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Journal of Applied Physics

Issue 10 • Date May 2006

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Displaying Results 1 - 25 of 78
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

    Page(s): toc1
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  • Passively Q-switched laser operation of Nd:LaB3O6 cleavage microchip

    Page(s): 103101 - 103101-4
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    Pumped by a Ti:sapphire laser, a passively Q-switched laser oscillation from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of the transmission of the output coupler on the pulse width and repetition rate at various absorbed pump powers has been investigated. A pulse with 2.8 μJ energy, 2.2 ns duration, and 29 kHz repetition rate at 1060 nm was obtained at the absorbed pump power of 1.25 W and output coupler transmission of 3.2%, which results in 1.25 kW peak power. The polarization and spectral properties of laser radiation were measured. View full abstract»

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  • Electroluminescence properties of the Gd3+ ultraviolet luminescent centers in SiO2 gate oxide layers

    Page(s): 103102 - 103102-5
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    Electroluminescence (EL) properties in the ultraviolet (UV) range were studied on Gd-implanted indium tin oxide/SiO2:Gd/Si metal-oxide-semiconductor light emitting devices. The efficient UV line at 316 nm from Gd3+ centers shows a maximum power density of 2 mW/cm2 and a quantum efficiency above 5%. The Gd3+ luminescent center has an excitation cross section above 7.4×10-15 cm2 with an EL decay time around 1.6 ms at a Gd concentration of 3%. A decrease of the EL efficiency is observed by a cross relaxation at a high Gd concentration and by clustering of Gd atoms at an annealing temperature of 1000 °C. A strong quenching of the UV EL due to electron trapping around optically active Gd3+ centers is observed during the injection of hot electrons. View full abstract»

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  • The application of an InGaAs/GaAsN strain-compensated superlattice to InAs quantum dots

    Page(s): 103103 - 103103-7
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    Application of InGaAs/GaAsN strain-compensated superlattice (SCSL) to InAs quantum dots (QDs) has been studied with atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and temperature-dependent photoluminescence (PL) measurements. The insertion of a tensile-strained GaAsN layer between InGaAs layers with high In concentrations can compensate the compressive strain in the InGaAs layers and reduce the flattening of QDs during the growth of the successive InGaAs layers. Compared with QDs capped with a single InGaAs layer of a high In concentration, QDs capped with such SCSLs can achieve almost the same redshift of emission wavelength, while the optical property is highly improved. The mechanism responsible for this is discussed based on the AFM, RHEED, and PL measurements. View full abstract»

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  • Nonperturbative dynamic photon absorption of quantum wells

    Page(s): 103104 - 103104-7
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    Optical photoresponse of quantum wells in the nonperturbative regime has been studied by high-power and ultrafast-oscillating free-electron laser (FEL) experiments, which revealed a profound deviation of the nonlinear power from conventional perturbative multiple photon absorption processes. By combining the experimental and theoretical works we have shown that the nonperturbative solution of the time-dependent Schrödinger equation is essential to understand the experimental observations. Optical transitions of electrons are dynamic. One photon is absorbed or emitted when an electron transits from one electron state to the other. The rates of absorption and emission are proportional to the time interval in the femtosecond time scale. In the picosecond time scale, multiphoton processes emerge. The strong and fast-oscillating FEL source intensifies the dynamic photon absorption and emission processes in the quantum wells, resulting in a much enhanced nonlinearity in the photoresponse spectrum. View full abstract»

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  • Liquid crystal infiltration of InP-based planar photonic crystals

    Page(s): 103105 - 103105-4
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    A procedure for the infiltration of planar photonic crystals (PhCs) with liquid crystals (LCs) is presented. InP-based PhCs are infiltrated with the nematic LC-K15 in a specially designed high-vacuum chamber. The infiltration technique is validated and systematically characterized by measuring the transmission through the infiltrated PhCs at different temperatures and for different polarizations. The reproducibility and reliability of our procedure are demonstrated and a high filling efficiency is obtained. View full abstract»

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  • Influence of doping density on electron dynamics in GaAs/AlGaAs quantum cascade lasers

