Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Flexible, light-weight and robust thermoelectric (TE) materials have attracted much attention to convert waste heat from low-grade heat sources, such as human body, to electricity. Carbon nanotube (CNT) yarn is one of the potential TE materials owing to its narrow band-gap energy, high charge carrier mobility, and excellent mechanical property, which is conducive for flexible and wearable devices. Herein, we propose a way to improve the power factor of CNT yarns fabricated from few-walled carbon nanotubes (FWCNTs) by two-step method; Joule-annealing in the vacuum followed by doping with p-type dopants, 2,3,5,6-tetrafluo-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Numerical calculations and experimental results explain that Joule-annealing and doping modulate the electronic states (Fermi energy level) of FWCNTs, resulting in extremely large thermoelectric power factor of 2250 µW m⁻¹ K⁻² at a measurement temperature of 423 K. Joule-annealing removes amorphous carbon on the surface of the CNT yarn, which facilitates doping in the subsequent step, and leads to higher Seebeck coefficient due to the transformation from (semi) metallic to semiconductor behavior. Doping also significantly increases the electrical conductivity due to the effective charge transfers between CNT yarn and F4TCNQ upon the removal of amorphous carbon after Joule-annealing.

DOI： 10.1038/s41598-020-64435-0

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Other Link： https://www.nature.com/articles/s41598-020-64435-0

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/1.5127993

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© 2019 Carbon nanotube (CNT) yarns comprise few-walled CNTs (FWCNTs), mainly consisting of double- and triple-walled CNTs, and have several properties which are beneficial for practical bulk-scale carbon devices. These features include high tensile strength, electrical conductivity, thermal conductivity, chemical stability, and environmental tolerance. However, the synthesis window for fabricating CNT yarns with FWCNTs by the dry-spinning method is quite narrow and optimal conditions have yet to be determined. In this study, we fabricated CNT forests mainly comprised of FWCNTs at various synthesis conditions (temperature and time). The drawability of the CNT forests was characterized depending on the synthesis conditions. Our results show that optimum values exist for continuously drawable CNT forests in terms of both their height (>130 μm) and bulk density (>90 mg/cm3) for satisfying enough entanglement force between the CNT bundles. The diameter and number of walls of the CNTs are controlled by the temperature during the formation of catalyst particles because the sizes of catalyst particles are approximately equal to the outer diameter of CNTs. All temperature conditions in the range 350–500 °C, used to form catalyst particles, resulted in a drawable FWCNT forest. These insights will be useful for developing devices based on FWCNT yarns.

DOI： 10.1016/j.carbon.2019.11.038

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/ACSAEM.9B01736

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpca.8b08455

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We fabricated thermally driven metal-free soft-actuators consisting of poly(ethylene terephthalate) (PET) threads as the actuator and carbon nanotube (CNT) yarns as the heating source. The mechanical force, displacement, and response behavior of various structures of the coil-shaped soft-actuators were characterized. The actuation performance of the soft-actuators containing a homogeneous arrangement of PET threads and CNT yarns in their cross-sectional profile was the highest. The results of the calculations based on the heat diffusion equations indicated that inhomogeneous heat generation in the soft-actuator causes parts of the actuator to remain unheated and this interferes with the mechanical motions. Homogeneous thermal distribution in the soft-actuators, namely, the use of a multifilament structure, yields the highest performance in terms of the mechanical force and displacement. (C) 2018 Author(s).

DOI： 10.1063/1.5033487

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We studied the dynamics of the expansion of a Shockley-type stacking fault (SSF) with 30° Si(g) partial dislocations (PDs) using a scanning electron microscope. We observed SSFs as dark lines (DLs), which formed the contrast at the intersection between the surface and the SSF on the (0001) face inclined by 8° from the surface. We performed experiments at different electron-beam scanning speeds, observing magnifications, and irradiation areas. The results indicated that the elongation of a DL during one-frame scanning depended on the time for which the electron beam irradiated the PD segment in the frame of view. From these results, we derived a formula to express the velocity of the PD using the elongation rate of the corresponding DL during one-frame scanning. We also obtained the result that the elongation velocity of the DL was not influenced by changing the direction in which the electron beam irradiates the PD. From this result, we deduced that the geometrical kink motion of the PD was enhanced by diffusing carriers that were generated by the electron-beam irradiation.

DOI： 10.1063/1.5010861

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this article, we report C60 Fullerene Nano Cylindrical Tubes (FNCT). The FNCTs were synthesized by a liquid-liquid interface precipitation (LLIP) method using m-Xylene as a saturating solvent and TBA (Tetra butyl alcoholic) as precipitation agent leading to the formation of FNCTs with uniquely structured and well oriented size and shape. The experiment was conducted in a closed atmosphere maintaining a low temperature. The main advantage of these structures is that they are stable up to 5 months in normal room temperature. Characterizations were done to the FNCTs and concluded to have applications in the field of electronics. Enhanced semiconducting properties have been observed in the nanostructures which can be used in the application of solar cells, FET transistors, etc.

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Corresponding author  

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Authorship：Corresponding author  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We studied the effects of antimony (Sb) doping on strain relaxation in a silicon germanium (SiGe) epitaxial film on a silicon substrate. Misfit strain relaxation proceeded faster in the Sb-doped SiGe than in the undoped film. However, the degree of enhancement did not correspond to the Sb concentration of the SiGe film below 700 degrees C. This was not expected from the effects of Sb on the threading dislocation velocity, which is larger in SiGe films with a higher Sb concentration. The results indicate that dislocation nucleation rather than the dislocation velocity had a substantial effect at low temperatures. On the other hand, relaxation was enhanced in the heavily Sb-doped film at 900 degrees C. We consider that this may be attributed to the enhancing effects of dislocation motion.

