Takahiro Kawashima

Bio: Takahiro Kawashima is an academic researcher from Panasonic. The author has contributed to research in topics: Layer (electronics) & Substrate (electronics). The author has an hindex of 17, co-authored 75 publications receiving 1245 citations. Previous affiliations of Takahiro Kawashima include Kobe University.

Optical properties of hexagonal GaN

Abstract: Single-crystalline hexagonal GaN (α-GaN) films have been grown on (0001) sapphire substrates by metalorganic chemical vapor deposition at 1040 °C. The complex dielectric functions, e(E)=e1(E)+ie2(E), of the epitaxial films have been measured by spectroscopic ellipsometry (SE) for E⊥c in the region between 1.5 and 5.0 eV at room temperature. Previously published ultraviolet SE spectra of α-GaN are examined by considering the effects of surface roughness using an analysis based on an effective medium model. Ex situ atomic force microscopy is used to assess independently surface flatness. By mathematically removing the effects of surface roughness, the most reliable e(E) values for α-GaN are presented in the 1.25–10 eV photon–energy range. Theoretical dispersion analysis suggests that the E0 structure could be characterized by a three-dimensional M0 critical point and the E1α (α=A,B,C) structures by two-dimensional M1 critical points. To facilitate design of various optoelectronic devices, dielectric-functio...

Control of surface migration of gold particles on Si nanowires.

Abstract: On the surface of silicon nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD), Au particles 5−20 nm in diameter are formed if the growth conditions are within a specific range. We studied the mechanism of Au particle formation by growing SiNWs under different conditions, specifically by dynamically changing the growth parameters during the growth process. We show that insufficient supply of Si source to the Au−Si eutectic on top of the SiNWs enhances the migration of Au atoms on the surface of SiNWs in the form of Au−Si eutectic, which is precipitated on the surface as Au particles during cooling. We also show that using Au−Si eutectic on the surface of SiNWs as a catalyst enables one-step growth of branched SiNWs.

Optical constants of CuGaSe2 and CuInSe2

Abstract: The complex dielectric functions, e(E)=e1(E)+ie2(E), of chalcopyrite semiconductors CuGaSe2 and CuInSe2 have been measured by spectroscopic ellipsometry in the photon energy range between 1.2 and 5.3 eV at room temperature. The measurements are carried out on the surface parallel to the optic axis c, which allow the determination of the optical properties for light polarized perpendicular (E⊥c) and parallel to the c axis (E∥c). The measured e(E) spectra reveal distinct structures at the lowest direct gap (E0) and higher energy critical points. These spectra are analyzed on the basis of a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-function-related optical constants, such as the complex refractive index n*(E)=n(E)+ik(E), absorption coefficient α(E), and normal-incidence reflectivity R(E), of these semiconductors are also presented.

Method for producing semiconductor chip, and field effect transistor and method for manufacturing same

Abstract: Disclosed is a method for producing a semiconductor chip. In this method, two or more semiconductor layers (12) are first formed on a substrate (10) by repeatedly forming a sacrifice layer (11) and a semiconductor layer (12) in this order on the substrate (10). Then, the semiconductor layers (12) are divided into a plurality of chips by partially etching the sacrifice layers (11) and the semiconductor layers (12). After that, the chips are separated from the substrate by removing the sacrifice layers (11).

Semiconductor crystal film and method for preparation thereof

Abstract: A multilayer film (10) in which a plurality of Si1-x1-y1Gex1Cy1 (0 ≤ x1 y2) layers having a composition having a greater proportion of Ge, such as Si0.2Ge0.8 layer (12), are alternately laminated. The multilayer film allows the expansion of the range wherein a semiconductor crystal layer having C atoms in lattice positions is capable of functioning as a SiGeC layer to a composition having a greater proportion of Ge.

Semiconductor device, and manufacturing method thereof

Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Surface-Plasmon-Enhanced Light Emitters Based on InGaN Quantum Wells

Abstract: Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP–QW coupling. Large enhancements of the internal quantum efficiencies (etaint) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.

25th Anniversary Article: Semiconductor Nanowires – Synthesis, Characterization, and Applications

Abstract: Semiconductor nanowires (NWs) have been studied extensively for over two decades for their novel electronic, photonic, thermal, electrochemical and mechanical properties. This comprehensive review article summarizes major advances in the synthesis, characterization, and application of these materials in the past decade. Developments in the understanding of the fundamental principles of "bottom-up" growth mechanisms are presented, with an emphasis on rational control of the morphology, stoichiometry, and crystal structure of the materials. This is followed by a discussion of the application of nanowires in i) electronic, ii) sensor, iii) photonic, iv) thermoelectric, v) photovoltaic, vi) photoelectrochemical, vii) battery, viii) mechanical, and ix) biological applications. Throughout the discussion, a detailed explanation of the unique properties associated with the one-dimensional nanowire geometry will be presented, and the benefits of these properties for the various applications will be highlighted. The review concludes with a brief perspective on future research directions, and remaining barriers which must be overcome for the successful commercial application of these technologies.

System comprising a semiconductor device and structure

Abstract: A system includes a semiconductor device. The semiconductor device includes a first single crystal silicon layer comprising first transistors, first alignment marks, and at least one metal layer overlying the first single crystal silicon layer, wherein the at least one metal layer comprises copper or aluminum more than other materials; and a second single crystal silicon layer overlying the at least one metal layer. The second single crystal silicon layer comprises a plurality of second transistors arranged in substantially parallel bands. Each of a plurality of the bands comprises a portion of the second transistors along an axis in a repeating pattern.