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18 May 2009

Volume 94, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 203301 (2009); http://dx.doi.org/10.1063/1.3133902 (3 pages)

Zihong Liu, Joon Hak Oh, Mark E. Roberts, Peng Wei, Bipul C. Paul, Masaki Okajima, Yoshio Nishi, and Zhenan Bao
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Many-body effects on terahertz quantum well detectors

X. G. Guo, Z. Y. Tan, J. C. Cao, and H. C. Liu

Appl. Phys. Lett. 94, 201101 (2009); http://dx.doi.org/10.1063/1.3134485 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2009

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Many-body effects have been investigated in the design of terahertz quantum well photon detectors. A large discrepancy between the theoretical and experimental photoresponse peak positions exist without considering the many-body interactions. The calculated results agree with the experimental data quantitatively with including the exchange-correlation and depolarization effects within the local density approximation. Our numerical results show that it is a must to consider the many-body interactions for designing the quantum well detectors for the terahertz region.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Generation of controllable nondiffracting beams using multimode optical fibers

X. Zhu, A. Schülzgen, L. Li, and N. Peyghambarian

Appl. Phys. Lett. 94, 201102 (2009); http://dx.doi.org/10.1063/1.3138780 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2009

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A method of generating nondiffracting beams using multimode optical fibers is reported. When a large-core multimode fiber is spliced onto a piece of single-mode fiber, only linearly polarized (LP0,n) modes are excited inside the multimode fiber segment because of mode orthogonality and on-axis excitation. Since the excited LP0,n modes are actually Bessel fields with different transverse wave vectors truncated by the core of the multimode fiber, the beam exiting the multimode fiber facet can form a variety of readily controllable and nearly nondiffracting optical patterns resulting from interference of apertured Bessel fields.
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42.81.Dp Propagation, scattering, and losses; solitons
42.81.Wg Other fiber-optical devices
42.25.Hz Interference

Highly temperature insensitive, deep-well 4.8 μm emitting quantum cascade semiconductor lasers

J. C. Shin, M. D’Souza, Z. Liu, J. Kirch, L. J. Mawst, D. Botez, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 94, 201103 (2009); http://dx.doi.org/10.1063/1.3139069 (3 pages) | Cited 8 times

Online Publication Date: 19 May 2009

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4.8 μm emitting, quantum cascade (QC) lasers that suppress carrier leakage out of their active regions to the continuum have been realized by using deep (in energy) quantum wells in the active regions, tall barriers in and around the active regions, and tapered conduction-band-edge relaxation regions. The characteristic temperature coefficients T0 and T1 for the threshold current density Jth and slope efficiency, respectively, reach values of 238 K over the 20–60 °C temperature range, which means that Jth and the slope efficiency vary with temperature half as fast as those of conventional QC lasers. In turn, significantly improved continuous wave performance is expected.
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42.55.Px Semiconductor lasers; laser diodes
68.65.Fg Quantum wells

Theoretical investigation on polarization control of semipolar-oriented InGaN quantum-well emission using (Al)InGaN alloy substrates

A. Atsushi Yamaguchi

Appl. Phys. Lett. 94, 201104 (2009); http://dx.doi.org/10.1063/1.3139080 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2009

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The polarization properties of InGaN quantum wells on semipolar AlInGaN alloy substrates are calculated numerically using a 6×6⋅k⋅p Hamiltonian. It is shown that the polarization direction of quantum-well emission changes, depending on the substrate alloy composition and quantum-well width, and that this polarization switching is caused by the strain anisotropy and quantum confinement effects in the quantum wells. The calculation results indicate that InGaN or AlInGaN alloy substrates can be beneficial in obtaining desirable polarization properties for the formation of cleaved-facet cavity mirrors in laser diodes on semipolar substrates.
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78.67.De Quantum wells

Single-mode operation of a high-brightness narrow-band single-photon source

M. Scholz, L. Koch, R. Ullmann, and O. Benson

Appl. Phys. Lett. 94, 201105 (2009); http://dx.doi.org/10.1063/1.3139768 (3 pages) | Cited 9 times