DOI： 10.1063/1.4865617

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

A Large-scale integration (LSI) has been improved by scaling contraction. Strained Si has been proposed as a higher carrier mobility than usual. We have evaluated the strained SiGe wafer by LTEM, which is a method of analyzing to detect THz waves generated by fs laser irradiated into the sample. © 2013 IEEE.

DOI： 10.1109/IRMMW-THz.2013.6665819

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

We have observed five electron traps with energy levels at 0.16, 0.30, 0.40, 0.53 and 0.67 eV below the conduction band in Pd and H doped Si by DLTS technique. Successive annealing at 373 K and 473 K for 30 min respectively caused two levels at E-c-0.16 eV and E-c-0.67 eV to disappear and simultaneously a new level to emerge at E-c-0.19 eV. From such annealing behavior and the comparison of the energy levels observed in the present study with those in the literature, we assign them to various Pd and H related defects as follows, Pd-H-2: E-c-0.16 eV and E-c-0.67 eV, Pd acceptor: E-c-0.19 eV, Pd-H-3: E-c-0.30 eV, Pd-H-1: E-c-0.40 eV.

DOI： 10.4028/www.scientific.net/MSF.725.213

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We have investigated a palladium-hydrogen complex in silicon by electron spin resonance (ESR) measurement. A new ESR spectrum was detected in a sample diffused with palladium and hydrogen. The hyperfine structure of hydrogen atoms in the ESR spectrum shows that the spectrum originates from a palladium-hydrogen complex containing three hydrogen atoms (Pd-H(3)). The anisotropic g-value of Pd-H(3) shows that the Pd-H(3) complex has an anisotropic character of orthorhombic (C(2v)) symmetry. The calculated g-values of the Pd-H(3) complex are g(1) 2.12, g(2) = 2.10, and g(3) = 2.03, and the g(2) axis is along the (100) direction. The anisotropic character of orthorhombic (C(2v)) symmetry results from a configuration consisting of one Pd atom at a substitutional site, two equivalent hydrogen atoms at interstitial sites along the (111) direction, and one hydrogen atom at the next-nearest-neighbor interstitial site along the (100)-twofold symmetry axis. We have also studied the dissociation of a platinum-hydrogen complex by thermal treatment. The activation energy for the dissociation of the Pd-H(3) complex is estimated to be about 1.6eV. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.091301

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We have investigated a chromium-platinum pair in silicon by electron spin resonance measurement. A new ESR spectrum originating from a chromium-platinum pair has been detected in both n- and p-type silicons diffused with chromium and platinum. The anisotropic g-tensor obtained by analyzing the angular dependence of the ESR spectrum shows a monoclinic (C(1h)) symmetry with g-values of g(1) = 4.67, g(2) = 2.99, and g(3) = 1.80. The g(1) axis is along the (110) direction. The g(2) and g(3) axes are perpendicular to the g(1) axis, and the g(2) axis is rotated from the (100) direction to the (111) direction at an angle of 20 degrees. The anisotropic character of monoclinic (C(1h)) symmetry results from the nearest-neighbor configuration consisting of a Pt atom at a substitutional site distorted by the displacement of Pt along the (100) direction and a Cr atom at the nearest-neighbor interstitial site. The ESR measurement under illumination suggests that a chromium-platinum pair forms a donor like electron trap level. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.081302

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WILEY-V C H VERLAG GMBH  

We have studied stress-induced splitting and shift of an infrared (IR) absorption line at 1880.7 cm(-1) of the Pt-H-1 complex in Si by Fourier-transform IR (FT-IR) spectroscopy at 10K combined with the application of uniaxial compressive stress up to 0.4 GPa. The line was split into two and three components under < 100 > and < 111 > stresses with intensity ratios of low- to high-wavenumber components being 1: 2 and 1: 1: 2, respectively. These results are consistent with C-1h symmetry in the piezospectroscopic theory of Kaplyanskii and the ESR results observed by Mchedlidze et al. Under < 110 > stress, however, the line was split only into two components, contradicting C-1h symmetry. Such inconsistency may be due to insufficient magnitude of stress. The split components were shifted linearly with increasing stress in the three directions. The isotope effects were observed for the Pt-H-1 complex. By replacing H with D, the IR line was shifted to 1358.5 cm(-1) and the < 100 > stress dependence of peak wavenumbers of two split components was weakened by a factor of 0.7. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201000118

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We demonstrated that remote hydrogen plasma treatment on silicon ring resonators can smooth the Si waveguides at lower than 100°C. This also provides a promising way to trim resonators for a designed add/drop wavelength. © 2011 IEEE.

