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1 Jan 2007

Volume 90, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 90, 012105 (2007); http://dx.doi.org/10.1063/1.2428402 (3 pages)

Jan Bauer, Frank Fleischer, Otwin Breitenstein, Luise Schubert, Peter Werner, Ulrich Gösele, and Margit Zacharias
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Intense visible photoluminescence in Ba(Zr0.25Ti0.75)O3 thin films

L. S. Cavalcante, M. F. C. Gurgel, A. Z. Simões, E. Longo, J. A. Varela, M. R. Joya, and P. S. Pizani

Appl. Phys. Lett. 90, 011901 (2007); http://dx.doi.org/10.1063/1.2425013 (3 pages) | Cited 21 times

Online Publication Date: 2 January 2007

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Photoluminescence at room temperature in Ba(Zr0.25Ti0.75)O3 thin films was explained by the degree of structural order-disorder. Ultraviolet-visible absorption spectroscopy, photoluminescence, and first principles quantum mechanical measurements were performed. The film annealed at 400 °C for 4 h presents intense visible photoluminescence behavior at room temperature. The increase of temperature and annealing time creates [ZrO6]–[TiO6] clusters in the lattice leading to the trapping of electrons and holes. Thus, [ZrO5]–[TiO6]/[ZrO6]–[TiO6] clusters were the main reason for the photoluminescence behavior.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics
81.40.Gh Other heat and thermomechanical treatments
77.55.-g Dielectric thin films

Imaging of closed cracks using nonlinear response of elastic waves at subharmonic frequency

Yoshikazu Ohara, Tsuyoshi Mihara, Ryouta Sasaki, Toshihiro Ogata, Setsu Yamamoto, Yuuki Kishimoto, and Kazushi Yamanaka

Appl. Phys. Lett. 90, 011902 (2007); http://dx.doi.org/10.1063/1.2426891 (3 pages) | Cited 13 times

Online Publication Date: 2 January 2007

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The authors constructed a novel apparatus based on subharmonic ultrasound for the accurate imaging of closed cracks. Linear and nonlinear responses not only from the tip but also from other parts of cracks were observed in fundamental and subharmonic images, which were changed with varying closure stress. The subharmonic images always gave an accurate length of partially closed cracks, in contrast to the fundamental images in which the crack length was underestimated. Significant similarities in generation and resonance phenomena of subharmonic waves, acoustic emission, and the vibration of microbubbles are discussed.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.65.+k Acoustical properties of solids

Anomalous photoluminescence behavior from amorphous Ge quantum dots produced by buffer-layer-assisted growth

A. S. Bhatti, V. N. Antonov, P. Swaminathan, J. S. Palmer, and J. H. Weaver

Appl. Phys. Lett. 90, 011903 (2007); http://dx.doi.org/10.1063/1.2426892 (3 pages) | Cited 4 times

Online Publication Date: 2 January 2007

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The authors present photoluminescence results from amorphous Ge quantum dots formed using buffer-layer-assisted growth. Their sizes, shapes, and densities were controlled by varying the thickness of the Xe buffer layer, with sizes varying from 2 to 8 nm. A relatively weak signal was observed at ∼ 3 K at ∼ 0.91 eV that was independent of size and was insensitive to laser intensity. Its temperature-dependent magnitude showed a Berthelot-type behavior that they associate with hopping of carriers between radiative tail states and shallow nonradiative states. These findings are similar to those from porous semiconductors.
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81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
78.67.Hc Quantum dots
61.43.Dq Amorphous semiconductors, metals, and alloys
73.63.Kv Quantum dots

Exciton spin relaxation in GaN observed by spin grating experiment

T. Ishiguro, Y. Toda, and S. Adachi

Appl. Phys. Lett. 90, 011904 (2007); http://dx.doi.org/10.1063/1.2430402 (3 pages) | Cited 15 times

Online Publication Date: 3 January 2007

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The authors studied the exciton spin relaxation of bulk GaN by creating spin polarization gratings using degenerate four-wave mixing spectroscopy. The spectrally resolved analysis achieved with this technique facilitated the direct evaluation of spin polarizations in the individual excitons (A and B excitons). The spin polarizations for each exciton decay very quickly (τs ∼ 1 ps) at low temperatures. Moreover the τs is faster than the dephasing time T2 throughout the measured temperature range, suggesting the existence of fast intrinsic spin relaxation processes, which can be attributed to a large exchange constant characterized in GaN.
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72.25.Dc Spin polarized transport in semiconductors
71.35.-y Excitons and related phenomena
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
71.70.Gm Exchange interactions

Dislocation junctions as barriers to threading dislocation migration

Siu Sin Quek, Zhaoxuan Wu, Yong-Wei Zhang, Yang Xiang, and David J. Srolovitz

Appl. Phys. Lett. 90, 011905 (2007); http://dx.doi.org/10.1063/1.2426971 (3 pages) | Cited 4 times

