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Applied Physics Letters

Issue 15 • Date Apr 2003

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Displaying Results 1 - 25 of 59
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Waveguide fabrication in phosphate glasses using femtosecond laser pulses

    Page(s): 2371 - 2373
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    We report on the response of glass to focused femtosecond (fs) laser pulses during waveguide fabrication in a commercial sodium aluminum phosphate glass (Schott IOG-1). Single-pass longitudinal translation of IOG-1 glass with respect to the focused laser beam at a rate of 20 μm/s and pulse energies of 3.5 μJ results in the formation of two waveguides located on opposite sides of the laser-exposed region, which itself does not guide light. This behavior is different from that of the more widely studied silica glass system. The precise location of the waveguides in IOG-1 glass depends on the relative tilt of the fs laser beam with respect to the sample translation direction. Fluorescence imaging of the modified glass using a confocal microscope setup reveals the formation of color center defects in the exposed region but not within the waveguides. © 2003 American Institute of Physics. View full abstract»

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  • Photonic crystal microcavities for cavity quantum electrodynamics with a single quantum dot

    Page(s): 2374 - 2376
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    We propose a planar photonic crystal microcavity design specially tailored for cavity quantum electrodynamics with a single quantum dot emitter embedded in semiconductor. With quality factor up to 45 000, mode volume smaller than a cubic optical wavelength in material, and electric field maximum located in the high-refractive index region at the cavity center, this design can enable both strong coupling and lasing with a single quantum dot exciton. The achievable range of the quality factor to mode volume ratios and the feasible fabrication of the proposed structure make it favorable to other semiconductor microcavities. © 2003 American Institute of Physics. View full abstract»

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  • 1.3 μm wavelength vertical cavity surface emitting laser fabricated by orientation-mismatched wafer bonding: A prospect for polarization control

    Page(s): 2377 - 2379
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    We propose and demonstrate a long-wavelength vertical cavity surface emitting laser (VCSEL) which consists of a (311)B InP-based active region and (100) GaAs-based distributed Bragg reflectors (DBRs), with an aim to control the in-plane polarization of output power. Crystal growth on (311)B InP substrates was performed under low-migration conditions to achieve good crystalline quality. The VCSEL was fabricated by wafer bonding, which enables us to combine different materials regardless of their lattice and orientation mismatch without degrading their quality. The VCSEL was polarized with a power extinction ratio of 31 dB. © 2003 American Institute of Physics. View full abstract»

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  • Finite-size effect on highly dispersive photonic-crystal optical components

    Page(s): 2380 - 2382
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    This letter describes using the large near band edge dispersion in the effective refractive index (neff) of photonic crystals (PCs) to design PC lenses with focal lengths that are very sensitive to small differences in incident wavelength. Our calculations show that practical PCs of finite thickness exhibit an neff with a thickness dependent oscillatory behavior. This results in broadening of the focal spot size along the optical axis when the number of periods in the PC lens is small, which limits the wavelength sensitivity of the lens. These results demonstrate the importance in accounting for the finite-size effect when designing high performance optical devices or components that use the highly dispersive properties of PCs. © 2003 American Institute of Physics. View full abstract»

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  • Electro-optic sampling system with a single-crystal 4-N,N-dimethylamino-4-N-methyl-4-stilbazolium tosylate sensor

    Page(s): 2383 - 2385
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    We present an electro-optic (EO) sampling system based on an organic ionic salt crystal, 4-N,N-dimethylamino-4-N-methyl-4-stilbazolium tosylate (DAST) transducer. Compared to LiTaO3, the DAST lower dielectric permittivity and much higher electro-optic coefficient dramatically improveme electric-field coupling into the EO crystal, which results in a much better signal-to-noise ratio of the sampling system. Submillivolt signals can be easily measured with the DAST sensor. Time resolution of the DAST-based EO system is the same as that of the LiTaO3-based sampler. © 2003 American Institute of Physics. View full abstract»

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  • Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes

    Page(s): 2386 - 2388
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    We demonstrate ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes operating under continuous-wave (cw) conditions. The laser diodes were grown on sapphire substrates by metalorganic chemical vapor deposition. Under pulsed bias conditions, we have achieved threshold current densities as low as 5 kA/cm2 for laser diodes with emission wavelengths between 368 nm and 378 nm and have demonstrated lasing at 363.2 nm at room temperature, the shortest wavelength yet reported for a semiconductor laser diode. The cw operation up to a heat sink temperature of 40 °C was demonstrated on a series of narrow ridge-waveguide devices processed with chemically assisted ion beam etched mirrors and high reflective coating on both facets. The shortest wavelength emission under cw operation conditions was 373.5 nm with output powers of more than 1 mW. © 2003 American Institute of Physics. View full abstract»

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  • Er3+-doped multicomponent sol-gel-processed silica glass for optical signal amplification at 1.5 μm

