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30 Apr 2007

Volume 90, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 182501 (2007); http://dx.doi.org/10.1063/1.2734874 (3 pages)

A. V. Silhanek, W. Gillijns, V. V. Moshchalkov, V. Metlushko, F. Gozzini, B. Ilic, W. C. Uhlig, and J. Unguris
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Enhancing photon harvesting in organic solar cells with luminescent concentrators

R. Koeppe, N. S. Sariciftci, and A. Büchtemann

Appl. Phys. Lett. 90, 181126 (2007); http://dx.doi.org/10.1063/1.2735671 (3 pages) | Cited 15 times

Online Publication Date: 4 May 2007

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The authors report on the application of luminescent concentrators on organic solar cells fabricated zinc-phthalocyanine and C60. These solar cells have their main absorption in the wavelength range between 600 and 800 nm. Below 600 nm, the low absorption limits the quantum efficiency. Luminescence concentrators are used to overcome this limitation by spectrally shifting blue and green light towards the red and waveguiding it to the solar cell. With a second solar cell harvesting the red light transmitted through the concentrator, the photocurrent density is increased compared to a single solar cell of equal active area from about 8.5 up to 10 mA/cm2.
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84.60.Jt Photoelectric conversion
85.60.Jb Light-emitting devices

Enhanced responsivity in membrane isolated split-grating-gate plasmonic terahertz detectors

E. A. Shaner, M. C. Wanke, A. D. Grine, S. K. Lyo, J. L. Reno, and S. J. Allen

Appl. Phys. Lett. 90, 181127 (2007); http://dx.doi.org/10.1063/1.2735943 (3 pages) | Cited 17 times

Online Publication Date: 4 May 2007

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A 50-fold increase in responsivity of plasmon resonant detectors is achieved by thermally isolating the detector on a thin membrane. Terahertz radiation is resonantly absorbed in the grating-gated channel while temperature modulation is sensed by the resistance of a narrow center region biased to pinch off. Thermal isolation enhances the temperature rise on absorption. Detectors with and without the additional thermal isolation demonstrate a linear power dependence.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Thin metal intracavity contact and lateral current-distribution scheme for GaN-based vertical-cavity lasers

D. F. Feezell, R. M. Farrell, M. C. Schmidt, H. Yamada, M. Ishida, S. P. DenBaars, D. A. Cohen, and S. Nakamura

Appl. Phys. Lett. 90, 181128 (2007); http://dx.doi.org/10.1063/1.2736478 (3 pages) | Cited 1 time

Online Publication Date: 4 May 2007

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The authors report an effective lateral current-distribution scheme to achieve uniform hole injection in GaN-based vertical-cavity lasers. A thin ( ∼ 5 nm) intracavity Pd/Au layer is used to simultaneously achieve a low-resistance Ohmic contact and effective lateral current distribution across a circular injection aperture. Precise placement of a thin metal layer in a vertical-cavity laser is shown to yield negligible single-pass optical loss. Light-emitting diodes utilizing this intracavity contact and lateral current-distribution scheme are demonstrated, with effective lateral current distribution observed for aperture diameters up to 36 μm. Continuous-wave operation at current densities exceeding 10 kA/cm2 is demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.60.Jb Light-emitting devices

Formation of Si clusters in AlGaN: A study of local structure

A. Somogyi, G. Martinez-Criado, A. Homs, M. A. Hernandez-Fenollosa, D. Vantelon, and O. Ambacher

Appl. Phys. Lett. 90, 181129 (2007); http://dx.doi.org/10.1063/1.2736649 (3 pages) | Cited 2 times

Online Publication Date: 4 May 2007

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In this study, the authors report on the application of synchrotron radiation x-ray microprobe to the study of Si impurities in plasma-induced molecular beam epitaxy grown Al0.32Ga0.68N. Elemental maps obtained by μ-x-ray fluorescence spectrometry show inhomogeneous distributions of Si, Al, and Ga on the micron scale. X-ray absorption near-edge structure spectra taken at the Si and Al K edges provided information about their local chemical environment and revealed the change of the spectral features as depending on the position compared to the sample surface and on the concentration of Si.
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61.72.S- Impurities in crystals
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.uj III-V and II-VI semiconductors
78.70.Dm X-ray absorption spectra
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Characterization of multicapillary dielectric cathodes