    Page(s): 103106 - 103106-9
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    A detailed theoretical and experimental study of the influence of injector doping on the output characteristics and electron heating in midinfrared GaAs/AlGaAs quantum cascade lasers is presented. The employed theoretical model of electron transport was based on a fully nonequilibrium self-consistent Schrödinger-Poisson analysis of the scattering rate and energy balance equations. Three different devices with injector sheet doping densities in the range of (4–6.5)×1011 cm–2 have been grown and experimentally characterized. Optimized arsenic fluxes were used for the growth, resulting in high-quality layers with smooth surfaces and low defect densities. A quasilinear increase of the threshold current with sheet injector doping has been observed both theoretically and experimentally. The experimental and calculated current-voltage characteristics are in a very good agreement. A decrease of the calculated coupling constant of average electron temperature versus the pumping current with doping level was found. View full abstract»

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  • Application of the diffraction theory for photothermal deflection to the measurement of the temperature coefficient of the refractive index of a binary gas mixture

    Page(s): 103107 - 103107-6
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    The application of recently developed diffraction theory for continuous wave photothermal deflection (PD) spectroscopy in the measurement of the temperature coefficient of the refractive index, dn/dT, of a gas as a deflecting medium was presented. Both amplitude and phase signals were elucidated for a better interpretation and a simultaneous measurement of the thermal diffusivity αg and dn/dT. The probe-beam size effect (PBSE) on the PD phase signal was also quantitatively analyzed to clearly show its physical meaning. A distance-scan method to measure the distance x between the probe beam and sample, which was difficult to determine in the PD, but a necessary parameter for measuring dn/dT, was proposed. The consistent values of x measured respectively from the amplitude and the phase could not be obtained without considering the PBSE. αg and dn/dT of pure gases (O2, N2, and CO2) and binary gas mixtures (O2-CO2 and N2-CO2) were precisely measured with the measured x. The measured αg and dn/dT of pure gases were in very good agreement with the literature values, and furthermore the measured dn/dT values of the pure gases had one more significant figure than the literature ones, demonstrating the high precision of this method. It was found the behavior of αg and dn/dT of a binary gas mixture versus concent- ration could be described by a thermodynamic theory and the Lorentz-Lorenz formula, respectively. View full abstract»

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  • Material-dependent high-frequency current fluctuations of cathodic vacuum arcs: Evidence for the ecton cutoff of the fractal model

    Page(s): 103301 - 103301-5
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    Current fluctuations of cathodic arcs were recorded with high analog bandwidth (up to 1 GHz) and fast digital sampling (up to 5 Gsamples/s). The power spectral density of the arc current was determined by fast Fourier transform clearly showing material dependent, nonlinear features in the frequency domain. These features can be associated with the nonlinear impedance of the conducting channel between cathode and anode, driven by the explosive nature of electron emission and plasma formation. The characteristic times of less than 100 ns can be associated with individual explosive processes, “ectons,” and therefore represent the short-time physical cutoff for the fractal model of cathodic arcs. View full abstract»

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  • Transition from unstable electrostatic confinement to stable magnetic confinement in a helicon reactor operating with Ar/SF6 gas mixtures

    Page(s): 103302 - 103302-6
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    Two types of instabilities were previously identified in inductive discharges having an expanding chamber when negative ions are present: (i) the source instability, occurring in the neighborhood of the capacitive-to-inductive (E to H) transition, and (ii) the downstream instability, which was shown to be the periodic formation and propagation of double layers. These unstable double layers were found over the entire parameter space (pressure/power) of interest, and they were born at the interface of the source and diffusion chambers. They acted as an internal electrostatic barrier separating a low-electronegativity, high-electron-density plasma upstream (in the source) and a high-electronegativity, low-electron-density plasma downstream. In this paper we have investigated the effect of adding a static axial magnetic field, classically used to increase the confinement and the plasma heating via helicon wave propagation. This had the following consequences: (i) the unstable double layers, and therefore the axial electrostatic confinement, were suppressed in a large part of the parameter space, and (ii) the magnetic confinement leads to a radially stratified plasma, the center being a low-electronegativity, high-density plasma and the edges being essentially an ion-ion plasma. View full abstract»

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  • Optimization of harmonic generation from boron plasma

    Page(s): 103303 - 103303-4
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    The plateau pattern of the harmonic distribution up to the 65th order (λ=12.24 nm) and the 5×10-7 conversion efficiency were achieved after the propagation of femtosecond pulses through the laser-produced boron plasma. The optimization of high-order harmonics generation was carried out at the focusing conditions when the confocal parameter of fundamental radiation was close to the plasma sizes. A study of cutoff energy showed its dependence on the second ionization potential of nonlinear medium. The spatial distribution of the radiation propagating through the boron plume showed the appearance of ringlike pattern at the intensities exceeding a saturated intensity of singly charged ions. View full abstract»

