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論文

Effects of growth temperature and growth rate on polytypes in gold-catalyzed GaAs nanowires studied by in situ X-ray diffraction

高橋 正光; 神津 美和*; 佐々木 拓生

Japanese Journal of Applied Physics, 55(4S), p.04EJ04_1 - 04EJ04_4, 2016/04

 被引用回数:4 パーセンタイル:67.17(Physics, Applied)

The polytypism of GaAs nanowires was investigated by in situ X-ray diffraction using a molecular-beam eppitaxy chamber combined with an X-ray diffractometer. The growth of nanowries was found to start with the formation of zincblende structure, followed by the growth of the wurtzite structure. The wurtzite structure tended to form at a low growth temperature and a high growth rate.

論文

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by X-ray diffraction

鈴木 秀俊*; 仲田 侑加*; 高橋 正光; 池田 和磨*; 大下 祥雄*; 諸原 理*; 外賀 寛崇*; 森安 嘉貴*

AIP Advances (Internet), 6(3), p.035303_1 - 035303_6, 2016/03

 被引用回数:4 パーセンタイル:74.49(Nanoscience & Nanotechnology)

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ X-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

論文

Anomalous lattice deformation in GaN/SiC(0001) measured by high-speed ${{it in situ}}$ synchrotron X-ray diffraction

佐々木 拓生; 石川 史太朗*; 高橋 正光

Applied Physics Letters, 108(1), p.012102_1 - 012102_5, 2016/01

AA2015-0769.pdf:2.43MB

 被引用回数:1 パーセンタイル:91.46(Physics, Applied)

We report an anomalous lattice deformation of GaN layers grown on SiC(0001) by molecular beam epitaxy. The evolution of the lattice parameters during the growth of the GaN layers was measured by in situ synchrotron X-ray diffraction. The lattice parameters in the directions parallel and normal to the surface showed significant deviation from the elastic strains expected for lattice-mismatched films on substrates up to a thickness of 10 nm. The observed lattice deformation was well explained by the incorporation of hydrostatic strains due to point defects. The results indicate that the control of point defects in the initial stage of growth is important for fabricating GaN-based optoelectronic devices.

論文

Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using ${{it in situ}}$ X-ray diffraction

下村 憲一*; 鈴木 秀俊*; 佐々木 拓生; 高橋 正光; 大下 祥雄*; 神谷 格*

Journal of Applied Physics, 118(18), p.185303_1 - 185303_7, 2015/11

 被引用回数:5 パーセンタイル:67.07(Physics, Applied)

Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by ${{it in situ}}$ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping, attributed to In-Ga intermixing between the QDs and the cap layer. Photoluminescence wavelength can be tuned by controlling the intermixing and the cap layer thickness. It is demonstrated that such information about strain is useful for designing and preparing novel device structures.

論文

Mechanisms determining the structure of gold-catalyzed GaAs nanowires studied by in situ X-ray diffraction

高橋 正光; 神津 美和*; 佐々木 拓生; Hu, W.*

Crystal Growth & Design, 15(10), p.4979 - 4985, 2015/10

 被引用回数:11 パーセンタイル:23.86(Chemistry, Multidisciplinary)

The evolution of polytypism during GaAs nanowire growth was investigated by in situ X-ray diffraction. The growth of nanowires was found to start with the formation of zincblende structure, followed by the growth of wurtzite structure. The growth process was well reproduced by a simulation based on a layer-by-layer nucleation mode. The good agreement between the measured and simulated results confirms that nucleation costs higher energy for the stackings changing the crystal structure than for those conserving the preceding structure. The transition in prevalent structure can be accounted for by the change of local growth conditions related to the shape of triple phase line rather than by the change in supersaturation level, which quickly reaches equilibrium after starting growth.

論文

その場放射光X線回折によるIII-Vエピ成長のひずみ解析

佐々木 拓生; 高橋 正光

日本結晶成長学会誌, 42(3), p.210 - 217, 2015/10

AA2015-0738.pdf:2.23MB

Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through in situ X-ray reciprocal space mapping (${{it in situ}}$ RSM). At the synchrotron facility SPring-8, a hybrid system of molecular beam epitaxy and X-ray diffractometry with a two-dimensional detector enabled us to perform ${{it in situ}}$ RSM at high-speed and high-resolution. Using this experimental setup, the strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In order to discuss this observation quantitatively, a strain relaxation model was proposed based on the Dodson-Tsao's kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. In addition to the single InGaAs layer, strain relaxation processes in multi-layer structures are discussed.

