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Applied Physics Letters

Issue 7 • Date Aug 2006

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Displaying Results 1 - 25 of 104
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Properties of an optical multipass surface plasmon resonance technique

    Page(s): 071101 - 071101-3
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    A fiber optic four-pass surface plasmon resonance technique with an approach to increase the number of passes to any arbitrary number is described. Within multipass regime, reflections off the gold sample surface that reduce the reflectivity to less than 0.1% are achieved by using a fiber optic collimator, a reflector, and a corner cube prism. In this case, the optical beam emits from and returns to the collimator. This technique holds the potential for significantly increasing the detection sensitivity of surface plasmon resonance device. View full abstract»

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  • Visible two-dimensional photonic crystal slab laser

    Page(s): 071102 - 071102-3
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    The authors describe the fabrication and performance of photonic crystal lasers fabricated within thin membranes of InGaP/InGaAlP quantum well material and emitting in the visible wavelength range. These lasers have ultrasmall mode volumes, emit red light, and exhibit low threshold powers. They can be lithographically tuned from 650 to 690 nm. Their cavity volumes of approximately 0.01 μm3 are ideally suited for use as spectroscopic sources. View full abstract»

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  • Traveling-wave photomixers fabricated on high energy nitrogen-ion-implanted GaAs

    Page(s): 071103 - 071103-3
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    The authors report on fabrication and measurement of traveling-wave photomixers based on high energy and low dose nitrogen-ion-implanted GaAs. They used 3 MeV energy to implant N+ ions into GaAs substrates with an ion concentration dose of 3×1012 cm-2. The N+-implanted GaAs photomixers exhibit improvements in the output power in comparison with their counterparts, photomixers fabricated on low-temperature-grown GaAs. The maximal output power was 2.64 μW at 850 GHz. No saturation of the output power with increased bias voltage and optical input power was observed. These characteristics make N+-implanted GaAs the material of choice for efficient high power sources of terahertz radiation. View full abstract»

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  • Complementary thermoreflectance and micro-Raman analysis of facet temperatures of diode lasers

    Page(s): 071104 - 071104-3
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    A methodological approach for advanced facet temperature characterization of operating diode lasers is presented. It relies on the concerted application of micro-Raman spectroscopy and thermoreflectance mapping. The latter technique allows for fast facet mapping, whereas the Raman data provide the temperature calibration. Residual effects, e.g., caused by the different reflectances of the materials involved into the laser structure, are discussed. Since both techniques provide rather complementary information, their concerted application appears as an effective tool for advanced device inspection. View full abstract»

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  • Fabrication of inorganic GeO2:SiO2 channel waveguides by ultraviolet imprinting technique

    Page(s): 071105 - 071105-3
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    The authors demonstrate the effective waveguiding channel formation inside an ∼3 μm thick photosensitive GeO2(20%):SiO2(80%) planar slab waveguide film prepared using the sol-gel technique by the direct ultraviolet (UV) imprinting technique. This is possible because of the ability to induce large refractive index change (∼10-3) in the films by the UV radiation. Channel waveguides with various refractive index values have been fabricated. The measured modal profiles of the waveguides match well with the simulation results. The simplicity of the direct UV imprinting technique is also shown by the fabrication of a 1×2 multimode-interference 3 dB light splitter in one single processing step. View full abstract»

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  • Actuation of cantilevers by optical trapping

    Page(s): 071106 - 071106-3
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    Cantilevers are commonly used in microelectromechanical systems for sensing and optical switching applications. The authors demonstrate the use of optical tweezers for all optical actuation of a tapered optical fiber used as a cantilever and to drive it as a micromechanical oscillator. A fiber optic confocal detection system is used to monitor backscattered trapping light to sense the position and oscillation characteristics of the cantilever. Potential applications include optical switching and dynamic reconfigurability of photonic circuits. View full abstract»

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  • Room temperature polariton luminescence from a GaN/AlGaN quantum well microcavity

