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Applied Physics Letters

Issue 13 • Date Mar 1992

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Displaying Results 1 - 25 of 40
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Pulsed amplification of continuous‐wave signal fields in photorefractive BaTiO3

    Page(s): 1529 - 1531
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    High‐gain pulsed amplification of low intensity continuous‐wave optical signals via two‐wave mixing in a photorefractive barium titanate (BaTiO3) crystal is demonstrated. The technique relies on the nonlinear mixing between a signal field and a pump field produced via pulsed amplification of a continuous‐wave field in excimer‐pumped dye amplifiers. View full abstract»

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  • Demonstration of photoluminescence in nonanodized silicon

    Page(s): 1532 - 1534
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    The formation of photoluminescent porous Si in an etchant solution made from the HF‐HNO3‐CH3COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400–600 Å. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si—H bonds on the porous Si surface. View full abstract»

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  • Large two‐dimensional arrays of phase‐locked vertical cavity surface emitting lasers

    Page(s): 1535 - 1537
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    The phase‐locking of two‐dimensional (2D) arrays incorporating a large number of electrically pumped, vertical cavity surface emitting lasers (VCSELs) is described. The InGaAs/GaAs quantum well VCSELs are phase locked by patterning the reflectivity of the laser back mirrors. Structures with both weak and strong modulation of the mirror reflectivity have been studied. The strongly modulated (weakly coupled) structures exhibit superior coherence and beam patterns, with up to 27×27 lasers oscillating in virtually a single (highest order) supermode. The weakly modulated (strongly coupled) arrays also emit highly coherent beams, but with lower threshold currents and higher differential efficiencies. Weakly modulated arrays of 20×20 elements (120×120 μm2) exhibited threshold currents of ≪1 mA per laser and ≳300 mW pulsed output powers. These coherent 2D arrays should be useful for optical signal processing and high optical power applications. View full abstract»

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  • Traveling‐wave polymeric optical intensity modulator with more than 40 GHz of 3‐dB electrical bandwidth

    Page(s): 1538 - 1540
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    A traveling‐wave electro‐optic intensity modulator with a 3‐dB electrical bandwidth of more than 40 GHz, negligible phase distortion, low drive voltages, and an extinction ratio of better than 20 dB is reported in nonlinear optical polymers. The velocity matching between the optical and electrical waves is excellent. The frequency response of the optical modulation is in good agreement with theory.   View full abstract»

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  • Electro‐optic and all‐optical phase modulator on an indium tin oxide single‐mode waveguide

    Page(s): 1541 - 1543
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    We have successfully demonstrated an In2O3:Sn semiconductor thin‐film waveguide. The energy gap of the film can be manipulated from 3.1 eV (0.4 μm) to 3.7 eV (0.335 μm) by changing the ratio of In2O3 and SnO2. Waveguide propagation losses of 3 dB/cm for transverse magnetic (TM) and 8 dB/cm for transverse electric (TE) guided waves were experimentally confirmed at the wavelength of 632.8 nm. A phase modulator containing an indium tin oxide waveguide, two holographic mirrors, two microprisms, and two ohmic contacts were fabricated. Electro‐optic (current injection) and all‐optical modulations were conducted. A modulation depth of 18% was experimentally confirmed for the current injection device, using 15‐V applied voltage, and a modulation depth of 15% using 250 mW 355 nm UV light as the activation sources. An In2O3:Sn waveguide device working at the cutoff boundary was made. A modulation depth of 26 dB was measured with an applied voltage of 30 V. An array of applications, including use in current sensors, ozone UV sensors, attenuated total reflection (ATR) modulators, delay lines for phased array antennae, and multiquantum wells are highly feasible. View full abstract»

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  • Narrow‐linewidth frequency stabilized AlxGa1-xAs/GaAs laser

    Page(s): 1544 - 1546
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    Velocity‐selective magnetic optical activity in Rb vapor was used to simultaneously narrow the linewidth (500 kHz) and stabilize the frequency of an AlxGa1-xAs/GaAs laser. The frequency stability was determined by heterodyning two similar lasers and measuring their relative stability. The square root of the Allan variance, a standard figure of merit, was σy(τ)=4.9×10-12 for an averaging time of 200 s. This corresponds to a standard deviation of the beat frequency fluctuations of 1.9 kHz. View full abstract»

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  • Photonic memory switch consisting of multiple quantum well reflection modulator and heterojunction phototransistor

