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Applied Physics Letters

Issue 2 • Date Jan 1997

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Displaying Results 1 - 25 of 48
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Optical properties of the epitaxial Pb1-xLaxTiO3 thin films grown by metalorganic chemical vapor deposition

    Page(s): 143 - 145
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    The dispersion of the refractive indices for the epitaxial Pb1-xLaxTiO3 thin films with x=0.28 and 0.23 grown on the MgO (100) and Al2O3 (0001) substrates, respectively, has been investigated. The refractive indices in the wavelength range of 435–1523 nm were measured by a prism coupling method. At a wavelength range of 632.8 nm, the refractive index of a PLT film grown with (100) orientation was determined to be 2.609. The transmission spectrum was used as an additional measurement for the dispersion of the refractive index and showed a good agreement with the prism coupling measurements. The dispersion of refractive index fits well to a single-term Sellmeier relation. © 1997 American Institute of Physics. View full abstract»

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  • A model for optically quenched lasers

    Page(s): 146 - 148
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    A model is presented for optically controlling the gain of a semiconductor laser by introducing photons from a second coherent source into the side of the laser. We find that the threshold current of the laser increases in direct proportion to the overlap between the two modes and the photon density from the coherent source. An easy-to-use, closed-form expression relates the optical power emitted from the laser to the bias and threshold currents. © 1997 American Institute of Physics. View full abstract»

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  • High continuous wave power, 0.8 μm-band, Al-free active-region diode lasers

    Page(s): 149 - 151
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    Efficient, high-power, Al-free active-region diode lasers emitting at λ=0.83 μm have been grown by low-pressure metalorganic chemical vapor deposition. Threshold-current densities as low as 220 A/cm2, maximum continuous wave (cw) power of 4.6 W, and a maximum cw wallplug efficiency of 45% are achieved from 1 mm long, uncoated devices with In0.5(Ga0.5Al0.5)0.5P cladding layers. Further improvement is obtained by replacing the p-In0.5(Ga0.5Al0.5)0.5P cladding layer with thin (0.1 μm) electron-blocking layers of Al0.85Ga0.15As and In0.5(Ga0.5Al0.5)0.5P, and a p-In0.5(Ga0.9Al0.1)0.5P cladding layer. Such devices provide a record-high T0 of 160 K and reach catastrophic optical mirror damage (COMD) at a record-high cw power of 4.7 W (both facets). The corresponding COMD power-density level (8.7 MW/cm2)is ∼2 times the COMD power-density level for uncoated, 0.81-μm-emitting AlGaAs-active devices. Therefore, 0.81-μm-emitting, Al-free a- - ctive-region devices are expected to operate reliably at roughly twice the power of AlGaAs-active region devices. © 1997 American Institute of Physics. View full abstract»

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  • Enhanced electron injection in organic electroluminescence devices using an Al/LiF electrode

    Page(s): 152 - 154
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    A bilayer is used as an electrode for organic electroluminescent devices. The bilayer consists of an ultrathin LiF layer adjacent to an electron-transporting layer and an aluminum outerlayer. Devices with the bilayer electrode showed enhanced electron injection and high electroluminescence efficiency as compared with a Mg0.9Ag0.1 cathode. Similar effects were observed when replacing MgO for LiF. The improvements are attributed to band bending of the organic layer in contact with the dielectrics. © 1997 American Institute of Physics. View full abstract»

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  • Frequency doubling in gallium-lanthanum-sulphide optical glass with microcrystals

    Page(s): 155 - 157
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    Second harmonic generation in gallium-lanthanum-sulphide (Ga:La:S) and germanium sulphide + Ga:La:S glasses is investigated. It is shown that microcrystals of Ga:La:S and α phase of gallium-sulphide (α-Ga2S3), whose presence in the glass matrix is revealed by energy dispersive spectroscopy and x-ray diffraction analysis, are responsible for the frequency doubling process. © 1997 American Institute of Physics. View full abstract»

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  • Ultrafast excitonic room temperature nonlinearity in neutron irradiated quantum wells

    Page(s): 158 - 160
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    Sharp room temperature exciton features and complete recovery of the excitonic absorption with 21 ps time constant are demonstrated in neutron irradiated (Ga,Al)As/GaAs multiple quantum wells. Carrier lifetime reduction is consistent with the EL2 midgap defect which is efficiently generated by fast neutrons. Influence of gamma rays accompanying neutron irradiation is discussed. Neutron irradiation provides a straightforward way to control carrier lifetime in semiconductor heterostructures with minor deterioration of their excitonic properties. © 1997 American Institute of Physics. View full abstract»

