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With the increase in dimensions of optical elements in addition to ever rising demand for aspherical optics, the millimeter-scale periodic waviness that is naturally produced by machining (such as diamond turning) process in precision optical engineering has been one of the most crucial issues in the development of high surface quality optical elements. Even an extremely small waviness can affect the laser beam profile significantly through interference caused by Bragg scattering. This paper presents a novel method for improving a laser beam profile by utilizing the characteristics of Bragg scattering without requiring established final surface finishing processes such as optical polishing. By engraving an artificial periodic structure with a period of a few hundred microns, the Bragg scattering angle that influences the formation of interference fringes in the laser beam profile was drastically enlarged. Consequently, the quality of the beam profile was improved at a propagation distance where the 0th and 1st (− 1st) order beam modes are spatially separated, only by diamond turning machining without the surface finishing process. In addition, this approach represents an important contribution to green technology, which seeks energy saving and waste reduction in the optical surface manufacturing process.

Wavelength-tunable optical vortices with a topological charge equal to l=1 of orbital angular momentum (OAM) were experimentally realized using a single off-axis spiral phase mirror (OSPM) with lasers of various visible-light wavelengths. Using an OSPM designed for 561 nm and an incidence angle of 45°, circular doughnut-shaped l=1 optical vortices were obtained at 561, 473, and 660 nm by rotating the OSPM to modify the laser incidence angle. Wavelength-tunable l=1 optical vortices were obtained at the respective incidence angles of 45°, 53.4°, and 33.7°, because the effective geometrical thickness of the OSPM, which determines the order of OAM, was identical at each wavelength. This flexible OSPM which operates over a wide wavelength range will provide continuously wavelength-tunable optical vortices for applications in the fields of advanced optics and photonics in which optical vortices with wide wavelength tunability are in demand.

In particular, the PES substrate, the crystal structure of the amorphous as well as the surface morphology is not good. So research of thin films growth for epitaxial growth by the use of a buffer layer on the amorphous PES substrate is essential. Therefore, in this study, we deposited ZnO thin-film on PES substrate, and grown ZnO nanorods at various ZnO concentrations during 1 hour. We used SEM, XRD, and HP 4145B for observe the structural and electrical characteristics of ZnO nanorods. UV-visible spectrometer was used to get the band gap and transmittance.

In this paper, we have demonstrated a metallic nano-structured SPR sensor for an improvement of biosensing sensitivity using a metallic nano-structure. Permittivity of metal is calculated with Drude model for analysis. The sensitivity of SPR sensor with metallic nano-structure is 65 degree/RIU, and that of conventional SPR configuration is 54.8 degree/RIU. We have fabricated the random metallic nano-structures on the metallic thin film using the RIE etching process. Moreover, we have analyzed the structure using the finite-difference time-domain method for the exact characteristic.

An integrated surface plasmon resonance (SPR) array sensor using wideband sources and a different incident angle with a single fluidic channel in order to increase the sensitivity is proposed and analyzed. The SPR reflectance was analyzed using the finite-difference time-domain gaussian source method. The maximum difference is shown at the incident angle of 24.6�. The sensitivity of the resonance shift used to change the refractive index of 1x10-3is 51000 nm/RIU at the wavelength interrogation. The extremely small integrated SPR array sensor is a very attractive component because of its promise of a high level of sensitivity, its easy measurement process, and its ease of integration into a sensor system.

Recently, the bending efficiency of vertical slot waveguide with different structure has been analyzed. However, the interface roughness of the waveguide which have high E-field intensity induces to high scattering loss. In addition, a vertical slot fabrication involves in a very narrow region etching which can cause large roughness in the vertical interfaces. In order to reduce the propagation loss and facilitate the fabrication process, horizontal slot waveguides have been proposed and fabricated, recently. In this paper, we have designed and analyzed total internal reflection (TIR) mirror for using a resonator based on horizontal slot waveguide. Our proposed structure is consisted horizontal slot waveguide of rib type to enlarge contact region with TIR mirror. To analyze Goos-Hänchen shift, we have theoretically calculated length of evanescent field at TIR mirror using 3D-FDTD method. The presented TIR mirror loss analysis can be applied to enhance the efficiency of horizontal slot waveguide resonator which can potentially be used in many silicon based optoelectronic devices.

