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Applied Physics Letters

Issue 14 • Date Oct 1998

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Displaying Results 1 - 25 of 48
  • 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
  • Facet roughness analysis for InGaN/GaN lasers with cleaved facets

    Page(s): 1925 - 1927
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    Atomic force microscope images reveal a root-mean-square roughness Δd=16 nm for InGaN/GaN double-heterostructure laser structures with cleaved a-plane facets. The c-plane sapphire substrate cleaves cleanly along both the a and m planes. A theoretical model is developed which shows that the power reflectivity of the facets decreases with roughness by a factor of e-16π2(nΔd/λ0)2, where n is the refractive index of the semiconductor and λ0 is the emission wavelength. Laser emission from the optically pumped cavities shows a TE/TM ratio of 100, an increase in differential quantum efficiency by a factor of 34 above threshold, and an emission line narrowing to 13.5 meV. © 1998 American Institute of Physics. View full abstract»

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  • Demonstration of an InGaN/GaN-based optically pumped multiquantum well distributed feedback laser using holographically defined third-order gratings

    Page(s): 1928 - 1930
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    We demonstrate an optically pumped InGaN/GaN-based multiquantum well distributed feedback laser in the blue spectral region. The third-order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion-beam etching. When aligning the stripe-shaped pump beam either parallel or perpendicular to the grating grooves, we found a considerably lower pumping threshold, higher slope efficiency, a slightly longer emission wavelength, and a much narrower linewidth for the geometry with the pump beam orthogonal to the grating lines. A nearly constant emission wavelength of 400.85 nm and a linewidth of 0.7 Å were observed under various pump intensities. To the best of our knowledge, this is the narrowest linewidth ever reported for an optically pumped device in this material system. © 1998 American Institute of Physics. View full abstract»

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  • Cleaved cavity stimulated emission from an optically pumped cubic GaN/AlGaN heterostructure grown on GaAs (100) substrate

    Page(s): 1931 - 1933
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    Cubic GaN/AlGaN double heterostructure was grown on semi-insulating GaAs (100) substrate by metalorganic vapor phase epitaxy. Strong stimulated emission was observed from the cleaved edge of the optically pumped cubic GaN/AlGaN heterostructure at 15 K. The cavity was formed simply by cleaving the substrate. The stimulated emission was demonstrated by the superlinear increase of the output intensity and the highly transverse electric polarized nature. The stimulated emission showed an obvious redshift compared with the spontaneous one. © 1998 American Institute of Physics. View full abstract»

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  • Ultrafast optical pulse noise suppression using a nonlinear spectral filter: 23 dB reduction of fiber laser 1/f noise

    Page(s): 1934 - 1936
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    Nonlinear spectral filtering provides a simple method for reducing noise in optical pulses to below the shot noise level. We show its effectiveness for excess noise reduction in an ultrafast optical pulse train by demonstrating 23 dB reduction of low frequency 1/f noise in pulses from a passively mode-locked erbium-doped fiber laser. The noise reduction is achieved by spectrally filtering pulses propagated as solitons through a 1.5 km length of optical fiber. © 1998 American Institute of Physics. View full abstract»

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  • Normal-incidence intersubband (In, Ga)As/GaAs quantum dot infrared photodetectors

    Page(s): 1937 - 1939
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    We report the device performance of normal-incidence (In, Ga)As/GaAs quantum dot intersubband infrared photodetectors. A primary intersubband transition peak is observed at the wavelength of 13 μm (E0→E1) and a secondary peak at 11 μm (E0→E2). The measured energy spacing in the conduction band of the quantum dots is in good agreement with low temperature photoluminescence measurement and calculations. A peak detectivity of 1×1010cm Hz1/2/W at 13 μm was achieved at 40 K for these devices. © 1998 American Institute of Physics. View full abstract»

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  • Optically induced polarization rotations in CdTe/CdMnTe multiple quantum wells