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  • High-speed resonant-cavity separate absorption and multiplication avalanche photodiodes with 130 GHz gain-bandwidth product

    Page(s): 161 - 163
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    Previously it has been shown that resonant-cavity, separate absorption and multiplication (SAM) avalanche photodiodes (APDs) exhibit high peak external quantum efficiency (∼75%), low dark current, low bias voltage (≪15 V), and low multiplication noise (0.2≪k≪0.3). We describe the frequency response of resonant-cavity AlGaAs/GaAs/InGaAs SAM APDs. A unity-gain bandwidth of 23 GHz and a high gain-bandwidth product of 130 GHz have been achieved. © 1997 American Institute of Physics. View full abstract»

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  • Amorphous KNbO3 thin films with ferroelectriclike properties

    Page(s): 164 - 166
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    Amorphous KNbO3 films are prepared by a low-cost sol–gel method. These films show a smooth surface morphology and have good waveguiding properties. Ferroelecticlike hysteresis loops are observed in these amorphous KNbO3 films with a remanant polarization of about C/cm2. After corona poling, a stable effective second harmonic generation coefficient of 0.523 pm/V is achieved. © 1997 American Institute of Physics. View full abstract»

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  • Observation of a new class of crystal sonoluminescence at piezoelectric crystal surface

    Page(s): 167 - 169
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    Ultrasonic vibrations of a single-piezoelectric crystal of LiNbO3 and CdS can excite luminescence of gas near the crystal surface. Light excitation starts at ultrasonic intensity above a certain threshold. This threshold lies in the range 3–10 W/cm2 and corresponds to the unpinning of dislocations and beginning of their reversible motion in the piezoelectric crystal. The effects constitute a new class of acousto-optic and dislocation phenomena having the main feature of energy transformation from ultrasound in solid to luminescence of gas at normal atmospheric pressure. The unpinning of dislocations is shown to be critical for sonoluminescence excitation. © 1997 American Institute of Physics. View full abstract»

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  • Fast commutation of high current in double wire array Z-pinch loads

    Page(s): 170 - 172
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    A dynamic model of multi-MA current commutation in a double wire array Z-pinch load is proposed and studied theoretically. Initially, the load is configured as nested concentric wire arrays, with the current driven through the outer array and imploding it. Once the outer array or the annular plasma shell formed from it approaches the inner array, the imploded plasma might penetrate through the gaps between the wires, but the azimuthal magnetic field is trapped due to both the high conductivity of the inner wires and the inductive coupling between the two parts of the array, causing a rapid switching of the total current to the inner part of the array. © 1997 American Institute of Physics. View full abstract»

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  • Activation energy for diamond growth from the carbon–hydrogen gas system at low substrate temperatures

    Page(s): 173 - 175
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    The growth kinetics of diamond films deposited at low substrate temperatures (600–400 °C) from the carbon–hydrogen gas system have been studied. When the substrate temperature alone was varied, independently of all other process parameters in the microwave plasma reactor, an activation energy in the order of 7 kcal/mol was observed. This value did not change with different carbon concentrations in hydrogen. It is supposed that growth kinetics in this temperature range are controlled by a single chemical reaction, probably the abstraction of surface bonded hydrogen by gas phase atomic hydrogen. © 1997 American Institute of Physics. View full abstract»

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  • Damage evolution and surface defect segregation in low-energy ion-implanted silicon

    Page(s): 176 - 178
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    We have combined computer simulations and atomic-resolution tunneling microscopy to investigate the kinetics of defect migration during annealing of ion implanted Si(111)-7×7. Using atomically-clean and flat surfaces as sinks for bulk point defects introduced by the irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials, and we demonstrate that the distinct kinetics of each type of bulk point defect govern their surface segregation kinetics. A combination of simulation tools provides a detailed description of the processes that underlie the observed temperature-dependence of defect migration. © 1997 American Institute of Physics. View full abstract»

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  • Low pressure synthesis of bulk, polycrystalline gallium nitride

