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)  

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

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  

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  

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

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

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

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

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

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

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

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

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

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

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)  

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  

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  

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  

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

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

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)  

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  

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  

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  

Publishing type：Research paper (scientific journal)   Publisher：IEEE Electron Devices Society  

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  

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

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

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

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

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

Publishing type：Research paper (scientific journal)  

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

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)  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

DOI： doi:10.1016/j.physe.2009.10.010

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)  

Publishing type：Research paper (scientific journal)  

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)  

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. © 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)  

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)  

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

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

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

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

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

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

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

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

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.

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.

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

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

DOI： 10.1016/0168-583X(88)90611-8

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

Language：Japanese   Publisher：日刊工業新聞社  

Language：Japanese   Publisher：工業調査会  

Language：Japanese   Publisher：The Surface Science Society of Japan  

DOI： 10.1380/jsssj.15.598

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)  

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 (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 (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.

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MBE成長されるInAs量子ドットに加わる歪の制御について。

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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。

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Cu2ZnSnS4 ナノ粒子の合成機構について。

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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.

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