A. Ogura

• PhD
• Professor (Full) at Meiji University

Electrochemical CO 2 reduction using a zero-gap reactor is promising for reducing power consumption compared with the other CO 2 electrochemical-reduced reactors due to its low applied voltage. However, the short lifetime caused by flooding and salt precipitation on the cathode is a problem. Several water transport mechanisms were proposed as the c...

Direct observation of the band structure variation of electrical devices, such as MOSFETs, during device operation is the most important for understanding MOSFET device operation. However, there are a few reports on the direct measurement of variation in the metal–oxide–semiconductor (MOS) interface band structure during operation, and further inve...

We present the temperature and Ge fraction dependence of the broad peaks at the lower wavenumber side of the Ge-Ge vibration mode in Raman spectra from Ge-rich Si1−xGex thin films (x = 0.750, 0.852, and 0.918) investigated by oil-immersion Raman spectroscopy. The sample temperature was elevated by increasing laser power and estimated using the rela...

Background and purpose Silicon-germanium (SiGe) alloy thin films are expected to be candidates for next-generation electronic and thermoelectric device materials because they have much lower thermal conductivity than Si and Ge single crystals and high hole-mobility. It is gradually becoming important to understand the physical properties of SiGe in...

Introduction Silicon Tin (Si 1- x Sn x ) is supposed to transfer from the indirect bandgap to the direct bandgap by adding Sn with Si. Hence, it is expected to be applied to the next-generation optical devices such as Si photonics due to its high affinity with Si devices [1, 2]. The crossover point from the indirect bandgap to the direct bandgap ha...

Introduction Uniformly ordered SiGe nanodot (ND) has the potential for optoelectronic device application. By engineering Si surface morphology, heteroepitaxial SiGe layer thickness distribution can be controlled by self-ordering [1]. The self-ordering is an attractive phenomenon for fabricating a vertically ordered stack of SiGe ND fabrication. Yam...

Background and Objective Silicon-germanium (SiGe) is applied to the next-generation electric and thermoelectric devices because it has higher hole mobility than Si and low thermal conductivity due to the alloy scattering. However, device performance is affected by temperature, strain, and composition. Therefore, it is significant to optimize these...

The optical properties of the multilayered staggered SiGe nanodots (NDs) embedded in the Si spacers fabricated at varying Si growth temperatures are clarified in conjunction with the effect of strain by Photoluminescence (PL) and Raman spectroscopy. We found that compressive strain is induced in the SiGe NDs, with higher growth temperatures of the...

We evaluated the bandgap energy and optical properties of single-crystalline silicon-tin (Si 1- x Sn x ) thin films utilizing Photoluminescence (PL), spectroscopic ellipsometry (SE), and X-ray photoelectron spectroscopy (XPS). The PL and SE results showed that the indirect and direct bandgap energy decrease with increasing Sn fraction. Furthermore,...

1. Background and purpose Silicon-germanium (SiGe) alloys have much lower thermal conductivity than Si and Ge single crystals and are expected to be candidates for next-generation thermoelectric device materials of internet of things society. It is important to achieve both high carrier mobility and low thermal conductivity on the basis of the dime...

Vehicles are expected to be a new application field for solar cells. Since vehicle bodies have complicated three-dimensional curved surfaces designed to improve aerodynamic performance, there is a need for flexible solar cells that can be installed on such surfaces. To this end, research has focused on single-crystalline Si solar cells with high co...

Oxygen transport mechanisms for two different Au/Ti/In2O3/Al2O3/p+-Si samples were experimentally evaluated by hard X-ray photoelectron spectroscopy (HAXPES). The deposition temperature for atomic layer deposition of In2O3, as well as the bias voltages applied on the entire stacked structures, were the main parameters used in the work. Chemical ana...

We reported the strain-free Raman shift ( ω 0 ) for all vibration modes (Ge–Ge, Si–Ge, and Si–Si) over the entire Ge fraction range using silicon–germanium (SiGe) single-crystals which were strain-free without boundaries and buffer/substrate layers. The determined Ge-fraction-shift coefficients varied with the Ge fraction as linear for the Si–Si an...

