Hikaru Kobayashi

Bio: Hikaru Kobayashi is an academic researcher from Osaka University. The author has contributed to research in topics: Silicon & Passivation. The author has an hindex of 27, co-authored 240 publications receiving 2751 citations.

Mechanism of carrier transport in highly efficient solar cells having indium tin oxide/Si junctions

Abstract: The carrier transport mechanism of the Si solar cells having n‐Si/indium tin oxide (ITO) junctions has been studied by use of the current‐voltage and capacitance‐voltage measurements and x‐ray photoelectron spectroscopy. An 11‐A‐thick nonstoichiometric Si oxide layer is formed when ITO is deposited by spray pyrolysis on a Si electrode etched with hydrofluoric acid. In this case, the tunneling probability of majority carriers through the oxide layer is high, and the thermionic emission current over the energy barrier in Si takes a dominant part of the dark current. On the other hand, for a Si electrode where a Si oxide layer is intentionally interposed between ITO and Si, the thermionic emission current is suppressed, and trap‐assisted multistep tunneling through the depletion layer becomes dominant. By making a mat‐structure treatment on the Si surface, a solar energy conversion efficiency of 13% and the photocurrent density of 42.5 mA cm−2 were attained under AM 1 100 mW cm−2 illumination.

Properties of indium tin oxide films prepared by the electron beam evaporation method in relation to characteristics of indium tin oxide/silicon oxide/silicon junction solar cells

Abstract: Indium tin oxide (ITO)/silicon oxide/silicon (Si) junction solar cells were produced by depositing ITO on a thin silicon oxide‐covered single‐crystal Si substrate using the electron‐beam evaporation method. The current‐voltage (I‐V) characteristics strongly depended on the incident angle (θi) of the evaporated ITO vapor to the Si substrate during the ITO deposition, as well as the post‐deposition heating temperature (Th) and the kind of the ambient gases during post‐deposition heat treatment. The ITO films deposited at θi=0° and treated at Th=380 °C in air formed a high‐energy barrier with p‐Si, and formed ohmic contact with n‐Si. X‐ray diffraction analysis showed that the ITO films deposited at θi=0° contained metal indium. The amount of the metal indium decreased either by reducing the deposition rate of the ITO film or by raising the substrate temperature during the ITO deposition. The ITO films deposited at θi=45° and treated at Th=350∼450 °C in hydrogen, on the other hand, formed a high‐energy barrie...

Beads-Milling of Waste Si Sawdust into High-Performance Nanoflakes for Lithium-Ion Batteries

Abstract: Nowadays, ca. 176,640 tons/year of silicon (Si) (>4N) is manufactured for Si wafers used for semiconductor industry. The production of the highly pure Si wafers inevitably includes very high-temperature steps at 1400-2000 °C, which is energy-consuming and environmentally unfriendly. Inefficiently, ca. 45-55% of such costly Si is lost simply as sawdust in the cutting process. In this work, we develop a cost-effective way to recycle Si sawdust as a high-performance anode material for lithium-ion batteries. By a beads-milling process, nanoflakes with extremely small thickness (15-17 nm) and large diameter (0.2-1 μm) are obtained. The nanoflake framework is transformed into a high-performance porous structure, named wrinkled structure, through a self-organization induced by lithiation/delithiation cycling. Under capacity restriction up to 1200 mAh g-1, the best sample can retain the constant capacity over 800 cycles with a reasonably high coulombic efficiency (98-99.8%).

Polycrystalline n-ZnO/p-Cu2O heterojunctions grown by RF-magnetron sputtering

Abstract: Polycrystalline n-ZnO/p-Cu2O heterojunctions were fabricated by reactive sputtering for photovoltaic applications Although electrical rectification was not reproducibly obtained in the as-grown samples, rectification was observed in the samples fabricated with cyanide treated Cu2O We have previously shown that cyanide treatment has an effective role in passivation of defects in Cu2O, in analogy to hydrogen passivation It is, therefore, believed that the observed improvement in the electrical rectification of the ZnO/Cu2O heterojunctions is attributable to the defect passivation near the hetero-interface The effectiveness of the cyanide treatment and the importance of defect passivation in ZnO/Cu2O heterojunctions are presented (© 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)

