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12 Oct 2009

Volume 95, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 95, 153101 (2009); http://dx.doi.org/10.1063/1.3244597 (3 pages)

Geunjae Kwak, Mikyung Lee, Karuppanan Senthil, and Kijung Yong
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Emission modification of CdSe quantum dots by titanium dioxide visible logpile photonic crystal

G. Subramania, Y.-J. Lee, A. J. Fischer, T. S. Luk, C. J. Brinker, and D. Dunphy

Appl. Phys. Lett. 95, 151101 (2009); http://dx.doi.org/10.1063/1.3245309 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2009

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Air band modes of three-dimensional photonic crystals (3DPCs) have a higher photonic density of states, potentially enabling greater emission enhancement. However, it is challenging to introduce emitters into the “air” region without significantly disturbing the photonic band structure of the PC. Here, we overcome this difficulty by introducing a low refractive index aerogel matrix containing CdSe quantum dots (625 nm peak emission) into a titanium dioxide logpile PC. We observe that the aerogel infiltration indeed preserves the bandstructure. We measure an emission suppression of ∼ 0.25 times inside and an enhancement of approximately three times outside the bandgap with only one vertical unit cell.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Engineering of low-loss metal for nanoplasmonic and metamaterials applications

D. A. Bobb, G. Zhu, M. Mayy, A. V. Gavrilenko, P. Mead, V. I. Gavrilenko, and M. A. Noginov

Appl. Phys. Lett. 95, 151102 (2009); http://dx.doi.org/10.1063/1.3237179 (3 pages) | Cited 24 times

Online Publication Date: 12 October 2009

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We have shown that alloying a noble metal (gold) with another metal (cadmium), which can contribute two electrons per atom to a free electron gas, can significantly improve the metal’s optical properties in certain wavelength ranges and make them worse in the other parts of the spectrum. In particular, in the gold-cadmium alloy we have demonstrated a significant expansion of the spectral range of metallic reflectance to shorter wavelengths. The experimental results and the predictions of the first principles theory demonstrate an opportunity for the improvement and optimization of low-loss metals for nanoplasmonic and metamaterials applications.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.10.Ca Electron gas, Fermi gas
42.70.-a Optical materials

Carrier distribution in InGaN/GaN tricolor multiple quantum well light emitting diodes

R. Charash, P. P. Maaskant, L. Lewis, C. McAleese, M. J. Kappers, C. J. Humphreys, and B. Corbett

Appl. Phys. Lett. 95, 151103 (2009); http://dx.doi.org/10.1063/1.3244203 (3 pages) | Cited 6 times

Online Publication Date: 12 October 2009

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Carrier transport in InGaN light emitting diodes has been studied by comparing the electroluminescence (EL) from a set of triple quantum well structures with different indium content in each well, leading to multicolor emission. Both the sequence and width of the quantum wells have been varied. Comparison of the EL spectra reveals the current dependent carrier transport between the quantum wells, with a net carrier flow toward the deepest quantum well.
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85.60.Jb Light-emitting devices
73.63.Hs Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

A spectral route to determining chirality

Jesper Goor Pedersen and Niels Asger Mortensen

Appl. Phys. Lett. 95, 151104 (2009); http://dx.doi.org/10.1063/1.3246153 (3 pages)

Online Publication Date: 13 October 2009

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We show how one-dimensional structured media can be used to measure chirality, via the spectral shift of the photonic band gap edges. Analytically, we show that a chiral contrast can, in some cases, be mapped unto an index contrast, thereby greatly simplifying the analysis of such structures. Using this mapping, we derive a first-order shift of the band gap edges with chirality. Potentially, this effect could be used for measuring enantiomeric excess.
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78.20.Ek Optical activity

Evidence of type-I direct recombination in InP/GaP quantum dots via magnetoluminescence

C. v. Dewitz, F. Hatami, M. Millot, J. M. Broto, J. Léotin, and W. T. Masselink

Appl. Phys. Lett. 95, 151105 (2009); http://dx.doi.org/10.1063/1.3246161 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2009