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  • Effect of sulfurization conditions and post-deposition annealing treatment on structural and electrical properties of silver sulfide films

    Page(s): 103501 - 103501-9
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    We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of 70-nm-thick Ag films. Variations in the sulfurization time caused variations in the Ag/S atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (Ag/S=1.59), stoichiometric (Ag/S=2), and Ag-rich (Ag/S=2.16) films were formed. Amongst the various as-grown films, Ag ions existed in the most polarizable environment in the Ag-rich films. All the films existed in the acanthite α-phase, and the sulfurization conditions did not cause any drastic change in the preferred orientation of this phase. The resistivity of these films strongly depended on the Ag/S ratio. While the resistivity of stoichiometric or S-rich films was about 107–108 Ω cm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The Ag/S ratio also played a significant role in our observation of the change in resistance within the films from high- to low-resistance state and vice versa with the reversal of the bias polarity of the film. Distinct switching of the resistance was observed only for the Ag-rich film. We also examined the effects of post-deposition annealing (PDA) of various films at 190 °C. PDA caused the formation of Ag-rich films (Ag/S=2.12–2.17) in all cases, and Ag ions existed in a more polarizable environment in all the films as compared w- ith stoichiometric film. All the annealed films contained mixed acanthite α-phase and argentite β-phase. Furthermore, all the films had low resistivities of about 0.01–0.02 Ω cm, which indicated that the coexisting metallic argentite β-phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar Ag/S ratio. Clear switching behavior of the resistance could be observed within all the annealed films, thereby indicating that excess Ag in the silver sulfide films is a requirement for observation of such a phenomenon. View full abstract»

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  • Correlation of Mn local structure and photoluminescence from CdS:Mn nanoparticles

    Page(s): 103502 - 103502-4
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    The structure and luminescence properties of Mn2+ in CdS nanoparticles are studied. Electron paramagnetic resonance measurements show the existence of three distinct Mn2+ centers with different local structures in CdS nanocrystals: Mn ions substitutionally incorporated on Cd sites [Signal SI: g=2.0025 and a hyperfine interaction constant A of 64.6×10-4 cm-1 (6.9 mT)], Mn located near the surface [Signal SII: g=2.0013 and A=89×10-4 cm-1 (9.5 mT)], and a broad background signal (SIII) correlated to interacting Mn ions or Mn clusters. Luminescence studies indicate that only substitutional ions located in the core of the nanocrystals contribute to the typical 4T1 to 6A1 (2.12 eV) emission. The colloidal preparation process of the nanoparticles allows selective incorporation of the Mn ions, i.e., core/shell doping of the nanoparticles. It shows that Mn located in the shell quenches the total luminescence via nonradiative processes. View full abstract»

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  • Raman scattering probe of anharmonic effects due to temperature and compositional disorder in GaNxAs1-x

    Page(s): 103503 - 103503-7
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    Using micro-Raman spectroscopy, we have investigated the vibrational properties of coherently strained GaNxAs1-x alloys grown on GaAs (001) substrates by molecular beam epitaxy. The effect of compositional disorder in GaNxAs1-x alloys has been studied by analyzing the broadening, asymmetry, and line shift of the first-order LO mode and nitrogen-induced localized vibration mode (NLVM). It is found that the line shape and peak shift of GaAs-like LO mode in GaNxAs1-x can be well described by the spatial correlation model. We have also analyzed Raman spectra of GaNxAs1-x alloys in the temperature range of 80–500 K. The intensity of GaAs-like LO phonon and NLVM decreases with temperature and the linewidth of both these modes shows substantial broadening at higher temperature. The temperature dependence of phonon linewidth and peak frequency of LO modes are analyzed in terms of anharmonic damping effect induced by thermal and compositional disorders. We have observed that the anharmonicity in GaNxAs1-x is higher than that in GaAs, and increases with the N content in GaNxAs1-x alloys. In addition, both thermal and compositional disorder-induced anharmonicities lead to an appreciable change of the LO phonon lifetime. These results obtained from Raman investigations would lead to a better understanding of the anharmonic effects in dilute nitrides. View full abstract»

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  • Elastic properties of the bcc structure of bismuth at high pressure

    Page(s): 103504 - 103504-3
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    First-principles calculations of the single-crystal elastic constants of the body-centered cubic phase of bismuth are carried out in the pressure range of 31–191 GPa. The calculations are performed in the framework of density functional theory with generalized gradient approximation using a plane wave basis set and pseudopotential scheme. These results confirm the conclusions drawn in a recent study based on the x-ray diffraction data under nonhydrostatic compression. The calculated unit cell volumes and the bulk moduli as a function of pressure agree well with the experimentally measured values. View full abstract»