The strain state, optical properties, and band structure of the self-ordered multilayered silicon-germanium (SiGe) nanodots, which are staggered and dot-on-dot alignment and embedded by Si spacer, were evaluated by Raman spectroscopy and low-temperature Photoluminescence (PL). These results suggest that the compressive strain applied to the stagger...

Using laser power sweep Raman spectroscopy, this research reports that the thermal transport changes with the wire width of silicon-germanium (SiGe) nanowires (NWs). The temperature in SiGe NWs was calculated using the relationship between Raman shift ω and temperature T (dω/dT) to evaluate the correlation between thermal transport mechanism and Si...

Despite the growing interest in hard X-ray photoelectron spectroscopy (HAXPES) due to its deeper probing depth and potential for investigating bulk properties, studies exploring its application for understanding the interface between biomaterials and biological substances (such as proteins) remain limited. The adsorption abilities of proteins on hy...

Locally dislocation-free SiGe-on-insulator(SGOI) is fabricated by chemical vapor deposition. Lateral selective SiGe growth of ~30%, ~45% and ~55% of Ge content is performed around ~1µm square Si(001) pillar located under the center of a 6.3µm square SiO 2 on Si-on-insulator substrate which is formed by H 2 -HCl vapor-phase etching. In the deposited...

Transition metal dichalcogenides (TMDs) have attracted much attention in recent years due to their excellent electrical properties and unique nature. Tungsten disulfide (WS 2 ) , as a representative TMD, is a typical two-dimensional stacking material with moderately wide band gap (single layer: 2.03 eV, bulk: 1.32 eV) and, therefore, has led to act...

Background and Objective Silicon germanium (SiGe)-on-insulator (SGOI) p-MOSFETs are expected for obtaining low power consumption and high current drive of CMOS since SiGe has higher hole career mobility than Si and the compressive strain can be induced in the SiGe channel without complicated heterostructures. In addition, the buried oxide between t...

Background and purpose Strain techniques and channel materials with high carrier mobility are the principal technology boosters for the realization of high-performance logic devices composed of group IV semiconductors such as silicon (Si). In particular, strain engineering plays an important role in improving the performance of metal-oxide semicond...

We evaluated the anisotropic biaxial strain in the channel region of extremely-thin body silicon-germanium-on-insulator p-MOSFETs by oil-immersion Raman spectroscopy. Oil-immersion Raman spectroscopy can measure the transverse optical (TO) phonon mode which cannot be detected by conventional Raman spectroscopy under the backscattering configuration...

Carbon-doped silicon films formed on Si substrates have large tensile strain, and the strain is relaxed by microfabrication into nanowires. We investigated the effects of crystalline orientation, width, and carbon concentration on lattice relaxations by reciprocal space mapping of x-ray diffraction. Reciprocal space mapping profiles of periodically...

We demonstrate the relationship between Raman shift ω and temperature T (dω/dT) of silicon-germanium (SiGe) for Si-Si, Si-Ge, and Ge-Ge vibration modes which should be useful in local temperature evaluation of SiGe devices at submicron levels. We investigated the dω/dT of single-crystalline SiGe for Si-Si, Si-Ge, and Ge-Ge vibration modes and its d...

We have evaluated InGaAs/InP PIN (p-I-n) photodiodes failed by electrostatic discharge (ESD) with forward or reverse biasing, using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive x-ray spectrometry (EDX), Raman spectroscopy, and photoluminescence (PL) imaging. First, localized traces and bump...

Carbon-doped silicon (Si:C) thin films with C concentrations of 0.60% and 0.83% were fabricated into nanowires, and the lattice strain relaxation with shrinking the nanowire width, W, was evaluated in detail by x-ray reciprocal lattice space mapping (RSM) measurements. The obtained RSM profiles showed a right-downward distribution. From the RSM pro...

Thermoelectric conversion devices based on group IV semiconductor elements can improve conversion efficiency by reducing the thermal conductivity of the material. In particular, it is known that introducing Sn into the system can dramatically reduce the conductivity. It has been experimentally shown that the thermal conductivity of polycrystalline...

WS 2 metal-organic (MO) chemical vapor deposition was demonstrated on Si and Al 2 O 3 substrates. Novel MO W precursor of n-BuNC-W(CO) 5 and (t-C 4 H 9 ) 2 S 2 . as S precursor were synthesized for the purpose. The obtained films were layered 1T structure as a typical transition metal di-chalcogenide with almost the stoichiometric compositions. The...

