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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Two-dimensional micromanipulation using liquid crystals

Yoshitaka Mieda and Katsushi Furutani

Appl. Phys. Lett. 86, 101901 (2005); http://dx.doi.org/10.1063/1.1872218 (3 pages) | Cited 7 times

Online Publication Date: 28 February 2005

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We developed a two-dimensional micromanipulation method using liquid crystals. The combination of the backflow effect in the twisted nematic cell and the electrostatic force for the naturally charged microparticles causes the net movement. By adjusting the polarity and the duty ratio of the rectangular voltage, the particles can be driven two-dimensionally and bidirectionally. The velocity of the particles depended on the duty ratio, amplitude, and frequency of the applied voltage.
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07.10.Cm Micromechanical devices and systems
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
87.80.Fe Micromanipulation of biological structures

Raman active phonon modes and heat capacities of Ti2AlC and Cr2AlC ceramics: first-principles and experimental investigations

Jingyang Wang, Yanchun Zhou, Zhijun Lin, Fanling Meng, and Feng Li

Appl. Phys. Lett. 86, 101902 (2005); http://dx.doi.org/10.1063/1.1873057 (3 pages) | Cited 23 times

Online Publication Date: 28 February 2005

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Raman active phonon frequencies and corresponding vibrational eigenmodes are reported for two M2AlC ceramics, Ti2AlC and Cr2AlC, by means of first-principles calculations. The theoretical modes are approved by the experimental Raman spectrum for Ti2AlC. Compared with that of the Ti3SiC2 counterpart, the number of Raman active modes is definitely determined by the chemical formula of transition-metal carbide layers; for example, TiC0.67 in Ti3SiC2 and TiC0.5 in M2AlC. All active modes originate from stretching and bending of Al–M–C covalent bond chains, whereas the vibration of M–C bond localized inside the M6C octahedra is not Raman active. The differences in vibration characteristics between Ti2AlC and Cr2AlC are discussed in terms of atomic force constants. By including the phonon and electron contributions, trends in heat capacities as a function of temperature were illustrated and compared.
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78.20.Fm Birefringence
82.45.Xy Ceramics in electrochemistry
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
63.50.-x Vibrational states in disordered systems

Comparison of blue and green InGaN/GaN multiple-quantum-well light-emitting diodes grown by metalorganic vapor phase epitaxy

Y. D. Qi, H. Liang, D. Wang, Z. D. Lu, W. Tang, and K. M. Lau

Appl. Phys. Lett. 86, 101903 (2005); http://dx.doi.org/10.1063/1.1866634 (3 pages) | Cited 24 times

Online Publication Date: 1 March 2005

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InGaN/GaN multiple-quantum-well (MQW) blue and green-light-emitting diodes (LEDs) were grown on sapphire substrates using metalorganic vapor phase epitaxy. High-resolution transmission microscopy shows that a much larger density of stacking faults exist in the quantum-well region of the blue LEDs than in the green LEDs. In the green LEDs, the blueshift in the electroluminescence (EL) emission energy at larger driving currents is more prominent than in the blue LEDs, which is explained by different strength of quantum-confined Stark effect as a result of different piezoelectric field intensity by different scales of strain relaxation in the blue and green MQWs. The steady broadening of the EL emission energy linewidth on the higher energy side with the increase of the driving current was observed in both blue and green LEDs, which is attributed to the band filling effect.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
78.60.Fi Electroluminescence
78.20.Jq Electro-optical effects
68.65.Fg Quantum wells
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Nn Stacking faults and other planar or extended defects
77.65.Ly Strain-induced piezoelectric fields
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Lp Transmission electron microscopy (TEM)

Optically probed wetting layer in InAs/InGaAlAs/InP quantum-dash structures

W. Rudno-Rudziński, G. Sęk, K. Ryczko, R. Kudrawiec, J. Misiewicz, A. Somers, R. Schwertberger, J. P. Reithmaier, and A. Forchel

Appl. Phys. Lett. 86, 101904 (2005); http://dx.doi.org/10.1063/1.1881782 (3 pages) | Cited 18 times