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  • Hydrogen induced roughening and smoothing in surface morphology during synchrotron-radiation-excited GeH4-source homoepitaxy on Ge(001)

    Page(s): 103505 - 103505-9
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    The kinetics of roughening and smoothing in Ge(001) surface morphology during synchrotron-radiation-excited GeH4-source homoepitaxy has been investigated. At high GeH4 pressures and low substrate temperatures, two-dimensionally flat surface morphology is maintained while passivating the epitaxially growing surface with a Ge hydride layer. After exceeding the critical temperature (330 °C), the delivery of GeHx species to the partially dangling bond terminated surface and the accelerated migration of Ge atoms result in roughening from the initial stage of growth, the onset of which can be detected in terms of a small loop in real-time ψ-Δ trajectories of ellipsometric monitoring. The roughening tendency is enhanced with increasing synchroton radiation beam intensity and substrate temperature and with decreasing GeH4 pressure. Submicrometer tall islands consisting of a (001) top surface surrounded by (113) sidewalls are produced. Roughening is terminated when all dangling bonds are tied up with H atoms, i.e., when the surface free energy is minimized. Then, preferential embedding into valleys between islands yields sinusoidal-like ripple morphology, which is eventually converted into a flat Ge epilayer with no inner defects. View full abstract»

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  • Surface deformation behavior of beta solution treated and overaged Ti–6Al–4V during laser shock processing

    Page(s): 103506 - 103506-7
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    The surface of a beta solution treated and overaged Ti–6Al–4V alloy specimen deformed by laser shock processing was studied using electron backscatter diffraction, scanning electron microscopy, and atomic force microscopy. Slip steps were observed within grains oriented with their c axis nearly parallel to the specimen surface normal. Based on the slip step traces and orientation information, the slip planes were determined to be {1122} for grains with their c axis within 15° of the specimen surface normal and {1121} for grains with their c axis between 15° and 40° away from the specimen surface normal. Although both these planes are known to belong to twinning systems, {1122}<1123> and {1121}<1126>, respectively, the latter has not been observed to operate as a slip system. Examination of the Taylor factors associated with these slip systems shows that the grains with slip steps have the lowest Taylor factors. Determination of localized lattice rotations showed a unique behavior in grains with slip steps, such that all the lattice rotations were concentrated about the steps, with almost no orientation variations in between slip steps. This distribution indicates that stress concentrations exist at the slip steps, which could potentially affect the performance of the material. View full abstract»

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  • Nonconservative Ostwald ripening of a dislocation loop layer under inert nitrogen-rich SiO2/Si interfaces

    Page(s): 103507 - 103507-9
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    In this work we perform a systematic study of the dissolution of a dislocation loop layer under the influence of inert SiO2/Si and nitrogen-rich SiO2/Si interfaces. The composition of the dislocation loop layer was just after its formation 10%–20% Frank dislocation loops and 90%–80% perfect prismatic loops. During subsequent inert (N2) ambient annealing the differences of the kinetics between the two loop populations have been studied as a function of the interface type. It has been shown that during the nonconservative Ostwald ripening process the defect band loses interstitials mainly due to the dissolution of perfect prismatic loops, while Frank loops remain almost unaffected by the presence of both interfaces. In parallel a competition between the interface and the population of Frank loops in absorbing the interstitials released by the prismatic loops took place. The nitrogen-rich SiO2/Si interface has been proved in general a less effective interstitial sink than the common one and under specific annealing conditions less effective even than the small Frank loops population. View full abstract»

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  • Optical properties of amorphous GeTe, Sb2Te3, and Ge2Sb2Te5: The role of oxygen

    Page(s): 103508 - 103508-10
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    Amorphous films of GeTe, Sb2Te3, and Ge2Sb2Te5 were grown to thicknesses of 0.3–3 μm using rf sputtering. The optical properties of these films are influenced by the presence of oxygen impurities. The absorption edge in these glasses is sometimes broader than in “standard” chalcogenide glasses, such as GeSe2 or As2Se3. This result implies either that the valance band consists of highly strained bonds or that large densities of defects exist. In some samples, there exists an electron paramagnetic resonance signal in the absence of any optical excitation, which implies that a large defect density (∼1019 cm-3) exists within the energy gap. Below the optical gap the refractive index for Ge2Sb2Te5 is approximately 3.5. Electron spin resonance signals associated with the glassy SiO2 interface with the chalcogenide films are also observed. View full abstract»

