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Applied Physics Letters

Issue 23 • Date Dec 2002

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Displaying Results 1 - 25 of 58
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Emission through one of two metal electrodes of an organic light-emitting diode via surface-plasmon cross coupling

    Page(s): 4315 - 4317
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    We report strong surface emission from an organic light-emitting diode in which the luminescent material resides between two nearly opaque metal electrodes. Experimental and theoretical analyses indicate that cross coupling between surface plasmons on opposite sides of the metal cathode layer enables the transmission of electroluminescence through the practically opaque metal. The application of this physical process has the potential to expand the range of device structures possible for organic light-emitting diodes and other electroluminescent devices. © 2002 American Institute of Physics. View full abstract»

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  • Influence of quasibound states on the carrier capture in quantum dots

    Page(s): 4318 - 4320
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    The interaction of carriers in quantum-dot quasibound states with longitudinal optical phonons is investigated. For a level separation between the quasibound state and a discrete quantum-dot state in the vicinity of the phonon energy, a strong electron–phonon coupling occurs. A mixed electron–phonon mode—polaron—is formed. The finite lifetime of the phonons is shown to give rise to another type of carrier capture into quantum dots. © 2002 American Institute of Physics. View full abstract»

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  • High-average-power, high-duty-cycle (λ∼6 μm) quantum cascade lasers

    Page(s): 4321 - 4323
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    High-power quantum cascade lasers emitting at λ=6.1 μm are demonstrated. Accurate control of growth parameters and strain balancing results in a near-perfect lattice match, which leads to excellent material quality. Excellent peak power for uncoated lasers, up to 1.5 W per facet for a 21 μm emitter width, is obtained at 300 K for 30 period structures. The threshold current density at 300 K is only 2.4 kA/cm2. From 300 to 425 K, the laser exhibits a characteristic temperature T0 of 167 K. Next, Y2O3/Ti/Au mirror coatings were deposited on 1.5 mm cavities and mounted epilayer down. These lasers show an average output power of up to 225 mW at 17% duty cycle, and still show 8 mW average power at 45% duty cycle. © 2002 American Institute of Physics. View full abstract»

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  • Promising ceramic laser material: Highly transparent Nd3+:Lu2O3 ceramic

    Page(s): 4324 - 4326
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    A solid-state laser material based on highly transparent cubic Nd3+:Lu2O3 ceramic was developed using nanocrystalline technology and a nonpress vacuum sintering method. Spectroscopic properties of this ceramic laser material were investigated. At room temperature under single-laser diode pumping, efficient continuous wave laser oscillation was demonstrated at two wavelengths of the 4F3/24I11/2 channel. The potential application of such a laser material was also discussed. © 2002 American Institute of Physics. View full abstract»

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  • Effects of hole depth on enhanced light transmission through subwavelength hole arrays

    Page(s): 4327 - 4329
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    We studied the role of the aperture depth on the enhanced transmission of light through subwavelength holes in free-standing Ag films by measuring the transmission properties of square arrays of cylindrical holes. Two regimes are found which give insight into the transmission mechanism and will be of importance for device applications. © 2002 American Institute of Physics. View full abstract»

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  • 1.3 μm continuous-wave GaInNAs/GaAs distributed feedback laser diodes

    Page(s): 4330 - 4331
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    GaInNAs/GaAs single-quantum-well lasers were grown by solid-source molecular-beam epitaxy using a radio-frequency source for nitrogen activation. Distributed feedback has been realized by a metal grating arranged laterally to the laser ridge. Single-mode emission between 1271 and 1304 nm could be demonstrated. Room-temperature continuous-wave operation has been obtained with a threshold current of 28 mA, an external efficiency of 0.16 W/A per facet, and a side-mode suppression ratio of 44 dB at 90 mA drive current. © 2002 American Institute of Physics. View full abstract»

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  • Ultrafast ac Stark effect switching of the active photonic band gap from Bragg-periodic semiconductor quantum wells

    Page(s): 4332 - 4334
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    The ultrafast suppression and recovery of an active photonic band-gap structure constructed from the periodic complex susceptibility of quantum well excitons is demonstrated. For resonant pumping, the corresponding superradiant mode is slaved by the external field, and the structure forms a mirror that can be switched on and off at a bandwidth limited only by the width of the pump-pulse and the photonic band gap. Absorption and creation of free carriers is suppressed by the accelerated decay of the superradiant mode of the light-coupled quantum wells. © 2002 American Institute of Physics. View full abstract»