DOI： 10.1109/GROUP4.2011.6053727

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Electronic levels in polycrystalline Si (pc-Si) substrates for solar cells were studied by means of deep level transient spectroscopy (DLTS). A broad peak was observed at around 250 K when samples with grain boundaries (GBs) were thermally treated. The origin of this peak was investigated and we conclude that it is attributed to Cu contaminants gathered around GBs. We found interesting character of this peak. The peak intensity became small by annealing with reverse-biased voltage on the Schottky junction and it was recovered after keeping the sample at room temperature for several days. We explained this character as bistability of the center depending on its charge state. From the application viewpoint, we tried remote hydrogen-plasma treatment and could annihilate the peak. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.08.227

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A different Pd-related defect from a substitutional Pd with (C(2v)) symmetry was detected by ESR measurement. New ESR signal of the Pd-related defect showed different g-value and symmetry from those of the substitutional Pd. The Pd-related defect has anisotropic character of monoclinic (C(1h)) symmetry. The calculated g-values are g(1) = 1.97, g(2) = 2.03, g(3) = 2.16, and the g(1) axis is along < 110 > direction. The g(2) and g(3) axes are perpendicular to the g(1) axis, and the g(2) axis is rotated from < 100 > to < 111 > direction at the angle of 51 degrees. In addition to the Pd-related defect, we have found other ESR signals in Pd and hydrogen-diffused Si. The ESR signals showed the hyperfine structure of hydrogen. Therefore, it is though that the ESR signals are originated from Pd H complex defect. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.08.141

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOCIETY APPLIED PHYSICS  

We have studied the stress-induced splitting and shift of infrared (TR) absorption lines of platinum-hydrogen complexes in Si by Fourier-transform IR (FT-IR) spectroscopy at 10 K combined with the application of uniaxial stress. We observed several peaks at 1873.0, 1880.7, 1891.8, 1922.3, 1929.9, and 1943.0 cm(-1). These peaks may be due to the previously observed local vibrational modes (LVMs) of various platinum-hydrogen complexes, that is, the anti symmetric-stretching mode of (Pt-H(2))(0), the LVM of (Pt-H(1))(0), the symmetric-stretching mode of (Pt-H(2))(0), LVMs of (Pt-H(3))(-) and (Pt-H(3))(0), and the LVM of an unidentified platinum-hydrogen complex, respectively. The peaks of (Pt-H(1))(0) and (Pt-H2)0 split into two components under < 100 > compressive stress, while those of (Pt-H(3))(-) and (Pt-H(3))(0) did not split. We measured the stress dependence of the two split components of the (Pt-H(1))(0) peak. The low-wavenumber component shifted by -3.2cm(-1)/GPa, and the highwavenumber component shifted by 4.2 cm(-1)/GPa. We show that these wavenumber shifts are equal to the piezospectroscopic tensor elements, A, and A?, respectively. We propose a structural model of the Pt-H(1) complex, where a hydrogen atom is bonded to one of four Si neighbors of the Pt atom in the {110} mirror plane perpendicular to the < 110 > symmetric axis with C(1h) symmetry.

DOI： 10.1143/JJAP.47.4392

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We briefly review our recent results of the strain effects on photoluminescence (PL) properties of Er in tensile strained Si on a SiGe layer (Si:Er:O/SiGe) and compressively strained SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy, and present new results of electroluminescence (EL) properties of Er in homo- and hetero-epitaxially grown p-i-n diodes (p-Si/i-Si:Er:O/n-Si, p-SiGe/i-SiGe:Er:O/n-Si), where we grew an intrinsic Si or SiGe layer doped with Er and oxygen on an n-type Si substrate and subsequently grew a p-type Si or SiGe top layer. We observed Er-related PL around 1.54 mu m at 77 K in both tensile and compressively strained samples. The PL intensity of these strained samples was much stronger than that of unstrained (Si:Er:O/Si) samples. Moreover, we still observed intensive PL in strained samples even with low Er concentrations far below 10(18) cm(-3), at which unstrained samples showed only weak or no luminescence. Such enhancing effects strongly suggest that the probability of Er optical transition can be enhanced by the presence of both tensile and compressive strains. We also observed Er-related PL and EL around 1.54 mu m at 77 K in the p-i-n diodes, and found that annealing at 800 degrees C increased both of PL and EL intensities. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2007.07.024

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We have studied effects of hydrogen treatment on the resistivity profile of the SiGe/Si episystem by spreading resistance (SR) method. In this paper, we present experimental findings that hydrogen treatment reduces the resistivity at a specific part in the Si substrate region. This position was confirmed to be under the interface between SiGe and Si that emerged on the bevel surface during hydrogen treatment. We investigated the depth of resistivity-reduced regions which was formed by various hydrogenating conditions and found that the region was extended to the same depth as the penetration depth of hydrogen. We concluded that the low-resistivity region was formed under the influence of hydrogen introduced from bevel surface. We attributed this resistivity reduction to formation of some defects which originally existed at the interface and diffused into Si substrate with hydrogen. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.08.150

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We have studied the effects of water vapor remote plasma treatment (H2O RPT) on emission from Si-doped and undoped n-type GaN films grown on c-face sapphire substrates by the atmospheric-pressure metalorganic chemical vapor deposition method. We found by photoluminescence (PL) spectroscopy at 77K that H2O RPT enhanced violet emission from the n-type GaN films, similarly to the previously observed enhancing effect on blue emission from Mg-doped p-type GaN films. We also observed that H2O RPT reduced the intensity of ESR signal comprising of two peaks detected at 4.2 K in undoped n-type films and increased their resistivity measured at room temperature. We ascribe the enhancing effect of H2O RPT to the passivation of non-radiative recombination centers by hydrogen produced by H2O RPT. We formed GaN p-n diodes from the layer structure of p-GaN:Mg/n-GaN:Si/sapphire, and carried out electroluminescence (EL) measurements of the diodes at 77 K. We observed that EL intensity was also enhanced by H2O RPT. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.08.180

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We investigated the resistivity depth profile of an episystem of a SiGe film on a Si substrate, which was hydrogen-treated by remote plasma by the spreading resistance method. We examined hydrogen penetration by monitoring the resistivity change of the Si substrate due to acceptor passivation by hydrogen. We found that the resistivity of the Si substrate covered by an as-grown SiGe film was not elevated. This indicates that it is extremely difficult for hydrogen atoms to penetrate strained SiGe epi-films. On the other hand, hydrogen atoms can easily penetrate Si films and annealed SiGe films. These results are presumably explained by the misfit strain of epifilms.

