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Applied Physics Letters

Issue 13 • Date Mar 2003

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Displaying Results 1 - 25 of 66
  • Issue Cover

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

    Page(s): toc1
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  • Displacement-sensitive photonic crystal structures based on guided resonance in photonic crystal slabs

    Page(s): 1999 - 2001
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    We introduce a mechanically tunable photonic crystal structure consisting of coupled photonic crystal slabs. Using both analytic theory, and first-principles finite-difference time-domain simulations, we demonstrate that a strong variation of transmission and reflection coefficients of light through such structures can be accomplished with only a nanoscale variation of the spacing between the slabs. Moreover, by specifically configuring the photonic crystal structures, high sensitivity can be preserved in spite of significant fabrication-related disorders. We expect such structures to play important roles in micromechanically tunable optical sensors and filters. © 2003 American Institute of Physics. View full abstract»

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  • Efficient 3–5-μm negative luminescence from HgCdTe/Si photodiodes

    Page(s): 2002 - 2004
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    The negative luminescence of a midwave-infrared HgCdTe photodiode (cutoff wavelength=5.3 μm at 295 K) was investigated using a modulated, self-referencing, optical technique. Internal efficiencies were measured to be 88% throughout the 3–5-μm spectral region, nearly independent of temperature in the 240–300-K range. This corresponds to an apparent temperature reduction of greater than 50 K at room temperature and greater than 35 K at 240 K when the reverse bias is applied. The reverse saturation current density of 1.3 A/cm2 is lower than any reported previously for a negative luminescence device with cutoff wavelength beyond 4 μm. © 2003 American Institute of Physics. View full abstract»

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  • Significant enhancement of terahertz radiation from InSb by use of a compact fiber laser and an external magnetic field

    Page(s): 2005 - 2007
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    We investigated the magnetic-field dependence of terahertz (THz) radiation power from InSb. Significant enhancement of THz-radiation power is observed by using a compact fiber laser that delivered 100 fs optical pulses at a center wavelength of 1560 nm. Additionally, applying external magnetic fields dramatically enhanced the THz-radiation power. THz-radiation power reaches a maximum value at around 1.2 T, and its enhancement factor exceeds 100. From an applications viewpoint, this is a significant finding for practical light source design, since it is easily achieved by using a compact fiber laser and a conventional magnet. © 2003 American Institute of Physics. View full abstract»

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  • Dynamics of causal beam refraction in negative refractive index materials

    Page(s): 2008 - 2010
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    A finite difference simulation of a causally excited electromagnetic Gaussian beam incident on an interface between free space and a physically realizable negative refractive index material shows that negative refraction of finite beams does occur. A discontinuity in the phase normal direction is established very quickly when the beam front reaches the interface of positive and negative index materials. Once the beam enters the negative index material, the causal wave-front propates with the group velocity consistent with theory. During the transient portion of the beam development, the beam undergoes small direction changes, which can be explained as a consequence of higher frequencies present during the beam turn-on. After this transient, the theoretically predicted sinusoidal steady state is reached. © 2003 American Institute of Physics. View full abstract»

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  • Intrinsic diffraction losses in photonic crystal waveguides with line defects

    Page(s): 2011 - 2013
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    Intrinsic diffraction losses of linear defect modes in photonic crystal slabs are calculated for membrane-type waveguides with strong refractive index contrast. In the frequency region of high group velocity of the defect mode, the radiative losses increase with the air fraction of the lattice and decrease on increasing the channel width or the slab thickness. Close to a mini-gap in the mode dispersion, a complex frequency dependence of the losses is found. The calculated losses agree well with those measured in a Si slab [M. Lončar etal, Appl. Phys. Lett. 80, 1689 (2002)]. © 2003 American Institute of Physics. View full abstract»

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  • Current control for magnetized plasma in direct-current plasma-immersion ion implantation