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  • Terahertz pulse generation in an organic crystal by optical rectification and resonant excitation of molecular charge transfer

    Page(s): 4335 - 4337
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    Organic molecular crystals that are extremely efficient at terahertz-pulse generation are in- vestigated. Terahertz pulses produced by optical rectification at 800 nm in (-)2-(α-methylbenzyl-amino)-5-nitropyridine have an order of magnitude higher power than those generated in the commonly used inorganic crystal ZnTe. The organic molecular crystals were also found to generate terahertz pulses when excited on resonance at 400 nm. This may pave the way for studying ultrafast charge-transport dynamics in three dimensions. © 2002 American Institute of Physics. View full abstract»

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  • Measurement of acoustic wavelength in optical fiber via acousto-optic interaction

    Page(s): 4338 - 4340
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    The wavelength of the lowest-order propagating flexural acoustic wave in a single-mode fiber is measured by creating an acoustic cavity with variable length. The amplitude of the acoustic standing wave is probed by means of acousto-optic coupling between the core and cladding modes in the optical fiber. By monitoring the periodic modulation of the core–mode transmittance versus the cavity length, the acoustic wavelength can be measured to a high degree of accuracy. Excellent agreement (≪1%) between the measured values and theoretical calculations for three types of 125 μm diameter single-mode fibers is obtained in the frequency range from 1.2 to 3.5 MHz. © 2002 American Institute of Physics. View full abstract»

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  • Low-pressure, high-current hollow cathode with a ferroelectric plasma source

    Page(s): 4341 - 4343
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    We report the parameters of a hollow cathode with a ferroelectric plasma source incorporated in it. It was found that this source allows the ignition and sustaining of a high-current discharge (≤1.4 kA, ≤2×10-5s) at N2 gas pressure of (3–5)×10-4Torr. It was shown that ∼85% of the discharge current is emitted by the ferroelectric sample. The plasma in the cathode acquires a positive potential (≤50 eV) with respect to the anode and the plasma density and temperature are ≤8×1012cm-3 and ≤18 eV, respectively. Generation of an electron beam (0.3–1.6 kA, 300 ns) was demonstrated under an accelerating pulse ≤300 kV. © 2002 American Institute of Physics. View full abstract»

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  • Dephasing in modulation-doped quantum structures probed by THz time-domain spectroscopy

    Page(s): 4344 - 4346
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    The dephasing of intersubband transitions in semiconductor heterostructures was investigated by time-resolved THz spectroscopy. Single quantum structures show dephasing rates, which are nearly identical to scattering rates obtained by conventional Hall measurements and allow insight into the dephasing dynamics. In multiple quantum wells, inhomogeneous broadening of the density of states is the main dephasing mechanism. © 2002 American Institute of Physics. View full abstract»

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  • Pressure effect on crystallization kinetics in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass

    Page(s): 4347 - 4349
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    Crystallization kinetics of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass in the supercooled liquid region have been investigated by performing in situ high-temperature and high-pressure x-ray diffraction measurements using synchrotron radiation. A pressure–time–temperature–transformation diagram, describing the onset of crystallization as a function of time during isothermal annealing under pressure, is presented. Different pressure dependences of crystallization kinetics in the temperature range for the glass have been observed and further be explained by a model of competing processes of the thermodynamic potential barrier of nucleation and the diffusion activation energy under pressure. © 2002 American Institute of Physics. View full abstract»

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  • Electroluminescence of mixed organic dyes via resonant energy transfer from polysilane molecules

    Page(s): 4350 - 4352
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    We have observed an electroluminescence (EL) of perylene (blue), coumarin 6 (green), 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran and/or zinc tetra-phenylporphyrin (red) via an efficient intermolecular energy transfer from poly (m-hexoxyphenyl)phenylsilane (PHPPS). The EL device has a single layer which was prepared simply by spin coating the mixed solution of PHPPS and energy-matched dye molecules. The EL spectrum can easily be tailored by intermixing appropriate dye molecules in the solution. We demonstrated a white EL from the mixture of PHPPS and these four dyes. The combination of a conducting polysilane and energy-matched dye molecules enabled us to open a field of Si-based EL devices through wet processes. © 2002 American Institute of Physics. View full abstract»