We investigated the effect of indium (In) doping (0.6, 1, 5, and 10 at. %) on the diode characteristics of heterostructures consisting of In-doped ZnO films on p-Si(111) substrates. In-doped ZnO films were deposited by pulsed laser deposition with an In-doped ZnO target, and heterojunction diodes were fabricated by photolithography and a lift-off method. The electrical properties of ZnO films were altered by In doping, with the In (10 at. %)-doped ZnO film having the highest electron concentration ($3.0\times 10^{19}$ cm-3) and lowest resistivity ($1.5\times 10^{-2}$ $\Omega$$\cdot$cm) of the analyzed ZnO films. In doping also had a strong effect on diode characteristics. In particular, In-doped ZnO/p-Si diodes show a very low reverse current density of approximately $2.8\times 10^{-6}$ A/cm2(In 10 at. %) at $-5$ V and a high on--off ratio (In 10 at. %) of about $2.5\times 10^{-6}$ at $\pm 5$ V. The heterostructure diodes exhibited typical current--voltage characteristics with turn-on voltages in the range 1.2--2.4 V and series resistances in the range 37--99 $\Omega$. The modified diode characteristics may be related to changes in the ZnO film structure induced by In doping. We also discuss the effect on diode characteristics of In doping of ZnO films.

In this paper, we propose a plasmonics-based optical polarization rotator. The proposed structure consists of a slotted waveguide and a metal film. The proposed device is designed using skewing phenomena of propagation waves at the slotted waveguide with metal film by 3D-FDTD method. We have analyzed various structures such as a slotted waveguide, a metal-clad optical waveguide, and a metal-clad optical waveguide with buffer layers. A metal film on the waveguide acts to rapidly rotate the optical polarization, because it has characteristics of slow group velocity according to the metal-clad optical waveguide. Therefore, an ultra-small sized polarization rotator can be realized by the plasmonics-based asymmetric cross sections of waveguides. The length of designed polarization rotator is just 5 m for 80% polarization rotation ratio.

In this work, basic characteristics of transmission line employing periodically perforated ground metal (PPGM) were investigated using theoretical and experimental analysis. Concretely, bandwidth and impedance were investigated using theoretical analysis, and wavelength and effective permittivity were extracted from experimental results. In addition, insertion loss and isolation characteristics were investigated using equivalent circuit analysis. For simplification of design process, equivalent circuits for the PPGM cell were extracted, and all circuit parameters were expressed by closed-form equation. Above results indicate that the transmission line employing PPGM is a promising candidate for a development of matching and passive elements on monolithic microwave integrated circuit (MMIC) including wireless communication circuit and compound semiconducting devices such as high electron mobility transistor (HEMT), diamond field effect transistor (FET) and light emitting diode (LED).

We investigated the effect of an annealed ZnO buffer layer on the structural and optical properties of hydrothermally grown ZnO nanorods. ZnO buffer layers were deposited on a p-type Si(100) substrate by radio-frequency (RF) sputtering. ZnO nanorods were grown on as-deposited and annealed ZnO buffer layers by a hydrothermal process at a low temperature for various growth times. Annealed ZnO buffer layers have higher $c$-axis texturing than as-deposited ZnO buffer layer. ZnO nanorods grown on annealed ZnO buffer layers had higher X-ray diffraction (002) peak intensities and ultraviolet (UV) emission intensities than those grown on the as-deposited ZnO buffer layer. The degree of $c$-axis texturing of ZnO buffer layer affects the perpendicular growth for hydrothermal ZnO nanorod.

