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5 Nov 2007

Volume 91, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages)

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle
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Dark periodic lattices in nonlinear liquid media

Edgar Alvarado-Méndez, Mónica Trejo-Durán, Miroslava Cano-Lara, Eduardo Huerta-Mascotte, and Víctor M. Castaňo

Appl. Phys. Lett. 91, 191101 (2007); http://dx.doi.org/10.1063/1.2806940 (3 pages)

Online Publication Date: 5 November 2007

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Experimental evidence of the formation of one- and two-dimensional dark periodic lattices in a negative Kerr-type nonlinear liquid media is presented. Bright periodic lattices propagate throughout two nonlinear liquids [alcohol with rhodamine (R6G), and acetone with R6G] as the negative nonlinear refractive index forms a dark periodic lattice. Our experiments demonstrate that the nonlinearity increases with the optical power and that a proper selection of the period leads to self-phase modulation of the lattice.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Gy Edge and boundary effects; reflection and refraction

Spherical aberration correction in nonlinear microscopy and optical ablation using a transparent deformable membrane

P. S. Tsai, B. Migliori, K. Campbell, T. N. Kim, Z. Kam, A. Groisman, and D. Kleinfeld

Appl. Phys. Lett. 91, 191102 (2007); http://dx.doi.org/10.1063/1.2804014 (3 pages) | Cited 7 times

Online Publication Date: 5 November 2007

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We describe the design and utilization of a deformable membrane to minimize the negative spherical aberration that occurs when a standard water-dipping objective is used to focus within a higher-index sample. In connection with two-photon laser scanning microscopy, we demonstrate twofold improved axial resolution of structures as deep as 1 mm in gels and brain tissue. In conjunction with plasma-mediated ablation, we demonstrate enhanced production of optical damage deep within a glass substrate. The present method provides a simple and inexpensive correction for a limited yet important class of optical aberrations.
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42.15.Fr Aberrations
07.60.Pb Conventional optical microscopes
07.79.-v Scanning probe microscopes and components

Active metamaterials: Sign of refractive index and gain-assisted dispersion management

Alexander A. Govyadinov, Viktor A. Podolskiy, and M. A. Noginov

Appl. Phys. Lett. 91, 191103 (2007); http://dx.doi.org/10.1063/1.2800309 (3 pages) | Cited 37 times

Online Publication Date: 5 November 2007

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We derive an approach to determine the causal direction of wavevectors of modes in optical metamaterials, which, in turn, determines signs of refractive index and impedance as a function of real and imaginary parts of dielectric permittivity and magnetic permeability. We use the developed technique to demonstrate that the interplay between resonant response of constituents of metamaterials can be used to achieve efficient dispersion management. Finally, we demonstrate broadband dispersionless index and impedance matching in active nanowire-based negative index materials. Our work has a potential to open new practical applications of negative index composites for broadband lensing, imaging, and pulse routing.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
61.46.-w Structure of nanoscale materials

Narrow-band single photons from a single-resonant optical parametric oscillator far below threshold

M. Scholz, F. Wolfgramm, U. Herzog, and O. Benson

Appl. Phys. Lett. 91, 191104 (2007); http://dx.doi.org/10.1063/1.2803761 (3 pages) | Cited 14 times

Online Publication Date: 5 November 2007

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We present a single-resonant optical parametric oscillator pumped far below threshold as a source for narrow-band single photons. Spontaneous generation of single photons via parametric downconversion is modified and follows the cavity transfer function. Cross-correlation measurements between signal and idler beams show a cavity bandwidth of 62 MHz. As the main improvement to prior realizations, our cavity is locked to the pump beam via the Hänsch-Couillaud method and therefore allows the continuous generation of heralded single photons with long-term stability.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Lm Parametric down conversion and production of entangled photons
42.65.Yj Optical parametric oscillators and amplifiers
42.50.-p Quantum optics