DOI： 10.1143/JJAP.46.1622

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We have studied the local motion of hydrogen around a platinum impurity in Si, which was directly probed by measuring the recovery process of stress-induced reorientation of the Pt-H-2 complex by isothermal deep-level transient spectroscopy (IT-DLTS), We found that hydrogen more easily moved in the singly negative charge state of the Pt-H-2 complex than in the doubly negative charge state, and determined the activation energies for the recovery process to be 0.28 and 0.4 eV in the singly and doubly negative charge states, respectively, from a series of isothermal annealing experiments. We also found that the recovery rate of the Pt-D-2 complex in the singly negative charge state is 80% that of the Pt-H-2 complex with the same activation energy of 0.28 eV. This isotope effect clearly proves that both complexes have the same atomic configuration and that their recovery process is governed by the atomic jump of hydrogen (deuterium).

DOI： 10.1143/JJAP.46.907

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We review our recent results and analyses of the effects of uniaxial compressive stress on the electronic states and atomic configurations of a platinum-dihydrogen (Pt-H-2) defect in Si, and discuss the results on the basis of the structural model that we proposed. We applied a technique of isothermal deep-level transient spectroscopy (IT-DLTS), combined with the application of uniaxial compressive stress. Our experiments showed that (111) and (10 0) stresses split the IT-DLTS peak of the Pt-H2 defect into two components, and a (110) stress split it into three components. Such a splitting pattern and the observed intensity ratios of split components uniquely determined that the defect had C-2v,C- symmetry, on which our structural model was based. We found that the electronic levels corresponding to split components varied linearly with (111) stress. Subtracting the stress shift of the conduction band minima, we have obtained 36 +/- 4 meV/GPa as a net increase in energy for the level with the higher energy with respect to the applied stress. This result strongly suggests that compressive stress raises the energy of the Pt-H-2 level, indicating its antibonding character. We observed that the Pt-H-2 defect was aligned above 80 K under uniaxial stress to the configuration with the higher electronic level. This indicates that the stress-induced increase of level energy was overcome by the energy gain due to electronic bonding and atomic relaxation, resulting in the decrease of the total energy of the Pt-H-2 defect system. We found that the intensity ratio of split components of the IT-DLTS peak was described by a Boltzmann factor, where the activation energy is proportional to the magnitude of the applied stress up to 0.4 GPa with a proportional factor, 49 meV/GPa, from which we determined an element A3 of the piezospectroscopic tensor to be -37 meV/GPa. (c) 2006 Elsevier BX All rights reserved.

DOI： 10.1016/j.mseb.2006.06.037

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We report that the resistivity of SiGe films deposited on a B-doped Si substrate by solid-source molecular beam epitaxy (MBE) is reduced by postgrowth hydrogen treatment and the subsequent annealing. This effect was observed near a bevel surface finished by mechanical polishing. Therefore, the damaged surface layer played an important role in this effect. The same reduction in the resistivity of the SiGe films was also observed by intentional supplying hydrogen during film deposition. These phenomena indicate that hydrogen assists the electrical activation of boron.

DOI： 10.1143/JJAP.45.3994

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We have studied the local motion of hydrogen around platinum in Si from the recovery kinetics of stress-induced reorientation of the Pt-H-2 Complex. We evaluated the degree of alignment using isothermal DLTS (IT-DLTS) technique under a stress of 0.6 GPa along the &lt; 111 &gt; direction at 70 K where hydrogen Could not move. We observed the recovery at temperatures of 80-85 K only in the singly negative charge state of the Pt-H-2 complex, indicating the similar charge-state-dependent motion of hydrogen as in the stress-induced reorientation of the complex. We obtained an activation energy of 0.25 eV for the recovery process, being comparable with that for the stress-induced reorientation. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.022

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We have studied stress-induced reorientation of the Pt-H-2 complex in Si using isothermal deep-level transient spectroscopy (IT-DLTS) technique under uniaxial compressive stress. We have found that the intensity ratio of split components of the IT-DILTS peak for various magnitudes of applied stress up to 0.4 GPa is described by a Boltzmann factor, where the activation energy is proportional to the magnitude of the applied stress. The proportional factor is connected to an element of the piezospectroscopic tensor. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.021

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Effects of hydrogen treatment on post-growth strain relaxation of GeSi epitaxial films on Ge substrate were studied. We found that pre-hydrogen treatment at room temperature enhanced strain relaxation during subsequent thermal treatment. We also confirmed that the relaxation enhancement effect became small as the annealing time was elongated and the temperature was raised. These results mean that the effect is more remarkable in the early stage of relaxation. In order to investigate the mechanism of this effect, threading dislocation velocity was measured. However, it was not enhanced by pre-hydrogenation. This fact strongly suggests that the relaxation enhancement effect was caused by increase of dislocation sources, which are attributed to hydrogen atoms incorporated into GeSi film. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.054

