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Applied Physics Letters

Issue 26 • Date Dec 2000

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Displaying Results 1 - 25 of 67
  • Issue Cover

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

    Page(s): toc1
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  • Quasi-phase matched second-harmonic generation in an AlxGa1-xAs asymmetric quantum-well waveguide using ion-implantation-enhanced intermixing

    Page(s): 4247 - 4249
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    Quasi-phase matched second-harmonic generation in the copropagating geometry is demonstrated in an asymmetric quantum-well waveguide. Modulation of the nonlinear susceptibility along the waveguide was achieved using a patterned quantum-well intermixing process. Photoluminescence measurements of the quantum-well bandedges indicate that a grating of alternating regions of intermixed and as-grown asymmetric quantum wells was produced for periods between 2 and 12 μm. The variation of the second-harmonic light intensity generated by guided incident light between λ=1480 and 1600 nm was measured. The resulting second-harmonic spectra show sharp quasi-phase matching resonances for grating periods near 3 μm, demonstrating that a periodic modulation of the quantum-well nonlinear susceptibility was produced. © 2000 American Institute of Physics. View full abstract»

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  • Stimulated emission induced by exciton–exciton scattering in ZnO/ZnMgO multiquantum wells up to room temperature

    Page(s): 4250 - 4252
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    The mechanism of ultraviolet stimulated emission was investigated in ZnO/ZnMgO multiquantum wells. Stimulated emission induced by exciton–exciton scattering occurred throughout a range of temperatures from 5 K to room temperature. At temperatures higher than 160 K, stimulated emission due to electron-hole plasma recombination was also observed with a higher excitation threshold than that of exciton–exciton scattering. The exciton binding energies of multiquantum wells were larger than that of bulk ZnO and increased with a decrease in the well widths. This enhancement of exciton binding energy is due to the quantum-confinement effect and is favorable for the stability of exciton states. © 2000 American Institute of Physics. View full abstract»

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  • Optically pumped InGaN/GaN lasers with wet-etched facets

    Page(s): 4253 - 4255
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    Optically pumped laser action is demonstrated in InGaN/GaN double heterostructure lasers with wet-etched facets. The facets are formed by a two-step etching process which creates vertical facets with less than 5 nm roughness. The first step, photoenhanced electrochemical wet etching, is used to define the laser cavities. The second step reduces the facet roughness by crystallographic wet chemical etching. Lasing is demonstrated by an increase in the differential quantum efficiency, linewidth narrowing, and strongly polarized output above threshold. The threshold varies with cavity length from 2.4 MW/cm2 for 500 μm cavities to 23 MW/cm2 for 50 μm cavities. A modal loss of 15 cm-1 is deduced from an analysis of the threshold pumping power as a function of cavity length. © 2000 American Institute of Physics. View full abstract»

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  • Drilled alternating-layer three-dimensional photonic crystals having a full photonic band gap

    Page(s): 4256 - 4258
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    We propose a three-dimensional photonic crystal structure having a wide full photonic band gap in the optical regime, which can be fabricated by an alternating-layer deposition and etching (drilling) process. This fabrication process is much simpler than that previously reported. The combination of current lithographic technology and autocloning bias-sputtering deposition is a promising way of realizing these photonic crystals. © 2000 American Institute of Physics. View full abstract»

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  • Patterned three-color ZnCdSe/ZnCdMgSe quantum-well structures for integrated full-color and white light emitters

    Page(s): 4259 - 4261
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    We report the growth and characterization of patterned ZnCdSe/ZnCdMgSe quantum-well (QW) structures grown adjacent to each other on a single InP substrate. Each structure emits at a different wavelength range spanning the visible range. Stripe and square-shaped QW structures of different emission wavelengths, with lateral dimensions between 15 and 60 μm, were deposited sequentially by shadow mask selective area epitaxy (SAE) steps. Conventional and microphotoluminescence measurements were used to characterize the patterned QWs. They exhibit well-defined excitonic emission in the red, yellow, and green regions of the visible spectrum. This result demonstrates the feasibility of fabricating integrated full-color light emitting diode and laser-based display elements and white light sources using the ZnCdMgSe material system and shadow mask SAE. © 2000 American Institute of Physics. View full abstract»

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  • Expanded viewing-angle reflection from diffuse holographic-polymer dispersed liquid crystal films