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Photoluminescence from InP quantum dots within a GaP matrix is investigated as a function of magnetic field. By fitting the magnetoluminescence data to the energy states of the electrons and holes confined in quantum dots in a perpendicular magnetic field, the electron-hole reduced effective mass is determined to be 0.094m0. The diamagnetic shift in the luminescence peak gives an average exciton radius of about 5 nm, smaller than the dot radius. These results indicate that the recombining electrons are primarily composed of states originating from the InP Γ valley although the conduction band discontinuity between the InP and the GaP barrier is expected to be very small or even negative.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
75.20.Ck Nonmetals

Tm3+-doped ion-exchanged aluminum germanate glass waveguide for S-band amplification

D. L. Yang, E. Y.B. Pun, and H. Lin

Appl. Phys. Lett. 95, 151106 (2009); http://dx.doi.org/10.1063/1.3247888 (3 pages) | Cited 9 times

Online Publication Date: 13 October 2009

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K+–Na+ ion-exchanged channel waveguide amplifiers have been fabricated in Tm3+-doped acid-resistant aluminum germanate glasses. The optical and relative gains of a 3.15-cm-long waveguide channel were achieved to be 4.05 and 2.29 dB at 1.482 μm wavelength under 110 mW 793 nm laser excitation, respectively. After compensating the propagation loss, an internal gain of 1.50 dB and a remarkable gain coefficient of 0.48 dB/cm were obtained, which reveals a definite S-band signal amplification in the low phonon energy glass waveguide. As an expectation, UV-radiation-sensitive glass waveguide should promote the developments of gain-flatten S-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact multifunctional integrated optical devices.
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42.82.Et Waveguides, couplers, and arrays
42.70.Ce Glasses, quartz
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Hj Laser materials

Electro-optic properties of BaTeMo2O9 single crystal

Zeliang Gao, Xin Yin, Weiguo Zhang, Shanpeng Wang, Minhua Jiang, and Xutang Tao

Appl. Phys. Lett. 95, 151107 (2009); http://dx.doi.org/10.1063/1.3242012 (3 pages) | Cited 11 times

Online Publication Date: 14 October 2009

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The electro-optic (EO) properties of monoclinic BaTeMo2O9 (BTM) single crystals are studied using the interference technique by applying the external electric field. The measured room temperature free EO coefficients at 632.8 nm are 10.2 and 9.0 pm/V for γ12 and γ41, respectively. The EO effect (−½ni3γijE) of BTM is about three times as high as that of KH2PO4 (KDP) crystal, which makes it a very promising candidate for the EO applications.
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78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effect of material properties on reverse flow in nematic liquid crystal devices with homeotropic alignment

Pieter J. M. Vanbrabant, Jeroen Beeckman, Kristiaan Neyts, Richard James, and F. Anibal Fernandez

Appl. Phys. Lett. 95, 151108 (2009); http://dx.doi.org/10.1063/1.3242018 (3 pages)

Online Publication Date: 14 October 2009

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Reverse flow is undesirable in liquid crystal devices with vertical alignment. The influence of the material properties on the onset of backflow is investigated for commercially available negative dielectric liquid crystals. It is shown that the threshold voltage VBF for the occurrence of backflow is an important material characteristic. This threshold is relevant for applications and a large value is desired in devices to avoid backflow while keeping a wide applicable voltage range. Accurate finite element simulation of the liquid crystal hydrodynamics allows extraction of VBF and the unknown Miesowicz coefficients ηij. The resulting values are tabulated at 20.0 °C.
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47.57.Lj Flows of liquid crystals
61.30.-v Liquid crystals
47.11.Fg Finite element methods

Plasmon enhanced light emission from InGaN quantum wells via coupling to chemically synthesized silver nanoparticles

John Henson, John C. Heckel, Emmanouil Dimakis, Josh Abell, Anirban Bhattacharyya, George Chumanov, Theodore D. Moustakas, and Roberto Paiella

Appl. Phys. Lett. 95, 151109 (2009); http://dx.doi.org/10.1063/1.3249579 (3 pages) | Cited 7 times

