Tetsuo Soga

Bio: Tetsuo Soga is an academic researcher from Nagoya Institute of Technology. The author has contributed to research in topics: Thin film & Solar cell. The author has an hindex of 47, co-authored 600 publications receiving 9070 citations. Previous affiliations of Tetsuo Soga include Shinshu University & Nagoya University.

Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78–4.77 eV) by spectroscopic ellipsometry and the optical transmission method

Abstract: Spectroscopic ellipsometry (SE) together with the optical transmission method is successfully used to determine the refractive index n and absorption coefficient α of undoped gallium nitride film over the spectral range of 0.78–4.77 eV of photon energy. The SE measurement is carried out at angle of incidence of 60° over the 1.5–4.77 eV energy range and optical transmission measurement over the 0.78–3.55 eV energy range. The refractive index n and absorption coefficient α obtained by both methods show unique results in the overlap wavelength region. Refractive index n is found to follow the Sellmeir dispersion relationship n2(λ)=2.272+304.72/(λ2−294.02) below the fundamental band edge. A free excitonic structure at the band is clearly observed at room temperature, with the transmission energy of free exciton at 3.44 eV, which is in reasonable agreement with the reported results.

Rare Earth Doped Zinc Oxide Nanophosphor Powder: A Future Material for Solid State Lighting and Solar Cells

Abstract: A comprehensive review of up-conversion (UP) and down-conversion (DC) or down shifting of rare earth (RE) doped zinc oxide (ZnO) nanophosphors is presented. Research interest in the development of RE3+ doped ZnO for UP and DC nanophosphors has been encouraged by the potential application of these materials in light emitting diodes and different types of photovoltaic cells. A range of remarkable characteristics, which are organized into different sections describing the structure, optical, and luminescence properties of these materials, are discussed in detail. Undoped ZnO has two characteristic emissions in the ultraviolet and visible regions related, respectively, to excitonic recombination and intrinsic defects. X-ray photoelectron spectroscopy (XPS) data demonstrated a correlation between the visible emission and intrinsic defects. In the case of the DC or shifting process, there was simultaneous emissions related to f → f transitions of RE ions and defects in ZnO host. These emissions were dependent o...

Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: a review

Abstract: Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.

Band parameters for nitrogen-containing semiconductors

Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

Effects of F- Doping on the Photocatalytic Activity and Microstructures of Nanocrystalline TiO2 Powders

Abstract: A novel and simple method for preparing highly photoactive nanocrystalline F--doped TiO2 photocatalyst with anatase and brookite phase was developed by hydrolysis of titanium tetraisopropoxide in a mixed NH4F−H2O solution. The prepared F--doped TiO2 powders were characterized by differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV−vis absorption spectroscopy, photoluminescence spectra (PL), transmission electron microscopy (TEM), and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results showed that the crystallinity of anatase was improved upon F- doping. Moreover, fluoride ions not only suppressed the formation of brookite phase but also prevented phase transition of anatase to rutile. The F--doped TiO2 samples exhibited stronger absorption in the UV−visible range with a red shift in the band gap transition. The photocatalytic activity of F--doped TiO2 powders prep...