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18 Apr 2011

Volume 98, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 98, 163701 (2011); http://dx.doi.org/10.1063/1.3579156 (3 pages)

Thomas Jetzfellner, Amir Rosenthal, K.-H. Englmeier, Alexander Dima, Miguel Ángel Araque Caballero, Daniel Razansky, and Vasilis Ntziachristos
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Nonlinear phononic crystals based on chains of disks alternating with toroidal structures

A. Spadoni, C. Daraio, W. Hurst, and M. Brown

Appl. Phys. Lett. 98, 161901 (2011); http://dx.doi.org/10.1063/1.3567753 (3 pages) | Cited 1 time

Online Publication Date: 18 April 2011

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We study experimentally the acoustic response of a load-bearing, phononic crystal composed of alternating steel disks, and polytetrafluoroethylene o-rings under precompression. The crystal allows for axial, rocking, and shear-polarized wavemodes when excited by a broad-band signal applied off-axis. Finite element analysis is employed to determine the system’s wave modes. The nonlinear interaction between disks and o-rings supports a dynamic response that is tunable with variations in static precompression, leading to controllable frequency shifts in a large band gap. A modal analysis reveals that four of the six principal wave modes are susceptible to external precompression while two modes are not.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Thermal stability of amorphous GaN1−xAsx alloys

A. X. Levander, Z. Liliental-Weber, R. Broesler, M. E. Hawkridge, S. V. Novikov, C. T. Foxon, O. D. Dubon, J. Wu, W. Walukiewicz, and K. M. Yu

Appl. Phys. Lett. 98, 161902 (2011); http://dx.doi.org/10.1063/1.3581894 (3 pages) | Cited 3 times

Online Publication Date: 19 April 2011

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GaN1−xAsx alloys grown across the composition range by low temperature molecular beam epitaxy have great technological potential for photovoltaic applications owing to their strong absorption coefficient and wide tunability of band gap and band edges. We found that amorphous GaN1−xAsx alloys that are formed for the compositions x, in the range of x ∼ 0.3–0.7 are stable up to 700 °C. This is surprising since growth of GaN1−xAsx above 400 °C results in phase segregation. At annealing temperatures higher than 700 °C the alloy phase segregates into GaAs:N and GaN:As. The relative size of the nanocrystals depends on the initial film composition and annealing conditions.
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68.60.Dv Thermal stability; thermal effects
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)
78.66.Fd III-V semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Jg Amorphous semiconductors; glasses

Optical waveguide loss minimized into gallium nitride based structures grown by metal organic vapor phase epitaxy

A. Stolz, E. Cho, E. Dogheche, Y. Androussi, D. Troadec, D. Pavlidis, and D. Decoster

Appl. Phys. Lett. 98, 161903 (2011); http://dx.doi.org/10.1063/1.3582055 (3 pages) | Cited 4 times

Online Publication Date: 19 April 2011

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The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.
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42.79.Gn Optical waveguides and couplers
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Spectroscopic evidence for nonradiative energy transfer between colloidal CdSe/ZnS nanocrystals and functionalized silicon substrates

H. M. Nguyen, O. Seitz, D. Aureau, A. Sra, N. Nijem, Yu. N. Gartstein, Y. J. Chabal, and A. V. Malko

Appl. Phys. Lett. 98, 161904 (2011); http://dx.doi.org/10.1063/1.3579545 (3 pages) | Cited 1 time

Online Publication Date: 19 April 2011

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We present the fabrication and properties of hybrid structures consisting of a monolayer of colloidal CdSe nanocrystals grafted on hydrogenated Si surfaces via amine modified carboxy-alkyl chain linkers. The wet chemical preparation ensures that Si surfaces are fully passivated with a negligible number of nonradiative surface state defects and that the separation between nanocrystals and Si is tightly controlled. An eightfold decrease in photoluminescence lifetime of nanocrystals on Si is observed as compared to glass. A quantitative analysis reveals that the nonradiative transfer from nanocrystals to Si is 65% efficient, demonstrating the potential of such hybrids for practical photovoltaic devices.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Rv Passivation
82.70.Dd Colloids
73.20.-r Electron states at surfaces and interfaces

High quality Ge thin film grown by ultrahigh vacuum chemical vapor deposition on GaAs substrate

Shih-Hsuan Tang, Edward Yi Chang, Mantu Hudait, Jer-Shen Maa, Chee-Wee Liu, Guang-Li Luo, Hai-Dang Trinh, and Yung-Hsuan Su

