Outcome：

2023
By comparing different precursor materials, the basic guidelines for passivating InAs surface quantum dots were proposed.

2022
The recipes and the mechanisms of passivating InAs surface quantum dots were studied.

Outcome：

2023
Shown that quantum discs can be prepared by using SML stacking.

2022
Preparation of quantum discs that are considered to be a strong candidate for photon upconversion is being investigated.

MBE growth of InGaAs quantum structures using submonolayer (SML) stacking is studied thereby precisely controlling the structure and electronic properties of the quantum structures.
Further, the potential of applying such structures to spintronics is investigated.

Outcome：

2023
Control of spin was shown by illuminating these 2D and 3D structures by circular polarized excitation light.

2022
The transition of 2D-3D in submonolayer growth has been studied and the critical conditions were identified and the mechanisms were studied.

Outcome：

2022
No progress.

Outcome：

2022
No progress.

Outcome：

2022
No progress.

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

We performed microscopic imaging of photoluminescence (PL) and photocurrent (PC) on InAs nanostructures including disklike structures (nanodisks) and quantum dots (QDs). The correlation between PL and PC images indicates that the major fraction of upconverted carriers originates from nanodisks. By analyzing the excitation spectra, we find evidence that nanodisks and QDs need to be spatially separated to enhance PC generation via upconversion. The efficient simultaneous use of both QDs and nanodisks is an alternative approach to intermediate-band solar cells, where low-energy photons are upconverted in the QDs and high-energy photons are efficiently upconverted in the nanodisks, resulting in enhanced carrier generation yields. With spatially resolved upconverted PL, we show that PC generation in nanodisks is due to ejection of both electrons and holes.

DOI： 10.1103/PhysRevB.89.125301

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

For intermediate-band solar cells, the broad absorption spectrum of quantum dots (QDs) offers a favorable conversion efficiency, and photocurrent generation via efficient two-step two-photon-absorption (TS-TPA) in QDs is essential for realizing high-performance solar cells. In the last decade, many works were dedicated to improve the TS-TPA efficiency by modifying the QD itself, however, the obtained results are far from the requirements for practical applications. To reveal the mechanisms behind the low TS-TPA efficiency in QDs, we report here on two- and three-beam photocurrent measurements of InAs quantum structures embedded in AlGaAs. Comparison of two-and three-beam photocurrent spectra obtained by subbandgap excitation reveals that the QD TS-TPA efficiency is improved significantly by suppressing the relaxation of hot TS-TPA carriers to unoccupied shallow InAs quantum structure states.

DOI： 10.1038/srep04125

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

Intermediate bands bear trap and recombination centers for carriers generated in other energy levels. Assessment of recombination centers is important for achieving efficient carrier generation. We measure the photocurrent (PC) originating from InAs quantum structures embedded in an undoped (Al)GaAs matrix due to excitation with multiple tunable beams. With an infrared light excitation the influence of trapping or recombination on the quantum dot PC generation efficiency via two-step two-photon-absorption processes is evaluated.

DOI： 10.1109/PVSC.2014.6924889

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

The mechanisms of upconverted photocurrent in InAs quantum structures embedded in AlxGa1-x As were studied with simultaneous measurements of photoluminescence and photocurrent spectra. Efficient upconversion was verified in samples with and without quantum dots. The dominant upconversion process from low temperatures to room temperature was found to occur through an Auger process in disklike InAs quantum structures. The results suggest the importance of shallow energy levels, which enable upconversion and efficient carrier extraction through multiparticle interactions. The disklike structure was concluded to be a suitable intermediate-band structure in terms of the energy conversion efficiency.

DOI： 10.1103/PhysRevB.87.245305

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Bilayer structures of colloidal PbS quantum dots (QDs) with different sizes are fabricated by two methods: chemical bond anchoring and electrostatic adsorption. Unlike the sample prepared by chemical bond anchoring, we find that the electronic connection between different layers is suppressed in the samples prepared by electrostatic adsorption with charged polyelectrolytes. To clarify the electronic coupling between the QDs and the polyelectrolytes, QDs directly stabilized by charged polyelectrolytes were synthesized. Transmission electron microscopy investigation shows that cross-linked QD networks are formed. Time-resolved photoluminescence measurements indicate that the carrier lifetimes of QDs in networks were greatly reduced. The photoluminescence peak energy increases with a third root of the excitation power. All these observations can be consistently explained considering spatially separated photoexcited carriers in a type-II band alignment. The abnormal behaviors of electrostatic adsorption sample are discussed based on these results. © 2013 World Scientific Publishing Company.

DOI： 10.1142/S1793292013500136

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AVS Science and Technology Society  

Upconversion through excitation of bulk GaAs is investigated by change in crystal growth conditions with electron beam (e-beam). The upconverted photoluminescence intensity is enhanced several times by striking the source fluxes with e-beam during molecular beam epitaxy (MBE) growth. Experimental evidence for a shallow intermediate state being responsible for this upconversion is presented. It is suggested that the intermediate state may be formed by shallow exciton trap states induced by As anti-site defects, which can be increased with e-beam during MBE growth. © 2012 American Vacuum Society.

DOI： 10.1116/1.3679547

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report on the upconversion of infrared photons to visible using a quantum structure based on an InAs wetting layer (WL) embedded in AlGaAs grown by molecular beam epitaxy. The grown structures are characterized by photoluminescence, and it is found that the upconversion center is a real intermediate state induced by the WL. The temperature dependence suggests that the intermediate state is of an exciton nature, which is supported by the result of an eight-band k . p calculation.

DOI： 10.1103/PhysRevB.83.081309

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report the fabrication and analysis of self-assembled monolayer and bilayer films of colloidal PbS quantum dots (QDs) on GaAs (001) substrates. 1,6-hexanedithiol is used as link molecule between QDs and GaAs substrates. Atomic force microscopy (AFM) and photoluminescence (PL) measurements confirm the formation of PbS QD film on GaAs. For the monolayer PbS QD film, the temperature-dependent PL shows a feature typical of close-packed film. For the bilayer PbS QD film fabricated from two different mean-sized PbS QDs, we find that the stacking sequence of QDs with different size affects the quantum yield and emission wavelength of the film. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/245/1/012069

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

Colloidal PbS quantum dots dispersed as close-packed film and in polystyrene (PS) matrix are prepared and photoluminescence (PL) spectra are measured in the temperature range of 5-300 K. The integrated PL intensity of the close-packed film increases as the temperature is raised from 5 to 120 K, and then decreases to 300 K, while that of the PS film decreases monotonously. This abnormal behavior of the close-packed film can be explained by a thermally activated electronic energy transfer model, which is supported by time resolved PL measurements.

DOI： 10.1063/1.3213349

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

A systematic study has been performed on the morphology of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy on (0 0 1) GaAs surfaces using atomic force microscopy while varying the growth conditions. It is shown that the size and density of these QDs can be controlled by the precise adjustment of growth temperatures and the amount of deposited InAs and also by post-growth annealing. One can now form QDs that are between 20 and 60 nm in diameter and between low 108 and mid 1011 cm-2 in density. Very low-density QDs prepared by post-annealing are particularly suitable for single QD studies. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00329-6

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

We observed the surface topography of CdSe colloidal nano-dot film by cyclic contact mode atomic force microscopy. The observed structure changes with cantilever oscillation amplitude, and non-uniform images with long-range corrugations are obtained with relatively large oscillation amplitude while fine structures are revealed with smaller oscillation amplitude. When the amplitude is larger and the surface is weakly 'tapped', the topography of the soft organic matrix of the film dominates, and when the tapping force is increased, the hard CdSe dots begin to reveal.

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Science B.V.  

Control on size and density of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy on (0 0 1)GaAs has been performed. By properly adjusting the substrate temperature and the amount of InAs deposition, it is possible to prepare QDs that are approximately 15 nm- approximately 50 nm in diameter, and low 108 to mid 1011/cm2 in density. Giant QDs that are typically 50-100 nm in diameter are also formed upon excess InAs deposition, and can act as nanoelectrodes. The capping process of these various QDs by GaAs is size dependent, and with a 5 nm thick cap, the previously reported volcano-like structure are seen only when the giant QDs are present.

DOI： 10.1016/S0022-0248(99)00005-6

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

Structures of (001)GaAs surfaces during organometallic vapor phase epitaxy (OMVPE) have been studied by simultaneous measurements using reflectance difference spectroscopy (RDS) and grazing incidence X-ray scattering (GIXS). The data obtained by the two techniques are strongly correlated. We find that RDS, although not a diffraction probe, can distinguish most surface reconstructions of (001)GaAs. The information obtained by these two probes is complementary, so by combining RDS and GIXS data obtained from surfaces under static and dynamic conditions we can gain detailed information about atomic arrangements and growth mechanisms. Under static conditions, we find that RD spectra under OMVPE conditions are similar to those previously observed in ultrahigh vacuum (UHV). By simultaneously monitoring the surface reconstructions using GIXS and RDS, we have established that RDS accurately reflects the local structural configurations but is not uniquely sensitive to changes in long range order or subtle differences in symmetry. Growth oscillations were also measured simultaneously by RDS and GIXS under various conditions. The observed oscillation periods agree with each other, but the details are condition dependent, thus providing important clues concerning the surface processes involved. For example, the one-to-one correlation observed between RDS and GIXS oscillations suggests that the RDS oscillations are related to island formation.

DOI： 10.1016/0022-0248(95)01051-3

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

Reflectance difference spectroscopy (RDS) and surface photoabsorption (SPA) are two optical characterization techniques that are now in common use for monitoring and controlling epitaxial growth. Here we establish the connection of SPA data to the surface dielectric response, using an anisotropic three phase model (substrate, anisotropic overlayer, ambient). In contrast to the generally accepted picture, our calculations show, that the contribution to the SPA signal from the dielectric component normal to the surface is negligible, and that the major contribution arises from the projection of the dielectric tensor on the line formed by the intersection of the surface and the plane of incidence. It follows, that the difference between SPA data taken with the plane of incidence along the different principal axis is related to, and in fact can be calculated from, RDS spectra. By comparing published data to our database of RD spectra, we are able to find the surface reconstruction present during flow modulated organo metallic chemical vapour epitaxial growth of GaAs epilayers.

DOI： 10.1016/0039-6028(93)91054-S

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Arsenic dimers and multilayers are shown to exist on (001)GaAs surfaces under atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) conditions. We obtained reflectance-difference spectra from surfaces in AP H2that are equivalent to those obtained from the (2×4) and disordered-c(4×4) reconstructions prepared in ultrahigh vacuum by molecular beam epitaxy. Implications for models of OMCVD growth.

DOI： 10.1063/1.107417

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Reflectance-difference spectroscopy (RDS) is employed to study in situ the (4×2), (1×6), (4×6), (3×1), (2×4)-, (2×4)-, (2×4)-, c(4×4), and d(4×4) reconstructions of (001) GaAs surfaces prepared in ultrahigh vacuum (UHV) by molecular-beam epitaxy and simultaneously characterized by reflection high-energy electron diffraction (RHEED). Reproducibility of the data is excellent. With the aid of previous theoretical calculations, we interpret characteristic spectral features at 1.9, 2.6, and 4.2 eV in terms of electronic excitations involving surface dimers of Ga, As, and As, respectively. Because RD couples to local electronic structure rather than to long-range order, RD spectra not only determine surface reconstructions but also provide details not accessible by RHEED, such as the existence of As dimers in the (1×6), (4×6), and (3×1) reconstructions and of the fractional coverage within a given reconstruction. Our data show that the (3×1), (1×6), and (4×6) reconstructions are at least partly determined by kinetics, since they can only be obtained by following specific heating or cooling procedures under very low As4 flux. More generally, it is possible to employ this optical technique to determine surface atomic and electronic structure. Because RD spectra can be obtained with the surface in any transparent ambient, the database that we have established here provides a new approach for elucidating surface reconstructions of (001) GaAs and hence the dynamics of surface reactions in non-UHV environments. © 1992 The American Physical Society.