論文

放射光その場X線回折による半導体成長機構の解明

高橋 正光

日本結晶成長学会誌, 42(3), p.201 - 209, 2015/10

AA2015-0739.pdf:0.82MB

An experimental approach to crystal growth dynamics using synchrotron X-ray diffraction is discussed. In the study of crystal growth, analysis of imperfect crystals lacking three-dimensional periodicity is inevitably required. Though diffuse scattering generated by such imperfect crystals is much weaker than the bulk Bragg diffraction, recent development of the synchrotron light source has enabled the in situ measurement of it during crystal growth. In this article, studies on surface structures, evolution of defects in growing films and the growth of nanostructures under molecular-beam epitaxy conditions are presented as well as a brief overview of the instrumentation.

論文

${it In situ}$ three-dimensional X-ray reciprocal-space mapping of InGaAs multilayer structures grown on GaAs(001) by MBE

佐々木 拓生; 高橋 正光; 鈴木 秀俊*; 大下 祥雄*; 山口 真史*

Journal of Crystal Growth, 425, p.13 - 15, 2015/09

 被引用回数:3 パーセンタイル:61.74(Crystallography)

${it In situ}$ three-dimensional X-ray reciprocal space mapping (${it in situ}$ 3D-RSM) was employed for studying molecular beam epitaxial (MBE) growth of InGaAs multilayer structures on GaAs(001). Measuring the symmetric 004 diffraction allowed us to separately obtain film properties of individual layers and to track the real-time evolution of both residual strain and lattice tilting. In two- layer growth of InGaAs, significant plastic relaxation was observed during the upper layer growth, and its critical thickness was experimentally determined. At the same thickness, it was found that the direction of lattice tilting drastically changed. We discuss these features based on the Dunstan model and confirm that strain relaxation in the multilayer structure is induced by two kinds of dislocation motion (dislocation multiplication and the generation of dislocation half-loops).

論文

Spontaneous formation of suboxidic coordination around Co in ferromagnetic rutile Ti$$_{0.95}$$Co$$_{0.05}$$O$$_2$$ film

Hu, W.*; 林 好一*; 福村 知昭*; 赤木 和人*; 塚田 捷*; 八方 直久*; 細川 伸也*; 大和田 謙二; 高橋 正光; 鈴木 基寛*; et al.

Applied Physics Letters, 106(22), p.222403_1 - 222403_5, 2015/06

 被引用回数:26 パーセンタイル:17.61(Physics, Applied)

The local atomic structures around Co in high temperature diluted ferromagnetic semiconductor Co-doped TiO$$_2$$ has been investigated using X-ray fluorescence holography and X-ray absorption fine structure experiments. While the Co atoms in the Ti$$_{0.99}$$Co$$_{0.01}$$O$$_2$$ simply substituted for Ti sites in the rutile structure, a suboxidic arrangement of CoO$$_2$$Ti$$_4$$ was found to form around Co in the Ti$$_{0.95}$$Co$$_{0.05}$$O$$_2$$ films. First-principles calculations supported the stability of the aggregated suboxidic clusters in the rutile TiO$$_2$$. The suboxidic coordination may be the source of strong exchange interaction, resulting in the high Curie temperature in Co-dopedTiO$$_2$$.

論文

Role of liquid indium in the structural purity of wurtzite InAs nanowires that grow on Si(111)

Biermanns, A.*; Dimakis, E.*; Davydok, A.*; 佐々木 拓生; Geelhaar, L.*; 高橋 正光; Pietsch, U.*

Nano Letters, 14(12), p.6878 - 6883, 2014/12

 被引用回数:21 パーセンタイル:23.84(Chemistry, Multidisciplinary)

The dynamic relation between the growth conditions and the structural composition of the catalyst-free InAs nanowires was investigated using time-resolved X-ray scattering and diffraction measurements during the growth by molecular beam epitaxy. A spontaneous build-up of liquid indium is directly observed in the beginning of the growth process and associated with the simultaneous nucleation of InAs nanowires predominantly in the wurtzite phase. After their nucleation, the nanowires grow in the absence of liquid indium, and with a highly defective wurtzite structure. A pathway to pure wurtzite nanowires is presented through this work.

論文

Acute and obtuse rhombohedrons in the local structures of relaxor ferroelectric Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Hu, W.*; 林 好一*; 大和田 謙二; Chen, J.*; 八方 直久*; 細川 伸也*; 高橋 正光; Bokov, A.*; Ye, Z.-G*

Physical Review B, 89(14), p.140103_1 - 140103_5, 2014/04

 被引用回数:31 パーセンタイル:15.45(Materials Science, Multidisciplinary)

The local structures around Nb and Pb in the relaxor ferroelectric Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$ were investigated by X-ray fluorescence holography. The Pb atomic images around Nb showed a rhombohedral distortion of the crystal unit cells. The Pb-Pb correlated images showed a local structure of body-center-like $$2a_0times 2a_0 times 2a_0$$ superlattice, proving a rigid three-dimensional network structural model combining the two kinds of rhombohedrons. This superstructure and the fluctuating Pb and Nb atoms play an important role in the relaxor behavior of this material.

