This paper proposes a planar monopole antenna with a parabolic edge shape. This antenna, which has notch characteristics in the wireless local area network (WLAN) band, can be miniaturized. To obtain the notch characteristics in the WLAN band, a slot with a parabolic edge shape identical to that of the monopole structure was implemented. Because the planar monopole antenna with a parabolic edge shape possesses characteristics similar to those in self-complementary structure conditions, it can be miniaturized by reducing the antenna components at the same proportion. For the antenna fabrication, an FR4 dielectric substrate with a dielectric constant of 4.7 was used. The size of the miniaturized antenna that satisfies the ultra-wide band requirement was 15.6 × 18.6 mm2, and the 10-dB band was 3.013–12.515 GHz. At each frequency, the radiation pattern was similar to that of a dipole antenna.

We have carried out simultaneous 22 GHz H2O and 44 GHz Class I CH3OH maser line surveys of more than 1500 intermediate- and high-mass YSOs in the Galaxy using newly-constructed KVN 21-m telescopes. As the central (proto)stars evolve, the detection rates of the two masers rapidly decrease for intermediate-mass YSOs while the rates increase for high-mass YSOs. These results suggest that the occurrence of the two masers is closely related both to the evolutionary stage of the central objects and to the circumstellar environments. CH3OH masers always have very similar velocities (<10 km s−1) to the natal dense cores, whereas H2O masers often have significantly different velocities. The isotropic luminosities of both masers are well correlated with the bolometric luminosities of the central (proto)stars.

Scanning electron microscopy and transmission electron microscopy images and selected area electron diffraction pattern showed that the one-dimensional GaN nanorods with [0001]-oriented single-crystalline wurzite structures were formed on Si (111) substrates by using hydride vapor-phase epitaxy without a catalyst. Although some stacking faults and inversion domain boundaries existed in the GaN nanorods, few other defects such as threading dislocations were observed. The formation of the facet plane in the N-polar region of the GaN nanorod containing an inversion domain boundary originated from the slow growth rate, followed by the lateral adatom diffusion from the Ga-polar region to reduce the length difference.

ZnO nanowires doped with Mn, Fe, Sn, and Li during the thermal growth following direct chemical synthesis were investigated using electric and magnetic measurements. Current-voltage characteristics of individual nanowires configured as a two-terminal device with Al electrodes show apparent rectify behavior indicating the Schottky-like barrier formation and resistivity being less 3 Ω·cm. Reproducible resistance modulation by a dc voltage at room temperature is observed. Magnetic susceptibility of the doped nanowires as a function of temperature demonstrates Curie–Weiss behavior. Magnetization versus field curves show hysteresis with the coercive field of about 200 Oe. The spatially-resolved magnetic force measurements of individual nanowires revealed the magnetic domain structure. The domains align perpendicular to c-axis and can be polarized in the external magnetic field.

Bonding process using indium-silver alloy which can withstand high temperature was investigated at relatively low temperature. We used a thermal evaporator and vacuum coater for making indium-silver contact. From the result of experiment, we observed that indium and silver films which have good quality are formed. From phase diagram of In-Ag alloy, we can find that melting point of these compounds increases with the silver content, i.e. eutectic (144° C) <AgIn2 (166° C) < (300° C) < (670° C) < (695° C). And these compounds are determined by the composition ratio of the source metal. Now we confirmed the thermal characteristics of Indium-Silver alloy is controlled by silver. Consequently we have developed Ag/In/Ag multi-layer composite which has higher melting point than that of normal contact. The melting point of Ag/In/Ag multi-layer is about 700° C. The joint cross-sections are studied using SEM(scanning electron microscopy) and EDX(Energy Dispersive X-rays). From these data, we observed that the composition and microstructure of Ag/In/Ag multi-layer were reliable and this bonding procedure is a better technique compared to the conventional structure of quantum well LED and GaN/Si LED structure was made by using sapphire for substrate and might be good for high temperature electronic devices in the future.

Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO2/SiOx multilayers (MLs). The SiO2(2nm)/SiOx(2nm) MLs have been prepared under various deposition temperature by ion beam sputtering. The annealing at temperatures ≥ 1100°C leads to the formation of Si nanocrystals (nc-Si) in the SiOx layer of MLs. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc-Lorentzian lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO2/nc-Si MLs as a mixture of nc-Si and SiO2. We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiOx layer. This result is compared to expected nc-Si volume fraction, which was estimated from stoichiometry of SiOx.

