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27 Feb 2012

Volume 100, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.
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Non-equilibrium longitudinal and transverse optical phonons in terahertz quantum cascade lasers

Miriam S. Vitiello, Rita C. Iotti, Fausto Rossi, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, David A. Ritchie, Qing Hu, and Gaetano Scamarcio

Appl. Phys. Lett. 100, 091101 (2012); http://dx.doi.org/10.1063/1.3687913 (4 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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We report on the experimental observation of non-equilibrium longitudinal (LO) and interface transverse-like (IF-TO) optical phonons populations associated with electron transport in resonant-phonon THz quantum-cascade lasers. The measured LO-phonon occupation numbers are in excellent agreement with the result of Monte Carlo simulations at a phonon in-plane wave number q = 4.2 × 10+4 cm−1, and they remain about 40% larger than the IF-TO ones.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
43.35.Gk Phonons in crystal lattices, quantum acoustics
02.70.Ss Quantum Monte Carlo methods

Ultrasonic variable-focus optical lens using viscoelastic material

Daisuke Koyama, Ryoichi Isago, and Kentaro Nakamura

Appl. Phys. Lett. 100, 091102 (2012); http://dx.doi.org/10.1063/1.3688937 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2012

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A variable-focus lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.
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42.79.Bh Lenses, prisms and mirrors
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound

Influence of a depletion layer on localized surface waves in doped semiconductor nanostructures

S. Vassant, F. Pardo, P. Bouchon, R. Haïdar, F. Marquier, J. J. Greffet, and J. L. Pelouard

Appl. Phys. Lett. 100, 091103 (2012); http://dx.doi.org/10.1063/1.3689747 (3 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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We report THz polarized reflectivity measurements on a doped GaAs grating made of thin walls with subwavelength dimensions and periodicity. A clear dip appears in the TM-polarized reflectivity spectrum, due to the excitation of a localized surface plasmon-phonon mode along the grating walls. The theoretical model used to describe the electromagnetic response of the grating shows the importance of the depletion layer at the GaAs surface and indicates a high sensitivity of the reflectivity dip frequency to the surface potential.
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73.22.Lp Collective excitations
78.30.Fs III-V and II-VI semiconductors
78.68.+m Optical properties of surfaces
81.05.Ea III-V semiconductors
42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

The polarization field dependence of Ti/Al based Ohmic contacts on N-type semipolar GaN

Roy B. Chung, Hung-Tse Chen, Chih-Chien Pan, Jun-Seok Ha, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 100, 091104 (2012); http://dx.doi.org/10.1063/1.3690878 (3 pages)

Online Publication Date: 28 February 2012

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We report on the polarization field dependence of the Ti/Al based n-type contacts on various polar and semipolar GaN planes. The contact resistance of the metal contacts on N-face GaN could be lowered by photoelectrochemical (PEC) etching, which formed a pyramidal feature on the surface with {10mathmath} facets. The contact resistance on the semipolar (10mathmath) surface was 6.3 × 10−5 Ω cm2, showing even lower contact resistance than the PEC etched N-face when annealed at 450 °C. Among few semipolar planes, (10mathmath), (11mathmath), and (11math2), the contact resistance was the lowest with (11mathmath) plane, which is the plane with the stronger polarization field than (10mathmath) and more Ga rich surface than (11math2) plane.
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73.40.Ns Metal-nonmetal contacts
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
73.40.Cg Contact resistance, contact potential

High-Q aluminum nitride photonic crystal nanobeam cavities

W. H. P. Pernice, C. Xiong, C. Schuck, and H. X. Tang

Appl. Phys. Lett. 100, 091105 (2012); http://dx.doi.org/10.1063/1.3690888 (4 pages) | Cited 8 times

Online Publication Date: 29 February 2012

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We demonstrate high optical quality factors in aluminum nitride (AlN) photonic crystal nanobeam cavities. Suspended AlN photonic crystal nanobeams are fabricated in sputter-deposited AlN-on-insulator substrates using a self-protecting release process. Employing one-dimensional photonic crystal cavities coupled to integrated optical circuits, we measure quality factors up to 146 000. By varying the waveguide-cavity coupling gap, extinction ratios in excess of 15 dB are obtained. Our results open the door for integrated photonic bandgap structures made from a low loss, wide-transparency, nonlinear optical material system.
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42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Experimental observation of leaky modes and plasmons in a hybrid resonance element

R. Magnusson, H. G. Svavarsson, J. Yoon, M. Shokooh-Saremi, and S. H. Song

Appl. Phys. Lett. 100, 091106 (2012); http://dx.doi.org/10.1063/1.3690951 (3 pages)

Online Publication Date: 29 February 2012

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We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799 nm wavelength and a modal resonance at 669 nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725 nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Enhancement of light extraction efficiency by evanescent wave coupling effect in ridge-shaped AlGaInP/GaInP quantum wells

Guo-Dong Hao and Xue-Lun Wang

Appl. Phys. Lett. 100, 091107 (2012); http://dx.doi.org/10.1063/1.3689005 (3 pages)

Online Publication Date: 29 February 2012

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The optical properties of a sub-wavelength-sized ridge-shaped AlGaInP/GaInP quantum well structure fabricated by selective-area metal organic vapor phase epitaxy are investigated. The ridge structure exhibits an 8.5 times stronger photoluminescence intensity at room temperature than a planar structure, corresponding to an enhancement of at least 13.6 times in the light extraction efficiency of the ridge sample with respect to the planar sample. Both emission pattern measurements and theoretical simulation demonstrate that the high light extraction efficiency originates from the evanescent wave coupling effect in a narrow ridge structure, which can directly extract the light outside the escape cones to air.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.55.Cr III-V semiconductors