DOI： 10.1103/PhysRevB.46.15894

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

We report the first direct observation of reconstructions of semiconductor surfaces in atmospheric pressure (AP) environments. We use reflectance difference spectroscopy (RDS), a surface-sensitive optical probe, to bridge the gap between ultrahigh vacuum (UHV) and AP, and show that the primary surface reconstructions that occur on (001)GaAs surfaces in UHV also occur in the AP environments used with organometallic chemical vapor deposition (OMCVD). Our results justify the applicability of the results of UHV surface science to understanding surfaces under non-UHV environments. Our results also show that during OMCVD growth conditions the surface is terminated with multilayers of As, contrary to generally accepted models. We also apply our newly developed approach, multi-transient spectroscopy (MTS), to the study of atomic layer epitaxy (ALE). Using MTS, we observe surface spectra within a time resolution of 100 ms during actual ALE growth cycles, thus allowing the dynamics of surface reactions to be investigated. © 1992.

DOI： 10.1016/0169-4332(92)90472-A

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

We report the first observation of reconstructions on semiconductor surfaces in atmospheric pressure (AP) environments. Using reflectance-difference spectroscopy we show that the primary reconstructions that occur on (001) GaAs in ultrahigh vacuum (UHV) also occur under AP, H2, He, and N2. These results demonstrate that dimer formation is not restrited to surfaces in UHV and justify the use of UHV studies to determine (001) GaAs chemistry during AP organometaliic chemical vapor deposition (OMCVD). Reconstructions observed during OMCVD growth are inconsistent with previous models and provide new insights concerning growth. © 1992 The American Physical Society.

DOI： 10.1103/PhysRevLett.68.627

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

DOI： 10.1016/j.mtener.2024.101786

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

DOI： 10.2139/ssrn.4948298

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

DOI： 10.2139/ssrn.4948296

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

DOI： 10.1117/1.OE.63.9.096101

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

DOI： https://doi.org/10.1117/1.JNP.18.036001

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

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

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0140035

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.apsusc.2022.155790

Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1361-6528/ac7ece

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IOP  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP  

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

A direct comparison of the structures of 2D and 3D types of capped stacked submonolayer (SML) InAs nanostructures is evaluated by transmission electron microscopy (TEM). Results of the TEM observation of SML samples with three stacks of InAs unambiguously show a stark contrast between the structures of 2D and 3D SML nanostructures, where the 2D SML nanostructures exhibit a planar structure with thickness that is consistent with the deposited stack height, whereas the 3D SML nanostructures exhibit several-nm-high structures that exceed the height of the deposited stack. In addition, structural evolution at the 2D to 3D transition in uncapped SML nanostructures is investigated by atomic force microscopy (AFM). The AFM results clearly reveal that the 2D to 3D transition occurred during the deposition of the third (and last) InAs SML stack in the present samples, where the density of 3D structures increases in orders of magnitude with the deposited amount of InAs on the order of a tenth of a monolayer at the onset. This effectively bridges the gap between the 2D and 3D nanostructures elucidating the abrupt nature of the transition.

DOI： 10.1063/5.0052722

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP  

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

We report the precise and broadband tuning of the photoluminescence (PL) from a stacked submonolayer (SML) InAs nanostructure across the 2D to 3D transition. We have recently reported the growth of stacked SML InAs nanostructures by molecular beam epitaxy, which leads to the formation of two distinct types of SML nanostructures: 2D islands and 3D structures. In contrast to the well-investigated transition in Stranski-Krastanov (SK) growth of InAs nanostructures, the transition in SML growth is still largely unexplored. Here, the properties of three- and four-stack SML InAs nanostructures are investigated by PL measurements and are interpreted in the context of the transition. At the transition, a characteristic change in the PL is observed, while the controllability of the PL is maintained across the transition. Furthermore, control of the transition itself is possible by changing the SML stack configuration. A brief comparison with the SK transition is also discussed.

DOI： 10.1063/5.0047287

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

The correlation between the structure, measured by atomic force microscopy (AFM), and luminescence, measured by photoluminescence (PL), of InAs submonolayer stacked (SMLS) nanostructures near the 2D to 3D transition is investigated. Topographic measurements using AFM reveal a significant change in the structure of uncapped InAs SMLS samples occurs under certain conditions. This structural change is attributed to the transition from 2D to 3D growth. Optical measurements by PL of corresponding capped SMLS samples showed a significant change in the luminescence properties, in the form of significant redshift and linewidth broadening, also occurs at the same conditions where the structural change occurred. Therefore, the data in the present work establishes a strong correlation between the structural and luminescence properties of InAs SMLS nanostructures. Furthermore, the results demonstrate that two forms of InAs SMLS, stacked 2D islands and 3D structures, possess distinct properties in terms of both structure and luminescence.

DOI： 10.35848/1347-4065/abd70a

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

An overview on the submonolayer stacking (SMLS) growth, by molecular beam epitaxy, is given for the growth of InAs-based quantum dots (QDs) and quantum well islands (QWIs) on GaAs in comparison with Stranski-Krastanov (SK) growth. While the size, shape, and density control of QDs by the substrate temperature or source fluxes has already been demonstrated by SK, SMLS provides novel possibilities due to its higher degree of freedom to control. By SMLS, QDs can be grown with higher size/shape control, and QWIs with varied thickness in disk-like shapes. These structures can be free from a wetting layer, being isolated from each other "floating"in the matrix. More importantly, the induced strain field is tunable, allowing us the opportunity to perform simultaneous strain and bandgap engineering. Our recent results in the tuning of photoluminescence wavelength and the transition from two-dimensional to three-dimensional structures together with atomic force microscopy are shown.

DOI： 10.35848/1347-4065/abef5f

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：JSAP  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

A strong topographical evidence of the 2D to 3D transition in InAs/GaAs nanostructures assembled by the submonolayer (SML) growth mode using molecular beam epitaxy (MBE) is reported. Whereas the 2D to 3D transition in InAs nanostructures assembled by the Stranski–Krastanov (SK) growth mode is well established with a critical thickness of around 1.7 monolayer (ML), the analogous phenomenon in SML-grown nanostructures is not yet well understood. Herein, atomic force microscopy (AFM) is utilized to investigate the topographical changes associated with the 2D to 3D transition in SML nanostructures, and it is unambiguously shown that for a given number of stacks and GaAs matrix (spacer) layer thickness, there exists a critical thickness in the amount of deposited InAs per cycle, beyond which the nucleation of 3D nanostructures abruptly begins. It is also shown that the critical thickness decreases with increasing number of stacks as well as with decreasing GaAs matrix layer thickness. Moreover, the present work shows that InAs/GaAs SML nanostructures exist in two distinct forms: 2D wetting layer (WL)-like islands and 3D quantum dot (QD)-like structures.

DOI： 10.1002/pssb.202000349

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IOP  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VHC  

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

Below-bandgap states induced by pre-epitaxial growth treatments in semi-insulating (s.i.) GaAs has previously been investigated by photoluminescence (PL). Various electronic states giving rise to near-infrared PL peaks are generated through processes such as annealing or buffer growth that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. These states often overlap with those from InGaAs structures, not only complicating the interpretation but also altering the electronic properties of the devices. The present study extends the investigation to the case of doped n-and p-Type (001) GaAs substrates. These substrates are widely utilized in various optoelectronic applications, and therefore information on below bandgap states are important to distinguish the desired electronic states from the pre-growth treatment-induced defect states. It was found that the behavior of n-and p-Type substrates subjected to pre-growth treatment are different from that of s.i. GaAs.

DOI： 10.35848/1347-4065/ab6e08

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP  

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

<jats:sec><jats:label /><jats:p>The below‐bandgap photoluminescence (PL) from semi‐insulating (s.i.) GaAs is investigated. It is found that various electronic states that give rise to near‐infrared (NIR) PL peaks are generated through processes that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. Moreover, the PL signals from these states overlap with those from InAs quantum dots, wetting layers, and InGaAs structures, complicating the design of devices for telecommunications or intermediate band solar cells. The spatial positions of the various defects are also investigated by below‐gap excitation and back‐illuminated PL measurements. The possible identities of the defects are also presented. The present results provide guidelines for distinguishing the desired electronic states from thermal treatment‐induced defect states.</jats:p></jats:sec>

DOI： 10.1002/pssb.201900391

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VHC  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP  

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

We report the observation of below-GaAs-bandgap photoluminescence (PL) emission from semi-insulating GaAs substrates subjected to thermal annealing during the standard pre-MBE-growth processes. The below-GaAs-bandgap luminescence from defects were investigated using a combination of PL techniques including below-gap-excitation (BGE) and backside illuminated (BI) PL. Using BGE and BI PL, defects deep within the substrates were probed, and their spatial positions along the sample were analyzed. A PL peak at 1000 nm was observed after pre-bake annealing at 300°C, and further peaks at 905, 940 and 1150 nm were found after oxide desorption annealing at 600°C. These are attributed to the Ga-vacancy related defect, Ga-vacancy-complex defect, As-vacancy defect, and InGaAs states, respectively. This is the first report of the formation of such optically-active defects after annealing of GaAs at moderate temperature ranges (≤600°C), providing guidelines to distinguish desired electronic states for device applications from those that arise from defects which often confuse, and also degrade the device performances.

DOI： 10.1063/1.5102088

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Kelvin probe force microscopy (KFM) measurements have been performed on cleaved p-Si/ITO (indium tin oxide) interfaces under light controlled conditions. The contact potential difference (CPD) measured by KFM are converted into work function, and hence the band alignment of the interfaces are obtained. We observe that the average work function differences between the p-Si and ITO layers are reduced from that in dark when illuminated.We tentatively attribute this result to the increase in the photogenerated hole density upon illumination, smoothing and widening the band bending in the ITO layer as well.

DOI： 10.1109/PVSC.2018.8547380

Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

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

A method for laser-induced local p-type activation of an as-grown Mg-doped GaN sample with a high lateral resolution is developed for realizing high power vertical devices for the first time. As-grown Mg-doped GaN is converted to p-type GaN in a confined local area. The transition from an insulating to a p-type area is realized to take place within about 1-2 μm fine resolution. The results show that the technique can be applied in fabricating the devices such as vertical field effect transistors, vertical bipolar transistors and vertical Schottkey diode so on with a current confinement region using a p-type carrier-blocking layer formed by this technique.

DOI： 10.1063/1.5009970

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

Up-converted photoluminescence (UPL) in InAs/GaAs heterostructures has been investigated. Relaxation process imposes a great challenge for efficient UPL. It is found that efficient UPL can be detected by the luminescence from InAs/GaAs multi quantum well (MQW), and that the intensity could be enhanced by further improving crystalline quality of GaAs barrier. In addition, choosing proper energy states as intermediate states is another important issue to enhance UPL. We describe how the overall UPL efficiency can be controlled by the epitaxial growth and selection of intermediate states. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2017.05.004

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

In the present work, {001}-faceted TiO2 nanosheets were prepared via a one-step hydrothermal method and used as backbone scaffold of photoanodes of solar cells. The graphitic carbon nitride (g-C3N4) was obtained by simple solid-state heat treatment and applied to modify the (001)-faceted TiO2 nanosheet photoanodes. Compared with the photoanodes prepared from pure (001)-faceted TiO2 nanosheets, the power conversion efficiency (PCE) of g-C3N4 modified (001)-faceted TiO2 nanosheet photoanodes was enhanced due to the suitable band-alignment between g-C3N4 and Ti-02. With 20% loading of g-C3N4 in the photoanode, a maximum PCE of 4.23% with an open circuit voltage of 0.58 V, a short circuit current density of 15.5 mA/cm2, and a fill factor (FF) of 0.48 was achieved, giving 24.7% enhancement in the cell efficiency. Various characterizations were performed to understand the role of g-C3N4 on the device performance, and the mechanisms that account for the improvement are suggested. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.spmi.2017.06.010

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6 degrees toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6 degrees toward the [1 (1) over bar0] direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.08MA06

Publishing type：Research paper (scientific journal)   Publisher：応用物理学会  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

DOI： 10.1117/12.2255021

Publishing type：Research paper (international conference proceedings)   Publisher：The Japan Society of Applied Physics and The Institute of Electrical and Electronic Engineers  

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The behavior of photogenerated charge carriers on SrTiO3 photocatalysts doped with transition metals (such as Ni and Ta) was examined by time-resolved visible to mid-IR absorption and emission spectroscopy. When SrTiO3 was co-doped with Ni and Ta, the catalyst absorbed visible light and exhibited photocatalytic activity undervisible light irradiation. However, activity under UV light was decreased significantly compared to that before doping. The results of time-resolved measurements showed that monodoping of Ni or Ta accelerated the recombination but co-doping Ni with Ta increased the lifetime of charge carriers compared to those without doping. Furthermore, electrons excited by a visible laser pulse had longer lifetimes compared to those excited by a UV laser pulse. Time-resolved photoluminescence measurements suggested that doped Ni cations act as recombination centers, giving a luminescence peak at similar to 8000 cm(-1) due to the downward d-d transition at Ni2+. However, the lifetime of the emission was much shorter than that of free or shallowly trapped electrons. These results suggest that recombination at the Ni cations is not the dominant process. In addition, the reactivity of photogenerated electrons was decreased dramatically by doping; electrons did not react with exposed O-2, although holes maintained reactivity with MeOH. These results confirm that the decrease in the steady-state activity of doped SrTiO3 under UV light irradiation is responsible for the decrease in reactivity of photogenerated electrons.