    Page(s): 1940 - 1942
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    We report large polarization state rotations of a weak pulsed beam in CdTe/CdMnTe quantum wells photoinduced by intense circularly polarized pulsed pump beam. Time-resolved analysis of the effect shows that, at moderate pump fluences, the polarization state rotation is due to the combined effect of many-body interactions and spectral hole burning at early times and to photoinduced magnetization at longer ones. At higher pump fluences, space filling and degenerate four-wave mixing become important. At low pump fluences (few μJ/cm2) already the polarization rotation photoinduced at early times can be as large as a few degrees making these multiple quantum wells potential candidates for applications. © 1998 American Institute of Physics. View full abstract»

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  • Design of one-dimensional band-limited uniform diffusers of light

    Page(s): 1943 - 1945
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    We present two methods for generating numerically a one-dimensional random surface, defined by the equation x3=ζ(x1), that has a prescribed probability density function of slopes. This problem arises in the design of a diffuser that scatters light uniformly within a range of scattering angles and produces no scattering outside this range. Numerical calculations of the scattering of light from random surfaces generated by these approaches show that the scattered intensity, indeed, has a rectangular distribution as a function of the scattering angle. © 1998 American Institute of Physics. View full abstract»

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  • Integrated optical isolator based on efficient nonreciprocal radiation mode conversion

    Page(s): 1946 - 1948
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    An integrated optical isolator is demonstrated based on efficient nonreciprocal conversion from a fundamental TM mode to a deep TE radiation mode away from the cutoff. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet, which has a very large Faraday rotation. 27 dB isolation is obtained at a wavelength of 1535 nm. © 1998 American Institute of Physics. View full abstract»

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  • Superradiant lasing from J-aggregated molecules adsorbed onto colloidal silver

    Page(s): 1949 - 1951
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    The picosecond time-resolved emission spectrum of the cyanine dye 1,1-diethyl-3,3bis-(3-sulfopropyl)-5,5,6,6-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state (i.e., the coherence length) was estimated to involve 8–9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states. © 1998 American Institute of Physics. View full abstract»

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  • Poisson’s ratio measurement in tungsten thin films combining an x-ray diffractometer with in situ tensile tester

    Page(s): 1952 - 1954
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    A direct determination of the Poisson’s ratio in 150 nm polycrystalline tungsten thin films deposited by ion-beam sputtering on Duralumin substrates has been performed by combining x-ray diffraction measurements with in situ traction on the sample. X-ray diffraction experiments using the sin2 ψ method have been done at LURE, the French synchrotron facility (Orsay, France) on a four-circle diffractometer. The method described in this letter allows us to extract in a simple way and with a good precision the Poisson’s ratio of thin films on substrates from the evolution of the sin2 ψ curves as a function of applied strains. In the case of tungsten thin film, the value obtained is close to the bulk material one. © 1998 American Institute of Physics. View full abstract»

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  • Analytical transmission electron microscopy of hydrogen-induced degradation in ferroelectric Pb(Zr, Ti)O3 on a Pt electrode

    Page(s): 1955 - 1957
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    Changes in the crystal structure of Pb(Zr, Ti)O3 (PZT) on a Pt electrode caused by annealing in hydrogen-containing ambient have been studied using analytical transmission electron microscopy. A decrease in Pb composition and distortion in Ti–O coordination occur at the PZT/Pt interface. These findings indicate that preferential reduction of Pb and sequential diffusion of Pb from the PZT to the Pt electrode play an important role in the changes of the PZT crystal. Thus, changes in crystal structure due to annealing in a hydrogen-containing ambient can be avoided by using electrode materials that prevent Pb diffusion. © 1998 American Institute of Physics. View full abstract»

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  • Laser-assisted low temperature processing of Pb(Zr, Ti)O3 thin film

    Page(s): 1958 - 1960
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    A method for lowering the processing temperature of PbZr1-xTixO3 (PZT) films was developed utilizing a laser-assisted two-step process. In the first step, perovskite phase was initiated in the PZT films to a furnace anneal at low temperatures in the range of 470–550 °C, depending on the Zr/Ti ratio. Later, the films were laser annealed (using KrF excimer laser) at room temperature to grow the perovskite phase, and to improve microstructure and ferroelectric properties. It was found that this two-step process was very effective in producing excellent quality ferroelectric PZT films at low temperatures. It should be noted that although laser annealing of amorphous and/or pyrochlore films directly (one-step process) produced perovskite phase, the ferroelectric properties of these films, irrespective of the composition, were rather unattractive. Some possible reasons for the ineffectiveness of the one-step process were discussed. © 1998 American Institute of Physics. View full abstract»