J. Z. Gleizer, Y. Hadas, D. Yarmolich, J. Felsteiner, and Ya. E. Krasik

Appl. Phys. Lett. 90, 181501 (2007); http://dx.doi.org/10.1063/1.2735544 (3 pages) | Cited 10 times

Online Publication Date: 2 May 2007

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Parameters of the plasma and electron beam produced by a multicapillary cathode in a diode powered by a ∼ 200 kV, ∼ 300 ns pulse are presented. It was found that the source of electrons is the plasma ejected from the capillaries. Inside the capillaries this plasma obtains electron density and temperature of ∼ 8×1015 cm−3 and ∼ 5 eV, respectively. In the vicinity of the cathode, the density and temperature of the plasma electrons were found to be 2×1014 cm−3 and 4.5 eV, respectively, for electron current density of ∼ 40 A/cm2. It was shown that the plasma expansion velocity is in the range of (1–2)×106 cm/s for current density of >12 A/cm2.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.50.Dg Plasma sources
52.40.Mj Particle beam interactions in plasmas
52.25.Tx Emission, absorption, and scattering of particles
52.25.Fi Transport properties
52.70.La X-ray and γ-ray measurements

Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength

J. White, P. Dunne, P. Hayden, F. O’Reilly, and G. O’Sullivan

Appl. Phys. Lett. 90, 181502 (2007); http://dx.doi.org/10.1063/1.2735944 (3 pages) | Cited 26 times

Online Publication Date: 4 May 2007

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Extreme ultraviolet lithography requires a light source at 13.5 nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO2 lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO2 laser. The influence of reduced electron density in the CO2 laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Acoustic wave propagation in a macroscopically inhomogeneous porous medium saturated by a fluid

L. De Ryck, J.-P. Groby, P. Leclaire, W. Lauriks, A. Wirgin, Z. E. A. Fellah, and C. Depollier

Appl. Phys. Lett. 90, 181901 (2007); http://dx.doi.org/10.1063/1.2431570 (3 pages) | Cited 15 times

Online Publication Date: 30 April 2007

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The equations of motion in a macroscopically inhomogeneous porous medium saturated by a fluid are derived. As a verification of their validity, these equations are reduced and solved for rigid frame porous systems. The reflection and transmission coefficients and their corresponding time signals are calculated numerically using wave splitting Green’s function approach for a two-layer porous system considered as one single porous layer with a sudden change in physical properties. The results are compared to experimental results and to those of the classical transfer matrix method for materials saturated by air in the ultrasonic frequency range.
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62.65.+k Acoustical properties of solids
61.43.Gt Powders, porous materials

Photoluminescence of individual doped GaAs/AlGaAs nanofabricated quantum dots

Sokratis Kalliakos, César Pascual García, Vittorio Pellegrini, Marian Zamfirescu, Lucia Cavigli, Massimo Gurioli, Anna Vinattieri, Aron Pinczuk, Brian S. Dennis, Loren N. Pfeiffer, and Ken W. West

Appl. Phys. Lett. 90, 181902 (2007); http://dx.doi.org/10.1063/1.2734397 (3 pages) | Cited 7 times

Online Publication Date: 30 April 2007

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Dilute arrays of GaAs/AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2 meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
71.35.-y Excitons and related phenomena

Shear strain in a shear band of a bulk-metallic glass in compression

W. H. Jiang, F. X. Liu, P. K. Liaw, and H. Choo

Appl. Phys. Lett. 90, 181903 (2007); http://dx.doi.org/10.1063/1.2734502 (3 pages) | Cited 18 times