DOI： 10.1021/acs.jpcc.6b01494

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：ACS Publications  

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

DOI： 10.1109/ICIPRM.2016.7528759

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

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

© 2015 IEEE. The reduction Cu2+ and the crystal growth processes during colloidal synthesis of Cu2ZnSnS4 nanoparticles are investigated. We observe that ions Cu2+, Zn2+, Sn2+, and S2- from the precursors initially form amorphous-like nanoparticles, maintaining charge balance. To form the ideal kesterite crystal structure, Cu atoms need to be reduced from Cu2+ in the precursor stage into Cu+. The reduction of Cu2+ into Cu+ take place as crystal growth of the nanoparticles occur, and coalescence of nanoparticles seems limited. We deduce that it is essential to control the reduction and crystal growth for obtaining stoichiometric Cu2ZnSnS4 crystals, which is important for realizing high quality absorber layers for solar cells. The mechanisms and the implications are discussed.

DOI： 10.1109/PVSC.2015.7356364

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

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

Improving the utilization of solar spectra of wide bandgap semiconductors that can potentially provide enough free energy is one of the promising strategies for realizing efficient and spontaneous integrated conversion of solar energy to chemical fuels. We demonstrate herein that nitrogen doped InP quantum dots (QDs) embedded in wide bandgap GaP could improve the solar energy conversion performance. Photoelectrochemical experiments in contact with a nonaqueous, reversible redox couple indicated that the QD-embedded devices exhibited improved performance relative to devices without QDs, with short-circuit current densities increasing from 0.16 mA cm(-2) for GaP-only devices to 0.23 and 0.29 mA cm(-2) for InP and InNP QD-embedded devices, respectively. Additionally, the open-circuit voltages increased from 0.95 V for GaP-only devices to 1.11 and 1.14 V for InP and InNP QD-embedded devices, respectively, and the external quantum yield of the devices was also enhanced by the embedded QDs. The improvement is attributed to the absorption of sub-bandgap photons by the In(N)P QDs. (C) 2015 Elsevier Ltd. All tights reserved.

DOI： 10.1016/j.nanoen.2015.06.003

Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Publishing type：Research paper (scientific journal)   Publisher：The American Institute of Physics  

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

We have grown conductive aluminum nitride (AlN) layers using the spontaneous via holes formation technique on an n(+)-Si substrate for vertical-type device fabrication. The size and density of the via holes are controlled through the crystal growth conditions used for the layer, and this enables the conductance of the layer to be controlled. Using this technique, we demonstrate the fabrication of a vertical-type deep ultraviolet (DUV) photo-sensor. This technique opens up the possibility of fabrication of monolithically integrated on-chip DUV sensors and DUV light-emitting devices (LEDs), including amplifiers, controllers and other necessary functional circuits, on a Si substrate. (C) 2014 Author(s).

DOI： 10.1063/1.4905135

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

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

Self-assembled dilute nitride InNP quantum dots (QDs) in GaP matrix grown under the Stranski-Krastanov mode by gas-source molecular beam epitaxy are studied. The N-related localized states inside the InNP QDs provide a spatially direct recombination channel, in contrast to the spatially indirect channel through the strained In(N) P QDs/GaP interface states. The N incorporation into InP QDs therefore causes a blueshift and double-peak features in photoluminescence, which are not observed in other dilute nitride materials. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4900960

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Efficient upconverted photocurrent (PC) generation was verified for excitation of shallow InAs quantum well island (QWI) structures embedded in AlGaAs. Despite the weak absorption of a single layer with height of a few monolayer, about 0.04% increased external quantum efficiency for conversion of narrow monochromatic near-infrared light to PC was achieved. The excitation power dependence of the PC spectra indicates that state filling in the InAs layer occurs, and this must be considered for exact analysis of the upconversion mechanisms. When PC through GaAs is used for normalization, nearly identical power exponents were obtained for PC via upconversion in QWIs at low and high temperatures. This indicates that the same QWI states are responsible for the efficient PC generation from cryogenic up to room temperatures. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.53.05FV01

Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Publishing type：Research paper (scientific journal)  

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

DOI： 10.1016/j.jcrysgro.2013.10.010

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

DOI： 10.1016/j.jcrysgro.2013.10.01.0

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

We performed workfunction mapping of the cleaved interface of silicon heterojunction (SHJ) solar cell. While it has been widely accepted that the efficiency of solar cells depends on their electric contacts at various interfaces, no direct information on the electronic properties had been obtained on nm-scale. In this work, we employed Kelvin probe force microscopy (KFM) and simultaneously measured the workfunction and morphology of the cleaved interfaces on nm-scale for the first time. We show the measured workfunction differences between the surface layers on the cleaved SHJ solar cell, and discuss how such information can be used to improve the quality of the devices.

DOI： 10.1109/PVSC.2014.6925576

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

We study the role of As during InAs quantum dots (QDs) growth by molecular beam epitaxy using reflection high-energy electron diffraction (RHEED). We observe that the RHEED intensity transient onset and the transition to the saturation region occur at less InAs thickness under higher As-4 flux. From the RHEED transients, we find that the diffusion time does not depend on the As-4 flux while the diffusion barrier does. The diffusion length of In adatoms can be reduced by increasing the diffusion barrier using higher As-4 flux, allowing us to grow InAs QDs at higher densities. (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2012.12.147

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

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

DOI： 10.1063/1.4804236

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：World Scientific  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

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

The size of surface buried oxide nanostructures are measured by electrostatic force microscopy (EFM). In contrast to atomic force microscopy that cannot probe subsurface structures and thickness, we show that EFM data include information about the thickness of individual nanostructures, consequently allowing us to determine the thickness of buried nanostructures on semiconductor substrates. We further show that this measurement can be performed simultaneously with AFM using EFM modulation spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2013.01.146

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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

A novel quantum structure that could be applied for next generation solar cells through photon up-conversion is proposed. The structure which we term quantum well island (QWI) is an In As based structure that is a few monolayer thick, confining the carriers quantum mechanically, and extended tens to a hundred nm laterally thereby weakly confining the carriers enhancing multi-exciton interactions. By embedding In As QWIs in Al GaAs barrier layers, near infrared photons can be up-converted into visible, which has not been realized by quantum dots. We show the preparation and control of QWIs by molecular beam epitaxy, and the examples of such photon upconversion together with the proposed mechanisms. We also discuss how the conversion efficiency can be improved and the application to photocurrent conversion.

DOI： 10.1109/PVSC.2013.6745102

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Vacuum Society  

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

In-plane asymmetric strain relaxation in lattice-mismatched InGaAs/GaAs(001) heteroepitaxy is studied by in situ three-dimensional X-ray reciprocal space mapping. Repeating crystal growth and growth interruptions during measurements allows us to investigate whether the strain relaxation is limited at a certain thickness or saturated. We find that the degree of relaxation during growth interruption depends on both the film thickness and the in-plane directions. Significant lattice relaxation is observed in rapid relaxation regimes during interruption. This is a clear indication that relaxation is kinetically limited. In addition, relaxation along the [110] direction can saturate more readily than that along the [110] direction. We discuss this result in terms of the interaction between orthogonally aligned dislocations. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.02BP01

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

In-plane asymmetric strain relaxation in lattice-mismatched InGaAs/GaAs(001) heteroepitaxy is studied by in situ three-dimensional X-ray reciprocal space mapping. Repeating crystal growth and growth interruptions during measurements allows us to investigate whether the strain relaxation is limited at a certain thickness or saturated. We find that the degree of relaxation during growth interruption depends on both the film thickness and the in-plane directions. Significant lattice relaxation is observed in rapid relaxation regimes during interruption. This is a clear indication that relaxation is kinetically limited. In addition, relaxation along the [110] direction can saturate more readily than that along the [110] direction. We discuss this result in terms of the interaction between orthogonally aligned dislocations. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.02BP01

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Compositionally step-graded InGaAs/GaAs(0 0 1) buffers with overshooting (OS) layers were evaluated by several characterization techniques for higher efficiency metamorphic III-V multijunction solar cells. By high-resolution X-ray diffraction, we found that fully relaxed or tensile strained top layers can be obtained by choosing appropriate OS layer thickness. Moreover, from real-time structural analysis using in situ X-ray reciprocal space mapping (in situ RSM), it was proved that the top layer is almost strained to the OS layers, and it is independent of the thicknesses of the OS layers. Dislocations in the vicinity of the OS layers were observed by transmission electron microscopy, and the validity of results of in situ RSM was confirmed from the viewpoint of misfit dislocation behavior. Finally, by photoluminescence measurements, we showed that tensile strained top layers may be suitable for the improvement of minority-carrier lifetime.

DOI： 10.1109/JPHOTOV.2011.2174198

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Scientific Publishers  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

We synthesized organic solvent-soluble and water-soluble PbS quantum dots (QDs) with different sizes. The organic solvent-soluble PbS QDs dispersed in tetrachloroethylene were used to prepare bilayers structures of QDs bound by dithiol linkers on GaAs. The water-soluble PbS QDs were used to prepare bilayer structures of QDs on quartz based on alternating adsorption of polyelectrolyte. For bilayer films on GaAs, it was found that the stacking sequence of QDs affects the quantum yield and emission wavelength of the larger QDs. However, for bilayer films with different stacking sequences on quartz, the larger QDs show similar PL intensities and emission wavelength independent of the sequence. The probable mechanism for this difference observed is discussed in terms of charge transfer between QDs.

DOI： 10.1166/jnn.2012.5361

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AVS Science and Technology Society  

The growth mechanisms of InAs self-assembled quantum dots (QDs) on GaAs(001) by molecular beam epitaxy are studied by reflection high-energy electron diffraction (RHEED) transients along the two major axes, [110] and [110]. The authors observe anisotropy in the intensity transients and that there are two stages in QD formation, which emerge as different slopes in the RHEED transients. The authors attribute the anisotropy of the RHEED transients to the shape of QDs based on analysis using atomic force microscopy. The difference in the QD formation processes at each slope is investigated together with photoluminescence measurements. The authors observe that the QD density increases during the first slope whereas the QD density remains constant and the QD size increases during the second slope. © 2012 American Vacuum Society.