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We studied on the photoluminescence (PL) properties of Er in tensile-strained Si on a SiGe layer (Si:Er:O/SiGe) and compressively strained SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy (MBE). Er-related luminescence was observed around 1.54 mu m in both tensile- and compressively strained samples. The PL intensities of strained Si:Er:O/SiGe and SiGe:Er:O/Si samples were much stronger than those of unstrained Si:Er:O/Si samples. Moreover, intensive luminescence was observed in strained samples with low Er concentrations far below 10(18)CM(-3). The PL spectra of Si:Er:O/SiGe samples were broader than those of unstrained Si:Er:O/Si samples. On the other hand, no significant differences in the width between SiGe:Er:O/Si and unstrained samples were observed. These differences in the PL intensity between strained and unstrained samples strongly suggest that the optical activation of Er in Si and SiGe can be enhanced by the presence of strain. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.031

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We investigated a Pt-Pt pair in Si by electron spin resonance (ESR) measurement. Two kinds of ESR spectra from Pt-Pt pairs which had been already reported were not detected. However, we observed other ESR spectrum of Pt-Pt pair. The ESR spectrum showed the hyperfine structure corresponding to two equivalent Pt atoms. The anisotropic g-tensor obtained by analyzing the angular dependence of the ESR signals indicated the orthorhombic (C-2 nu) symmetry with the g-values of g(x) = 2.11, g(y), = 2.3 1, g(z) = 2.09. The g(z) axis was along [001] direction. The g(y) and g(z) axes were along [110] and [1 (1) over bar0] directions, respectively. The ESR spectrum of Pt-Pt pair was observed in the sample only tinder illumination. This Suggests that a change in the charge state of Pt-Pt pair is caused by carrier excitation. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.12.024

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We have found for the first time that blue emission from Mg-doped GaN was greatly enhanced by remote plasma treatment (RPT) with plasma containing atomic hydrogen, in particular, water vapor plasma, at low temperatures of 300-400 degrees C. The highest enhancing factor was twenty, achieved by water vapor RPT at 400 degrees C for 30 min. The enhanced blue emission was stable up to 500 degrees C, similarly to blue emission from as-grown samples, suggesting the same origin and mechanism. We have confirmed that the emission mechanism is donor-acceptor pair (DAP) recombination, and have concluded that RPT produces a hydrogen-related donor level at E-c - 0.37 eV involved in the DAP emission.

DOI： 10.1143/JJAP.44.L926

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We studied the change in the 3d-shell configurations of Fe in B-doped Si under illumination by electron spin resonance (ESR) measurement. ESR signals originating from Fe-i(+)(3d(7)) and Fe-i(0)(3d(8)) were observed in Fe- and B-doped Si. The ESR signal of Fe-i(+)(3d(7)) disappeared and the signal intensity of Fe-i(0)(3d(8)) increased under illumination. These changes of the ESR signals under illumination were caused by the change in the charge state from Fe-i(+)(3d(7)) to Fe-i(0)(3d(8)) due to the capture of an electron. Subsequently, the process of recovery from Fe-i(0)(3d(8)) to Fe-i(+)(3d(7)) due to the capture of a hole was observed after the light was turned off. We found that the relaxation time from Fe-i(0)(3d(8)) to Fe-i(+)(3d(7)) was approximately 30 s at 8 K. This was much longer than the lifetime of a free hole.

DOI： 10.1143/JJAP.43.9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have combined isothermal deep-level transient spectroscopy (IT-DLTS) technique with the application of uniaxial compressive stress along &lt;111&gt; direction to study the effect of stress on the electronic state of a platinum-dihydrogen complex in Si and the kinetics of charge-state-dependent motion of hydrogen around the Pt atom during stress-induced reorientation. We have found that the application of stress splits the IT-DLTS peak into two components and the electronic energy of the short-time component increases linearly with &lt;111&gt; compressive stress as 35+/-4 meV/GPa, indicating antibonding character. We have also studied the reorientation kinetics of the complex under the applied stress, and have found that the defect aligned at 78-88 K in the configuration with the smallest activation energy of the level only when the level was not occupied by an electron. This indicates a clear charge-state effect on the local motion of hydrogen around the Pt atom, that is, hydrogen is mobile only in the singly negative charge state of the complex. We have estimated an activation energy 0.27 eV for the hydrogen motion around the Pt atom under a stress of 0.6 GPa. We have examined three structural models, among which a model where the two hydrogen atoms are directly bonded to the platinum atom may be the most plausible candidate. In this structure, defect reorientation needs no bond switching but only the rotation of the whole Pt-H-2 entity. A possible mechanism of the charge-state-dependent reorientation observed may be that if the electronic state with antibonding character is occupied by an electron, the two hydrogen atoms may be displaced outward, probably retarding their motion for the reorientation.

