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Applied Physics Letters

Issue 21 • Date Nov 1997

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Displaying Results 1 - 25 of 50
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Low pressure organic vapor phase deposition of small molecular weight organic light emitting device structures

    Page(s): 3033 - 3035
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    A new technique for the deposition of amorphous organic thin films, low pressure organic vapor phase deposition (LP-OVPD), was used to fabricate organic light emitting devices (OLEDs) consisting of a film of aluminum tris-(8 hydroxyquinoline) (Alq3) grown on the surface of a film of N-diphenyl-N,N-bis(3-methylphenyl)1-1biphenyl-4-4diamine. The resulting heterojunction OLED was found to have a performance similar to conventional, small molecular weight OLEDs grown using thermal evaporation in vacuum. The LP-OVPD grown device has an external quantum efficiency of 0.40±0.05% and a turn-on voltage of approximately 6 V. The rapid throughput demonstrated with LP-OVPD has the potential to facilitate low cost mass production of conventional small molecule based OLEDs, and its use of low vacuum in a horizontal reactor lends itself to roll-to-roll deposition of organic films for many photonic device applications. © 1997 American Institute of Physics. View full abstract»

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  • Enhancement of nonlinear optical response due to cavity-induced double resonance in a semiconductor ultrathin film

    Page(s): 3036 - 3038
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    A mechanism for a large enhancement of nonlinear response due to microcavity effect is theoretically proposed for excitons coupled strongly with radiation field. For an appropriate choice of microcavity parameters, the energy of a coupled mode of cavity and exciton coincides with the transition energy between exciton and biexciton states. This scheme leads to a remarkable enhancement of a degenerate pump-probe signal due to the simultaneous enhancement of the internal field and nonlinear susceptibility. © 1997 American Institute of Physics. View full abstract»

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  • Bistable operation of coupled in-plane and oxide-confined vertical-cavity laser 1×N routing switches

    Page(s): 3039 - 3041
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    We report on the observation of two-mode intensity bistability in intracavity-coupled in-plane lasers and oxide-confined vertical-cavity surface emitting lasers (VCSELs) operating under room-temperature CW conditions. © 1997 American Institute of Physics. View full abstract»

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  • Long-term reliability of Al-free InGaAsP/GaAs (λ=808 nm) lasers at high-power high-temperature operation

    Page(s): 3042 - 3044
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    We report the long-term reliability measurement on uncoated Al-free InGaAsP/GaAs (λ=808 nm) lasers at high-power and high-temperature operation. No degradation in laser performance has been observed for over 30 000 h of lifetime testing in any of randomly selected several 100-μm-wide uncoated lasers operated at 60 °C with 1 W continuous wave output power. This is the first and the most conclusive evidence ever reported that directly shows the high long-term reliability of uncoated Al-free lasers. © 1997 American Institute of Physics. View full abstract»

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  • Performance of corrugated quantum well infrared photodetectors

    Page(s): 3045 - 3047
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    Corrugated quantum well infrared photodetectors (C-QWIPs) utilize total internal reflection to couple normal incident light into the detectors. In this work, we performed a systematic study on C-QWIPs with cutoff wavelength λc ranging from 5 to 17.3 μm and device areas ranging from 50×50 μm2 to 500×500 μm2. We found that the coupling efficiency of the C-QWIPs is, indeed, independent of both the detection wavelength and the pixel size, as expected. Compared to devices with a standard 45° edge coupling, the C-QWIP increases the background photocurrent to a dark current ratio by a factor between 2.4 and 4.4, thereby increasing the background limited temperature by 3–5 K. At the same time, the detectivity D* is also increased by a factor around 2.4. For λc=9.4 μm, the peak detectivity Dp* and the blackbody detectivity Dbb* at 78 K are measured to be

    4.5×1010cm 
     Hz
    /W
    and
    4.5×109cm
     Hz
    /W,
    respectively. © 1997 American Institute of Physics. View full abstract»

