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13 May 2013

Volume 102, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 102, 192401 (2013); http://dx.doi.org/10.1063/1.4803908 (4 pages)

Shawn Pollard, Marek Malac, Marco Beleggia, Masahiro Kawasaki, and Yimei Zhu
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Minority current distribution in InGaAs/GaAs transistor-vertical-cavity surface-emitting laser

Y. Xiang, X. Yu, J. Berggren, T. Zabel, M. Hammar, and M. N. Akram

Appl. Phys. Lett. 102, 191101 (2013); http://dx.doi.org/10.1063/1.4803175 (3 pages)

Online Publication Date: 13 May 2013

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We compare experimental data with three-dimensional numerical calculations of the local minority current in an InGaAs/GaAs transistor vertical-cavity surface-emitting laser at different bias levels. It is demonstrated that lateral potential variations within the device greatly affect the transistor operating conditions. As a result, it locally operates in the active mode in the center of the device, allowing for efficient stimulated recombination, while it globally operates in the saturation regime as reflected by the measured current-voltage characteristics. This allows for excellent laser performance, including mW-range output power, sub-mA threshold base current, and continuous-wave operation well above room temperature.
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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.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
85.30.Pq Bipolar transistors

Effect of excited states on the ground-state modulation bandwidth in quantum dot lasers

Yuchang Wu, Robert A. Suris, and Levon V. Asryan

Appl. Phys. Lett. 102, 191102 (2013); http://dx.doi.org/10.1063/1.4804994 (5 pages)

Online Publication Date: 13 May 2013

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We consider direct and indirect (excited-state-mediated) capture of carriers from the waveguide region into the lasing ground state in quantum dots (QDs) and calculate the modulation response of a QD laser. We show that, when only indirect capture is involved, the excited-to-ground-state relaxation delay strongly limits the ground-state modulation bandwidth of the laser—at the longest tolerable relaxation time, the bandwidth becomes zero. When direct capture is also involved, the effect of excited-to-ground-state relaxation is less significant and the modulation bandwidth is considerably higher.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Residual strain and piezoelectric effects in passivated GaAs/AlGaAs core-shell nanowires

Moïra Hocevar, Le Thuy Thanh Giang, Rudeesun Songmuang, Martien den Hertog, Lucien Besombes, Joël Bleuse, Yann-Michel Niquet, and Nikos T. Pelekanos

Appl. Phys. Lett. 102, 191103 (2013); http://dx.doi.org/10.1063/1.4803685 (5 pages)

Online Publication Date: 13 May 2013

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We observe a systematic red shift of the band-edge of passivated GaAs/Al0.35Ga0.65As core-shell nanowires with increasing shell thickness up to 100 nm. The shift is detected both in emission and absorption experiments, reaching values up to 14 meV for the thickest shell nanowires. Part of this red shift is accounted for by the small tensile strain imposed to the GaAs core by the AlGaAs shell, in line with theoretical calculations. An additional contribution to this red shift arises from axial piezoelectric fields which develop inside the nanowire core due to Al fluctuations in the shell.
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81.05.Ea III-V semiconductors
81.07.Gf Nanowires
81.65.Rv Passivation
77.65.-j Piezoelectricity and electromechanical effects

Optical time domain reflectometry with low noise waveguide-coupled superconducting nanowire single-photon detectors

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

Appl. Phys. Lett. 102, 191104 (2013); http://dx.doi.org/10.1063/1.4803011 (4 pages)

Online Publication Date: 13 May 2013

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We demonstrate optical time domain reflectometry over 200 km of optical fiber using low-noise NbTiN superconducting single-photon detectors integrated with Si3N4 waveguides. Our small detector footprint enables high timing resolution of 50 ps and a dark count rate of 3 Hz with unshielded fibers, allowing for identification of defects along the fiber over a dynamic range of 37.4 dB. Photons scattered and reflected back from the fiber under test can be detected in free-running mode without showing dead zones or other impairments often encountered in semiconductor photon-counting optical time domain reflectometers.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
07.60.Hv Refractometers and reflectometers
84.40.Az Waveguides, transmission lines, striplines

Importance of the localization for inter-subband scattering rates in quasi two-dimensional structures

C. Ndebeka-Bandou, F. Carosella, R. Ferreira, and G. Bastard

Appl. Phys. Lett. 102, 191105 (2013); http://dx.doi.org/10.1063/1.4804551 (4 pages)