We investigated 1-D and 2-D chemical depth mapping using SIMS, XPS and TEM-EDX. For strain/lattice spacing engineering effects, we used XRD and Raman analysis for Ge, Sn and C implantation into Si and SiGe wafers followed by RTA or laser melt annealing to form surface thin layers of SiGe, SiGeSn and SiGeC. Up to 1.15% lattice strain was measured in...

We evaluated damage to crystalline silicon (c-Si) induced by plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated amorphous silicon (a-Si:H). The damaged layer +-on the c-Si surface under the a-Si:H film was evaluated by lifetime measurements using the photoconductance method in conjunction with step etching. This damaged layer is appr...

The cost of solar cell production can be reduced by wafer thinning. A thinner wafer provides flexibility, and crystalline silicon solar cells are promising as flexible solar cells due to their flexibility. However, as wafers become thinner, production yield decreases due to wafer breakage caused by sawing damage; thus, to further reduce wafer thick...

Background and Objectives Silicon-germanium (SiGe) is used for thermoelectric devices since its thermal conductivity is lower than either pure Si or Ge. Indeed, the material was used in components of the Voyager and New Horizons deep-space craft because of its superior nanoscale heat conductivity. Improving SiGe for better thermoelectric devices re...

1. Background and purpose Strain techniques are one of the principal technology boosters for the realization of high-performance logic devices composed of group IV semiconductors such as Si, Ge and their alloy. Recently, it is gradually difficult to measure strain states as miniaturization proceeds to the nanometer scale. Raman spectroscopy is one...

1. Background and purpose Silicon tin (SiSn) alloys are attractive candidate for the next-generation group-IV semiconductors. It is well known that Si and Ge change from indirect to direct transition types with the addition of Sn. Among them, SiSn alloys are expected to be applied for the near-infrared optical devices because it is predicted to bec...

Background and Objectives Silicon germanium (SiGe) is expected to be applied for the optical devices such as infrared sensors, because of its narrower band gap than Si. Therefore, it is important to understand the optical properties of SiGe. In general, SiGe films epitaxially grown on Si or Ge substrates are the candidate materials for the optical...

1. Background and purpose Silicon germanium (SiGe) is expected as a next-generation electronic and thermoelectric device materials because of its higher carrier mobility than Si and lower thermal conductivity than Si and Ge. Therefore, it is important to understand the carrier scattering and phonon transport properties in order to apply SiGe as a d...

We investigated stress evaluation of strained group IV semiconductor devices by oil-immersion Raman spectroscopy. In the oil-immersion Raman spectroscopy the high-numerical-aperture lens gives evaluation of complicated stress states in strained group IV semiconductor devices. As an example of the stress evaluation, a clear stress relaxation of the...

We report on the distribution of the optical properties in strain-relaxed SiGe films. We confirmed that the SiGe film (Ge fraction: 50%) has a larger variation of the extinction coefficient than the SiGe film (Ge fraction: 20%) in the near-infrared region. This result suggests that the distribution of the optical properties of the SiGe film (Ge fra...

We evaluated the optical properties and the band structure of strained single crystalline Si 1- x Sn x using spectroscopic ellipsometry. The results suggest a reduction of the band gap at the Γ point and the formation of an optical transition by Van-Hove singularity with higher Sn fraction. In addition, since the reduction of the band gap with incr...

We report on the behavior of an acoustic phonon spectral linewidth of bulk single-crystalline Si 1− x Ge x alloy with the x of 0.16, 0.32, and 0.45 in the phonon dispersion relation along the Γ–X ([00 q]) direction. Broadening of both transverse acoustic (TA) and longitudinal acoustic (LA) modes of the bulk Si 1− x Ge x alloy was directly observed...

We investigate the factors that degrade the conversion efficiency in the crystalline silicon heterojunction (SHJ) solar cell using hard X-ray photoelectron spectroscopy (HAXPES) and the potential of new materials for the carrier selective contact (CSC). Regarding the emerging transparent conductive oxide film (TCO) used in the SHJ solar cell, the h...