Transparent flexible displays can be realized using active matrix organic light emitting device (AMOLED) with transparent electrodes on transparent plastic substrates. In this study, we developed low-temperature, high-performance [ZITO, $\text{ZnO}:\text{In$_{2}$O$_{3}$}:\text{SnO$_{2}$}=3:1:1$ molar ratio] thin-film transistors (TFTs) on polyarylate films. After optimizing the sputtering condition, the ZITO TFT with an ITO electrode had a high mobility of 16.93 cm2V-1s-1, and an SS of 0.39, while the ZITO TFT with a ZTO:B electrode showed no hysteresis on sweeping, a mobility of 2.29 cm2V-1s-1and an SS of 0.18.

GdVO4(GVO) thin films were successfully deposited on n-GaN/Al2O3substrates used as a bottom electrode at 600 \mbox{\circC} by radio frequency magnetron sputtering. The GVO films annealed at temperatures up to 800 \mbox{\circC} exhibited epitaxial growth but the films annealed above 900 \mbox{\circC} showed polycrystalline properties. In the photoluminescence (PL) spectrum, broadband emission was observed at 450 nm for all the films. The auger electron spectroscopy (AES) line-shape of the annealed films was similar to that of the as-deposited film but the Gd/V and Gd/O ratios increased linearly with increasing annealing temperature. The dielectric constant and dielectric loss of the GdVO4films decreased with increasing annealing temperature with values of 12--26 and 0.04--0.05 at 1 MHz, respectively.

The relation between Ti silicidation and base resistance in SiGe hetero-junction bipolar transistors (HBT) was investigated. The Ti layer deposited on the Si/SiGe/Si base converted to Ti silicide during two-step annealing. The thickness of the Ti silicide, which was identified as the Ti(Si1-xGex) phase of uniform composition, abruptly increased over the annealing temperature of 650/850 °C, and as a result it accomplished a very low extrinsic base resistance. The Ti silicidation affected the base resistance of real devices (RB), which was extracted from simulating the electrical data of SiGe HBTs such as I –V curves, forward Gummel plots, forward current gain curves, and s-parameter plots. It was shown that the RBwas compatible with the theoretical relation which included the small-signal unity-gain frequency (fT), the maximum oscillation frequency (fmax) and RB. fmaxvaried more sensitively with RBthan fT, which was due to the inherent property of fmaxbeing inversely proportional to √RB. The fmaxof the SiGe HBT reached 47.4 GHz when Ti silicidation was performed at the annealing temperature of 650/850 °C. This silicidation condition is thought to be an appropriate temperature for Ti silicidation applicable to SiGe HBT fabrication. © 2001 Kluwer Academic Publishers

Two-step growth has been developed to achieve in situ phosphorous-doped epitaxial and polycrystalline Si films, and the characteristic transitions in microstructures have been investigated for different phosphorus concentrations and annealing conditions of Si buffers. Our experimental results showed microstructures of Si films were controlled significantly by phosphorus doping and annealing of Si buffers grown at low temperature. While undoped Si buffers grown at 500°C were deposited as amorphous, Si buffers with phosphorus doping above ∼1020cm−3converts the growth modes from amorphous to single crystalline. Moreover, we thought that heavily doped phosphorus could dissociate native oxide at Si buffers/substrate interface by kinetically activated process during annealing. Using heavily phosphorus doped buffers, we can get high quality epi Si films. In addition, uniform polycrystalline Si films grew on undoped Si buffers.

Abstract: We investigated the change in the structural and optical properties of InAs/InP quantum structures during growth interruption (GI) for various times and under various atmospheres in metalorganic chemical vapor deposition. Under AsH3 + H2 atmosphere, the mass transport for the 2D-to-3D transition was observed during the GI. Photoluminescence peaks from both quantum dots (QDs) and quantum wells were observed from the premature QD samples. The fully developed QDs showed the two distinct temperature regimes in the PL peak position, full width at half maximum (FWHM) and wavelength-integrated peak intensity. The two characteristic activation energies were obtained from the InAs/InP QDs: ∼10 meV for intra-dot excitation and 90 ∼ 110 meV for the excitation out of the dots, respectively. It was also observed that the QD evolution kinetics could be suppressed in PH3 + H2 and H2 atmospheres. The proper control of GI time and atmosphere might be a useful tool to further improve the properties of QDs.