Online Publication Date: 1 March 2005

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Photoluminescence and photoreflectance measurements have been performed to investigate molecular-beam-epitaxy-grown InAs/InGaAlAs/InP structures with different-size InAs quantum dashes. Optical features related to all relevant parts of the structure have been detected and recognized, including a line which has been attributed to the ground-state wetting layer quantum well transition. The spectral position of the latter is independent of the nominal InAs layer thickness in contrast to quantum-dash emission peak, which shifts sequentially to the red due to an increase of the islands’ size. The interpretation has been supported by energy level calculations showing that the wetting layer has to be approximately 2 ML thick and that only one state is confined in such a thin well for each kind of carriers, i.e., electrons, heavy, and light holes.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Mechanisms of B deactivation control by F co-implantation

N. E. B. Cowern, B. Colombeau, J. Benson, A. J. Smith, W. Lerch, S. Paul, T. Graf, F. Cristiano, X. Hebras, and D. Bolze

Appl. Phys. Lett. 86, 101905 (2005); http://dx.doi.org/10.1063/1.1870131 (3 pages) | Cited 37 times

Online Publication Date: 1 March 2005

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Thermal annealing after preamorphization and solid-phase epitaxy of ultrashallow B implants leads to deactivation and diffusion driven by interstitials released from end-of-range defects. F inhibits these processes by forming small clusters that trap interstitials. A competing B–F interaction causes deactivation when F and B profiles overlap. Both pathways suppress B transient enhanced diffusion.
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61.72.uf Ge and Si
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals

High pressure study of Ti4AlN3 to 55 GPa

Bouchaib Manoun, S. K. Saxena, and M. W. Barsoum

Appl. Phys. Lett. 86, 101906 (2005); http://dx.doi.org/10.1063/1.1875750 (3 pages) | Cited 29 times

Online Publication Date: 1 March 2005

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Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti4AlN3 sample up to a pressure of 55 GPa. No phase transformations were observed. As observed in Ti3SiC2, Ti3Si0.5Ge0.5C2, and Zr2InC, the compressibility of Ti4AlN3 along the c axis was larger than along the a axis which leads to a decrease in the c/a ratio with increasing pressure. The bulk modulus is 216±2 GPa, with a pressure derivative of 3.84±0.06.
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81.05.Mh Cermets, ceramic and refractory composites
62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Plastic flow localization in bulk tungsten with ultrafine microstructure

Q. Wei, K. T. Ramesh, E. Ma, L. J. Kesckes, R. J. Dowding, V. U. Kazykhanov, and R. Z. Valiev

Appl. Phys. Lett. 86, 101907 (2005); http://dx.doi.org/10.1063/1.1875754 (3 pages) | Cited 27 times

Online Publication Date: 3 March 2005

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Shear localization is demonstrated in bulk tungsten (W) of commercial purity under dynamic uniaxial compression. Microstructure refinement via severe plastic deformation was the strategy used to induce this unusual deformation mode for W. The ultrafine microstructure achieved in bcc materials leads to elevated strength and ductility, as well as reduced strain hardening and strain rate hardening, thus enhancing the propensity for adiabatic plastic flow localization.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Growth and characterization of single quantum dots emitting at 1300 nm

B. Alloing, C. Zinoni, V. Zwiller, L. H. Li, C. Monat, M. Gobet, G. Buchs, A. Fiore, E. Pelucchi, and E. Kapon

Appl. Phys. Lett. 86, 101908 (2005); http://dx.doi.org/10.1063/1.1872213 (3 pages) | Cited 64 times

Online Publication Date: 3 March 2005

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We have optimized the molecular-beam epitaxy growth conditions of self-organized InAs/GaAs quantum dots (QDs) to achieve a low density of dots emitting at 1300 nm at low temperature. We used an ultralow InAs growth rate, lower than 0.002 ML/s, to reduce the density to 2 dots/μm2 and an InGaAs capping layer to achieve longer emission wavelength. Microphotoluminescence spectroscopy at low-temperature reveals emission lines characteristic of exciton-biexciton behavior. We also study the temperature dependence of the photoluminescence, showing clear single QD emission up to 90 K. With these results, InAs/GaAs QDs appear as a very promising system for future applications of single photon sources in fiber-based quantum cryptography.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
73.21.La Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

Luminescence studies of Ti-doped Al2O3 using vacuum ultraviolet synchrotron radiation

V. B. Mikhailik, H. Kraus, D. Wahl, and M. S. Mykhaylyk

Appl. Phys. Lett. 86, 101909 (2005); http://dx.doi.org/10.1063/1.1880451 (3 pages) | Cited 10 times