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  • Second harmonic generation in a domain-inverted MgO-doped LiNbO3 waveguide by using a polarization axis inclined substrate

    Page(s): 3048 - 3050
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    We demonstrate quasiphase matched second harmonic generation by use of annealed proton-exchanged 87° Z-cut MgO 5 mol % doped LiNbO3 (MgO:LN) waveguides supporting a TE-mode guided wave. Formation of a domain inversion was achieved by applying electric fields in 3° Y-cut and 87° Z-cut MgO:LN. In 3° Y-cut and 87° Z-cut MgO:LN substrates, a polarization axis inclines at an angle θ equal to 3° to the surface. The domain inversion was formed in a direction parallel to the polarization axis like needles stuck into the substrate. The depth of the domain inversion was 2.5 μm with a period of 4.75 μm. The depth was about 2.5 times deeper than that in X- and Y-cut substrate at an angle θ equal to 0°. By forming a waveguide on the domain-inverted substrate, a blue light of wavelength 475 nm, and a power of 37 mW has been obtained and a normalized second harmonic conversion efficiency was 300%/W cm2 with interaction length of 10 mm, using a tunable external cavity laser diode as a fundamental wave source. © 1997 American Institute of Physics. View full abstract»

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  • Comparison of photorefractive damage effects in LiNbO3, LiTaO3, and Ba1-xSrxTiyNb2-yO6 optical waveguides at 488 nm wavelength

    Page(s): 3051 - 3053
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    Photorefractive-induced damage effects at 488 nm wavelength in LiNbO3, LiTaO3, and Ba1-xSrxTiyNb2-yO6 (BSTN) optical waveguides are compared for the extraordinary mode of polarization. The damage effects are strongest in LiNbO3 and weakest in BSTN. At an input power density of 3000 W/cm2, the output power from passive channel waveguide in LiNbO3 is more than 12 dB lower than in BSTN. Optically induced index changes measured using a Fabry–Perot interferometric method show a nonlinear behavior with increasing input intensity for all these materials. For incident power densities greater than 200 W/cm2 on the waveguides, the optically induced index-change damage increases at a rate of 2.8×10-3cm2/μW in LiNbO3, 4.9×10-4cm2/μW in LiTaO3, and 3.1×10-4cm2/μW in BSTN. © 1997 American Institute of Physics. View full abstract»

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  • Observing lateral temperature and refractive index profiles in an optically pumped midinfrared laser through temporally and spatially resolved spectra

    Page(s): 3054 - 3056
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    We show how temporally and spatially resolved lasing spectra may be interpreted to obtain quantitative information on the lattice temperature and refractive index distribution in an optically pumped GaInAsSb/AlGaAsSb quantum well 1.8 μm midwave-infrared laser. We present this technique as a method for evaluating and comparing high power laser structures in terms of optical and thermal efficiency. We also suggest how this method might provide insight into the particulars of filamentation and heat transport in both electrically and optically pumped structures. © 1997 American Institute of Physics. View full abstract»

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  • Extremely low excitation threshold, superradiant, molecular aggregate lasing system

    Page(s): 3057 - 3059
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    An extremely low threshold for lasing from a specially formulated system involving self-assembled, aggregated molecules enables the system to function as a mirrorless laser. Superradiant energy states created in coherently coupled aggregated molecules emit photons that stimulate emission from other spatially distributed superradiant states. This study focuses on a cyanine dye (specifically, 1,1-3,3-tetraethyl-5,5,6,6-tetrachlorobenzimidazolocarbocyanine iodide) adsorbed onto silica colloid on which the dye aggregates, forming excitonic states involving coherent domains in which a finite number of molecules act cooperatively in the process of emitting photons. It is found that lasing from such a system is induced at a threshold of ca. 39 pJ/pulse, which corresponds to a factor of 3×10+4 times smaller than the lowest lasing threshold reported in the literature. © 1997 American Institute of Physics. View full abstract»

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  • Preferential Co–Si bonding at the Co/SiGe(100) interface

