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26 Dec 2005

Volume 87, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 87, 263102 (2005); http://dx.doi.org/10.1063/1.2150278 (3 pages)

Z. Zhong, G. Katsaros, M. Stoffel, G. Costantini, K. Kern, O. G. Schmidt, N. Y. Jin-Phillipp, and G. Bauer
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Spectral dependencies of terahertz emission from InAs and InSb

R. Adomavičius, G. Molis, A. Krotkus, and V. Sirutkaitis

Appl. Phys. Lett. 87, 261101 (2005); http://dx.doi.org/10.1063/1.2143111 (3 pages) | Cited 17 times

Online Publication Date: 19 December 2005

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Spectral dependences of the THz radiation from the laser-illuminated surfaces of InAs and InSb have been investigated experimentally at high optical fluences for the laser wavelengths ranging from 0.6 to 2 μm. Efficient THz generation was discovered in the excitation range around 1.6 μm. The influence of the intervalley scattering was clearly evidenced. The energy position of the subsidiary conduction band valleys was evaluated from this study to be equal 1.08 and 0.53 eV for InAs and InSb, respectively. It has been concluded that THz emission at high excitation fluencies is dominated by the shift current effect.
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78.70.Gq Microwave and radio-frequency interactions
78.66.Fd III-V semiconductors
68.47.Fg Semiconductor surfaces
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Neutral ion-implantation-induced selective quantum-dot intermixing

H. S. Djie, B. S. Ooi, and V. Aimez

Appl. Phys. Lett. 87, 261102 (2005); http://dx.doi.org/10.1063/1.2150279 (3 pages) | Cited 16 times

Online Publication Date: 20 December 2005

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High spatial band-gap tuning has been observed from an InGaAs/GaAs quantum-dot (QD) structure implanted with electrically neutral species, As and P ions, at 200 °C followed by a rapid thermal annealing. Phosphorous was found to be a more effective species to induce QD intermixing than the As at similar dose level. A blueshift as large as 126 meV has been observed from the P+-implanted and intermixed sample, while only ∼ 14 meV has been measured from the SixNy-capped sample.
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61.72.uf Ge and Si
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
61.72.Cc Kinetics of defect formation and annealing

High-efficiency red light-emitting diodes based on polyfluorene copolymers with extremely low content of 4,7-di-2-thienyl-2,1,3-benzothiadiazole-comparative studies of intrachain and interchain interaction

Jie Luo, Junbiao Peng, Yong Cao, and Qiong Hou

Appl. Phys. Lett. 87, 261103 (2005); http://dx.doi.org/10.1063/1.2150251 (3 pages) | Cited 27 times

Online Publication Date: 20 December 2005

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High-efficiency red light-emitting diodes based on poly(9,9-dioctylfluorene) (PFO) doped chemically into the polymer main chain with extremely low dopant content of 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) (comonomer ratio:99.9/0.1) are realized. External quantum efficiency of PFO-DBT0.1 reached 2.66% (photon/electron) with a luminance efficiency of 2.5 cd/A, significantly higher than that of the device with high DBT content. The copolymer exclusively emits red light peaked at 615 nm due to strong intrachain energy transfer. Comparing photophysical properties and device performance between single copolymer PFO-DBT0.1 and blends with the same DBT composition by adding neat PFO into a PFO-DBT15, PFO-DBT25, or PFO-DBT35 copolymers, we concluded that energy transfer via intrachain interaction along a conjugated polymer main chain is more efficient than via interchain interaction in such copolymers and that chemically doped copolymers show higher device performance than polymer blend.
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85.60.Jb Light-emitting devices

Signal processing by opto-optical interactions between self-localized and free propagating beams in liquid crystals

Alessia Pasquazi, Alessandro Alberucci, Marco Peccianti, and Gaetano Assanto

Appl. Phys. Lett. 87, 261104 (2005); http://dx.doi.org/10.1063/1.2158026 (3 pages) | Cited 28 times

Online Publication Date: 20 December 2005

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The reorientational nonlinearity of nematic liquid crystals enables a self-localized spatial soliton and its waveguide to be deflected or destroyed by a control beam propagating across the cell. We demonstrate a simple all-optical readdressing scheme by exploiting the lens-like perturbation induced by an external beam on both a nematicon and a copolarized guided signal of different wavelength. Angular steering as large as 2.2 deg was obtained for control powers as low as 32 mW in the near infrared.
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42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.30.-d Imaging and optical processing
42.65.Tg Optical solitons; nonlinear guided waves
42.79.Gn Optical waveguides and couplers

Optical Tamm states for the fabrication of polariton lasers

Alexey Kavokin, Ivan Shelykh, and Guillaume Malpuech

Appl. Phys. Lett. 87, 261105 (2005); http://dx.doi.org/10.1063/1.2136414 (3 pages) | Cited 22 times

