Akira Fujimoto

An evidence of trap activation for positive temperature coefficient of resistivity in BaTiO3 ceramics with substitutional Nb and Mn as impurities

The mechanism of the electrical resistivity increase above the Curie temperature TC [so-called positive temperature coefficient of resistivity (PTCR) effect] in BaTi1−x−yNbxMnyO3 ceramics is studied with the temperature-dependent resistivity and electron paramagnetic resonance (EPR) data and the calculated energy levels of various Mn-associated centers. The activation energy of trapped electrons at grain boundary interface states is deduced from the resistivity data. The deduced value is found to be nearly equal to the activation energy of Mn2+ and/or singlet EPR signals. This indicates that the EPR signals arising at the cubic phase are due to trapped-electron centers at grain boundaries, and that the centers responsible for the EPR signals contribute to the rise of grain boundary barrier above TC. The PTCR mechanism is separately discussed for mode I of abrupt resistivity jump at TC and mode II of moderate resistivity increase at higher temperatures. From the analyses of resistivity and EPR data, we fou...

Photoreflectance characterization of the plasma-induced damage in Si substrate

Si surface damage induced during Ar and CHF3/CF4/Ar plasma processing has been characterized by photoreflectance spectroscopy (PRS). The photoreflectance (PR) signal intensity decreases drastically as the rf input power increases in the Si substrate exposed to the plasma. The recovery of the plasma-induced damage is confirmed by PRS after subsequent annealing over 500u200a°C. We found, from the shift of the PR spectra, the strain at the Si surface induced by the plasma treatment might be due to the introduction of the ions, C, F, or H, not to those of Ar. The depth profile of the defect density in the Si substrate is estimated quantitatively by analyzing the depth profile of the PR signal intensities.

Electron spin coherence of phosphorus donors in silicon: Effect of environmental nuclei

Phosphorus-doped silicon single crystals with 0.19 %<= f<= 99.2 %, where f is the concentration of 29^Si isotopes, are measured at 8 K using a pulsed electron spin resonance technique, thereby the effect of environmental 29^Si nuclear spins on the donor electron spin is systematically studied. The linewidth as a function of f shows a good agreement with theoretical analysis. We also report the phase memory time T_M of the donor electron spin dependent on both f and the crystal axis relative to the external magnetic field.

Transparent Aluminum Nanomesh Electrode Fabricated by Nanopatterning Using Self-Assembled Nanoparticles

A novel transparent aluminum nanomesh electrode with nanoapartures smaller than the wavelength of the light was proposed. Unlike conventional conducting oxides such as indium tin oxide, it has the potential to realize a rare-metal-free and low-resistivity transparent electrode. It was fabricated by nanopatterning with our embedded particle monolayer method, which enables the formation of a self-assembled particle monolayer over a large area, and its optical properties were investigated. As a result, the transmittance of the fabricated aluminum nanomesh electrode was found to be more than 55% at the peak wavelength when the opening ratio was 47%.

Large Area Fabrication of Moth-Eye Antireflection Structures Using Self-Assembled Nanoparticles in Combination with Nanoimprinting

A moth-eye structure, which suppresses the reflection on a surface, was fabricated on the entire surface of a large silicon wafer by the formation of a self-assembled particle monolayer as a dry-etch mask formed by our embedded particle monolayer (EPM) method. We optimized the shape of moth-eye structures by optical calculation and improved the fabrication procedure to allow formation over a large area. As a result, we succeeded in fabricating a moth-eye structure on the entire surface of a 12-in. silicon wafer and the surface reflectance was reduced to less than 0.8% in the visible light range. A large nickel mold, which is able to transfer the pattern to an 8-in. display, could be formed using the 12-in. silicon substrate as a master. A moth-eye film was fabricated by UV nanoimprinting using the nickel mold and the high antireflection performance was confirmed. The fabrication cost of the moth-eye structure over a large area would be markedly reduced by the use of the self-assembly technique in combination with nanoimprinting.

Nondestructive and Contactless Monitoring Technique of Si Surface Stress by Photoreflectance

Strain and stress at the Si surface have been studied by photoreflectance (PR) spectroscopy. A Si diaphragm structure has been fabricated in order to produce the surface strain caused by N2 gas pressure which changes the PR spectra of the Si diaphragm. The transition energy obtained from the PR peak energy of approximately 3.4 eV is proportional to the surface stress, which is calculated by elastic analysis. Additionally, PR spectroscopy was applied to measure stress at the interface between the Si and thermal oxide. As the SiO2 growth temperature increases, the interface stress decreases. From our experimental results, it is considered that PR spectroscopy is effective as a contactless and nondestructive monitoring technique for Si surface stress.

Characterization of Surface Potential and Strain at Ultrathin Oxide/Silicon Interface by Photoreflectance Spectroscopy

Si surface potential and strain at the Si-SiO 2 structure with a thermally grown or a native SiO 2 ultrathin film have been characterized by photoreflectance (PR) spectroscopy. The surface potentials of Si-SiO 2 structures are determined from the modulation light intensity dependence of the PR signal intensity. Although the signal intensity decreases drastically with increasing SiO 2 film thickness, it can be increased by applying dc bias voltage and increasing the surface potential of Si. The strains at the Si surface have been obtained by an analysis of the transition energy shift in the SiO 2 /Si structure with a thermally oxidized ultrathin film.

Very Short Wavelength (621.4 nm) Room Temperature Pulsed Operation of InGaAsP Lasers

Page L488, Wrong Central R & D Laboratory OMRON Tateisi Electronics Co., 20 Igadera, Shimokaiinji, Nagaokakyo Niigata 617 Correct Central R & D Laboratory OMRON Tateisi Electronics Co., 20 Igadera, Shimokaiinji, Nagaokakyo 617

Linewidth of low-field electrically detected magnetic resonance of phosphorus in isotopically controlled silicon

The linewidth of the low-field electrically detected magnetic resonance (LFEDMR) of phosphorus electrons in silicon is investigated using samples with various 29Si nuclear spin fractions and is compared to that of X-band electron paramagnetic resonance (EPR). The linewidths of LFEDMR and EPR are the same even though LFEDMR signals are obtained based on spin-dependent recombination, suggesting that the interaction between electron spins of phosphorus and recombination centers is strong enough for the LFEDMR detection but weak enough not to affect the linewidths. This favorable balance makes LFEDMR an attractive method to elucidate the low-field behavior of paramagnetic defects in semiconductors.

Liquid Phase Epitaxial Growth of lnGaAsP on GaAs1-yPy Substrates (y=0.31 and 0.39)

Lattice matched InGaAsP mixed crystals with various energy bandgaps were grown by liquid phase epitaxy (LPE) on GaAs1-yPy substrates (y=0.31 and 0.39). The growth layers had smooth and shiny surfaces with undulated morphology reflecting the cross-hatching pattern of GaAsP substrates. The influences of offset angle and crystal composition of the InGaAsP growth layer on the surface morphology of the InGaAsP growth layer were investigated. The offset angle was not the main cause of the undulated morphology in our experiments. Photoluminescence spectra and X-ray rocking curves of the growth layers were measured in order to determine their energy bandgaps and lattice constants. The doping characteristics of zinc and tellurium were also investigated. The growth conditions and properties of the InGaAsP layers on GaAsP substrates are described in detail.