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8 Oct 2012

Volume 101, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages)

Brandon G. Cook, William R. French, and Kálmán Varga
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Optofluidic random laser

B. N. Shivakiran Bhaktha, Nicolas Bachelard, Xavier Noblin, and Patrick Sebbah

Appl. Phys. Lett. 101, 151101 (2012); http://dx.doi.org/10.1063/1.4757872 (4 pages) | Cited 2 times

Online Publication Date: 8 October 2012

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Random lasing is reported in a dye-circulated structured polymeric microfluidic channel. The role of disorder, which results from limited accuracy of photolithographic process, is demonstrated by the variation of the emission spectrum with local-pump position and by the extreme sensitivity to a local perturbation of the structure. Thresholds comparable to those of conventional microfluidic lasers are achieved, without the hurdle of state-of-the-art cavity fabrication. Potential applications of optofluidic random lasers for on-chip sensors are discussed. Introduction of random lasers in the field of optofluidics is a promising alternative to on-chip laser integration with light and fluidic functionalities.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
47.85.-g Applied fluid mechanics
47.85.Np Fluidics
87.80.-y Biophysical techniques (research methods)

Efficient Cherenkov-type terahertz generation in Si-prism-LiNbO3-slab structure pumped by nanojoule-level ultrashort laser pulses

M. I. Bakunov, E. A. Mashkovich, M. V. Tsarev, and S. D. Gorelov

Appl. Phys. Lett. 101, 151102 (2012); http://dx.doi.org/10.1063/1.4757882 (4 pages) | Cited 1 time

Online Publication Date: 8 October 2012

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We demonstrate, both theoretically and experimentally, that a sandwich-type structure consisting of a thin LiNbO3 slab and Si prism outcoupler can be an efficient convertor of unamplified laser pulses into broadband terahertz radiation. Pumping a 1 cm long sandwich structure with a 35 μm thick LiNbO3 slab by 8 nJ, 100 fs optical pulses from Ti:sapphire oscillator we achieved the conversion efficiency of 0.8×10−4, i.e., two orders of magnitude higher than in the conventional generation scheme with ZnTe crystal. Using laser oscillator as a pump has an advantage of high repetition rate and, therefore, potentially high signal-to-noise ratio (∼50 dB in our experiment).
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors
42.79.Gn Optical waveguides and couplers
42.60.-v Laser optical systems: design and operation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Gallium nitride-based light-emitting diodes with embedded air voids grown on Ar-implanted AlN/sapphire substrate

Jinn-Kong Sheu, Shang-Ju Tu, Yu-Hsiang Yeh, Ming-Lun Lee, and Wei-Chih Lai

Appl. Phys. Lett. 101, 151103 (2012); http://dx.doi.org/10.1063/1.4757996 (4 pages)

Online Publication Date: 8 October 2012

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GaN-based light-emitting diodes (LEDs) grown on sapphire with ex situ AlN nucleation layer prepared by radio-frequency sputtering were investigated. GaN-based epitaxial layers grown on the Ar-implanted AlN/sapphire (AIAS) substrates exhibited selective growth and subsequent lateral growth due to the difference of lattice constants between the implanted and implantation-free regions. Consequently, air voids over the implanted regions were formed around the GaN/AlN/sapphire interfaces. We proposed the growth mechanisms of the GaN layer on the AIAS substrates and characterized the LEDs with embedded air voids. With a 20 mA current injection, experimental results indicate that the light output power of LEDs grown on the AIAS substrates was enhanced by 25% compared with those of conventional LEDs. This enhancement can be attributed to the light scattering at the GaN/air void interfaces to increase the light extraction efficiency of the LEDs.
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85.60.Jb Light-emitting devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.40.Sz Deposition technology

Analysis of electron and light scattering in a fluorescent thin film by combination of Monte Carlo simulation and finite-difference time-domain method

Wataru Inami, Jun Fujiwara, Fukuta Masahiro, Atsushi Ono, and Yoshimasa Kawata

Appl. Phys. Lett. 101, 151104 (2012); http://dx.doi.org/10.1063/1.4758290 (4 pages) | Cited 1 time