Online Publication Date: 3 March 2005

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In this study, we examined the luminescence response of Ti-doped Al2O3 crystals to high-energy vacuum ultraviolet (UV) excitation. In addition to the thoroughly studied emission band of Ti3+ in the near-infrared region and blue emission at 420 nm, we detected a UV emission band at 290 nm. The excitation spectra of all emission bands were measured over the 4–20 eV spectral range. Our results indicate that intrinsic anion defects are involved in the process of the excitation of the 420 nm emission assigned to the charge transfer transitions 2pO2−→3dTi4+. Analysis of the spectral and decay characteristics of the UV emission enables us to suggest that this band is associated with radiative decay of excitons localized at Ti ions.
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78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Extremely low surface recombination velocity in GaInAsSb/AlGaAsSb heterostructures

C. A. Wang, D. A. Shiau, D. Donetsky, S. Anikeev, G. Belenky, and S. Luryi

Appl. Phys. Lett. 86, 101910 (2005); http://dx.doi.org/10.1063/1.1873042 (3 pages) | Cited 5 times

Online Publication Date: 3 March 2005

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Low surface recombination velocity is critical to the performance of minority carrier devices. Minority carrier lifetime in double heterostructures (DHs) of 0.53-eV p-GaInAsSb confined with 1.0-eV p-AlGaAsSb, and grown lattice-matched to GaSb, was measured by time-resolved photoluminescence. The structures were designed to be dominated by the heterointerface while minimizing the contribution of photon recycling to minority carrier lifetime. Surface recombination velocity as low as 30 cm/s for DHs was achieved. This value is over an order of magnitude lower than that reported in previous studies.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena

Relaxation of packaging-induced strains in AlGaAs-based high-power diode laser arrays

Tran Quoc Tien, Axel Gerhardt, Sandy Schwirzke-Schaaf, Jens W. Tomm, Holger Müntz, Jens Biesenbach, Myriam Oudart, Julien Nagle, and Mark L. Biermann

Appl. Phys. Lett. 86, 101911 (2005); http://dx.doi.org/10.1063/1.1880438 (3 pages) | Cited 1 time

Online Publication Date: 3 March 2005

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We monitor the mechanical strain evolution with typical use in the quantum well of AlGaAs/GaAs-based high-power diode laser arrays (cm bars) by spectroscopic means. We show experimentally that pristine devices are essentially uniaxially compressed along the 110-direction with a strain maximum of −0.16% at the center of the device. At the device edges, almost no packaging-induced strain is detectable. After 500 h of continuous wave operation at a current of I = 80 A, the strain is reduced by 50%. Furthermore, we observe the growth of a localized region of compressive strain, of hydrostatic symmetry, in one emitter of a particular cm-bar. A compression of about −0.017% is observed, and is most likely caused by point defect accumulation. Our results demonstrate information about absolute strain values and, at least in part, about strain symmetry as well can be obtained by spectroscopic means even within packaged complex optoelectronic devices.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Effects of Eu interfacial mobility on the growth of epitaxial EuBa2Cu3O7−δ films

H. Wang, X. Z. Liao, H. F. Xu, X. Zhang, Y. Lin, S. R. Foltyn, P. N. Arendt, J. L. MacManus-Driscoll, Y. T. Zhu, and Q. X. Jia

Appl. Phys. Lett. 86, 101912 (2005); http://dx.doi.org/10.1063/1.1881779 (3 pages)

Online Publication Date: 4 March 2005

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By inserting a thin YBa2Cu3O7−δ (Y123) seed layer, high quality EuBa2Cu3O7−δ (Eu123) films can grow with epitaxial c-axis orientation on SrTiO3 (STO) substrate without increasing the growth temperature. The interfacial structures of Eu123/STO and Eu123/Y123/STO were investigated using scanning transmission electron microscopy. Results show that the Eu mobility on the STO substrate is very low at the regular deposition temperature. This leads to nonuniform composition distribution at the Eu123/STO interface and a mixture of c-axis and a-axis growth. A thin Y123 seed layer greatly improves the Eu mobility and therefore facilitates high quality c-axis growth.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
68.55.A- Nucleation and growth
74.72.-h Cuprate superconductors
74.25.F- Transport properties
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification
81.15.Kk Vapor phase epitaxy; growth from vapor phase
74.78.Fk Multilayers, superlattices, heterostructures
81.15.Fg Pulsed laser ablation deposition
68.37.Lp Transmission electron microscopy (TEM)