Isotropic frequency selective surfaces made of cubic resonators

J. D. Baena, L. Jelinek, R. Marqués, J. J. Mock, J. Gollub, and D. R. Smith

Appl. Phys. Lett. 91, 191105 (2007); http://dx.doi.org/10.1063/1.2806915 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2007

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Isotropic frequency selective surface (FSS) made of cubic arrangements of split ring resonators (SRRs) is proposed and analyzed. For this purpose, a suitable isotropic modification of the SRR was used in the design of a cubic unit element invariant under the tetrahedral point symmetry group. It was experimentally demonstrated that the transmission through such a FSS is angle and polarization independent. For comparison, another FSS, whose unit elements do not satisfy necessary symmetries, was measured, showing clearly anisotropic behavior. We feel then that symmetries play an important role. Potential device applications are envisioned for antenna technology at microwave and terahertz frequencies.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Hexagonal structures on metal-coated two-dimensional microlens arrays

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle

Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2007

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Hexagonally shaped apertures on metal-coated colloidal lattices of microspheres have been observed within certain parameter regimes of femtosecond Ti:sapphire-laser irradiation. The occurrence of such structures is explained by electromagnetic field interferences caused by the array of microspheres. The calculations are based on the splitting of the incident laser field into narrow paraxial Gaussian beams and their subsequent tracing and summation.
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82.70.Dd Colloids
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors

The variable stripe-length method revisited: Improved analysis

C. Lange, M. Schwalm, S. Chatterjee, W. W. Rühle, N. C. Gerhardt, S. R. Johnson, J.-B. Wang, and Y.-H. Zhang

Appl. Phys. Lett. 91, 191107 (2007); http://dx.doi.org/10.1063/1.2802049 (3 pages) | Cited 14 times

Online Publication Date: 6 November 2007

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The variable stripe length method described by Shaklee and Leheny, [Appl. Phys. Lett. 18, 475 (1971)] is a straightforward way to determine the steady-state gain spectrum of laser material. Here, common sources of error are identified and several new, robust ways of calculating the gain from the data are presented. The advantages of these methods are underlined by applying them to data obtained from a Ga(AsSb)/GaAs/(AlGa)As heterostructure.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrafast optical switching in distributed feedback polymer laser

Stefano Perissinotto, Guglielmo Lanzani, Margherita Zavelani-Rossi, Marco Salerno, and Giuseppe Gigli

Appl. Phys. Lett. 91, 191108 (2007); http://dx.doi.org/10.1063/1.2800800 (3 pages) | Cited 13 times

Online Publication Date: 6 November 2007

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We show that polymer distributed feedback lasers can be optically controlled at high bit-rate by using an ultrashort gate pulse. We perform switching-off of the laser emission exploiting the photogeneration of charge carriers from the singlet, emitting state induced, by the gate. We study this resonant non-linear process and we show that the system can in principle work at 500 GHz repetition rate. There could be the possibility for our devices to be integrated into plastic waveguides or fibers, to develop plastic, large-scale integrated, ultrafast optical logic.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.55.Wd Fiber lasers

Improving efficiency of organic photovoltaic cells with pentacene-doped CuPc layer

Wei-Bing Chen, Hai-Feng Xiang, Zong-Xiang Xu, Bei-Ping Yan, V. A. L. Roy, Chi-Ming Che, and Pui-To Lai

Appl. Phys. Lett. 91, 191109 (2007); http://dx.doi.org/10.1063/1.2806195 (3 pages) | Cited 28 times

Online Publication Date: 6 November 2007

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We have fabricated efficient heterojunction organic photovoltaic (OPV) cells based on pentacene-doped copper(II) phthalocyanine (CuPc) layer as donor and fullerene (C60) layer as acceptor. The power conversion efficiency of 4% pentacene-doped CuPc/C60 OPV cell (3.06%) is increased by 77% compared with that of the standard CuPc/C60 OPV cell (1.73%). The efficiency improvement can be attributed to the higher carrier mobility instead of the stronger photon absorption of the pentacene-doped CuPc layer.
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85.60.Bt Optoelectronic device characterization, design, and modeling