Online Publication Date: 8 October 2012

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We analyzed light intensity distributions in a subwavelength fluorescent film, which was excited by a focused electron beam. We have developed an analyzing method using Monte Carlo simulation and the finite-difference time-domain (FDTD) method. Electron scattering and trajectories were calculated by Monte Carlo simulation. Propagation and scattering of light excited with the electrons was calculated by FDTD method. A nanometric light spot was formed on the fluorescent film surface and its light intensity and its full width at half maximum (FWHM) were evaluated. We discuss the intensity and the FWHM dependence on the thickness of the fluorescent thin film and the acceleration voltage of an incident electron beam.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Light trapping in solar cells: Analytical modeling

Mathieu Boccard, Corsin Battaglia, Franz-Josef Haug, Matthieu Despeisse, and Christophe Ballif

Appl. Phys. Lett. 101, 151105 (2012); http://dx.doi.org/10.1063/1.4758295 (4 pages) | Cited 1 time

Online Publication Date: 8 October 2012

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We model analytically light harvesting in realistic solar cells by extending a formalism suggested by Deckman et al. [Appl. Phys. Lett. 42, 110968 (1983)], based on tracing of an average ray of light. Arbitrary light scattering schemes and parasitic absorption are implemented in the model, and we validate our approach by comparing with experimental measurements from microcrystalline silicon devices. The intuitive understanding obtained with this extended model is discussed. This approach enables identifying parasitic absorption as main limitation of state-of-the-art light harvesting schemes, and highlights that a better light trapping requires improving the first scattering events.
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88.40.jj Silicon solar cells
85.30.De Semiconductor-device characterization, design, and modeling

Light-management in ultra-thin polythiophene films using plasmonic monopole nanoantennas

Binxing Yu, Sarah Goodman, Alexa Abdelaziz, and Deirdre M. O'Carroll

Appl. Phys. Lett. 101, 151106 (2012); http://dx.doi.org/10.1063/1.4754665 (4 pages)

Online Publication Date: 8 October 2012

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Deposition of vertical, cone-shaped plasmonic nanorod arrays onto sub-50 nm polythiophene films on Ag substrates is shown to result in significant absorption enhancement (>12 at the polythiophene band edge) and spectral broadening (more than 250 nm increase) relative to polythiophene/Ag films without plasmonic nanorod arrays. Full-field electromagnetic simulations are used to identify the modes of the plasmonic nanorod array/polythiophene/Ag film system. Both gap modes and longitudinal monopole antenna modes give rise to highly localized electric fields in the polythiophene film and are the primary contributors to polythiophene absorption enhancement. This approach is suitable for large area optoelectronic applications where light management in ultrathin active layers is desired.
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73.61.-r Electrical properties of specific thin films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.66.-w Optical properties of specific thin films
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Localized optical resonances in low refractive index rolled-up microtube cavity for liquid-core optofluidic detection

Vladimir A. Bolaños Quiñones, Libo Ma, Shilong Li, Matthew Jorgensen, Suwit Kiravittaya, and Oliver G. Schmidt

Appl. Phys. Lett. 101, 151107 (2012); http://dx.doi.org/10.1063/1.4758992 (3 pages) | Cited 1 time

Online Publication Date: 9 October 2012

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Spatially localized high order axial resonant modes are observed in a SiO/SiO2-based microtube cavity rolled-up from a prestrained nanomembrane. A diameter variation of the tube structure is revealed which provides localized axial confinement. Optofluidic detection is demonstrated by filling the tube core with salt solution and subsequently detecting the shifts of spectral mode positions and axial mode spacings. A sensing methodology is proposed by monitoring axial mode spacing changes.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
47.85.Np Fluidics

Ground state terahertz quantum cascade lasers

Chun Wang I. Chan, Qing Hu, and John L. Reno

Appl. Phys. Lett. 101, 151108 (2012); http://dx.doi.org/10.1063/1.4759043 (4 pages)

Online Publication Date: 9 October 2012

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A terahertz quantum cascade laser (THz QCL) architecture is presented in which only the ground state subbands of each quantum well are involved in the transport and lasing transition. Compared to state-of-the art THz QCLs based on the resonant-phonon scheme, ground state QCLs employ narrower wells so that all high-energy subbands are pushed up far above the occupied subband levels, significantly reducing parasitic interactions. Data on the experimental realization of two types of ground state QCLs are presented, in which the result of lasing above 5 THz is demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Mimicing surface phonon polaritons in microwave band based on ionic-type phononic crystal