    Page(s): 2389 - 2391
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    We have developed a multicomponent K–Er codoped silica-based sol-gel glass that presents high luminescence quantum yield (∼100 times larger than that of an Er-doped silica sol-gel glass) and long emission lifetime at 1.54 μm (17 ms). The glass was heat treated to melting temperature with the optical properties of the system remaining practically unchanged. The IR absorption data shows that the hydroxyl content of this multicomponent glass is drastically reduced to a few tens of parts per million by using optimized compositions. The maximum gain coefficient expected for this glass is ∼4.5 dB/cm at 1.5 μm. © 2003 American Institute of Physics. View full abstract»

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  • Switching and regulation of a pulsed discharge channel in a coplanar plasma tetrode

    Page(s): 2392 - 2394
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    Control of a pulsed coplanar discharge by two-dimensional potential tailoring is investigated experimentally in a flat tetrode configuration. One pair of electrodes generates a coplanar discharge, and the other electrodes play roles of switching and controlling the discharge current by changing their electrical potential, where their electrical isolation from the discharge channel is kept without an insulator layer. All the electrodes are cold and arranged on a completely flat plate immersed in discharge gas with the pressure which is in the region to the right of and near the minimum sparking voltage condition. © 2003 American Institute of Physics. View full abstract»

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  • Quantum screening effects on occurrence scattering time for elastic collisions in electron–positron plasmas

    Page(s): 2395 - 2397
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    Quantum screening effects on the occurrence time advance or delay for elastic collisions in electron-positron plasmas are investigated using the corrected Kelbg potential taking into account the classical effect as well as the quantum-mechanical effect. The eikonal method is applied to obtain the scattering amplitudes for electron–electron, positron–positron, and electron–positron elastic collisions in electron–positron plasmas. The results show that the occurrence time delay for electron–electron and positron–positron collisions increases with increasing plasma temperature. However, it is found that the occurrence time advance for electron–positron collisions has the maximum value at the temperature kBT≈4.5 eV and decreases with increasing the plasma temperature. © 2003 American Institute of Physics. View full abstract»

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  • Epitaxial growth of group III nitrides on silicon substrates via a reflective lattice-matched zirconium diboride buffer layer

    Page(s): 2398 - 2400
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    Growth of metallic and reflecting ZrB2 films is conducted on Si(111) substrates at 900 °C using a single-source unimolecular precursor Zr(BH4)4 in a molecular beam epitaxy chamber. Epitaxial growth of ZrB2(0001) is accomplished despite the very large lattice mismatch between ZrB2 and Si(111). High-resolution cross-sectional transmission electron microscopy images of the sharp ZrB2/Si(111) interface show a heteroepitaxial relationship involving a “magic mismatch” of coincidence lattices. The GaN films grown on the ZrB2/Si(111) template is virtually homoepitaxy because of the very small lattice mismatch, 0.6%, between the in-plane lattice parameters of ZrB2(0001) and GaN(0001). © 2003 American Institute of Physics. View full abstract»

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  • In(Ga)As self-assembled quantum ring formation by molecular beam epitaxy

    Page(s): 2401 - 2403
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    The effect of growth conditions on the morphological properties of InAs/GaAs(001) quantum dots covered by a thin (≪3 nm) GaAs cap has been studied by atomic force microscopy. Each dot turns into an elongated nanostructure at 540 °C upon deposition of the cap in As4 atmosphere, while structures with two humps are obtained when capping at 500 °C. The use of As2 atmosphere instead of As4 at 500 °C leads to the formation of quantum rings. Photoluminescence spectroscopy and polarization photoluminescence (PL) at 15 K show dramatic changes due to the different kinds of confinement. This allows the possibility of tailoring PL emission by controlling the size and shape. © 2003 American Institute of Physics. View full abstract»

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  • Stretchable gold conductors on elastomeric substrates

    Page(s): 2404 - 2406
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    Stripes of thin gold films are made on an elastomeric substrate with built-in compressive stress to form surface waves. Because these waves can be stretched flat they function as elastic electrical conductors. Surprisingly, we observe electrical continuity not only up to an external strain of ∼2% reached by stretching the films first flat (∼0.4%) and then to the fracture strain of free-standing gold films (∼1%), but up to ∼22%. Such large strains will permit making stretchable electric conductors that will be essential to three-dimensional electronic circuits. © 2003 American Institute of Physics. View full abstract»

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  • Thermally bandwidth-controllable reflective polarizers from (polymer network/liquid crystal/chiral dopant) composites

    Page(s): 2407 - 2409
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    A (polymer network/nematic liquid crystal/chiral dopant) composite exhibiting a chiral nematic (N*) phase at room temperature has been developed. Because the helical twisting power of the chiral dopant increases with increasing temperature and the polymer network affects the molecular rearrangement of the liquid crystal, the bandwidth of the selective reflection spectrum of the N* phase becomes wider and narrower reversibly with increasing and decreasing temperature, respectively. © 2003 American Institute of Physics. View full abstract»

