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Applied Physics Letters

Issue 19 • Date May 1997

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Improved performance of laterally oxidized GaInP/AlGaInP lasers by thermal annealing

    Page(s): 2493 - 2495
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    The improvement of efficiency and threshold of visible AlGaInP/GaInP laser diodes, which use buried AlAs native oxides for carrier and optical confinement, is described. Annealing of completed laser bars in an inert atmosphere lowers the threshold current and dramatically increases the external differential quantum efficiency. The characteristic temperature of the devices also increases from 74.8 to 125 K, indicating that the electron confinement is greatly enhanced in the annealed lasers, resulting in the observed improved performance. Secondary-ion mass spectrometry measurements reveal a reduction in hydrogen concentration in the laser cladding regions. This suggests that the improved electron confinement can be attributed to increased acceptor activation due to reduced hydrogen passivation. © 1997 American Institute of Physics. View full abstract»

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  • Evanescent-light guiding of atoms through hollow optical fiber for optically controlled atomic deposition

    Page(s): 2496 - 2498
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    This work demonstrates that the technique of guiding atoms through hollow optical fiber escorted by evanescent light is useful as a novel scheme of optical atom deposition. To show the feasibility of fabricating micron-sized structures with nanometric depth on a substrate, we measure the spatial distribution of the guided atom flux with a hot-wire detector. Moreover, precise control of the deposition rate is illustrated with a 1.4-μm-hollow fiber via photoionization spectroscopy. The ratio of the guided atom flux relative to the background transmission is enhanced up to 80-fold with a slightly tilted hollow fiber. © 1997 American Institute of Physics. View full abstract»

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  • Self-trapping of two-dimensional optical beams and light-induced waveguiding in photorefractive InP at telecommunication wavelengths

    Page(s): 2499 - 2501
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    We demonstrated an experimental observation of self-trapping and self-deflection of a two-dimensional optical beam by the photorefractive effect at telecommunication wavelengths under an applied dc field. Self-trapping is effective for an intensity range related to the intensity-temperature resonance known for two-wave mixing in InP:Fe. The photorefractive index change giving rise to the trapping is measured at 10-4, while the photorefractive space-charge field is measured at about 50 kV/cm, ten times higher than the applied field. We show experimentally that this index change creates a waveguide that can be used to guide a second beam at 1.55 μm. © 1997 American Institute of Physics. View full abstract»

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  • Far-infrared propagation in metal wire microstructures

    Page(s): 2502 - 2504
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    Densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of ∼103, relative to an indium foil of equal thickness for far-infrared (k≪80 cm-1) propagating along the wire length. The absorption increases as k0.45±0.07 and is explained by the dynamic Maxwell–Garnett model, which includes eddy current dissipation. The effective surface conductivity is depressed fiftyfold with respect to the bulk. The implications for plasmons in metal wire microstructures and for developing simultaneously transmissive and conductive composites are discussed. © 1997 American Institute of Physics. View full abstract»

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  • Influence of temperature on the optical properties of LiTaO3:Cr

    Page(s): 2505 - 2507
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    Optical absorption, photoluminescence, and luminescence lifetimes of Cr3+ in LiTaO3 were studied. It was found that a relatively sharp absorption band assigned previously to the no-phonon 4A22E transition shifted by 68 cm-1 when temperature decreased from 300 to 5 K. A sharp, four-component emission band recorded at low temperature was assigned on the basis of lifetime measurements to the no-phonon 2E–4A2 transitions of Cr3+ ions in Li+ and Ta5+ sites. Frequencies of these transitions are lower than that of the sharp absorption band at the same temperature implying that the latter band is not the no-phonon 4A22E line but it may be associated with a phonon satellite of the 4T2 state. Strong thermal quenching of broad band luminescence of Cr3+ was observed. © 1997 American Institute of Physics. View full abstract»

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  • Cd1-xMnxTe magneto-optical waveguide integrated on GaAs substrate

    Page(s): 2508 - 2510
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    The refractive indices of diluted magnetic semiconductor Cd1-xMnxTe films on sapphire substrates have been determined by m-line spectroscopy to precision 0.001 at the wavelengths λ=670, 785, and 1150 nm. Using these data, we designed double-layer Cd1-xMnxTe structures on a GaAs substrate, achieving the integration of the magneto-optical waveguide on a semiconductor substrate. Good optical confinement of the waveguide mode was confirmed. © 1997 American Institute of Physics.   View full abstract»