Online Publication Date: 19 May 2009

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We demonstrate a narrow-band single-photon source based on cavity-enhanced parametric downconversion for efficient coupling to atomic quantum memories. Selecting a single longitudinal cavity mode by spectral filtering, we achieve a spectral brightness of ∼ 330 biphotons/(s mW MHz) and an overall bandwidth of 2.7 MHz, which suits the width of naturally broadened transitions in alkali gases like rubidium or cesium.
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42.72.-g Optical sources and standards
42.65.Lm Parametric down conversion and production of entangled photons
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Ci Filters, zone plates, and polarizers

Ultralow dark current Ge/Si(100) photodiodes with low thermal budget

J. Osmond, G. Isella, D. Chrastina, R. Kaufmann, M. Acciarri, and H. von Känel

Appl. Phys. Lett. 94, 201106 (2009); http://dx.doi.org/10.1063/1.3125252 (3 pages) | Cited 20 times

Online Publication Date: 20 May 2009

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Vertical incidence photodiodes were fabricated from Ge grown epitaxially on Si(100) by low-energy plasma-enhanced chemical vapor deposition. Consideration of the energy band profiles of n-i-p and p-i-n heterostructures, and optimization of growth processes and thermal budget, allowed the performance of Ge photodectors integrated on Si(100) substrates to be optimized. Record low dark current density of Js = 4.1×10−5 A/cm2 and external quantum efficiency at 1550 nm of η = 32% were measured.
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85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.20.Mq Elemental semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Midwave infrared InAs/GaSb strained layer superlattice hole avalanche photodiode

Koushik Banerjee, Siddhartha Ghosh, Shubhrangshu Mallick, Elena Plis, Sanjay Krishna, and Christoph Grein

Appl. Phys. Lett. 94, 201107 (2009); http://dx.doi.org/10.1063/1.3139012 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2009

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Midwavelength infrared InAs–GaSb strained layer superlattice n+-n−-p avalanche photodiodes, specifically designed to have hole dominated avalanching, with a zero percent cutoff wavelength of ∼ 6.3 μm are fabricated and characterized. Maximum multiplication gain of 105 is measured at −3.6 V at 77 K. Measured excess noise factors are significantly improved compared to unity hole to electron ionization ratio and corresponds to a theoretical value between 40 and 50 when compared with the McIntyre model. Exponential nature of the gain as a function of reverse bias along with low excess noise factors confirms single carrier hole dominated impact ionization.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Rabi oscillations in semiconductor quantum dots revisited: Influence of LO-phonon collisions

K. Schuh, J. Seebeck, M. Lorke, and F. Jahnke

Appl. Phys. Lett. 94, 201108 (2009); http://dx.doi.org/10.1063/1.3140534 (3 pages) | Cited 1 time

Online Publication Date: 20 May 2009

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Coherence properties of semiconductor quantum dots are of central importance for a variety of applications. Previous studies of decoherence in these systems mainly focused on the interaction with LA phonons, only giving rise to dephasing. In contrast, the interaction with LO phonons additionally causes carrier scattering. To show the importance of the combined influence of dephasing and carrier scattering, we revisit the case of Rabi oscillations in semiconductor quantum dots using a quantum-kinetic treatment of the carrier-LO-phonon interaction.
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78.67.Hc Quantum dots
71.38.-k Polarons and electron-phonon interactions

Spectral and spatial investigation of midinfrared surface waves on a plasmonic grating

T. Ribaudo, D. C. Adams, B. Passmore, E. A. Shaner, and D. Wasserman

Appl. Phys. Lett. 94, 201109 (2009); http://dx.doi.org/10.1063/1.3140569 (3 pages) | Cited 1 time

Online Publication Date: 21 May 2009

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A patterned metal film with a periodic array of subwavelength apertures, fabricated upon a semiconductor substrate and designed to possess transmission resonances in the midinfrared is interrogated with a wavelength-tunable external cavity quantum cascade laser. The interaction of the coherent light with this plasmonic structure is studied using a spatially resolved transmission experiment, allowing for the far-field imaging of propagating waves on the surface of the metal film. Spatial and spectral transmission is investigated for a range of near-normal incidence angles. For nonzero angles of incidence, coupling of laser light, at distinct frequencies, to surface waves propagating in opposite directions is demonstrated.
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42.79.Dj Gratings
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