Estimation of parametric gain in GaAs/AlOx waveguides by fluorescence and second harmonic generation measurements

M. Ravaro, M. Le Dû, J.-P. Likforman, S. Ducci, V. Berger, G. Leo, and X. Marcadet

Appl. Phys. Lett. 91, 191110 (2007); http://dx.doi.org/10.1063/1.2806933 (3 pages) | Cited 7 times

Online Publication Date: 7 November 2007

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Efficient parametric fluorescence is obtained from a pump wavelength λ = 1.06 μm in low-loss, form-birefringent GaAs/AlOx waveguides. Besides showing a 1 μm wide tuning range and the onset of amplification regime for continuous-wave pump levels around 50 mW, an 8% parametric gain is determined. This is the highest figure reported to date in semiconductor waveguides, and confirms GaAs/AlOx waveguides as a candidate for an integrated parametric optical source.
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42.82.Et Waveguides, couplers, and arrays
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Yj Optical parametric oscillators and amplifiers
42.79.Gn Optical waveguides and couplers

Surface plasmon excitation via Au nanoparticles in n-CdSe/p-Si heterojunction diodes

R. B. Konda, R. Mundle, H. Mustafa, O. Bamiduro, A. K. Pradhan, U. N. Roy, Y. Cui, and A. Burger

Appl. Phys. Lett. 91, 191111 (2007); http://dx.doi.org/10.1063/1.2807277 (3 pages) | Cited 37 times

Online Publication Date: 7 November 2007

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We report on the significant enhancement of photocurrent in pn heterojunction diode, consisting of n-CdSe/p-Si substrates, in situ deposited with Au nanoparticles on the surface by the pulsed-laser deposition technique. This is attributed due to the large enhancement in electromagnetic field that occurs in the vicinity of the metal surface, causing surface plasmons. The large enhancement in Raman and photoluminescence intensity was observed due to surface plasmon resonance. Our results suggest that the photodetectors, optoelectronic, such as high-performance thin-film solar cells, optical communication, and sensing devices, including bio- and molecular sensors, can be fabricated with improved functionality.
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85.30.Kk Junction diodes
85.35.-p Nanoelectronic devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.22.Lp Collective excitations

Phase effects on the exciton polariton amplifier

Yongyou Zhang, Guojun Jin, and Yu-qiang Ma

Appl. Phys. Lett. 91, 191112 (2007); http://dx.doi.org/10.1063/1.2807280 (3 pages) | Cited 5 times

Online Publication Date: 7 November 2007

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We study the phase effects on the exciton polariton amplifier excited by the signal, pump, and idler lasers simultaneously. The signal amplification can be largely enhanced or depressed in this arrangement, compared with that where only the signal and pump lasers are applied. Moreover, a signal polariton switch can be achieved by controlling the excitation phases and it has a high on-off ratio under certain excitation intensities. For a typical GaAs–AlGaAs microcavity, the switching time is about 50 ps and the operating power is about 50 mW.
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42.55.Px Semiconductor lasers; laser diodes

Application of NaYF4:Yb, Er upconversion fluorescence nanocrystals for solution-processed near infrared photodetectors

Cheng-Jun Sun, Zhihua Xu, Bin Hu, G. S. Yi, G. M. Chow, and Jian Shen

Appl. Phys. Lett. 91, 191113 (2007); http://dx.doi.org/10.1063/1.2807841 (3 pages) | Cited 11 times

Online Publication Date: 7 November 2007

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In an attempt to overcome the technical challenges in the conventional solution-processed near infrared (NIR) photodetectors, we have used NaYF4:Yb, Er upconversion fluorescence nanocrystals to replace the semiconductor quantum dots in conjugated polymers. Under NIR excitation, the NaYF4:Yb, Er nanocrystals emit visible light in the solution-processed NIR photodetectors. The emitted visible light is simultaneously absorbed by the host conjugated polymer to generate photocurrent, which indicates that our approach is applicable to fabricate NIR photodetectors while avoiding the major technical challenges associated with semiconductor quantum dot based NIR photodetectors.
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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

