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3 May 2004

Volume 84, Issue 18, pp. 3435-3703

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 3648 (2004); http://dx.doi.org/10.1063/1.1737470 (3 pages)

Jingbo Li and Lin-Wang Wang
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Epitaxial growth of AlxGa1−xN on Si(111) via a ZrB2(0001) buffer layer

John Tolle, John Kouvetakis, Dae-Woo Kim, S. Mahajan, A. Bell, Fernando A. Ponce, I. S. T. Tsong, Michael L. Kottke, and Zhihao D. Chen

Appl. Phys. Lett. 84, 3510 (2004); http://dx.doi.org/10.1063/1.1738944 (3 pages) | Cited 9 times

Online Publication Date: 20 April 2004

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Epitaxial growth of an Al0.2Ga0.8N(0001) film by metalorganic chemical vapor deposition (MOCVD) at 1050 °C on a Si(111) substrate via a ZrB2(0001) buffer layer has been accomplished free of unintentional Si doping. The in-plane lattice mismatch between Al0.2Ga0.8N(0001) and ZrB2(0001) is only 0.3% and good epitaxial relation is established with [11math0]AlGaN//[11math0]ZrB2//[math10]Si. The cathodoluminescence (CL) spectrum of the Al0.2Ga0.8N shows a band-edge emission at 3.87 eV with full width at half maximum (FWHM) of 40 meV. Both the intensity and FWHM of the CL emission are comparable to those from a high-quality undoped Al0.2Ga0.8N film grown by MOCVD on sapphire. The close lattice match and the reflective nature of the ZrB2(0001) buffer layer are both attributes accountable for the optical quality of the Al0.2Ga0.8N grown on Si(111). © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
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Optical coupling between a self-assembled microsphere grating and a rib waveguide

Chao-Yi Tai, Bayram Unal, James S. Wilkinson, Mohamed A. Ghanem, and Philip N. Bartlett

Appl. Phys. Lett. 84, 3513 (2004); http://dx.doi.org/10.1063/1.1739275 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2004

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We report the fabrication of a linear array of self-assembled polystyrene microspheres side coupled to a rib waveguide. The optical coupling between the lateral evanescent field and the periodically perturbed effective refractive index alongside the waveguide results in a transmission stopband at the Bragg wavelength. The observed transmission spectrum shows a notch centered at λ≈1590 nm, which is in close agreement with theory. The coupling coefficient, κ, and the spectral response are derived for variable cladding medium index using perturbation theory. Structures of this type are expected to find application in wavelength selection, optical sensing, and optical delays. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
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Large high-frequency magnetoelectric response in laminated composites of piezoelectric ceramics, rare-earth iron alloys and polymer

Ning Cai, Ce-Wen Nan, Junyi Zhai, and Yuanhua Lin

Appl. Phys. Lett. 84, 3516 (2004); http://dx.doi.org/10.1063/1.1739277 (3 pages) | Cited 44 times

Online Publication Date: 20 April 2004

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Multiferroic laminated composites consisting of lead-zirconate titanate (PZT)/polyvinylidene-fluoride (PVDF) and Tb–Dy–Fe alloy (Terfenol-D)/PVDF particulate composite layers, prepared by a simple hot-molding technique, are reported. In the laminated composites, the polymer PVDF is used just as a matrix binder. Our results demonstrate that the three-phase laminated composites exhibit remarkable magnetoelectric response especially at high frequency where an electromechanical resonance appears. The maximum magnetoelectric sensitivity of the laminated composites is as high as over 3000 mV/cm Oe at the resonance frequency of around 100 kHz. © 2004 American Institute of Physics.
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81.05.Qk Reinforced polymers and polymer-based composites
77.65.Bn Piezoelectric and electrostrictive constants
81.10.Fq Growth from melts; zone melting and refining
75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Bb Fe and its alloys
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Broadband laser mirrors made from porous silicon

W. H. Zheng, P. Reece, B. Q. Sun, and M. Gal

Appl. Phys. Lett. 84, 3519 (2004); http://dx.doi.org/10.1063/1.1739507 (3 pages) | Cited 22 times