DOI： 10.1116/1.3694019

Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics  

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

Dislocation-mediated strain relaxation during lattice-mismatched InGaAs/GaAs(001) heteroepitaxy was studied through in situ x-ray reciprocal space mapping (in situ RSM). At the synchrotron radiation facility SPring-8, a hybrid system of molecular beam epitaxy and x-ray diffractometry with a two-dimensional detector enabled us to perform in situ RSM at high-speed and high-resolution. Using this experimental setup, four results in terms of film properties were simultaneously extracted as functions of film thickness. These were the lattice constants, the diffraction broadenings along in-plane and out-of-plane directions, and the diffuse scattering. Based on correlations among these results, the strain relaxation processes were classified into four thickness ranges with different dislocation behavior. In addition, the existence of transition regimes between the thickness ranges was identified. Finally, the dominant dislocation behavior corresponding to each of the four thickness ranges and transition regimes was noted. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3664832]

DOI： 10.1063/1.3664832

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The structure of interfaces plays an important role in determining the electronic properties of semiconductor nanostructures. Here, such examples are shown and discussed using semiconductor nanostructures prepared by molecular beam epitaxy and colloidal synthesis. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1757-899X/24/1/012006

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

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

We have characterized the electron transport properties of n-decylamine-functionalized Si nanosheets (NSs) using atomic force microscopy with a conductive cantilever under vacuum conditions at room temperature. Electrons are transported from the cantilever to the substrate through Si NSs. The Si NSs exhibit nonresonant tunneling; the transport mechanisms are based on direct tunneling at low bias voltages and Fowler-Nordheim tunneling at high bias voltages. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610486]

DOI： 10.1063/1.3610486

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We investigated the influence of an unfocused electron beam (e-beam) passing in front of a sample during molecular beam epitaxy (MBE) growth of GaAs on the upconverted photoluminescence efficiency and found a strong influence on the intermediate states. A clear difference in the Stokes and anti-Stokes photoluminescence (PL) is observed. Time-resolved PL correlation spectroscopy results allow us to suggest that an unfocused e-beam increases the density of a specific GaAs bulk state also found in samples grown without an e-beam. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/APEX.4.065501

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Physics  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

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

The growth of self-assembled (SA) quantum dots (QDs) on GaAs(0 0 1) by molecular beam epitaxy (MBE) is studied as a function of the In and As fluxes. Under growth rates below 0.05 ML/s, we find that the density of QDs increases not only with increasing In flux but also with As flux. The formation mechanisms are discussed based on the results obtained by atomic force microscopy (AFM), and that As flux alters the surface diffusion, leading to the control of QD nucleus density. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2011.01.034

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

Growth temperature dependence of strain relaxation during In0.12Ga0.88As/GaAs(0 0 1) molecular beam epitaxy was studied by in situ X-ray reciprocal space mapping. Evolution of the residual strain and crystal quality for the InGaAs film was obtained as a function of film thickness at growth temperatures of 420, 445 and 477 degrees C. In the early stages of strain relaxation, it was found that evolution of the residual strain and crystal quality was dependent on the growth temperature. In order to discuss this observation quantitatively, the strain relaxation model was proposed based on the Dodson-Tsao kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. Additionally, rate coefficients reflecting dislocation motions during strain relaxation were obtained as a function of growth temperature and strain relaxation was discussed in terms of the thermally active dislocation motion. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2010.10.005

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Publishing type：Research paper (scientific journal)  

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

An attempt to control surface electronics of III-V semiconductor using wet chemical processes has been performed. Here, we report results on the use of self-assembled monolayers (SAMs) of organic molecules on (001) GaAs surface. Octadecanethiol (ODT) and benzenethiol (BT) have been the choice in the present study.
GaAs wafers were modified by thiol molecules on the flat surface after the native oxide layers are removed by chemical etching under optimized conditions. The change in the electronic properties was measured in terms of transport properties via the SAM layer by conductive probe atomic force microscopy. The current-voltage characteristics thus obtained show that ODT functions as a tunnel barrier while BT is conductive due to the presence of pi-electrons. As a result, we can control the electronic states of GaAs-molecule interface for realizing novel device structures by the selection of functional molecules. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2010.01.018

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

Resonant tunneling of electrons through a quantum level in single self-assembled InAs quantum dot (QD) embedded in thin AlAs barriers has been studied. The embedded InAs QDs are sandwiched by 1.7-nm-thick AlAs barriers, and surface InAs QDs, which are deposited on 8.3 nm-thick GaAs cap layer, are used as nano-scale electrodes. Since the surface InAs QD should be vertically aligned with a buried one, a current flowing via the buried QD can be measured with a conductive tip of an atomic force microscope (AFM) brought in contact with the surface QD-electrode. Negative differential resistance attributed to electron resonant tunneling through a quantized energy level in the buried QD is observed in the current-voltage characteristics at room temperature. The effect of Fermi level pinning around nano-scale QD-electrode on resonance voltage and the dependence of resonance voltage on the size of QD-electrodes are investigated, and it has been demonstrated that the distribution of the resonance voltages reflects the size variation of the embedded QDs. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2009.10.010

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Vacuum Society  

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

Real-time three-dimensional reciprocal space mapping (3D-RSM) measurement during In(0.12)Ga(0.88)As/GaAs(001) molecular beam epitaxial growth has been performed to investigate anisotropy in relaxation processes along [110] and [(1) over bar 10] directions caused by alpha and beta misfit dislocations (MDs). Anisotropies, strain relaxation, and crystal quality in both directions were simultaneously evaluated via the position and broadness of 022 diffraction in 3D-RSM. In the small-thickness region, strain relaxation caused by alpha-MDs is higher than that caused by beta-MDs, and therefore crystal quality along [110] is worse than that along [(1) over bar 10]. Rapid relaxation along both [110] and [(1) over bar 10] directions occurs at almost the same thickness. After rapid relaxation, anisotropy in strain relaxation gradually decreases, whereas crystal quality along [(1) over bar 10] direction, presumably due to beta-MDs, becomes better that along [110] direction and the ratio does not decay with thickness. (C) 2010 American Institute of Physics. [doi:10.1063/1.3458695]

DOI： 10.1063/1.3458695

Authorship：Last author   Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AVS Science and Technology Society  

GaAs surface was modified by self-assembled monolayer of organic molecules through wet chemical processes, which include etching and coating. Octadecanethiol (ODT) and benzenethiol (BT) were the choice as modifiers. Etched surface of the GaAs, whose quality greatly affects the morphology and properties of the resulting modified GaAs, was investigated by x-ray photoelectron spectroscopy combined with atomic force microscopy (AFM). Nanometer-scale particlelike structures of Ga2O3 appeared on the surface after etching by etchant with low acid concentration. The particle size was controllable by the acid concentration and etching time. Almost the entire surface of the GaAs substrate was successfully covered with thiol molecules when GaAs etched by the etchant with high acid concentration was used. The conduction of the ODT-coated GaAs measured with conductive prove AFM using Rh coated cantilevers was below the detection limit of the current amplifier. However, current-voltage characteristics of BT-coated GaAs showed electron rectification proving electron transport via the π-orbital. The molecular modification of the semiconductors by wet chemical processes may afford a promising route to control the surface states of organic molecule-semiconductor interface for novel device structures. © 2010 American Vacuum Society.

DOI： 10.1116/1.3447228

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AVS Science and Technology Society  

The authors report the self-assembly and characterization of monolayer PbS quantum dots (QDs) on GaAs substrates and the effect of thermal annealing on close-packed PbS QD films. The QD monolayer film was prepared using a 1,6-hexanedithiol self-assembled monolayer to link PbS QDs to GaAs substrates. Atomic force microscopy measurement confirmed the formation of PbS QD monolayer on GaAs. The temperature dependence of photoluminescence (PL) intensity of PbS QDs shows a feature typical for close-packed PbS QD films. For investigation of the influence of thermal annealing, three close-packed films of colloidal PbS QDs were prepared by drop coating and treated at different annealing temperatures. By controlling the annealing temperature, the PL intensity of close-packed films at room temperature can be improved. The room temperature PL intensity can be adjusted to be higher than that at 10 K. These results provide insights for future applications of colloidal QDs and the improvement of their performances. © 2010 American Vacuum Society.

DOI： 10.1116/1.3456172

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

In situ real-time X-ray diffraction measurements during In(0.12)Ga(0.88)As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-m is matched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/APEX.2.085501

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

In situ real-time X-ray diffraction measurements during In(0.12)Ga(0.88)As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-m is matched system. The high resolution reciprocal space maps of 004 diffraction obtained at interval of 6.2 nm thickness enable transient behavior of residual strain and crystal quality to be observed simultaneously as a function of InGaAs film thickness. From the evolution of these data, five thickness ranges with different relaxation processes and these transition points are determined quantitatively, and the dominant dislocation behavior in each phase is deduced. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/APEX.2.085501

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

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H(2)O and CO(2) generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4-24 nm and diameter of 10-36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO(2) or Al(2)O(3). These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.10.128

Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)  

DOI： doi:10.1016/j.physe.2009.10.010

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A self-assembled monolayer of polystyrene (PS) beads is formed on a silicon wafer by spin-coating. After drying at 80 degrees C, a thin film of metal/oxide is deposited. During the deposition, the PS beads are detached due to forces such as the inner stress induced by plasma sputtering deposition, mechanical vibration, and centrifugal shearing induced by substrate rotation, resulting in nanoring/nanohole formation. Further experiments demonstrate that the PS detachment can be controlled by scanning probe microscopy (SPM) tip manipulation. We believe this is a promising set of processes for fabricating nanodevice structures such as those of vertical nanotransistors, which provides high flexibility for nanocrystal characterizations and application for single-electron devices.

DOI： 10.1088/0957-4484/19/31/315303

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

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

Resonant tunneling of electrons through a quantum level in a self-assembled InAs quantum dot (QD) has been measured by conductive atomic force microscopy (AFM) at room temperature. InAs QDs are embedded in a 3.4 nm thick AlAs layer, and capped with 8.3 nm-thick GaAs layer on which surface InAs QDs are deposited as nano-scale electrodes. Bringing the conductive AFM tip on the surface InAs QD which ahould be vertically aligned with a buried QD, a bias voltage is applied to the samle, and a current flowing via the bruied QD is measeured. Negative differntial resistance attributed to electron resonant tunnelling through a quantized energy lelvel in the buried QD is observed in the current-voltage characteristics. The voltage loss by nano-scale electrode and the dependence of resonance voltage on the size of the surface QD-electrodes are discussed. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200779302

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

Real-time observation of self-assembled (SA) InAs quantum dot (QD) growth on GaAs(001) by MBE has been performed. Through transient measurements on reflection high energy electron diffraction (RHEED) specular beam, we obtain information about nucleation and evolution of the QDs in situ, in contrast to most previous reports that required growth interruption. Based on the observation, we have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. We also provide a quantitative discussion on these processes. © 2007 Materials Research Society.

Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：Material Research Society  

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MATERIALS RESEARCH SOCIETY  

Inorganic/organic hybrid material of CdSe/ZnS core/shell nanocrystals (NCs) covered with organic ligands was prepared with ligand exchange reaction in order to facilitate carrier injection into NCs through the organic ligands. The organic ligands used in this study, 2-naphtalenethiol and bathophenanthroline, were selected as model compounds according to adjustment of highest occupied molecular orbital and lowest unoccupied molecular orbital of the ligand to valence band maximum and conduction band minimum of the CdSe NCs, respectively. The prepared hybrid NCs easily disperse in polar organic solvents such as CHCl3 and show photoluminescence only from the CdSe/ZnS core/shell NCs. Current-voltage characteristics of the ligand exchanged NCs thin films sandwiched between electrodes were investigated. It was shown that conductivity of the film was improved by the introduction of carrier injecting ligands in comparison to the ligand unexchanged trioctylphosphine oxide-capped CdSe/ZnS NC thin film. © 2005 Materials Research Society.