Online Publication Date: 20 December 2005

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We propose to embed the ultrathin layer of an organic or inorganic material at the boundary between two specially designed periodic dielectric structures in order to achieve the strong coupling between Frenkel or Wannier-Mott excitons and optical Tamm states localized at the interface. This would allow the fabrication of polariton lasers without microcavities that could be easier from the technological point of view. Analytical formulas are given for the energies of optical Tamm states and the constant of their coupling to excitons.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
63.20.Pw Localized modes

Short-period InAs/GaSb type-II superlattices for mid-infrared detectors

H. J. Haugan, F. Szmulowicz, K. Mahalingam, G. J. Brown, S. R Munshi, and B. Ullrich

Appl. Phys. Lett. 87, 261106 (2005); http://dx.doi.org/10.1063/1.2150269 (3 pages) | Cited 17 times

Online Publication Date: 21 December 2005

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Using a newly developed envelope function approximation model that includes interface effects, several InAs/GaSb Type-II superlattices (SLs) were designed for the 4 μm detection threshold. The present model predicts that a given threshold can be reached with a wide range of progressively thinner SL periods and these thinner designs hold a promise of higher mobilities and longer Auger lifetimes, thus higher detector operating temperatures. The proposed SL structures were grown by molecular-beam epitaxy with slow growth rates. As predicted, the band gaps of SLs determined by low-temperature photoluminescence remained constant around 330 meV for the samples in the period range from 50.6 to 21.2 Å.
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73.21.Cd Superlattices
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.63.-b Electronic transport in nanoscale materials and structures
85.60.Gz Photodetectors (including infrared and CCD detectors)

Metal-wire terahertz time-domain spectroscopy

Markus Walther, Mark R. Freeman, and Frank A. Hegmann

Appl. Phys. Lett. 87, 261107 (2005); http://dx.doi.org/10.1063/1.2158025 (3 pages) | Cited 34 times

Online Publication Date: 21 December 2005

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Terahertz (THz) pulses propagating on a metal-wire waveguide are used to perform terahertz time-domain spectroscopy of lactose powder dispersed on top of the wire. The THz pulses are generated by a photoconductive switch at one end of the metal wire and are detected at the other end by electro-optic sampling in a ZnTe crystal that can be moved parallel to the axis of the metal wire. A large enhancement in the peak amplitude of the THz signal is observed by contacting the metal wire to one of the electrodes of the photoconductive switch. The propagation characteristics of the THz pulse along the metal wire and near its end are studied. Potential applications of metal-wire terahertz time-domain spectroscopy are discussed.
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78.30.-j Infrared and Raman spectra
78.70.Gq Microwave and radio-frequency interactions
78.20.Jq Electro-optical effects

Limitations of active carrier removal in silicon Raman amplifiers and lasers

D. Dimitropoulos, S. Fathpour, and B. Jalali

Appl. Phys. Lett. 87, 261108 (2005); http://dx.doi.org/10.1063/1.2155071 (3 pages) | Cited 21 times

Online Publication Date: 21 December 2005

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The lifetime of two-photon generated carriers has been established as the critical parameter that determines the performance of silicon Raman lasers and amplifiers since it determines the optical loss. Here, we investigate the intensity dependence of the carrier lifetime in the case where the carriers are swept out by means of a p‐n junction. Numerical simulations show that at sufficiently high pump intensities, the generated carriers screen the applied electric field and therefore result in a higher lifetime and hence a lower net Raman gain. We also quantify the electrical power dissipation necessary to maintain low optical losses.
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42.55.Ye Raman lasers
42.55.Px Semiconductor lasers; laser diodes

Gain and carrier losses of (GaIn)(NAs) heterostructures in the 1300–1550 nm range

C. Schlichenmaier, A. Thränhardt, T. Meier, S. W. Koch, W. W. Chow, J. Hader, and J. V. Moloney

Appl. Phys. Lett. 87, 261109 (2005); http://dx.doi.org/10.1063/1.2149371 (3 pages) | Cited 3 times

Online Publication Date: 21 December 2005

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A microscopic model is used to analyze gain and loss properties of (GaIn)(NAs)/GaAs quantum wells in the 1.3–1.55 μm range, including Auger and radiative recombination. The calculations show that, as long as good material quality can be achieved, growing highly compressively strained samples is preferable due to their specific band structure properties. Optimum laser operation is possible slightly above a peak gain of 1000 cm−1.
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78.66.Fd III-V semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
79.20.Fv Electron impact: Auger emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

A “standing-wave meter” to measure dispersion and loss of photonic-crystal waveguides

R. Wüest, D. Erni, P. Strasser, F. Robin, H. Jäckel, B. C. Buchler, A. F. Koenderink, V. Sandoghdar, and R. Harbers

Appl. Phys. Lett. 87, 261110 (2005); http://dx.doi.org/10.1063/1.2151254 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2005

