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Applied Physics Letters

Issue 5 • Date Jul 2000

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Displaying Results 1 - 25 of 56
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Green upconversion luminescence in Er3+:BaTiO3 films

    Page(s): 609 - 611
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    Green upconversion emissions at 548 and 528 nm have been obtained from sol-gel derived nanocrystalline Er3+:BaTiO3 films under 980 nm excitation. The green emissions are attributed to the ground-state (4I15/2) -directed transitions from 2H11/2 (528 nm) and 4S3/2 (548 nm) of Er3+ ions. Analysis of the temporal evolution of the emission at 548 nm shows that both excited state absorption of individual ion and energy transfer between the two neighboring ions contribute to the upconversion emissions in Er3+ (3 mol %):BaTiO3 film. The lifetime of the dominant emission at 548 nm is about 90 μs. © 2000 American Institute of Physics. View full abstract»

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  • Depolarization by high aperture focusing

    Page(s): 612 - 614
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    We introduce a method employing ferroelectric monomolecular layers, by which it is possible to measure the light field polarization in the focus of a lens. This method allowed us to noninvasively establish the perpendicularly oriented focal field that is anticipated at high apertures. For a numerical aperture 1.4 oil immersion lens illuminated with linearly polarized plane waves, the integral of the modulus square of the perpendicular component amounts to (1.51±0.2) % of that of the initial polarization. It is proven that depolarization decreases with decreasing aperture angle. Whereas for regular imaging conditions depolarization is largely negligible, it plays a significant role in microscopy of highest resolution, microspectroscopy, and single molecule studies. © 2000 American Institute of Physics. View full abstract»

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  • 2.79 μm erbium laser with lead–lanthanum zirconate titanate ceramics electro-optic Q-switching output coupler

    Page(s): 615 - 617
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    Highly refractive and transparent lead–lanthanum zirconate titanate (PLZT) ceramics are used for an output coupler of the erbium yttrium scandium gallium garnet laser (λ=2.79 μm) that simultaneously serves as the laser electro-optic Q switch. The optical aperture of such a dual-function PLZT element was 6×6 mm2 and the thickness was 3 mm. For Q switching, short ≈3 μs negative voltage pulses (1500–1800 V) were applied to the positively direct current biased (≈1400 V) PLZT element. Single-pulse lasing with a pulse half width of 160–170 ns was observed at short and long delays of the Q switch with respect to the pump flash. The highest output energy of 20–22 mJ within 1.5–2.5 μs, consisting of two or three pulses with 130 ns half width was obtained at an intermediate delay of 90–110 μs. © 2000 American Institute of Physics. View full abstract»

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  • Estimation of interwell terahertz gain by photon-assisted tunneling measurement in triple-barrier resonant tunneling diodes

    Page(s): 618 - 620
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    Terahertz (THz) gain due to electron transition between adjacent quantum wells was estimated from a measurement of current change in triple-barrier resonant tunneling diodes under the THz irradiation. Measured current change was separated into stimulated emission and absorption components, and the gain coefficient was estimated from the difference between these components. For a sample with relatively thick barriers and peak current density of 70 A/cm2, the room-temperature peak gain coefficient was about 0.15 cm-1 at 2.24 THz. The estimated gain coefficient is in reasonable agreement with an approximate theory. High gain is expected by increasing the current density with thin barriers. © 2000 American Institute of Physics. View full abstract»

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  • Artifact-free near-field optical imaging by apertureless microscopy

    Page(s): 621 - 623
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    A method for optical near field discrimination, leading to drastic artifact reduction in superresolved imaging by scanning interference apertureless microscopy is presented. The method relies on second harmonic detection of the modulated optical signal scattered by a vibrating silicon tip. An edge resolution of 15 nm, or 7 nm Rayleigh-type resolution, with optical contrast as high as 50%, has been obtained on aluminum projection pattern samples in the constant gap width mode. Our method has been determined not to be affected by topographical artifacts by constant height mode scans. © 2000 American Institute of Physics. View full abstract»

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  • Enhanced degradation resistance of quantum dot lasers to radiation damage