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

The resonant tunneling process of electrons through a single self-assembled InAs quantum dot (QD) has been studied by conductive-tip atomic force microscopy. The unique structure employed here consists of two layers of InAs QDs, which are separated by 5-nm-thick undoped GaAs layer. The conductive tip is placed in contact with the surface InAs QD which functions as a nano-sized electrode to measure the flow of electrons from the n(+)-GaAs substrate via a buried QD. A conductance structure attributed to resonant electron tunneling through the quantized level of QD is observed in the current-voltage characteristics. The resonant voltage is larger than the usual flat band voltage, indicative of a considerable voltage loss caused by the Fermi level pinning around the nano-sized electrode. &COPY; 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2004.12.117

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC CHEMICAL ENG JAPAN  

A mesh-type Cu-Mn-CeOxAl2O3/Al alumite catalyst was employed to investigate the selective reduction of NO with C3H6 in the presence of SO2 and H2O. The effect of SO2 on the de-NOx activity closely depended on SO2 concentration and temperature. At a low temperature (673 K), SO2 of 50 ppm greatly improved the NO, reduction, but a further increase in SO2 concentration (up to 500 ppm) caused a rapid catalyst deactivation. As temperature increased to 723 K, the catalyst deactivation caused by 500 ppm SO2 disappeared, and further the presence of SO2 also produced a remarkable promotion in the de-NOx activity. The effect of SO2 was observed to be an irreversible course associated with irreversible chemical phase transition. The presence of SO2 was considered to inhibit the over-oxidation of the organic-intermediates by oxygen, and to make the organic-intermediates more available for the NOx reduction. However, a high concentration of SO2 inhibited not only this over-oxidation but also propene activation, and led to catalyst deactivation. The inhibition of SO2 in the propene activation, mainly attributed to the over-adsorption of SO2, could be weakened as temperature increases. Although the presence of water vapor depressed the de-NOx activity, this change was almost reversible. In comparison with the separate presence of SO2, the coexistence of H2O and SO2 More dramatically improved the NOx reduction. It was considered possible that the coexisting H2O diluted SO2 to lessen the inhibition effect of SO2 on activating propene.

DOI： 10.1252/jcej.37.895

Authorship：Last author   Publishing type：Research paper (international conference proceedings)   Publisher：Materials Research Society  

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We report the changes in surface state of tri-n-octylphosphine oxide (TOPO) capped CdSe nacocrystals by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In the photobrightening state, where photoluminescence (PL) intensity increased during the illumination, surface ligand rearrangement such as the TOPO-Se compelx and TOPO dimers; are formed, which might be deeply correlated with the PL enhancement. It was also observed that surface oxidation and decomposition of TOPO, which is followed by the desorption, occurred in photodarkening state.

DOI： 10.1021/jp035484a

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MATERIALS RESEARCH SOC  

We have investigated current-voltage characteristics of individual CdSe colloidal nanodots by conductive-tip atomic force microscopy (AFM). The colloidal nanodots were spun-coat and scattered on a self-assembled monolayer of thiophene molecules formed on Au (111) surfaces for single dot measurements. A thin SiO2layer was deposited on the sample surface in order to prevent the dots being moved by the tip during measurement. We imaged the topography of isolated single dots by AFM operated in contact mode, and measured current-voltage characteristics with the conductive tip positioned on single dots; large conductivity changes which suggest resonant tunneling through a quantized energy level in the dot was observed even at room temperature.

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

Electronic properties of individual Use colloidal nanodots have been investigated by conductive-tip atomic force microscopy (AFM). Submonolayer-thick films of the colloidal nanodots were fabricated on a self-assembled monolayer of alkanethiol molecules formed on Au(111) surfaces for single dot measurements. First, we simultaneously imaged the topography and conductivity of isolated single dots by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the Use dots. We found a 10-nm scale,electric inhomogeneity around the dots, which may correspond to the previously reported etch-pits of Au(111) surfaces formed during the deposition of the alkanethiol molecules. Then, current-voltage characteristics were measured with the conductive tip positioned on the single dots; large changes in the conductivity which suggest resonant tunneling through the quantized energy level in the dot were observed even at room temperature. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00088-8

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The change in the photoluminescence intensity of CdSe nanocrystal/polymer thin films with duration of illumination is investigated. The choice of polymer has an influence on photobrightening and photodarkening. In particular, photodarkening in CdSe nanocrystal/poly(vinyl carbazole) thin film occurs immediately upon illumination, in contrast to the slow changes observed with polystyrene and poly (2-vinylpridine). We discuss the mechanisms of this phenomenon in comparison with interaction between surface of CdSe nanocrystals and polymer side chain.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

A single chromophore detection using video-microscopy is one of the latest methodologies to reveal unique characteristics, which could not be obtained from ensemble measurements. Among many kinds of subjects, dynamic optical properties observed in colloidal semiconductor nanoparticles are attractive and important not only for the basis of photo-physics but also for application studies, e.g. biological labeling, electronic devices. In this study, fluorescence video-microscopy was performed on cadmium selenide (CdSe) quantum dots (QDs) spin-coated on a glass substrate. From single CdSe QDs detection, emissions at wavelengths separated over 60 nm were observed for the first time. This spectral feature was attributed to the existence of double-emissive relaxation processes in CdSe QDs. Photoluminescence intermittency was also observed both from relaxation processes. Fluorescence video-microscopy, which was advanced in biology, can be applicable for the real-time monitoring of dynamic properties in semiconductor photo-physics. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.stam.2003.12.008

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MATERIALS RESEARCH SOCIETY  

We have fabricated submonolayer-thick films of CdSe colloidal nanodots in order to investigate electronic properties of individual nanodots by conductive-tip atomic force microscopy (AFM). Topographic and current images of isolated single CdSe colloidal dots on single crystalline Au (111) surface which was covered with dodecanethiol self-assembled monolayer were obtained by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We also found 10 nm-scale electric inhomogeneity around the dots, which may corresponds to the previously reported etch-pits of Au (111) surfaces formed during the deposition of the dodecanethiol molecules.

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

By forming a micron-scale Schottky diode on a GaAs/n+-GaAs wafer with low density (∼ 4 × 108 cm-2) self-assembled InAs quantum dots (QDs) embedded in the top GaAs layer, we have studied resonant tunneling transport of electrons via single QDs. As the diode defined by electron-beam lithography and chemical etching has a size of about 1 μm2 and the edges of each diode are depleted, the number of active InAs QD contained in each microdiode can be reduced to less than unity in average. Current-voltage measurements were performed using conductive probe atomic force microscope, and current peaks caused by electrons resonantly tunneling through quantum levels of single QDs have been observed at temperatures as high as ∼ 130 K. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(01)00503-3

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The change in the photoluminescence intensity of CdSe nanocrystal./polymer thin films with duration of illumination is investigated. The choice of polymer has an influence on photobrightening and photodarkening. In particular, photodarkening in CdSe nanocrystal/poly(vinyl carbazole) thin film occurs immediately upon illumination, in contrast to the slow changes observed with polystyrene and poly(2-vinylpridine). We discuss the mechanisms of this phenomenon in comparison with interaction between surface of CdSe nanocrystals and polymer side chain.

DOI： 10.1142/S0219581X02000814

Publishing type：Research paper (scientific journal)  

We report the fabrication and characterization of the self-assembled structure of tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals in binary polymer phase separated films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(2-vinylpyridine) (P2VP). These structures are formed via demixing of CdSe nanocrystals and binary polymer during spin coating. The nanocrystals preferentially segregate to the PS-rich phase in phase separated PS/PMMA and to the P2VP-rich phase in phase separated PS/P2VP, as shown by optical microscopy and photoluminescence images. For CdSe/PS/PMMA, we attribute the driving force for CdSe segregating to the PS-rich domain to the stronger attractive interaction of TOPO on PS with respect to PMMA due to polarity, and in the case of CdSe/PS/P2VP, segregating to the P2VP-rich domain to the interaction such as coordinate bonds being formed between pyridine groups and surface Cd atoms.

Publishing type：Research paper (scientific journal)  

We observed the surface topography of CdSe colloidal nano-dot film by cyclic contact mode atomic force microscopy. The observed structure changes with cantilever oscillation amplitude, and non-uniform images with long-range corrugations are obtained with relatively large oscillation amplitude while fine structures are revealed with smaller oscillation amplitude. When the amplitude is larger and the surface is weakly &#039;tapped&#039;, the topography of the soft organic matrix of the film dominates, and when the tapping force is increased, the hard CdSe dots begin to reveal.

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

One-dimensional disorder in a reconstructed surface can give rise to sheetlike structures in reciprocal space. For disorder caused by one-dimensional domain boundaries such as those that occur on the GaAs{100}(2 × 4) surface, sheetlike structures are only present at fractional order diffraction features. The absence of these sheets at integral diffraction features is explained using kinematic theory of diffraction and "selection rules" for these sheetlike structures are established. Applications of these rules are demonstrated using optical transmission diffraction.

DOI： 10.1016/S0218-625X(01)00130-0

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

Capacitance images responsible for surface depletion were observed on an InAs dot-covered GaAs surface by scanning capacitance microscopy. We performed local capacitance versus bias voltage measurements on quantum dots (QDs) and a wetting layer (WL) as well as conductance versus bias voltage (G-V) measurements. Both results indicate that the surface depletion is more suppressed beneath the QDs than under the WL. In addition, the conventional thermionic equation theory fitted to the measured G-V curves shows that the interface barrier height between the GaAs and the InAs QD increases as the QD size is reduced. We ascribe this result to the influence of the surrounding WL, whose surface Fermi level is strongly pinned at the midgap of the n-GaAs. (C) 2000 American Institute of Physics. [S0003- 6951(00)02239-7].

DOI： 10.1063/1.1312257

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Sci B.V.  

We have imaged surface potential of InAs self-assembled quantum dots on GaAs (0 0 1) surface by scanning Maxwell stress microscopy. Simultaneously obtained constant tip-sample capacitance image and surface potential image were compared with atomic force microscope (AFM) image, and was found that the surface potential on large dots of about 100-nm diameter is approximately 610 mV which is 30-40 mV lower than that on regular size dots. This result well coincides with previously reported Schottky barrier heights which were estimated from current versus voltage measurements with the same type of samples using conductive probe AFM.

DOI： 10.1016/S1386-9477(99)00344-6

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

We performed atomic force microscopy in contact mode while applying an ac bias voltage between a conductive tip and a sample to characterize near surface band structures of InAs-covered n-type (001) GaAs, where self-assembled dot structures were formed. Electrostatic force of less than 10 pN was detectable, and clear electrostatic force images and topographic images were simultaneously obtained with lateral resolution higher than 20 nm. The electrostatic force images from single and double frequency components reveal that the gap width between the tip and the conductive region under the dot-covered area of the sample is smaller and is less modulated by the bias voltage than under the wetting layer. The results indicate that surface depletion is more suppressed beneath the dots. (C) 1999 American Institute of Physics. [S0003-6951(99)00930-4].

DOI： 10.1063/1.124432

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

We performed simultaneous imaging of photoinduced current and topography on an InAs-covered GaAs surface by scanning tunneling microscopy (STM) under modulated laser irradiation to investigate the difference in the electronic properties between quantum dots and a wetting layer. We also performed time-resolved tunneling current measurements to clarify the origin of the photoinduced effects on its surface. We observed a spiky transient current, resulting from photocarrier separation by a built-in field in the surface depletion layer. Images of the photoinduced current mainly originating from the surface depletion were obtained at a chopping frequency of 900 Hz, and both the photoinduced current images, and the current transients observed at this frequency reveal that the surface depletion is more suppressed under the dots than under the wetting layer.

DOI： 10.1143/JJAP.38.3871

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

Atomic force microscopy with a conductive probe has been used to study both the topography and the electronic properties of 10-nm-scale self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy on n-type GaAs. The current flowing through the conductive probe normal to the sample surface is measured for imaging local conductance, while the deflection of cantilever is optically detected for disclosing geometrical structure. The conductance on InAs QDs is found to be much larger than that on the wetting layer, allowing imaging of QDs through measurements of local current. We attribute this change in conductance to the local modification of surface band bending associated with surface states on InAs QD surface. Mechanisms of electron transport through QDs are discussed based on current-voltage characteristics measured on QDs of various sizes. (C) 1999 American Institute of Physics. [S0003-6951(99)03206-4].