Appl. Phys. Lett. 98, 161905 (2011); http://dx.doi.org/10.1063/1.3580605 (3 pages) | Cited 7 times

Online Publication Date: 19 April 2011

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High-quality epitaxial Ge films were grown on GaAs substrates by ultrahigh vacuum chemical vapor deposition. High crystallinity and smooth surface were observed for these films by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Direct band gap emission (1550 nm) from this structure was detected by photoluminescence. Valence band offset of 0.16 eV at the Ge/GaAs interface was measured by x-ray photoelectron spectroscopy. N-type arsenic self-doping of 1018/cm−3 in the grown Ge layers was determined using electrochemical capacitance voltage measurement. This structure can be used to fabricate p-channel metal-oxide-semiconductor field-effect transistor for the integration of Ge p-channel device with GaAs n-channel electronic device.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Ps Atomic force microscopy (AFM)
78.66.Db Elemental semiconductors and insulators
73.61.Cw Elemental semiconductors

Surface-plasmon-enhanced band-edge emission from Au/GaN powders

Toshihiro Nakamura, Tomohiro Hosaka, and Sadao Adachi

Appl. Phys. Lett. 98, 161906 (2011); http://dx.doi.org/10.1063/1.3581214 (3 pages)

Online Publication Date: 19 April 2011

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Band-edge emission from GaN nanopowders is strongly enhanced by the deposition of Au nanoparticles. This enhancement in photoluminescence emission results from resonant absorption of the defect-related emission caused by the localized surface plasmons in the Au nanoparticles and subsequent charge transfer from Au to GaN. The enhanced band-edge emission is also found to be due to the recombination of excitons bound to shallow defect states. Furthermore, such enhanced band-edge emission shows phonon replicas with an energy separation of 69±2 meV. This energy value corresponds to that of transverse-optical phonons, and not to that of the commonly observed longitudinal-optical phonons.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.-j Infrared and Raman spectra
78.55.Hx Other solid inorganic materials
71.55.-i Impurity and defect levels
73.22.Lp Collective excitations

Complementary chiral metamaterials with giant optical activity and negative refractive index

Zhaofeng Li, Kamil Boratay Alici, Evrim Colak, and Ekmel Ozbay

Appl. Phys. Lett. 98, 161907 (2011); http://dx.doi.org/10.1063/1.3574909 (3 pages) | Cited 8 times

Online Publication Date: 20 April 2011

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A complementary bilayer cross-wire chiral metamaterial is proposed and studied experimentally and numerically. It exhibits giant optical activity and a small circular dichroism. The retrieval results reveal that a negative refractive index is realized for right circularly polarized waves due to the strong chirality. Our numerical results show that the mechanism of the chiral behavior at the resonance of lower frequency can be interpreted as the coupling effects between two sets of mutually twisted virtual magnetic dipoles, while the resonance of higher frequency shows complicated nonlocal features.
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78.20.Ek Optical activity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Selective growth of perovskite oxides on SrTiO3 (001) by control of surface reconstructions

Soo-hyon Phark, Young Jun Chang, and Tae Won Noh

Appl. Phys. Lett. 98, 161908 (2011); http://dx.doi.org/10.1063/1.3583443 (3 pages) | Cited 3 times

Online Publication Date: 21 April 2011

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We report surface reconstruction (RC)-dependent growths of SrTiO3 and SrVO3 on a SrTiO3 (001) surface with two different coexisting surface RCs, namely, (2×1) and c(6×2). Up to the coverage of several layers, epitaxial growth was forbidden on the c(6×2) RC under the growth conditions that permitted layer-by-layer epitaxial growth on the (2×1) RC. Scanning tunneling microscopy on the lattice structure of the c(6×2) RC revealed that this RC-selective growth mainly originated from the significant structural/stoichiometric dissimilarity between the c(6×2) RC and the cubic perovskite films. On the c(6×2) RC, therefore, formation of perovskite islands was forbidden from the nucleation stage.
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68.55.aj Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Bi Elemental solids
61.66.Dk Alloys

Orientation dependence of the elastic instability on strained SiGe films

J.-N. Aqua, A. Gouyé, T. Auphan, T. Frisch, A. Ronda, and I. Berbezier

Appl. Phys. Lett. 98, 161909 (2011); http://dx.doi.org/10.1063/1.3576916 (3 pages) | Cited 2 times