Enhanced boron activation in silicon by high ramp-up rate solid phase epitaxial regrowth

B. J. Pawlak, W. Vandervorst, A. J. Smith, N. E. B. Cowern, B. Colombeau, and X. Pages

Appl. Phys. Lett. 86, 101913 (2005); http://dx.doi.org/10.1063/1.1882756 (3 pages) | Cited 18 times

Online Publication Date: 4 March 2005

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We investigate the influence of thermal conditions during solid phase epitaxial regrowth (SPER) on the electrical activation level of boron in preamorphized silicon, both with respect to heating ramp rates and the use of low temperature preanneals. Enhancement of electrically active boron concentration by 36% is observed for activation with the fastest ramp rate (487 °C/s) compared to the slowest one (1 °C/s). An important clustering pathway occurs within the amorphous silicon phase (during low temperature preanneal) prior to completion of the SPER process. In these junctions boron deactivation during isochronal post-annealing is almost independent on the maximum boron activation level.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.uf Ge and Si
61.72.S- Impurities in crystals
81.15.Np Solid phase epitaxy; growth from solid phases
61.72.Cc Kinetics of defect formation and annealing

Scintillators based on aromatic dye molecules doped in a sol-gel glass host

M. Nikl, N. Solovieva, K. Apperson, D. J. S. Birch, and A. Voloshinovskii

Appl. Phys. Lett. 86, 101914 (2005); http://dx.doi.org/10.1063/1.1882758 (3 pages) | Cited 4 times

Online Publication Date: 4 March 2005

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Ultraviolet and x-ray excited luminescence of fluorescein and rhodamine-6G doped sol-gel glasses were studied at room temperature with the aim of characterizing and understanding the scintillation performance of such materials. Fast energy transfer from the glass host to the dye luminescent centers was found. While the overall radioluminescence efficiency was rather low due to nonradiative losses in the glass host, our results demonstrate the potential of sol-gel technology as a versatile tool in controlling the spectral and time response of such unusual organic–inorganic scintillators.
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42.70.Ce Glasses, quartz
78.55.Qr Amorphous materials; glasses and other disordered solids

Deformation twinning during nanoindentation of nanocrystalline Ta

Y. M. Wang, A. M. Hodge, J. Biener, A. V. Hamza, D. E. Barnes, Kai Liu, and T. G. Nieh

Appl. Phys. Lett. 86, 101915 (2005); http://dx.doi.org/10.1063/1.1883335 (3 pages) | Cited 26 times

Online Publication Date: 4 March 2005

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The deformation mechanism of body-centered cubic (bcc) nanocrystalline tantalum with grain sizes of 10–30 nm is investigated by nanoindentation, scanning electron microscopy and high-resolution transmission electron microscopy. In a deviation from molecular dynamics simulations and existing experimental observations on other bcc nanocrystalline metals, the plastic deformation of nanocrystalline Ta during nanoindentation is controlled by deformation twinning. The observation of multiple twin intersections suggests that the physical mechanism of deformation twinning in bcc nanocrystalline materials is different from that in face-centered cubic (fcc) nanocrystalline metals.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
68.35.Gy Mechanical properties; surface strains
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Scanning electron microscopy of dopant distribution in semiconductors

P. G. Merli, V. Morandi, G. Savini, M. Ferroni, and G. Sberveglieri

Appl. Phys. Lett. 86, 101916 (2005); http://dx.doi.org/10.1063/1.1883708 (3 pages) | Cited 4 times

Online Publication Date: 4 March 2005

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We show that, in scanning electron microscopy, it is possible to use the secondary electrons produced by the backscattered electrons to obtain chemical information on the dopant distribution in Sb-implanted silicon. Theoretical investigations and experimental data concur to point out that the resolution of the method is defined by the probe size—values of 1 nm or even lower are possible in the present instruments—while the contrast depends on the electron range and on the boundary conditions. A proper choice of beam energy and boundaries of the doped layer may allow a sensitivity below 1%, suitable to characterize the high-dose near-surface region of the ultrashallow junctions in cross-sectioned bulk specimens.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.72.S- Impurities in crystals
79.20.Hx Electron impact: secondary emission
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