DOI： 10.1103/PhysRevB.69.045206

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY  

We have studied the local motion of hydrogen in the neighborhood of carbon and platinum impurities by observing the stress-induced reorientation and subsequent recovery of two H-related (H-C and Pt-H-2) complexes in Si, using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. We notice two interesting differences in hydrogen motion around carbon and platinum atoms. The first one is a difference in the temperature where stress-induced reorientation occurs. That of the H-C complex occurs at high temperatures above 250 K, while it occurs at low temperatures around 80 K for the Pt-H2 complex. The second difference is the effect of charge state of the complexes on their stress-induced reorientation and subsequent recovery. It occurs preferentially when an electron occupies the level of the H-C complex, but the Pt-H-2 complex has the reverse effect of level occupancy. These differences are discussed from viewpoint of different atomic configurations and electronic states of two H-related complexes.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We studied on the effect of the strain on photoluminescence (PL) properties of Er-doped Si on a SiGe layer (Si:Er:O/SiGe) and Er-doped SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy. Er-related luminescence was observed around 1.54 mum in all the samples. The PL spectra of the Si:Er:O/SiGe samples are much broader and stronger than those of the Si:Er:O/Si samples prepared as reference. Moreover, the intensive luminescence was observed in the Si:Er:O/SiGe sample that had much lower Er concentration of about 2.5 x 10(16) cm(-3). On the other hand, the significant differences in the PL spectra between the SiGe:Er:O/Si and Si:Er:O/Si samples were not observed. These indicate that the tensile strained Si enhances the optical activation of Er. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2003.09.225

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have applied a novel technique to combine isothermal deep-level transient spectroscopy (DLTS) with the application of uniaxial compressive stress to studying the structure of a platinum- and hydrogen-related defect, which has a gap state at 0.14 eV below the conduction band in Si. The application of &lt;100&gt; and &lt;111&gt; stresses split the DLTS peak of the defect into two components with intensity ratios of 23:1 and 1.1:1, respectively, which were ratios of short- to long-time components. Under &lt;110&gt; stress, the peak split into three components with an intensity ratio of 0.8:3.7:1. Comparing this splitting pattern to the piezospectroscopic theory of Kaplyanskii, we have uniquely determined that the defect has the orthorhombic symmetry with the C-2v point group, and have identified the defect as the Pt-H-2 complex previously identified by Uftring et al. [Phys. Rev. B 51 (1995) 9612]. We also observed that the defect was reoriented above 80 K along the applied uniaxial stress. Such reorientation occurred only when the defect level was not occupied by an electron. Our observation strongly suggests that the local motion of hydrogen around the Pt atom is remarkably affected by the charge state of the defect. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0167-9317(02)00941-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The ion implantation process used in silicon device processing needs a postannealing at as high as 1000 degreesC to recover the damages induced by high-energy ion bombardment and to electrically activate implanted impurities. We developed a postannealing treatment using remote-hydrogen plasma to reduce the annealing temperature. We found that our postannealing treatment more greatly reduced the resistivity of the surface region, which was very high just after implantation. The dependence of resistivity-reduction rate on annealing temperature was weaker for the annealing with hydrogen plasma than for the normal annealing. Therefore the enhancing effect by hydrogen was remarkable at lower temperature in the range of 250-350 degreesC. The less the dose quantity was, the stronger the enhancing effect was observed. The postannealing using hydrogen plasma with the power of 50 W at 300 degreesC for 2 h showed almost the same performance as the usual rapid thermal annealing process at 1000 degreesC for 30 s. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1527713

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied photoluminescence of Er in strained Si on a SiGe layer (Si:Er:O/SiGe) and unstrained Si on a Si layer (Si:Er:O/Si) grown by molecular beam epitaxy. Er-related photoluminescence was observed in both Si:Er:O/SiGe and Si:Er:O/Si samples. The peak intensity of Si:Er:O/SiGe at 1.54 mum was higher than that of Si:Er:O/Si. Moreover, the spectrum of strained Si (Si:Er:O/SiGe) was much broader than that of unstrained Si (Si:Er:O/Si). These differences between Si:Er:O/SiGe and Si:Er:O/Si suggest that the optical activation of Er can be enhanced by the presence of strain. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1506391

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We report on the quantitative study of charge-state-dependent local motion of hydrogen around carbon in Si, which was directly probed by measuring the recovery of stress-induced alignment of a hydrogen-carbon complex by means of deep-level transient spectroscopy under uniaxial stress. We have found that hydrogen jumps from a bond-centered site between C and Si atoms to another with an activation energy of 1.33 eV and a frequency factor of 7.1 × 1014s-1in the electron-empty charge state while hydrogen jumps much faster in the electron-occupied charge state with a lower activation energy of 0.55 eV and a smaller frequency factor of 3.3 × 106s-1. We have concluded that the hydrogen-carbon complex captures an electron from the conduction band at its gap state with antibonding character, lowering the barrier and frequency factor for hydrogen motion in the electron-occupied charge state.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We report on the quantitative study of charge-state-dependent local motion of hydrogen around carbon in Si, which was directly probed by measuring the recovery of stress-induced alignment of a hydrogen-carbon complex by means of deep-level transient spectroscopy under uniaxial stress. We have found that hydrogen jumps from a bond-centered site between C and Si atoms to another with an activation energy of 1.33 eV and a frequency factor of 7.1 x 10(14) s(-1) in the electron-empty charge state while hydrogen jumps much faster in the electron-occupied charge state with a lower activation energy of 0.55 eV and a smaller frequency factor of 3.3 x 10(6) s(-1). We have concluded that the hydrogen-carbon complex captures an electron from the conduction band at its gap state with antibonding character, lowering the barrier and frequency factor for hydrogen motion in the electron-occupied charge state.