Tungsten disulfide (WS 2 ) is one of the representative two-dimensional layered materials, and its applications in various fields have been actively studied due to its preferable properties such as reasonably wide band gap (monolayer: 2.03 eV, bulk: 1.32 eV) [1] and excellent stability. In particular, large area, a few layer WS 2 has a high potenti...

We review photoluminescence processes due to donor and acceptor impurities with the concentrations ranging from 1×10 ¹⁰ to 1×10 ²⁰ cm ⁻³ in both uncompensated and compensated Si at 4.2 K for application to the impurity characterization. Systematic evolution and extinction were found of the impurity bound exciton and impurity cluster bound exciton e...

Operando hard X-ray photoelectron spectroscopy (operando-HAXPES) with synchrotron radiation source was used under an applied bias voltage to investigate prototypical Au/InO1.16C0.04/Al2O3/p+-Si structure. First, HAXPES analysis reveals a successful incorporation of carbon in the In2O3 matrix (InO1.16C0.04) which is intentionally used to stabilized...

In this paper, we describe the basic performance of laboratory-based hard X-ray photoelectron spectroscopy (HAXPES Lab.) as well as various measurement examples and future prospects. We investigated the energy resolution and measurement time using Au plate and 30 nm thickness thermal oxide on the Si substrate. The energy resolution of HAXPES Lab. i...

The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low temperature growth of t...

ZnO films were successfully fabricated by non-seed chemical bath deposition (CBD) using a rotating flow reactor without seed layers. The microstructural control of the ZnO films is important for various...

Using molecular dynamics, the effect of an atomic mass difference on a localized phonon mode in SiGe alloys was investigated. Phonon dispersion relations revealed that a change in atomic mass causes the optical and acoustic modes to shift frequency. The results indicate that the local mode is sensitive to both Si and Ge atomic mass changes; reducin...

The current research focuses on the Intracellular biosynthesis of Ag/AgCl nanohybrids in microalgae, Scenedesmus sp. The effect of biosynthesis process on growth and lipid profile of cells is key element of this study. Ag/AgCl nanohybrids synthesized intracellularly were characterized by UV–Vis spectrophotometer, Powder X-Ray Diffraction (P-XRD), S...

We investigated the degradation factor of the conversion efficiency of the silicon heterojunction solar cells. In particular, we clarified the effect of the transparent conductive oxide film deposition conditions on the film quality and interface states, and the relationship between these factors and the conversion efficiency. Heat process causes a...

Using molecular dynamics, we found that the localized phonon-mode spectrum in SiGe alloys, which was recently discovered by an inelastic x-ray scattering experiment, changes according to the size distribution of compositional clusters in alloys. By varying the spatial distributions of Si and Ge, alloy models with differing compositions of Si and Ge...

We evaluated the fill factor (FF) degradation mechanism in silicon heterojunction (SHJ) solar cells with high mobility In 2 O 3 film as a high carrier mobility transparent conductive oxide (TCO) film. In particular, we focused on the electrode formation using a high productive screen-printing technique. We found the In 2 O 3 film is easier to be re...

In this paper, we report on the fabrication of Ta-doped TiO2 (TiO2:Ta) electron-selective contacts and their improved passivation qualities. By using thermal atomic layer deposition, 3.5 nm-thick, undoped TiO2 films and 3.5 nm-thick TiO2:Ta films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed at 150 °C on n-type crystalline silicon su...

Thin film growth of Zn x Mn 1− x S on a Si (100) substrate by sputtering was investigated for nonpolar AlN film growth on Si (100) substrate. The Zn x Mn 1− x S buffer layer reduces the large differences in thermal expansion coefficient and lattice constants between AlN and Si. Although the solubility of ZnS in MnS is less than 5% at 800 °C in bulk...

We evaluated the damage to crystalline silicon caused by sputtering deposition of transparent conductive oxide films (TCO). We confirmed that direct deposition of TCO on the crystalline silicon deteriorates the carrier lifetime. Also, the difference in discharge voltage during the TCO sputtering has an influence on plasma damage and damage penetrat...

The change in the interplanar spacing (d-spacing) including the ferroelectric orthorhombic (O) phase in the low-temperature fabricated HfxZr1−xO2 (HZO) films was studied using synchrotron grazing-incidence wide-angle x-ray scattering analysis. The 10-nm-thick HZO films were fabricated by thermal and plasma-enhanced atomic layer deposition (TH- and...