Online Publication Date: 15 October 2009

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Chemically synthesized single-crystal silver nanoparticles are used to demonstrate plasmon enhanced visible light emission from nitride semiconductor quantum wells. For ease of assembly and testing, the nanoparticles are embedded onto the surface of flexible resin films, which are then simply adhered on top of the light emitting samples. Large enhancements in photoluminescence efficiency are correspondingly measured at emission wavelengths near the nanoparticle plasmonic resonance. At the same time, when samples emitting at a sufficiently far detuned wavelength are used, the measured efficiency is not affected by the nanoparticles, which confirms the plasmonic origin of the observed enhancement.
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78.67.De Quantum wells
78.55.-m Photoluminescence, properties and materials
73.22.Lp Collective excitations
73.21.Fg Quantum wells
68.65.Fg Quantum wells
81.16.Be Chemical synthesis methods

Terahertz spectroscopy of shift currents resulting from asymmetric (110)-oriented GaAs/AlGaAs quantum wells

Shekhar Priyadarshi, Markus Leidinger, Klaus Pierz, Ana M. Racu, Uwe Siegner, Mark Bieler, and Philip Dawson

Appl. Phys. Lett. 95, 151110 (2009); http://dx.doi.org/10.1063/1.3249611 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2009

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We report the observation and the study of an additional shift current tensor element in (110)-oriented GaAs quantum wells, which arises from an out-of-plane asymmetry of the quantum well structure. The current resulting from this tensor element is optically induced with 150 fs laser pulses and detected by measuring the simultaneously emitted terahertz radiation. This terahertz spectroscopy of shift currents is a powerful technique for symmetry investigations, which shows, for example, that our nominally symmetric (110)-oriented GaAs/AlGaAs quantum wells grown by molecular beam epitaxy are in reality asymmetric structures with different right and left interfaces.
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78.67.De Quantum wells
81.07.St Quantum wells
68.65.Fg Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.70.Gq Microwave and radio-frequency interactions
81.05.Ea III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Förster resonance energy transfer enhanced color-conversion using colloidal semiconductor quantum dots for solid state lighting

Sedat Nizamoglu and Hilmi Volkan Demir

Appl. Phys. Lett. 95, 151111 (2009); http://dx.doi.org/10.1063/1.3222902 (3 pages) | Cited 6 times

Online Publication Date: 15 October 2009

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In this paper, we present Förster resonance energy transfer (FRET)-enhanced color-conversion using colloidal semiconductor quantum dot nanocrystals (NCs) to make reddish-orange light-emitting diodes for use in ultraefficient solid state lighting. To achieve FRET enhancement at 614 nm, we use an energy gradient hybrid structure made of cyan- and orange-emitting CdSe/ZnS NCs (λPL = 492 and 588 nm in solution, respectively). This enables recycling of trapped excitons using FRET and achieves a relative quantum efficiency enhancement of 15.1% in reddish-orange full color-conversion for the integrated hybrid cyan-orange NC layer with respect to the case of full color-conversion using only orange NCs without FRET.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
85.60.Jb Light-emitting devices
71.35.-y Excitons and related phenomena

High power thermoelectrically cooled and uncooled quantum cascade lasers with optimized reflectivity facet coatings

Richard Maulini, Arkadiy Lyakh, Alexei Tsekoun, Rowel Go, Christian Pflügl, Laurent Diehl, Federico Capasso, and C. Kumar N. Patel

Appl. Phys. Lett. 95, 151112 (2009); http://dx.doi.org/10.1063/1.3246799 (3 pages) | Cited 17 times

Online Publication Date: 15 October 2009

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We present a method of preserving the device wall-plug efficiency by adjusting mirror losses with facet coatings for longer cavity quantum cascade lasers. An experimental study of output power and wall-plug efficiency as functions of mirror losses was performed by varying the front facet coating reflectivity with a high-reflectivity-coated rear facet. The use of optimized reflectivity coatings on 7-mm-long chips resulted in continuous-wave output power of 2.9 W at 293 K for thermoelectrically cooled devices mounted on AlN submounts and average and continuous-wave output power in excess of 1 W for uncooled devices emitting at 4.6 μm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Enhancement of p-type conductivity by modifying the internal electric field in Mg- and Si-δ-codoped AlxGa1−xN/AlyGa1−yN superlattices