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  • Structure of stacking faults formed during the forward bias of 4H-SiC p-i-n diodes

    Page(s): 2410 - 2412
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    Using site-specific plan-view transmission electron microscopy (TEM) and light emission imaging, we have identified stacking faults formed during forward biasing of 4H-SiC p-i-n diodes. These stacking faults (SFs) are bounded by Shockley partial dislocations and are formed by shear strain rather than by the condensation of vacancies or interstitials. Detailed analysis using TEM diffraction contrast experiments reveal SFs with leading carbon-core Shockley partial dislocations as well as with the silicon-core partial dislocations observed in plastic deformation of 4H-SiC at elevated temperatures. The leading Shockley partials are seen to relieve both tensile and compressive strain during p-i-n diode operation, suggesting the presence of a complex inhomogeneous strain field in the 4H-SiC layer. © 2003 American Institute of Physics. View full abstract»

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  • Low-temperature layer splitting of (100) GaAs by He+H coimplantation and direct wafer bonding

    Page(s): 2413 - 2415
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    The present letter introduces a low-temperature GaAs layer splitting approach by He+H coimplantation which—in combination with direct wafer bonding—enables monolithic integration of GaAs with different substrates. The influence of He+H coimplantation on blistering and layer splitting of GaAs is studied and the optimum coimplantation conditions are determined. Thin GaAs layers are transferred onto Si after bonding of He+H coimplanted GaAs and Si substrates via a spin-on glass intermediate layer and subsequent annealing at only 225 °C for 14 h. Cross-sectional transmission electron microscopy investigations show a high quality of the GaAs/SOG bonding interface. © 2003 American Institute of Physics. View full abstract»

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  • Analysis of self-focusing beams of concentric symmetry in As2S3 glass using a near-field scanning optical microscope

    Page(s): 2416 - 2418
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    The self-focusing (SF) effect for concentric laser beams passing through As2S3 glass was studied using a near-field scanning optical microscope. In the case of radially symmetric laser beams at the wavelength 633 nm, there was no special bright spot caused by the SF effect at local areas, except for the central part of the light beam. The minimum beam size that was arrested by nonparaxiality was less than 0.3 μm, which is approximately equal to the wavelength of light in the As2S3 glass, 0.265 μm. Qualitatively, the experimental results agreed with the theoretical prediction of the nonparaxial approximation. © 2003 American Institute of Physics. View full abstract»

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  • Study of interfacial reaction and its impact on electric properties of Hf–Al–O high-k gate dielectric thin films grown on Si

    Page(s): 2419 - 2421
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    Amorphous thin films of Hf–Al–O (with atomic ratio of Al/Hf of about 1.4) were deposited on (100) p-Si substrates by pulsed-laser deposition using a HfO2 and Al2O3 composite target. Transmission electron microscopy was employed for a detailed study of the interfacial reaction between the Hf–Al–O films and the Si substrates. Islands of Hf silicide formed from interfacial reaction were observed on the surface of the Si substrate. The formation of Hf silicide is attributed to the presence of Al oxide in the films that triggers the reaction between Hf atoms in the amorphous Hf–Al–O films and Si under an oxygen deficient condition. The impact of silicide formation on the electrical properties was revealed by high-frequency capacitance–voltage (C–V) measurements on metal–oxide–semiconductor capacitors. The observed abnormal C–V curve due to interfacial reaction was discussed. © 2003 American Institute of Physics. View full abstract»

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  • Blue organic electrophosphorescence using exothermic host–guest energy transfer

    Page(s): 2422 - 2424
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    We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N-dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate (FIrpic). By examining the temperature dependence of the radiative lifetime and the photoluminescence of a film of mCP doped with FIrpic, we confirm the existence of exothermic energy transfer in contrast to the endothermic transfer characteristic of the N,N-dicarbazolyl-4-4-biphenyl and FIrpic system. In employing exothermic energy transfer between mCP and FIrpic, a maximum external electroluminescent quantum efficiency of (7.5±0.8)% and a luminous power efficiency of (8.9±0.9)lm/W are obtained, representing a significant increase in performance over previous endothermic blue electrophosphorescent devices. © 2003 American Institute of Physics. View full abstract»

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  • Temperature dependence of the ionic conductivity in Li3xLa2/3-xTiO3: Arrhenius versus non-Arrhenius