    Page(s): 2014 - 2016
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    A method to control the ion current in direct-current plasma-immersion ion implantation (PIII) is reported for low-pressure magnetized inductively coupled plasma. The ion current can be conveniently adjusted by applying bias voltage to the conducting grid that separates plasma formation and implantation (ion acceleration) zones without the need to alter the rf input power, gas flux, or other operating conditions. The ion current that diminishes with an increase in grid bias in magnetized plasmas can be varied from 48 to 1 mA by increasing the grid voltage from 0 to 70 V at -50 kV sample bias and 0.5 mTorr hydrogen pressure. High implantation voltage and monoenergetic immersion implantation can now be achieved by controlling the ion current without varying the macroscopic plasma parameters. The experimental results and interpretation of the effects are presented in this letter. This technique is very attractive for PIII of planar samples that require on-the-fly adjustment of the implantation current at high implantation voltage but low substrate temperature. In some applications such as hydrogen PIII-ion cut, it may obviate the need for complicated sample cooling devices that must work at high voltage. © 2003 American Institute of Physics. View full abstract»

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  • Atomistic simulation of strain-induced amorphization

    Page(s): 2017 - 2019
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    The process of solid-state amorphization through extensive plastic straining (i.e., mechanical alloying) is studied through molecular simulation of binary Cu–Zr alloys. Without such confounding factors as impurity pick-up, or such thermal effects as melting or diffusion, we find that amorphization can be driven solely by accumulation of crystal defects and interfacial roughening between the component phases. The tendency for glass formation is also seen to depend on composition, and the results are in line with extensive prior experimental work. © 2003 American Institute of Physics. View full abstract»

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  • Observation of interface defects in thermally oxidized SiC using positron annihilation

    Page(s): 2020 - 2022
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    Positron annihilation has been applied to study thermally oxidized 4H- and 6H-SiC. The SiC/SiO2 interface is found to contain a high density of open-volume defects. The positron trapping at the interface defects correlates with the charge of the interface determined by capacitance–voltage experiments. For oxides grown on n-SiC substrates, the positron annihilation characteristics at these defects are nearly indistinguishable from those of a silicon/oxide interface, with no discernable contribution from C-related bonds or carbon clusters. These results indicate that those defects at the SiC/oxide interface, which are visible to positrons, are similar to those at the Si/oxide interface. The positron annihilation characteristics suggest that these defects are vacancies surrounded by oxygen atoms. © 2003 American Institute of Physics. View full abstract»

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  • Optical properties of single-crystalline ZnO nanowires on m-sapphire

    Page(s): 2023 - 2025
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    ZnO nanowires have been synthesized using a catalyst-assisted heteroepitaxial carbothermal reduction approach on a m-sapphire substrate. Intricate and uniform arrays have been obtained with each nanowire forming an angle ∼30° with the substrate normal. Photoluminescence studies at room temperature for wavelengths between 335 and 620 nm reveal a strong single exciton peak at ∼380 nm (3.26 eV) with accompanying deep-level blueshifted emission peaks at ∼486, 490, and 510 nm. UV resonant Raman spectroscopy has been used to characterize the nanowires at room temperature with multiphonon scattering exhibiting phonon quantum confinement. © 2003 American Institute of Physics. View full abstract»

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  • High-electric-field photocurrent in thin-film ZnS formed by pulsed-laser deposition

    Page(s): 2026 - 2028
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    Photocurrent spectra of thin-film ZnS on glass fabricated by pulsed-laser deposition have been studied employing electric fields up to 20 kV/cm. The spectra show a shift towards lower energy at and beyond 10 kV/cm. By modeling the film absorption with the density of states and the Urbach rule, it is shown that, without the involvement of the Franz–Keldysh effect and excitonic transitions, the slope of the Urbach tail depends on the electric field, owing to impurity ionization. © 2003 American Institute of Physics. View full abstract»

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  • Color variation of ZnGa2O4 phosphor by reduction-oxidation processes

    Page(s): 2029 - 2031
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    The color of the emission of zinc gallate (ZnGa2O4) oscillates between ultraviolet and blue by hydrogen ambient reduction and air ambient oxidation heat treatments. The photoluminescence spectra and electron paramagnetic resonance signals show that ultraviolet emission of reduced ZnGa2O4 always accompanies 680 nm emission originating from single oxygen vacancies (VO*). The increasing difference in binding energy between Ga3+ and O2- in reduced ZnGa2O4 indicates that the configuration of octahedral sites is distorted due to VO* generation and it becomes more ionic which shifts the emission band from 430 to 360 nm. The x-ray diffraction patterns and Raman scattering spectra show that β-Ga2O3 from ZnGa2O4 is formed in both reduction and oxidation processes which suggests the vaporization of Zn ions. We propose a model in which the origin of 360 nm emission is the Ga–O transition at distorted octahedral sites with VO* in ZnGa2O4, whereas 430 nm emission originates from the Ga–O transition of regular octahedral sites without VO* in ZnGa2O4. © 2003 American Institute of Physics. View full abstract»