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  • Spatial and temporal luminescence dynamics in an InxGa1-xN single quantum well probed by near-field optical microscopy

    Page(s): 4353 - 4355
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    Spatial distribution of photoluminescence (PL) with spectral, spatial, and/or time resolution has been assessed in an InxGa1-xN single-quantum-well (SQW) structure using scanning near-field optical microscope (SNOM) under illumination-collection mode at 18 K. The near-field PL images revealed the variation of both intensity and peak energy in PL spectra according to the probing location with the scale less than a few hundredths of a nanometer. PL linewidth, the value of which was about 60 meV in macroscopic PL, was as small as 11.6 meV if the aperture size was reduced to 30 nm. Clear spatial correlation was observed between PL intensity and peak wavelength, where the regions of strong PL intensity correspond to those of long wavelength. Time-resolved SNOM–PL study showed the critical evidence that supports the model of diffusion of carriers to potential minima. © 2002 American Institute of Physics. View full abstract»

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  • Crystal structure of κ-In2Se3

    Page(s): 4356 - 4358
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    Structural properties of single-phase films of κ-In2Se3 and γ-In2Se3 were investigated. Both films were polycrystalline but their microstructures differed considerably. The a-lattice parameter of κ-In2Se3 has been measured. A comparison between these two materials indicates that κ-In2Se3 has a significantly larger unit cell (Δc=2.5±0.2% and Δa=13.5±0.5%) and a structure more similar to the α-phase of In2Se3. © 2002 American Institute of Physics. View full abstract»

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  • Engineering kinetic barriers in copper metallization

    Page(s): 4359 - 4361
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    In metallization processes of integrated circuits, it is desirable to deposit the metal lines (aluminum or copper) fast and at low temperatures. However, the lines (films) usually consist of undesirable columns and voids, because of the absence of sufficient diffusion—a direct result of large kinetic barriers. Following the proposal and realization of the three-dimensional Ehrlich-Schwoebel (3D ES) barrier, we present here a method to engineer this kinetic barrier so as to improve quality of deposited copper films. We deposit copper films by magnetron sputtering, characterize the film structure and texture by using the scanning electron microscope and the x-ray diffraction, respectively. Taking indium as surfactant during copper deposition, we have achieved much better density and bottom coverage of copper filled trenches. The characterizations show that the improvement is the result of the 3D ES barrier reduction caused by indium addition. Engineering the 3D ES barrier therefore leads to improved film quality. © 2002 American Institute of Physics. View full abstract»

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  • Effect of nitrogen at SiO2/Si interface on reliability issues—negative-bias-temperature instability and Fowler–Nordheim-stress degradation

    Page(s): 4362 - 4364
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    Degradation process of a metal–oxide–semiconductor (MOS) structure with NO-nitrided SiO2 under negative-bias-temperature (NBT) and Fowler–Nordheim (FN) stresses has been investigated. The FN stress immunity improves with increasing nitrogen concentration at the SiO2/Si interface, while the incorporation of excess nitrogen (more than 3 at. %) at the SiO2/Si interface accelerates NBT instability (NBTI). This stronger immunity of NO-nitrided SiO2 under FN stress is due to the stronger Si–N bonds formed by NO nitridation at the interface. Without hydrogen annealing to form Si–H bonds, the MOS capacitors do not show NBTI. This indicates that the Si–N bonds are not broken under NBT stress and the main cause of the NBTI is the breaking of the Si–H bonds. The NO nitridation decreases the number of Si–H bonds and thus suppresses NBTI. However, nitrogen provides hole-trap centers. Hydrogen at the interface is dissociated and bonds to the hole-trapping nitrogen, so interface traps are left behind. An excess amount of nitrogen thus accelerates NBTI. © 2002 American Institute of Physics. View full abstract»

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  • Size effect on intragranular elastic constants in thin tungsten films