    Page(s): 2425 - 2427
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    We report on the temperature dependence of the ionic conductivity at low temperatures in the crystalline lithium ionic conductor Li0.18La0.61TiO3. Time domain measurements of the electric modulus have been performed to investigate ion dynamics in the frequency range 10-5–102Hz and for conductivity values in the range 10-14–10-8S/cm. Ionic conductivity shows an Arrhenius temperature dependence below 300 K and down to 120 K, in contrast to the non-Arrhenius behavior found at higher temperatures, demonstrating that the temperature dependence of ionic conductivity in Li0.18La0.61TiO3 cannot be described by a Vogel–Fulcher–Tamman law. © 2003 American Institute of Physics. View full abstract»

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  • Structural and optical properties of near-surface GaInNAs/GaAs quantum wells at emission wavelength of 1.3 μm

    Page(s): 2428 - 2430
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    X-ray diffraction, x-ray-induced photoelectron emission, and low-temperature photoluminescence have been used to investigate structural and optical properties of near-surface Ga1-xInxNyAs1-y/GaAs double quantum wells. The evolution of x-ray diffraction fringes, due to post-growth annealing, provides evidence for In/Ga interdiffusion at elevated temperatures. Photoelectron spectra indicate that indium tends to re-evaporate from the surface. Photoluminescence exhibits a strong feature, as part of the GaInNAs/GaAs material system. This feature is assigned to a hybridized state that is created by an interaction between surface states and quantum-confined states of the near-surface quantum well. © 2003 American Institute of Physics. View full abstract»

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  • Morphological instability of GaInNAs quantum wells on Al-containing layers grown by metalorganic vapor-phase epitaxy

    Page(s): 2431 - 2433
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    We report on the optical and structural integrity of metalorganic vapor-phase epitaxy-grown GaInNAs/GaAs single quantum wells on AlGaAs/GaAs distributed Bragg reflectors (DBRs). Photoluminescence and surface morphology as measured by atomic force microscopy were investigated for different numbers of DBR periods and different DBR-growth temperatures. An increasing number of DBR periods may severely degrade the quantum well surface morphology and photoluminescence. Surface secondary-ion mass spectroscopy revealed surface segregation of an Al-containing species. Decreasing the DBR-growth temperature lowers the surface concentration of Al and improves the GaInNAs quantum-well morphology. © 2003 American Institute of Physics. View full abstract»

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  • Designing the refractive indices by using magnetic fluids

    Page(s): 2434 - 2436
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    Magnetic fluid is a type of colloid consisting of magnetic nanoparticles dispersed in liquid carriers with the aid of surfactants and Brownian motion. Thus, the optical properties of magnetic fluids can be manipulated through the careful selection of magnetic particles and carriers. In this work, we give an example by designing a refractive index by using magnetic fluids composed of various carriers and particles, around 1.465 at 1.557 μm wavelength, which plays an important role in optical fiber communication. In addition, we also show how to achieve a desired flexibility in the tunable refractive index with externally varying fields by adopting suitable magnetic fluid films. These results reveal the feasibility of developing index-match or index-tunable devices using magnetic fluids. © 2003 American Institute of Physics. View full abstract»

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  • Effect of stress-induced phase transformation on nanomechanical properties of sputtered amorphous carbon films

    Page(s): 2437 - 2439
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    The nanomechanical properties of radio-frequency sputtered ultrathin carbon films measured by surface force microscopy were correlated to the carbon bonding structures analyzed by x-ray photoelectron and Auger electron spectroscopy. The films consisted of amorphous carbon (a-C) comprising both trigonal (sp2) and tetrahedral (sp3) carbon hybridizations. The sp3 carbon content in the a-C materials of films with nanohardness of 19–40 GPa was found to be in the range of 22%–28%. From variations of the binding energy of Ar 2p electrons and the sp3 carbon content with the film Ar content, a stress-induced phase transformation from sp2 to sp3 carbon was determined at compressive residual stress of about 14 GPa. Film hardening occurs due to material densification, which is controlled by the intensity of the energetic Ar+ bombardment and the flux ratio of incoming C atoms and Ar+ ions during film growth. The results of this study elucidate the underlying hardening mechanism in ultrathin sputter-deposited carbon films. © 2003 American Institute of Physics. View full abstract»

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  • Temperature-dependent photoinduced third-harmonic-generation variation in azo-homopolymer and azo-doped polymer thin films

    Page(s): 2440 - 2442
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    The temperature effect on the variation of photoinduced third-harmonic generation (THG) of an azo-polyurethane homopolymer and an azo guest–host polymer is studied at several different temperatures. At higher temperatures, both angular hole burning and molecule angular redistribution motions weaken, due to the decreases of cis-to-trans thermal relaxation time and the cis population and the increase of orientational diffusion coefficient. Smaller photoinduced THG variation is observed in both samples at higher temperatures. Results from the THG recovery experiment show that polyurethane homopolymer thin films pumped at a high temperature have the best photoinduced THG variation stability after turning off the pump beam. © 2003 American Institute of Physics. 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