Direct and wavelength modulation spectroscopy using a cw external cavity quantum cascade laser

G. Hancock, J. H. van Helden, R. Peverall, G. A. D. Ritchie, and R. J. Walker

Appl. Phys. Lett. 94, 201110 (2009); http://dx.doi.org/10.1063/1.3141521 (3 pages) | Cited 16 times

Online Publication Date: 21 May 2009

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A continuous wave external cavity quantum cascade laser (EC-QCL) operating between 1872 and 1958 cm−1 has been used to make rotationally resolved measurements in the fundamental band of nitric oxide at 140 mTorr, and the ν2 band of water at atmospheric pressure. These measurements demonstrate the advantages of wide tunability and high resolution of the EC-QCL system. From direct absorption spectroscopy on nitric oxide a laser bandwidth of 20 MHz has been deduced and a sensitivity of 8.4×10−4 cm−1 Hz−1/2 was achieved. Wavelength modulation spectroscopy using current modulation enhances the sensitivity by a factor of 23 to 3.7×10−5 cm−1 Hz−1/2.
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42.55.Px Semiconductor lasers; laser diodes

Symmetry breaking in metallic cut wire pairs metamaterials for negative refractive index

Shah Nawaz Burokur, Alexandre Sellier, Boubacar Kanté, and André de Lustrac

Appl. Phys. Lett. 94, 201111 (2009); http://dx.doi.org/10.1063/1.3141729 (3 pages) | Cited 6 times

Online Publication Date: 21 May 2009

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Metamaterials made of exclusively metallic cut wire pairs have been experimentally demonstrated to exhibit a negative refractive index at optical frequencies. However, other related works have not shown a negative index. In this paper, we propose an easy way to manipulate the magnetic and electric resonances of these metamaterials to produce a negative index. We show that judiciously breaking the symmetry of the structure allows tuning of both resonances leading to an overlapping between the negative permeability and negative permittivity regions. Numerical and experimental parametric studies of several cut wire pairs metamaterials are presented to validate our method at microwave frequencies.
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42.70.-a Optical materials
42.25.-p Wave optics

4.5 μm wavelength vertical external cavity surface emitting laser operating above room temperature

M. Rahim, A. Khiar, F. Felder, M. Fill, and H. Zogg

Appl. Phys. Lett. 94, 201112 (2009); http://dx.doi.org/10.1063/1.3139778 (3 pages) | Cited 9 times

Online Publication Date: 21 May 2009

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A midinfrared vertical external cavity surface emitting laser with 4.5 μm emission wavelength and operating above room temperature has been realized. The active part consists of a single 850 nm thick epitaxial PbSe gain layer. It is followed by a 2 1/2 pair Pb1−yEuyTe/BaF2 Bragg mirror. No microstructural processing is needed. Excitation is done optically with a 1.5 μm wavelength laser. The device operates up to 45 °C with 100 ns pulses and delivers 6 mW output power at 27 °C heat-sink temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Two-photon induced amplified spontaneous emission from needlelike triphenylamine-containing derivative crystals with low threshold

Qi-Dai Chen, Hong-Hua Fang, Bin Xu, Jie Yang, Hong Xia, Fei-Peng Chen, Wen-Jing Tian, and Hong-Bo Sun

Appl. Phys. Lett. 94, 201113 (2009); http://dx.doi.org/10.1063/1.3142383 (3 pages) | Cited 12 times

Online Publication Date: 22 May 2009

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Two-photon induced amplified spontaneous emission (ASE) characteristics of a needlelike crystal were studied. Under two-photon excitation, the upconverted light emission was confined within the crystal and self-waveguided along the needle axis then radiated from the needle tips. The full width at half maximum of the two-photon excited fluorescence reaches 6.5 nm and ASE threshold is as low as 0.29 mJ pulse−1 cm−2 for the N-(4-(4-(4-(diphenylamino)styryl)styryl)phenyl)-N-phenylbenzene amine crystal, comparable with those achieved by single-photon pumping. The needlelike crystal is shown to be a promising candidate for frequency up-converted organic semiconductor microlasers.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Photoalignment effect in a liquid-crystal film doped with nanoparticles and azo-dye