    Page(s): 179 - 181
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    Thick films of polycrystalline GaN were grown at low pressures by direct reaction of atomic nitrogen with liquid Ga without the presence of a substrate. The crystals were confirmed to be wurtzitic GaN by x-ray diffraction, transmission electron microscopy, Raman spectroscopy, and elemental analysis. Photoluminescence spectra showed near band edge peaks and broad yellow band emission at both 298 and 10 K. The results show that atomic nitrogen is an attractive alternative to high pressure N2 for the saturation of liquid gallium with nitrogen for the synthesis of bulk GaN. © 1997 American Institute of Physics. View full abstract»

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  • Effect of energetic particles on island formation in sputter deposition of Pt on Pt(111)

    Page(s): 182 - 184
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    During ion beam sputter deposition besides the deposited atoms, which reach the substrate with kinetic energies in the 10 eV range, a certain amount of energetic particles also hit the substrate. These particles which have been reflected or sputtered at the target represent only a small fraction of the atoms reaching the substrate, but have energies of the order of the sputtering beam. The influence of these particles on the island formation of Pt films on a Pt(111) surface has been examined by variation of the deposition geometry, the primary ion energy, and the substrate temperature. It is demonstrated that the main effect is a dramatic increase in island density. The experimental results are in quantitative agreement with the results of a newly developed computer code. © 1997 American Institute of Physics. View full abstract»

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  • Direct identification of diamond growth precursor using almost pure CH4 or C2H2 near growth surface

    Page(s): 185 - 187
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    Diamond growth was studied by injecting thermally decomposed Cl atoms into CH4/H2 or C2H2/H2. Owing to the extremely short residence time (25 μs) and low gas temperature (≪1000 °C) in the decomposition system, the gas reaction is insignificant. Therefore, the carbon species near the substrate surface can be nearly identical to the input carbon source. With 0.3% CH4 being the input carbon source, CH4 remained the dominant carbon species near the surface (only 2.5% C2H2 was formed), and an almost continuous diamond film was deposited after 2 h growth. Raman spectra confirmed the formation of diamond. With 0.15% C2H2 being the input carbon source, C2H2 remained the dominant carbon species near the surface (10% CH4 was formed), but only a few very small particles were deposited. Therefore, we conclude that CH3 radicals seem the only diamond growth precursor under the Cl-rich conditions, whereas C2H2 is not efficient to grow diamond. © 1997 American Institute of Physics. View full abstract»

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  • 29Si nuclear magnetic resonance of luminescent silicon

    Page(s): 188 - 190
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    Nuclear magnetic resonance of 29Si is used to study structural properties of porous silicon and siloxene. Evidence for changes in the chemical shift of porous silicon due to quantum confinement could not be observed. A hydride phase exhibiting a chemical shift of -75 ppm versus tetramethyl silane (TMS) is found in both porous silicon and siloxene. In as-prepared Wöhler siloxene, a chemical shift of -83 ppm versus TMS is assigned to threefold coordinated Si atoms forming a planar polysilane. © 1997 American Institute of Physics. View full abstract»

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  • Porous silicon structure studied by nuclear magnetic resonance

    Page(s): 191 - 193
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    We present a nuclear-magnetic-resonance (NMR) study of the structure of porous silicon. Cross-polarization–magic-angle-spinning 29Si NMR shows that the silicon crystalline structure is preserved in porous silicon and that there are three protonated silicon species at the surface, which are tentatively identified as belonging to different faces. The occurrence of different environments for the surface protons is supported by the heterogeneous 1H NMR line. HF and SiF62- species were detected by 19F NMR in the electrolyte left in the pores. © 1997 American Institute of Physics. View full abstract»

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  • Spreading of a void along a singular surface during electromigration: A failure mode

    Page(s): 194 - 196
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    Previous treatments of void shape evolution during electromigration have been restricted to nonsingular void surfaces. We consider the lateral spreading of a void when its leading surface is a singular facet. The facet may nucleate at the leading surface of a void migrating within one grain or may develop when a singular surface is exposed by impingement of the void at a (transverse) grain boundary. Advance of the facet requires a source of steps that we assume to be absent; void spreading results. A stationary void shape is possible when a dimensionless parameter is less than a critical value (estimated), whereas above this value the void spreads indefinitely. © 1997 American Institute of Physics. View full abstract»

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  • Theory of composite BxCyNz nanotube heterojunctions