    Page(s): 1547 - 1549
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    We report a photonic memory operation of an exciton absorptive reflection switch, consisting of a multiple quantum well modulator, a distributed Bragg reflector (DBR), and a heterojunction phototransistor (HPT). For the memory function, some of the bias light incident on the modulator passes through the DBR to illuminate the HPT. The state of the device is maintained after removing the input light incident on the phototransistor and is reset by removing the bias light incident on the modulator. Waveform reshaping and retiming of the disordered input pulse is also demonstrated. View full abstract»

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  • Improved mode locking of a femtosecond titanium‐doped sapphire laser by intracavity second harmonic generation

    Page(s): 1550 - 1552
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    The inclusion of a frequency doubling crystal in a self mode‐locked titanium‐doped sapphire laser stabilizes the mode‐locking regime. 125 fs pulses at ∼800 nm are generated at 90 MHz repetition rate. Femtosecond second harmonic pulse trains of 10 mW average power are obtained for the first time in the spectral region around 400 nm. View full abstract»

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  • Modeling a collisional, capacitive sheath for surface modification applications in radio‐frequency discharges

    Page(s): 1553 - 1555
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    Starting from previous analytical theories of the plasma sheath of an (rf) excited molecular discharge, we introduce an extension of these theories for the whole pressure range from the collision‐free up to the collision‐dominated sheath, including the region between these extremes. Collisions of the ions are taken into account via a viscous drag fluid model, leading to a set of integral equations. They are solved numerically using a fast‐converging iteration scheme. The time‐average potential distribution, electric field, sheath length, and ion and electron distribution within the sheath are obtained.   View full abstract»

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  • Demonstration of vacuum field emission from a self‐assembling biomolecular microstructure composite

    Page(s): 1556 - 1558
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    We report the first demonstration of vacuum field emission from an electron source fabricated from self‐assembling biomolecular composite microstructures. Diacetylenic lipid DC8,9PC is used to form hollow, 0.5 μm diam, ≳50 μm long, tubelike structures that are subsequently plated with metal and formed into an aligned composite in an epoxy matrix. The composite material is thin‐sectioned across the axis of alignment and then etched to expose the plated tubules. The sharp edges of the exposed metal tubules produce a very large local electric field enhancement, allowing for the vacuum field emission of significant current densities at relatively low applied macroscopic fields (≤60–80 kV/cm). View full abstract»

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  • Effects of local facet and lattice damage on nucleation of diamond grown by microwave plasma chemical vapor deposition

    Page(s): 1559 - 1561
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    Diamond deposition on an anisotropic etched Si and ion implanted Si surfaces have been examined here for the first time. Local facets on an anisotropic etched surface shows no nucleation of diamond. Synthetic diamond, in contrast, has been able to nucleate on an As+ or Si+ ion implanted Si substrate without diamond abrasive pretreatment. Selective deposition of diamond occurs only for low dose ion implantation, 100 keV 1014 cm-2, but not for high dose ion implantation, 100 KeV 1016 cm-2. Strain is proposed as the main reason for nucleation of diamond on the ion implanted Si substrates. View full abstract»

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  • Formation of amorphous aluminum tantalum nitride powders by mechanical alloying

    Page(s): 1562 - 1563
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    Aluminum tantalum nitride amorphous alloy powders have been synthesized by a high energy ball mill under purified nitrogen gas (N2) flow at room temperature. The alloy powders were characterized by means of transmission electron microscopy, differential thermal analysis, and chemical analysis. An amorphous phase containing 18 at. % N2 was obtained after 65 ks of the milling time. At the final stage of milling (72 ks) the crystallization temperature, Tx, and enthalpy change of crystallization, ΔHx, are 1115 K and -95 kJ mol-1, respectively. View full abstract»

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  • Study of the defects induced by low‐energy (100 eV) hydrogen‐ions on amorphous silicon dioxide

    Page(s): 1564 - 1566
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    The low‐energy (100 eV) hydrogen‐ion bombardment effects on a‐SiO2 have been investigated by using synchrotron radiation photoemission spectroscopies. The argon bombardment effects have also been studied, in order to discriminate between physical and chemical characters in the hydrogen/a‐SiO2 interaction. Our results show that hydrogen treatment produces predominantly Si‐H defects, which are observed to induce gap states in a‐SiO2. View full abstract»