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  • Reversible bending of carbon nanotubes using a transmission electron microscope

    Page(s): 1961 - 1963
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    Multiwall carbon nanotubes can be bent by changing the current density of the electron beam in a transmission electron microscope. The effect could be observed in a small fraction of nanotubes in the investigated samples. The bending can be varied continuously, is reversible, and highly reproducible. On removing the force which makes them bend, they relax to their originally straight shape without any damage, thus exhibiting spring-like behavior. Possible mechanisms for this effect are discussed. © 1998 American Institute of Physics.   View full abstract»

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  • Electronic origin of the stability trend in TiSi2 phases with Al or Mo layers

    Page(s): 1964 - 1966
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    Through a tight-binding rigid-band approach we show that changes in the relative stability of the C54, C49, and C40 phases of TiSi2, with electrons per atom ratio, are produced by the corresponding differences in the electronic density of states at the Fermi level. In particular, by increasing this ratio the stable phase evolves from C49 to C54, and then to C40. Our microscopic model provides a straightforward interpretation of very recent experimental findings concerning the sizeable variations in the transition temperature between C49 and C54 TiSi2 in the presence of Al or Mo layers. © 1998 American Institute of Physics. View full abstract»

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  • Growth of CaF2 on Si(111): Imaging of the CaF interface by friction force microscopy

    Page(s): 1967 - 1969
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    The initial growth state of CaF2/Si(111) has been investigated in the high-temperature regime (700 °C). At these growth temperatures the interface between CaF2 and Si consists of CaF with the Ca atoms bound to the Si. Using friction force microscopy it is possible to distinguish between the interfacial CaF layer and the overgrowing CaF2 with high lateral resolution: the CaF layer has a higher friction coefficient than the bulklike CaF2. This material contrast has been used to investigate the CaF2 nucleation on the interfacial CaF layer. © 1998 American Institute of Physics. View full abstract»

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  • Atomic transport across the interfaces during the formation of ultrathin silicon oxide/nitride/oxide films

    Page(s): 1970 - 1972
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    The redistribution of O and N during the final, thermal oxidation in dry O2 step in the formation of ultrathin silicon oxide/nitride/oxide dielectric films (ONO) was investigated using isotopic tracing and depth profiling with nanometer resolution. The results show that the final oxidation step induces atomic transport of O and N species in the system, such that the formed ONO structures are not stacked layer structures, but rather a silicon oxynitride ultrathin film, having moderate concentrations of N in the near-surface and near-interface regions, and a high N concentration in the bulk. © 1998 American Institute of Physics. View full abstract»

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  • Effect of hydrogen on Pb(Zr,Ti)O3-based ferroelectric capacitors

    Page(s): 1973 - 1975
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    The properties of ferroelectric films are known to degrade when subjected to hydrogen in forming gas anneals. Earlier studies have attributed this degradation to the loss of oxygen from these films during these anneals. In this study, we show that though oxygen is lost during forming gas annealing, hydrogen incorporation is the primary mechanism for the degradation of ferroelectric properties. Raman spectra obtained from the forming gas-annealed films show evidence of polar hydroxil [OH-] bonds in the films. The most probable site for hydrogen ions is discussed based on ionic radii, crystal structure, electrical properties, and Raman spectra. We propose that the hydrogen ion is bonded with one of the apical oxygen ions and prevents the Ti ion from switching. Pyroelectric measurements on forming gas-annealed capacitors confirm that the capacitors no longer possess spontaneous polarization. © 1998 American Institute of Physics. View full abstract»

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  • Nanometer-scale patterning of self-assembled monolayer films on native silicon oxide

