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18 Apr 2011

Volume 98, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

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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Low-resistance Ni/Al Ohmic contacts applied to a nonpolar a-plane n-type GaN

Dong Ho Kim, Su Jin Kim, Yu Jeong Seo, Tae Geun Kim, and Sung Min Hwang

Appl. Phys. Lett. 98, 161101 (2011); http://dx.doi.org/10.1063/1.3579252 (3 pages) | Cited 4 times

Online Publication Date: 18 April 2011

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The authors report upon a low-resistance Ni/Al Ohmic contact to a nonpolar n-type a-plane GaN with respect to the annealing temperature. The Schottky behavior of the Ni/Al contact changes to a linear Ohmic behavior at a 700 °C annealing, at which the specific contact resistivity of the Ni/Al contact became as low as 5.8×10−5 whereas that of a typical Ti/Al contact was 1.6×10−3 Ω cm2. This improvement is attributed to a lowering of the Schottky barrier height via a Ni–Al interdiffused layer, formed at the interface between the metal and the nonpolar a-plane n-type GaN during the annealing process.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Experimental demonstration of dielectric-loaded plasmonic waveguide disk resonators at telecom wavelengths

Sukanya Randhawa, Alexey V. Krasavin, Tobias Holmgaard, Jan Renger, Sergey I. Bozhevolnyi, Anatoly V. Zayats, and Romain Quidant

Appl. Phys. Lett. 98, 161102 (2011); http://dx.doi.org/10.1063/1.3574606 (3 pages) | Cited 6 times

Online Publication Date: 18 April 2011

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Dielectric-loaded plasmonic waveguide disk resonators (WDRs) operating at telecom wavelengths are fabricated and investigated. Disks resonators of various radii coupled to a straight waveguide are studied both numerically and experimentally. For each disk radius, the gap between the disk and the waveguide is varied from 0 to 300 nm. Performance of the fabricated WDRs is characterized in the wavelength range of 1500–1620 nm using near-field optical microscopy. Wavelength selectivity and efficiency of the WDRs are evaluated and are in good agreement with numerical results.
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42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.82.Cr Fabrication techniques; lithography, pattern transfer

Giant dynamical Stark shift in germanium quantum wells

Niko S. Köster, Kolja Kolata, Ronja Woscholski, Christoph Lange, Giovanni Isella, Daniel Chrastina, Hans von Känel, and Sangam Chatterjee

Appl. Phys. Lett. 98, 161103 (2011); http://dx.doi.org/10.1063/1.3580630 (3 pages) | Cited 3 times

Online Publication Date: 18 April 2011

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We report a strong dynamical (ac) Stark shift of the direct gap transitions in Ge quantum wells at both cryogenic and room temperature. A blueshift of 67 meV is observed, exceeding values reported for III-V materials by about an order of magnitude. The fast intervalley scattering in the Ge material system leads to short dephasing times which in return causes larger shifts.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects

Luminescence dynamics in Ga(AsBi)

Sebastian Imhof, Christian Wagner, Angela Thränhardt, Alexej Chernikov, Martin Koch, Niko S. Köster, Sangam Chatterjee, Stephan W. Koch, Oleg Rubel, Xianfeng Lu, Shane R. Johnson, Daniel A. Beaton, and Thomas Tiedje

Appl. Phys. Lett. 98, 161104 (2011); http://dx.doi.org/10.1063/1.3580773 (3 pages) | Cited 2 times

Online Publication Date: 18 April 2011

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The temporal evolution of the spectrally resolved luminescence is measured for a Ga(AsBi) sample at low temperatures. The results are analyzed with the help of kinetic Monte Carlo simulations incorporating two disorder scales attributed to alloy disorder and Bi- clustering. An average time of 5 ps is identified as the upper limit for carrier capture into the Bi clusters whereas the extracted hopping rate associated with alloy fluctuations is much faster than the transitions between the individual cluster sites.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Tunable semiconductor vertical-cavity surface-emitting laser with an intracavity liquid crystal layer

O. Castany, L. Dupont, A. Shuaib, J. P. Gauthier, C. Levallois, and C. Paranthoën

Appl. Phys. Lett. 98, 161105 (2011); http://dx.doi.org/10.1063/1.3569591 (3 pages) | Cited 2 times