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We demonstrate a “standing-wave meter” for measuring dispersion and loss along the length of a planar InP-based photonic-crystal waveguide. Light from a tunable cw laser was coupled into a single line-defect waveguide that terminated inside the crystal structure to form a retroreflector. This structure created a standing wave which was imaged using a scanning near-field optical microscope. By measuring the intensity distribution of the standing wave for a range of optical frequencies, waveguide dispersion and loss were measured with high accuracy. Comparisons of the measurement results with three-dimensional numerical simulations reveal that material dispersion effects as small as 0.8% affect the band structure measurably.
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07.79.Fc Near-field scanning optical microscopes
42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials

Photorefractive properties of an unsensitized polymer composite based on a dicyanostyrene derivative as nonlinear optical chromophore

José A. Quintana, Pedro G. Boj, José M. Villalvilla, Javier Ortíz, Fernando Fernández-Lázaro, Ángela Sastre-Santos, and María A. Díaz-García

Appl. Phys. Lett. 87, 261111 (2005); http://dx.doi.org/10.1063/1.2158032 (3 pages) | Cited 6 times

Online Publication Date: 23 December 2005

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We report on the photorefractive (PR) properties at the 633 nm laser wavelength of a polymer composite based on the polymer poly(n-vinyl carbazole) (PVK), doped with the dicyanostyrene derivative 4-piperidinobenzylidene-malonitrile (PDCST) as nonlinear optical chromophore and the liquid plasticizer butyl benzyl phthalate (BBP), without the presence of sensitizer. The PR-effect is observed only when samples are previously subjected to an electric field (i.e., 20 V/μm for 10 min). Photoconductivity and birefringence of the composite become significant when the electric field treatment is performed at temperatures higher than room temperature (24 °C). Gain coefficient and PR speed, determined from two-beam coupling experiments, are compared to those obtained with the PVK/PDSCT/BBP/C60 standard sensitized composite.
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42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
42.70.Mp Nonlinear optical crystals
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses

Shingo Ono, Hidetoshi Murakami, Alex Quema, Gilbert Diwa, Nobuhiko Sarukura, Ryujiro Nagasaka, Yo Ichikawa, Hiraku Ogino, Eriko Ohshima, Akira Yoshikawa, and Tsuguo Fukuda

Appl. Phys. Lett. 87, 261112 (2005); http://dx.doi.org/10.1063/1.2158514 (3 pages) | Cited 7 times

Online Publication Date: 27 December 2005

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Terahertz (THz) radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide (ZnO) is presented. The THz-radiation power is saturated at bias voltages above 800 V/cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
85.60.-q Optoelectronic devices

Electronic anti-Stokes–Raman emission in quantum-cascade lasers

A. Gomez-Iglesias, D. Wasserman, C. Gmachl, A. Belyanin, and D. L. Sivco

Appl. Phys. Lett. 87, 261113 (2005); http://dx.doi.org/10.1063/1.2150585 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2005

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In this letter, the observation of electronic anti-Stokes–Raman emission in quantum-cascade lasers is reported. We present two distinct active region designs with enhanced anti-Stokes–Raman nonlinearity. The pump laser is monolithically integrated with the nonlinear region in a two-stack active core within the same waveguide. Electronic Raman emission was observed in both designs. Additionally, for the design with positive detuning, an incoherent upconversion signal resulting from optical pumping is detected.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.60.Bt Optoelectronic device characterization, design, and modeling
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Two-dimensionally localized modes of a nanoscale gap plasmon waveguide

D. F. P. Pile, T. Ogawa, D. K. Gramotnev, Y. Matsuzaki, K. C. Vernon, K. Yamaguchi, T. Okamoto, M. Haraguchi, and M. Fukui

Appl. Phys. Lett. 87, 261114 (2005); http://dx.doi.org/10.1063/1.2149971 (3 pages) | Cited 88 times

Online Publication Date: 29 December 2005

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We report numerical analysis and experimental observation of two dimensionally localized plasmonic modes guided by a nanogap in a thin metal film. Dispersion, dissipation, and field structure of these modes are analyzed using the finite-difference time-domain algorithm. The experimental observation is conducted by the end-fire excitation of the proposed gap plasmon waveguides and detection of the generated modes using their edge scattering and charge coupled device camera imaging. Physical interpretation of the obtained results is presented and origins of the described modes are discussed.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Gn Optical waveguides and couplers

Electronic electrooptic phase modulation using bent-core liquid crystals

Malcolm Rickard, Michi Nakata, Hideo Takezoe, Junji Watanabe, and Noel A. Clark

Appl. Phys. Lett. 87, 261115 (2005); http://dx.doi.org/10.1063/1.2149152 (3 pages) | Cited 2 times

Online Publication Date: 30 December 2005

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The electronic contribution to the second-order nonlinear polarizability of a ferroelectric liquid-crystal phase formed by the spontaneously polar organization of bent-core molecules has been demonstrated. Application of a 40 MHz driving voltage and measurement of the refractive index modulation of light of wavelength 1.3 μm yields electrooptic coefficients r ∼ 10 pm/V, comparable to that found in poled polymers.
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78.20.Jq Electro-optical effects
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
77.80.-e Ferroelectricity and antiferroelectricity
42.65.-k Nonlinear optics
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