Xi-kui Hu, Yang Ming, Xue-jin Zhang, Yan-qing Lu, and Yong-yuan Zhu

Appl. Phys. Lett. 101, 151109 (2012); http://dx.doi.org/10.1063/1.4758467 (4 pages) | Cited 1 time

Online Publication Date: 9 October 2012

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We propose an approach to scale the frequency of surface phonon polariton to megahertz-gigahertz region via an artificial microstructure, ionic-type phononic crystal (ITPC). The period of ITPC can be intentionally controlled on all relevant length scales, which allows the creation of surface phonon polariton with almost arbitrary dispersion in frequency and space. A field of surface phonon polariton optics in microwave band is expected with similar optical properties to those of ionic crystals in infrared.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.70.-y Disperse systems; complex fluids
63.20.-e Phonons in crystal lattices
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Broadband switching functionality based on defect mode coupling in W2 photonic crystal waveguide

Kaiyu Cui, Xue Feng, Yidong Huang, Qiang Zhao, Zhilei Huang, and Wei Zhang

Appl. Phys. Lett. 101, 151110 (2012); http://dx.doi.org/10.1063/1.4758471 (4 pages) | Cited 1 time

Online Publication Date: 9 October 2012

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Broadband switching functionality realized by an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with an integrated titanium/aluminum microheater on its surface. Due to the enhanced coupling between the defect modes in W2 PCW, switching functionality with bandwidth up to 24 nm is achieved by the PCW with footprint of only 8 μm × 17.6 μm, while the extinction ratio is in excess of 15 dB over the entire bandwidth. Moreover, the switching speed is measured by alternating current modulation. Response time for this thermo-optic switch is 11.0 ± 3.0 μs for rise time and 40.3 ± 5.3 μs for fall time, respectively.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics

High power femtosecond Bessel-X pulses directly from a compact fiber laser system

Chen Xie, Minglie Hu, Zongwei Xu, Wei Wu, Haifeng Gao, Peng Qin, Dapeng Zhang, Bowen Liu, and Ching-Yue Wang

Appl. Phys. Lett. 101, 151111 (2012); http://dx.doi.org/10.1063/1.4758687 (4 pages)

Online Publication Date: 9 October 2012

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We report on high power ultrashort Bessel-X pulses directly from a compact fiber laser system. For spatial profiles, non-diffracting Bessel-like wavepackets were generated with the combination of a collimating lens and a silica-based inverse micro-axicon, which is specially designed and fabricated on the facet of an amplifying fiber doped by ytterbium. For temporal profiles, the seed pulses from a mode-locked dissipative soliton fiber laser at a repetition rate of 56.9 MHz were pre-shaped by a grating pair and a spectral filter. Amplified 18.7 W average power chirped ps pulses were obtained and then dechirped to a duration of 38 fs.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.-v Laser optical systems: design and operation
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.65.Tg Optical solitons; nonlinear guided waves
42.60.Fc Modulation, tuning, and mode locking
42.79.Dj Gratings

Systematic optimization of quantum junction colloidal quantum dot solar cells

Huan Liu, David Zhitomirsky, Sjoerd Hoogland, Jiang Tang, Illan J. Kramer, Zhijun Ning, and Edward H. Sargent

Appl. Phys. Lett. 101, 151112 (2012); http://dx.doi.org/10.1063/1.4757866 (3 pages) | Cited 2 times

Online Publication Date: 10 October 2012

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The recently reported quantum junction architecture represents a promising approach to building a rectifying photovoltaic device that employs colloidal quantum dot layers on each side of the p-n junction. Here, we report an optimized quantum junction solar cell that leverages an improved aluminum zinc oxide electrode for a stable contact to the n-side of the quantum junction and silver doping of the p-layer that greatly enhances the photocurrent by expanding the depletion region in the n-side of the device. These improvements result in greater stability and a power conversion efficiency of 6.1% under AM1.5 simulated solar illumination.
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88.40.jp Multijunction solar cells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.60.Bt Optoelectronic device characterization, design, and modeling
88.40.hj Efficiency and performance of solar cells

Blue monolithic AlInN-based vertical cavity surface emitting laser diode on free-standing GaN substrate