Online Publication Date: 13 May 2013

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The inter-subband scattering in quasi two-dimensional heterostructures is critically examined in the case of cascade structures with a double well design. We show that when two kinds of elastic scatterers are present, the scattering frequencies may markedly differ from the one evaluated for plane wave states for the in-plane motion at the Born approximation. We argue that this feature results from the disorder-induced spatial localization of the eigenstates in the layer plane. The scatterer location dependence of the scattering frequencies is also discussed. At low concentration the in-plane localization is found to increase the inter-subband scattering.
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73.21.Fg Quantum wells
81.07.St Quantum wells
73.63.Hs Quantum wells

Enhancing the energy of terahertz radiation from plasma produced by intense femtosecond laser pulses

Fazel Jahangiri, Masaki Hashida, Shigeki Tokita, Takeshi Nagashima, Masanori Hangyo, and Shuji Sakabe

Appl. Phys. Lett. 102, 191106 (2013); http://dx.doi.org/10.1063/1.4804582 (4 pages)

Online Publication Date: 13 May 2013

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Terahertz (THz) radiation from atomic clusters illuminated by intense femtosecond laser pulses is investigated. By studying the angular distribution, polarization properties and energy dependence of THz waves, we aim to obtain a proper understanding of the mechanism of THz generation. The properties of THz waves measured in this study differ from those predicted by previously proposed mechanisms. To interpret these properties qualitatively, we propose that the radiation is generated by time-varying quadrupoles, which are produced by the ponderomotive force of the laser pulse.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Strong quantum-confined Stark effect from light hole related direct-gap transitions in Ge quantum wells

P. Chaisakul, D. Marris-Morini, M. S. Rouifed, J. Frigerio, G. Isella, D. Chrastina, J.-R. Coudevylle, X. Le Roux, S. Edmond, D. Bouville, and L. Vivien

Appl. Phys. Lett. 102, 191107 (2013); http://dx.doi.org/10.1063/1.4805004 (4 pages)

Online Publication Date: 14 May 2013

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A strong quantum-confined Stark effect (QCSE) from light hole related transitions at the Γ point (LH1-cΓ1) in Ge/Si0.15Ge0.85 multiple quantum wells is demonstrated from both photocurrent and optical transmission measurements. Our experimental results show a large and sharp optical absorption peak due to LH1-cΓ1 transitions, and its associated strong absorption change based on the QCSE. By exploiting LH1-cΓ1 transitions, optical modulators with improved compactness and competitive extinction ratio and optical loss can be envisioned for low energy chip-scale optical interconnect applications.
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78.20.Jq Electro-optical effects
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.67.De Quantum wells
72.40.+w Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Fabrication of two-dimensional InGaN/GaN photonic crystal structure using a modified nanosphere lithography technique

M. Athanasiou, T. K. Kim, B. Liu, R. Smith, and T. Wang

Appl. Phys. Lett. 102, 191108 (2013); http://dx.doi.org/10.1063/1.4805035 (5 pages)

Online Publication Date: 14 May 2013

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By means of combining a very cost-effective lift-off process and a nanosphere lithography technique, we have fabricated two dimensional (2D) photonic crystal (PhC) structures on an InGaN/GaN multiple quantum well structure. Significant enhancement in photoluminescence (PL) intensity has been observed when the emission wavelength is within the photonic bandgap. Time-resolved PL measurements have shown that the spontaneous emission rate is strongly reduced by a factor of ∼4 due to the PhC effect. As a consequence, the emission intensity along 2D PhC slab-plane directions is effectively suppressed and redistributed to the direction normal to the 2D PhC slab-plane simultaneously. Temperature-dependent PL measurements have confirmed that the enhanced PL intensity is due to an increase in extraction efficiency as a result of the PhC effect.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Terahertz transmission and sheet conductivity of randomly stacked multi-layer graphene

I. H. Baek, K. J. Ahn, B. J. Kang, S. Bae, B. H. Hong, D.-I. Yeom, K. Lee, Y. U. Jeong, and F. Rotermund

Appl. Phys. Lett. 102, 191109 (2013); http://dx.doi.org/10.1063/1.4805074 (5 pages)