Online Publication Date: 20 April 2004

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We have designed, fabricated, and tested laser mirrors made entirely from porous silicon (PSi). PSi high reflectors and output couplers were designed for continuous-wave and mode-locked Ti:Sapphire lasers that were tuned between 730 nm and 940 nm. The mode-locked version of this laser produced 80 fs pulses at 85 MHz, parameters very similar to those observed with the commercial mirrors. We also made a PSi-dye laser by inserting a dye-filled cuvette between two PSi mirrors that was pumped from the side with a pulsed, frequency doubled, Nd:YAG laser. Lasers working with the PSi mirrors exhibited stable operation over time. © 2004 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques
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High efficiency low operating voltage polymer light-emitting diodes with aluminum cathode

X. Y. Deng, W. M. Lau, K. Y. Wong, K. H. Low, H. F. Chow, and Y. Cao

Appl. Phys. Lett. 84, 3522 (2004); http://dx.doi.org/10.1063/1.1739510 (3 pages) | Cited 43 times

Online Publication Date: 20 April 2004

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By blending poly(ethylene glycol) (PEG) into an electroluminescence (EL) polymer, significantly enhanced EL efficiency in a polymer light-emitting diode (PLED) with aluminum electrode was achieved. An orange-color-emitting PLED with 10 wt % PEG blending achieved device efficiencies exceeding 2.6 cd/A for a wide range of bias voltage, which is more than two orders of magnitude higher than that of a similar PLED without the PEG blending. The enhanced efficiency was a result of the reduction of electron injection barrier height at the cathode–polymer interface. It is believed that interfacial interaction that is specific to Al plays an important role in the enhancement mechanism. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
42.70.Jk Polymers and organics
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Device deformation during low-frequency pulsed operation of high-power diode bars

Axel Gerhardt, Fritz Weik, Tien QuocTran, Jens W. Tomm, Thomas Elsaesser, Jens Biesenbach, Holger Müntz, Gabriele Seibold, and Mark L. Biermann

Appl. Phys. Lett. 84, 3525 (2004); http://dx.doi.org/10.1063/1.1739516 (3 pages) | Cited 6 times

Online Publication Date: 20 April 2004

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Thermal tuning rates of single emitters in “cm-bar” high-power diode laser arrays are analyzed. We find these tuning rates to consist of purely thermal and mechanical pressure contributions, of −0.48 and −0.08 meV(K)−1, respectively. We estimate the mechanical deformation such a device experiences during pulsed operation to be 0.07%, and then apply an adequate external force to single segments of cm bars. These single segments model the central emitters within the array. Effects that arise due to gradual aging, such as nonequilibrium carrier lifetime decrease, sheet carrier concentration increase, and defect concentration rise are monitored and analyzed over up to 2×106 deformation cycles. These experiments provide the basis for a type of accelerated aging experiment for device testing, especially of devices designed for low-frequency pulsed operation. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
85.30.Kk Junction diodes
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Crossover of thickness dependence of critical current density Jc(T,H) in YBa2Cu3O7−δ thick films

Qiang Li, M. Suenaga, Z. Ye, S. R. Foltyn, and H. Wang

Appl. Phys. Lett. 84, 3528 (2004); http://dx.doi.org/10.1063/1.1737067 (3 pages) | Cited 15 times

Online Publication Date: 20 April 2004

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Critical current density Jc as a function of temperature T and magnetic field H was studied for high quality YBa2Cu3O7−δ (YBCO) films with thickness d = 0.2, 1, and 3 μm by means of magnetization measurements of a circular disk in perpendicular field. We found that the thickness dependence of Jc(H) for the YBCO thick films crossovers at high fields for T>50 K, where the 0.2-μm-thick film carries significantly lower Jc(H) than the 3-μm-thick film at high fields, even though the zero- or low-field Jc for the 0.2-μm-thick film is more than twice the value for the 3-μm-thick film. © 2004 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
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Growth and properties of molecular beam epitaxially grown ferromagnetic Fe-doped TiO2 rutile films on TiO2(110)

Y. J. Kim, S. Thevuthasan, T. Droubay, A. S. Lea, C. M. Wang, V. Shutthanandan, S. A. Chambers, R. P. Sears, B. Taylor, and B. Sinkovic

Appl. Phys. Lett. 84, 3531 (2004); http://dx.doi.org/10.1063/1.1703845 (3 pages) | Cited 39 times

Online Publication Date: 20 April 2004

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We have grown epitaxial Fe-doped TiO2 rutile films on rutile TiO2(110) substrates, and have explored the resulting compositional, structural, morphological and magnetic properties. Clusters of mixed TiO2 rutile and Fe3O4 form on the surface of a continuous rutile epitaxial film during growth. Room-temperature ferromagnetism is observed, and is associated with the formation of secondary phase Fe3O4 rather than a true diluted magnetic oxide semiconductor. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.50.Dd Nonmetallic ferromagnetic materials
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Birefringence reduction method for optical polymers by the orientation-inhibition effect of silica particles