    Page(s): 624 - 626
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    We compare the degradation of InAs/GaAs quantum well (QW) and quantum dot (QD) laser diodes following irradiation by high energy (8.56 MeV) phosphorous ions. Over a fluence range of 108–1011ions/cm2, the degradation of the low temperature QD photoluminescence and electroluminescence emission is greatly suppressed relative to that of QW based devices (×100 and ×1000, respectively at the highest dose studied). Irradiated QD laser diodes demonstrated lasing action over the entire range of fluences, and 2 orders of magnitude beyond the maximum dose sustainable by QW devices. The improved damage response of QD based structures results from efficient collection and localization of electrons and holes by QDs in the active region, which limit carrier transfer to nonradiative centers. This work suggests the suitability of QD device architectures for use in radiation environments, and in high power applications, wherever nonradiative processes promote the degradation or failure of traditional QW devices. © 2000 American Institute of Physics. View full abstract»

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  • High-quality phase conjugation even in a highly transient regime of stimulated Brillouin scattering

    Page(s): 627 - 629
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    A high-quality phase conjugation of the stimulated Brillouin scattering has been achieved even in a highly transient regime, as proved by the mask restoration in the backscattered signal. A special two-lens system of laser beam insertion into a scattering medium was used. A reliable onset of the phase conjugation has been reached using a splitted part of the oscillator Q-switched pulse as a prepulse in the Brillouin cell. Results with and without the prepulse are compared. A possibility of the creation of the phase conjugated mirrors even in high-power gaseous lasers with short pulses is thus proved. © 2000 American Institute of Physics. View full abstract»

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  • Gain in 1.3 μm materials: InGaNAs and InGaPAs semiconductor quantum-well lasers

    Page(s): 630 - 632
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    The absorption and gain for an InGaNAs/GaAs quantum-well structure is calculated and compared to that of a more conventional InGaAs/InGaPAs structure, both lasing in the 1.3 μm range. Despite significant differences in the band structures, the gain value is comparable for high carrier densities in both structures and the transition energy at the gain maximum shows a similar blueshift with increasing carrier density. For low and intermediate carrier densities, the calculated gain in the InGaPAs system is significantly lower and the bandwidth smaller than in the InGaNAs system. © 2000 American Institute of Physics. View full abstract»

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  • Experimental observation of the mobility edge in a waveguide with correlated disorder

    Page(s): 633 - 635
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    The tight-binding model with correlated disorder introduced by Izrailev and Krokhin [Phys. Rev. Lett. 82, 4062 (1999)] has been extended to the Kronig–Penney model. The results of the calculations have been compared with microwave transmission spectra through a single-mode waveguide with inserted correlated scatterers. All predicted bands and mobility edges have been found in the experiment, thus demonstrating that any wanted combination of transparent and nontransparent frequency intervals can be realized experimentally by introducing appropriate correlations between scatterers. © 2000 American Institute of Physics. View full abstract»

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  • Dependence of crystallographic tilt and defect distribution on mask material in epitaxial lateral overgrown GaN layers

    Page(s): 636 - 638
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    We have investigated the dependence of crystallographic tilt and defect distribution on mask material in metalorganic chemical vapor deposition grown GaN layers formed utilizing an epitaxial lateral overgrowth (ELO) technique using x-ray diffraction and transmission electron microscopy. Crystallographic tilt in the ELO GaN layer was suppressed by changing the mask material from electron beam (EB)-evaporated SiO2 to plasma enhanced chemical vapor deposition (PECVD) grown SiO2 and PECVD SiNx. Defect distribution also changes in accordance with mask materials. By depositing a thin PECVD SiNx layer on the PECVD SiO2 mask, the crystalline quality of the ELO layer changes from that used with the SiO2 mask to that used with the SiNx mask. These results suggest that the interface between the ELO GaN layer and the mask has a significant effect on crystallographic tilt and defect distribution. © 2000 American Institute of Physics. View full abstract»

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  • Quantum confinement energies in zinc-blende III–V and group IV semiconductors

    Page(s): 639 - 641
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    Blueshift of the band gap due to quantum confinement is calculated in a tight-binding model for a series of nine III–V zinc-blende AB (A=Al, Ga, or In, B=As, P, or Sb) and two diamond group-IV (Si and Ge) semiconductor clusters. Analytic expressions for the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels are given as a function of the cluster size. Comparison is made to results obtained by the pseudopotential method and to experimental results. © 2000 American Institute of Physics. View full abstract»