    Page(s): 3060 - 3062
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    The initial stages of the reaction of Co with Si0.79Ge0.21(100) were studied in situ with extended x-ray absorption fine structure spectroscopy and reflection high energy electron diffraction. The Si:Ge ratio in the first coordination shell of Co in sub-monolayer Co films was found to increase with film thickness and annealing temperature, indicating preferential formation of Co–Si bonds. The impact of the observed preference for Co–Si bonding on the morphology of epitaxial CoSi2/Si1-xGex heterostructures is discussed. © 1997 American Institute of Physics.   View full abstract»

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  • The effect of surface nucleation on the evolution of crystalline microstructure during solid phase crystallization of amorphous Si films on SiO2

    Page(s): 3063 - 3065
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    The effect of surface nucleation on the evolution of crystalline microstructure during the solid phase crystallization (SPC) of an amorphous Si (a-Si) film, deposited by low pressure chemical vapor deposition (LPCVD) on SiO2, has been investigated. The surface nucleation phenomenon was observed by suppressing the interface (a-Si/SiO2) nucleation by the incorporation of oxygen atoms during the initial deposition period of a-Si. It was found that the surface-nucleated polycrystalline Si (poly-Si) had equiaxial grains with the size of about 3–5 μm, while interface-nucleated one had elliptical grains with the size of about 0.3–1 μm. © 1997 American Institute of Physics. View full abstract»

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  • Theory of ripple topography inhibition in depth profiling with sample rocking

    Page(s): 3066 - 3068
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    A theory is developed which explains how sample rocking during ion beam sputtering erosion can inhibit ripple formation, observed with monodirectional ion incidence, on radiation amorphisable materials. The model assumes curvature dependent sputtering yield and random ion arrival and sputtering as roughening processes and radiation mediated viscous flow and ballistically driven effective surface diffusion as smoothing processes. © 1997 American Institute of Physics. View full abstract»

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  • Evidence of heteroepitaxial growth of copper on beta-tantalum

    Page(s): 3069 - 3071
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    Crystallographic orientations between thin-sputtered Cu film and β-Ta adhesion layer have been studied using high resolution electron microscopy and electron diffraction. Tetragonal β-Ta deposited on SiO2 has a strong texture with its closest packed plane (002) parallel to the film surface. On (002) β-Ta, the growth of (111) Cu is preferred. Even though more than 100 β-Ta grains are found under a single Cu grain, the Ta grains under a Cu grain have long range in-plane texture with [330] direction aligned parallel to the [220] direction of Cu. This orientational coincidence is explained by the heteroepitaxial relationship between the hexagonal close-packed atomic array in Cu (111) plane and the pseudohexagonal configuration of β-Ta atoms in (002) plane with a misfit strain of 7.6%. © 1997 American Institute of Physics.   View full abstract»

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  • Nucleation and growth of chemical beam epitaxy gallium nitride thin films

    Page(s): 3072 - 3074
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    Gallium nitride films have been grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia (NH3) precursors. Prior to the CBE epi-GaN layer growth, electron cyclotron resonance plasma-assisted metal-organic molecular beam epitaxy was utilized to deposit a nucleation layer at lower temperatures. The crystallinity of CBE-grown GaN films was found to be strongly growth–temperature dependent. The degree of crystallinity was correlated with the surface carbon composition as measured in situ by mass spectroscopy of recoiled ions. The optimum growth–temperature range for CBE GaN growth was found to be between 800 and 825 °C. Within this narrow window, thin films with streaky two-dimensional reflection high-energy electron diffraction patterns and good photoluminescence properties were obtained. The surface rms roughness, as measured by atomic force microscopy, was as low as 40 Å/1 μm2 for the highest quality thin films; lattice-resolved images supported the deposition of crystalline GaN revealing hexagonal structures with the spacing anticipated for GaN. © 1997 American Institute of Physics. View full abstract»

