Ken'ichi Ono

Completely Bi-Substituted Iron Garnet (BIG) Films Prepared by Electron Cyclotron Resonance (ECR) Sputtering

Completely Bi-substituted iron garnet (BIG) films were epitaxially synthesized on garnet substrates by electron cyclotron resonance (ECR) sputtering. The critical temperature for the epitaxial growth, crystallinities, and Faraday rotation θF of BIG films depend on the O2 gas flow rate. With an optimum flow rate of 7 sccm, single-crystal BIG films were obtained at temperatures above 390°C, and θF achieved its largest value of 8.4×104 deg/cm (λ=0.633 µm). The minimum ferromagnetic resonance (FMR) linewidth ΔH was 70 Oe; this is the smallest value ever reported. The uniaxial perpendicular magnetic anisotropy is mainly caused by the elastic deformation induced by the thermal expansion mismatch between the film and the substrate.

A Few Techniques for Preparing Conductive Material Films for Sputtering-Type Electron Cyclotron Resonance Microwave Plasma

A few techniques are developed for preparing conductive material films for sputtering type electron cyclotron resonance microwave plasma. Microwave pressure window contamination, which is the most serious obstacle to conductive film preparation, can be avoided by using a vacuum microwave guide. Dense plasmas of 1011 cm-3 are obtained at a gas pressure of 10-2 Pa, and several metal films, including Al, Mo, Cu, and Fe films, are continuously deposited. Much denser plasmas of 1012 cm-3 are generated by high rate sputtering apparatus with an electric mirror, and films are deposited at rates of over 2000A/min.

Preparation of Bi Iron Garnet Film with a Two-Step Growth Technique

Completely Bi-substituted iron garnet (Bi3Fe5O12, BiIG) film with a smooth surface is synthesized by electron cyclotron resonance (ECR) sputtering using a two-step growth technique. Consequently, the waveguide propagation loss of BiIG film at a wavelength of 1.55 µm can be measured. The surface smoothness and the propagation loss can be improved with a buffer layer as thin as 2 nm, as the growth temperature Tb (400°C≤Tb≤600°C) is increased. This shows that buffer layer crystallinity plays an important role in making the BiIG film surface smooth and the propagation loss low.

Optical properties of Cd1-xMnxTe epitaxial films deposited on sapphire substrates

Cd1-xMnxTe epitaxial thin films with a smooth surface and high crystal quality were prepared on sapphire substrates by vacuum evaporation, and their Faraday effect and optical properties were investigated. The peak-to-peak rotation in the Verdet constant spectrum is 1.5 deg/Oe cm near the 0.57 µm wavelength at the energy gap for films where x=0.5. The refractive index at a 0.63 µm wavelength is 2.8~3.0 for the x=0~0.68 composition range, and it decreases as the Mn content increases. The optical attenuation at 1.52 µm decreases as the crystal quality improves, and the minimum attenuation is 2 dB/cm. Films with different structures have different attenuations. The wavelength dependence of the attenuation obeys Rayleighs law of scattering. It is thought from these results that the attenuation is due to scattering based on the structure of the films.

Stress-Induced Perpendicular Magnetic Anisotropy in PtMnSb Thin Films

Stress-induced perpendicular magnetic anisotropy is studied for PtMnSb thin films deposited on various substrates having different expansion coefficients. The magnetostriction constant λ of PtMnSb thin film is -30 × 10-6. The films perpendicular magnetic anisotropy constant Ku increases as tensile thermal stress in the film plane increases.

Investigation of Anomalous Optical Characteristics of InGaAsP Layers on GaAs Substrates Grown by Metalorganic Vapor Phase Epitaxy

We investigated the growth of InGaAsP layers on GaAs substrates by metalorganic vapor phase epitaxy (MOVPE) for application in optical devices. Anomalous large redshifts of photoluminescence (PL) were observed for samples of specific In1-xGaxAsyP1-y compositions (x and y are approximately 0.85 and 0.65, respectively). We showed that these large redshifts were induced by phase separation in the miscibility gap of InGaAsP. In order to clarify the threshold value of the phase separation that causes this anomalous PL emission, the phase separation was quantified by combining PL spectroscopy and energy dispersive X-ray spectroscopy (EDX). It was found for the first time that PL redshifts start to occur when the phase-separation quantity of the group-III element of In1-xGaxAsyP1-y crystals (Δx) exceeds ~0.05. Such large PL redshifts can be attributed to the emission from defect-related energy levels caused by phase separation.

Faraday Effect of Cd0.55-yHgyMn0.45Te Thin Films

The energy gap (Eg) and the Verdet constant were examined for quaternary Cd0.55-yHgyMn0.45Te thin films with y≤0.11. As the Hg content increases, the Eg decreases and the S-shaped dispersion of the Verdet constant spectrum shifts to a lower photon energy. The magnitude of the Verdet constant for the film with Eg=1.78 eV (y=0.11) is about 1.9 times larger than that for the Cd0.8Mn0.2Te film with Eg=1.78 eV. It is thought that the large Faraday effect of the Cd0.55-yHgyMn0.45Te films in the lower-photon-energy region is based on the large Zeeman splitting enhanced by Mn2+, as in the case of ternary Cd1-xMnxTe.

Metalorganic Vapor Phase Epitaxial Growth Parameter Dependence of Phase Separation in Miscibility Gap of InGaAsP

The generation mechanism of the immiscibility of InGaAsP grown by metalorganic vapor phase epitaxy (MOVPE) is investigated. The growth condition dependence of the immiscibility is examined in detail using particular photoluminescence (PL) characteristics observed in the boundary composition between stable and unstable compositional regions. A lower growth rate or a larger V/III ratio is effective for suppressing phase separation. To explain this growth condition dependence, some factors related to surface energy should be taken into consideration.

Development of Pixel-Readout Micro-Pixel Chamber for X-ray Polarimetry

We developed a pixel-readout micro-pixel chamber (µ-PIC) as an astronomical X-ray polarimeter and demonstrated its ability to achieve a higher sensitivity than a strip-readout one by a beam test. The µ-PIC is one of the micropattern gas detectors that have been developed so far. However, its readout was of the strip type. This limits the sensitivity to polarization because it cannot determine the polarization angle uniquely without rotating the detector. Thus, we started developing the pixel-readout type of µ-PIC. A beam test at a synchrotron-radiation facility was carried out to examine the performance for polarimetry. Without rotating the detector, we successfully detected the polarization angle. The modulation factor for 8 keV X-rays in a neon-based mixture was 0.12±0.03, which is at the same level as that of the strip-type µ-PIC, and 0.07±0.01 at 15 keV in an argon-based mixture. These results indicate the ability of the new µ-PIC to achieve a higher sensitivity to X-ray polarization than that obtainable with the strip-type µ-PIC.

Development of the X-ray polarimeter by using pixel-readout μ-PICs (micro pixel chambers)

We developed the new readout system for the pixel-readout μ-PIC (micro pixel chamber), which is one of the micro-pattern gas detectors that have been developed as a X-ray polarimeter so far. By using this system, we succeeded in achieving the sensitivity predicted by the simulation, i.e, the modulation factors, which is one of the most important factors for X-ray polarimeter as defined later in this paper, 0.24±0.08 at 8 keV, 0.18±0.07 at 15 keV in the neon-based gas mixture, and 0.18±0.04 in the argon-based gas although there still remain problems such as the pitch size among pixels and the non-uniformity of the response.