Online Publication Date: 30 April 2007

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Using an infrared camera, the authors observe in situ the dynamic shear-banding operations in the geometrically constrained specimens of a bulk-metallic glass during compression at various strain rates. Based on the observed number of shear bands in a collection of simultaneous shear-banding operations that cause a serration, the authors calculate the shear strains in individual shear bands. The results demonstrate that the shear strain in a shear band is up to 103%–104% and dependent on strain rates. The higher the strain rates, the larger the strain in a shear band.
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81.05.Kf Glasses (including metallic glasses)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties

Y. J. Zhou, Y. Zhang, Y. L. Wang, and G. L. Chen

Appl. Phys. Lett. 90, 181904 (2007); http://dx.doi.org/10.1063/1.2734517 (3 pages) | Cited 60 times

Online Publication Date: 30 April 2007

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Alloys with composition of AlCoCrFeNiTix (x: molar ratio; x = 0,0.5,1,1.5) were designed by using the strategy of equiatomic ratio and high entropy of mixing. The alloy system is composed mainly of body centered cubic solid solution and possesses excellent room-temperature compressive mechanical properties. Particularly for AlCoCrFeNiTi0.5 alloy, the yield stress, fracture strength, and plastic strain are as high as 2.26 GPa, 3.14 GPa, and 23.3%, respectively, which are superior to most of the high-strength alloys such as bulk metallic glasses.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials

Surface plasmon resonance of gold nano-sea-urchin

Yen Hsun Su, Wei Hao Lai, Wei-Yu Chen, Min Hsiung Hon, and Shih-Hui Chang

Appl. Phys. Lett. 90, 181905 (2007); http://dx.doi.org/10.1063/1.2732823 (3 pages) | Cited 4 times

Online Publication Date: 30 April 2007

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The authors synthesized high-quality gold nano-sea-urchin in aqueous solution with an environment-friendly method. They found that the gold nano-sea-urchin can induce the interaction of surface plasmon resonance (SPR) mode with substrate. The SPR peak splits and blueshifts from 630 to 440 nm and the result has potential application for enhanced-Raman scattering, optical communications, and solar cells.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations

Effect of residual solvent and thermal annealing on a light-emitting polymer-based electrochemical cell

Wei Zhao and J. M. White

Appl. Phys. Lett. 90, 181906 (2007); http://dx.doi.org/10.1063/1.2734392 (3 pages)

Online Publication Date: 30 April 2007

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The effect of residual solvents and thermal annealing on light-emitting electrochemical cells constructed using poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] and poly(ethylene oxide) (PEO) doped with lithium trifluoromethanesulfonate (Li triflate) was investigated. The turn-on voltage dropped when the films were annealed in dry and vacuum atmospheres. This is attributed to the removal of residual solvents that are detected by mass spectrometry in ultrahigh vacuum. The results are interpreted in terms of a model in which ionized Li triflate has higher ionic conductivity in the presence of dry PEO than when solvated by water or cyclohexanone within a PEO matrix.
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82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices

Atomic arrangement variations of [0001]-tilt grain boundaries in ZnO thin films grown on p-Si substrates due to thermal treatment

J. W. Shin, J. Y. Lee, Y. S. No, J. H. Jung, T. W. Kim, and W. K. Choi

Appl. Phys. Lett. 90, 181907 (2007); http://dx.doi.org/10.1063/1.2732177 (3 pages) | Cited 3 times

Online Publication Date: 30 April 2007

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The plane-view high-resolution transmission electron microscopy (HRTEM) images in ZnO thin films grown on p-Si substrates showed that (10math0) asymmetric grain boundaries with a periodic array of strain contrast features existed in a sparse columnar structure for as-grown ZnO thin films and that (11math0) asymmetric grain boundaries and (85math0) symmetric grain boundaries existed in a dense columnar structure for annealed ZnO thin films. The atomic arrangement variations of [0001]-tilt grain boundaries in ZnO thin films grown on Si substrates due to thermal treatment are described on the basis of the HRTEM results.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
61.72.Cc Kinetics of defect formation and annealing
68.37.Lp Transmission electron microscopy (TEM)

Coefficient of thermal expansion and biaxial elastic modulus of β phase tantalum thin films