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  • Grating coupling for intersubband emission

    Page(s): 2511 - 2513
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    Grating coupling for surface-emitting intersubband light-emitting diodes (LEDs) and lasers are analyzed with a numerical method. The grating efficiency is calculated as functions of the grating periodicity and filling factor, and the vertical confinement thickness. The coupling loss is related linearly with the grating efficiency, which should be maximized for LEDs to couple out the spontaneous emission, but kept low for lasers to reduce the lasing threshold. © 1997 American Institute of Physics. View full abstract»

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  • Chirp of monolithic colliding pulse mode-locked diode lasers

    Page(s): 2514 - 2516
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    Spectrally resolved streak camera measurements of picosecond pulses emitted by hybridly colliding pulse mode-locked (CPM) laser diodes are presented in this letter. Depending on the modulation frequency both blue-chirped (upchirped) and red-chirped (downchirped) pulses can be observed. The two different regimes and the transition between them are characterized experimentally and the behavior is explained on the basis of our model for the CPM laser dynamics. © 1997 American Institute of Physics. View full abstract»

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  • Second harmonic generation in LaBGeO5:Nd3+

    Page(s): 2517 - 2519
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    The nonlinear properties relevant to second harmonic generation in LaBGeO5:Nd3+ are reported. This work focuses on the infrared region of the spectrum leading to blue-green laser radiation by self-frequency doubling, but covers a wide spectral range useful for other lanthanide Ln3+ rare-earth doping ions. Phase matching conditions, walk-off angle, and thermo-optic tuning sensitivity for second harmonic generation are reported. © 1997 American Institute of Physics. View full abstract»

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  • Polarization switching control in vertical-cavity surface-emitting lasers

    Page(s): 2520 - 2522
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    Orthogonal polarizations within vertical-cavity surface-emitting lasers (VCSEL) lase at slightly different wavelengths. We describe the use of optical feedback to confine polarization variations to reproducible injection currents. An external cavity is used to select specific wavelengths that reflect back into the VCSEL, hence, changing the cavity Q for the different polarization states. With this control, we can change the polarization state of the laser output. © 1997 American Institute of Physics. View full abstract»

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  • Excited state absorption of Cr4+ ion in forsterite

    Page(s): 2523 - 2525
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    Polarized differential absorption spectra of Cr4+-doped forsterite have been studied using a picosecond pump–probe technique. For pump beam and probe beam polarization parallel to the a axis, an excited state absorption in the 450–800 nm region is observed and assigned to the 3T23T1(3P) transition of Cr4+ ion. The lifetime of the 3T1(3F) state is estimated to be less than 15 ps. © 1997 American Institute of Physics. View full abstract»

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  • Observation of triatomic ionic excimers: Emission spectra of Kr2+Cs

    Page(s): 2526 - 2528
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    Triatomic ionic excimers have now been observed. Alkali rare-gas triatomic ionic molecules have been produced by electron beam excitation. Emission spectra centered at ∼159 nm due to Kr2+Cs radiative decay were recorded. Lifetime and binding energy of the lowest excited state are estimated; the ground state is repulsive. Two formation channels for these triatomic ions are proposed and their rate coefficients estimated. © 1997 American Institute of Physics. View full abstract»

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  • Self-oscillating mode for frequency modulation noncontact atomic force microscopy

    Page(s): 2529 - 2531
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    Frequency modulation atomic force microscopy (FM-AFM) has made imaging of surfaces in ultrahigh vacuum with atomic resolution possible. Here, we demonstrate a new approach which simplifies the implementation of FM-AFM considerably and enhances force sensitivity by directly exciting the cantilever with the thermal effects involved in the deflection measurement process. This approach reduces the mechanically oscillating mass by 6 to 8 orders of magnitude as compared to conventional FM-AFM, because external actuators and oscillating cantilever mounts are not needed. Avoiding external actuators allows the use of cantilevers with very high oscillation frequencies, which results in improved force sensitivity. Further, the implementation and operation of this new technique is significantly simplified, because external actuator, bandpass filter, and phase shifter are eliminated. © 1997 American Institute of Physics. View full abstract»

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  • Voltage tunable plasma resonances in induced-base hot-electron transistors