Hisanori Ohkita, Yasuyuki Abe, Hiroshi Kojima, Akihiro Tagaya, and Yasuhiro Koike

Appl. Phys. Lett. 84, 3534 (2004); http://dx.doi.org/10.1063/1.1703846 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2004

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A method for reducing the orientational birefringence of polymers by doping with optically isotropic silica particles is reported. Particles with a diameter of 16 nm were selected and their surface was treated with dimethyldichlorosilane. Doping with 1 wt% of the particles reduced about 15% of the orientational birefringence of polycarbonate and poly(methylmethacrylate) films regardless of the sign and the magnitude of their birefringence. The analysis of the infrared dichroic ratio confirmed an effect in which the particles reduced the orientation of polycarbonate main chains. The effect that caused the reduction of birefringence was named “the orientation-inhibition effect.” © 2004 American Institute of Physics.
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42.70.Jk Polymers and organics
78.20.Fm Birefringence
61.72.S- Impurities in crystals
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Depth-resolving structural analysis of GaN layers by skew angle x-ray diffraction

A. Reiher, J. Bläsing, A. Dadgar, and A. Krost

Appl. Phys. Lett. 84, 3537 (2004); http://dx.doi.org/10.1063/1.1704870 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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The method of skew angle x-ray diffraction is presented as the example of GaN-based light emitting diodes (LED) grown by metalorganic vapor phase epitaxy on silicon substrates. This technique in conjunction with a newly developed calculation algorithm allows the depth-resolving structural analysis of multilayer structures. The analysis algorithm, basing on a triangular matrix approximation for the intensity decrease in dependence on the layer depth, the absorption coefficient, and the incident angle, provides information on the real full width at half maximum (FWHM) values of the GaN (10math3) reflection in distinct depths of the device. The sensitivity of this technique was found to be smaller than 50 nm. We show the different characteristics of the measured and calculated FWHMs for two GaN-based LEDs containing a fivefold InGaN/GaN-multi-quantum well. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
68.65.Fg Quantum wells
68.55.-a Thin film structure and morphology

Optical characterization of n- and p-doped 4H–SiC by electroreflectance spectroscopy

Gazi Demir, Timothy E. Renfro, R. Glosser, and S. E. Saddow

Appl. Phys. Lett. 84, 3540 (2004); http://dx.doi.org/10.1063/1.1712037 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2004

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We have studied the electroreflectance (ER) spectra of n- and p-type 4H–SiC polytype samples from 3 to 6.5 eV. The fundamental band gap and higher lying critical points are measured at room temperature. For this polytype, we observe band-gap narrowing in one of the structures with higher doping concentration. © 2004 American Institute of Physics.
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78.20.Jq Electro-optical effects
61.72.S- Impurities in crystals
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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High frequency oscillation in photonic crystal nanolasers

Tomoyuki Yoshie, Marko Lončar, Axel Scherer, and Yueming Qiu

Appl. Phys. Lett. 84, 3543 (2004); http://dx.doi.org/10.1063/1.1713051 (3 pages) | Cited 11 times

Online Publication Date: 20 April 2004

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We observed modulated oscillations in lasers of up to 130 GHz by conducting frequency domain measurements on photonic crystal lasers with built-in saturable absorbers. This is an example of how the small volumes of photonic crystal lasers lead to increases in the internal modulation frequencies and enables dramatic improvements of the laser modulation rate. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.70.Qs Photonic bandgap materials
42.60.Fc Modulation, tuning, and mode locking
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Sb-mediated growth of Si-doped AlGaAs by molecular-beam epitaxy

Yu. G. Sadofyev, S. R. Johnson, S. A. Chaparro, Y. Cao, D. Ding, J.-B. Wang, K. Franzreb, and Y.-H. Zhang

Appl. Phys. Lett. 84, 3546 (2004); http://dx.doi.org/10.1063/1.1715153 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2004

