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Applied Physics Letters

Issue 26 • Date Dec 2002

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Displaying Results 1 - 25 of 63
  • Issue Cover

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

    Page(s): toc1
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  • Optical microcavities with subnanometer linewidths based on porous silicon

    Page(s): 4895 - 4897
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    We have fabricated a number of high-quality porous silicon optical microcavities operating in the near infrared that exhibit cavity resonances with subnanometer linewidths. This was achieved through the low temperature anodic oxidation of highly doped p-type silicon wafers. We have investigated the optical properties of these microcavities using reflectivity and photoluminescence measurements and compared our results with theoretical predictions. From our analysis, we conclude that, for the low temperature fabrication process, the refractive index difference between adjacent layers of the multilayered structure is maximized while optical losses in the cavity are minimized. Furthermore, by considering the origin of optical losses in these microcavities, we demonstrate that fluctuations in the position of the resonance wavelength and optical absorption play an important role in the realization of high-quality interferometric structures. © 2002 American Institute of Physics. View full abstract»

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  • Optical spectroscopy of single InAs/InGaAs quantum dots in a quantum well

    Page(s): 4898 - 4900
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    We have grown self-assembled InAs quantum dots embedded in the center of an InGaAs quantum well by molecular-beam epitaxy. Using electron-beam lithography and wet etching techniques, small mesas with only a few quantum dots were fabricated. At room temperature, the quantum dots have an emission wavelength of 1.3 μm. By photoluminescence spectroscopy at low temperatures, we observe the emission lines of excitons and biexcitons in single-dot structures. The assignment of exciton and biexciton recombination is based on the characteristic excitation intensity dependence of these states. A biexciton binding energy of about 3.5 meV is obtained for the present dots. © 2002 American Institute of Physics. View full abstract»

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  • Comprehensive above-threshold analysis of large-aperture (8–10 μm) antiresonant reflecting optical waveguide diode lasers

    Page(s): 4901 - 4903
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    An above-threshold analysis of 8–10-μm-core antiresonant reflecting optical waveguide (ARROW) lasers is performed, including the carrier-induced index depression, carrier diffusion, and gain spatial hole burning (GSHB). The study is done as a function of the (transverse) optical-mode confinement factor Γ and the core width. Just as for index-guided devices, it is found that ARROW devices (i.e., index-antiguided devices) are much less immune to multimoding via GSHB the smaller the value of Γ. For the case Γ=3%, the high-order mode of most concern reaches the threshold much earlier than for the case Γ=1%, due both to gain-profile distortion as well as to distortion of the effective-index profile (in the device core) with increasing drive level. Devices of 8.5-μm-wide cores and Γ=1%, are found to stay single-mode to at least 40× threshold, which in turn allows the projection of stable, single-mode operation to 1.2 W output power. In contrast, 10-μm-core devices become multimode at around 10× threshold. Preliminary experimental results from 10-μm-wide core ARROW lasers, with Γ=1.5%, are stable, single-mode operation to 300 mW at 10× threshold, in good agreement with the presented study. © 2002 American Institute of Physics. View full abstract»

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  • Experimental investigation of the effect of wetting-layer states on the gain–current characteristic of quantum-dot lasers

    Page(s): 4904 - 4906
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    Using experimental measurements of the gain–current characteristic as a function of temperature in InGaAs quantum-dot lasers, we demonstrate that it is the population of wetting-layer states that leads to a saturation of the population inversion in dot states and hence to the saturation of gain in a quantum-dot laser. At 300 K, the maximum modal gain for a three-layer structure is reduced from 53 to 14 cm-1. © 2002 American Institute of Physics. View full abstract»

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  • Optimal rubbing angle for reflective in-plane-switching liquid crystal displays

    Page(s): 4907 - 4909
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    Rubbing angle effects on the response time and optical threshold voltage of the reflective in-plane-switching homogeneous liquid crystal displays were analyzed. As the rubbing angle increases, the rise time decreases except that its operating voltage also increases. The optimal rubbing angle is around 30°–40°. © 2002 American Institute of Physics. View full abstract»

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  • Milliwatt power deep ultraviolet light-emitting diodes over sapphire with emission at 278 nm

