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16 Aug 2010

Volume 97, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 073101 (2010); http://dx.doi.org/10.1063/1.3478515 (3 pages)

Hon-Way Lin (林弘偉), Yu-Jung Lu (呂宥蓉), Hung-Ying Chen (陳虹穎), Hong-Mao Lee (李弘貿), and Shangjr Gwo (果尚志)
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Temperature dependence of the key electro-optical characteristics for midinfrared emitting quantum cascade lasers

D. Botez, S. Kumar, J. C. Shin, L. J. Mawst, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 97, 071101 (2010); http://dx.doi.org/10.1063/1.3478836 (3 pages) | Cited 15 times

Online Publication Date: 16 August 2010

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The equations for threshold-current density Jth, differential quantum efficiency ηd, and maximum wallplug efficiency ηwp,max for quantum-cascade lasers (QCLs) are modified for electron leakage and backfilling. A thermal-excitation model of “hot” injected electrons from the upper laser state to upper active-region states is used to calculate leakage currents. The calculated characteristic temperature T0 for Jth is found to agree well with experiment for both conventional and deep-well (DW) QCLs. For conventional QCLs ηwp,max is found to be strongly temperature dependent; explaining experimental data. At 300 K for optimized DW-QCLs, front-facet, continuous-wave ηwp,max values >20% are projected.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Terahertz superconductor metamaterial

Jianqiang Gu, Ranjan Singh, Zhen Tian, Wei Cao, Qirong Xing, Mingxia He, Jingwen W. Zhang, Jiaguang Han, Hou-Tong Chen, and Weili Zhang

Appl. Phys. Lett. 97, 071102 (2010); http://dx.doi.org/10.1063/1.3479909 (3 pages) | Cited 19 times

Online Publication Date: 16 August 2010

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We characterize the behavior of split ring resonators made up of high transition temperature yttrium barium copper oxide superconductor using terahertz time-domain spectroscopy measurements and numerical simulations. The superconductor metamaterial is found to show a remarkable change in the transmission spectra at the fundamental inductive-capacitive resonance as the temperature dips below the critical transition temperature. This resonance switching effect is normally absent in traditional metamaterials made up of regular metals. The temperature-dependent resonance behavior of the superconducting metamaterial would lead to development of low loss terahertz switches at cryogenic temperatures.
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85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology
74.62.-c Transition temperature variations, phase diagrams

Coherent coupling of ring cavity surface emitting quantum cascade lasers

Clemens Schwarzer, Elvis Mujagić, Yu Yao, Werner Schrenk, Jianxin Chen, Claire Gmachl, and Gottfried Strasser

Appl. Phys. Lett. 97, 071103 (2010); http://dx.doi.org/10.1063/1.3479913 (3 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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We present investigations on coherent coupling of surface emitting quantum cascade lasers (QCLs). For this purpose, the evanescent field coupling method is exploited under incorporation of a ring cavity surface emitting QCL pair with an emission wavelength of ≈ 8 μm. A series of these pairs with intercavity separations of 1 and 3 μm was fabricated. The coupling gap of 1 μm yields robust phase-locked light source pairs with coherent emission at all injection currents and a corresponding threshold current density of 2.65 kA/cm2 at room-temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Active control of group velocity by use of folded dielectric axes structures

Kun Liu, Wenjie Lu, Yuping Chen, and Xianfeng Chen

Appl. Phys. Lett. 97, 071104 (2010); http://dx.doi.org/10.1063/1.3480404 (3 pages)

Online Publication Date: 16 August 2010

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A method was demonstrated for slowing light signals in electro-optical periodically poled lithium niobate. A forbidden band gap can be formed when the transverse electric field exceeds zero. The group velocity of a light near the band gap can be delayed via changes in electric field strength or wavelength, with a maximum delay of 20 ns in the experiment, which is attractive for electro-optical signal processing and all-optical signal processing.
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42.25.Bs Wave propagation, transmission and absorption

Self-phase modulation at visible wavelengths in nonlinear ZnO channel waveguides

Edgar Yoshio Morales Teraoka, Daniel H. Broaddus, Tomohiro Kita, Atsushi Tsukazaki, Masashi Kawasaki, Alexander L. Gaeta, and Hirohito Yamada

Appl. Phys. Lett. 97, 071105 (2010); http://dx.doi.org/10.1063/1.3480422 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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We report the observation of nonlinear optical effects in the visible spectrum using ZnO channel waveguides. We demonstrate sixfold spectral broadening and a 2π phase shift due to self-phase modulation in ZnO channel waveguides using femtosecond optical pulses with a center wavelength of 840 nm. We measured a value for the nonlinear parameter γ of 13.9±3.0 W−1 m−1, which is more than 1300 times that of a highly nonlinear fiber. The calculated intensity-dependent refractive index is found to be consistent with previously reported values of bulk single-crystal ZnO.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Highly sensitive terahertz measurement of layer thickness using a two-cylinder waveguide sensor