Microcavity enhanced single photon emission from an electrically driven site-controlled quantum dot

C. Schneider, T. Heindel, A. Huggenberger, T. A. Niederstrasser, S. Reitzenstein, A. Forchel, S. Höfling, and M. Kamp

Appl. Phys. Lett. 100, 091108 (2012); http://dx.doi.org/10.1063/1.3689782 (4 pages) | Cited 10 times

Online Publication Date: 29 February 2012

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In this work we report on the integration of single site-controlled quantum dots (SCQDs) into electrically driven micropillar cavities. The electroluminescence of these devices features emission of single SCQDs with inhomogeneous broadenings down to 170 µeV. The enhancement of electroluminescence by quantum dot-cavity coupling is demonstrated by temperature dependent investigations. Single photon emission from a spatially and spectrally coupled SCQD-resonator system is confirmed by photon autocorrelation measurements under electrical excitation yielding a g(2)(0) value of 0.42.
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78.67.Hc Quantum dots
07.10.Cm Micromechanical devices and systems
78.60.Fi Electroluminescence

Site-controlled InP/GaInP quantum dots emitting single photons in the red spectral range

Vasilij Baumann, Florian Stumpf, Christian Schneider, Stefan Kremling, Lukas Worschech, Alfred Forchel, Sven Höfling, and Martin Kamp

Appl. Phys. Lett. 100, 091109 (2012); http://dx.doi.org/10.1063/1.3690872 (3 pages) | Cited 5 times

Online Publication Date: 1 March 2012

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We report on site-controlled growth of InP/GaInP quantum dots (QDs) on GaAs substrates. The QD nucleation sites are defined by shallow nanoholes etched into a GaInP layer. Optimized growth conditions allow us to realize QD arrays with excellent long range ordering on nanohole periods as large as 1.25 µm. Single QD lines with an average linewidth of 553 µeV and best values below 200 µeV are observed. Photoluminescence spectroscopy reveals excitonic and biexcitonic emission in the wavelength range of about 670 nm (1.85 eV) with an exciton-biexciton splitting of 1.8 meV. Second-order photon-autocorrelation measurements show clear single photon emission with g(2)(0) = 0.13 ± 0.01.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots

Experimental observation of helical microbunching of a relativistic electron beam

E. Hemsing, A. Knyazik, F. O’Shea, A. Marinelli, P. Musumeci, O. Williams, S. Tochitsky, and J. B. Rosenzweig

Appl. Phys. Lett. 100, 091110 (2012); http://dx.doi.org/10.1063/1.3690900 (4 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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Experimental observation of the microbunching of a relativistic electron beam at the second harmonic interaction frequency of a helical undulator is presented. The microbunching signal is observed from the coherent transition radiation of the electron beam and indicates experimental evidence of a dominantly helical electron beam density distribution. This result is in agreement with theoretical and numerical predictions and provides a proof-of-principle demonstration of proposed schemes designed to generate light with orbital angular momentum in high-gain free-electron lasers.
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41.60.Cr Free-electron lasers

Excitations of surface plasmon polaritons in double layer metal grating structures

N. Anttu, Z. Q. Guan, U. Håkanson, H. X. Xu, and H. Q. Xu

Appl. Phys. Lett. 100, 091111 (2012); http://dx.doi.org/10.1063/1.3690947 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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We study the light scattering properties of double layer gratings (DLGs) made from Au on SiO2 substrates. It is found that surface plasmon polaritons (SPPs) can be excited in the DLGs for a separation of up to 150 nm between the two Au grating layers and the collective reflectance spectra exhibit a strong resonant peak and a closely lying dip as a result of the surface plasmon polariton excitations. It is also found that the angle-resolved specular reflectance spectra show a dip-peak pair structure, while the angle-resolved reflectance spectra of higher diffracted orders show a complementary peak-dip pair structure. Finally, operation of the DLGs for efficient wavelength demultiplexing is proposed and discussed in light of these results.
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42.79.Dj Gratings
73.43.Lp Collective excitations
78.66.Bz Metals and metallic alloys

Robust generation of bright two-color entangled optical beams from a phase-insensitive optical parametric amplifier

Xiaomin Guo, Junjun Zhao, and Yongmin Li

Appl. Phys. Lett. 100, 091112 (2012); http://dx.doi.org/10.1063/1.3690876 (3 pages)

Online Publication Date: 2 March 2012

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Bright two-color continuous variable (CV) entangled optical beams at 0.8 and 1.5 μm are generated by utilizing a phase-insensitive optical parametric amplifier with only 1.5 μm signal field injected. Without locking the relative phase between the signal and pump fields, the amplitude quadrature difference squeezing of 3.30 dB and phase quadrature sum squeezing of 3.35 dB are observed, which satisfy the entanglement criterion. The demonstrated scheme here eliminates the necessity of precise phase control between the signal and pump fields and enables robust generation of two-color CV entangled states.
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42.65.Yj Optical parametric oscillators and amplifiers
03.67.Bg Entanglement production and manipulation
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
42.50.Dv Quantum state engineering and measurements
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Terahertz emission from a two-color plasma filament in a slot waveguide

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

Appl. Phys. Lett. 100, 091113 (2012); http://dx.doi.org/10.1063/1.3691921 (3 pages)

Online Publication Date: 2 March 2012

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Terahertz emission in forward direction from a long two-color filament placed in the center of a slot waveguide is reported. The waveguide improves the collection and imaging of the generated THz radiation. By tuning the plate separation and position of the waveguide along the filament axis, the emitted mode can be matched to the collection optics. We achieved an increase of the detected electric field by 40% and of the THz pulse energy by four times compared to the case without waveguide.
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84.40.Az Waveguides, transmission lines, striplines
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
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