    Page(s): 071107 - 071107-3
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    The authors report on the demonstration of strong light-matter coupling at room temperature using a crack-free UV microcavity containing GaN/AlGaN quantum wells (QWs). Lattice-matched AlInN/AlGaN distributed Bragg reflectors (DBRs) with a maximum peak reflectivity of 99.5% and SiO2/Si3N4 DBRs were used to form high finesse hybrid microcavities. State-of-the-art GaN/Al0.2Ga0.8N QWs emitting at 3.62 eV with a linewidth of 45 meV at 300 K were inserted in these structures. For a 3λ/2 microcavity containing six QWs, the interaction between cavity photons and QW excitons is sufficiently large to reach the strong coupling regime. A polariton luminescence is observed with a vacuum field Rabi splitting of 30 meV at 300 K. View full abstract»

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  • Tailoring holes for improving the efficiency of single-mode photonic crystal waveguide lasers on InP substrate

    Page(s): 071108 - 071108-3
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    The authors show that the use of triangular lattice photonic crystals (PhCs) with wide holes can significantly improve the lasing performances of PhC waveguides in the InP substrate approach. The study is carried out on W2-3 waveguides made in PhCs whose air filling factor is varied from ∼25% to 55%. Intrinsically single-mode laser emissions with reduced threshold (/2) are obtained when the laser mode folds deeply into the gap. Concurrently, the slope of the light-light characteristic is increased by a factor of 14. The laser spectral behavior and threshold evolution are explained from three-dimensional finite difference time domain calculations. View full abstract»

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  • High performance thin-film flip-chip InGaN–GaN light-emitting diodes

    Page(s): 071109 - 071109-3
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    Data are presented on the operation of thin-film flip-chip InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs). The combination of thin-film LED concept with flip-chip technology is shown to provide surface brightness and flux output advantages over conventional flip-chip and vertical-injection thin-film LEDs. Performance characteristics of blue, white, and green thin-film flip-chip 1×1 mm2 LEDs are described. Blue (∼441 nm) thin-film flip-chip LEDs are demonstrated with radiance of 191 mW/mm2 sr at 1 A drive, more than two times brighter than conventional flip-chip LEDs. An encapsulated thin-film flip-chip blue LED lamp is shown to have external quantum efficiency of 38% at forward current of 350 mA. A white lamp based on a YAG:Ce phosphor coated device exhibits luminous efficacy of 60 lm/W at 350 mA with peak efficiency of 96 lm/W at 20 mA and luminance of 38 Mcd/m2 at 1 A drive current. Green (∼517 nm) devices exhibit luminance of 37 Mcd/m2 at 1 A. View full abstract»

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  • Tunable silicon microring resonator with wide free spectral range

    Page(s): 071110 - 071110-3
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    The authors present a silicon-on-insulator single ring resonator with a free spectral range equal to 47 nm, which is the widest known value for this type of resonators. The ring radius is 2 μm and is the smallest ring resonator ever reported, achieving experimentally such a wide spectral range. For this ring resonator, the authors demonstrate the quality factor to be equal to 6730±60. They thermally tune the resonant wavelength with 0.11 nmC, thus showing the ring resonator as an attractive component for on-chip ultracompact photonic add/drop filters and switches. View full abstract»

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  • Nonlocality-controlled interaction of spatial solitons in nematic liquid crystals

    Page(s): 071111 - 071111-3
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    The authors demonstrate experimentally that interaction between nonlocal solitons in nematic liquid crystals (NLCs) can be controlled by the degree of nonlocality. For a given beam width, the degree of nonlocality can be modulated by changing the pretilt angle θ0 of NLC molecules through bias voltage V. As V increases (so does θ0), the degree of nonlocality decreases. When the degree of nonlocality is below a critical value, the solitons behave in the way like their local counterpart, i.e., in-phase solitons attract while out-of-phase solitons repulse each other. Such a voltage-controlled interaction between the solitons can be readily implemented in experiments. View full abstract»