Online Publication Date: 18 April 2011

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A tunable vertical-cavity surface-emitting laser is fabricated where tunability is achieved with an intracavity layer of nematic liquid crystal and gain is provided by a semiconductor quantum well structure. The anisotropic liquid crystal layer enables a continuously tunable single-mode emission along the extraordinary axis of the layer. Polarization control is achieved when the layer thickness is such that the ordinary modes are out of the spectral gain region. Laser emission in the 1.5μm telecom wavelength range is demonstrated under optical pumping with a tuning range of more than 30 nm for an applied voltage of less than 3 V.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.70.Df Liquid crystals

Tuning random lasers by engineered absorption

Ramy G. S. El-Dardiry and Ad Lagendijk

Appl. Phys. Lett. 98, 161106 (2011); http://dx.doi.org/10.1063/1.3571452 (3 pages) | Cited 7 times

Online Publication Date: 19 April 2011

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We achieve control over the emission wavelength of a random laser experimentally by adjusting the amount of absorption of emission light. The random laser consists of elastic scatterers in a high quantum efficiency gain medium to which a nonfluorescent dye is added. This nonfluorescent dye shifts the net gain curve and thereby the emission peak of the random laser. Mode competition effects are observed and explained. We interpret our results using a theoretical model that describes the spectral response of the system as a function of the effective cavity decay time and (re)absorption processes.
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42.60.Fc Modulation, tuning, and mode locking
42.25.Bs Wave propagation, transmission and absorption
FREE

Indirect Auger recombination as a cause of efficiency droop in nitride light-emitting diodes

Emmanouil Kioupakis, Patrick Rinke, Kris T. Delaney, and Chris G. Van de Walle

Appl. Phys. Lett. 98, 161107 (2011); http://dx.doi.org/10.1063/1.3570656 (3 pages) | Cited 36 times

Online Publication Date: 19 April 2011

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InGaN-based light-emitting diodes (LEDs) exhibit a significant efficiency loss (droop) when operating at high injected carrier densities, the origin of which remains an open issue. Using atomistic first-principles calculations, we show that this efficiency droop is caused by indirect Auger recombination, mediated by electron-phonon coupling and alloy scattering. By identifying the origin of the droop, our results provide a guide to addressing the efficiency issues in nitride LEDs and the development of efficient solid-state lighting.
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85.60.Jb Light-emitting devices

Ultrasmall and ultrafast all-optical modulation based on a plasmonic lens

Song Yue, Zhi Li, Jianjun Chen, and Qihuang Gong

Appl. Phys. Lett. 98, 161108 (2011); http://dx.doi.org/10.1063/1.3581895 (3 pages) | Cited 2 times

Online Publication Date: 20 April 2011

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By exciting a plasmonic lens with femtosecond laser and utilizing the optical nonlinearity of the gold, an ultrasmall and ultrafast all-optical modulation spot was achieved inside a thin gold film. Near-field pump-probe measurements indicated a modulation spot size of about 600 nm, and a response time of about 1.5 ps. Even smaller spot size of about 300 nm was inferred from numerical simulations, beyond the diffraction limit given an incident wavelength of 1000 nm. Moreover, the optical nonlinearity and the modulation depth were increased by one order of magnitude at the focus compared to that at positions without structures.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.47.J- Ultrafast spectroscopy (<1 psec)

Optofluidic Tomography on a Chip

Serhan O. Isikman, Waheb Bishara, Hongying Zhu, and Aydogan Ozcan

Appl. Phys. Lett. 98, 161109 (2011); http://dx.doi.org/10.1063/1.3548564 (3 pages) | Cited 7 times

Online Publication Date: 20 April 2011

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multimedia

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Using lensfree holography we demonstrate optofluidic tomography on a chip. A partially coherent light source is utilized to illuminate the objects flowing within a microfluidic channel placed directly on a digital sensor array. The light source is rotated to record lensfree holograms of the objects at different viewing directions. By capturing multiple frames at each illumination angle, pixel super-resolution techniques are utilized to reconstruct high-resolution transmission images at each angle. Tomograms of flowing objects are then computed through filtered back-projection of these reconstructed lensfree images, thereby enabling optical sectioning on-a-chip. The proof-of-concept is demonstrated by lensfree tomographic imaging of C. elegans.
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87.63.L- Visual imaging
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.30.Wb Image reconstruction; tomography