Online Publication Date: 14 May 2013

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We investigate transmission characteristics and sheet conductivity of mono- to multi-layer graphene deposited on quartz in the terahertz (THz) frequency region. The free carrier absorption and Fabry-Perot interference between graphene layers give rise to nonlinear decrease of THz transmission from 76.7% to 27% for mono- to 12-layer graphene. These phenomena are well explained with a modified theoretical model based on Drude conductivity. The optical sheet conductivity of multi-layer graphene, made by layer-by-layer random stacking of high-quality mono-layer graphene, at 1 THz exhibits two orders of magnitude higher values than the universal optical conductivity due to intraband transition of intrinsic graphene.
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78.67.Wj Optical properties of graphene
81.05.ue Graphene
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

Single-peak narrow-bandwidth mid-infrared thermal emitters based on quantum wells and photonic crystals

Takuya Inoue, Menaka De Zoysa, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 102, 191110 (2013); http://dx.doi.org/10.1063/1.4807174 (4 pages)

Online Publication Date: 15 May 2013

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We experimentally demonstrate single-peak narrow-bandwidth thermal emission with a quality factor (Q factor) of more than 100 at a wavelength of 9.1 μm. The emission is significantly suppressed at all other wavelengths. Our emitter is based on an intersubband transition in a multiple quantum well structure combined with a single high-Q resonant mode in a two-dimensional photonic crystal slab, which allows strong light-matter interaction only at a specific wavelength. Strong thermal emission is exhibited only in a limited angular range (∼20°) from the normal direction. Our results have potential applications in bio- and environmental sensors.
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07.20.-n Thermal instruments and apparatus

Coupling of InAs/InP quantum dots to the plasmon resonance of In nanoparticles grown by metal-organic vapor phase epitaxy

Jiayue Yuan, C. Y. Jin, Matthias Skacel, Adam Urbańczyk, Tian Xia, P. J. van Veldhoven, and Richard Nötzel

Appl. Phys. Lett. 102, 191111 (2013); http://dx.doi.org/10.1063/1.4805043 (4 pages)

Online Publication Date: 15 May 2013

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We report strongly modified optical emission of InAs/InP quantum dots (QDs) coupled to the surface plasmon resonance (SPR) of In nanoparticles grown by metal-organic vapor phase epitaxy. With increasing In deposition time, the In nanoparticle size increases and the SPR redshifts significantly. When overlapping with the SPR, the excited state photoluminescence of the QDs is strongly enhanced due to QD-SPR coupling while the ground state photoluminescence is quenched due to non-radiative energy transfer. This is underpinned by the wavelength dependence of the spontaneous emission decay time which shows an opposite trend compared to that of bare QDs.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.La Quantum dots

Broadband saturable absorption and optical limiting in graphene-polymer composites

S. Husaini, J. E. Slagle, J. M. Murray, S. Guha, L. P. Gonzalez, and R. G. Bedford

Appl. Phys. Lett. 102, 191112 (2013); http://dx.doi.org/10.1063/1.4805060 (4 pages)

Online Publication Date: 15 May 2013

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Nonlinear optical properties of a graphene-polyvinyl alcohol composite are studied using an irradiance-scan setup. The measurements are carried out at 785 nm and 1064 nm in the nanosecond and picoseconds temporal regimes, respectively. It is shown that the output fluence readily clamps with increasing input and graphene concentration due to nonlinear absorption and scattering. Furthermore, the nonlinear transmission demonstrates weak saturable absorption followed by strong optical limiting. The nonlinear coefficients βeff and Isat calculated via numerical fitting show that βeff depends on the graphene content and increases significantly in nanosecond regime due to high degree of thermally induced nonlinear scattering.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.Sc Nanoaggregates; nanocomposites

Energy resolved X-ray grating interferometry

T. Thuering, W. C. Barber, Y. Seo, F. Alhassen, J. S. Iwanczyk, and M. Stampanoni

Appl. Phys. Lett. 102, 191113 (2013); http://dx.doi.org/10.1063/1.4805073 (4 pages)

Online Publication Date: 15 May 2013

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Although compatible with polychromatic radiation, the sensitivity in X-ray phase contrast imaging with a grating interferometer is strongly dependent on the X-ray spectrum. We used an energy resolving detector to quantitatively investigate the dependency of the noise from the spectral bandwidth and to consequently optimize the system—by selecting the best energy band matching the experimental conditions—with respect to sensitivity maximization and, eventually, dose. Further, since theoretical calculations of the spectrum are usually limited due to non-ideal conditions, an energy resolving detector accurately quantifies the spectral changes induced by the interferometer including flux reduction and beam hardening.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