Spectroscopic observation of interface states of ultrathin silicon oxide

Abstract: Interface states in the Si band gap present at oxide/Si(100) interfaces for ∼3‐nm‐thick Pt/2.1∼3.6‐nm‐thick silicon oxide/n‐Si(100) metal–oxide–semiconductor devices are investigated by measurements of x‐ray photoelectron spectra under biases between the Pt layer and the Si substrate, and their energy distribution is obtained by analyzing the amount of the energy shift of the substrate Si 2p3/2 peak measured as a function of the bias voltage. All the interface states observed using this new technique have discrete energy levels, showing that they are due to defect states. For the oxide layer formed in H2SO4+H2O2, the interface states have three density maxima at ∼0.3, ∼0.5, and ∼0.7 eV above the valence‐band maximum (VBM). For the oxide layer produced in HNO3, two density maxima appear at ∼0.3 and ∼0.7 eV above the VBM. The energy distribution for the oxide layer grown in HCl+H2O2 has one peak at ∼0.5 eV. The 0.5 eV interface state is attributed to the isolated Si dangling bond defect. The 0.3 and 0.7 eV ...

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

The surface science of titanium dioxide

Abstract: Titanium dioxide is the most investigated single-crystalline system in the surface science of metal oxides, and the literature on rutile (1 1 0), (1 0 0), (0 0 1), and anatase surfaces is reviewed This paper starts with a summary of the wide variety of technical fields where TiO 2 is of importance The bulk structure and bulk defects (as far as relevant to the surface properties) are briefly reviewed Rules to predict stable oxide surfaces are exemplified on rutile (1 1 0) The surface structure of rutile (1 1 0) is discussed in some detail Theoretically predicted and experimentally determined relaxations of surface geometries are compared, and defects (step edge orientations, point and line defects, impurities, surface manifestations of crystallographic shear planes—CSPs) are discussed, as well as the image contrast in scanning tunneling microscopy (STM) The controversy about the correct model for the (1×2) reconstruction appears to be settled Different surface preparation methods, such as reoxidation of reduced crystals, can cause a drastic effect on surface geometries and morphology, and recommendations for preparing different TiO 2 (1 1 0) surfaces are given The structure of the TiO 2 (1 0 0)-(1×1) surface is discussed and the proposed models for the (1×3) reconstruction are critically reviewed Very recent results on anatase (1 0 0) and (1 0 1) surfaces are included The electronic structure of stoichiometric TiO 2 surfaces is now well understood Surface defects can be detected with a variety of surface spectroscopies The vibrational structure is dominated by strong Fuchs–Kliewer phonons, and high-resolution electron energy loss spectra often need to be deconvoluted in order to render useful information about adsorbed molecules The growth of metals (Li, Na, K, Cs, Ca, Al, Ti, V, Nb, Cr, Mo, Mn, Fe, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) as well as some metal oxides on TiO 2 is reviewed The tendency to ‘wet’ the overlayer, the growth morphology, the epitaxial relationship, and the strength of the interfacial oxidation/reduction reaction all follow clear trends across the periodic table, with the reactivity of the overlayer metal towards oxygen being the most decisive factor Alkali atoms form ordered superstructures at low coverages Recent progress in understanding the surface structure of metals in the ‘strong-metal support interaction’ (SMSI) state is summarized Literature is reviewed on the adsorption and reaction of a wide variety of inorganic molecules (H 2 , O 2 , H 2 O, CO, CO 2 , N 2 , NH 3 , NO x , sulfur- and halogen-containing molecules, rare gases) as well as organic molecules (carboxylic acids, alcohols, aldehydes and ketones, alkynes, pyridine and its derivates, silanes, methyl halides) The application of TiO 2 -based systems in photo-active devices is discussed, and the results on UHV-based photocatalytic studies are summarized The review ends with a brief conclusion and outlook of TiO 2 -based surface science for the future

The work function of the elements and its periodicity

Abstract: A new compilation, based on a literature search for the period 1969–1976, is made of experimental data on the work function. For these 44 elements, preferred values are selected on the basis of valid experimental conditions. Older values, which are widely accepted, are given for 19 other elements on which there is no recent literature, and are so identified. In the data for the 63 elements, trends that occur simultaneously in both the columns and the rows of the periodic table are shown to be useful in predicting correct values and also for identifying questionable data. Several illustrative examples are given, including verifications of predictions published in 1950.