    Page(s): 4262 - 4264
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    A switchable diffuse reflective film with high color purity is demonstrated using holographic-polymer dispersed liquid crystals (HPDLC). By recording a diffuse hologram directly into the LC/polymer film, the diffuse mode HPDLC exhibit viewing angles an order of magnitude larger than the conventional mode. A simple phenomenological model based on coupled-wave theory is developed to describe our observations. © 2000 American Institute of Physics. View full abstract»

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  • Feasibility of 5 Gbit/s wavelength division multiplexing using quantum dot lasers

    Page(s): 4265 - 4267
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    The dynamics of single-mode quantum dot lasers is modeled theoretically. It is predicted that, assuming reasonable material properties, eye-patterns remain open for 5 Gbit/s large signal modulation within a finite spectral range (≫50 nm), corresponding to 64 wavelength division multiplexing channels with 0.8 nm separation. © 2000 American Institute of Physics. View full abstract»

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  • Fast accurate wavelength switching of an erbium-doped fiber laser with a Fabry–Perot semiconductor filter and fiber Bragg gratings

    Page(s): 4268 - 4270
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    We propose a simple passive method for achieving fast accurate wavelength switching in an erbium-doped fiber laser. The method relies on a laser cavity formed with a Fabry–Perot semiconductor filter (FPSF) and narrow-band fiber Bragg gratings (FBGs), where the FBGs set the wavelength references and the FPSF can be tuned by changing its injection current to select a particular wavelength from those set by the FBGs. Because of the nonlinearity in the FPSF, optical negative feedback can be built up in the laser to suppress relaxation oscillations caused by wavelength switching. With this method, a wavelength switching time of less than 25 μs has been achieved experimentally. © 2000 American Institute of Physics. View full abstract»

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  • Efficient red electroluminescence from devices having multilayers of a europium complex

    Page(s): 4271 - 4273
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    In order to get red electroluminescence from a europium (Eu) complex with high efficiency, a hole-injection layer was inserted between the Eu-complex layer and an indium–tin–oxide electrode, and a hole-blocking layer was inserted between the Eu-complex and electron-transporting layers. To further improve the efficiency, devices having multiple-stacked Eu-complex (2.5 nm)/hole blocking (2.5 nm) units were fabricated. By stacking six units, the maximal luminance and emission efficiency of the red emission were increased to more than twice that from a device with a single Eu-complex layer. © 2000 American Institute of Physics. View full abstract»

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  • Fast-scanning shear-force microscopy using a high-frequency dithering probe

    Page(s): 4274 - 4276
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    We have demonstrated high-speed scanning shear-force microscopy using a fiber tip attached to quartz crystal vibrating at 2.0 MHz resonance frequency. With a high-frequency dithering probe, we have obtained clear images at the scanning speed of 1.2 mm/s and it takes only 0.5 s to image the surface area of 55 μm2 for 64×64 pixels without any compromise of spatial lateral resolution. This speed is more than five times faster than that obtained by other topographic imaging methods and can be further improved to realize real-time shear-force probe microscopy. © 2000 American Institute of Physics. View full abstract»

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  • Grazing-incidence diffraction strain analysis of a laterally-modulated multiquantum well system produced by focused-ion-beam implantation

    Page(s): 4277 - 4279
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    Focused Ga+ ion beam implantation was used to define a laterally periodic modulation of the electronic band gap in a GaAs/Ga0.97In0.03As/Al0.2Ga0.8As/GaAs [001] multiquantum well structure. The samples were investigated as-implanted and after a rapid thermal annealing (60 s at 650 and 800 °C) by means of x-ray grazing-incidence diffraction. The method provides a separate inspection of the induced strain and the damage profiles as a function of depth below the sample surface. For samples with an ion dose of 5×1013cm-2, we found a nearly uniform lateral strain amplitude of about 2×10-3 up to the maximum information depth of about 500 nm. It was accompanied by the appearance of structural defects. Rapid thermal annealing at 650 °C has reduced the strain amplitude by a factor of five as well as the density of volume defects. The maximum strain amplitude were found in a depth of about 100 nm. After rapid thermal annealing at 800 °C, the strain has disappeared. © 2000 American Institute of Physics. View full abstract»

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  • Preferential amorphization and defect annihilation at nanocavities in silicon during ion irradiation