    Page(s): 2532 - 2534
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    The excitation of the standing plasma waves in induced-base hot-electron transistors (IBHETs) and its impact on the IBHET high-frequency operation are considered. It is shown that the plasma waves result in resonant behavior of the IBHET performance at high frequencies. The frequency dependent small-signal transconductance of the IBHET is calculated using an analytical model. The resonant frequencies and the sharpness of the resonant peaks are found as functions of structural parameters and bias voltage. The resonant frequencies can correspond to the terahertz range. The resonant transconductance can significantly exceed the steady-state transconductances of the IBHET. © 1997 American Institute of Physics. View full abstract»

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  • Observation of nanocrystalline diamond in diamondlike carbon films deposited at room temperature in electron cyclotron resonance plasma

    Page(s): 2535 - 2537
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    Diamondlike carbon (DLC) thin films have been prepared by chemical vapor deposition assisted by electron cyclotron resonance plasma at low pressure with radio frequency (rf) power applied to the substrate. The microstructure studies by transmission electron microscopy and electron energy loss spectroscopy show the existence of nanocrystalline diamond grains in DLC films prepared at 0.35 Pa. The cluster’s size varies from 4 to 30 nm with bias voltage (Vb) varying from -200 to -600 V. A phase transition from hexagonal to cubic diamond was also observed with increasing Vb. © 1997 American Institute of Physics. View full abstract»

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  • Spontaneous production of 10-nm Si structures by plasma etching using self-formed masks

    Page(s): 2538 - 2540
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    When a Si substrate is etched in a SF6 electron cyclotron resonance plasma with the sample maintained at ∼-130 °C, reaction products condense preferentially at nucleation sites on the surface, and automatically form etch masks. Si pillars, ∼10 nm in diameter and ∼0.1 μm high, are then formed. When deposited Au clusters (diameter=1.5±0.7 nm) are used as condensation nuclei, fabricated pillars with an average diameter of 9 nm, standard deviation of 1.5 nm, are formed. This remarkably narrow diameter distribution confirms that the phenomenon is useful in nanostructure formation, and that the process is compatible with electron beam lithography. © 1997 American Institute of Physics. View full abstract»

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  • Healing processes in submicron Al interconnects after electromigration failure

    Page(s): 2541 - 2543
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    Investigations of the healing of electromigration-induced open-circuit failed submicron Al(0.5%Cu) interconnects were performed using in situ transmission electron microscopy (TEM). The samples consisted of 4000 Å thick Al (0.5%Cu) patterned over a TEM-transparent window into five runners in parallel, with linewidths 0.2, 0.3, 0.5, 0.8, and 1.0 μm. A novel sample design minimized any Joule heating in the runners. Our approach has allowed us to observe voids form, grow, migrate, fail a runner, and heal all with respect to the detailed local microstructure of the runners. In this letter, we focus on our time-resolved observations of the mechanisms of healing. © 1997 American Institute of Physics. View full abstract»

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  • Complex photothermal refractive index change in host-guest liquid crystals determined with a novel interferometric method

    Page(s): 2544 - 2546
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    A complex photothermal refractive index change in host-guest liquid crystals was determined with a novel interferometric method. The complex refractive index change was proportional to the pump beam intensity. The absolute value of the real part was about ten times as large as that of the imaginary one. The absolute value of the extraordinary refractive index change was about nine times as large as that of the ordinary one. The real part of the extraordinary refractive index change was negative, while that of the ordinary one was positive, and the imaginary part of both the extraordinary and ordinary refractive index change was negative. These results can be explained by the photothermal effects in the host-guest liquid crystals and dyes. © 1997 American Institute of Physics. View full abstract»

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  • Precise determination of the cholesteric pitch of a chiral liquid crystal in a circularly aligned configuration

    Page(s): 2547 - 2549
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    We propose a novel method of measuring the cholesteric pitch of a liquid crystal (LC) in a circularly aligned configuration. The LC cell is made with one homogeneously rubbed surface and one circularly rubbed surface so that it produces a disclination line passing through the singularity created by the circular rubbing. This disclination line is associated with two domains with different twist orientations. In such a geometry, the relationship between the angular deviation of the disclination line and the cholesteric pitch is analytically derived. The concept of a homogeneous-circular configuration is adopted to accurately measure the cholesteric pitch of LC in a broad range from 0.5 to 500 μm. © 1997 American Institute of Physics. View full abstract»

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  • Lateral growth kinetics of α-alumina accompanying the formation of a protective scale on (111) NiAl during oxidation at 1100 °C