Gatien Cosendey, Antonino Castiglia, Georg Rossbach, Jean-François Carlin, and Nicolas Grandjean

Appl. Phys. Lett. 101, 151113 (2012); http://dx.doi.org/10.1063/1.4757873 (4 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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We report on III-nitride based blue vertical cavity surface emitting lasers using defect-free highly reflective AlInN/GaN distributed Bragg reflectors grown on c-plane free-standing GaN substrates. Lasing is demonstrated at room temperature under pulsed electrical injection. The high lasing threshold current density still prevents devices from continuous wave lasing because of large self-heating. The reasons for such a high threshold are discussed and we show that it mainly comes from large light absorption in the indium tin oxide current spreading layer. Properly tuning both its thickness and its position with respect to the electrical field could remarkably decrease the threshold.
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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
42.82.-m Integrated optics

Reduced temperature sensitivity of the polarization properties of hydrogenated InGaAsN V-groove quantum wires

Marco Felici, Antonio Polimeni, Elena Tartaglini, Andrea Notargiacomo, Marta De Luca, Romain Carron, Dan Fekete, Benjamin Dwir, Alok Rudra, Mario Capizzi, and Eli Kapon

Appl. Phys. Lett. 101, 151114 (2012); http://dx.doi.org/10.1063/1.4758685 (5 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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We investigated the effects of hydrogen irradiation on the degree of linear polarization, ρ, of the light emitted by site-controlled, dilute-nitride InGaAsN V-groove quantum wires (QWRs). While in the as-grown sample the polarization of the QWR emission is highly sensitive to the increasing temperature (T), after sample hydrogenation the value of ρ remains nearly unchanged (and ∼25%) for T ≤ 220 K. This observation—potentially important for the development of devices based on the QWR polarization—points to a larger energy separation between hole subbands in the hydrogenated QWRs, due to the strain increase associated with the H-induced passivation of nitrogen.
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78.67.Lt Quantum wires
81.65.Rv Passivation
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires

Diffusion of photoexcited carriers in graphene

F. T. Vasko and V. V. Mitin

Appl. Phys. Lett. 101, 151115 (2012); http://dx.doi.org/10.1063/1.4759034 (4 pages)

Online Publication Date: 11 October 2012

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The diffusion of electron-hole pairs, which are excited in an intrinsic graphene by the ultrashort focused laser pulse in mid-IR or visible spectral region, is described for the cases of peak-like or spread over the passive region distributions of carriers. The spatio-temporal transient optical response on a high-frequency probe beam appears to be strongly dependent on the regime of diffusion and can be used for verification of the elasic relaxation mechanism. Sign flip of the differential transmission coefficient takes place due to interplay of the carrier-induced contribution and weak dynamic conductivity of undoped graphene.
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66.30.-h Diffusion in solids
78.40.Ri Fullerenes and related materials
78.30.Na Fullerenes and related materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Terahertz beam focusing based on plasmonic waveguide scattering

Yasuaki Monnai, Kristian Altmann, Christian Jansen, Martin Koch, Hartmut Hillmer, and Hiroyuki Shinoda

Appl. Phys. Lett. 101, 151116 (2012); http://dx.doi.org/10.1063/1.4759042 (3 pages) | Cited 2 times

Online Publication Date: 11 October 2012

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We demonstrate free-space focusing of terahertz (THz) radiation by scattering plasmonic surface-waves into the air. We use a grating of shallow holes which contains non-equidistant defects which act as scattering centers. The scattering occurs with defined phase delays such that the waves emitted in free-space interfere constructively to form a focus above the waveguide surface. In contrast to conventional lenses, this structure does not require any free-space on its backside and has great potential for integrated THz optics.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics

Lithium niobate photonic crystal wire cavity: Realization of a compact electro-optically tunable filter

Huihui Lu, Fadi Issam Baida, Gwenn Ulliac, Nadège Courjal, Manuel Collet, and Maria-Pilar Bernal

Appl. Phys. Lett. 101, 151117 (2012); http://dx.doi.org/10.1063/1.4760224 (4 pages)