    Page(s): 4280 - 4282
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    Si containing a band of nanocavities has been irradiated with Si+ ions at elevated temperatures to study interactions of irradiation-induced defects with open volume defects. For irradiation at 100 °C, nanocavities are shown to be preferential nucleation sites for amorphization. It is proposed that this behavior occurs to minimize the local free energy, whereby less dense amorphous Si is free to expand into the cavity open volume. Furthermore, for irradiation at 300 °C, cavities are very efficient sinks for Si interstitials during irradiation, leaving a region denuded of interstitial-based clusters surrounding each nanocavity. © 2000 American Institute of Physics. View full abstract»

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  • Temperature dependence of the surface plasmon resonance of Au/SiO2 nanocomposite films

    Page(s): 4283 - 4285
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    The optical response of Au/SiO2 nanocomposite films at temperatures spanning the transition to the liquid state has been measured. The change in the optical constants of gold from those corresponding to the crystalline material to those of the liquid occurs gradually and at temperatures below the bulk melting point. The similarity of the temperature-induced changes in the Au interband absorption edge to that observed with decreasing particle size suggests that a gradual transition to the liquid phase also occurs in small particles. © 2000 American Institute of Physics. View full abstract»

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  • Atom-scale optical determination of Si-oxide layer thickness during layer-by-layer oxidation: Theoretical study

    Page(s): 4286 - 4288
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    Optical anisotropy spectra of SiO2/Si(001) interfaces were theoretically investigated based on the sp3s* tight-binding calculation. In the spectra, we found three types of optical transitions originating from the E1 and E2 transitions of bulk Si, the interface Si–Si bonds, and the dangling-bond states at the interface. It was shown that the sign of these transitions oscillates during the layer-by-layer oxidation, which indicates that by counting the oscillation one can determine the layer thickness of oxidized Si layers in an atomic scale. © 2000 American Institute of Physics. View full abstract»

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  • Preparation and single molecule structure of electroactive polysilane end-grafted on a crystalline silicon surface

    Page(s): 4289 - 4291
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    Electrically active polysilanes of poly(methylphenylsilane) (PMPS) and poly[bis(p-n-butylphenyl)silane] (PBPS), which are, respectively, known as a good hole transporting material and a near-ultraviolet electroluminescent material, are end-grafted directly on a crystalline silicon surface. The single polysilane molecules are clearly distinguished one from the other on the surface by means of atomic force microscopy observations. End-grafted single molecules of PMPS are observed as dots while end-grafted PBPS appear as worms extending for more than 100 nm on the crystalline silicon surface. © 2000 American Institute of Physics. View full abstract»

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  • Material properties of bulk InGaAs and InAlAs/InGaAs heterostructures grown on (111)B and (111)B misoriented by 1° towards 〈211〉 InP substrates

    Page(s): 4292 - 4294
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    High-quality bulk InGaAs and InAlAs/InGaAs heterostructures have been grown on InP substrates with different orientation using molecular-beam epitaxy. It was found that the electrical and structural properties were strongly dependent on growth temperature and substrate misorientation. The electrical and structural properties of the film were investigated by high-resolution x-ray diffraction, Nomarski microscope, and Hall measurements. Full-width at half-maximum of 380 arcsec for bulk InGaAs on (111)B and 70 arcsec on (111)B misoriented by 1° towards <211> InP substrates were measured by x-ray diffraction. The room temperature electron Hall mobility for bulk InGaAs of 5100 cm2/V s, doped with Si concentration at the mid-1017/cm3, and two-dimensional electron gas mobility of 11 200 cm2/V s, and sheet density of 3.0×1012/cm2 for InAlAs/InGaAs heterostructures on (111)B misoriented by 1° towards <211> InP substrates were achieved. © 2000 American Institute of Physics. View full abstract»

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  • Scanning thermal microscopy of carbon nanotubes using batch-fabricated probes

    Page(s): 4295 - 4297
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    We have designed and batch-fabricated thin-film thermocouple cantilever probes for scanning thermal microscopy (SThM). Here, we report the use of these probes for imaging the phonon temperature distribution of electrically heated carbon-nanotube (CN) circuits. The SThM images reveal possible heat dissipation mechanisms in CN circuits. The experiments also demonstrate that heat flow through the tip-sample nanoscale junction under ambient conditions is dominated by conduction through a liquid film bridging the two surfaces. With the spatial resolution limited by tip radius to about 50 nm, SThM now offers the promising prospects of studying electron-phonon interactions and phonon transport in low dimensional nanostructures. © 2000 American Institute of Physics. View full abstract»

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  • Atomic force microscopy study of plastic deformation and interfacial sliding in Al thin film: Si substrate systems due to thermal cycling