    Page(s): 2550 - 2552
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    During the early stages of oxidation of (111) NiAl at 1100 °C, an alumina scale forms and undergoes a series of allotropic phase transformations. In the final stages of phase development, the metastable Θ-alumina transforms to the equilibrium α-alumina phase. Images formed using the photoluminescence from trace Cr3+ impurities in the scale, in conjunction with scanning electron microscopy, indicate that the α-alumina forms by a nucleation and growth process within the Θ-alumina matrix. Lateral impingement of the growing α-alumina islands coincides with the reported drop in oxidation kinetics to those characteristic of long-term oxidation of NiAl. Unlike most interface-controlled transformations, the kinetics of the θ–to–α transformation in the lateral growth are found to be logarithmic. Possible causes of these unusual kinetics are proposed. © 1997 American Institute of Physics. View full abstract»

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  • Effect of substrate miscut on low-temperature homoepitaxial growth on Si(111) mediated by overlayers of Au: Evidence of step flow

    Page(s): 2553 - 2555
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    Observations of homoepitaxial growth on low-angle miscut (∼0.1°) Si(111) substrates through an overlayer of Au, together with earlier results on highly miscut Si(111) surfaces, indicate that growth in this system occurs by step flow. The growth temperatures were between 375 and 500 °C. In the optimum range of Au coverage (0.6–1.0 ML), ion channeling measurements yield at best χmin=5.0%, and cross-sectional transmission electron microscopy reveals stacking faults on (111) planes. Films produced under similar conditions on bare Si(111) substrates are much more defective. On the other hand, the defect density in the present films is higher than that in films grown on substrates with a higher miscut angle. The improvement in film quality resulting from the Au overlayers is attributed to an increase in the diffusion length of the Si adatoms, caused by Au passivation of the Si terraces. It is suggested that Au is more efficient than other overlayers in promoting step flow because Au passivates the Si(111) terraces without passivating the step edges. © 1997 American Institute of Physics. View full abstract»

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  • Effect of adding Ar on the thermal stability of chemical vapor deposited fluorinated silicon oxide using an indirect fluorinating precursor

    Page(s): 2556 - 2558
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    For a low dielectric constant intermetal dielectric application, fluorinated silicon oxide (FxSiOy) films were deposited in an electron cyclotron resonance chemical vapor deposition system, with SiH4, O2, and CF4 as the reaction gases. Since the CF4 is an indirect fluorinating precursor, the fluorinating mechanism resembles that of the oxide etching by a fluorocarbon plasma. Thermal stability of the incorporated fluorine (and hence, the dielectric constant) relies heavily on the deposition parameters and technologies. According to experimental results, adding Ar gas during deposition can improve the thermal stability of incorporated fluorine. Such an improvement is due to the fact that Ar sputtering enhances the removal of weakly bonded silicon fluoride on the as-deposited film surface, thereby elevating the mean bonding strength of fluoride remaining in the oxide. © 1997 American Institute of Physics. View full abstract»

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  • Potential pinch-off effect in inhomogeneous Au/Co/GaAs67P33(100)-Schottky contacts

    Page(s): 2559 - 2561
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    In this work ballistic electron emission microscopy was used to probe on nanometer scale the local Schottky barrier height in metal-semiconductor (MS) contacts with an intentionally inhomogeneously prepared metallization. Schottky barrier maps of heterogeneous Au/Co/ GaAs67P33(100)-Schottky contacts show areas with different barrier heights which can be correlated to different metallizations (Au or Co) at the interface. The local Schottky barrier height of the Co patches depends on their lateral extension. This result can be explained by the theory of the potential pinch-off effect in inhomogeneous MS contacts. © 1997 American Institute of Physics. View full abstract»

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  • Micro-electroreflectance and photoreflectance characterization of the bias dependence of the quantum confined Stark effect in a fabricated 0.98 μm InGaAs/GaAs/InGaP laser

    Page(s): 2562 - 2564
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    Using electro- and photoreflectance with a spatial resolution of ≈10 μm we have evaluated the energy of the fundamental conduction to heavy-hole (1C–1HH) quantum transition of a fabricated 0.98 μm InGaAs/GaAs/InGaP p-i-n quantum well laser structure as a function of bias and position on the laser stripe. From a comparison of the measured forward/reverse bias dependence of the 1C–1HH energy with a theoretical calculation of the quantum confined Stark effect, we have been able to evaluate the built-in electric field and width of the insulating region. © 1997 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