High-power low-divergence tapered quantum cascade lasers with plasmonic collimators

Romain Blanchard, Tobias S. Mansuripur, Burc Gökden, Nanfang Yu, Mikhail Kats, Patrice Genevet, Kazuue Fujita, Tadataka Edamura, Masamichi Yamanishi, and Federico Capasso

Appl. Phys. Lett. 102, 191114 (2013); http://dx.doi.org/10.1063/1.4806985 (5 pages)

Online Publication Date: 15 May 2013

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We demonstrate a tapered quantum cascade laser with sloped side-walls emitting a high-brightness single-lobe beam at 8.1 μm with a peak power of 4 W at room temperature. Using a combination of high and low reflectivity facet coatings, the power output is increased to 6.2 W while a high beam quality is maintained. Plasmonic collimators are fabricated on the facet of the uncoated lasers without compromising power output, demonstrating the viability of this beam-shaping strategy for high-power lasers. The collimated lasers emit a beam with a more circular cross-section, which is more amenable to high-efficiency coupling into mid-infrared optical fibers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Ag Apertures, collimators
42.79.Wc Optical coatings

ZnO-SiO2 solar-blind photodetectors on flexible polyethersulfone substrate with organosilicon buffer layer

Wei-Chih Lai, Jiun-Ting Chen, and Ya-Yu Yang

Appl. Phys. Lett. 102, 191115 (2013); http://dx.doi.org/10.1063/1.4807124 (4 pages)

Online Publication Date: 16 May 2013

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The ZnO-SiO2 nanocomposite solar-blind metal-semiconductor-metal photodetectors (PDs) on flexible polyethersulfone (PES) with an organosilicon (SiOx(CH3)) buffer layer improved the −10 V-biased responsivity of PDs illuminated wavelength of 240 nm from 0.75 A/W (without SiOx(CH3) buffer layer) to 3.86 A/W and the deep-ultraviolet (DUV)–visible rejection ratio of PDs from 8.10 × 104 (without SiOx(CH3) buffer layer) to 1.75 × 105. Moreover, the inserted SiOx(CH3) buffer layer would reduce the responsivity and DUV-visible rejection ratio of degradation of the severely bended ZnO-SiO2 nanocomposite PDs on PES.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

High quality factor nonpolar GaN photonic crystal nanocavities

Tzeng-Tsong Wu, Sheng-Yun Lo, Huei-Min Huang, Che-Wei Tsao, Tien-Chang Lu, and Shing-Chung Wang

Appl. Phys. Lett. 102, 191116 (2013); http://dx.doi.org/10.1063/1.4807137 (4 pages)

Online Publication Date: 16 May 2013

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High quality factor a-plane nonpolar GaN two-dimensional photonic crystal (PC) nanocavities on r-plane sapphire substrates have been demonstrated. Nonpolar GaN PC nanocavities on a thin membrane structure were realized by using e-beam lithography to define the PC patterns and focused-ion beam milling to fabricate the suspended thin membrane. A dominant resonant mode at 388 nm with a high quality factor of approximately 4300 has been demonstrated at 77 K by the micro-photoluminescence system. Moreover, the degree of polarization of the emission from the non-polar GaN PC nanocavity was measured to be 64% along the m crystalline direction.
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42.79.-e Optical elements, devices, and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials

Dominant deuteron acceleration with a high-intensity laser for isotope production and neutron generation

A. Maksimchuk, A. Raymond, F. Yu, G. M. Petrov, F. Dollar, L. Willingale, C. Zulick, J. Davis, and K. Krushelnick

Appl. Phys. Lett. 102, 191117 (2013); http://dx.doi.org/10.1063/1.4807143 (5 pages)

Online Publication Date: 16 May 2013

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Experiments on the interaction of an ultra-short pulse laser with heavy-water, ice-covered copper targets, at an intensity of 2×1019 W/cm2, were performed demonstrating the generation of a “pure” deuteron beam with a divergence of 20°, maximum energy of 8 MeV, and a total of 3×1011 deuterons with energy above 1 MeV—equivalent to a conversion efficiency of 1.5% ± 0.2%. Subsequent experiments on irradiation of a 10B sample with deuterons and neutron generation from d-d reactions in a pitcher-catcher geometry, resulted in the production of ∼ 106 atoms of the positron emitter 11C and a neutron flux of (4±1)×105 neutrons/sterad, respectively.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.Fi Transport properties
41.75.Ak Positive-ion beams

Fabrication and characterization of a room-temperature ZnO polariton laser

Feng Li, L. Orosz, O. Kamoun, S. Bouchoule, C. Brimont, P. Disseix, T. Guillet, X. Lafosse, M. Leroux, J. Leymarie, G. Malpuech, M. Mexis, M. Mihailovic, G. Patriarche, F. Réveret, et al.