Exciton-polariton microphotoluminescence and lasing from ZnO whispering-gallery mode microcavities

J. Dai, C. X. Xu, X. W. Sun, and X. H. Zhang

Appl. Phys. Lett. 98, 161110 (2011); http://dx.doi.org/10.1063/1.3579140 (3 pages) | Cited 4 times

Online Publication Date: 21 April 2011

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Hexagonal ZnO microrods were employed as whispering-gallery mode (WGM) optical microcavities to investigate exciton-polariton microphotoluminescence and lasing emission. Using a confocal microphotoluminescence system, the exciton-polariton emission with a large Rabi splitting of about 90 meV was observed from a ZnO microrod with the diameter of 9.38 μm. The spatial-resolved spectra demonstrated a collective nonlinear blueshift in the WGM resonance peaks along a tapered microrod and proved the anticross dispersion property of the exciton-polariton. Furthermore, the exciton-polariton WGM lasing was stimulated and blueshifted in the strong coupling region under the excitation of a 355 nm nanosecond pulsed laser.
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78.55.Et II-VI semiconductors
42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Second harmonic generation with zero phase velocity waves

Walter R. C. Somerville, David A. Powell, and Ilya V. Shadrivov

Appl. Phys. Lett. 98, 161111 (2011); http://dx.doi.org/10.1063/1.3580616 (3 pages)

Online Publication Date: 21 April 2011

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We design a dual-band nonlinear composite right-left handed transmission line with phase-matching achieved between the fundamental frequency and second harmonic when both interacting waves have zero phase velocity. Additionally, we show that such a transmission line supports a new regime where the generation of backward second harmonic waves is achieved from a backward fundamental frequency wave.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media

Nonorthodox heterodyne electro-optic detection for terahertz optical systems

J. Darmo, D. Dietze, M. Martl, and K. Unterrainer

Appl. Phys. Lett. 98, 161112 (2011); http://dx.doi.org/10.1063/1.3567754 (3 pages)

Online Publication Date: 22 April 2011

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An electro-optic detector of terahertz electromagnetic waves with boosted performance is presented. The detector utilizes a heterodyne detection technique to achieve orders of magnitude better responsivity compared to a standard detector setup. We prove theoretically as well as demonstrate experimentally the feasibility of this technique for electro-optic detection.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Twin-beam optical parametric generation in χ(2) nonlinear photonic crystals

Katia Gallo, Martin Levenius, Fredrik Laurell, and Valdas Pasiskevicius

Appl. Phys. Lett. 98, 161113 (2011); http://dx.doi.org/10.1063/1.3583444 (3 pages) | Cited 3 times

Online Publication Date: 22 April 2011

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We demonstrate optical parametric generation in two-dimensional purely nonlinear lattices. Experiments performed in hexagonally poled LiTaO3 crystals pumped around 800 nm indicate a coherent contribution to the parametric gain arising from multiple resonances of the lattice, resulting in dual-beam signal outputs in the 1–1.7 μm range.
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42.70.Qs Photonic bandgap materials
42.65.Lm Parametric down conversion and production of entangled photons
42.65.Yj Optical parametric oscillators and amplifiers

Ultimate fast optical switching of a planar microcavity in the telecom wavelength range

Georgios Ctistis, Emre Yuce, Alex Hartsuiker, Julien Claudon, Maela Bazin, Jean-Michel Gérard, and Willem L. Vos

Appl. Phys. Lett. 98, 161114 (2011); http://dx.doi.org/10.1063/1.3580615 (3 pages) | Cited 8 times

Online Publication Date: 22 April 2011

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See Also: Erratum

Show Abstract
We have studied a GaAs–AlAs planar microcavity with a resonance near 1300 nm in the telecom range by ultrafast pump-probe reflectivity. By the judicious choice of pump frequency, we observe an ultimate fast and reversible decrease in the resonance frequency by more than half a linewidth due to the instantaneous electronic Kerr effect. The switch-on and switch-off of the cavity is only limited by the cavity storage time of τcav = 0.3 ps and not by intrinsic material parameters. Our results pave the way to supraterahertz switching rates for on-chip data modulation and real-time cavity quantum electrodynamics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.-e Optical elements, devices, and systems
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