    Page(s): 4910 - 4912
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    We report on AlGaN multiple-quantum-well (MQW)-based deep ultraviolet light-emitting diodes over sapphire with peak emission at 278 nm. A new buffer layer growth process was used to reduce the number of defects and hence the nonradiative recombination. The improved material quality and carrier confinement resulted in pulsed powers as high as 3 mW at 278 nm and a significantly reduced deep-level-assisted long-wavelength emission. © 2002 American Institute of Physics. View full abstract»

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  • Pure red electroluminescence from a host material of binuclear gallium complex

    Page(s): 4913 - 4915
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    By using a binuclear gallium complex, bis(salicylidene-o-aminophenolato)-bis(8quinolinoato)-bisgallium(III)[Ga2(saph)2q2], as the host material, organic light emitting diodes (OLEDs) with pure red emission were developed, which used a red fluorescent dye of 4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB). Ga2(saph)2q2 proves to be of much better film-forming ability and a smaller energy gap than tris(8-quinolinolato)aluminum (Alq3). And the doped device with a configuration of indium tin oxide/N,N-bis-(1-naphthl)-diphenyl-1,1-biphenyl-4,4-diamine/Ga2(saph)2q2: DCJTB (2 wt %)/Ga2(saph)2q2/Mg:Ag, exhibited a turn-on voltage as low as 2.2 V, and a pure red emission with Commission Internationale de l’Eclairage (CIE 1931) coordinates of (0.67, 0.33). The improved energy transfer gave a high current efficiency of 2.04 cd/A at 20 mA/cm2, which is about two times higher than that of the doped Alq3 device. This letter indicates that developing host materials is a promising way to achieve excellent red emission OLEDs. © 2002 American Institute of Physics. View full abstract»

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  • Post-growth p-type doping enhancement for ZnSe-based lasers using a Li3N interlayer

    Page(s): 4916 - 4918
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    A method to increase decisively the p-type doping level in ZnSe-based laser diodes is described. Upon Li3N indiffusion, the formation of a stable acceptor complex is observed. Free hole concentrations of 8×1018cm-3 are obtained. This value is at least one order of magnitude larger than typical p-type doping levels achieved by molecular-beam epitaxy of ZnSe. In addition, no compensation effects occur, as usually observed for p-type doping using either Li or N. ZnSe-based lasers processed by applying this post-growth p-doping enhancement technology show significantly improved properties. © 2002 American Institute of Physics. View full abstract»

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  • Scattering rings in optically anisotropic porous silicon

    Page(s): 4919 - 4921
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    We report the observation of strongly anisotropic scattering of laser light at oblique incidence on a (100)-oriented porous silicon layer. The scattered light forms cones tangent to the incident and reflected beams. The conical pattern is caused by scattering on the vertical walls of pores, which are straight along the layer thickness. The light cone defines structured light rings onto a screen normal to the cone axis. We explain the various structures by optical anisotropy of porous silicon. For the sample under analysis, we directly measure from the ring patterns a value of Δn/nord=8% of positive birefringence. © 2002 American Institute of Physics. View full abstract»

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  • Evidence of local and global scaling regimes in thin films deposited by sputtering: An atomic force microscopy and electrochemical study

    Page(s): 4922 - 4924
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    The surface morphology of NiOx thin films deposited by rf sputtering was studied by atomic force microscopy and by cyclic voltammetry. Linear relationships were observed in log–log plots of the interface width versus window length and in log–log plots of the peak current versus scan rate. Two different slopes were observed, by both techniques, indicating that distinct growth dynamics present in the system can be measured in different ways. Moreover, the calculated fractal dimensions are in excellent agreement: the local scaling regime corresponds to high scan rates and the global scaling regime corresponds to low scan rates, in accordance with the expected behavior for diffusion fronts. © 2002 American Institute of Physics. View full abstract»

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  • Optical study of the full photonic band gap in silicon inverse opals

    Page(s): 4925 - 4927
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    An optical study of the band structure of both silicon–silica composite and silicon inverse opals is presented. The study is aimed at demonstrating the development of a full photonic band gap for a system already revealed as paradigmatic. The characterization is based on the comparison between the band structure calculations and optical reflectance spectroscopy experiments. This study is carried out for various symmetry points in the Brillouin zone, some never explored before as K, (110) and W, (210). The results show that, in accordance with the band structure, there is a certain frequency range that produces a reflectance peak regardless of orientation and can be assigned to the band gap. Similarly all other reflectance peaks can be accounted for by other band structure features. © 2002 American Institute of Physics. View full abstract»

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  • Determination of the azimuthal orientational spread of GaN films by x-ray diffraction