DOI： 10.1063/1.123402

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：John Wiley &amp; Sons Ltd  

We performed atomic force microscopy (AFM) on an InAs-covered GaAs surface on which InAs dot structures are formed surrounded by a wetting layer. In order to characterize its surface band structures, we applied an a.c. bias voltage (f = 25 kHz) between a conductive AFM tip and a sample. By means of a lock-in detection technique, clear electrostatic force images as well as topographic images were obtained with high resolution. The electrostatic force images of the different frequency components (f and 2f) reveal that the gap width between the tip and the conductive region of the sample is modulated very little by the bias voltage in the dot-covered area, whereas the gap width is obviously modulated in the wetting layer area. These results indicate that the surface depletion is more suppressed in the dot-covered area than in the wetting layer area.

DOI： 10.1002/(SICI)1096-9918(199905/06)27:5/6<547::AID-SIA481>3.0.CO;2-Q

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Science B.V.  

Electronic properties of self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy have been investigated by atomic force microscopy (AFM) with conductive tip. The conductive AFM tip is brought to contact with QDs of various sizes, which are oxidized due to the sample transfer through the air, and current versus voltage (I-V) characteristics are measured under forward bias condition. The obtained I-V curves indicate that the Schottky barrier is lower on large QDs of 70-90 nm diameter compared to that on small QDs of 30-40 nm diameter, i.e. the surface band structure is locally modified by the QDs. This modification is considered to be due to the positive surface charges on the InAs QDs which compensate for the negative surface states of the surrounding wetting layer.

DOI： 10.1016/S0022-0248(99)00029-9

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have investigated the terahertz photoresponse of a single semiconductor quantum dot, electrostatically defined by a sharp conducting Atomic Force Microscope (AFM) tip in contact with a resonant tunneling diode structure. The quantum dot is excited by radiation from a Free Electron Laser in experiments both at room temperature and at cryogenic temperatures. Pronounced resonant tunneling features and classical rectification at frequencies from 0.3 to 3THz are observed in the I-V curves of these devices. These results demonstrate a novel approach to achieving terahertz excitation and studying transport in quantum dots.

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

The morphological evolution of thin layers of InAs deposited on (0 0 1)GaAs has been investigated by photoluminescence (PL) and atomic force microscopy (AFM). We observe PL features that correspond to the transformation of the InAs wetting layer and 2D islands into quantum dots (QDs), which is supported by the AFM study. Variation in the PL spectra is also observed as a function of the thickness of the GaAs layer deposited on top of the InAs layer. Luminescence intensity from both the QDs and the wetting layer (WL) picks up at a thickness of about 10-20 monolayers. As the thickness is increased, uprise in PL intensity for both QDs and WL together with a narrowing in the WL peak is observed. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(98)00130-1

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

The terahertz photoresponse of a single semiconductor quantum dot is measured at room temperature. Pronounced resonant tunneling and a rectified response at frequencies from 0.6 to 3 THz are observed in the I-V curve of the submicron device. We use this to demonstrate a novel approach to the study of quantum dots, in which a submicron resonant tunneling device is electrostatically defined using a conducting atomic force microscope (AFM) tip. In addition, the conducting AFM tip electrically contacts the device and serves as an antenna to couple far-infrared radiation into the dot. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(98)00143-X

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

We have studied electronic states near the surface of InAs-covered GaAs(001) by tunneling spectroscopic measurements. Differential conductance was measured on samples with an InAs wetting layer or InAs dot structures on n-type GaAs by a scanning tunneling microscope operated in air under laser irradiation. The modulation effect of laser irradiation on the tunneling properties reveals that for the sample with the InAs wetting layer on n-GaAs, surface electronic properties - such as band bending and surface Fermi level - are very similar to those of a bare n-GaAs sample. In contrast, additional deposition of InAs over the wetting layer, which forms InAs dots, leads to a drastic change in electronic properties near the surface. © 1998 Springer-Verlag.

DOI： 10.1007/s003390051296

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0022-0248(96)01204-3

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE - INT SOC OPTICAL ENGINEERING  

Various optical techniques have been developed over the last few years for real-time analysis of surfaces and near-surface regions of semiconductor epitaxy. These techniques are providing insights into microscopic mechanisms of epitaxy and opportunities for sample-driven closed- loop feedback control of the epitaxial growth process. Both aspects are expected to become increasingly important as device complexity increases and tolerances become more stringent. Examples are provided and opportunities discussed.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Growth of InAs on InAs (111)A by molecular beam epitaxy has been studied using reflection high energy electron diffraction intensity oscillations. The period of the intensity corresponds to the flux of In for lower substrate temperatures and/or higher As fluxes and is independent of growth conditions. However, for higher substrate temperatures and/or lower As fluxes, the period is longer than the value expected from the In flux and strongly depends on the growth conditions. A critical growth condition, defined as the boundary between the two regions, is a strong function of the As flux and substrate temperature. The increase of the period is explained by the deficiency of As on the growing surface due to its low sticking coefficient.

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

We report the first real-time observation of atomic ordering in a semiconductor alloy during epitaxial growth. (001) In0.53Ga0.47As layers deposited below about 400°C exhibit a strong anisotropy in the broadening parameters of the E1,E11 transitions that is observable with reflectance-difference spectroscopy. This unusual optical behavior results from intraband mixing driven by triple-period ordering along both [111] and [111»] directions simultaneously. This microstructure is realizable with stoichiometry In0.556Ga0.444As virtually identical to that needed to lattice match InP. © 1995 The American Physical Society.

DOI： 10.1103/PhysRevLett.74.3640

Publishing type：Research paper (scientific journal)  

This paper reviews our present understanding of particular aspects of the surface processes involved in the growth of epitaxial semiconductor films by molecular beam epitaxy. Emphasis is placed on adatom migration and incorporation on GaAs (001) substrates during the growth of GaAs, a comparison with equivalent growth effects on (110) and (111)A oriented substrates, and the influence of mismatch and substrate orientation on growth mode and strain relaxation in the InAs/GaAs system. A brief indication of surface segregation behaviour is also included. © 1995.

DOI： 10.1016/0921-5107(94)09003-3

Publishing type：Research paper (scientific journal)  

In this work, in‐situ grazing incidence X‐ray scattering is used to correlate surface structures observed during organometallic vapor phase growth of GaAs with in‐situ optical measurements using reflectance difference spectroscopy (RDS). Our observations of several reconstructions confirm that RDS signals vary among the different surfaces present under vapor phase epitaxy conditions, as also occurs under ultra‐high vacuum growth conditions. In addition, the simultaneous observation of intensity oscillations in the X‐ray scattering signal and the reflectance difference signal indicates that both of these techniques can be used to monitor layer‐by‐layer growth processes under some conditions. Copyright © 1995 WILEY‐VCH Verlag GmbH &amp; Co. KGaA

DOI： 10.1002/pssa.2211520102

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

Molecular beam epitaxy (MBE) growth of GaAs buffer layer and subsequent deposition of InAs layers on GaAs (110) misoriented by 1.5 degrees towards (111) A are studied using transmission electron microscopy. The observations show that step bunching occurred during the buffer layer growth. InAs is found to nucleate and grow on the bunched step edges.

DOI： 10.1016/0022-0248(95)00736-9

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

Structure and growth dynamics of vicinal GaAs (001) surfaces during metalorganic vapour phase epitaxy (MOVPE) are studied using reflectance anisotropy/difference spectroscopy (RAS or RDS). Spectra at different temperatures from (001)‐surfaces tilted with angles between 0° and 6° towards the [110]‐ or [110]‐axis are compared to those taken from nominally untilted (singular) surfaces. Under AsH3 stabilized conditions singular surfaces show c(4×4)‐like RAS spectra for temperatures up to around 900 K. This type of spectrum is only observed at lower temperatures for vicinal surfaces. At higher temperatures RAS spectra which are characteristic of Ga dimer formation are obtained. The temperature at which this change from an As dimer‐ to a Ga dimer‐dominated spectrum occurs, decreases with increasing misorientation angle and thus increasing number of steps. These results strongly indicate that there is an arsenic deficiency at steps resulting in formation of Ga dimers. Similarly, spectra during growth of vicinal surfaces show enhanced coverage with Ga dimers compared to those of singular surfaces. Growth kinetics, however, does not seem to be influenced by the presence of steps. The growth dynamics are studied in dependence of the misorientation by time‐resolved RAS measurements. RAS monolayer oscillations are observed only for misorientations up to 2°. The temperature, above which the oscillations disappear, decreases with increasing misorientation. This confirms that the upper temperature limit for the existence of MOVPE‐RAS growth oscillations is given by the transition from island‐ to step flow‐growth mode. In contrast to typical molecular beam epitaxy (MBE) growth large diffusion lengths need to be assumed in MOVPE but the differences between different misorientation directions turn out to be small. Copyright © 1995 WILEY‐VCH Verlag GmbH &amp
Co. KGaA

DOI： 10.1002/pssa.2211520105

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

InAs layers of different layer thicknesses grown on GaAs (110) with an off cut of 1.5 degrees towards (111)A were studied by TEM. It was found that at the early stage of growth, InAs preferentially deposited along the step edges forming elongated strips along [110] direction on the surface. The cross-sections showed that as the layer thickness increased, the width of InAs strips expanded on both the upper and lower terraces, although predominantly the latter. The complete coverage of the GaAs surface occurred when the InAs strips coalesced laterally.

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

We have made a reflection high-energy diffraction (RHEED) intensity oscillation study of the growth of (Al,Ga)As on GaAs and (Al,Ga)As (111)A surfaces. The RHEED intensity oscillations during growth of (Al,Ga)As are dependent on both growth temperature and As4:Ga flux ratio. In addition, the oscillation period decreases as the Al fraction in the (Al,Ga)As is increased. Changes in the oscillation period during growth of the first few monolayers of both GaAs on (Al,Ga)As and (Al,Ga)As on GaAs may indicate the intermixing of Al and Ga near the heterointerface. © 1995, All rights reserved.

DOI： 10.1016/0022-0248(95)80184-E

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

We have made a reflection high-energy diffraction (RHEED) intensity oscillation study of the growth of (Al,Ga)As on GaAs and (Al,Ga)As (111)A surfaces. The RHEED intensity oscillations during growth of (Al,Ga)As are dependent on both growth temperature and As4:Ga flux ratio. In addition, the oscillation period decreases as the Al fraction in the (Al,Ga)As is increased. Changes in the oscillation period during growth of the first few monolayers of both GaAs on (Al,Ga)As and (Al,Ga)As on GaAs may indicate the intermixing of Al and Ga near the heterointerface. © 1995, All rights reserved.

DOI： 10.1016/0022-0248(95)80184-E

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCANNING MICROSCOPY INT  

The origin of and diffraction effects associated with reflection high energy electron diffraction (RHEED) intensity oscillations which occur during layer-by-layer growth of epitaxial thin films of III-V compounds by molecular beam epitaxy (MBE) are explained. It is shown that on (001) oriented substrates the period of the oscillations is in general a direct measure of the film growth rate which corresponds to the group III element flux. There are, however, exceptions to this simple concept including growth under group III rich-conditions, vicinal plane growth and growth from pulsed beams; each is considered.
On non-(001) low index orientations, the RHEED oscillation period only provides a measure of the growth rate over a very limited range of conditions. The fundamental reason appears to be the more restricted reactivity between the group III and V elements, so the oscillations are induced by the group V element, not the group III, which is quite different from (001) surfaces, at least for conventional growth conditions.
Finally, growth modes and strain relaxation differences between (001) and (110)-based growth of InAs on GaAs are illustrated. It is shown that there is no real relationship between strain and growth mode and it is suggested that adatom mobility is the essential parameter which determines growth mode.
In more general terms, it appears that kinetic factors rather than equilibrium considerations are responsible for the growth mode. Models based on purely equilibrium concepts are therefore unlikely to have general validity.

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

Due to the recent development of optical probes, monitoring of surface structures during organometallic chemical vapor deposition (OMCVD) has now become possible. Reflectance-difference spectroscopy (RDS) revealed that the (001)GaAs surface under OMCVD conditions reconstructs into structures similar or identical to those that occur in ultrahigh vacuum as encountered during molecular beam epitaxy (MBE). Here, I review recent real-time studies on the OMCVD and MBE growth using RDS and complementary techniques such as grazing-incidence x-ray scattering.