    Page(s): 4365 - 4367
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    The size effect on the elastic constants of nanocrystalline tungsten has been investigated in the case of W/Cu multilayers with two modulation wavelengths (3.1 and 24.0 nm). Tungsten Young’s modulus and Poisson’s ratio have been measured thanks to a technique coupling x-ray diffraction with in situ tensile testing. It is demonstrated that the in-grain thin film elastic constants are highly microstructure—sensitive: in the “3.1 nm” multilayer, tungsten Poisson’s ratio is larger than the bulk one while it is smaller in the “24.0 nm” multilayer; a softening of tungsten Young’s modulus is evidenced in the case of the specimen with the smallest period. © 2002 American Institute of Physics. View full abstract»

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  • On the nature of radiative recombination in GaAsN

    Page(s): 4368 - 4370
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    Radiative recombination at low temperatures in GaAsN is often associated with localized excitons. In this short note, we report results from high-resolution time-resolved photoluminescence spectroscopy that indicate that excitons, localized or otherwise, cannot be involved in the recombination process of this alloy system. The risetime of the photoluminescence signal is more than two orders of magnitude shorter than that expected, and found from excitonic recombination in other III–V materials, such as GaAs. We suggest that the radiative recombination in GaAsN takes place between localized electrons and delocalized holes. © 2002 American Institute of Physics. View full abstract»

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  • Structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass during crystallization

    Page(s): 4371 - 4373
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    The structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass (BMG) upon crystallization are investigated by the ultrasonic method, x-ray diffraction, density measurement, and differential scanning calorimetry. The elastic constants and Debye temperature of the BMG are obtained as a function of annealing temperature. Anomalous changes in ultrasonic velocities, elastic constants, and density are observed between 600–750 K, corresponding to the formation of metastable phases as an intermediate product in the crystallization process. The changes in acoustic velocities, elastic constants, density, and Debye temperature of the BMG relative to its fully crystallized state are much smaller, compared with those of other known BMGs, the differences being attributed to the microstructural feature of the BMG. © 2002 American Institute of Physics. View full abstract»

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  • High-efficiency SiO2:Ce3+ glass scintillators

    Page(s): 4374 - 4376
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    We present the effect of a rapid thermal treatment (RTT) at high temperature (1800 °C) on the radio-luminescence properties of Ce-doped SiO2 glasses prepared by the sol–gel method and previously densified at 1050 °C. Cerium concentrations ranging from 0.05 up to 1 mol % were considered. We found that, for all concentrations, the RTT induces a strong increase of the Ce3+ radio-luminescence efficiency; the x-ray-induced luminescence intensity of the SiO2:0.1% Ce is about twice that of Bi3Ge4O12. The decay time of the scintillation response, evaluated as ≈50 ns, is not affected by RTT. Infrared absorption measurements indicate that the luminescence increase cannot be related to significant release of OH groups during RTT. The conversion of Ce4+ ions into Ce3+ ions can also be ruled out since an increase of about 20% of the intensity of the 4.8 eV optical absorption band related to Ce4+ was observed after RTT. The occurrence of dissolution of rare-earth aggregates is suggested. © 2002 American Institute of Physics. View full abstract»

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  • Biaxial strain-modified valence and conduction band offsets of zinc-blende GaN, GaP, GaAs, InN, InP, and InAs, and optical bowing of strained epitaxial InGaN alloys

    Page(s): 4377 - 4379
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    Using density-functional calculations, we obtain the (001) biaxial strain dependence of the valence and conduction band energies of GaN, GaP, GaAs, InN, InP, and InAs. The results are fit to a convenient-to-use polynomial and the fits provided in tabular form. Using the calculated biaxial deformation potentials in large supercell empirical pseudopotential calculations, we demonstrate that epitaxial strain reduces the InGaN alloy bowing coefficient compared to relaxed bulk alloys. © 2002 American Institute of Physics. View full abstract»

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  • Size effects on generation-recombination noise

    Page(s): 4380 - 4382
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    We carry out an analytical theory of generation-recombination noise for a two-level resistor model which goes beyond those presently available by including the effects of both space charge fluctuations and diffusion current. Finite size effects are found responsible for the saturation of the low frequency current spectral density at high enough applied voltages. The saturation behavior is controlled essentially by the correlations coming from the long range Coulomb interaction. It is suggested that the saturation of the current fluctuations for high voltage bias constitutes a general feature of generation-recombination noise. © 2002 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