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  • 1 μm saturable absorber with recovery time reduced by lattice mismatch

    Page(s): 071112 - 071112-3
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    Metamorphic growth of lattice mismatched InGaP on GaAs has been used to fabricate a fast semiconductor saturable absorber mirror operating at the 1060 nm wavelength range. The absorption recovery time could be reduced to ∼5 ps without deteriorating the nonlinear absorption properties. The device was used to demonstrate self-starting operation of a mode-locked Yb-doped fiber laser and obtain high quality picosecond pulses. View full abstract»

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  • InN nanoflowers grown by metal organic chemical vapor deposition

    Page(s): 071113 - 071113-3
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    Hexangular indium nitride nanoflower pattern is observed from scanning electron microscopy and atomic force microscopy. The sample is grown on c-plane (0001) sapphire by metal organic chemical vapor deposition with intentional introduction of hydrogen gas. With the aid of hydrogen, a stable existence of metallic indium is achieved. This will induce the growth of InN nanoflowers via self-catalysis vapor-liquid-solid (VLS) process. It is found that the VLS process is modulated by the interface kinetics and thermodynamics among the sapphire substrate, indium, and InN, which leads to the special morphology of the authors’ InN nanoflower pattern. View full abstract»

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  • Carrier lifetime reduction in 1.5 μm AlGaAsSb saturable absorbers with air and AlAsSb barriers

    Page(s): 071114 - 071114-3
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    The optical properties of different AlGaAsSb semiconductor saturable absorber mirrors and InP/AlGaAsSb heterostructures have been investigated by pump-probe and low temperature photoluminescence measurements. The results show that the type-II electron-hole recombination process at the InP–AlGaAsSb interface is responsible for the slow carrier decay time in the absorber. Nevertheless, this slow transition can be avoided by growing an AlAsSb barrier layer between InP and the absorber layer promoting the fast electron-hole recombination at the surface states on the absorber/air interface. This allows reducing the carrier decay time from several nanoseconds down to 20 ps. View full abstract»

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  • Observation of optical bistability in a ZnO powder random medium

    Page(s): 071115 - 071115-3
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    Optical bistability has been observed in photoluminescence from a ZnO powder random medium. The emission spectra and the excitation intensity dependence of 420 nm emission clearly exhibit the existence of bistable steady states with changing excitation intensity. View full abstract»

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  • Laser emission from GaN photonic crystals

    Page(s): 071116 - 071116-3
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    In this study, photonic crystals have been designed, fabricated, and characterized in GaN bulk materials. The energy dependent measurement showed that the emission peak width can be significantly reduced as the pumping pulse energy was larger than 0.7 μJ at room temperature. The mode at the wavelength of 371 nm emitted from the defect due to the structure disorder unintentionally introduced during the fabrication process of the GaN photonic crystals can be obtained. View full abstract»

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  • High bandwidth Ge p-i-n photodetector integrated on Si

    Page(s): 071117 - 071117-3
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    The authors present a germanium on silicon p-i-n photodiode for vertical light incidence. For a Ge p-i-n photodetector with a radius of 5 μm a 3 dB bandwidth of 25 GHz is measured at an incident wavelength of 1.55 μm and zero external bias. For a modest reverse bias of 2 V, the 3 dB bandwidth increases to 39 GHz. The monolithically integrated devices are grown on Si with solid source molecular beam epitaxy. The complete detector structure consisting of a highly p-doped Ge buried layer, an intrinsic absorption region, and a highly n-doped top contact layer of Ge/Si is grown in one continuous epitaxial run. A low growth temperature sequence was needed to obtain abrupt doping transitions between the highly doped regions surrounding the intrinsic layer. A theoretical consideration of the 3 dB bandwidth of the Ge detector was used to optimize the layer structure. For a photodiode with 5 μm mesa radius the maximum theoretical 3 dB frequency is 62 GHz with an intrinsic region thickness of 307 nm. View full abstract»