Monolithically integrated low-loss silicon photonic wires and three-dimensional tapered couplers fabricated by self-profile transformation

Ming-Chang M. Lee, Wei-Chao Chiu, Tse-Ming Yang, and Chin-Hung Chen

Appl. Phys. Lett. 91, 191114 (2007); http://dx.doi.org/10.1063/1.2809359 (3 pages) | Cited 7 times

Online Publication Date: 7 November 2007

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A subwavelength silicon photonic wire integrated with three-dimensional (3D) tapered couplers fabricated through self-profile transformation is presented. Unlike the conventional process of defining the silicon wire by etching, the profile transformation, which is induced by surface diffusion of silicon atoms during hydrogen annealing, is applied on as-etch silicon structures to make photonic wires. Additionally, this process is able to reduce sidewall roughness to be less than 1 nm, substantially meliorating the unwanted scattering loss. Exploiting this technology, the authors demonstrated that the photonic wire has low propagation loss of 1.26 dB/cm and the 3D tapered coupler has coupling efficiency of 54%.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

1.54 μm photoluminescence emission and oxygen vacancy as sensitizer in Er-doped HfO2 films

Junzhuan Wang, Yan Xia, Yi Shi, Zhuoqiong Shi, Lin Pu, Rong Zhang, Youdou Zheng, Zhensheng Tao, and Fang Lu

Appl. Phys. Lett. 91, 191115 (2007); http://dx.doi.org/10.1063/1.2806188 (3 pages) | Cited 13 times

Online Publication Date: 7 November 2007

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In this letter, we report on the characteristics of 1.54 μm photoluminescence emission of Er-doped HfO2 films synthesized by pulsed laser deposition and ion implantation. An efficient emission at 1.54 μm in the annealed HfO2 films has been observed under a broad band excitation from 400 nm to a higher energy at room temperature. X-ray diffraction and electron paramagnetic resonant measurements were used to analyze the correlation between the optical properties and microstructures. An energy transfer mechanism is proposed that the O vacancy in the bulk acts as an effective sensitizer for the neighboring Er ions and greatly enhances the 1.54 μm band emission. These results lay an important basis for the future silicon-based integrated optoelectronic device applications of Er-doped HfO2 films.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals
76.30.Lh Other ions and impurities

Two-photon photocurrent spectroscopy of electron intersubband relaxation and dephasing in quantum wells

Harald Schneider, Thomas Maier, Martin Walther, and H. C. Liu

Appl. Phys. Lett. 91, 191116 (2007); http://dx.doi.org/10.1063/1.2806963 (3 pages) | Cited 4 times

Online Publication Date: 8 November 2007

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Resonantly enhanced nonlinear absorption between conduction subbands in InGaAs/AlGaAs quantum wells induces a two-photon photocurrent under femtosecond excitation, which is exploited to determine electron intersubband relaxation and dephasing times. The approach allows us to study systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes.
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78.67.De Quantum wells
73.21.Fg Quantum wells
73.63.Hs Quantum wells
72.40.+w Photoconduction and photovoltaic effects
61.72.uj III-V and II-VI semiconductors
68.65.Fg Quantum wells

Electrically tunable photonic crystals with nonlinear composite materials

G. Wang, J. P. Huang, and K. W. Yu

Appl. Phys. Lett. 91, 191117 (2007); http://dx.doi.org/10.1063/1.2809389 (3 pages) | Cited 9 times

Online Publication Date: 8 November 2007

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Based on nonlinear composite materials, we exploit theoretically a class of electrically tunable one-dimensional double-layer photonic crystals (PCs), namely, composite-dielectric and composite-composite PCs. For such PCs, extensive and precise tunability of photonic band gaps can be readily achieved by choosing appropriate pump ac or dc electric fields.
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42.70.Qs Photonic bandgap materials
42.70.Mp Nonlinear optical crystals

High-resolution imaging of local oxidation in polyfluorene thin films by nonlinear near-field microscopy