Robert Knepper and Shefford P. Baker

Appl. Phys. Lett. 90, 181908 (2007); http://dx.doi.org/10.1063/1.2734468 (3 pages) | Cited 6 times

Online Publication Date: 1 May 2007

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The coefficient of thermal expansion and biaxial elastic modulus of metastable tetragonal β-tantalum thin films were determined from the thermoelastic slopes of films deposited on (100) silicon and fused silica substrates. Measurements were made during heating, when the film was in the β phase, and during cooling, after the film had transformed to the stable bcc α phase. While the thermal expansion coefficients of the two phases were similar, β phase films were much more compliant than α films. The thermal expansion coefficient and biaxial elastic modulus of the α phase were consistent with values reported for bulk α tantalum.
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68.60.Bs Mechanical and acoustical properties
65.40.De Thermal expansion; thermomechanical effects
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Gh Other heat and thermomechanical treatments

Dimensional transition of CdxZn1−xTe nanostructures grown on ZnTe layers

H. S. Lee, H. L. Park, and T. W. Kim

Appl. Phys. Lett. 90, 181909 (2007); http://dx.doi.org/10.1063/1.2734479 (3 pages) | Cited 8 times

Online Publication Date: 1 May 2007

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The atomic force microscopy images showed that the dimensional structural transformation from CdxZn1−xTe quantum dots (QDs) with Cd mole fractions of 0.5 and 0.6 to CdxZn1−xTe quantum wires occurred at a Cd mole fraction of 0.8. Photoluminescence spectra showed that the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band in CdxZn1−xTe/ZnTe nanostructures shifted to a lower energy with increasing Cd mole fraction. The activation energy of the electrons confined in the CdxZn1−xTe/ZnTe QDs with a Cd mole fraction of 0.6 was higher than those of electrons in CdxZn1−xTe/ZnTe nanostructures.
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64.70.K- Solid-solid transitions
68.65.La Quantum wires (patterned in quantum wells)
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors
73.21.Hb Quantum wires
73.21.La Quantum dots

Binary-collision modeling of ion-induced stress relaxation in cubic BN and amorphous C thin films

B. Abendroth, H. U. Jäger, W. Möller, and M. Bilek

Appl. Phys. Lett. 90, 181910 (2007); http://dx.doi.org/10.1063/1.2734472 (3 pages) | Cited 2 times

Online Publication Date: 1 May 2007

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It is demonstrated that ion-bombardment-induced stress release during physical vapor deposition of cubic boron nitride (cBN) and amorphous carbon (aC) films is related to collisional relocation of atoms. A model based on TRIM and molecular dynamics computer simulations is presented. Experimental results obtained using pulsed substrate bias are in good agreement with the model predictions at adequately chosen threshold energies of atomic relocation. The collisional relaxation model describes the experimental data significantly better than the widely applied thermal spike model.
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68.60.Bs Mechanical and acoustical properties
61.80.Jh Ion radiation effects
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.43.Er Other amorphous solids

Isotopic study of the nitrogen-related modes in N+-implanted ZnO

L. Artús, R. Cuscó, E. Alarcón-Lladó, G. González-Díaz, I. Mártil, J. Jiménez, B. Wang, and M. Callahan

Appl. Phys. Lett. 90, 181911 (2007); http://dx.doi.org/10.1063/1.2734474 (3 pages) | Cited 14 times

Online Publication Date: 1 May 2007

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Micro-Raman measurements were performed to study the nitrogen-related modes in ZnO samples implanted with N+. The two stable N isotopes, 14N and 15N, were implanted. Distinct peaks at 277 and 512 cm−1 are observed irrespective of the implanted isotope, both before and after rapid thermal annealing. The insensitivity of the mode frequencies to the implanted isotope rules out the explanation of these modes as local vibrational modes involving N motion. These modes were not detected in ZnO samples implanted with Zn+, O+, or P+, which suggests that they may be associated with distortions∕defects favored by the presence of N.
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63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors

Anodic nanoclusters of GaN

Keunjoo Kim, Jaeho Choi, and Tae Sung Bae

Appl. Phys. Lett. 90, 181912 (2007); http://dx.doi.org/10.1063/1.2734901 (3 pages) | Cited 6 times