Jinchai Li, Weihuang Yang, Shuping Li, Hangyang Chen, Dayi Liu, and Junyong Kang

Appl. Phys. Lett. 95, 151113 (2009); http://dx.doi.org/10.1063/1.3248026 (3 pages) | Cited 2 times

Online Publication Date: 15 October 2009

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The internal electric field is modified by using Mg- and Si-δ-codoped AlxGa1−xN/AlyGa1−yN superlattices (SLs). The first-principles simulation results show that the internal electric field in SL has been significantly intensified due to the charge transferring from Si-doped interface to Mg-doped interface. Accordingly, the Mg- and Si-δ-codoped p-type Al0.2Ga0.8N/GaN SLs are grown by metalorganic vapor phase epitaxy and higher hole concentration as much as twice of that in modulation-doped SL has been achieved, as determined by Hall effect measurements. Furthermore, by applying Mg- and Si-δ-codoped AlxGa1−xN/AlyGa1−yN SLs with high Al content as the p-type layers, we have fabricated deep ultraviolet light emitting diodes with superior current-voltage characteristics by lowering Mg-acceptor activation energy.
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73.61.Ey III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.21.Cd Superlattices
61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Emission of Tamm plasmon/exciton polaritons

C. Symonds, A. Lemaître, E. Homeyer, J. C. Plenet, and J. Bellessa

Appl. Phys. Lett. 95, 151114 (2009); http://dx.doi.org/10.1063/1.3251073 (3 pages) | Cited 13 times

Online Publication Date: 16 October 2009

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We report on the observation of the strong coupling regime occurring between a Tamm plasmon (TP) mode and an exciton from inorganic quantum wells (QWs). The sample is formed by a silver thin film deposited onto an AlAs/GaAlAs Bragg reflector containing InGaAs QWs located in the high refractive index layers. Angular resolved reflectometry experiments evidence a clear anticrossing in the dispersion relations, a signature of the strong coupling regime. The Rabi splitting energy is 11.5 meV. The experimental data are in very good agreement with simple transfer matrix calculations. The emission from low and high energy TP/exciton polaritons is also demonstrated.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.Fg Quantum wells
68.55.-a Thin film structure and morphology

Two-directional lasing from a dye-doped two-dimensional hexagonal photonic crystal made of holographic polymer-dispersed liquid crystals

D. Luo, X. W. Sun, H. T. Dai, Y. J. Liu, H. Z. Yang, and W. Ji

Appl. Phys. Lett. 95, 151115 (2009); http://dx.doi.org/10.1063/1.3251078 (3 pages) | Cited 3 times

Online Publication Date: 16 October 2009

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Lasing actions are demonstrated in two high-symmetry directions (ΓM and ΓK) of a two-dimensional hexagonal photonic crystal from dye-doped holographic polymer-dispersed liquid crystals. The group velocity anomaly, which is peculiar to two-dimensional and three-dimensional photonic crystals, leads to substantial enhancement in local fields in the two-dimensional photonic crystal with a low-index contrast. The difference on the lasing thresholds between the two directions is interpreted as the result of different group velocities of the flat bands where laser oscillation occurred.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Df Liquid crystals
42.70.Hj Laser materials
42.40.My Applications
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems

40 Gb/s surface-illuminated Ge-on-Si photodetectors

Johann Osmond, Laurent Vivien, Jean-Marc Fédéli, Delphine Marris-Morini, Paul Crozat, Jean-François Damlencourt, Eric Cassan, and Y. Lecunff

Appl. Phys. Lett. 95, 151116 (2009); http://dx.doi.org/10.1063/1.3243694 (3 pages) | Cited 4 times

Online Publication Date: 16 October 2009

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This paper reports on surface illuminated Ge photodetectors monolithically integrated on Si substrate operating in the C and L wavelength bands. The responsivity at a wavelength of 1.5 μm ranges from 0.08 to 0.21 A/W without bias voltage for Ge mesa diameter ranging from 10 to 25 μm, respectively. The measured −3 dB cut-off frequency is as high as 49 GHz under a reverse bias of 5 V at a wavelength of 1.5 μm. An open eye diagram up to 40 Gbit/s is also demonstrated.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
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