M. Theuer, R. Beigang, and D. Grischkowsky

Appl. Phys. Lett. 97, 071106 (2010); http://dx.doi.org/10.1063/1.3481080 (3 pages) | Cited 12 times

Online Publication Date: 17 August 2010

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We report on the layer thickness determination on dielectrically coated metal cylinders using terahertz (THz) time-domain spectroscopy. A considerable sensitivity increase of up to a factor of 150 is obtained for layers down to 2.5 μm thickness by introducing an experimental geometry based on a two-cylinder waveguide sensor. The layer attached on one metal cylinder is guided in contact with the second metal cylinder in the THz beam waist. This approach uses concepts of adiabatic THz wave compression and the advantages of THz waveguides. The results are compared to measurements on free-standing layers.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Resonant enhancement transmission in a Ge subwavelength periodic membrane

Tian Sang, Zhanshan Wang, Xun Zhou, and Shaohong Cai

Appl. Phys. Lett. 97, 071107 (2010); http://dx.doi.org/10.1063/1.3473774 (3 pages) | Cited 1 time

Online Publication Date: 17 August 2010

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In this letter, the effect of resonant enhancement transmission in a Ge subwavelength periodic membrane is presented. The key idea is that the strong refractive-index modulation of the Ge subwavelength periodic membrane can support the excitation of three leaky mode resonances TE1,1, TE2,1, and TE3,0 in a reflection band, and every leaky mode resonance relates a transmission peak on its edge, thus the overlapping of the edges of these multiple leaky mode resonances can be tailored to create resonant enhancement transmission. Resonant enhancement transmission with single and double channels near λ = 10.60 μm is designed to demonstrate this concept.
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42.79.Wc Optical coatings
78.66.Db Elemental semiconductors and insulators
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Femtosecond laser pulse energy transfer induced by plasma grating due to filament interaction in air

Xuan Yang, Jian Wu, Yuqi Tong, Liang’en Ding, Zhizhan Xu, and Heping Zeng

Appl. Phys. Lett. 97, 071108 (2010); http://dx.doi.org/10.1063/1.3479499 (3 pages) | Cited 5 times

Online Publication Date: 17 August 2010

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We experimentally demonstrate the formation of a thin plasma grating lasted for several tens of picosecond induced by the strong interaction between two noncollinear femtosecond filaments in air. A time-delayed second-harmonic pulse propagating along one of the incident filaments is coupled and nonlinearly diffracted by the thin plasma grating, leading to an energy transfer to the other noncollinearly crossed femtosecond filament. The dependences of the plasma grating on the intensity ratios and relative polarizations between the input pulses are investigated.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
42.79.Dj Gratings

Photoinduced nonlinear refraction in a polymeric film encapsulating a bacteriorhodopsin mutant

Xue-lei Teng, Ming Lu, You-yuan Zhao, De-wang Ma, Ying-chun Zhao, Jian-dong Ding, and Wei-da Huang

Appl. Phys. Lett. 97, 071109 (2010); http://dx.doi.org/10.1063/1.3480410 (3 pages) | Cited 1 time

Online Publication Date: 17 August 2010

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The absorption change versus time after switching off the illumination on a polymeric film that contained a bacteriorhodopsin (BR) mutant has been measured. The M-lifetime of this BR mutant is ∼ 320 s. A pertinent Z-scan was performed to study the BR optical nonlinearity. A physical model with multi-level transitions in the Z-scan was suggested. The minimum saturated light intensity measured at 633 nm is ∼ 0.9 mW/cm2. A low intensity of 70 μW/cm2 has been used for recording in this film. The change in refraction index Δn633 is −3.0×10−3 and Δn476 is 8.5×10−3 with the intensity all at ∼ 100 mW/cm2.
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78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Me Organic compounds and polymers
42.79.Wc Optical coatings

The effect of plasmonic particles on solar absorption in vertically aligned silicon nanowire arrays

Chenxi Lin and Michelle L. Povinelli

Appl. Phys. Lett. 97, 071110 (2010); http://dx.doi.org/10.1063/1.3475484 (3 pages) | Cited 7 times

Online Publication Date: 17 August 2010

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In this paper, we used the finite-difference time domain method to determine whether metallic caps provide plasmonic enhancement of absorption in vertically aligned silicon nanowire arrays. Metallic caps result naturally from the vapor-liquid-solid growth process, which uses metal catalyst particles to initiate growth. We found that gold, copper, and silver catalysts all decrease the integrated optical absorption across the solar spectrum.
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73.22.Lp Collective excitations
78.66.Db Elemental semiconductors and insulators
78.40.Fy Semiconductors
88.40.H- Solar cells (photovoltaics)