Online Publication Date: 3 January 2007

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Level set simulations of dislocation dynamics in biaxially strained, heteroepitaxial films reveal interesting kinetic and thermodynamic mechanisms for blocking the migration of threading dislocations. Two dislocations on the same or on intersecting slip planes may react to form a threading dislocation segment that does not glide under the influence of the misfit strain. In the coplanar case, a kinetic barrier exists that slows down dislocation migration. For the reaction involving dislocations on intersecting planes, an energetic barrier impedes other advancing dislocations. These barriers create significant and frequent impediment to threading dislocation flow, resulting in pileups and high threading dislocation densities.
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61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations
66.30.Lw Diffusion of other defects

Initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates

C. Liu, S. H. Chang, T. W. Noh, M. Abouzaid, P. Ruterana, H. H. Lee, D.-W. Kim, and J.-S. Chung

Appl. Phys. Lett. 90, 011906 (2007); http://dx.doi.org/10.1063/1.2428489 (3 pages) | Cited 11 times

Online Publication Date: 3 January 2007

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The initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates were investigated. High-resolution x-ray diffraction and transmission electron microscopy studies revealed that the initial growth behavior and the microstructure of the films were significantly dependent on the growth parameters employed. ZnO films grown at 700 °C with an O2 partial pressure of 20 mTorr initiated in a columnar growth mode and contained two types of domains. These domains were in plane orientated either ZnO[11math0]‖Al2O3[10math0] or ZnO[10math0]‖Al2O3[10math0] and were surrounded by highly defective domain boundaries with threading dislocations. ZnO films grown at 800 °C with 1 mTorr O2 showed a two-dimensional layered growth with only one in-plane epitaxial relationship, ZnO[11math0]‖Al2O3[10math0]. Most of the defects in the layered grown films were basal plane stacking faults near the interface between the ZnO and the substrate. The mechanism of formation of the 30°-twisted domains with the in-plane orientation of ZnO[10math0]‖Al2O3[10math0] is discussed.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Control of fine-structure splitting of individual InAs quantum dots by rapid thermal annealing

D. J. P. Ellis, R. M. Stevenson, R. J. Young, A. J. Shields, P. Atkinson, and D. A. Ritchie

Appl. Phys. Lett. 90, 011907 (2007); http://dx.doi.org/10.1063/1.2430489 (3 pages) | Cited 21 times

Online Publication Date: 4 January 2007

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Degeneracy of the bright single exciton spin state is a prerequisite for the production of triggered polarization-entangled photon pairs from the biexciton decay of a quantum dot. Normally, however, the exciton spin states are split due to in-plane asymmetries. Here the authors demonstrate that the exciton splitting of an individual dot can be tuned through zero by thermal annealing. Repeated annealing blueshifts the exciton emission line of the dot, accompanied by a reduction and inversion in polarization splitting. Annealing is also demonstrated to control the detuning between the exciton and biexciton transitions in any selected dot.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.67.Hc Quantum dots
61.72.Cc Kinetics of defect formation and annealing

Electrotunable in-plane one-dimensional photonic structure based on silicon and liquid crystal

V. A. Tolmachev, T. S. Perova, S. A. Grudinkin, V. A. Melnikov, E. V. Astrova, and Yu. A. Zharova

Appl. Phys. Lett. 90, 011908 (2007); http://dx.doi.org/10.1063/1.2430626 (3 pages) | Cited 15 times

Online Publication Date: 4 January 2007

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The model of the electro-optical effect, due to the reorientation of liquid crystal molecules from a pseudoisotropic to a homeotropic state, in a composite photonic structure with a liquid crystal filler, is elaborated. A composite (110) grooved silicon photonic structure for the middle infrared range was designed and fabricated on a silicon-on-insulator platform. Polarized reflection spectra, demonstrating the electro-optical effect, have been obtained by means of Fourier transform infrared microscopy. The relative shift of the band edge at half intensity in the region of 10 μm was found experimentally to be 1.6% compared to 2.2% as predicted by theory.
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42.70.Df Liquid crystals
42.70.Qs Photonic bandgap materials
61.30.-v Liquid crystals
78.20.Jq Electro-optical effects
42.15.Eq Optical system design
78.30.-j Infrared and Raman spectra

OsN2: Crystal structure and electronic properties

Javier A. Montoya, Alexander D. Hernandez, Chrystèle Sanloup, Eugene Gregoryanz, and Sandro Scandolo

Appl. Phys. Lett. 90, 011909 (2007); http://dx.doi.org/10.1063/1.2430631 (3 pages) | Cited 29 times

Online Publication Date: 4 January 2007

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Osmium nitride belongs to a family of nitrides synthesized recently at high pressures from their parent elements. Here we show, based on first-principles calculations, that the crystal structure of osmium nitride is isostructural to marcasite. Excellent agreement is obtained between the authors’ results and x-ray, Raman, and compressibility measurements. In the OsN2 marcasite structure single-bonded N2 units occupy the interstitial sites of the Os close-packed lattice, giving rise to a metallic compound. A comparison between the formation energies of OsN2 and PtN2 explains the similar thermodynamic conditions of formation reported experimentally for the two compounds.
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61.66.Fn Inorganic compounds
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.30.Hv Other nonmetallic inorganics
61.72.J- Point defects and defect clusters
71.20.Ps Other inorganic compounds