Publishing type：Research paper (scientific journal)  

From the reflectance expressions for a thin biaxial layer on an isotropic substrate we relate reflectance-difference spectroscopy (RDS), surface photoabsorption (SPA), and spectroellipsometry. Using these results and our recently acquired RD database, we determine surface reconstructions present during flow-modulated organometallic chemical vapor growth of epitaxial GaAs from SPA data that were published by others.

DOI： 10.1063/1.109890

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

Under typical atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) growth conditions with trimethylgallium (TMG) and arsine sources, reflectance-difference (RD) spectra show that the (001) GaAs surface is in the d(4 X 4)-like state. With sufficiently high TMG and low AsH3 exposures, we observe RD spectra similar to those obtained during atomic layer epitaxy (ALE) at lower temperatures.

DOI： 10.1063/1.110200

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Two new peaks are observed in resonant Raman scattering from GaSb/InAs quantum wells grown on (001) GaAs by MBE. These two lines are assigned to the coupled LO phonon intersubband plasmon modes originating from the InAs wells. The lower-frequency branch of the coupled system (L- mode) lies between the Lo and the TO frequencies of InAs, and the line intensity depends strongly on the two-dimensional carrier concentration and the laser excitation energies (resonant near the E1 gap of InAs). The L+ line is weak and relatively broad. Its frequency increases with increasing carrier concentration in the InAs wells and is not observed when the carrier concentration is low.

DOI： 10.1088/0268-1242/8/12/029

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC LONDON  

Surface reconstruction of GaAs (001) during organometallic chemical vapour deposition (OMCVD) growth has been investigated with reflectance-difference spectroscopy (RDS). RD spectra reveal that surface reconstructions similar or identical to (4 x 2), (2 x 4), and c(4 x 4) that occur on surface prepared by molecular beam epitaxy (MBE) in ultrahigh vacuum (UHV) occur even in atmospheric pressure OMCVD growth environments. Based on the RDS database we established on static surfaces in UHV, we studied the structure of surfaces under both static and dynamic conditions in non-UHV ambients. We find, in contrast to previous models, that the surfaces under various non-UHV conditions exhibit dimer formation. In addition, OMCVD growth and atomic layer epitaxy (ALE) typically occur under disordered c(4 x 4)[d(4 x 4)]-like conditions where the surface is terminated by multilayers of As. When trimethylgallium (TMG) and arsine (AsH3) are supplied simultaneously, the surface structure varies as a function of the supply rates of TMG and AsH3, and the substrate temperature.

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

We summarize recent applications of two real-time optical diagnostic techniques, reflectance difference spectroscopy (RDS) and spectroellipsometry (SE), to epitaxial growth on GaAs and atomic layer epitaxy (ALE) in particular. Using RDS, we obtain the first real-time spectroscopic data of the evolution of the (001) GaAs surface to cyclic and non-cycle exposures of atmospheric pressure H-2, H-2 and trimethylgallium, and H-2 and arsine, which simulate growth by ALE. None of our observations is consistent with any previously proposed simple model, emphasizing the necessity of real-time measurements for the analysis of complex surface reactions. Using SE we have constructed a closed-loop system for controlling the compositions of AlxGa1-x As layers grown by chemical beam epitaxy. We have produced various graded-compositional structures, including parabolic quantum wells 200 angstrom wide where the composition was controlled by analysis of the running outermost 3 angstrom (about 1 monolayer) of depositing material.

DOI： 10.1016/0040-6090(93)90121-5

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

Reflectance-difference spectroscopy (RDS) is employed to study in situ the (4 X 2), (1 X 6), (4 x 6), (3 X 1), (2 X 4)-alpha, (2 X 4)-beta, (2 X 4)-gamma, c (4 X 4), and d (4 X 4) reconstructions of (001) GRAS surfaces prepared in ultrahigh vacuum (UHV) by molecular-beam epitaxy and simultaneously characterized by reflection high-energy electron diffraction (RHEED). Reproducibility of the data is excellent. With the aid of previous theoretical calculations, we interpret characteristic spectral features at 1.9, 2.6, and 4.2 eV in terms of electronic excitations involving surface dimers of Ga, As, and As, respectively. Because RD couples to local electronic structure rather than to long-range order, RD spectra not only determine surface reconstructions but also provide details not accessible by RHEED, such as the existence of As dimers in the (1 X 6), (4 X 6), and (3 X 1) reconstructions and of the fractional coverage within a given reconstruction. Our data show that the (3 X 1), (1 X 6), and (4 X 6) reconstructions are at least partly determined by kinetics, since they can only be obtained by following specific heating or cooling procedures under very low AS4 flux. More generally, it is possible to employ this optical technique to determine surface atomic and electronic structure. Because RD spectra can be obtained with the surface in any transparent ambient, the database that we have established here provides a new approach for elucidating surface reconstructions of (001) GaAs and hence the dynamics of surface reactions in non-UHV environments.

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

We report the first evidence of dimer formation on semiconductor surfaces under atmospheric Pressure (AP) conditions. We successfully employ reflectance-difference spectroscopy to link structures of well-defined (001) GaAs surfaces prepared in ultrahigh vacuum (UHV) by molecular-beam epitaxy with structures of (001) GaAs surfaces prepared in AP by organometallic chemical vapor deposition (OMCVD). These measurements reveal that surface reconstructions also occur under AP-OMCVD conditions, forming structures similar, possibly identical, to the (4 X 2), (2 X 4), c(4 X 4), and disordered c(4 X 4), that occur in UHV. Our results provide a justification for applying the results of UHV studies of these surfaces to non-UHV environments and yield new insights on the mechanisms and kinetics of non-UHV growth.

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

Using reflectance-difference spectroscopy, we perform the first real-time spectroscopic investigation of the evolution of the (001) GaAs surface to cyclic and noncyclic exposures to atmospheric pressure H-2, H-2 and trimethylgallium, and H-2 and AsH3 that simulate growth by atomic layer epitaxy. None of our observations are consistent with any previously proposed simple model. The results emphasize the necessity of real-time measurements for the analysis of complex surface reactions.

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

We provide a perspective on current capabilities for optically monitoring and controlling epitaxial growth, and discuss examples taken from recent work at Bellcore.

DOI： 10.1016/0022-0248(92)90366-Q

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

We determine types and concentrations of free carriers in GaAs layers under organometallic chemical vapor deposition growth conditions from the linear electro-optic structure observed near 3 eV in reflectance-difference spectroscopy. The sensitivity is about 10(17) cm-3 at 400-degrees-C and 10(18) cm-3 at 600-degrees-C, sufficient to measure common doping levels at or near growth temperatures. We observed the transition between n- and p-type doping during atomic layer epitaxy of a carbon-doped p-type layer on an n-type substrate at 470-degrees-C.

DOI： 10.1063/1.105672

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

Reflectance-difference (RD) studies were performed on variously reconstructed (001) GaAs and AlAs surfaces. The spectra of the (2 X 4) and (4 X 2) reconstructions on (001) GaAs show prominent features due to electronic transitions between lone-pair orbitals and dimer states, as previously identified by theoretical calculations. The spectra of the c(4 X 4) reconstructions on (001) GaAs and AlAs show similar features that we also interpret in terms of surface dimer excitations. These dimer features provide a capability of obtaining real-time, in situ information of dynamics on polar surfaces.

DOI： 10.1116/1.585731

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

The initial oxidation stages of Ni and Ni-Cu alloys have been studied using the atom-probe field ion microscope (AP-FIM). Oxide layers were formed in situ in the FIM chamber on the clean metal surfaces at 1 x 10(-4) Torr (10(-2) Pa) O2 at 870, 970 or 1070 K for less than 1 min. The atom-probe analysis on the {111} and {100} surfaces of these oxidized alloys showed that only NiO formed on all of the alloys for this relatively low oxygen partial pressure, although incipient Cu2O formation could not be ruled out in a few samples of the Cu-rich alloys. The concentration of oxygen in the NiO fluctuated layer-by-layer in the &lt;111&gt; direction as expected for its NaCl-type structure. Ne field ion images and atom-probe analyses of the oxidized samples revealed a sharp NiO/metal interface for pure Ni and for the Cu-rich alloys, and a diffuse interface extending over a few atomic layers for the Ni-rich alloys. The NiO and Ni were cube/cube oriented.

DOI： 10.1016/0039-6028(91)90474-7

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

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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

We have constructed a scanning tunneling microscope (STM) equipped with a field ion microscope (FIM), by which one can monitor and shape the STM probe tip on an atomic scale in situ in the STM chamber. Taking advantage of a well-defined tip prepared by a FIM, we have greatly improved the stability and reproducibility of the performance of the STM. Li and K adsorption on the Si(001) 2x1 surface has been investigated by field ion-scanning tunneling microscopy (FI-STM). The STM images have shown that at the initial stage of adsorption, Li (K) atoms (1) adsorb on top of one of the dimer-forming Si surface atoms and (2) stabilize the asymmetric (buckled) dimerization, and (3) form linear chains, perpendicular to the substrate 2x1 dimer rows. Our observations suggest that alkali metal adsorption on the Si(001) 2x1 surface may be significantly different from the conclusions of earlier reports. © 1990, American Vacuum Society. All rights reserved.

DOI： 10.1116/1.577073

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

Chemisorption of atomic hydrogen on the Si (111)7x7 surface was investigated using scanning tunneling microscopy. Contrary to the recent report by Golovchenko’s group that the monohydride phase is not stable even at room temperature, resulting in the formation of the trihydride phase, our scanning tunneling microscopy (STM) experiment has shown that the monohydride phase is indeed the stable phase on the clean Si (111) 7x7 surface. © 1990, American Vacuum Society. All rights reserved.

DOI： 10.1116/1.577080

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

Using a field ion-scanning tunneling microscope (FI-STM), the adsorption process of Li on the Si(111) 7 X 7 surface has been studied. At the initial stage, trimers are formed preferentially in the faulted half of the 7 X 7 unit cell. At higher coverages, these trimers coalesce to form six-atom and nine-atom clusters across the interface between the faulted and unfaulted halves. It is suggested, based on the careful study of the adsorption sites, that the Si adatoms of the dimer-adatom-stacking fault (DAS) model may be removed upon the Li adsorption. © 1990, American Vacuum Society. All rights reserved.

DOI： 10.1116/1.577074

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

We have designed and developed a series of room-temperature field ion scanning tunneling microscopes (RT FI-STMs). The great advantages of the RT FI-STM are (1) almost simultaneous use of both the STM mode and FIM mode is possible without wasting machine time and thermal drift; (2) inspection and manipulation of a STM tip in situ in the STM system can be performed and, thus, each tip can be used over several months, maintaining a desired atomic resolution; and (3) a well-characterized tip ensures a very high (—100%) success rate in STM imaging with a known resolution. Several examples are given. © 1990, American Vacuum Society. All rights reserved.

DOI： 10.1116/1.577098

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A scanning tunneling microscope combined with a field ion microscope, which we call &quot;FI-STM&quot; has been constructed and tested successfully. The details of the principles and performance of the FI-STM are described. Several examples of its applications for Si (111) and Si (100) surfaces are presented as illustrations of the power of the instrument. © 1990.

DOI： 10.1016/0079-6816(90)90012-9

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

Li and K adsorption on the Si(001)-(2×1) surface have been investigated by use of scanning tunneling microscopy (STM). We found that, at the initial stage of adsorption, Li (K) atoms (1) adsorb on top of one of the dimer-forming Si atoms to form covalentlike directional bonds with Si atoms and tend to stabilize asymmetric (buckled) dimerization, and (2) form linear chains, perpendicular to the substrate dimer rows. Our STM results are significantly different from the conclusions of earlier reports. © 1990 The American Physical Society.

DOI： 10.1103/PhysRevB.41.9688

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

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

DOI： 10.1116/1.576070

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

The atom-probe field ion microscope was employed to study oxygen adsorption and oxidation on surfaces of two grades of copper: low-grade tough-pitch copper (99.9%) and high purity copper (99.999%). The source of the oxygen is the Cu2O inclusions which were present in the low-grade tough-pitch copper. The 99.9% grade copper was annealed in ultra-high vacuum (UHV). During heating the Cu2O inclusions dissolve and the oxygen content of the matrix increases. Surface enrichment of oxygen and oxide formation on the surface were found depending on the annealing conditions. No indication of oxidation and oxygen enrichment was found in the high purity copper (99.999%) under the same UHV conditions. © 1989.