論文

RI施設における排気中$$^{14}$$Cモニタリング; 捕集及び酸化方法の比較評価

上野 有美; 小嵐 淳; 岩井 保則; 佐藤 淳也; 高橋 照彦; 澤畠 勝紀; 関田 勉; 小林 誠; 角田 昌彦; 菊地 正光

保健物理, 49(1), p.39 - 44, 2014/03

原子力科学研究所第4研究棟(RI施設)では、排気中の$$^{14}$$Cを1か月間連続で捕集し、施設から大気中へ放出される$$^{14}$$Cのモニタリングを行っている。しかし、CuO触媒を600$$^{circ}$$C以上に加熱する必要があることやモノエタノールアミン(MEA)が毒劇物に指定されていることから、管理区域内でのモニタリング手法として改良の余地が残っている。本試験では、異なる捕集剤を用いた捕集法の比較、使用する捕集剤の量とCO$$_{2}$$捕集効率の関係についての検討、異なる酸化触媒の異なる温度条件下における酸化性能の比較を行った。CO$$_{2}$$捕集剤の検討では、MEAに加えて、Carbo-Sorb Eを評価の対象とした。酸化触媒の検討では、CuO触媒に加えて、Ptアルミナ触媒、Pd/ZrO$$_{2}$$触媒を評価の対象とした。試験の結果、Carbo-Sorb Eはガスの通気による気化量が大きく、1か月の連続捕集には適さず、MEAは1か月間を通して安定したCO$$_{2}$$捕集能力があることが確認できた。各触媒の酸化効率を比較した結果、Pd/ZrO$$_{2}$$触媒のCH$$_{4}$$に対する酸化性能が最も優れており、加熱炉の温度を200$$^{circ}$$C以上下げることができ、モニタリングの安全性を向上できる。

論文

Defect characterization in compositionally graded InGaAs layers on GaAs (001) grown by MBE

佐々木 拓生; Norman, A. G.*; Romero, M. J.*; Al-Jassim, M. M.*; 高橋 正光; 小島 信晃*; 大下 祥雄*; 山口 真史*

Physica Status Solidi (C), 10(11), p.1640 - 1643, 2013/11

 被引用回数:3 パーセンタイル:16.17

Defect characterization in compositionally step graded In$$_{x}$$Ga$$_{1-x}$$As layers with different thickness of the overshooting (OS) layer was performed using cathodoluminescence (CL) and transmission electron microscopy (TEM). We found that the type and in-plane distribution of defects generated in the top InGaAs layer grown on step graded layers strongly depend on the thickness of the OS layer. In the thin OS layer, a high density of threading dislocations aligned along [110] was observed. In the thick OS layer, significant line defects associating composition variation were dominantly present. These features on defect type and distribution would relate to strain and configuration of the OS layer.

論文

Real-time observation of crystallographic tilting InGaAs layers on GaAs offcut substrates

西 俊明*; 佐々木 拓生; 池田 和磨*; 鈴木 秀俊*; 高橋 正光; 下村 憲一*; 小島 信晃*; 大下 祥雄*; 山口 真史*

AIP Conference Proceedings 1556, p.14 - 17, 2013/09

 被引用回数:0 パーセンタイル:100

${it In situ}$ X-ray reciprocal space mapping during In$$_{x}$$Ga$$_{1-x}$$As/GaAs(001) MBE growth is performed to investigate effects of substrate misorientations on crystallographic tilting. It was found that evolution of the crystallographic tilt for the InGaAs films is strongly dependent on both layer structures and substrate misorientations. We discuss these observations in terms of an asymmetric distribution of dislocations.

論文

In situ three-dimensional X-ray reciprocal-space mapping of GaAs epitaxial films on Si(001)

高橋 正光; 仲田 侑加*; 鈴木 秀俊*; 池田 和磨*; 神津 美和; Hu, W.; 大下 祥雄*

Journal of Crystal Growth, 378, p.34 - 36, 2013/09

 被引用回数:5 パーセンタイル:51.42(Crystallography)

Epitaxial growth of III-V semiconductors on silicon substrates is a longstanding issue in semiconductor technology including optoelectronics, high-mobility devices and solar cells. In addition to a lattice mismatch of 4%, formation of antiphase domain boundaries makes the growth of GaAs/Si(001) more complicated than that of congeneric combinations, such as Ge/Si(001) and InGaAs/GaAs(001). In the present study, defects in GaAs/Si(001) epitaxial films are investigated by three-dimensional X-ray reciprocal-space mapping technique, which we have successfully applied for InGaAs/GaAs(001) growth. Experiments were carried out at a synchrotron beamline 11XU at SPring-8 using a molecular-beam epitaxy chamber integrated with a multi-axis X-ray diffractometer. Streaky scattering extending from the GaAs 022 peak in the $$langle 111rangle$$ directions was observed, indicating development of plane defects, such as facets and stacking faults.