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  • Double-hump diffusion profiles of copper and nickel in germanium wafers yielding vacancy-related information

    Page(s): 642 - 644
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    Diffusion of Cu and Ni into Ge was investigated between 700 and 900 °C with the aid of rapid isothermal lamp annealing and spreading-resistance profiling. Using low-dislocation-density single-crystal Ge wafers with a backside gold layer, we observed typical double-hump diffusion profiles of both Cu and Ni. These profiles can be described within the dissociative model by taking into account that the front surface acts as source for both vacancies (V) and Cu or Ni while the back surface combines the V-source feature with a Cu, Ni-sink property. Profile fitting yields data regarding the V-assisted Ge self-diffusion coefficient and the equilibrium concentration of vacancies as a function of temperature. © 2000 American Institute of Physics. View full abstract»

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  • Kinetic oscillations of red photoluminescence from nanocrystalline Si/SiO2 films

    Page(s): 645 - 647
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    Experimental investigations on the red photoluminescence (PL) from nanocrystalline Si (nc-Si) embedded in a SiO2 matrix, fabricated by plasma-enhanced chemical vapor deposition and a subsequent post-treatment, reveal under certain conditions the occurrence of kinetic oscillations. For the red PL between 1.5 and 1.75 eV, the spectral shift and the peak intensity versus annealing times show temporal oscillations. The spectral variations are explained by the growth and decay kinetics of two oxygen thermal donors (TDs) upon annealing. The oscillatory behavior is a pure kinetic one. It reflects the regrowth of oxygen TDs by an autocatalytic process during their decay. Although the source for the autocatalysis is not clear, this PL oscillation adds more evidence that the red PL observed in our system originates from oxygen TDs-related defect states. © 2000 American Institute of Physics. View full abstract»

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  • Ultrafast intersubband relaxation (⩽150 fs) in AlGaN/GaN multiple quantum wells

    Page(s): 648 - 650
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    The ultrafast intersubband relaxation in GaN quantum wells has been verified. Al0.65Ga0.35N/GaN multiple quantum wells, with as many as 200 wells, were grown by optimizing the barrier thickness and introducing GaN intermediate layers. The intersubband absorption is sufficiently strong for the relaxation time to be measured. A pump–probe measurement is performed to investigate the relaxation. An ultrashort relaxation time of less than 150 fs is obtained at a wavelength of 4.5 μm. The transient time is shorter than that of InGaAs quantum wells by approximately an order of magnitude. This result is promising for realizing ultrafast optical switches. © 2000 American Institute of Physics. View full abstract»

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  • Semiconductor wafer bonding via liquid capillarity

    Page(s): 651 - 653
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    Liquid surface tension has been used to pull different semiconductor wafers to very close contact and strong bonding. Bonded wafers, such as GaAs/GaP, were heat treated without pressure application to achieve wafer fusion. The bonding process has been analyzed, and criteria for surface tension, wafer flatness, and elasticity have been derived. © 2000 American Institute of Physics. View full abstract»

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  • Initial growth of heteroepitaxial 3C–SiC on Si using energetic species

    Page(s): 654 - 656
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    Structural evolution of initial growth of heteroepitaxial 3C–SiC on Si(100) using mass-separated energetic (∼60 eV) ions of C+ and CH3+ has been investigated by in situ reflection high energy electron diffraction (RHEED). RHEED patterns indicated that carbonization reaction of Si occurred at as low as 590–690 °C by irradiation of C+ and CH3+ with 60 eV. The diffraction pattern of 3C–SiC using CH3+ ions exhibited sharp streak shapes in comparison with the use of C+ ions. The features of a carbonization process using energetic species is discussed. © 2000 American Institute of Physics. View full abstract»

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  • Self-induced light polarization rotation in azobenzene-containing polymers

    Page(s): 657 - 659
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    We report here a light-induced phenomenon—a self-induced rotation of the azimuth of elliptically polarized light passing through photobirefringent azopolymers. The experiments are carried out with films of amorphous and liquid-crystalline polymers. It has been shown that the induced rotation angle depends on the ellipticity of the input light. A theoretical analysis of the phenomenon has been done and it has been shown that light induces chiral structure in the polymer films. © 2000 American Institute of Physics. View full abstract»