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  • (YBa2Cu3O7-δ,Au)/SrTiO3/LaAlO3 thin film conductor/ferroelectric coupled microstripline phase shifters for phased array applications

    Page(s): 3075 - 3077
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    We report on the design, fabrication, and testing of novel YBa2Cu3O7-δ/SrTiO3/LaAlO3 (YBCO/STO/LAO) and Au/SrTiO3/LaAlO3 (Au/STO/LAO) coupled microstrip line phase shifters (CMPS). These CMPS were tested at frequencies within the Ku and K bands (12–20 GHz), at temperatures from 24 to 77 K, and at dc voltages (Vdc) from zero to 350 V. A relative insertion phase shift (ΔΦ) of 390° was measured for an eight-element YBCO/STO/LAO CMPS at Vdc=350 V, 16 GHz, and 40 K. At 77 K, a ΔΦ ∼260° was obtained for the CMPS at the same bias and frequency. Both results correspond to an effective coupling length of 0.33 cm. At both temperatures, the phase shifter exhibits a figure of merit of ∼30°/dB. To our knowledge, these are the best results published so far at these frequencies where miniaturization, insertion loss, and phase delay are key considerations. © 1997 American Institute of Physics. View full abstract»

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  • Indexing the hopper shaped {111} face produced in chemical vapor deposited diamond

    Page(s): 3078 - 3080
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    The hopper shaped {111} face frequently observed in cubo octahedral crystallites of diamond has been analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The diamond was grown via hot filament assisted chemical vapor deposition with a feed gas composition of 1% methane in hydrogen. The SEM images of these crystallites show that the {100} faces are usually flatter than the {111}. The hopper shaped {111} faces have been imaged using the tapping mode of the AFM and the angles between planes and their orientations determined. The planes comprising the hoppered {111} face were found to belong to the {221} and {331} family. The implications of the presence of higher index planes as well as other growth features on the growth mechanisms involved are presented. © 1997 American Institute of Physics. View full abstract»

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  • Investigation of neutralized (NH4)2S solution passivation of GaAs (100) surfaces

    Page(s): 3081 - 3083
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    Synchrotron radiation photoelectron spectroscopy combined with scanning electron microscopy (SEM) and gravimetry has been used to study GaAs (100) surfaces treated with a neutralized (NH4)2S solution. Compared to the conventional basic (NH4)2S solution treatment, a thick Ga sulfide layer and strong Ga–S bond were formed on the GaAs surface after dipping GaAs wafers in a neutralized (NH4)2S solution. Gravimetric data show that the etching rate of GaAs in the neutralized (NH4)2S solution is about 15% slower than that in the conventional (NH4)2S solution. From SEM observation, fewer etching pits with smaller sizes were found on the neutralized (NH4)2S-treated GaAs surface. © 1997 American Institute of Physics. View full abstract»

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  • Optical evaluation of the ionized EL2 fraction in proton (24 GeV) irradiated semi-insulating GaAs

    Page(s): 3084 - 3086
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    Semi-insulating SI GaAs samples from a zone refined crystal were irradiated with high energy protons (24 GeV/c, fluences up to 1.64×1014p/cm2). Optical spectra in transmittance and reflectance were accurately measured in the energy range of 0.6–1.4 eV to determine, through the absorption coefficient, the concentrations of both neutral and ionized EL2 defects as a function of the proton fluence. Both these concentrations have been shown to increase linearly with the proton fluence; this behavior well explains the remarkable decrease of the charge collection efficiency observed in proton irradiated GaAs detectors at doses associated with high luminosity beams at a new particle collider accelerator (e.g., the LHC at the CERN laboratory). © 1997 American Institute of Physics. View full abstract»

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  • Strong Hall voltage modulation in hybrid ferromagnet/semiconductor microstructures