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  • Direct observation of chemical vapor deposited diamond films by atomic force microscopy

    Page(s): 1567 - 1569
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    Diamond polycrystals deposited by the hot‐filament chemical vapor deposition method on silicon (100) substrates have been examined by atomic force microscopy (AFM) in air. Measurements of the diamond unit cell show periodic spacings between 0.34 to 0.37 nm in a very good agreement with the theoretical value of the bulk constant of natural diamond (0.356 nm). Hybridized sp3 bonds can also be observed at the (111) surface. View full abstract»

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  • Photoionization energy variation among three types of As‐stabilized GaAs (001) 2×4 surfaces

    Page(s): 1570 - 1572
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    Variation in ionization energy is studied for 2×4‐α,β,γ phases of As‐stabilized GaAs (001) 2×4 surfaces. Photoemission due to energy scanned monochromatic light is measured in a molecular beam epitaxy (MBE) chamber. The results show that ionization energy does not change monotonically with the surface As coverage but exhibits a maximum in the region of the 2×4‐β phase. This is explained in terms of surface dipole variation among the three phases. These findings confirm that these three surfaces have different electrical properties. View full abstract»

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  • X‐ray reflectivity analysis of giant‐magnetoresistance spin‐valve layered structures

    Page(s): 1573 - 1575
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    The amount of intermixing at the interfaces of sputter‐deposited spin‐valve layered structures, comprising Si/Ta (50 Å)/NiFe (75 Å)/Cu (22.5 Å)/NiFe (50 Å)/FeMn (110 Å)/Ta (50 Å), were obtained from least‐squares refinement of x‐ray reflectivity data. The observations were modeled by layers of nominal composition with compositional inhomogeneity at the interfaces. Layer thicknesses deduced from x‐ray analysis were generally within a few percent of the nominal values. Interface widths between the two NiFe layers and the Cu spacer were 6.2‐7.4 Å, indicating intermixing of atoms of about three monolayers at the interfaces. A 10.0‐Å interface width was found at the FeMn interface suggesting a mixed‐phase layer of α‐ and γ‐FeMn. Layer densities, except those of the less dense Ta underlayer and the oxidized Ta surface, agreed to within 10% of bulk values. The results were in agreement with those obtained from closely related Si/Ta/NiFe/Cu/NiFe/Ta, Si/Ta/NiFe/Cu/Ta, Si/Ta/NiFe/Ta, and Si/Ta films. View full abstract»

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  • Unusually high thermal conductivity in diamond films

    Page(s): 1576 - 1578
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    Chemical‐vapor‐deposited (CVD) polycrystalline diamond films have recently been reported with a thermal conductivity that is only 25% less than that of high quality single‐crystal natural diamond. By studying a series of such films of various thicknesses grown under virtually identical conditions, we have discovered a significant (factor of four) through the thickness gradient in thermal conductivity. The observed gradient is attributed mainly to phonon scattering by the roughly cone‐shaped columnar microstructure. For 350 μm films, the material near the top (growth) surface has a conductivity of at least 21 W/cm °C, i.e., comparable to the best single crystals. This remarkable dependence of thermal conductivity on microstructure has important implications for thermal management of microelectronic devices using CVD diamond. View full abstract»

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  • Novel annealing scheme for fabricating high‐quality Ti‐silicided shallow n+p junction by P+ implantation into thin Ti films on Si substrate

    Page(s): 1579 - 1581
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    A TiSi2 silicided shallow n+p junction with a leakage current density of about 3 nA/cm2, a forward ideality factor of 1.00, and a junction depth of about 0.11 μm has been fabricated by implanting P+ ions into thin amorphous‐Si/Ti bilayer films on silicon substrate and subsequently processed by a rapid thermal annealing (RTA) at 800 °C/60 s with a post‐conventional furnace annealing (CFA) at 600 °C/30 m. RTA not only minimizes the diffusion of knock‐on Ti into the junction region, but also facilitates the silicidation and damage annihilation. The low‐temperature CFA treatment following the high‐temperature RTA process greatly increases the diffusion of dopants into the junction region and thus improves the junction characteristics significantly. The increased diffusion of dopants from the silicide layer into the junction region by the post‐CFA process is attributed to the crystallization of the titanium silicide. View full abstract»

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  • Planar native‐oxide AlxGa1-xAs‐GaAs quantum well heterostructure ring laser diodes