Demonstration of mode splitting in an optical microcavity in aqueous environment

Woosung Kim, Şahin Kaya Özdemir, Jiangang Zhu, Lina He, and Lan Yang

Appl. Phys. Lett. 97, 071111 (2010); http://dx.doi.org/10.1063/1.3481352 (3 pages) | Cited 12 times

Online Publication Date: 18 August 2010

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Scatterer induced modal coupling and the consequent mode splitting in a whispering gallery mode resonator is demonstrated in aqueous environment. The rate of change in splitting as particles enter the resonator mode volume strongly depends on the concentration of particle solution. The higher is the concentration, the higher is the rate of change. Polystyrene nanoparticles of radius 50 nm with concentration as low as 5×10−6 wt % have been detected using the mode splitting spectra. Observation of mode splitting in water paves the way for constructing advanced resonator based sensors for measuring nanoparticles and biomolecules in various environments.
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42.79.-e Optical elements, devices, and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Polarity-controlled visible/infrared electroluminescence in Si-nanocrystal/Si light-emitting devices

Zhihong Liu, Jiandong Huang, Pooran C. Joshi, Apostolos T. Voutsas, John Hartzell, Federico Capasso, and Jiming Bao

Appl. Phys. Lett. 97, 071112 (2010); http://dx.doi.org/10.1063/1.3480403 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2010

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We report the demonstration of a room-temperature visible/infrared color-switchable light-emitting device comprising a Si nanocrystal-embedded silicon oxide thin film on a p-type Si substrate. The device emits band-edge infrared light from the silicon substrate when the substrate is positively (forward) biased with respect to the Si-nanocrystal film. Under reverse bias, visible emission from the Si-nanocrystal film is observed. Compared to the photoluminescence of the Si-nanocrystal film, the visible electroluminescence is broader and blueshifted to shorter wavelength, and is ascribed to impact ionization in the Si-nanocrystal/SiO2 film.
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85.60.Jb Light-emitting devices
85.30.-z Semiconductor devices

Low-threshold terahertz quantum-cascade lasers based on GaAs/Al0.25Ga0.75As heterostructures

M. Wienold, L. Schrottke, M. Giehler, R. Hey, W. Anders, and H. T. Grahn

Appl. Phys. Lett. 97, 071113 (2010); http://dx.doi.org/10.1063/1.3480406 (3 pages) | Cited 7 times

Online Publication Date: 18 August 2010

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We investigated the influence of the barrier composition on the performance of GaAs-based terahertz (THz) quantum-cascade lasers (QCLs). Based on a nine-quantum-well active region design for 3–4 THz emission, QCLs with an Al content of x = 0.15 and x = 0.25 in the AlxGa1−xAs barriers are compared. We found a significantly reduced threshold current density for QCLs with x = 0.25 as compared to QCLs with x = 0.15, which is due to a weaker coupling of the subband states. The maximum output power and operating temperature of such lasers are reduced due to the onset of negative differential resistance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Continuous wave operation of current injected GaN vertical cavity surface emitting lasers at room temperature

Tien-Chang Lu, Shih-Wei Chen, Tzeng-Tsong Wu, Po-Min Tu, Chien-Kang Chen, Cheng-Hung Chen, Zhen-Yu Li, Hao-Chung Kuo, and Shing-Chung Wang

Appl. Phys. Lett. 97, 071114 (2010); http://dx.doi.org/10.1063/1.3483133 (3 pages) | Cited 11 times

Online Publication Date: 18 August 2010

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We report the demonstration of the continuous wave laser action on GaN-based vertical cavity surface emitting lasers at room temperature. The laser structure consists of a ten-pair Ta2O5/SiO2 distributed Bragg reflector (DBR), a 7λ-thick optical cavity, ten-pairs InGaN/GaN multiquantum wells with an AlGaN electron blocking layer, and a 29-pair AlN/GaN DBR. The laser has a threshold current of about 9.7 mA corresponding to the current density of about 12.4 kA/cm2 and a turn-on voltage about 4.3 V at 300 K. The lasing wavelength was 412 nm with a linewidth of about 0.5 nm. A spontaneous emission coupling efficiency factor of about 5×10−3 and the degree of polarization of about 55% were measured, respectively. The laser beam has a narrow divergence angle of about 8°.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Genetic algorithm designed silicon integrated photonic lens operating at 1550 nm

José Marqués-Hueso, Lorenzo Sanchis, Benoit Cluzel, Frédérique de Fornel, and Juan P. Martínez-Pastor

