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Fe-diluted Si alloys grown on p-type Si (100) substrates by pulsed-laser deposition method were studied for tructural, electrical, and magnetic properties. The X-ray diffraction patterns for these alloy samples showed a few of peaks with cubic structures such as FeSi, Fe3Si, and Fe4Si. The Fe-composition in alloys are confirmed as Fe atomic percent about 1.25∼6.49 % from energy dispersive spectroscopy measurement. The resistivity as a function of the reciprocal temperature was indicated an exponential increase with two activation energies of 5.21 and 7.79 meV. The maximum value of the magnetization at 10 K was about 100 emu/cc, and the ferromagnetism was also observed until 350 K from total magnetization as a function of temperature with applied magnetic field of 3,000 Oe.

This study investigates the coupling modes of a-plane InGaN/GaN mutiquantum wells (MQWs) with single-walled carbon nanotubes (SWCNTs). The enhancement of light emissions at resonance photon energies can be explained by the surface plasmon coupling of the MQW-SWCNT hybrid structure. The photoluminescence (PL) enhancement ratios of the indigo (2.90 eV) emission from MQWs with SWCNTs reveal three coupling modes at 2.50 eV, 2.97 eV, and 3.42 eV. In addition, the trend of the PL intensity ratios and efficiencies corresponds to that of the PL enhancement ratios. The PL efficiencies for the green (2.46 eV) and indigo (2.90 eV) emissions of SWCNT-coated MQWs are 32% and 110% better than the corresponding values of uncoated MQWs, respectively. The results show that the MQW-SWCNT hybrid structure has the potential to be applied in high-efficiency light emitters in the visible and ultraviolet range.

The Ohmic contact of Ti/Au metals on n-type ZnO thin film deposited on c-plane sapphire substrates by pulsed laser deposition was investigated by TLM (transfer length method) patterns. The Ti/Au metal films with thickness of 35 nm and 90 nm were deposited by electron-beam evaporator and thermal evaporator, respectively. By using the photo-lithography method, the TLM patterns with gaps were formed. To improve the electrical properties as well as to decrease an interface states and stress between metal and semiconductor, the post-annelaing process was done in oxygen ambient by rapid thermal annealing system at temperature of for 1 min. In this study, it appeared that the minimum specific contact resistivity shows about in annealed sample, which may be originated from formation of oxygen vacancies of ZnO during an oxidation of Ti metal at the interface of Ohmic contacts.

Optical emissions from ZnO films were enhanced by a formation of hybrid structures with single wall carbon-nanotubes (SWCNTs). The SWCNTs were characterized by the presence of the associated fibers and islands together with many carbon nanotube structures and their average height was about < or = 40 nm from atomic force microscope and scanning electron microscope measurements. The intensities of photoluminescence on ZnO films with SWCNTs were increased up to about 30 and 60% in the region of 3.3 eV (near band edge) and 2.3 eV (deep-level) bands, respectively. It was considered that the enhancement of optical emissions from ZnO might be resulted from the effects of an excitation light scattering by SWCNTs and a surface plasmon resonance between bandgap of ZnO and SWCNTs. The surface plasmon resonance mode in the ultra-violet regions is smaller than the deep-level region relatively. This result showed that the commercial ZnO/carbon nanotubes have a feasibility of application to optoelectronic device.

Nonpolar (1 1–2 0) a-plane GaN films have been grown using the multi-buffer layer technique on (1–1 0 2) r-plane sapphire substrates. In order to obtain epitaxial a-plane GaN films, optimized growth condition of the multi-buffer layer was investigated using atomic force microscopy, high resolution X-ray diffraction, and transmission electron microscopy measurements. The experimental results showed that the growth conditions of nucleation layer and three-dimensional growth layer significantly affect the crystal quality of subsequently grown a-plane GaN films. At the optimized growth conditions, omega full-width at half maximum values of (11–20) X-ray rocking curve along c- and m-axes were 430 and 530 arcsec, respectively. From the results of transmission electron microscopy, it was suggested that the high crystal quality of the a-plane GaN film can be obtained from dislocation bending and annihilation by controlling of the island growth mode.

We have investigated the magnetoresistance (MR) of a polycrystalline indiumantimonide (InSb) van der Pauw (vdP) disk with an embedded concentric gold (Au) core. A polycrystalline InSb sample was prepared in a thermal evaporator. The size of the Au core embedded in a InSb disk with a constant 100-μm diameter varied from 0 to 70 μm. The MR of the devices with different Au size was measured in order to find the optimum Au size and the origin of the enhanced MR. The room temperature MR of the InSb vdP disk with a 70-μm Au inhomogeniety was 614% at 1 T, and 9,900% at 5 T. The MR significantly depended on the size of embedded Au. The results can be well understood by considering field dependent current deflection around the embedded Au core, which is called geometrical MR.

The new hybrid device consisting of single array of Co nanodots on top of GaMnAs is presented to explore a new functionality of GaMAs diluted magnetic semiconductor (DMS). Magnetic state of Co dots was observed by magnetic force microscopy (MFM). Magnetoresistance of pure GaMnAs microbridge strongly depends on the orientation of applied magnetic field. Magnetization reversal of the single domain state definitely affects the longitudinal magnetoresistance of GaMnAs. Inhomogeneous magnetic field induced by Co nanodot is a dominant contribution to the resistance change. This field was regarded to act as an effective potential that may affect the spin polarized carriers in GaMnAs.

We investigated the structural anisotropy of a‐plane GaN films grown by using multi‐buffer layer technique on (1‐102) r‐plane sapphire substrates. For high quality a‐plane GaN films, multi‐buffer layers with various growth conditions were grown by metal‐organic chemical vapor deposition, and analyzed by using several measurement systems such as optical microscopy, scanning electron microscopy, high resolution x‐ray diffraction. The experimental results showed that the nucleation‐layer thickness and the growth temperature of three‐dimensional (3D) growth layer affect significantly the crystal quality of subsequently grown a‐plane GaN films. When the nucleation‐layer thickness was 150 nm, nuclei were fully coalesced. From the x‐ray diffraction results, it appeared that the growth temperature during 3D islands growth affects the full‐width at half maximum (FWHM) values of x‐ray rocking curves along c‐ or m‐directions. At optimized growth conditions, the omega FWHM values of (11–20) x‐ray rocking curve along ...

This study explores the possible scalability of the device by investigating the magnetoresistance (MR) of small sized devices around 100 mum in diameter. Polycrystalline InSb film (1 mum thick) is thermally evaporated onto the insulating Si substrate. InSb van der Pauw disk (100 mum size) was fabricated by standard microfabrication techniques. Subsequently, the core and contact pads are covered by a Ti/Au, with Au being the dominant component. The MR of prepared devices with different embedded Au size is systematically investigated to find out the optimum embedded Au size and the origin of geometrical MR.

We studied oxygen incorporation into ZnTe thin films with oxygen ambient and oxygen plasma during pulsed laser deposition (PLD). The ZnTe layers deposited by oxygen-plasma-assisted PLD under oxygen partial pressures showed the enhancement of visible absorption due to TeO x formation by oxygen incorporation, which was confirmed by X-ray photoelectron spectroscopy measurement. The ZnTe:O thin films grown under oxygen ambient and plasma produced an energy band structure at about 0.5–0.8 eV below the ZnTe band edge, indicating strong radiative properties. The ZnTe:O samples showed the formation of intermediate bands and p-type semiconducting characteristics, which will be useful for intermediate/defect band solar cells.