(001) oriented (Ba, Sr)TiO3 (BST) thin films were deposited on MgO (001) single crystal substrates by the pulsed laser deposition method. Structural properties of BST films were investigated using X-ray diffractometer. Coplanar waveguide (CPW) device based on BST/MgO layer structure was fabricated by dc sputtering deposition, photolithography and etching process. To study the geometrical factor dependent microwave performance of the CPW phase shifter based on (001) oriented BST film, the CPW devices having various gap and width were fabricated. The microwave dielectric properties of BST CPW phase shifter devices were examined by calculating the scattering parameter obtained using a HP 8510C vector network analyzer with the frequency range 0.5 ∼ 20 GHz at room temperature under the dc bias field of 0 ∼ 40V. The measured return loss and insertion loss at 10 GHz with no dc bias were about -12 ∼ -4 dB and -14 ∼ -3 dB, respectively, which mainly depended on the impedances of the CPW transmission lines. The measured differential phase shift values were about 20 ° ∼ 140 ° at 10 GHz with 40 V dc bias variations, which depended on the gap size.

This work demonstrates the properties of InGaN nanorod arrays with various In mole fractions by modified HVPE using In metal at the low growth temperature. The nanorods grown on (0001) sapphire substrates are preferentially oriented in the c-axis direction. We found that the In mole fractions in the nanorods were linearly increased at x ≤ 0.1. However, In mole fractions were slightly increased at x > 0.1 and then were gradually saturated at x = 0.2. CL spectra show strong blue emissions from 428 nm (x = 0.1, 2.89 eV) to 470 nm (x = 0.2, 2.64 eV) at room temperature. From this result, we found the fact that increasing In mole fraction in the InGaN nanorod shift the peak position of CL spectrum emitted from InGaN nanorod to the low energy region.

In this letter, we investigated the correlation between as-grown surface morphologies and Mn compositions of Ga1-xMnxAs epilayers - a III-V diluted magnetic semiconductor - grown by liquid phase epitaxy (LPE). Ga1-xMnxAs epilayers were grown at 595 °C from 50 % Ga + 50 % Bi mixed solvent. The grown layers were characterized by energy dispersive x-ray analysis (EDS) and atomic forced microscopy (AFM). The Mn composition measured by EDS after growth process was varied from 1 to 7 %. As increasing Mn composition surface morphologies of as-grown Ga1-xMnxAs epilayers were varied. At higher Mn compositions, the morphology of the surface layers degrades strongly, preventing removal of the solution-melt from it. Key words: LPE, as-grown, surface morphology, Mn composition, Ga1-xMnxAs, energy-dispersive x-ray analysis (EDS), atomic forced microscopy (AFM).

GaN nanorods were grown on (0001) sapphire substrates by hydride vapor phase epitaxy HVPE) through a self-assemble process. The nanorods were grown at high growth rate, with the c-axis maintained perpendicular to the substrate surface. The dependence of rod diameter and density on growth conditions was systematically investigated. The average diameter was minimized to 80-120 nm and the density of the GaN nanorods was 100×1012 rods/m2.

In this study, free-standing GaN was produced from 350- to 400-μm-thick GaN films grown on sapphire by using hydride vapor phase epitaxy. The thick films were separated from the substrate by using the mechanical polishing method with a diamond slurry. After liftoff, the bow is slight or absent in the resulting free-standing GaN. Double-crystal X-ray diffraction, hall measurements, and cathodoluminescence were used for characterizing the free-standing GaN wafer. To investigate spatially the backside of the free-standing GaN substrate, we controlled the electron beam energy from 5 keV to 30 keV. As the beam energy increased, dark regions, i.e., nonradiative regions, become smaller than bright regions. We think this means that nonradiative centers, i.e., threading dislocations, merge during film growth.

We investigated the solid phase crystallization (SPC) behavior of 1000 Å amorphous Si (a- Si) films deposited by plasma enhanced chemical vapor deposition (PECVD) at various temperatures and were able to enhance the grain size of the crystallized polysilicon films using double layers of a-Si filns. The deposition temperature of monolayer a-Si films varied from 200 to 400 °C and the films were recrystallized at 600 °C in nitrogen. As the deposition temperature increased, the incubation time was decreased and both the nucleation rate and growth rate were increased. Especially, the nucleation rate strongly depended on the deposition temperature.

Since the Si-SiO2 interface provides a large number of nucleation sites, it is desirable to suppress nucleation at the interface. As an idea we employed a structure with double layer a-Si films. The bottom a-Si layer deposited at lower temperature could suppress the nucleation at the Si-SiO2 interface while the top a-Si layer deposited at higher temperature could nucleate with a smaller number of nucleation sites. The incubation time and transformation behavior were determined by the deposition temperature of the top layer. As an example, the grain size of the double layer film deposited sequentially at 150 °C and 200 °C enhanced to 1.8 μm while that of the monolayer film deposited at 200 °C was 1.4 μm.

A new annealing method, a combination of rapid thermal annealing (RTA) and furnace annealing, has been developed to obtain a high quality poly-Si from a-Si deposited by LPCVD. This method produces a large grain poly-Si with good uniformity, which may result from the growth of relatively defect-free nucleus generated at a high temperature by RTA. Poly-Si thin film transistors fabricated by this new annealing method have higher field effect mobility and better uniformity compared with those by the conventional furnace annealing.