Appl. Phys. Lett. 102, 191118 (2013); http://dx.doi.org/10.1063/1.4804986 (4 pages)

Online Publication Date: 16 May 2013

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A ZnO planar optical microcavity displaying room-temperature polariton lasing over a wide range of cavity-exciton detunings has been fabricated. The cavity combines optimum crystalline quality, given by a ZnO single-crystal substrate, and optimum photonic quality, obtained by the use of two dielectric SiO2/HfO2 Bragg mirrors. A maximum cavity quality factor of about 4000 has been measured. Typically, the polariton lasing transition is accompanied by an increase of the output intensity by more than two orders of magnitude, a reduction of the emission linewidth and a relatively small blueshift of the lower polariton branch (less than 5% of the Rabi splitting).
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Tunable 1.6–2 μm near infrared few-cycle pulse generation by filamentation

S. Driever, D. Bigourd, N. Fedorov, M. Cornet, M. Arnold, F. Burgy, S. Montant, S. Petit, D. Descamps, E. Cormier, E. Constant, and A. Zaïr

Appl. Phys. Lett. 102, 191119 (2013); http://dx.doi.org/10.1063/1.4807008 (4 pages)

Online Publication Date: 16 May 2013

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We present results on tunable few-cycle laser pulses generated in the near infrared region obtained by filamentation in a krypton cell combined with group velocity dispersion compensation in fused silica. We obtain a spectral broadening of a factor ∼2–3 over the entire spectral domain studied. The central wavelength is tuned from 1.6 μm to 2 μm via an optical parametric amplification source. In optimum experimental conditions, where the input central wavelength is set to 1.7 μm, 1.8 μm, and 1.9 μm, the incident power to the gas cell exceeded the critical power of Krypton by a factor of ∼4 and the achieved spectral broadening covered ∼300 nm. Using group velocity compensation in bulk fused silica, we obtain near infrared output pulses as short as 2–3 optical cycles with 200 μJ energy per pulse. This near infrared filamentation tunable few-cycle pulse source is an important achievement for strong field physics applications such as attoscience, where wavelength scaling has an important effect.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.65.Yj Optical parametric oscillators and amplifiers

19 μm quantum cascade infrared photodetectors

Shen-Qiang Zhai, Jun-Qi Liu, Xue-Jiao Wang, Ning Zhuo, Feng-Qi Liu, Zhan-Guo Wang, Xi-Hui Liu, Ning Li, and Wei Lu

Appl. Phys. Lett. 102, 191120 (2013); http://dx.doi.org/10.1063/1.4807030 (4 pages)

Online Publication Date: 16 May 2013

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Two InP based InGaAs/InAlAs photovoltaic quantum cascade detectors operating at peak wavelengths of 18 μm and 19 μm using different electronic transport mechanisms are reported. A longitudinal optical phonon extraction stair combined with energy mini-steps are employed for electron transport, which suppresses the leakage current and results in high device resistance. Altogether, this quantum design leads to 15 K peak responsivity of 2.34 mA/W and Johnson noise limited detectivity of 1 × 1011 Jones at 18 μm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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Improving information density in ferroelectric polymer films by using nanoimprinted gratings

D. E. Martínez-Tong, M. Soccio, M. C. García-Gutiérrez, A. Nogales, D. R. Rueda, N. Alayo, F. Pérez-Murano, and T. A. Ezquerra

Appl. Phys. Lett. 102, 191601 (2013); http://dx.doi.org/10.1063/1.4804427 (5 pages)

Online Publication Date: 13 May 2013

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In this work, well-defined low aspect ratio nanostructures based on nanogratings on thin films of poly(vinylidene fluoride–trifluoroethylene) copolymers were prepared. By using these nanogratings, an improved management of writing and reading information of about 500 Gbit/in.2 (0.01 bit/nm2) can be reached as revealed by Piezoresponse Force Microscopy. Structural investigation by means of X-ray diffraction techniques indicates that the physical confinement generated by nanoimprint promotes the development of smaller and edge-on oriented crystals. Our results evidence that one-dimensional nanostructuring can be a straightforward approach to improve the control of the polarization in ferroelectric polymer thin films.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
77.80.-e Ferroelectricity and antiferroelectricity
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology

Influence of SnO2:F/ZnO:Al bi-layer as a front electrode on the properties of p-i-n amorphous silicon based thin film solar cells

Hyeongsik Park, Jaehyeong Lee, Heewon Kim, Doyoung Kim, Jayapal Raja, and Junsin Yi

Appl. Phys. Lett. 102, 191602 (2013); http://dx.doi.org/10.1063/1.4807127 (3 pages)

Online Publication Date: 14 May 2013

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The effect of aluminum doped zinc oxide film used between a fluorine doped tin oxide layer and a hydrogenated amorphous silicon carbide layer to improve the open circuit voltage (Voc) and fill factor (FF) for high efficiency thin film solar cells. The efficiency enhancement was accomplished by the insertion of high work-function layers engineered in the interfaces to raise FF as well as Voc. Therefore, we were able to obtain the conversion efficiency of 10.34% at 16.14 mA/cm2 of the current density (Jsc) and 70.37% of FF.
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88.40.hj Efficiency and performance of solar cells
88.40.jp Multijunction solar cells

Electron and hole mobilities at a Si/SiO2 interface with giant valley splitting

Yoshitaka Niida, Kei Takashina, Yukinori Ono, Akira Fujiwara, and Yoshiro Hirayama

Appl. Phys. Lett. 102, 191603 (2013); http://dx.doi.org/10.1063/1.4803014 (4 pages)

Online Publication Date: 16 May 2013

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We examine the electron mobility and hole mobility at the Si/buried oxide (BOX) interface at which the valley splitting of the electron system is strongly enhanced, and compare the values observed to those at a standard Si/thermal oxide (T-SiO2) interface in the same silicon-on-insulator device. In contrast to the electron mobility, which is lower at the Si/BOX interface, the hole mobility at the Si/BOX interface is found to be slightly higher than that at the Si/T-SiO2 interface.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Ee Mobility edges; hopping transport

Electron microscopy investigations of purity of AlN interlayer in AlxGa1−xN/GaN heterostructures grown by plasma assisted molecular beam epitaxy

D. V. Sridhara Rao, Anubha Jain, Sushil Lamba, K. Muraleedharan, and R. Muralidharan

Appl. Phys. Lett. 102, 191604 (2013); http://dx.doi.org/10.1063/1.4805027 (3 pages)

Online Publication Date: 17 May 2013

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The electron microscopy was used to characterize the AlN interlayer in AlxGa1−xN/AlN/GaN heterostructures grown by plasma assisted molecular beam epitaxy (PAMBE). We show that the AlN interlayer grown by PAMBE is without gallium and oxygen incorporation and the interfaces are coherent. The AlN interlayer has the ABAB stacking of lattice planes as expected for the wurtzite phase. High purity of AlN interlayer with the ABAB stacking leads to larger conduction band offset along with stronger polarization effects. Our studies show that the origin of lower sheet resistance obtained by PAMBE is the purity of AlN interlayer.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Faraday rotation in magnetically biased graphene at microwave frequencies

D. L. Sounas, H. S. Skulason, H. V. Nguyen, A. Guermoune, M. Siaj, T. Szkopek, and C. Caloz

Appl. Phys. Lett. 102, 191901 (2013); http://dx.doi.org/10.1063/1.4804437 (4 pages)

Online Publication Date: 13 May 2013

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Show Abstract
Faraday rotation is experimentally observed at microwave frequencies in a large-area graphene sheet biased with a static magnetic field, and interrogated by polarized fields in a hollow circular waveguide. A Faraday rotation of up to 1.5° and an isolation of more than 30 dB is observed, suggesting possible applications to graphene based isolators, circulators, and other non-reciprocal devices. An analytic model is developed for the scattering parameters of the measured structure. The model shows excellent agreement with the measurements and is used to extract the graphene conductivity, carrier density, and mobility.
Show PACS
78.20.Ls Magneto-optical effects
72.80.Vp Electronic transport in graphene
81.05.ue Graphene
72.20.Fr Low-field transport and mobility; piezoresistance
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