    Page(s): 4928 - 4930
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    We present a simple but reliable method to determine the azimuthal orientational spread of imperfect epitaxial layers by x-ray diffraction. This method requires the measurement of ω-scans in skew geometry from reflections with increasing lattice plane inclination φ, and a fit of the data by a geometrical model that considers the simultaneous presence of polar and azimuthal orientational spread within the layer. The values thus obtained for various GaN layers grown on SiC are shown to be in good agreement with those measured directly by Φ-scans of the (11¯00) reflection in grazing incidence, and with those deduced from the edge dislocation densities determined by plan-view transmission electron microscopy. © 2002 American Institute of Physics. View full abstract»

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  • Magnetically-modulated refractive index of magnetic fluid films

    Page(s): 4931 - 4933
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    We developed a setup to probe the refractive index of the magnetic fluid films under external magnetic fields. This setup possesses a high resolution of 0.0001 in the measured refractive index. It was found that the refractive index of the magnetic fluid depends linearly on the concentration of the dilute magnetic fluid under zero field. For a given magnetic fluid film, the refractive index increases with the increasing field strength over a critical value, and then becomes saturated as the field reaches around 200 Oe. It is noteworthy that the magnetically modulated refractive index of the magnetic fluid films could have great potential in electro-optical applications. © 2002 American Institute of Physics. View full abstract»

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  • Optical characteristics of hexagonal GaN self-assembled quantum dots: Strong influence of built-in electric field and carrier localization

    Page(s): 4934 - 4936
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    Optical characteristics of hexagonal GaN self-assembled quantum dots (QDs) were systematically studied by photoluminescence (PL), PL excitation (PLE), time-resolved PL, and cathodoluminescence (CL). We observed a Stokes-like shift between PLE absorption edge and PL emission from the GaN QDs as well as from the Al(Ga)N base layer. With decreasing emission energy, the measured lifetime of the hexagonal GaN QDs emission increased, while that of the cubic GaN QDs kept almost constant. The optical emission from the GaN QDs was measured as a function of temperature from 10 to 300 K, and their properties were compared with GaN quantum-well structures. With increasing temperature, the PL intensity of Al(Ga)N base layer or GaN quantum wells was dramatically decreased, while that of GaN QDs was not changed much. We observed CL images showing strong carrier localization in GaN QDs. Therefore, we conclude that the GaN QD emissions are strongly influenced by built-in electric field as well as by carrier localization in the QDs. © 2002 American Institute of Physics. View full abstract»

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  • Lasing from a single-quantum wire

    Page(s): 4937 - 4939
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    A laser with an active volume consisting of only a single-quantum wire in the one-dimensional (1D) ground state is demonstrated. The single wire is formed quantum mechanically at the T-shaped intersection of a 14 nm Al0.07Ga0.93As quantum well and a 6 nm GaAs quantum well, and is embedded in a 1D single-mode optical waveguide. We observe single-mode lasing from the quantum-wire ground state by optical pumping. The laser operates from 5 to 60 K, and has a low threshold pumping power of 5 mW at 5 K. © 2002 American Institute of Physics. View full abstract»

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  • Spinodal patterning in organic–inorganic hybrid layer systems

    Page(s): 4940 - 4942
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    We demonstrate a general feature of organic films between a substrate and a deformable cladding layer: the capability of forming periodic structures by heating above the glass transition temperature of the organic film. This patterning process by self-organization is caused by the interplay of dispersion interactions and mechanical stress which leads to spinodal deformation. The dynamic evolution of the structures was investigated by time-resolved light diffraction. By prepatterning the substrate, the direction of the waves can be controlled. © 2002 American Institute of Physics. View full abstract»

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  • Giant polarized photoluminescence and photoconductivity in type-II GaAs/GaAsSb multiple quantum wells induced by interface chemical bonds

    Page(s): 4943 - 4945
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    Anisotropic property of type-II GaAs/GaAsSb heterostructures was studied by photoluminescence (PL) and photoconductivity (PC). It was found that the PL and PC spectra exhibit a strong in-plane polarization with respect to 〈011〉 axis with polarization degrees up to 40%. We showed that the polarization does not depend on the excitation intensity as well as temperature, which excludes any extrinsic mechanisms related to the in-plane anisotropy. The observed polarized optical properties of GaAsSb/GaAs multiple quantum wells was attributed to the intrinsic property of the orientation of chemical bonds at heterointerfaces. © 2002 American Institute of Physics. View full abstract»