Online Publication Date: 11 October 2012

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We report an electro-optically tunable filter using a lithium niobate photonic crystal cavity configuration with an efficient optical guiding geometry. The compact device (5.5 μm × 2.8 μm) was made on a hybrid waveguide combining an annealed proton exchange waveguide and a ridge waveguide realized by focused ion beam with vertically deposited electrodes. Due to the slow light and nonlinear effect in lithium niobate photonic crystal, experimental results show an enhanced tunability of ∼0.56 nm/V. This compact tunable photonic crystal cavity demonstration opens the path for the development of micro and nano-scale low-power driving active photonic devices.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
FREE

Relative intensity noise of a quantum well transistor laser

F. Tan, R. Bambery, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 101, 151118 (2012); http://dx.doi.org/10.1063/1.4760225 (4 pages) | Cited 1 time

Online Publication Date: 11 October 2012

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A quantum well transistor laser with a base cavity length L = 300 μm has been designed, fabricated, and operated at threshold ITH = 25 mA (0 °C). As a consequence of the inherent advantage of the picosecond base recombination lifetime, the transistor laser is able to achieve nearly a quantum shot-noise limited laser relative intensity noise (RIN) with a peak amplitude of −151 dB/Hz at frequency 8.6 GHz. Compared with a diode laser (a charge storage device) at the same output power, the transistor laser (a charge flow device) has a better than 28 dB (number dependent on the laser device design) peak RIN advantage.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Resonant plasmonic effects in periodic graphene antidot arrays

A. Yu. Nikitin, F. Guinea, and L. Martin-Moreno

Appl. Phys. Lett. 101, 151119 (2012); http://dx.doi.org/10.1063/1.4760230 (4 pages) | Cited 4 times

Online Publication Date: 11 October 2012

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We show that a graphene sheet perforated with micro- or nano-size antidots has prominent absorption resonances in the microwave and terahertz regions. These resonances correspond to surface plasmons of a continuous sheet “perturbed” by a lattice. They are excited in different diffraction orders, in contrast to cavity surface plasmon modes existing in disconnected graphene structures. The resonant absorption by the antidot array can essentially exceed the absorption by a continuous graphene sheet, even for high antidot diameter-to-period aspect ratios. Surface plasmon-enhanced absorption and suppressed transmission are more efficient for higher relaxation times of the charge carriers.
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78.70.Gq Microwave and radio-frequency interactions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Wj Optical properties of graphene
81.05.ue Graphene
81.07.Ta Quantum dots
78.67.Hc Quantum dots

A semiconductor under insulator technology in indium phosphide

K. Mnaymneh, D. Dalacu, S. Frédérick, J. Lapointe, P. J. Poole, and R. L. Williams

Appl. Phys. Lett. 101, 151120 (2012); http://dx.doi.org/10.1063/1.4760231 (3 pages)

Online Publication Date: 11 October 2012

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This letter introduces a semiconductor-under-insulator (SUI) technology in InP for designing strip waveguides that interface InP photonic crystal membrane structures. Strip waveguides in InP-SUI are supported under an atomic layer deposited insulator layer in contrast to strip waveguides in silicon supported on insulator. We show a substantial improvement in optical transmission when using InP-SUI strip waveguides interfaced with localized photonic crystal membrane structures when compared with extended photonic crystal waveguide membranes. Furthermore, SUI makes available various fiber-coupling techniques used in SOI, such as sub-micron coupling, for planar membrane III-V systems.
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42.79.Gn Optical waveguides and couplers

Modified Faraday rotation in a three-dimensional magnetophotonic opal crystal consisting of maghemite/silica composite spheres

Shunsuke Murai, Situ Yao, Tadashi Nakamura, Takahiro Kawamoto, Koji Fujita, Kazuhisa Yano, and Katsuhisa Tanaka

Appl. Phys. Lett. 101, 151121 (2012); http://dx.doi.org/10.1063/1.4757608 (4 pages)

Online Publication Date: 11 October 2012

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We have prepared a three-dimensional magnetophotonic crystal and observed modulated Faraday rotation around its photonic band gap. The magnetophotonic crystal was prepared by the self-assembly of highly monodispersed silica spheres, which were heavily impregnated with maghemite (γ−Fe2O3) nanoparticles. The slab sample with a thickness of 10 μm shows a clear photonic band gap centered at λ = 620 nm in optical transmittance. Faraday rotation is notably modified inside the photonic band gap.
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81.16.Dn Self-assembly
75.75.-c Magnetic properties of nanostructures
75.75.Cd Fabrication of magnetic nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.40.Ha Other nonmetallic inorganics