    Page(s): 1582 - 1584
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    Native‐oxide planar AlxGa1-xAs‐GaAs quantum well heterostructure ring laser diodes (25‐μm‐ wide annulus, 250‐μm inside diameter, 300‐μm outside diameter) are demonstrated. The curved cavities (full‐ring, half‐ring, and quarter‐ring) are defined by native oxidation (H2O vapor+N2 carrier gas, 450 °C) of the entire upper confining layer inside and outside of the annulus. The native oxide provides current confinement and a sufficiently large lateral index step, and thus photon confinement, to support laser oscillation along the ring. Half‐ring laser diodes fabricated in a self‐aligned geometry exhibit continuous wave (cw) 300‐K thresholds as low as ∼105 mA (∼500‐μm circular cavity length), high total external differential quantum efficiencies (∼49%), and cw output powers of ≳40 mW. View full abstract»

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  • Selectivity in copper chemical vapor deposition

    Page(s): 1585 - 1587
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    The fundamental surface chemistry underlying selectivity in copper chemical vapor deposition (CVD) from COD‐Cu‐hfac and Cu(hfac)2 has been determined. Both electronic and chemistry contributions strongly influence the precursor reactivity on oxide as compared to metal surfaces. These results have important implications regarding the role of surface preparation and cleaning for initiating and maintaining selective deposition. View full abstract»

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  • Gate tunneling current in In0.53Ga0.47As junction field‐effect transistors

    Page(s): 1588 - 1590
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    Band‐to‐band tunneling leakage current is identified as the dominant source of dark current leakage at the gates of In0.53Ga0.47As/InP junction field‐effect transistors (FETs) optimized for use in linear, optoelectronic integrated circuit applications. Both the temperature and voltage dependencies of the gate leakage in such devices is studied, and the results are in agreement with calculations based on the FET two‐region model modified to include the effects of tunneling. Due to the fundamental nature of this leakage mechanism, and due to the fact that gate leakage induces shot noise, these results suggest that both low noise and high gain can be achieved by limiting the channel doping to ∼9×1016 cm-3 for FETs operated at a frequency of 1 GHz. View full abstract»

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  • Intersubband transitions for differently shaped quantum wells under an applied electric field

    Page(s): 1591 - 1593
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    Calculations were made to compare the Stark shifts of electron intersubband transitions in Al0.4Ga0.6As/AlxGa1-xAs quantum wells. Several differently shaped quantum wells, having the same subband spacing between the ground and first excited states, E21=124 meV (=10 μm) under zero bias, were considered. The asymmetric steplike wells showed larger intersubband Stark shifts and a relatively high oscillator strength as well as a small linewidth broadening. A linear intersubband Stark shift of ±10 meV for ±100 kV/cm with a moderate change of the oscillator strength was found for an asymmetric well with its potential shape intermediate between a square and an asymmetric triangular one. View full abstract»

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  • Highly doped p+ regions by zinc diffusion utilizing metalorganic vapor‐phase epitaxy

    Page(s): 1594 - 1596
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    Zinc‐diffusion doping of GaAs using metalorganic vapor‐phase epitaxy and DEZn as a dopant source is evaluated. The dependence of the diffusion profile on DEZn flow and diffusion time is presented. Typical zinc concentrations and depths obtained are 1019–1021 cm-3 and 40–200 nm, respectively. The largest concentration gradient obtained in this manner was four orders of magnitude in 500 Å, and the highest zinc concentration was measured as 2×1021 cm-3 at a sample surface. A heterojunction bipolar transistor fabricated using zinc‐diffusion doping of the base and a regrown emitter showed an fmax of 50 GHz. View full abstract»

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  • Photoluminescence characterization of nonradiative recombination in carbon‐doped GaAs

    Page(s): 1597 - 1599
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    Room‐temperature photoluminescence is used to investigate the basic recombination mechanisms in carbon‐doped GaAs samples, with hole concentrations ranging from 3.0×1016 to 1.2×1020 cm-3. The solution of a one‐dimensional, steady‐state continuity equation for minority carriers indicates that in heavily carbon‐doped GaAs, surface recombination is minimal, while bulk nonradiative recombination is dominant. The bulk nonradiative recombination rate depends not only on p2, which represents Auger recombination, but also on p3. By using a single p+‐GaAs:C (1×1020 cm-3) base layer in an AlGaAs/GaAs heterojunction bipolar transistor, the surface recombination is minimized. 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