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  • Surface domain engineering in congruent lithium niobate single crystals: A route to submicron periodic poling

    Page(s): 4946 - 4948
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    We describe a technique for surface domain engineering in congruent lithium niobate single crystals. The method is based on conventional electric-field poling, but involves an intentional overpoling step that inverts all the material apart from a thin surface region directly below the patterned photoresist. The surface poled structures show good domain uniformity, and the technique has so far been applied to produce domain periods as small as ∼1 μm. The technique is fully compatible with nonlinear optical integrated devices based on waveguide structures. © 2002 American Institute of Physics. View full abstract»

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  • A neutron reflectometry study of the interface between poly(9,9-dioctylfluorene) and poly(methyl methacrylate)

    Page(s): 4949 - 4951
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    Neutron reflectivity was used to study the interface between the semiconducting polymer poly(9,9-dioctylfluorene) (PFO) and the insulating polymer poly(methyl methacrylate) (PMMA). The PFO/PMMA interfacial width was measured in the nematic and crystalline phases of the PFO, both with the PMMA on top of the PFO and vice versa. These interfaces are broad compared to atomic length scales, with measured interfacial widths in the range from 10 to 20 Å. We found that the interfacial width was independent of both the chosen geometry and the thermal processing history. The equilibrium interfacial width only depended on temperature, with the width in the nematic phase of the PFO being broader than in the crystalline regime. © 2002 American Institute of Physics. View full abstract»

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  • Millisecond minority carrier lifetimes in n-type multicrystalline silicon

    Page(s): 4952 - 4954
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    Exceptionally high minority carrier lifetimes have been measured in n-type multicrystalline silicon (mc-Si) grown by directional solidification and subjected to phosphorus gettering. The highest effective lifetimes, up to 1.6 ms averaged over several grains and 2.8 ms within some of them, were measured for relatively lowly doped, 2–3 Ωcm, wafers. The lifetime was found to decrease for lower resistivities, still reaching 500 μs for 0.9 Ωcm and 100 μs for 0.36 Ωcm. Several important findings are reported here: (i) achievement of carrier lifetimes in the millisecond range for mc-Si, (ii) effectiveness of phosphorus gettering in n-type mc-Si, and (iii) demonstration of good stability under illumination for n-type mc-Si. © 2002 American Institute of Physics. View full abstract»

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  • Metal–insulator–metal transition in Sr2Rh1-xRuxO4(0≤x≤1)

    Page(s): 4955 - 4957
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    Structural and electrical properties of c-axis oriented epitaxial Sr2Rh1-xRuxO4 (0≤x≤1) films were systematically investigated. The composition-spread films were fabricated on a temperature gradient (LaAlO3)0.3(Sr2AlTaO6)0.7 substrate to quickly optimize the growth temperature for a high-quality crystalline film having each composition (x). An anomalous c-axis length dependence on x was observed, and it was accompanied by a distinct change in electric property, that is, a metal–insulator–metal transition. © 2002 American Institute of Physics. View full abstract»

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  • Low-dose n-type nitrogen implants in 4H-SiC

    Page(s): 4958 - 4960
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    Lightly-doped n-type layers have been fabricated in 4H-SiC by low-dose implantation of nitrogen ions and characterized using the Hall effect. Near-bulk electron mobility is achieved in the implanted layers. Activation rates for the implanted nitrogen ions, energies and densities of the two-level nitrogen donor, and compensation are found from fitting the measured Hall free-electron density to a charge neutrality model as a function of temperature. Measured nitrogen activation rates are 55% and 71% for 1300 and 1600 °C anneal temperatures, respectively. Compensation due to unannealed implant damage is 32% and 17% of the implant dose for 1300 and 1600 °C anneal temperatures, respectively. © 2002 American Institute of Physics. View full abstract»

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  • AlGaN layers grown on GaN using strain-relief interlayers

    Page(s): 4961 - 4963
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    We report on a study to compare the growth of thick AlGaN layers on GaN with different strain-relief interlayers. A set of ten period AlN/AlGaN superlattices was found to be the most efficient approach for the strain relief. The superlattice interlayer not only decreases the tensile strain but also improves the crystal structural quality. Thus, 2-μm-thick, high quality n+-Al0.2Ga0.8N layers can be grown on GaN epilayers without any cracks. © 2002 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