Passively Q-switching induced by gold nanocrystals

Tao Jiang, Yang Xu, Qijun Tian, Lai Liu, Zhe Kang, Renyuan Yang, Guanshi Qin, and Weiping Qin

Appl. Phys. Lett. 101, 151122 (2012); http://dx.doi.org/10.1063/1.4759120 (4 pages)

Online Publication Date: 12 October 2012

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Passive Q-switching was experimentally demonstrated in an erbium-doped fiber laser (EDFL) by using gold nanocrystals (GNCs). The GNCs were mixed with sodium carboxymethylcellulose (NaCMC) to form GNCs-NaCMC films. The films exhibited a broad absorption band in the range of 400–1750 nm. By placing the GNCs-NaCMC film in an EDFL cavity pumped by a 980 nm laser diode, stable passive Q-switching was achieved for a threshold pump power of ∼30 mW, and 3.2 μs pulses at 1560 nm with a repetition rate of 24.2 kHz were obtained for a pump power of ∼125 mW.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers

Emission wavelength of multilayer distributed feedback dye lasers

Christoph Vannahme, Cameron L. C. Smith, Mads Brøkner Christiansen, and Anders Kristensen

Appl. Phys. Lett. 101, 151123 (2012); http://dx.doi.org/10.1063/1.4759131 (4 pages)

Online Publication Date: 12 October 2012

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Precise emission wavelength modeling is essential for understanding and optimization of distributed feedback (DFB) lasers. An analytical approach for determining the emission wavelength based on setting the propagation constant of the Bragg condition and solving for the resulting slab waveguide mode is reported. The method is advantageous to established methods as it predicts the wavelength precisely with reduced complexity. Four-layered hybrid polymer-TiO2 first order DFB dye lasers with different TiO2 layer thicknesses are studied. Varying the TiO2 thickness from 0 nm to 30 nm changes the emission wavelength by 7 nm with compelling agreement of modeling results to experimental measurements.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Enhanced low-noise gain from InAs avalanche photodiodes with reduced dark current and background doping

S. J. Maddox, W. Sun, Z. Lu, H. P. Nair, J. C. Campbell, and S. R. Bank

Appl. Phys. Lett. 101, 151124 (2012); http://dx.doi.org/10.1063/1.4757424 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2012

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We reduced the room temperature dark current in an InAs avalanche photodiode by increasing the p-type contact doping, resulting in an increased energetic barrier to minority electron injection into the p-region, which is a significant source of dark current at room temperature. In addition, by improving the molecular beam epitaxy growth conditions, we reduced the background doping concentration and realized depletion widths as wide as 5 μm at reverse biases as low as 1.5 V. These improvements culminated in low-noise InAs avalanche photodiodes exhibiting a room temperature multiplication gain of ∼80, at a record low reverse bias of 12 V.
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85.60.Dw Photodiodes; phototransistors; photoresistors
07.50.Hp Electrical noise and shielding equipment
85.40.Ry Impurity doping, diffusion and ion implantation technology
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Transition from planar to island growth mode in SiGe structures fabricated on SiGe/Si(001) strain-relaxed buffers

M. V. Shaleev, A. V. Novikov, D. V. Yurasov, J. M. Hartmann, O. A. Kuznetsov, D. N. Lobanov, and Z. F. Krasilnik

Appl. Phys. Lett. 101, 151601 (2012); http://dx.doi.org/10.1063/1.4758486 (4 pages)

Online Publication Date: 9 October 2012

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The specifics of the two-to-three dimensional growth mode transition of pure Ge on SiGe/Si(001) strain-relaxed buffers (SRBs) were investigated. It was shown that the critical thickness for elastic relaxation is influenced not only by the lattice mismatch between the substrate and the film but also by Ge segregation and surface roughness dependent on parameters of strained layers. Critical thickness was found to be smaller for Ge grown on SiGe strain-relaxed buffers than on pure Si(001) substrates, in spite of the lesser lattice mismatch. Insertion of thin tensile-strained Si layers between Ge and SiGe strain-relaxed buffers increased the critical thickness.
Show PACS
68.55.ag Semiconductors
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.47.Fg Semiconductor surfaces
64.70.kg Semiconductors
81.40.Lm Deformation, plasticity, and creep
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