Wen-Zheng Chen, Yi-Tai Tsai, and Tsung-Hsien Lin

Appl. Phys. Lett. 94, 201114 (2009); http://dx.doi.org/10.1063/1.3142390 (3 pages) | Cited 6 times

Online Publication Date: 22 May 2009

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This study discusses the photoalignment effect in a liquid-crystal (LC) film that is doped with nanoparticles and azo-dye. The vertical alignment induced by nanoparticles of polyhedral oligomeric silsesquioxanes can be changed into homogeneous alignment by the absorption of photoexcited azo-dye. An electrically tunable polarization-dependent LC phase grating is also produced using the method. Both nanoparticle- and azo-dye-induced vertical and homogeneous alignments are noncontact alignment and are highly promising for low-temperature plastic processes.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
42.79.Dj Gratings

Low-temperature time-resolved cathodoluminescence study of exciton dynamics involving basal stacking faults in a-plane GaN

P. Corfdir, J. Ristić, P. Lefebvre, T. Zhu, D. Martin, A. Dussaigne, J. D. Ganière, N. Grandjean, and B. Deveaud-Plédran

Appl. Phys. Lett. 94, 201115 (2009); http://dx.doi.org/10.1063/1.3142396 (3 pages) | Cited 13 times

Online Publication Date: 22 May 2009

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Time-resolved cathodoluminescence at 27 K has been performed on a-plane GaN grown by epitaxial lateral overgrowth. We detail the relaxation and recombination mechanisms of excitons [free or bound to neutral donors, or bound to I1-type basal stacking faults (BSFs)] in relation to the local density in BSFs. We describe the slow exciton capture rate on isolated BSFs by a diffusion model involving donors via a hopping process. Where BSFs are organized into bundles, we relate the shorter rise time to intra-BSF localization processes and the multiexponential decay to the type-II band alignment of BSFs in wurtzite GaN.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.47.jd Time resolved luminescence
71.35.-y Excitons and related phenomena
66.30.Lw Diffusion of other defects
61.72.Nn Stacking faults and other planar or extended defects

Integrated continuum-atomistic modeling of nonthermal ablation of gold nanofilms by femtosecond lasers

Yong Gan and J. K. Chen

Appl. Phys. Lett. 94, 201116 (2009); http://dx.doi.org/10.1063/1.3142878 (3 pages) | Cited 15 times

Online Publication Date: 22 May 2009

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Ultrafast nonthermal ablation of gold nanofilms is studied using a combined two-temperature model and molecular dynamics method. The results show that for thinner films the tensile stress is directly reversed from the initially generated compressive stress. For thicker films, on the other hand, the tensile stress wave is reflected from the irradiated surface. The key driving force for ultrafast nonthermal material ablation is conventional thermal stress, instead of the hot electron blast force.
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81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.38.Mf Laser ablation

Relativistic plasma shutter for ultraintense laser pulses

Stephen A. Reed, Takeshi Matsuoka, Stepan Bulanov, Motonobu Tampo, Vladimir Chvykov, Galina Kalintchenko, Pascal Rousseau, Victor Yanovsky, Ryousuke Kodama, Dale W. Litzenberg, Karl Krushelnick, and Anatoly Maksimchuk

Appl. Phys. Lett. 94, 201117 (2009); http://dx.doi.org/10.1063/1.3139860 (3 pages) | Cited 5 times

Online Publication Date: 22 May 2009

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A relativistic plasma shutter technique is proposed and tested to remove the sub-100 ps pedestal of a high-intensity laser pulse. The shutter is an ultrathin foil placed before the target of interest. As the leading edge of the laser ionizes the shutter material it will expand into a relativistically underdense plasma allowing for the peak pulse to propagate through while rejecting the low intensity pedestal. An increase in the laser temporal contrast is demonstrated by measuring characteristic signatures in the accelerated proton spectra and directionality from the interaction of 30 TW pulses with ultrathin foils along with supporting hydrodynamic and particle-in-cell simulations.
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42.79.-e Optical elements, devices, and systems
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