This publisher’s note contains corrections to Opt. Lett.46, 4216 (2021)OPLEDP0146-959210.1364/OL.432413.

We successfully fabricated lateral Schottky diodes with a thin MgZnO layer inserted between the ZnO and Schottky contact metal layers. The MgZnO/ZnO heterostructure was deposited onto a $c$-sapphire substrate by pulsed laser deposition using Mg0.3Zn0.7O and ZnO targets. Ti/Au was used to achieve ohmic contact with the Mg0.3Zn0.7O thin film layer, whereas Schottky contacts were prepared using silver (Ag), gold (Au), and palladium (Pd). The Ag Schottky diode devices exhibited rectification ratios as high as ${\sim}10^{3}$ at a bias voltage of $\pm 1$ V, with an ideality factor of 2.37 and a work function of 0.73 eV. The possibility of preparing Schottky contacts with a high carrier concentration on the ZnO layer is discussed as a function of the presence or absence of a MgZnO thin layer and in terms of the measured current--voltage properties.

We report the growth of hexagonal Zn0.58Mg0.42O thin films on a $c$-plane sapphire substrate via pulsed laser deposition using Zn0.7Mg0.3O/Zn0.9Mg0.1O/ZnO stacked buffer layers of various thicknesses. The effects of the stacked buffer layer thickness on the structural and optical properties were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive X-ray (EDX), and UV--visible spectroscopy. The XRD results showed that whereas the cubic and hexagonal phases formed without a stacked buffer layer, only the hexagonal Zn0.58Mg0.42O phase grew in the stacked buffer layer configuration. The stacked buffer layer could accommodate structural inconsistencies and prevent phase separation in high-Mg films. As the thickness of each stacked buffer layer decreased, the crystalline quality of the hexagonal Zn0.5Mg0.5O film was enhanced.

In this paper, we have theoretically analyzed and designed a 1D PhC microcavity sensor with SPR based on the total internal reflection mirror using analytic calculation and FDTD methods. The proposed structure has many advantages. One of that is a high sensitivity using SPR characteristics. Another is a high Q-factor of the characteristics in the PhC microcavity structure. The incident light has double resonance characteristics, because the filtered light by PhC structure is met the thin metal film for SPR effect. We have also observed the change of resonance characteristics according to the variation of effective index on the metal film.

We have proposed and analyzed high sensitivity and high Q-factor triangular ring resonator (TRR) with a total internal reflection (TIR) mirror in silicon-on-insulator (SOI) -based slot waveguide. Different from the conventional integrated optical devices such as waveguide, bend, splitter, and filter, in which the light is guided in high-index medium by the total internal reflection, the slot waveguide confines the E-field in the low-index region by way of strong discontinuities at the interface between the low-index core and the high-index claddings. Because the waveguide using these characteristic has a lower effective index than high-index waveguide, the TRR have been achieved high sensitivity, in which the long evanescent fields on a TIR mirror. Optical quality factor of up to 9.461x102is calculated in such filters, and the sensitivity of the resonance shift for changing the refractive index of 1x10-4at the incidence angle of 34.11° has been identified as high as 1.02x105nm/RIU.

In this paper, we propose an integrated photonic sensor structure using triangular ring resonator (TRR), in which surface plasmon resonance (SPR) is combined for the enhancement of sensitivity. In our previous experimental work on TRR without SPR, we have shown that the Q-factor and the sensitivity of the resonance shift were approximately 7×102and 8.4 nm/RIU, respectively, near 1550 nm. By employing a thin-metal layer for SPR at the total-internal-refection mirror in TRR, we have obtained significantly enhanced sensitivity of the resonance shift up to 55 nm/RIU maintaining similar Q-factor.