    Page(s): 3087 - 3089
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    We present a new magnetoelectronic device consisting of a μm-scale semiconductor cross junction and a patterned, electrically isolated, ferromagnetic overlayer with in-plane magnetization. The large local magnetic field emanating from the edge of the thin ferromagnetic film has a strong perpendicular magnetic component, B(r), which induces a Hall resistance, RH, in the microjunction. External application of a weak in-plane magnetic field reverses the magnetization of the ferromagnet and with it B(r), thus modulating RH. Our data demonstrate that this strong “local” Hall effect is operative at both cryogenic and room temperatures, and is promising for device applications such as field sensors or integrated nonvolatile memory cells. © 1997 American Institute of Physics. View full abstract»

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  • Microstructure of Al contacts on GaAs

    Page(s): 3090 - 3092
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    The microstructure of Al films deposited on GaAs(100) 2×4 surfaces through chemical vapor deposition from dimethylethylamine alane in the 100–160 °C temperature range exhibits a dominant (111) texture which is not encountered in evaporated films. Such a texture has been associated with enhanced electromigration resistance in related systems. Growth of (111)-oriented grains is observed when the deposition rate is limited by the surface reaction of the impinging precursor molecules, while at higher temperatures (160–400 °C) only the conventional texture is observed. © 1997 American Institute of Physics. View full abstract»

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  • On the spectral strength of the noise source entering the transfer impedance method

    Page(s): 3093 - 3095
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    We show that within the transfer impedance method, the spectral strength of the local noise source originally defined by Van Vliet etal [J. Appl. Phys. 46, 1804 (1975)] should be more generally replaced by the two-point spectral density of current fluctuations. The theoretical arguments are further supported by numerical results for the voltage noise spectrum associated with conduction–current fluctuations in submicron n+nn+ structures. The above two-point spectral strength is, in general, a complex quantity related to fluctuations induced by velocity fluctuations only. © 1997 American Institute of Physics. View full abstract»

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  • Cathodoluminescence study of laser recrystallized CdTe layers

    Page(s): 3096 - 3098
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    CdTe(100)/GaAs(100) and CdTe(111)/CdTe(111) layers grown by metalorganic vapor phase epitaxy (MOVPE) were investigated. The layers were recrystallized to improve their morphology by scanning the surface with a 100 μm diameter spot from an Ar ion laser beam (λ=514.4 nm). Cathodoluminescence spectra from both as-grown and recrystallized CdTe MOVPE layers are used to monitor the effect of the recrystallization procedure. The laser recrystallization results in important changes on the spectral distribution of luminescence. Deep-level bands associated to different defects are shown to be very sensitive to the laser recrystallization procedure. The effect of the different substrates on the defect structure of the layers is also related to the changes observed in the cathodoluminescence spectra. © 1997 American Institute of Physics. View full abstract»

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  • A work-hardening based model of the strain relief in multilayer graded-buffer structures

    Page(s): 3099 - 3101
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    This paper describes the modeling of the dislocation distribution and of the strain relief in linearly and step-graded structures, based on work-hardening considerations. The model considers the energy variation in an InGaAs/GaAs system upon introducing a new dislocation into the interfacial fixed array of misfit dislocations. An analytical expression for the strain relaxation in graded-buffer structures is proposed. Transmission electron microscopy observation confirms the model predictions and reveals that the saturation state of relaxation is reached in the buried layers. © 1997 American Institute of Physics. View full abstract»

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  • Novel features in the strain profile and gate oxide capacitance of through-gate-oxide implanted structures

    Page(s): 3102 - 3104
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    Oxidized silicon samples were implanted with O, Si, or Ar ions. The samples were characterized by x-ray triple crystal diffractometry and metal-oxide-semiconductor admittance spectroscopy to reveal information on the nature of the ion-induced damage. The experimental results on the strain profile, gate oxide capacitance, etc., exhibited novel features. These interesting results suggest ion-damage-induced precipitation of SiO2 particles in silicon and oxidation of the silicon subsurface by the injection of the recoil O atoms from the gate oxide into the silicon subsurface, both at room temperature. © 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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Meet Our Editors

Editor
Nghi Q. Lam
Argonne National Laboratory