Online Publication Date: 1 May 2007

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The authors report an anodization of the deposited Al layer on a p-GaN surface of InGaN/GaN multiquantum-well light-emitting-diode structures, which forms the anodic nanoclusters of GaN as well as the disordered alumina nanopore layer. The GaN nanoclusters show the shape of the radial hemisphere similar to an orange. The formation mechanism comes from the nanofluidic channel for supplying the electrolyte in electrochemical etching reaction. The nanorods with a diameter of about 100 nm in nanocluster structures enhance the photoluminescence intensity by three times compared to the bare sample without anodization.
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85.60.Jb Light-emitting devices
81.65.Cf Surface cleaning, etching, patterning

Sellmeier equations for green, yellow, and orange colored HgGa2S4 crystals

Tie-Jun Wang, Zhi-Hui Kang, Hong-Zhi Zhang, Zhi-Shu Feng, Feng-Guang Wu, Hai-Yan Zang, Yun Jiang, Jin-Yue Gao, Yury Andreev, Grigory Lanskii, Victor Atuchin, and Oleg Parasyuk

Appl. Phys. Lett. 90, 181913 (2007); http://dx.doi.org/10.1063/1.2734923 (3 pages) | Cited 2 times

Online Publication Date: 1 May 2007

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Modeling and experimental study on phase matching of second harmonic generation in different color HgGa2S4 crystals are carried out. Using the known Sellmeier equations, the dispersion relation with weighting proportionally to short-wavelength boundary of the crystal transparency band is proposed. Optimal dispersion relations and phase-matched conditions for different color HgGa2S4 crystals can be specified.
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42.70.Mp Nonlinear optical crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Application of Czochralski-grown SiGe bulk crystal as a substrate for luminescent strained quantum wells

Noritaka Usami, Ryota Nihei, Ichiro Yonenaga, Yoshitaro Nose, and Kazuo Nakajima

Appl. Phys. Lett. 90, 181914 (2007); http://dx.doi.org/10.1063/1.2735286 (3 pages) | Cited 3 times

Online Publication Date: 1 May 2007

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Czochralski-grown Si1−xGex bulk crystal (x = 0.085) was utilized as a substrate for strained Si-based quantum wells (QWs). The linewidth of the (400) x-ray rocking curve of the SiGe(100) substrate was comparable with that of the Si(100) substrate, and no peak splitting was observed in the line scan all over the substrate. Epitaxial growth of strained QWs designed as a couple of strained Si/strained Ge QWs have been attempted simultaneously on SiGe(100) and Si(100). Photoluminescence measurements revealed that the sample on SiGe(100) exhibits peaks from excitons confined in QWs without any dislocation-related luminescence in contrast to that on Si(100).
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81.10.Fq Growth from melts; zone melting and refining
68.65.Fg Quantum wells
78.67.De Quantum wells
81.07.St Quantum wells
78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena

Photoluminescence properties of Cr2+:ZnSe films deposited by radio frequency magnetron cosputtering

N. Vivet, M. Morales, M. Levalois, J. L. Doualan, and R. Moncorgé

Appl. Phys. Lett. 90, 181915 (2007); http://dx.doi.org/10.1063/1.2735284 (3 pages) | Cited 7 times

Online Publication Date: 1 May 2007

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Cr2+:ZnSe films were grown at room temperature by the radio frequency magnetron cosputtering technique. The structural characterization of the films shows that the corresponding films are well crystallized mainly in the cubic zinc-blende structure with strong ⟨111⟩ orientations. Using direct (1850 nm) and indirect (visible) excitations, photoluminescence experiments in the midinfrared spectral region reveal that Cr is incorporated in the optically active Cr2+ state, and the shape of the spectra agrees with that reported for bulk materials. This study shows that magnetron cosputtering can provide viable structures for the realization of optically and electrically pumped midinfrared microlasers.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors

Angle multiplexed storage with object beam alone

Hon-Fai Yau and Jung-Ping Liu

Appl. Phys. Lett. 90, 181916 (2007); http://dx.doi.org/10.1063/1.2733629 (3 pages)

Online Publication Date: 2 May 2007

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Making use of the interference of incident light waves and the accompanying fanning waves in a photorefractive LiNbO3 crystal, the authors have recorded binary images as well as gray-tone images in a crystal with only an object beam. Angle multiplexing has also been demonstrated with this one beam recording method. Basing on a model that the recording is accomplished through the interference of the object light and its fanning light, the authors have estimated the minimal angular separation for achieving a cross-talk-free multiplexing.
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42.79.Vb Optical storage systems, optical disks
42.70.Ln Holographic recording materials; optical storage media
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials

Observation of largely enhanced hardness in nanomultilayers of the Ag–Nb system with positive enthalpy of formation

W. S. Lai and M. J. Yang

Appl. Phys. Lett. 90, 181917 (2007); http://dx.doi.org/10.1063/1.2735670 (3 pages) | Cited 6 times

Online Publication Date: 2 May 2007

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Ag/Nb nanomultilayers with different modulation wavelengths Λ were prepared on silicon wafers by electron beam evaporation. Nanoindenter measurements show that with decreasing Λ of the multilayers, the nanohardness increases up to ∼ 80% for Λ = 4 nm, whereas the modulus is almost unchanged. This unusual behavior originates from a unique microstructure where amorphous Ag–Nb alloys form at the interfaces and grain boundaries of silver nanoparticles, as observed by cross-section high resolution transmission electron microscopy. The amorphous phases favor hardness enhancement by preventing dislocation emission and movement, whereas they have a negative contribution to the modulus because of their free volume.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Bx Metals, semimetals, and alloys
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.25.-g Mechanical properties of nanoscale systems
68.65.Ac Multilayers

Strain analysis in ultrathin SiGe-on-insulator layers formed from strained Si-on-insulator substrates by Ge-condensation process

Tsutomu Tezuka, Norio Hirashita, Yoshihiko Moriyama, Shu Nakaharai, Naoharu Sugiyama, and Shin-ichi Takagi

Appl. Phys. Lett. 90, 181918 (2007); http://dx.doi.org/10.1063/1.2735672 (3 pages) | Cited 13 times

Online Publication Date: 2 May 2007

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Ultrathin strained SiGe-on-insulator (sSGOI) layers were fabricated by Ge condensation, in which Si1−xGex layers on strained Si-on-insulator (sSOI) substrates were oxidized, and their strain and defects were investigated. With increasing the Ge fraction x, the compressive strain in the SGOI layers was found to linearly increase up to ∼ 2%. The linear strain dependence on x was offset by the preexisting tensile strain in the sSOI substrate compared to that of conventional SGOI layers formed on unstrained SOI substrates. As a result, pseudomorphic sSGOI layers were obtained on the sSOI substrate up to higher x ( ∼ 0.75) than on a SOI substrate.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Intersubband absorption with different sublevel couplings in [(CdS/ZnSe/BeTe)/(ZnSe/BeTe)] double quantum wells

G. W. Cong, R. Akimoto, K. Akita, T. Hasama, and H. Ishikawa

Appl. Phys. Lett. 90, 181919 (2007); http://dx.doi.org/10.1063/1.2735930 (3 pages) | Cited 6 times

Online Publication Date: 2 May 2007

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The authors demonstrated the strong sublevel coupling on the intersubband absorption at telecommunication wavelengths in asymmetric II-VI double quantum wells consisting of a deep CdS well and a shallow ZnSe well coupled by a 1-monolayer-thick BeTe barrier. With increasing ZnSe well thickness, the sublevel coupling between excited states first increases to a maximum and then decreases, which results in a transition energy anticrossing and a reverse intensity evolution for e1-e2 and e1-e3 transitions. These results are in good agreement with the self-consistent Schrödinger-Poisson calculation. For optical switch applications, the sublevel-coupling-dependent relaxation time could be increased to lower the switching energy.
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78.67.De Quantum wells
73.21.Fg Quantum wells
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
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