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The Sb-mediated growth of Al0.65Ga0.35As is studied for Sb/III flux ratios from 0 to 2% and growth temperatures from 580 to 720 °C. The electrical properties and surface morphology are found to depend strongly on both the growth temperature and the Sb flux. As an isoelectronic dopant, Sb improves the conductivity of n-Al0.65Ga0.35As with the highest conductivities occurring at the highest growth temperatures. As a surfactant, Sb improves the surface morphology at all growth temperatures, with the most dramatic improvement occurring at 670 °C. The smoothest surface (0.2 nm rms roughness) was obtained at 700 °C using a Sb/III flux ratio of 0.02. Furthermore, we have demonstrated that the use of Sb during the molecular-beam-epitaxy growth of AlGaAs effectively eliminates the “forbidden temperature gap.” © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
61.72.uj III-V and II-VI semiconductors
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.61.Ey III-V semiconductors
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Influence of Pt addition on the texture of NiSi on Si(001)

C. Detavernier and C. Lavoie

Appl. Phys. Lett. 84, 3549 (2004); http://dx.doi.org/10.1063/1.1719276 (3 pages) | Cited 34 times

Online Publication Date: 20 April 2004

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We report on the texture of Ni1−xPtxSi films on Si(001) substrates. X-ray diffraction measurements in Bragg–Brentano geometry appear to indicate that pure NiSi films are randomly oriented, while the addition of Pt was reported to induce an epitaxial alignment. However, detailed texture analysis using pole figure measurements shows that pure NiSi films are in fact strongly textured. The NiSi grains exhibit five different types of preferential orientation. The addition of an increasing amount of Pt gradually changes these five texture components. This texture evolution can be understood on the basis of the expansion of the monosilicide unit cell, caused by the incorporation of Pt. © 2004 American Institute of Physics.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.-a Thin film structure and morphology
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Fundamental limits to detection of low-energy ions using silicon solid-state detectors

H. O. Funsten, S. M. Ritzau, R. W. Harper, and R. Korde

Appl. Phys. Lett. 84, 3552 (2004); http://dx.doi.org/10.1063/1.1719272 (3 pages) | Cited 9 times

Online Publication Date: 20 April 2004

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Recent advances in solid-state detector (SSD) technology have demonstrated the detection of ions and electrons down to 1 keV. However, ions at keV energies lose a substantial amount of energy ΔN in a SSD through Coulombic interactions with target nuclei rather than through interactions that contribute to the SSD output pulse, whose magnitude is a measure of the ion’s incident energy. Because ΔN depends on the ion species, detector material, and interaction physics, it represents a fundamental limitation of the output pulse magnitude of the detector. Using 100% quantum collection efficiency silicon photodiodes with a thin (40–60 Å) SiO2 passivation layer, we accurately quantify ΔN for incident 1–120 keV ions and, therefore, evaluate the detection limits of keV ions using silicon detectors. © 2004 American Institute of Physics.
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29.40.Wk Solid-state detectors
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Room-temperature operation of an electrically driven terahertz modulator

T. Kleine-Ostmann, P. Dawson, K. Pierz, G. Hein, and M. Koch

Appl. Phys. Lett. 84, 3555 (2004); http://dx.doi.org/10.1063/1.1723689 (3 pages) | Cited 44 times

Online Publication Date: 20 April 2004

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In this letter, we report the room-temperature operation of an electrically controlled THz modulator. The modulation is achieved by reducing the electron density in a gated two-dimensional electron gas structure, which leads to an increase in the transmitted intensity of an incident beam of THz radiation. By depleting an electron gas of density 1012 cm−2, we achieved a maximum modulation depth of 3% for a pulse of terahertz radiation covering the range of frequencies from 0.1 to 2 THz. © 2004 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
84.40.-x Radiowave and microwave (including millimeter wave) technology
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Patterning-free integration of polymer light-emitting diode and polymer transistor

Z. L. Li, S. C. Yang, H. F. Meng, Y. S. Chen, Y. Z. Yang, C. H. Liu, S. F. Horng, C. S. Hsu, L. C. Chen, J. P. Hu, and R. H. Lee

Appl. Phys. Lett. 84, 3558 (2004); http://dx.doi.org/10.1063/1.1728301 (3 pages) | Cited 14 times

Online Publication Date: 20 April 2004

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We demonstrate an integration of polymer light-emitting diode (LED) and polymer transistor in which no patterning of the organic layers is needed. Intrinsic high-mobility semiconducting conjugated polymer poly(3-hexylthiophene)(P3HT) is used as the hole-transport layer for polymer LED. The light emission efficiency is only slightly lower than the LED with conventional heavily doped hole-transport layer. Such LED is easily integrated with a P3HT transistor without patterning.© 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
42.70.Jk Polymers and organics
85.65.+h Molecular electronic devices
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Nondestructive depth profile of the chemical state of ultrathin Al2O3/Si interface