    Page(s): 197 - 199
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    The stability and electronic properties of composite BxCyNznanotube heterojunctions were studied using both ab initio and semi-empirical approaches. C/BN and BC2N/BN superlattices or isolated junctions were investigated as specific examples of the wide variety of electronic devices that can be realized using such nanotubes. The characteristics of these junctions are predicted to be largely independent of the radius, helicity, multiplicity, or degree of perfection of the constituting nanotubes. © 1997 American Institute of Physics. View full abstract»

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  • Synthesis of diamondlike films by an electrochemical method at atmospheric pressure and low temperature

    Page(s): 200 - 202
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    A technique of carbon film synthesis based on an electrochemical process was developed. A solution of acetylene in liquid ammonia was employed as the electrolyte. Films were deposited at the metallic anode. Two types of films were produced. Films of type I are transparent and fragile, whereas those of type II are black and plastic. The films were investigated by the electron diffraction method and Raman spectroscopy. The electron diffraction data for type I films demonstrate the films’ high degree of crystallinity. Values of lattice plane spacings agree with data on cubic diamond modifications. The Raman spectrum of type I films shows a line at 1334 cm-1 (full width at half-maximum equal to 15 cm-1), inherent in that of diamond and an essentially amorphous carbon component. Spectra of the type II films do not feature the Raman peak of diamond. © 1997 American Institute of Physics. View full abstract»

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  • SiH bond-bending modes of the HSi-(OSi)3 group in amorphous hydrogenated silicon dioxide

    Page(s): 203 - 205
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    The cluster-Bethe-lattice method is used to investigate SiH bond-bending modes of the HSi-(OSi)3 group in a-SiO2:H alloys. When the HSi-(OSi)3 group has C3 symmetry, the SiH bond-bending mode has a double degenerate frequency at 876 cm-1 as found by experiments. But when the HSi-(OSi)3 group does not have C3 symmetry, the nonsymmetrical coupling between SiH and its local bonding environment may cause the SiH bond-bending mode to split off and have an additional feature in the spectrum that is not revealed by experiments. © 1997 American Institute of Physics. View full abstract»

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  • Ferroelectric field effect in ultrathin SrRuO3 films

    Page(s): 206 - 208
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    We report the observation of a ferroelectric field effect in the conducting oxide SrRuO3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Upon reversing the polarization of the ferroelectric Pb(Zr0.52Ti0.48)O3 layer, we measured a 9% change in the resistance of a nominally 30 Å SrRuO3 film at room temperature. This change was nonvolatile for a period of several days. Conductivity measurements taken between 4.2 and 300 K are consistent with n-type conduction throughout this temperature range. Hall effect measurements also yield n-type conduction, with n≈2×1022 electrons/cm3, and furthermore allow us to understand quantitatively the magnitude of the observed resistivity change. © 1997 American Institute of Physics. View full abstract»

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  • Achievement of zero temperature coefficient of resistance with RuOx thin film resistors

    Page(s): 209 - 211
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    The temperature coefficient of resistance (TCR) for an as-deposited RuO2.2 thin film resistor changes from -131.6 to 1007.95 ppm/°C after the annealing at 600 °C for 30 min. Typically, a near zero TCR about 0±0.12 ppm/°C can be obtained after annealing at 300 °C for 30 min in an Ar ambient. The changes of TCR from negative to positive is attributed to the grain growth of RuOx films from fine grain (30–40 Å) to a larger one (500–800 Å) during the annealing process. Rutherford backscattering spectroscopy and in situ x-ray photoemission spectroscopy show that the ratio of O/Ru in the RuOx film decreases from 2.2 to 2.0, due to the out diffusion of oxygen during the annealing process, which is independent of the changes in TCR. © 1997 American Institute of Physics. View full abstract»

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  • Electronic structure of delta-doped quantum well as a function of temperature

    Page(s): 212 - 213
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    We report on the electronic structure of a delta-doped quantum well of B in Si as a function of temperature from 0 K to room temperature. The calculation is carried out self-consistently in the framework of a Hartree approximation. The energy levels and the occupation number of the discrete states is reported. We conclude that the temperature is not an important factor below 60 K. If temperature is greater than 80 K the level positions are shifted but the changes in carrier concentration are not significant. We give a possible qualitative explanation of the widths of the intersubband absorption peaks. © 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