    Page(s): 4298 - 4300
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    A method is proposed to measure the plastic deformation of thin metallic films on Si substrates induced by thermal cycling. The cross-sectional profiles of pattern-grown square Al films with a thickness of ∼250 nm and a size of ∼6 μm×6 μm were measured before and after thermal cycling by employing an atomic force microscope. With the assistance of statistical analysis, the change in the size and shape of the thin films were determined. Based on theoretical considerations, the thermal cycling deformation of thin films is attributed to creep and plasticity effects, accommodated by diffusion-controlled interfacial sliding. © 2000 American Institute of Physics. View full abstract»

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  • Optical characterization of relaxation processes in nitrogen-doped ZnSe layers

    Page(s): 4301 - 4303
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    Linear polarization of the nitrogen acceptor bound exciton I1N luminescence, which reflects the anisotropic strain relief of the ZnSe lattice, is exploited to monitor two independent relaxation processes in nitrogen-doped ZnSe films. An inhomogeneous vertical strain profile is identified by a maximum in-plane polarization when 800 nm of the sample surface are removed. After exposure of nitrogen-doped ZnSe films to intense light, an isotropic strain relief is observed. The I1N peak position is shifted to lower energies, whereas the anisotropic polarization remains constant. © 2000 American Institute of Physics. View full abstract»

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  • Growth of nanocrystalline diamond films by biased enhanced microwave plasma chemical vapor deposition: A different regime of growth

    Page(s): 4304 - 4306
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    Hard and smooth nanocrystalline diamond films are grown on mirror polished silicon substrates by biased enhanced growth (BEG) in microwave plasma chemical vapor deposition at lower temperatures. Hardness of the films varies with deposition condition and can be defined by the relative concentration of nanocrystalline diamond in the films, as measured by the Raman intensity ratio of the feature near 1150 cm-1 to the intensity of graphitic G band. The hardness of the films approaches the hardness of diamond at conditions giving maximum concentration of nanocrystalline diamond while still having a low amount of stress (1–2 GPa). A different regime of growth appears to exist in the films deposited by the BEG process that may, however, be a combination of surface and subsurface processes. © 2000 American Institute of Physics. View full abstract»

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  • Interaction of a Ti-capped Co thin film with Si3N4

    Page(s): 4307 - 4309
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    The reaction of a Ti (8 nm) capped Co film (15 nm) with a Si3N4 layer (150 nm) is studied after rapid thermal annealing at 660 °C for 120 s in a N2 ambient. X-ray photoelectron spectroscopy, transmission electron microscopy, electron energy-loss spectroscopy, and Auger electron spectroscopy are used to study the reaction products. Combining the results of the different analyses yields a layer stack consisting of: TiO2/TiO/unreacted Co/(Ti,Co)2N/Co2Si, followed by amorphous Si3N4. The reaction mechanisms are discussed. Conclusions concerning the risk for degradation of nitride spacers in advanced devices are drawn. © 2000 American Institute of Physics. View full abstract»

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  • Phase separation in metalorganic vapor-phase epitaxy AlxGa(1-x)N films deposited on 6H–SiC

    Page(s): 4310 - 4312
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    The microstructure of AlxGa(1-x)N films deposited on 6H–SiC substrates by metalorganic vapor-phase epitaxy is studied by transmission electron microscopy and energy-dispersive x-ray analysis. It is shown that in the first step of the growth (three-dimensional), the deposit is constituted of a thin Al-rich AlGaN wetting layer covering the substrate surmounted by pure GaN islands. In a second step, a homogeneous AlxGa(1-x)N film, with nominal Al concentration, is deposited and smoothing is observed. The results of the high-resolution transmission electron microscopy about the strain state of the different parts of the deposit indicate that the driving force for the phase separation phenomena is the decrease of the interfacial energy due to the low mismatch between Al-rich AlGaN and 6H–SiC (1% for pure AlN). © 2000 American Institute of Physics. View full abstract»

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  • Fabrication of highly ordered porous structures

    Page(s): 4313 - 4315
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    We describe a simple method for the fabrication of highly ordered porous structures. That is, utilizing capillary forces, ultrafine particles are directly used to assemble themselves in the voids of template while the template is being assembled. The highly ordered porous structures with larger area and uniform orientation can be produced after removing the template. The majority of the single domains with uniform orientation prepared can reach 0.1 mm2 in area. Scanning electron microscope images and transmission spectrum of these samples have confirmed the success of this simple method. © 2000 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