P. Biagioni, M. Celebrano, M. Zavelani-Rossi, D. Polli, M. Labardi, G. Lanzani, G. Cerullo, M. Finazzi, and L. Duò

Appl. Phys. Lett. 91, 191118 (2007); http://dx.doi.org/10.1063/1.2805214 (3 pages) | Cited 4 times

Online Publication Date: 8 November 2007

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The authors demonstrate nonlinear near-field two-photon photoluminescence imaging of organic semiconductors by coupling femtosecond light pulses to a scanning near-field optical microscope (SNOM) based on hollow-pyramid cantilevered probes. Two-photon excitation of the blue-emitting poly(9,9-dioctylfluorene) (PFO) is found to selectively address keto-defect units, which are responsible for a shifted green-orange emission. This effect is exploited to map oxidized sites in PFO thin films with high contrast and spatial resolution, introducing nonlinear SNOM as an effective technique to characterize oxygen-induced degradation in electroluminescent materials.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
81.05.Hd Other semiconductors

Beyond the bandwidth-length product: Graded index microstructured polymer optical fiber

R. Lwin, G. Barton, L. Harvey, J. Harvey, D. Hirst, S. Manos, M. C. J. Large, L. Poladian, A. Bachmann, H. Poisel, and K.-F. Klein

Appl. Phys. Lett. 91, 191119 (2007); http://dx.doi.org/10.1063/1.2805216 (3 pages) | Cited 9 times

Online Publication Date: 8 November 2007

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Large core multimode polymer fibers for high data rate transmission are an important growth area. The conventional approach to reducing the intermodal dispersion in such fibers is to use a graded index (GI) profile. More recently, microstructures rather than differences in chemical composition have been used to produce the GI structure. We compare the bandwidth performance of two GI microstructured fibers to a conventional GI fiber made from the same material. The microstructured fibers not only show excellent bandwidth performance but also their bandwidth has an unconventional length dependence: no additional pulse broadening beyond a characteristic length.
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42.81.Wg Other fiber-optical devices
42.81.Dp Propagation, scattering, and losses; solitons
42.81.Ht Gradient-index (GRIN) fiber devices

Terahertz radiation from ultrahigh-speed field-effect transistors induced by ultrafast optical gate switching

T. Kondo and K. Hirakawa

Appl. Phys. Lett. 91, 191120 (2007); http://dx.doi.org/10.1063/1.2801363 (3 pages) | Cited 1 time

Online Publication Date: 8 November 2007

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We have observed terahertz radiation due to ultrafast change in drain current induced by optical gate-field modulation in high-speed field-effect transistors (FETs). This time-domain measurement is potentially applicable to the characterization of cutoff frequencies of ultrahigh-speed FETs beyond the frequency range covered by conventional swept-frequency measurements. The cutoff frequencies of sample FETs deduced by the present technique were in good agreement with those determined by a network analyzer.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.65.Pc Optical bistability, multistability, and switching, including local field effects
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.68.+m Photography, photographic instruments; xerography

Intersubband relaxation dynamics in single and double quantum wells based on strained InGaAs/AlAs/AlAsSb

C. V.-B. Grimm, M. Priegnitz, S. Winnerl, H. Schneider, M. Helm, K. Biermann, and H. Künzel

Appl. Phys. Lett. 91, 191121 (2007); http://dx.doi.org/10.1063/1.2809409 (3 pages) | Cited 5 times

Online Publication Date: 9 November 2007

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Intersubband relaxation dynamics in single and coupled double quantum well (QW) structures based on strained InGaAs/AlAs/AlAsSb are studied by femtosecond pump probe spectroscopy at wavelengths around 2 μm. For single QWs, the transient transmission was observed to decay exponentially with a time constant of 2 ps, showing that side valleys have negligible influence on the intersubband relaxation dynamics for strained InGaAs QWs. For double QWs, the pump-probe signal at the intersubband energy involving the two electronic levels located at the wider QW exhibits an induced absorption component attributed to the population of the second subband (associated with the narrow QW) by hot electrons.
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73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
78.67.De Quantum wells