Jong Cheol Lee and S.-J. Oh

Appl. Phys. Lett. 84, 3561 (2004); http://dx.doi.org/10.1063/1.1734684 (3 pages) | Cited 13 times

Online Publication Date: 20 April 2004

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We investigated a depth profile of the chemical states of an Al2O3/Si interface using nondestructive photon energy-dependent high-resolution x-ray photoelectron spectroscopy (HRXPS). The Si 2p binding energy, attributed to the oxide interfacial layer (OIL), was found to shift from 102.1 eV to 102.9 eV as the OIL region closer to Al2O3 layer was sampled, while the Al 2p binding energy remains the same. This fact strongly suggests that the chemical state of the interfacial layer is not Al silicate as previously believed. We instead propose from the HRXPS of Al 2p and Si 2p depth-profile studies that the chemical states of the Al2O3/Si interface mainly consist of SiO2 and Si2O3. © 2004 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
71.15.Nc Total energy and cohesive energy calculations
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
81.70.Fy Nondestructive testing: optical methods
73.20.-r Electron states at surfaces and interfaces
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Formation mechanism of wide stacking faults in nanocrystalline Al

X. Z. Liao, S. G. Srinivasan, Y. H. Zhao, M. I. Baskes, Y. T. Zhu, F. Zhou, E. J. Lavernia, and H. F. Xu

Appl. Phys. Lett. 84, 3564 (2004); http://dx.doi.org/10.1063/1.1734689 (3 pages) | Cited 16 times

Online Publication Date: 20 April 2004

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A full dislocation often dissociates into two partial dislocations enclosing a stacking fault (SF) ribbon. The SF width significantly affects the mechanical behavior of metals. Al has very high stacking fault energy and, consequently, very narrow SF width in its coarse-grained state. We have found that some SFs in nanocrystalline Al are surprisingly 1.4–6.8 nm wide, which is 1.5–11 times higher than the reported experimental value in single crystal Al. Our analytical model shows that such wide SFs are formed due to the small grain size and possibly also to the interaction of SF ribbons with high density of dislocations. © 2004 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Room-temperature deep-ultraviolet lasing at 241.5 nm of AlGaN multiple-quantum-well laser

Takayoshi Takano, Yoshinobu Narita, Akihiko Horiuchi, and Hideo Kawanishi

Appl. Phys. Lett. 84, 3567 (2004); http://dx.doi.org/10.1063/1.1737061 (3 pages) | Cited 49 times

Online Publication Date: 20 April 2004

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Room-temperature deep-ultraviolet lasing of AlxGa1−xN multiple-quantum-well lasers with an Al composition x of 0.66 was achieved at 241.5 nm under pulsed optical pumping. The threshold pumping power was approximately 1200 kW/cm2 at room temperature. The shortest lasing wavelength was 231.8 nm at 20 K. The laser structure was grown on a high-quality AlN layer, which was grown on a 4H-SiC substrate by inserting an AlN/GaN multibuffer-layer structure between the substrate and the AlN layer. Temperature dependence of lasing wavelength was also estimated to be 0.01 and 0.03 nm/K in the temperature region from 20 to 150 K and from 160 K to room temperature, respectively. The laser cavity was made of a cleaved facet of AlGaN epitaxial layers and a SiC substrate. For this purpose, it was necessary to polish the wafer to a thickness of less than 100 μm. The optimal wafer thickness for cleaving in our experiments was 60–70 μm. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.66.Bi Elemental solids
61.66.Dk Alloys
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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1 micron wavelength photo- and electroluminescence from a conjugated polymer

Miaoxiang Chen, Erik Perzon, Mats R. Andersson, Saulius Marcinkevicius, S. K. M. Jönsson, Mats Fahlman, and Magnus Berggren

Appl. Phys. Lett. 84, 3570 (2004); http://dx.doi.org/10.1063/1.1737064 (3 pages) | Cited 39 times