    Page(s): 1976 - 1978
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    A nanoscale-patterning method on silicon oxide using a self-assembled monolayer (SAM) was developed. The silicon surface with native oxide was additionally oxidized locally in dry nitrogen atmosphere by the field-induced oxidation (FIO) technique using an atomic force microscope with a conductive cantilever, and then immersed in octadecyltrichlorosilane (OTS) solution. The contact angle and topography image revealed that the OTS layer was formed only on the native oxide. In contrast, when FIO was performed under the humidity of 88%, OTS SAM was formed on both FIO and native oxide. These results indicate that SAM formation on silicon oxides can be locally suppressed by FIO in a dry environment. By using this technique, we could fabricate a line structure of OTS SAM as narrow as 22 nm. © 1998 American Institute of Physics. View full abstract»

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  • Alloy ordering in GaInP alloys: A cross-sectional scanning tunneling microscopy study

    Page(s): 1979 - 1981
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    We present a cross-sectional scanning tunneling microscopy (XSTM) study of the spontaneous ordering of Ga0.48In0.52P and Ga0.52In0.48P grown on (001) GaAs substrates by molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE), respectively. The (111)-type alloy ordering could be seen clearly in the OMVPE-grown alloy region. On the other hand, the MBE-grown region shows a very small degree of ordering as revealed by the STM. Most of the ordered region shows (InP)1(GaP)1-type ordering: alternating InP- and GaP-like (1¯11) planes. In addition to this type of ordering, we also observe another type of ordering consisting of two InP-like (1¯11) planes and one GaP-like (1¯11) plane that we call (InP)2(GaP)1-type ordering. © 1998 American Institute of Physics. View full abstract»

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  • Single-electron effects in slim semiconductor superlattices

    Page(s): 1982 - 1984
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    We fabricated laterally confined GaAs–AlGaAs superlattices with diameters between 500 nm and 2 μm. With decreasing device diameter, a gap evolves in the current–voltage curve around zero bias and steps show up at the onset of the current. This behavior is interpreted in terms of Coulomb blockade, a depletion of the center of the superlattice, and single-electron tunneling through donor levels. © 1998 American Institute of Physics. View full abstract»

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  • Temperature and stress polarity-dependent dielectric breakdown in ultrathin gate oxides

    Page(s): 1985 - 1987
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    Temperature and stress polarity-dependent dielectric breakdown in thin silicon dioxides has been carefully investigated. The experimental data show that the time to breakdown under a constant-current injection has two kinks around 330 and 230 K for 4- and 10-nm-thick oxides under both stress polarities. It has been found that thinner oxides have a stronger temperature dependence (a larger activation energy) even if the field dependence of the activation energy is taken into consideration, and also that, from the gate voltage shift during the constant-current injection, the postbreakdown characteristics strongly depends on the stress polarity for thinner oxides. © 1998 American Institute of Physics. View full abstract»

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  • Characterization of a semi-insulating GaAs photoconductive semiconductor switch for ultrawide band high power microwave applications

    Page(s): 1988 - 1990
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    Simulation results depicting physical conditions in a photoconductive semiconductor switch in the pulse charging state, prior to high power switching, are analyzed. Results show that surface conditions and EL2 traps in semi-insulating GaAs influence the conduction process, specifically at high bias. Formation of trap-filled regions renders the device inhomogeneous for stable conduction and premature breakdown occurs, due to a large extent on unstable current filamentation within the device. Unlike insulators, the breakdown of desorbed gas from the surface (surface flashover) does not contribute to premature breakdown. © 1998 American Institute of Physics. View full abstract»

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  • 19.8% efficient “honeycomb” textured multicrystalline and 24.4% monocrystalline silicon solar cells

    Page(s): 1991 - 1993
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    Multicrystalline silicon wafers, widely used in commercial photovoltaic cell production, traditionally give much poorer cell performance than monocrystalline wafers (the previously highest performance laboratory devices have solar energy conversion efficiencies of 18.6% and 24.0%, respectively). A substantially improved efficiency for a multicrystalline silicon solar cell of 19.8% is reported together with an incremental improvement in monocrystalline cell efficiency to 24.4%. The improved multicrystalline cell performance results from enshrouding cell surfaces in thermally grown oxide to reduce their detrimental electronic activity and from isotropic etching to form an hexagonally symmetric “honeycomb” surface texture. This texture reduces reflection loss as well as substantially increasing the cell’s effective optical thickness by causing light to be trapped within the cell by total internal reflection. © 1998 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