We demonstrate that the passivation quality of TiO2 electron-selective contacts can be improved by Ta doping. By using atomic-layer deposition, 3.5-nm-thick, undoped TiO2 films and Ta-doped TiO2 (TiO2:Ta) films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed on n-type crystalline silicon substrates with chemical SiO2 layers. After 130°...

To clarify a factor on the reliability, we investigated the characteristics of carbon-doped indium oxide (InO 1.16 C 0.04 ) thin-film transistors by varying the O 2 concentration from 0.001% to 100% at atmospheric pressure under negative bias stress (NBS) and positive bias stress (PBS). A positive threshold voltage ( V th ) shift was observed when...

Characteristics of thin-film transistors (TFTs) with amorphous In 2 O 3 (InO 1.2 ) and carbon-doped In 2 O 3 (InO 1.16 C 0.04 ) channels by post-metallization annealing (PMA) process were investigated. The InO 1.2 TFT changed from metallic to switching behavior after PMA at 200 °C. In contrast, the InO 1.16 C 0.04 TFT exhibited superior properties...

The theoretical lateral current of the surface inversion layer in a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was calculated using computer simulation and was compared with the experimental one to study defects/traps at the aSi:H/cSi interface and/or in the cSi surface and to detect the acceptor con...

The impact of Sn on Si 1-x Ge x through its thermal conductivity and phonon properties was investigated to develop an attractive material for thermoelectric devices. The Si-rich polycrystalline Si 1-x-y Ge x Sn y alloy was synthesized by ball-milling technique. The as-synthesized alloy had substitutional Sn content of 1.60%, which it maintained as...

The behavior of oxide precipitates during solar cell fabrication processes and the resulting effect on device performance have been investigated by transmission electron microscopy (TEM) observation. Samples were prepared with different carbon concentration and under different crystal growth conditions, namely using the conventional and an advanced...

We determined the entire spectral shape of a broad band around 0.8 eV, previously termed the C08-band, which was observed commonly in Si by room-temperature photoluminescence after electron irradiation. The band has a peak at 0.77±0.01 eV with long tails on both sides. We identified that the C08-band has the same origin as the C-line and occurs as...

The ferroelectricity of metal–ferroelectric–metal capacitors with a ferroelectric HfxZr1−xO2/ZrO2 (HZO/ZO) bilayer thicker than 20 nm formed by atomic layer deposition and postdeposition annealing at 600 °C was investigated. The HZO/ZO capacitors exhibited a higher remanent polarization (2Pr = Pr⁺ − Pr⁻) and breakdown voltage (Vbd) than capacitors...

Strain technology has been widely employed to enhance the performance of MOSFETs. Recently, it has been desired that Sn as a stressor, is implanted into channel region in MOSFETs for compressive strain introduction since Sn can induce lager compressive strain than Ge. In this study, evaluation of strain in Si layers annealed with laser or rapid the...

We investigated the detection limit of carbon in Si for the photoluminescence (PL) method after electron irradiation. The detection limit was obtained from the intensity ratio of the G-line to the free exciton line with the G-line intensity twice as high as the noise level, and was estimated at 4 × 10^13 cm-3 under the measurement condition in acco...

In recent years, the fabrication of transition metal dichalcogenide (TMD) alloys is drawing attention due to their controllable bandgap. Fabrication of MoS 2(1− x ) Te 2 x is expected to be difficult due to its thermal instability although it shows wide tunable bandgap range. In this study, MoS 2(1− x ) Te 2 x fabrication is carried out by sputteri...

Hf x Zr 1−x O 2 (HZO) has been an attractive material for future ferroelectric memory devices because of their high scalability ~10 nm, stable ferroelectricity over a wide Hf:Zr composition range, and compatibility with CMOS manufacturing process. [1] Considering the ferroelectric device manufacturing, the stable ferroelectricity in the thicker fil...

1. Introduction As a packing density in the large-scale integration (LSI) becomes higher, the devices exhibit three-dimensional complicated structure. The deep trench with high aspect ratio (AR), i.e. opening/depth, is one of the components to realize the structure [1]. The atomic layer deposition (ALD) is one of techniques suitable for trench stru...