Online Publication Date: 22 April 2011

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At low strain, SiGe films on Si substrates undergo the Asaro–Tiller–Grinfeld morphological instability. We demonstrate experimentally that this instability develops on Si(001) but not on Si(111) even after long annealing. Using a continuum description of surface diffusion in presence of wetting, elasticity, and surface energy anisotropy, we find a retardation of the instability on Si(111) due to a strong dependence of the instability onset as function of the surface stiffness. This retardation is at the origin of the inhibition of the instability on experimental time scales even after long annealing.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Gh Other heat and thermomechanical treatments
65.40.gp Surface energy

An analytical model for the growth of quantum dots on ultrathin substrates

S. P. A. Gill

Appl. Phys. Lett. 98, 161910 (2011); http://dx.doi.org/10.1063/1.3583447 (3 pages) | Cited 1 time

Online Publication Date: 22 April 2011

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The self-assembly of heteroepitaxial quantum dots on ultrathin substrates is analyzed within the context of small perturbation theory. Analytical expressions are derived for the dependence of the quantum dot separation on the substrate thickness. It is shown that the substrate thickness is critical in determining this separation when it is below the intrinsic material length scale of the system. The model is extended to simultaneous dot growth on both sides of the substrate. It is shown that vertically anticorrelated structures are preferred with an increase in the dot separation of 15% above that found in the one-sided case.
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81.07.Ta Quantum dots
81.15.Aa Theory and models of film growth

Electroabsorption spectra of PbSe nanocrystal quantum dots

Xiaoming Liu, Toshifumi Iimori, Ruriko Ohshima, Takakazu Nakabayashi, and Nobuhiro Ohta

Appl. Phys. Lett. 98, 161911 (2011); http://dx.doi.org/10.1063/1.3583450 (3 pages) | Cited 1 time

Online Publication Date: 22 April 2011

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The quantum-confined Stark effect of PbSe nanocrystal quantum dots (QDs) in a polymer film has been studied for the near-infrared absorption in the region of 1300–1600 nm (corresponding to diameters of 4.0–7.0 nm) by using electric field modulation spectroscopy. Electroabsorption spectra of QDs show the electric-field-induced energy shift in the exciton state, resulting in the spectral broadening given by the second derivative of the absorption spectra. It is shown that the magnitude of the change in electric dipole moment following excitation into the first exciton state increases with an increase in the size of QDs.
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78.20.Jq Electro-optical effects
78.30.Hv Other nonmetallic inorganics
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
73.21.La Quantum dots

Optical anisotropy and photoluminescence polarization in single InAlAs quantum dots

S. Ohno, S. Adachi, R. Kaji, S. Muto, and H. Sasakura

Appl. Phys. Lett. 98, 161912 (2011); http://dx.doi.org/10.1063/1.3583453 (3 pages) | Cited 3 times

Online Publication Date: 22 April 2011

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We have investigated the optical anisotropy in individual self-assembled quantum dots. The linear polarization analysis of the positive trion photoluminescence reveals the effect of the strain-induced valence band mixing since the positive trion has the spin-paired holes and therefore exchange interaction has no influence. Meanwhile, the neutral exciton indicates the complex polarization states due to both the in-plain asymmetries of the dot shape and the strain distributions. The experimental and theoretical polarization analysis has been performed for tens of InAlAs quantum dots and the correlation between the important parameters was investigated.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots

Effect of dislocation density on thermal boundary conductance across GaSb/GaAs interfaces

Patrick E. Hopkins, John C. Duda, Stephen P. Clark, Christopher P. Hains, Thomas J. Rotter, Leslie M. Phinney, and Ganesh Balakrishnan

Appl. Phys. Lett. 98, 161913 (2011); http://dx.doi.org/10.1063/1.3581041 (3 pages) | Cited 8 times

Online Publication Date: 22 April 2011

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We report on the thermal boundary conductance across structurally-variant GaSb/GaAs interfaces characterized by different dislocations densities, as well as variably-rough Al/GaSb interfaces. The GaSb/GaAs structures are epitaxially grown using both interfacial misfit (IMF) and non-IMF techniques. We measure the thermal boundary conductance from 100 to 450 K with time-domain thermoreflectance. The thermal boundary conductance across the GaSb/GaAs interfaces decreases with increasing strain dislocation density. We develop a model for interfacial transport at structurally-variant interfaces in which phonon propagation and scattering parallels photon attenuation. We find that this model describes the measured thermal boundary conductances well.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
66.70.Df Metals, alloys, and semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
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