DOI： 10.1103/PhysRevB.65.113205

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We have studied the stress-induced shift of a deep level at E-c - 0.15 eV due to a hydrogen-carbon complex in Si using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. Linear stress dependencies of the ionization energy of the above level were observed for five components of split DLTS peaks altogether for (111), (110) and (100) stresses. By subtracting the stress shifts of conduction band minima from the stress dependencies of ionization energy, die net stress shifts of the energy level were obtained. Two piezospectroscopic parameters, A(1) and A(2), were determined as approximately 4 and -9.5 meV/GPa, respectively. Considering a molecular-orbital schematic suggested here and throughout, we conclude that the stress-induced level shifts and the split pattern of DLTS peaks reflect the trigonal symmetry and antibonding character of the electronic state of the complex. These properties are completely consistent with the atomic configuration in which a hydrogen atom occupies the bond-centered site between Si and C atoms.

DOI： 10.1143/JJAP.40.6700

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have applied deep-level transient spectroscopy (DLTS) under uniaxial compressive stress to study the structure of a platinum- and hydrogen-related defect, which has a gap state at 0.14 eV below the conduction band minima in Si. The application of &lt;100&gt; and &lt;111&gt; stresses split the DLTS peak of the defect into two components with intensity ratios of 2.7:1 and 1.4:1, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. Under &lt;110&gt; stress, this peak split into three components as an intensity ratio of two lower-temperature peaks to the high-temperature peak was 1.4:5:1. In addition, we observed the stress-induced alignment of the defect to the configuration corresponding to the low-temperature DLTS peak during the DLTS scan in the temperature range of 65-100 K, for all stress directions. Our results provide the first evidence to connect the electronic level at E-c-0.14 eV to the atomic configuration of the Pt-H-2 complex with the C-2v symmetry previously identified by EPR. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)00682-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We applied deep-level transient spectroscopy (DLTS) under uniaxial stress to study the structure and bonding character of a hydrogen-carbon complex. The application of (1 1 1) and (1 1 0) compressive stresses split the DLTS peak into two as intensity ratios of 1:3 and 2:2, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. No splitting was observed under the (1 0 0) stress. These results indicate the trigonal symmetry of the complex and the antibonding character of its electronic state, and are consistent with the previously proposed atomic model of the complex, in which the hydrogen atom occupies the bond-centered site between silicon and carbon atoms. Furthermore, under the (1 1 1) stress, we observed that the energy of the electronic state corresponding to the low-temperature DLTS peak increased linearly with stress by 23 +/- 5 meV/GPa while that of the high-temperature peak only slightly decreased with stress by 6 +/- 5 meV/GPa. Under the (1 1 0) stress, the energy of the electronic state of the low-temperature peak had almost no stress dependency and that of the high-temperature peak decreased linearly with stress by 15 +/- 5 meV/GPa. Based on the above atomic model, we can consistently understand the opposite stress dependencies under (1 1 1) and (1 1 0) compressive stresses, considering the atomic displacement of the H-C complex under the stress. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(01)00433-1

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Language：English   Publisher：The Japan Society of Applied Physics  

We have found, by deep-level transient spectroscopy (DLTS), that the dissociation rate of a deuterium-carbon complex in silicon is about half that of a hydrogen-carbon complex, while the activation energies for the dissociation of both the complexes are the same. This clearly proves that both the complexes have the same atomic configuration and their dissociation is governed by the atomic jump of hydrogen (deuterium).

DOI： 10.1143/JJAP.39.1098

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

We performed systematic experiments on the annihilation of six species of thermal double donors, or TDDs (TDD1-TDD6) under various conditions in both carbon-lean and carbon-rich Si crystals, by means of low-temperature infrared spectroscopy. We found that two kinds of TDD annihilation occurred in two different time regions. The first annihilation occurred typically within 1000 min at 500°C, and is ascribed to the dissociation of oxygen clusters responsible for TDDs. We analyzed TDD annihilation on the basis of the model of successive dissociation of oxygen clusters, and obtained an activation energy of about 4 eV and a pre-exponential factor of the order of 1022s-1, regardless of TDD species and carbon density. We discuss the origin of such a high activation energy and a large pre-exponential factor. The second annihilation occurred typically after 1000 min at 500°C, and is ascribed to the neutralization of TDDs. The neutralization behavior strongly depends on the amount of carbon in the silicon crystals. The C-rich crystal shows the usual thermal activation process with an activation energy of 1.7 eV and a pre-exponential factor of about 106s-1, independently of TDD species. On the other hand, the C-lean crystal shows no distinct temperature dependence on neutralization rate, suggesting an athermal process. These results strongly suggest two different mechanisms of TDD neutralization, one of which is related to carbon and the other independent of carbon. We propose models to explain the features of these two kinds of TDD neutralization. © 2000 American Institute of Physics.

DOI： 10.1063/1.372077

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We have studied the effects of irradiation of hydrogen plasma on the dislocation glide motion. The velocity of dislocation motion was remarkably enhanced by the irradiation in the temperature range below about 480 degrees C and the activation energy was reduced to 1.2 eV under hydrogen plasma from 2.2 eV in the hydrogen-free condition. We experimentally confirmed that this effect is owing neither to the light from the plasma nor to any defects induced by the irradiation but is due to the hydrogens incorporated into the sample. We also found that pre-hydrogenation treatments play an essential role for this effect to occur. The microscopic mechanism and implications of the experimental findings are discussed in the framework of the Peierls mechanism.

DOI： 10.1002/(SICI)1521-396X(199901)171:1<27::AID-PSSA27>3.3.CO;2-S

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOCIETY INC  

The diffusion of phosphorus into ultrathin oxides from phosphorus doped polysilicon sources was studied. The two boundary diffusion model can be applied to the diffusion of phosphorus in ultrathin oxides, and the diffusivity and segregation coefficient were obtained using by the model. The dependence of the diffusion coefficient on oxide thickness and drive-in ambients was investigated. The enhanced diffusion, which has been seen for boron diffusion in ultrathin oxides, was not observed for the phosphorus diffusion. For the diffusion in dry O-2 and wet O-2 ambients, the enhanced diffusion was observed and is attributed to melt through diffusion in glassy compounds.

