t (GGG) substrates. The second harmonic of YAG laser (532 nm) with a high laser fluence was employed to produce YIG droplets efficiently. It was found that YIG films prepared at RT substrates have a large number of solidified droplets of various sizes. Highly oriented YIG crystals were grown on the (111) GGG substrate heated at 860°C by PLA using a large number of molten droplets, suggesting an LPE-like growth. This YIG film shows a small ferrimagnetic resonance linewidth of 7.5 Oe. This value is quite small for films prepared by vapor-phase epitaxy techniques. © Springer-Verlag 1999.
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| 8.
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Kumeda, Minoru ; Sekizawa, Yoshitaka ; Morimoto, Akiharu ; Shimizu, Tatsuo
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金沢大学大学院自然科学研究科電子物性デバイス<br />金沢大学工学部<br />The crystal-field potential at the Er3+ ion surrounded by six oxygen ions is ex
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panded in terms of polynomials. After converting it into equivalent angular momentum operators, the Stark-splitting of the 4I15/2 ground state of the Er3+ ion is calculated. Influence of the change in the environment of the Er3+ ion on the shift of the energy levels is investigated and compared with the observed Er photoluminescence spectrum in a-Si:H. The scattering of the calculated energy levels by the structural fluctuation around the Er 3+ ion is also compared with the linewidth of the component photoluminescence lines. © 2006 Materials Research Society.
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| 9.
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Morimoto, Akiharu ; Takizawa, Hidetoshi ; Yonezawa, Yasuto ; Kumeda, Minoru ; Shimizu, Tatsuo
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金沢大学工学部<br />Silicon oxide films were prepared at room temperature by pulsed laser ablation using an ArF or KrF excimer
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laser in a gas mixture of He and O2. The effect of an ArF excimer laser irradiation on the deposited film was investigated. As-deposited transparent films containing Si crystallites with sizes greater than 10 nm show photoluminescence. However, after laser irradiation with 1000 shots, the photoluminescence (PL) intensity was increased by two orders of magnitude. The PL spectrum is centered around 570 nm (2.2 eV). The origin of the large PL enhancement is discussed
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| 10.
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Yonezawa, Yasuto ; Minamikawa, Toshiharu ; Matsuda, Kazuko ; Takezawa, Katsuhito ; Morimoto, Akiharu ; Shimizu, Tatsuo
概要:
金沢大学工学部<br />Volume and size distribution of droplets in oxide films were investigated for a variety of laser fluences,
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wavelengths and target temperatures. Effects of both the ambient gas pressure and the substrate temperature on the droplet formation was investigated. It was found that the increase in the ratio of the droplet volume to the film volume Vd/Vf caused by increasing the maximum etching depth of target per laser shot de (Vd/Vfde3, as previously reported) due to changes in the deposition conditions other than the target temperature is mainly attributed to an increase in the formation of large droplets. It was also found that the correlation Vd/Vfde3 is also valid for elevated target-temperatures, and the increase in the target temperature enhances the formation of small droplets compared with large ones. The effect of cooling of droplets after the ejection from the target due to the ambient pressure and/or the substrate temperature is discussed.
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