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  • Optical properties, spectral narrowing of photoluminescence and blue electroluminescence of poly(phenylene pyridine) derivatives

    Page(s): 660 - 662
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    Optical properties of poly(phenylene pyridine) derivatives, poly(2,5-dialkoxy-1,4phenylenealt-2,5-pyridine) (PHOnPY25), such as optical absorption, photoluminescence (PL), and electroluminescence (EL), have been studied. The electronic energy structures of PHOnPY25 have been determined by optical and electrochemical measurements. Strong PL with high quantum efficiency has been clarified in the films, and spectral narrowing has been observed by pulse excitation of a nitrogen laser. Intense blue EL has also been demonstrated. © 2000 American Institute of Physics. View full abstract»

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  • Structural anisotropy of magnetically aligned single wall carbon nanotube films

    Page(s): 663 - 665
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    Thick films of aligned single wall carbon nanotubes and ropes have been produced by filtration/deposition from suspension in strong magnetic fields. We measured mosaic distributions of rope orientations in the film plane, for samples of different thicknesses. For an ∼1 μm film the full width at half maximum (FWHM) derived from electron diffraction is 25°–28°. The FWHM of a thicker film (∼7 μm) measured by x-ray diffraction is slightly broader, 35±3°. Aligned films are denser than ordinary filter-deposited ones, and much denser than as-grown material. Optimization of the process is expected to yield smaller FWHMs and higher densities. © 2000 American Institute of Physics. View full abstract»

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  • Electrical and thermal transport properties of magnetically aligned single wall carbon nanotube films

    Page(s): 666 - 668
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    Dense, thick films of aligned single wall carbon nanotubes and nanotube ropes have been produced by filtration/deposition from suspension in strong magnetic fields. Electrical resistivity exhibits moderate anisotropy with respect to the alignment axis, while the thermopower is the same when measured parallel or perpendicular to this axis. Both parameters have identical temperature dependencies in the two orientations. Thermal conductivity in the parallel direction exceeds 200 W/mK, within a decade of graphite. © 2000 American Institute of Physics. View full abstract»

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  • Effect of surface steps on the microstructure of lateral composition modulation

    Page(s): 669 - 671
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    Growth of InAs/AlAs short-period superlattices on appropriately miscut (001) InP substrates is shown to alter the microstructure of composition modulation from a two-dimensional organization of short compositionally enriched wires to a single dominant modulation direction with wire lengths up to ∼1 μm. The effects of miscut are interpreted in terms of surface step orientation and character. The material is strongly modulated and exhibits intense optical emission. The one-dimensional modulations appear potentially useful for new devices that take advantage of the preferred direction formed in the growth plane. © 2000 American Institute of Physics. View full abstract»

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  • Ultraviolet-blue electroluminescence from Gd3Ga5O12:Ag

    Page(s): 672 - 674
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    UV-blue light was obtained from a thin-film electroluminescence device using Gd3Ga5O12:Ag as a light-emitting layer, which was deposited by using electron-beam evaporation. The crystal composition and structure of Gd3Ga5O12:Ag were studied by x-ray powder diffraction. The Gd3Ga5O12:Ag has a photoluminescence emission which peaked at around 397 and 467 nm, which were attributed to the oxide vacancies and Ag+, respectively. The brightness of 32 cd/m2 was obtained when an alternating voltage of 130 V at 1 kHz was applied. © 2000 American Institute of Physics. View full abstract»

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  • Photoconductive properties of polysilane copolymers with pendant siloxane groups

    Page(s): 675 - 677
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    The oxygen durability of poly(methylphenylsilane) (PMPS) in photoconduction has been improved by the use of copolysilanes with disiloxane-pendant groups. X-ray photoelectron spectroscopy analysis shows that disiloxane groups of the copolysilanes accumulate on their top-most surface at a much higher concentration than the bulk disiloxane concentration. The preferential coverage of disiloxane groups on the surface evidently leads to formation of a highly oxygen durable surface. The hole drift mobility of the charge carriers in copolysilanes with 5 mol % of disiloxane-pendant groups is over 10-4cm2 V-1 s-1 at E≫105V cm-1, almost comparable to that of PMPS. It was noted that the practical Xerographic potential decay was stabilized by the copolysilanes, while PMPS deteriorated after oxygen exposure. © 2000 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