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  • X-ray scattering study of hydrogen implantation in silicon

    Page(s): 103509 - 103509-7
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    The effect of hydrogen implantation in silicon single crystals is studied using high-resolution x-ray scattering. Large strains normal to the sample surface are evidenced after implantation. A simple and direct procedure to extract the strain profile from the scattering data is described. A comparison between different crystallographic orientation of the implanted silicon surface is then presented, namely, for 〈100〉, 〈110〉, and 〈111〉 orientations, showing a dependence that can be related to bond orientation. Effect of annealing on the stressed structure is finally described. View full abstract»

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  • Fluorine in preamorphized Si: Point defect engineering and control of dopant diffusion

    Page(s): 103510 - 103510-8
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    While it is known that F modifies dopant diffusion in crystalline Si, the physical mechanisms behind this process are still unclear. In this work we report experimental studies about the F control of the point defect density in preamorphized Si layers. These studies put the basis for the understanding of the F behavior and for the realization of ultra-shallow junctions. We first investigated the F incorporation process during the solid phase epitaxy (SPE) of amorphous Si layers. We elucidated the role of the SPE temperature on the F incorporation and suggested a new route towards a F profile engineering. Moreover, we explained the role of F in modifying the point defect population (self-interstitials, Is, and vacancies, Vs), employing B and Sb spike layers as markers for Is and Vs, respectively. We clearly showed that F decreases the B diffusion while enhances the Sb one, pointing out the capacity to induce an Is undersaturation or a Vs supersaturation. These data rule out the hypothesis of a chemical bonding between F and the dopants. Such F ability in modifying the Is/Vs density resulted to be a transient effect, because strictly correlated with the presence of F in the Si samples, which decreases with the annealing time. In addition, we evidenced that even if F is spatially separated from B, i.e., localized between shallow-implanted B and the end-of-range (EOR) region, it still suppresses the enhancement of B diffusivity, due to the EOR defects dissolution. These studies, besides improving the current understanding of the physical mechanisms by which F influences the dopant diffusion in Si, could be helpful for the realization of ultra-shallow junctions for the future metal-oxide-semiconductor devices. View full abstract»

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  • Optical properties of stacked InGaAs sidewall quantum wires in InGaAsP/InP

    Page(s): 103511 - 103511-5
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    We report on the optical properties of threefold stacked InGaAs sidewall quantum wires (QWires) with quaternary InGaAsP barriers grown on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent quantum wells (QWells) into the QWires at low temperature, thermally activated repopulation of the QWells at higher temperature, and negligible localization of carriers along the QWires. Strong broadening of power dependent PL indicates enhanced state filling in the QWires compared to that in the QWells. Clear linear polarization of the PL from the QWires confirms the lateral quantum confinement of carriers. These results demonstrate excellent optical quality of the sidewall QWire structures with room temperature PL peak wavelength at 1.55 μm for applications in fiber-based optical telecommunication systems. © 2006 American Institute of Physics. View full abstract»

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  • Experimental measurement of the principal isentrope for aluminum 6061-T6 to 240 GPa

    Page(s): 103512 - 103512-6
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    Using a magnetic pressure drive, an absolute measurement of stress and density along the principal compression isentrope is obtained for solid aluminum to 240 GPa. Reduction of the free-surface velocity data relies on a backward integration technique, with approximate accounting for unknown systematic errors in experimental timing. Maximum experimental uncertainties are ±4.7% in stress and ±1.4% in density, small enough to distinguish between different equation-of-state (EOS) models. The result agrees well with a tabular EOS that uses an empirical universal zero-temperature isotherm. View full abstract»

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  • Saturated gain in GaN epilayers studied by variable stripe length technique

    Page(s): 103513 - 103513-6
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    Optical gain in GaN epilayers was investigated by using the variable stripe length (VSL) technique. The light amplification was studied for the propagation directions along and perpendicular to the layer surface. Experimental stripe length and excitation intensity dependencies were measured and saturation of gain modes and appearance of new modes was observed. The limitations of the VSL technique due to gain saturation and one-dimensional light propagation model are discussed. Gain peak values up to ∼7500 cm-1 (which is the limit of applicability of the VSL technique) have been demonstrated in GaN epilayers grown on AlN buffer layers deposited on sapphire by migration enhanced metal-organic chemical vapor deposition. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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P. James Viccaro
Argonne National Laboratory