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  • Electromigration reliability of dual-damascene Cu/porous methylsilsesquioxane low k interconnects

    Page(s): 2032 - 2034
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    Electromigration (EM) reliability was investigated for Cu/porous low k interconnects. The porous low k dielectric was a methylsilsesquioxane (MSQ) based spin-on organosilicate material with k of 2.2. The activation energy for EM failure was found to be about 0.9 eV for Cu/porous MSQ between 208 and 367 °C, which is commonly associated with mass transport at the Cu/SiNx cap-layer interface. The threshold product of current density and line length (jL)c for Cu/porous MSQ was found to be 2500–3000 A/cm. The reduction in EM lifetime compared with Cu/oxide interconnect can be attributed to smaller back stress, due to less thermomechanical confinement of Cu/low k interconnects. Most interconnects failed by voiding at the cathode. Some lateral Cu extrusion followed by interfacial breakdown was also observed near the anode. © 2003 American Institute of Physics. View full abstract»

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  • Observation of metal–insulator transition in Al–Pd–Re quasicrystals by x-ray absorption and photoemission spectroscopy

    Page(s): 2035 - 2037
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    Using x-ray absorption and valence-band photoelectron spectroscopy (PES) we investigated the electronic structures of icosahedral (i)-Al70Pd22.5Re7.5 quasicrystals (QCs) with a 4.2 K/300 K resistivity ratio, r, ranging from 8.3 to 107 obtained under various annealing conditions. Our Al K- and Pd L3-edge x-ray absorption results show that the density of states, N(E), near the Fermi level, EF, jumps to a larger value when r decreases down to below about 20.6. The valence-band PES results show that N(E) near EF is greatly reduced in i-Al70Pd22.5Re7.5 QCs relative to that of the pure metal, which confirms the existence of the pseudogap. The PES spectrum has a sharp cutoff at EF for r=8.3 QC, while it decreases smoothly down to zero at EF for larger r’s. The combined results suggest the occurrence of metal–insulator transition at an r between 13 and 20.6. © 2003 American Institute of Physics. View full abstract»

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  • Atomistic modeling of amorphization and recrystallization in silicon

    Page(s): 2038 - 2040
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    We propose an atomistic model to describe the evolution of the damage generated by irradiation in Si, going from isolated point defects to the formation of continuous amorphous layers. The elementary units used to reproduce the defective zones are Si interstitials, vacancies and the bond defect, which is a local distortion of the Si lattice without any excess or deficit of atoms. More complex defect structures can be formed as these elementary units cluster. The amorphous pockets are treated as agglomerates of bond defects characterized by their local coordination. The model is able to reproduce the abrupt regime in the crystal-amorphous transition in Si and the epitaxial recrystallization upon annealing as observed in the experiments. The model extends the atomistic kinetic Monte Carlo simulation technique to high implant doses, adequately describing the amorphization and regrowth in Si. © 2003 American Institute of Physics. View full abstract»

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  • Density functional theory analysis of infrared modes in carbon-incorporated SiO2

    Page(s): 2041 - 2043
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    Low dielectric constant (low k) materials become increasingly important for microelectronics as interconnect delays limit circuit performance. One of the most promising low k candidates is carbon-incorporated SiO2 (SiOC:H). Despite the technological relevance of these materials, little is known about their atomistic structure. In order to address this issue, this letter compares structures obtained from the density functional theory to experimental data. This is done by analyzing both the calculated vibrational modes and experimental Fourier-transform infrared spectra. The resulting agreement is excellent. This can allow for future modeling of mechanical and electronic properties of low k dielectrics. © 2003 American Institute of Physics. View full abstract»

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  • Strain-induced band gap shrinkage in Ge grown on Si substrate

    Page(s): 2044 - 2046
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    Band gap shrinkage induced by tensile strain is shown for Ge directly grown on Si substrate. In Ge-on-Si pin diodes, photons having energy lower than the direct band gap of bulk Ge were efficiently detected. According to photoreflectance measurement, this property is due to band gap shrinkage. The origin of the shrinkage is not the Franz–Keldysh effect but rather tensile strain. It is discussed that the generation of such a tensile strain can be ascribed to the difference of thermal expansion between Ge and Si. Advantages of this tensile Ge for application to photodiode are also discussed. © 2003 American Institute of Physics. View full abstract»