論文

Quantitative monitoring of InAs quantum dot growth using X-ray diffraction

高橋 正光

Journal of Crystal Growth, 401, p.372 - 375, 2013/09

 被引用回数:2 パーセンタイル:73.51(Crystallography)

The high controllability of molecular-beam epitaxy (MBE) for the growth of nanostructures relies on the use of a monitoring technique, which is reflection-high energy electron diffraction (RHEED) in a typical MBE system. Even sub-monolayer control of the thickness of quantum well structures is achievable using the RHEED oscillation. However, as the semiconductor nanostructures are diversified into lower-dimensional structures including quantum wires and dots, more sophisticated monitoring techniques has become required for full characterization of the nanostructures beyond the thickness of two-dimensional layered structures. In this work, we present in situ X-ray diffraction techniques enabling growth monitoring of a wide variety of low-dimensional structures on the basis of the MBE system combined with an X-ray difftactometer developed at a synchrotron beamline, 11XU, at SPring-8.

論文

X-ray micro-beam focusing system for in situ investigation of single nanowire during MBE growth

Hu, W.; 高橋 正光; 神津 美和*; 仲田 侑加*

Journal of Physics; Conference Series, 425(20), p.202010_1 - 202010_4, 2013/03

 被引用回数:1 パーセンタイル:38.87

A ternary Fresnel zone plate (FZP) has been fabricated and installed at the beamline 11XU of SPring-8, in the aim of in situ studies on the growth of semiconductor nanostructures using an X-ray diffractometer integrated with a molecular-beam epitaxial (MBE) chamber. The FZP is designed for an X-ray energy of 9.5 keV with peak efficiency of 48% for the 1st-order diffraction. The full width at half maximum of the focused beam profile is around 1 micrometer in both horizontal and vertical directions measured by the dark-field knife-edge scan of a gold wire which was 0.3 mm in diameter. Using this FZP, we will be able to perform in situ study of the growth mechanism of nanowire (NW) in atomic scale and carry out in situ X-ray diffraction (XRD) studies of single NW during MBE growth with a micro-beam. In this work, the performance test of this focusing system is presented and preliminary applications to monitoring the growth of single NW by in situ XRD were also carried out.

論文

X-ray diffraction study of crystal growth dynamics during molecular-beam epitaxy of III-V semiconductors

高橋 正光

Journal of the Physical Society of Japan, 82(2), p.021011_1 - 021011_14, 2013/02

 被引用回数:6 パーセンタイル:50.02(Physics, Multidisciplinary)

An experimental approach to crystal growth dynamics using surface-sensitive X-ray diffraction techniques is discussed. In crystal growth, two essentially different kinds of dynamics are involved. One is the evolution of a statistical structure averaged over the sample area under consideration. The other is the temporal fluctuation of local structures associated with elemental processes of crystal growth. Over the past few decades, combination of a synchrotron X-ray beamlines and specially designed crystal growth systems has played a great role in ${it in situ}$ studies of the dynamics of average structures during the epitaxial growth of crystalline films. The recent development of coherent X-ray sources has provided an opportunity to elucidate local structure fluctuation, which is also important for solving many technological problems in crystal growth.

論文

High-speed three-dimensional reciprocal-space mapping during molecular beam epitaxy growth of InGaAs

Hu, W.; 鈴木 秀俊*; 佐々木 拓生*; 神津 美和*; 高橋 正光

Journal of Applied Crystallography, 45(5), p.1046 - 1053, 2012/10

 被引用回数:9 パーセンタイル:29.31(Chemistry, Multidisciplinary)

This paper describes the development of a high-speed three-dimensional reciprocal-space mapping method designed for the real-time monitoring of the strain relaxation process during the growth of heterostructure semiconductors. Each three-dimensional map is obtained by combining a set of consecutive images, which are captured during the continuous rotation of the sample, and calculating the reciprocal-space coordinates from the detector coordinate system. Using this method, the strain relaxation process of InGaAs heteroepitaxial films grown on GaAs(001) has been investigated.

論文

結晶成長条件下におけるGaAs(001)表面構造

高橋 正光

表面科学, 33(9), p.507 - 512, 2012/09

結晶成長条件下のGaAs(001)表面構造をその場X線回折により研究した。分子線エピタキシー真空槽とX線回折計とを一体化した装置を用い、ヒ素雰囲気・成長温度下におけるGaAs(001)表面の原子配列を定量的に決定した。放射光の高い角度分解能により、(2$$times$$4)構造から他の構造に相転移するさいの構造の乱れを評価することができた。放射光のエネルギー可変性を利用して、c(4$$times$$4)構造の元素選択的な解析が可能になり、Ga-Asダイマー形成の直接的証拠が得られた。

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