DOI： 10.1016/0039-6028(89)90253-7

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

DOI： 10.1116/1.575128

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

DOI： 10.1016/0168-583X(88)90611-8

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

DOI： 10.1116/1.575128

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

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDITIONS PHYSIQUE  

Language：Japanese  

Language：Japanese  

Language：English  

In situ real-time x-ray diffraction measurements during In 0.12Ga0.88As/GaAs(001) epitaxial growth are performed for the first time to understand the strain relaxation mechanisms in a lattice-mismatched system. The reciprocal space maps of 004 diffractions are obtained, and allow us to evaluate the evolution of residual strain and crystal quality simultaneously as a function of layer thickness. In the time evolution, we have classified five thickness ranges, and deduced the dominant dislocation behavior in each phase. ©2009 IEEE.

DOI： 10.1109/PVSC.2009.5411191

Language：Japanese  

Language：Japanese  

Thermal annealing effects on lattice relaxations and defects were investigated in lattice-mismtached InGaAs layers on GaAs substrates. In the psudomorpic thin InGaAs layers, the lattice relaxation occurred by the annealing. In the partially relaxed thick InGaAs layers, the lattice relaxation was enhanced and the distribution of dislocation was changed. We found that the 2-step growth method was effective to reduce the residual strain and dislocation density in lattice mismatched InGaAs layers. © 2008 IEEE.

DOI： 10.1109/PVSC.2008.4922903

Language：Japanese  

Language：Japanese   Publisher：エヌ・ティー・エス  

Language：Japanese   Publisher：科学技術と経済の会  

Language：Japanese   Publisher：Japan Society of Colour Material  

DOI： 10.4011/shikizai1937.77.410

Language：Japanese   Publisher：日刊工業新聞社  

Language：Japanese   Publisher：アグネ技術センター  

Language：Japanese   Publisher：科学技術と経済の会  

Language：Japanese   Publisher：工業調査会  

Language：Japanese   Publisher：The Surface Science Society of Japan  

DOI： 10.1380/jsssj.15.598

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

Event date： 2024.9

Presentation type：Oral presentation (general)  

Event date： 2024.9

Presentation type：Oral presentation (general)  

Event date： 2024.9

Presentation type：Oral presentation (general)  

Event date： 2024.9

Presentation type：Poster presentation  

Event date： 2024.9

Presentation type：Oral presentation (general)  

Event date： 2024.6

Presentation type：Poster presentation  

Event date： 2024.3

Presentation type：Oral presentation (general)  

Event date： 2024.3

Presentation type：Oral presentation (general)  

Event date： 2024.3

Presentation type：Poster presentation  

Event date： 2024.1 - 2024.2

Presentation type：Oral presentation (general)  

Event date： 2024.1 - 2024.2

Presentation type：Oral presentation (general)  

Event date： 2023.9

Presentation type：Poster presentation  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

ALDにおいて、ジエチル亜鉛を用いたInAs量子ドットのパッシベーション効果に関する報告。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

MBEによるGaAs(001)上のInAs量子ドットの GaAs によるキャッピング中のAs流量等の影響に関する報告。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

MBEによるサブモノレイヤー積層法を用いたInAs/GaAsの成長における積層変調を用いた量子ドット密度の制御に関する報告。

Presentation type：Oral presentation (general)  

ALD法によるDEZを用いたInAs量子ドットのパッシベーション被覆によるPL発光強度の増強に関する報告。

Presentation type：Oral presentation (general)  

MBE で InAs/GaAs 交互積層するサブモノレイヤー成長法を用いて量子構造を作製する際の、GaAs 層の膜厚による構造制御の結果を報告した。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Photoluminescence enhancement of InAs surface quantum dots by Al2O3 passivation using atomic layer deposition was reported.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

GaAs(001)上にMBEで成長されるInAs量子ドットについて、GaAsで被覆する際の初期過程で相互拡散や歪による形状変化と電子物性を検討した結果を報告した。

Presentation type：Oral presentation (general)  

The influence of underlying quantum dots (QDs) on InAs surface quantum dots (SQDs) on their photoluminescence (PL) properties were discussed. The insertion of underlying QDs resulted in enhancement of the PL intensity, and the wavelength was shown to be controlled by the spacer layer thickness.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Stacked submonolayer (SML) growth of InAs nanostructures by MBE has been gaining interest recently for various optoelectronic applications. In contrast to the well-known Stranski-Krastanov (SK) growth of InAs nanostructures, stacked SML growth involves the cycled deposition of SML-thick InAs and few ML-thick GaAs. We have recently reported evidence of the 2D to 3D transition in SML InAs nanostructures. This transition leads to the existence of two distinct kinds of stacked SML nanostructures: 2D islands and 3D structures. Compared to the analogous transition in SK growth, the properties of the stacked SML transition is not yet well investigated. Hence, this study aims to elucidate the controllability of the density of 3D structures by As2 flux. It will be demonstrated that a wide control of 3D structure density (10^8 ~ 10^10 cm^-2) is possible simply by adjusting the As2 flux in stacked SML growth.

Presentation type：Oral presentation (general)  

ポスター　10P-14

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

The correlation between the structural and photo-luminescence (PL) properties of InAs submonolayer (SML) nanostructures at the 2D to 3D transition is in-vestigated. Significant changes in the topography of uncapped InAs nanostructures assembled by SML growth have been observed, indicating the transition from 2D to 3D growth regime. The influence of these structural changes to the luminescence properties of the nanostructure are investigated by PL measure-ments.

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

The submonolayer (SML) growth mode has been attracting attention as an alternative to the well-known Stranski-Krastanov (SK) growth mode as a method of assembling InAs nanostructures, e.g. quantum dots (QDs), on GaAs by MBE. While the 2D to 3D transition in SK-growth has been well investigated with a critical thickness of ~1.7 ML, different conditions are employed for SML-growth. Here, atomic force microscopy (AFM) is utilized to study the topographical changes at the 2D to 3D transition in InAs SML nanostructures.

Presentation type：Oral presentation (general)  

Deemed

Presentation type：Oral presentation (general)  

Cu/ZnS 薄膜を電析で作製し、その光学特性と電気化学特性で評価を行っている。　電析条件による違いについて報告。

Presentation type：Oral presentation (general)  

GaAs(001)上に、SML法とSK法でIn(Ga)As量子ドットを作製し、成長条件の適正化により、幅広い波長範囲を持った近赤外蛍光体の実現を目指している経過を報告。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Below-bandgap states induced by pre-epitaxial growth treatments in GaAs have been investigated by photoluminescence (PL). Various electronic states giving rise to near-infrared (NIR) PL peaks are generated through processes such as annealing or buffer growth that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. These states often overlap with those from InGaAs structures, not only complicating the interpretation by also altering the electronic properties of the devices. The present work provides guides for distinguishing the desired electronic states from the pregrowth treatment-induced defect states.

Presentation type：Oral presentation (general)  

Below-bandgap photoluminescence (PL) from GaAs has been investigated. We find that various electronic states giving rise to near-infrared (NIR) PL peaks can be generated through processes that are standard for epitaxial growth of InAlGaAs structures on (001) GaAs substrates. The PL signals from these states overlap with those from InAs quantum dots, wetting layers, and InGaAs structures, complicating the design of devices for telecommunications or intermediate band solar cells. The present result provides guides for distinguishing the desired electronic states from the thermal treatment-induced defect states.

Presentation type：Oral presentation (general)  

We report the observation of below-GaAs-bandgap photoluminescence (PL) emission from GaAs substrates subjected to thermal annealing during the standard pre-MBE-growth processes. Using below-bandgap excitation as well as backside PL measurements, defects deep within the substrates were probed. A broad PL emission peak at 1000 nm appear after pre-bake annealing at 300° and further defects at 905 and 1150 nm appear after oxide desorption annealing at 600°. These findings confirm the presence of optically-active defects in pre-MBE-growth annealed GaAs substrates.

Presentation type：Oral presentation (general)  

MBEサブモノレイヤー法で成長したInAs量子構造を介した光アップコンバージョンの機構の検討。

Presentation type：Oral presentation (general)  

MBE成長において、変調中間層の導入によるInAs量子ドットの発光特性の変化とその機構について。

Presentation type：Oral presentation (general)  

ZnO/ZnMgO コアシェル粒子の合成法と形状制御についての検討。

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

レーザーを用いた GaN のドーピング活性化法を用いた縦型素子作製について

Presentation type：Oral presentation (general)  

MBEサブモノレイヤー法で作製したInAs量子構造を介しての光アップコンバージョンの報告。

Presentation type：Oral presentation (general)  

MBE成長によるInAs量子ドットの中間層変調による形状の変化をAFMを中心に検討した。

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

ZnOをコアとしたコアシェルナノ粒子の作製の実験的検討。

Presentation type：Oral presentation (general)  

InAs量子井戸島構造のサブモノレイヤー結晶成長の手法と制御に関する実験的検討。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

InAs 量子ドット、量子島構造による光アップコンバージョンに関する理論考察。

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

KFM を用いた InAs 量子ドットの電子状態解析。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

GaAs(001)上にMBE成長されたInAs量子ドットとその近傍の表面ポテンシャルへの歪の与える効果の解析。

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Kelvin probe force microscopy has been employed to study the interfaces of Si heterostructure solar cell structures. The depth profile near the electrode-Si interface has been investigated.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

InGaAs layers on vicinal GaAs substrates have been grown by MBE. The processes have been studied in situ using X-ray diffraction at SPring-8. The influence and the mechanisms of the influence of miscut is discussed.

Presentation type：Oral presentation (general)  

The RHEED intensity transients during MBE growth of InAs quantum dots on GaAs(001) has been simulated. The results agree with our former observations, and hence provides insights into the possible mechanisms of dot formation processes.

Presentation type：Oral presentation (general)  

The surface potential of In(Ga)As quantum dots grown on GaAs(001) has been studied by KFM. We observe potential dip at the peripheral of the dots forming a ring-like structure.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

GaAs(001)上にMBE成長されたInAs量子ドットとその周辺の表面ポテンシャルに関する、下地層のSiドープによる変化の解析。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Over 1.7 micron light emission from InAs quantum dots on GaAs(001) has been realized by the clever design of the device structure that controls the strain induced.

Presentation type：Oral presentation (general)  

Conductive AlN layer grown on a Si substrate using MOCVD has been realized by the spontaneously formed nano-size via-holes. The layer has been applied for the preparation of vertical AlGaN FETs.

Presentation type：Oral presentation (general)  

In situ measurements on the growth of InAs quantum dots (QDs) and cap layers during molecular beam epitaxy (MBE) are performed using a combined MBE - X-ray diffraction (XRD) system at SPring-8. The evolution of strain induced both in the QDs and cap layers during capping is followed by XRD intensity transients. From the XRD intensities that arise from different lattice constants, we compare the evolution of the strain induced in the QDs and cap layers. Prominent differences are observed between those obtained during InGaAs and GaAs capping, and also when modulated cap structures are grown.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

MBE成長されるInAs量子ドットに加わる歪の制御について。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

長波長発光するInAs量子ドット素子におけるキャリアダイナミクスについて。

Presentation type：Oral presentation (general)  

Cu2ZnSnS4 ナノ粒子の合成機構について。

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Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Vertical AlGaN deep ultra violet (DUV) photo-detector has been successfully fabricated on n+Si substrate using spontaneous via holes growth technique. The spontaneous via holes make the insulating AlN buffer layer to be conductive, which is indispensable to grow AlGaN epitaxial layer, and makes possible the direct current flow from p electrode to n+Si substrate without any trench etching to form n-contact. This vertical device is easily enlarged to realize large area solar-blind photo-detector which is necessary for many applications for sensing contamination of water, biological material and so on under the sunshine.

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)