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  • Reaction of SiO2 with hafnium oxide in low oxygen pressure

    Page(s): 2047 - 2049
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    A dynamic process consisting of a series of reactions during deposition of HfO2 films on SiO2-covered silicon under oxygen-deficient conditions is identified. The oxygen-deficient HfOx≪2 layer absorbs the oxygen in the SiO2 layer to form fully oxidized metal oxide film. As a result, there is no silicate and silicon oxide formed at the interface with silicon substrate. Thermodynamic analysis indicates that even if there is a layer of silicate forming at the initial stage of deposition, the silicate layer will be decomposed with the progress of HfOx≪2 deposition. © 2003 American Institute of Physics. View full abstract»

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  • Time-resolved cathodoluminescence assessment of deep-level transitions in hydride-vapor-phase-epitaxy GaN

    Page(s): 2050 - 2052
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    The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 μs, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of μs were measured at 87 K for all the deep-level emissions found in the layers. © 2003 American Institute of Physics. View full abstract»

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  • Proton-irradiation-induced intermixing of InGaAs quantum dots

    Page(s): 2053 - 2055
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    Proton irradiation was used to create interdiffusion in In0.5Ga0.5As quantum dots (QDs), grown by low-pressure metalorganic chemical vapor deposition. After 25-keV proton irradiation, the QD samples were annealed at two temperatures (700 or 750 °C) for 30 s. It was found that much lower annealing temperatures were needed to recover the photoluminescence signals than in the quantum-well case. Large blueshifts (120 meV) and narrowing of the photoluminescence spectra were seen. Various doses (5×1013–1×1015cm-2) and implant temperatures (20–200 °C) were used to study the interdiffusion processes in these samples. In QD samples, much lower doses were required to achieve similar energy shifts than reported in quantum-well samples. © 2003 American Institute of Physics. View full abstract»

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  • Buckling phenomena in Y2O3 thin films on GaAs substrates

    Page(s): 2056 - 2058
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    Worm-like buckling structures have been investigated by atomic force microscopy to estimate the relevant parameters for the mechanical stability of Y2O3 thin films deposited by ion beam sputtering technique on GaAs substrates. The internal stresses involving in the observed buckling phenomena have been estimated to be around 8.5 GPa in compression. The critical thicknesses up to which the various damaging mechanisms occur have also been determined. © 2003 American Institute of Physics. View full abstract»

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  • Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy

    Page(s): 2059 - 2061
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    We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (TeAs), Ga vacancies (VGa), and Ga vacancy–donor complexes (VGaTeAs). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy–donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a -3e charge state of VGa in bulk GaAs. © 2003 American Institute of Physics. View full abstract»

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  • Investigation of trap processes in polycrystalline silicon thin film transistors by ac measurement

    Page(s): 2062 - 2064
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    We report a method for characterizing trap generation–recombination processes in polycrystalline silicon thin film transistors. A small ac voltage was superimposed on a dc gate voltage and the ac current was measured at the source. A theoretical model was developed, whereby n-channel thin film transistors were analyzed. A resonant peak in the imaginary part of the ac current and a corresponding step in the real part were found at frequency of 147 Hz. Our data indicate that the ac response is dominated by a single trap level. By combining the ac current measurement with a low frequency capacitance measurement, we have determined the trap energy, capture cross section, and trap density to be, respectively, 0.91 eV above the valence band, 3.1×10-21cm2, and 5.7×1015cm-3. © 2003 American Institute of Physics. View full abstract»

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  • Thermoelectric properties of Al1-xInxN and Al1-y-zGayInzN prepared by radio-frequency sputtering: Toward a thermoelectric power device

    Page(s): 2065 - 2067
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    With the aim of fabricating a thermoelectric power device using III-nitride semiconductors, we recently studied thermoelectric properties of Al1-xInxN and Al1-y-zGayInzN prepared by rf sputtering. For Al0.35In0.65N with 0.63-μm thickness, the maximum power factor was 3.63×10-4W/mK2. For Al0.26Ga0.44In0.30N, the maximum power factor was 5.58×10-5W/mK2. © 2003 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