Characteristics of InN grown on SiC under the In-rich regime by molecular beam heteroepitaxy

Maria Losurdo, Maria M. Giangregorio, Giovanni Bruno, Tong-Ho Kim, Pae Wu, Soojeong Choi, April Brown, F. Masia, M. Capizzi, and A. Polimeni

Appl. Phys. Lett. 90, 011910 (2007); http://dx.doi.org/10.1063/1.2424664 (3 pages) | Cited 7 times

Online Publication Date: 4 January 2007

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InN epitaxial films were grown by N2 plasma-assisted molecular beam epitaxy on 4H- and 6H-SiC substrates using low-temperature InN nucleation layers. InN films grown at various In fluxes under the In-rich regime show improved crystal quality, surface morphology, and optical properties, without sizable metallic In incorporation. Photoluminescence measurements show emission up to room temperature, band gap values as low as 0.64 eV at T = 10 K, and carrier concentrations of the order of 8×1017 cm−3.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

Double bands of negative refractive index in the left-handed metamaterials with asymmetric defects

Weiren Zhu, Xiaopeng Zhao, and Ning Ji

Appl. Phys. Lett. 90, 011911 (2007); http://dx.doi.org/10.1063/1.2426888 (3 pages) | Cited 17 times

Online Publication Date: 4 January 2007

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The authors present a left-handed metamaterial (LHM) with asymmetric defects at microwave frequencies. The LHM is composed of the periodic arrays of hexagonal split ring resonators and wires, and the defects are introduced into the integrated LHM. It is shown with beam shifting experiment that the transmittance spectrum of the sample appears to have two peaks with maximum value frequencies of 9.10 and 9.80 GHz, and double bands of negative refractive index, n = −0.48 and n = −1.09, are clearly found. The LHM proposed here offers the potential applications such as bandpass filters, wavelength divider, and antennas.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions

High quantum efficiency of violet-blue to green light emission in InGaN quantum well structures grown by graded-indium-content profiling method

Yong-Hoon Cho, Y. P. Sun, H. M. Kim, T. W. Kang, E.-K. Suh, H. J. Lee, R. J. Choi, and Y. B. Hahn

Appl. Phys. Lett. 90, 011912 (2007); http://dx.doi.org/10.1063/1.2430401 (3 pages) | Cited 2 times

Online Publication Date: 5 January 2007

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Optical characteristics of high-efficiency violet-blue, blue, and green light emissions in InxGa1−xN quantum well (QW) structures with graded In content are investigated. Appearance of additional higher energy peaks at 410, 429, and 459 nm above the main peaks at 430, 463, and 509 nm with an effective carrier transfer from the higher to main peak sides is characteristic of these structures with various In contents of x<0.2, 0.2<x<0.3, and x>0.3, respectively. Robust carrier localization by uniform, small-size, and high-density phase segregation plays an important role in maintaining high efficiencies over a wide range of In contents in graded-In-content InGaN QW structures.
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78.67.De Quantum wells
73.63.Hs Quantum wells
78.55.Cr III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
64.75.-g Phase equilibria

Local electronic and optical behaviors of a-plane GaN grown via epitaxial lateral overgrowth

J. C. Moore, V. Kasliwal, A. A. Baski, X. Ni, Ü. Özgür, and H. Morkoç

Appl. Phys. Lett. 90, 011913 (2007); http://dx.doi.org/10.1063/1.2429901 (3 pages) | Cited 7 times

Online Publication Date: 5 January 2007

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Conductive atomic force microscopy and near-field optical microscopy (NSOM) were used to study the morphology, conduction, and optical properties of a-plane GaN films grown via epitaxial lateral overgrowth (ELO) by metal organic chemical vapor deposition. The AFM images for the coalesced ELO films show undulations, where the window regions appear as depressions with a high density of surface pits. At reverse bias below 12 V, very low uniform conduction (2 pA) is seen in the window regions. Above 20 V, a lower-quality sample shows localized sites inside the window regions with significant leakage, indicating a correlation between the presence of surface pits and leakage sites. Room temperature NSOM studies explicitly showed enhanced optical quality in the wing regions of the overgrown GaN due to a reduced density of dislocations, with the wings and the windows clearly discernible from near-field photoluminescence mapping.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Influence of the AlN interlayer crystal quality on the strain evolution of GaN layer grown on Si (111)

W. Liu, J. J. Zhu, D. S. Jiang, H. Yang, and J. F. Wang

Appl. Phys. Lett. 90, 011914 (2007); http://dx.doi.org/10.1063/1.2430396 (3 pages) | Cited 11 times

Online Publication Date: 5 January 2007

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The strain evolution in metal organic chemical vapor deposition growth of GaN on Si (111) substrate with an AlN interlayer is studied. During the growth of GaN film on AlN interlayer, the growth stress changes from compression to tension. The study shows that the density of V trenches in the AlN interlayer surface and the threading dislocations generated in the AlN interlayer have a significant influence on this strain evolution process. The dislocations generated in AlN interlayer may thread across the interface and play a key role in the strain evolution process of the GaN layer grown on AlN interlayer.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
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