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Language：English   Publisher：The Japan Society of Applied Physics  

We studied the effect of UV-light irradiation on annealing of as-grown Mg-doped GaN films by resistivity and Hall measurements. The annealing temperature where the resistivity reduction due to the electrical activation of hydrogen-passivated Mg occurred with the increase of hole density and the decrease of hole mobility, was reduced from 550 to 450&deg;C by the irradiation of UV light with a peak wavelength around 350 nm. This suggests that electronic excitation reduces the thermal stability of Mg-H complexes in GaN.

DOI： 10.1143/JJAP.37.L970

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Other Link： https://jlc.jst.go.jp/DN/JALC/00055004602?from=CiNii

Language：English   Publisher：The Japan Society of Applied Physics  

We observed that a defect related to carbon and phosphorus was formed during the carbon-enhanced annihilation of thermal donors at 470&deg;C in silicon. We determined, using deep-level transient spectroscopy (DLTS), that the defect has a deep level at Ec-0.36 eV and its density has positive correlation with carbon and phosphorus densities. The formation rate of the defect is proportional to the phosphorus density. We also observed the 767 meV photoluminescence line (P-line) that had been identified as the complex with a core of interstitial carbon, vacancy and oxygen dimer. We tentatively ascribe the Ec-0.36 eV defect to the pair of interstitial carbon and substitutional phosphorus.

DOI： 10.1143/JJAP.37.L101

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Language：English   Publisher：The Japan Society of Applied Physics  

We studied, by deep-level transient spectroscopy (DLTS), the dissociation mechanism of a hydrogen-carbon (H-C) complex, which has a donor level at E _c-0.15 eV and acts as an electron trap in crystalline silicon. On the basis of our results and a previously proposed atomic model of the H-C complex, in which the hydrogen atom resides inside a silicon-carbon bond, we have proposed the following dissociation mechanism. The complex is stable in the positive charge state, and to dissociate it needs a hydrogen jump with an activation energy of 1.3 eV to break the bond with carbon and silicon. The complex becomes neutral by capturing an electron from the conduction band or accepting an electron directly from the valence band under electronic excitation, and is consequently dissociated at an activation energy of 0.5 eV due to the loss of binding. Strong evidence for the existence of the negative charge state of hydrogen in crystalline silicon is also presented.

DOI： 10.1143/JJAP.36.6579

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Language：English   Publisher：The Japan Society of Applied Physics  

We applied deep-level transient spectroscopy (DLTS) under uniaxial stress to study the structure and bonding nature of a hydrogen-carbon (H-C) complex in Si. The application of <111> and <110> compressive stresses split the DLTS peak into two as ratios of 1:3 and 2:2, respectively, which were the ratios of the low-temperature peak to the high-temperature peak. No splitting was observed under the <100> stress. These results indicate the trigonal symmetry of the H-C complex and the anti-bonding nature of its electronic state. We observed a stress-induced alignment of the complex at 250K for 50 min under a <110> stress of 1 GPa.

DOI： 10.1143/jjap.36.L1419

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Trans Tech Publications Ltd  

We have measured the velocity of dislocation glide motion in phosphorus-doped FZ-silicon during hydrogen plasma irradiation, and, have found for the first time that the velocity was drastically promoted under hydrogen plasma by a factor of 10 to 100 in the temperature range of 390-480°C, and the activation energy of dislocation motion was reduced to 1.2eV from the value 2.3eV, in the dark. We exclude the possibility that the observed phenomenon is due to so called radiation-enhanced dislocation glide induced by plasma light, since no enhancement of dislocation motion occurred at all under nitrogen plasma with the same light intensity as hydrogen plasma, and hydrogen plasma irradiation with covers to prevent light exposure promoted dislocation motion as well. In addition, it is confirmed by spreading resistance measurements that hydrogen atoms were actually incorporated up to about 10 μm beneath the surface to passivate boron. This assures us that hydrogen atoms were incorporated to enough depths at the temperatures where dislocation velocity was measured. These results clearly indicate that hydrogen itself enhances dislocation motion. Some discussions are made on the enhancement mechanisms of dislocation motion.

DOI： 10.4028/www.scientific.net/msf.258-263.313

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Event date： 2008.12.12

Language：Japanese  

Er-doped Si has attracted much attention as a possible candidate for 1.5μm light-emitting material in silicon photonics. However, there has been a problem of the strong luminescence quenching toward higher temperatures. In this work, we propose a method for effective light emition from Er-doped Si using quantum well structures. The fabrication process using thermal oxidation of silicon-on-insulator (SOI) later is also described.

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Event date： 2005.8.19

Language：Japanese  

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Event date： 2005.8.19

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Event date： 2005.3.4

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Event date： 2004.8.25

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Event date： 2003.8.15

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Event date： 2003.3.6

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Event date： 2002.8.13

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Event date： 2001.9.3

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Event date： 1998.9.5

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Event date： 1997.9.16

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Event date： 1993.9.20

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Event date： 1993.3.16

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Event date： 1991.9.12

Language：Japanese  

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Event date： 1990.9.12

Language：Japanese  

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Event date： 1990.3.16

Language：Japanese  

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