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  • Silicon surface periodic structures produced by plasma flow induced capillary waves

    Page(s): 071501 - 071501-3
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    Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations. View full abstract»

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  • Self-driven formation and structure of single crystal platelets of Zn3As2

    Page(s): 071901 - 071901-3
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    In this work the authors introduce and provide details on the stoichiometrically controlled self-driven formation of freestanding single crystal platelets in Zn3As2 by a direct self-catalytic vapor-solid growth mechanism. The platelets feature dimensions of up to ∼1 cm and mirrorlike microscopically flat top surfaces. A coherent formation of pyramids and wires has been further observed on some of the platelet top surfaces, the growth mechanism of which is discussed. This study might open pathways for facile engineering of high-performance semiconductor via a direct vapor-solid conversion of polycrystalline semiconductor powders into single crystal substrates on a large scale and with low cost. View full abstract»

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  • Optimization of the surface and structural quality of N-face InN grown by molecular beam epitaxy

    Page(s): 071902 - 071902-3
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    The authors demonstrate the impact of growth kinetics on the surface and structural properties of N-face InN grown by molecular beam epitaxy. Superior surface morphology with step-flow growth features is achieved consistently under In-rich conditions in a low-temperature region of 500–540 °C. Remarkably, off-axis x-ray rocking curve (ω scans) widths are found to be independent of the growth conditions. The band gap determined from optical absorption measurements of optimized InN is 0.651 eV, while photoluminescence peak emission occurs at even lower energies of ∼0.626 eV. Hall measurements show room temperature peak electron mobilities as high as 2370 cm2/V s at a carrier concentration in the low 1017 cm-3 region. Analysis of the thickness dependence of the carrier concentration demonstrates a n-type surface accumulation layer with a sheet carrier concentration of ∼3×1013 cm-2. View full abstract»

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  • On the solute coupling at the moving solid/liquid interface during equiaxed solidification

    Page(s): 071903 - 071903-3
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    Integral mass conservation was widely accepted for the solute coupling to solve solute redistribution during equiaxed solidification so far. The present study revealed that the integral form was invalid for moving boundary problems as it could not represent the mass balance at the moving interface. Accordingly, differential mass conservation at the solid/liquid interface was used to solve solute diffusion for spherical geometry. The model was applied for hydrogen diffusion in solidification to validate that the hydrogen enrichment was significant and depended on the growth rate. View full abstract»

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  • Shear-strain induced decomposition of 1,1-diamino-2,2-dinitroethylene

    Page(s): 071904 - 071904-3
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    The structural and electronic features of shear strains in the molecular crystal 1,1-diamino-2,2-dinitroethylene and their effect on decomposition of the material are investigated. The authors demonstrate that shear strains lower the decomposition barrier and narrow the band gap of the solid and thus facilitate thermal chemistry in molecular materials. The appearance of defect-related electronic states in the band gap is consistent with previous results for dislocation modeling in molecular solids and with experiments on energetic materials. The dynamic behavior of the band gap contains a rich variety of information about the details of the decomposition processes at the initiation stage. View full abstract»

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  • Influence of N incorporation on In content in GaInNAs/GaNAs quantum wells grown by plasma-assisted molecular beam epitaxy

    Page(s): 071905 - 071905-3
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    The authors investigated the synthesis of GaIn(N)As/Ga(N)As multiple quantum wells by molecular beam epitaxy. Introducing N into the GaInAs appears to suppress the incorporation of In as indicated by reflective high-energy electron diffraction (RHEED). This effect is mainly due to the N-induced enhancement of In surface segregation at the growth front and is evidenced by the increasing damping rate of RHEED oscillations with N incorporation. The N-induced enhancement of In segregation in the GaInNAs quantum wells is confirmed by secondary-ion-mass spectroscopy and high-resolution x-ray diffractions, and its origin is discussed. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory