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Applied Physics Letters

Issue 15 • Date Oct 1998

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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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    Freely Available from IEEE
  • A laser pumped ultranarrow bandwidth optical filter

    Page(s): 2069 - 2071
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    An atomic optical filter with ultranarrow bandwidth has been developed. This filter has two operating channels generated from two hyperfine energy levels in the Cs ground state with a 9.2 GHz frequency separation. By employing a cw Ti:sapphire laser to alternatively pump the polarized Cs atoms to a selected hyperfine energy level, each of the two channels can be, respectively, used as emitting and receiving terminals. Compared to a normal Faraday anomalous dispersion optical filter, there is an increase in transmittance and a decrease in total equivalent bandwidth in this filter. © 1998 American Institute of Physics. View full abstract»

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  • 1.1 W continuous-wave, narrow spectral width (≪1 Å) emission from broad-stripe, distributed-feedback diode lasers (λ=0.893 μm)

    Page(s): 2072 - 2074
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    By etching a distributed-feedback grating directly into the Al-free optical confinement region of a 100 μm stripe InGaAs/InGaP/GaAs diode laser, 1.1 W cw front-facet output power has been obtained at 0.893 μm with a spectral full width at half maximum of 0.9 Å. These devices have 1 mm long cavities and shallow gratings with a coupling coefficient, κ∼7 cm-1. The combination of long device length and low grating coupling results in both efficient operation as well as a longitudinally uniform field profile. As a result, all excited lateral modes oscillate at the same longitudinal cavity resonance to high power levels. Using shallow gratings etched in an InGaP upper confinement layer permits the growth of a high-quality cladding layer over the grating surface yielding excellent device performance. Facet-coated (5%/95%) devices demonstrate external differential quantum efficiencies of 51% and peak wallplug efficiencies of 32% at 1.1 W cw output power. © 1998 American Institute of Physics. View full abstract»

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  • Electron–plasmon relaxation in quantum wells with inverted subband occupation

    Page(s): 2075 - 2077
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    We have considered the electron-plasmon interaction and intersubband resonance screening in a quantum well with inverted subband occupation. We show that in such a system the intersubband plasmon emission leads to an efficient deexcitation of the nonequilibrium initial state and raises the occupation of states at the lower-subband bottom. Downshift and resonance narrowing of the intersubband optical emission spectra are obtained and shown to be influenced by the process of intersubband plasmon excitation. © 1998 American Institute of Physics. View full abstract»

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  • An approach for recording and readout beyond the diffraction limit with an Sb thin film

    Page(s): 2078 - 2080
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    A technique for recording and retrieving small marks beyond the optical diffraction limit was proposed. The basic experiment with this technique was also carried out at a constant linear velocity of 2.0 m/s, rotating a disk with a multi-layered structure of Sb and GeSbTe, which were separated by a thin film of SiN. By use of the optically nonlinear property of the Sb thin film, carrier to noise ratio of more than 10 dB was obtained from recorded marks of 90 nm, using an optical system with the laser wavelength of 686 nm and a numerical aperture of 0.6. © 1998 American Institute of Physics. View full abstract»

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  • Photochemical color switching behavior of induced cholesteric liquid crystals for polarizer free liquid crystalline devices

    Page(s): 2081 - 2083
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    Photoresponsive cholesteric (Ch) liquid crystals (LCs) showing reflection of visible light were prepared by the addition of chiral molecules and azobenzene molecules in a host nematic LC. The Ch–isotropic phase transition temperature and wavelength of reflected light were controlled by varying the enantiomer excess. Switching between reflection and transparent states was achieved by ultraviolet irradiation. In addition, the switching time was also explored by means of time-resolved measurements. © 1998 American Institute of Physics. View full abstract»

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  • Large frequency range of negligible transmission in one-dimensional photonic quantum well structures

    Page(s): 2084 - 2086
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    We show that it is possible to enlarge the range of low transmission in one-dimensional photonic crystals by using photonic quantum well structures. If a defect is introduced in the photonic quantum well structures, defect modes with a very high quality factor may appear. The transmission of the defect mode is due to the coupling between the eigenmodes of the defect and those at the band edges of the constituent photonic crystals. © 1998 American Institute of Physics. View full abstract»

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  • Theoretical performance of wurtzite and zincblende InGaN/GaN quantum well lasers

    Page(s): 2087 - 2089
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    The theoretical gain, radiative and Auger recombination rates, and threshold current densities of ideal wurtzite (WZ) and zincblende (ZB) 20 Å In0.2Ga0.8N/70 Å GaN multiple quantum well laser diodes are compared. We obtain upper bounds on device performance, which are based on reliable calculations for both band structure and recombination dependent features and show (1) that the performance of present devices having the ZB and WZ structures are within 20% of each other in InGaN/GaN, and (2) that present performance of the best currently available devices is only a factor of 3–4 below the theoretical limit. Radiative recombination is far more important than Auger processes. The calculations are performed using a superlattice K∙p formalism and density functional theory within the local-density approximation. The latter yields bulk zone-center energies, wave functions, and directly calculated momentum matrix elements. © 1998 American Institute of Physics. View full abstract»

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  • Increasing throughput of a near-field optical fiber probe over 1000 times by the use of a triple-tapered structure

    Page(s): 2090 - 2092
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    We fabricated a new probe with extremely high throughput introducing a triple-tapered structure to reduce the loss in a tapered core, to focus the light, and to excite effectively the HE11 mode. A focused ion beam and selective chemical etching were used for fabrication. Over a 1000-fold increase in the throughput of the triple-tapered probe with the aperture diameter D≪100 nm was realized in comparison with the conventional single-tapered probe. Furthermore, due to the third taper with a small cone angle, the localized optical near field on the triple-tapered apertured probe with D=60 nm has been confirmed. © 1998 American Institute of Physics. View full abstract»

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  • Photothermal displacement measurement of transient melting and surface deformation during pulsed laser heating

    Page(s): 2093 - 2095
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    A photothermal displacement method has been developed to probe the pulsed laser-induced transient melting and surface deformation of Ni–P hard disk substrates. A probing He–Ne laser beam is aligned collinearly with the near-infrared nanosecond pulsed heating beam. The He–Ne beam spot is scanned on the microfeatures formed on the sample surface by the pulsed laser heating. The deflection signals show the variation of the feature shape resulting from different pulse energies of the heating laser beam. The transient deflection signal also reveals that the time scale of the surface motion is in the range of several hundred nanoseconds. © 1998 American Institute of Physics. View full abstract»

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  • Adjustable x-ray phase plate and phase modulator

    Page(s): 2096 - 2097
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    Diffractive birefringence of a crystal in the x-ray region is shown to be adjustable by high-frequency ultrasonic waves (USWs). An increase in diffractive birefringence can be used for fine tuned transformation of linearly polarized synchrotron radiation into circular polarized x rays by a quarter-wave plate. For a stationary USW, x-ray polarization changes with the ultrasound frequency, providing the design parameters for an x-ray phase modulator. © 1998 American Institute of Physics. View full abstract»

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  • Self-starting passively mode-locked tunable Cr4+: yttrium–aluminum–garnet laser with a single prism for dispersion compensation

    Page(s): 2098 - 2100
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    A self-starting passive mode-locked Cr4+:yttrium–aluminum–garnet laser that uses a saturable Bragg reflector with a single prism for dispersion compensation instead of the standard prism pair is demonstrated. We observed over 230 mW average output power with a pulse width of 400 fs at center wavelengths shorter than 1.5 μm. The tuning range for cw laser operation extends from 1345 to 1557 nm. The mode-locked pulses are self-starting and tunable from 1420 to 1510 nm by means of lossless prism tuning without aperture. © 1998 American Institute of Physics. View full abstract»

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  • High performance interminiband quantum cascade lasers with graded superlattices

    Page(s): 2101 - 2103
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    A new class of quantum cascade lasers is presented. They are based on interminiband transitions in chirped superlattices (SL), where the applied electric field is compensated by the quasielectric field resulting from a gradually varying SL period length and average composition. In this way “flat” minibands can be obtained without the need for dopants. At room temperature record high peak (0.5 W) and average (14 mW) powers are obtained for a laser of 7.6 μm wavelength, with the lowest threshold current densities (5 kA/cm2) reported so far for quantum cascade lasers. The maximum temperature for continuous wave operation is an unprecedented 160 K. © 1998 American Institute of Physics. View full abstract»

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  • ZnSe-based blue-green lasers with a short-period superlattice waveguide

    Page(s): 2104 - 2106
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    We report the successful application of alternatively strained short-period superlattices for the waveguide region of optically pumped and injection room-temperature ZnSe-based lasers operating within the 470–523 nm spectral range. The design of optically pumped ZnMgSSe/ZnSSe/ZnCdSe lasers provides extremely low threshold power densities due to the enhanced electronic and optical confinement. Room-temperature BeMgZnSe/ZnCdSe injection lasers with threshold current density of about 750 A/cm2 and characteristic temperature as high as 366 K are demonstrated. The peculiarities of carrier transport across the short-period superlattices are explained by a thermally activated mechanism. © 1998 American Institute of Physics. View full abstract»

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  • Frequency dependence of radar cross section for arbitrarily shaped scatterers

    Page(s): 2107 - 2109
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    This letter introduces a method to perform frequency dependence of radar cross section for either simple or complex scatters in terms of model measurement. To do so, the expressions of physical scale factor based on the electromagnetic similarity are suggested by means of dimensional analysis, geometric and physical optics approximation. Using the results of model measurement within a small range of frequency, the frequency dependence of an arbitrarily shaped scatterer can be obtained. For the purpose of verification and comparison, some measurements of simple and complex shapes have been carried out. The calculated results agree well with the experimental data on the prototype itself. © 1998 American Institute of Physics. View full abstract»

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  • Effect of cooling rate on the precipitation of quasicrystals from the Zr–Cu–Al–Ni–Ti amorphous alloy

    Page(s): 2110 - 2112
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    The Zr57Cu20Al10Ni8Ti5 alloy solidifies into an amorphous phase upon rapid quenching or casting at low cooling rates. However, the amorphous alloys formed at different cooling rates exhibit different crystallization behavior. The slowly cooled bulk amorphous alloys prepared by copper mold casting reveal a first crystallization peak at 715 K upon heating at 0.33 K/s and crystallize via precipitation of an icosahedral quasicrystalline phase in the first crystallization step. The rapidly quenched ribbons exhibit a first crystallization peak at 720 K and crystallize by simultaneous precipitation of the quasicrystalline phase together with Zr2Cu and Zr2Ni intermetallic phases in the first stage of crystallization. It is supposed that the undercooled Zr57Cu20Al10Ni8Ti5 melt has a tendency to develop an icosahedral short-range order, which is favored by low cooling rate. As a result, the bulk amorphous alloy has a short-range order close to a quasicrystalline phase. In contrast, the structure of the ribbon is more similar to that of the melt at high temperature and the atoms are oriented more randomly. © 1998 American Institute of Physics. View full abstract»

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  • Electron field emission from phase pure nanotube films grown in a methane/hydrogen plasma

    Page(s): 2113 - 2115
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    Phase pure nanotube films were grown on silicon substrates by a microwave plasma under conditions which normally are used for the growth of chemical vapor deposited diamond films. However, instead of using any pretreatment leading to diamond nucleation we deposited metal clusters on the silicon substrate. The resulting films contain only nanotubes and also onion-like structures. However, no other carbon allotropes like graphite or amorphous clustered material could be found. The nanotubes adhere very well to the substrates and do not need any further purification step. Electron field emission was observed at fields above 1.5 V/μm and we observed an emission site density up to 104/cm2 at 3 V/μm. Alternatively, we have grown nanotube films by the hot filament technique, which allows to uniformly cover a two inch wafer. © 1998 American Institute of Physics. View full abstract»

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  • Deposition of (Zn, Mn)2SiO4 for plasma display panels using charged liquid cluster beam

    Page(s): 2116 - 2118
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    Films of manganese doped zinc silicate have been deposited using the charged liquid cluster beam technique. The deposition conditions were found to have a large impact on the morphology and photoluminescence intensity of these films. The photoluminescence intensity was maximized at a manganese content near δ=0.04 in (Zn1-δMnδ)2SiO4. No phases other than zinc silicate were detectable with manganese contents up to δ=0.08. © 1998 American Institute of Physics. View full abstract»

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  • Field emission from aligned high-density graphitic nanofibers

    Page(s): 2119 - 2121
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    Field emission data from aligned graphitic nanofibers have been obtained. The aligned nanofibers are 50–100 nm in diameter and 6–10 μm in length, with a density of 109–1010/cm2. The fibers were grown on polycrystalline nickel substrate by plasma-assisted hot filament chemical vapor deposition using a gas mixture of nitrogen and acetylene. The onset of emission current in microampere level was detected at about 1.8 V/μm with an emission area of 1 mm2. The Fowler–Nordheim model was used to analyze the data obtained. The field emission current required for flat panel display can be easily achieved at 2.5 V/μm. © 1998 American Institute of Physics. View full abstract»

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  • Interlayer exchange in (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As semiconducting ferromagnet/nonmagnet/ferromagnet trilayer structures

    Page(s): 2122 - 2124
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    Magnetic properties of all-semiconductor (Ga,Mn)As/(Al,Ga)As/(Ga,Mn)As trilayer structures are studied. The interactions between the two ferromagnetic (Ga,Mn)As layers are investigated by magnetotransport measurements in a number of samples with different GaAs thickness or with different Al content in the intermediary nonmagnetic (Al,Ga)As layer. The results indicate that carriers present in the nonmagnetic layer mediate the coupling between the two ferromagnetic layers. © 1998 American Institute of Physics. View full abstract»

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  • High-quality germanium photodiodes integrated on silicon substrates using optimized relaxed graded buffers

    Page(s): 2125 - 2127
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    The integration of Ge photodetectors on silicon substrates is advantageous for various Si-based optoelectronics applications. We have fabricated integrated Ge photodiodes on a graded optimized relaxed SiGe buffer on Si. The dark current in the Ge mesa diodes, Js=0.15 mA/cm2, is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measurements indicate that the detectors are capable of operating at high frequencies (2.35 GHz). The photodiodes exhibit an external quantum efficiency of η=12.6% at λ=1.3 μm laser excitation in the photodiodes. The improvement in Ge materials quality and photodiode performance is derived from an optimized relaxed buffer process that includes a chemical mechanical polishing step within the dislocated epitaxial structure. © 1998 American Institute of Physics. View full abstract»

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  • Giant acoustoelectric effect in GaAs/LiNbO3 hybrids

    Page(s): 2128 - 2130
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    The acoustoelectric effect in a hybrid of a strong piezoelectric material and a semiconductor layer containing a two-dimensional electron system is investigated. Caused by the very strong interaction between a surface acoustic wave and the mobile carriers in the semiconductor, the acoustoelectric effect is very large as compared to other materials, which might be interesting for device applications. Moreover, the tunability of the sheet conductivity of the electron system enables us to tune the magnitude of the acoustoelectric effect over a wide range. We present experimental results for a GaAs/LiNbO3 layered hybrid system at room temperature and describe our experimental findings quantitatively using a recently developed model calculation. © 1998 American Institute of Physics. View full abstract»

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  • Neutron reflectometry, x-ray reflectometry, and spectroscopic ellipsometry characterization of thin SiO2 on Si

    Page(s): 2131 - 2133
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    We present here a comparison of neutron reflectometry, x-ray reflectometry, and spectroscopic ellipsometry on a thin oxide film. These three probes each independently determine the structure of the film as a function of depth. We find an excellent agreement between the three techniques for measurements of thicknesses and interfacial roughnesses for both the SiO2 and surface contamination layers found in the sample. Realistic models based on interface parameters measured herein indicate that as the SiO2 layers decrease to sizes projected for future generations of electronic devices, both spectroscopic ellipsometry and neutron reflectometry can easily measure SiO2 films to 2 nm thick or less. View full abstract»

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  • Silicon single electron memory cell

    Page(s): 2134 - 2136
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    A compact single-electron memory cell has been fabricated in silicon using a process that is compatible with complementary metal–oxide–semiconductor circuit fabrication. The device is based on the Coulomb blockade effect observed in highly doped silicon nanowires. The circuit shows clear memory operation with a ≫100 mV gap between “0” and “1” levels when tested at a temperature of 4.2 K. The response of the circuit to write and erase pulse sequences is also presented. © 1998 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