Online Publication Date: 20 April 2004

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We report photo- and electroluminescence from an alternating conjugated polymer consisting of fluorene units and low-band gap donor-acceptor-donor (D–A–D) units. The D–A–D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of 1.27 eV. The corresponding electro- and photoluminescence spectra both peak at approximately 1 μm. Light-emitting diodes, based on a single layer of the polymer, demonstrated external quantum efficiencies from 0.03% to 0.05%. © 2004 American Institute of Physics.
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78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
78.55.Qr Amorphous materials; glasses and other disordered solids
42.70.Jk Polymers and organics
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Avoiding cracks in self-assembled photonic band-gap crystals

A. A. Chabanov, Y. Jun, and D. J. Norris

Appl. Phys. Lett. 84, 3573 (2004); http://dx.doi.org/10.1063/1.1737066 (3 pages) | Cited 50 times

Online Publication Date: 20 April 2004

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Thin colloidal crystals (or synthetic opals) composed of Stöber silica spheres typically develop cracks when they are utilized to obtain photonic band-gap crystals (or inverted opals). We find that, by sintering the silica spheres prior to assembly of the opal, these cracks can be avoided. We report the effects of temperature and duration of the heat treatment on 850 nm silica spheres using electron microscopy, thermogravimetry, and light scattering. We also find a large dependence of the refractive index of the silica on the temperature of the heat treatment. This may allow tuning of the refractive index of silica spheres. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
82.70.Dd Colloids
81.40.Gh Other heat and thermomechanical treatments
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
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Spin relaxation dynamics in highly uniform InAs quantum dots

A. Tackeuchi, R. Ohtsubo, K. Yamaguchi, M. Murayama, T. Kitamura, T. Kuroda, and T. Takagahara

Appl. Phys. Lett. 84, 3576 (2004); http://dx.doi.org/10.1063/1.1737068 (3 pages) | Cited 24 times

Online Publication Date: 20 April 2004

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We have investigated carrier spin dynamics in highly uniform self-assembled InAs quantum dots. The highly uniform quantum dots allowed us to observe the spin dynamics in the ground state and that in the second state separately, without the disturbance of inhomogeneous broadening. The spin relaxation times in the ground state and the second state were measured to be 1.0 and 0.6 ns, respectively. Our measurements reveal the absence of the carrier density dependence of the spin relaxation time. The measured spin relaxation time decreases rapidly from 1.1 ns at 10 K to 200 ps at 130 K. This large change in the spin relaxation time is well explained in terms of the mechanism of acoustic phonon emission. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
72.25.Rb Spin relaxation and scattering
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Hc Quantum dots
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Screened-exchange determination of the optical properties of large gap insulators: CaF2

Miyoung Kim, Yu-Jun Zhao, A. J. Freeman, and W. Mannstadt

Appl. Phys. Lett. 84, 3579 (2004); http://dx.doi.org/10.1063/1.1737073 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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Optical measurements have provided an extremely difficult challenge to existing electronic band structure calculations. Although CaF2, an important large gap insulator, has been intensively investigated, no parameter-free first-principles calculations have been done due to the well-known failure of the local density approximation (LDA) in treating excited states. Here, we present results of fully first-principles calculations of the electronic structure and optical properties of CaF2 with the self-consistent screened-exchange LDA method implemented in the highly precise full-potential linearized augmented plane wave approach. The calculated optical energy gap, 12.05 eV, is in excellent agreement with experiment (12.0±0.1 eV) and so greatly improves the LDA result (7.23 eV). The optical properties, including the imaginary part of the dielectric function and the reflectance determined ab initio with full matrix elements and no parameters, are found to be in good agreement with experiment. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Qe Excited states: methodology
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
77.22.Ch Permittivity (dielectric function)
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Spin polarization in ferromagnet/insulator/superconductor structures with the superconductor on top of the barrier

C. Kaiser and S. S. P. Parkin

Appl. Phys. Lett. 84, 3582 (2004); http://dx.doi.org/10.1063/1.1737485 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2004

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The tunneling spin polarization of CoFe, NiFe, and pure Ni was measured using superconducting tunneling spectroscopy for Al2O3 tunnel barriers with the ferromagnetic material both above and below the barrier. The spin polarization was found to be very similar for Co–Fe in both cases but for Ni and Ni–Fe alloys the spin polarization was significantly lower when the Al2O3 barrier was deposited on top of the ferromagnetic material. We attribute this to oxidation of the ferromagnet at the ferromagnet/Al2O3 interface resulting from an imperfect formation of the barrier. © 2004 American Institute of Physics.
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75.50.Bb Fe and its alloys
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
75.30.Ds Spin waves
81.65.Mq Oxidation
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
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