Integrated waveguide-coupled terahertz microcavity resonators

Paul A. George, Christina Manolatou, Farhan Rana, Adam L. Bingham, and Daniel R. Grischkowsky

Appl. Phys. Lett. 91, 191122 (2007); http://dx.doi.org/10.1063/1.2809608 (3 pages) | Cited 7 times

Online Publication Date: 9 November 2007

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We demonstrate integrated square terahertz microcavity resonators side coupled to waveguides. We present the microcavity transmission spectra for different resonator sizes and coupling strengths. The measured quality factors due to external coupling and cavity loss are found to be between 40 and 90 and between 30 and 40, respectively, for cavity resonance frequencies between 1.077 and 1.331 THz.
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42.82.Et Waveguides, couplers, and arrays
84.40.Az Waveguides, transmission lines, striplines

Polarization dependence study of electroluminescence and absorption from InAs/GaAs columnar quantum dots

Philipp Ridha, Lianhe Li, Andrea Fiore, Gilles Patriarche, Meletios Mexis, and Peter M. Smowton

Appl. Phys. Lett. 91, 191123 (2007); http://dx.doi.org/10.1063/1.2811720 (3 pages) | Cited 16 times

Online Publication Date: 9 November 2007

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Semiconductor optical amplifiers based on InGaAs columnar quantum dots (CQDs) with different numbers of superlattice periods were fabricated and tested. The polarization dependence of the electroluminescence (EL) and absorption of such CQDs structures were measured. Compared to standard QDs a large improvement in the ratio of transverse-magnetic (TM) and -electric (TE) integrated EL was obtained in CQDs, depending on the number of stacked GaAs/InAs superlattice periods, which can be attributed to the more symmetric shape of CQDs. TM and TE resolved photovoltage absorption spectroscopy confirmed this improvement. A small spectral separation between TE- and TM-EL peaks has been observed showing that heavy and light holelike states are energetically close in these QDs.
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78.67.Hc Quantum dots
78.60.Fi Electroluminescence
42.55.Px Semiconductor lasers; laser diodes
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Time dependent plasma properties during microarcing in radio frequency plasmas

Y. Yin, S. Y. Allan, M. M. M. Bilek, and D. R. McKenzie

Appl. Phys. Lett. 91, 191501 (2007); http://dx.doi.org/10.1063/1.2806186 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2007

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We report experimental results for time dependent plasma properties during microarcing in a rf plasma system. A cutoff discriminator bias voltage can be defined as a parameter representing plasma potential. The cutoff voltage during the microarcing does not exactly follow the dependence of floating potential. The plasma/ion density increases significantly after microarc initiation and then reduces slowly. We propose that a significant number of electrons enter the plasma in the initial period of the microarc and gain very high energy. These high energy electrons lose their energy through a relatively slower process of collisions while generating a significantly higher plasma density.
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52.25.-b Plasma properties
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Optical spectroscopic study of the SiN/HfO2 interfacial formation during rf sputtering of HfO2

M. Toledano-Luque, M. L. Lucía, A. del Prado, E. San Andrés, I. Mártil, and G. González-Díaz

Appl. Phys. Lett. 91, 191502 (2007); http://dx.doi.org/10.1063/1.2811958 (3 pages) | Cited 7 times

Online Publication Date: 9 November 2007

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High-k stacks formed by chemical-vapor-deposited SiN and high-pressure sputtered HfO2 in either O2 or Ar atmosphere have been studied. The introduction of a SiN layer is proposed to prevent the uncontrollable SiO2 growth while sputtering. The formation of Si–O bonds after the sputtering of the HfO2 film in O2 atmosphere was observed by infrared spectroscopy. Optical diagnosis of the plasma demonstrated a high density of O radicals in the system when working with O2. The small radius and high reactivity of these O radicals are the source of the SiN oxidation. However, the structure of the SiN film is preserved during Ar sputtering.
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81.15.Cd Deposition by sputtering
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
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