Appl. Phys. Lett. 97, 071115 (2010); http://dx.doi.org/10.1063/1.3479046 (3 pages) | Cited 2 times

Online Publication Date: 19 August 2010

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We experimentally demonstrate a photonic integrated lens made of holes in a silicon slab operating at λ0 = 1550 nm. The lens has been designed using a genetic algorithm in conjunction with the two-dimensional multiple scattering theory and fabricated using silicon-on-insulator technology. scanning near field optical microscopy measurements have been performed in order to measure the light intensity distribution on the device surface. The obtained full width at half maximum of the focus is 0.23 λ0, which is in good agreement with three-dimensional finite-difference time-domain simulations, and overcomes the diffraction limit in air, where the measurements are made.
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42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Nearly zero transmission through periodically modulated ultrathin metal films

Sanshui Xiao, Jingjing Zhang, Liang Peng, Claus Jeppesen, Radu Malureanu, Anders Kristensen, and N. Asger Mortensen

Appl. Phys. Lett. 97, 071116 (2010); http://dx.doi.org/10.1063/1.3481397 (3 pages) | Cited 18 times

Online Publication Date: 19 August 2010

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Transmission of light through an optically ultrathin metal film with a thickness comparable to its skin depth is significant. We demonstrate experimentally nearly-zero transmission of light through a film periodically modulated by a one-dimensional array of subwavelength slits. The suppressed optical transmission is due to the excitation of surface plasmon polaritons and the zero-transmission phenomenon is strongly dependent on the polarization of the incident wave.
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42.79.Wc Optical coatings
78.66.Bz Metals and metallic alloys
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.25.Bs Wave propagation, transmission and absorption
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Mid-infrared transmission properties of amorphous germanium optical fibers

Priyanth Mehta, Mahesh Krishnamurthi, Noel Healy, Neil F. Baril, Justin R. Sparks, Pier J. A. Sazio, Venkatraman Gopalan, John V. Badding, and Anna C. Peacock

Appl. Phys. Lett. 97, 071117 (2010); http://dx.doi.org/10.1063/1.3481413 (3 pages) | Cited 5 times

Online Publication Date: 19 August 2010

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Germanium optical fibers have been fabricated using a high pressure chemical deposition technique to deposit the semiconductor material inside a silica capillary. The amorphous germanium core material has a small percentage of hydrogen that saturates the dangling bonds to reduce absorption loss. Optical transmission measurements were performed to determine the linear losses over a broad mid-infrared wavelength range with the lowest loss recorded at 10.6 μm. The extended transmission range measured in the germanium fibers demonstrates their potential for use in mid-infrared applications.
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42.81.Bm Fabrication, cladding, and splicing
42.25.Bs Wave propagation, transmission and absorption

Reverse-emission-state-transition mode locking of a two-section InAs/InGaAs quantum dot laser

Stefan Breuer, Mattia Rossetti, Wolfgang Elsässer, Lukas Drzewietzki, Paolo Bardella, Ivo Montrosset, Michel Krakowski, and Mark Hopkinson

Appl. Phys. Lett. 97, 071118 (2010); http://dx.doi.org/10.1063/1.3480405 (3 pages) | Cited 1 time

Online Publication Date: 19 August 2010

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Reverse-emission-state-transition mode locking in a two-section InAs/InGaAs quantum dot laser is experimentally investigated and confirmed by simulations. Stable mode locking starts on the first excited state (λ = 1207 nm) and then, with increasing gain current, a transition to stable simultaneous two-state mode locking on excited state and ground state (λ = 1270 nm) takes place. This particular state-transition occurs already at 0 V reverse-bias and at moderate gain-section currents. It is attributed to the strong active region chirping of the gain medium and in particular to a photon pumping process in the saturable absorber section.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Interface engineering for improved light transmittance through photonic crystal flat lenses

Geoffroy Scherrer, Maxence Hofman, Wojciech Śmigaj, Boris Gralak, Xavier Mélique, Olivier Vanbésien, Didier Lippens, Colette Dumas, Benoit Cluzel, and Frédérique de Fornel

Appl. Phys. Lett. 97, 071119 (2010); http://dx.doi.org/10.1063/1.3473760 (3 pages) | Cited 3 times

Online Publication Date: 20 August 2010

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In this paper, we present photonic crystal flat lenses with interfaces engineered to improve the light transmittance thanks to a broad angles impedance matching. The interface engineering consists in the realization of antireflection gratings on the edges of the lenses which are designed to reduce the propagative waves reflectivity over a wide range of incident angles. The fabricated structures were measured in optical near-field and a four times enhancement of the light transmission efficiency is reported.
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42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Thermal trimming and tuning of hydrogenated amorphous silicon nanophotonic devices

Shankar Kumar Selvaraja, Wim Bogaerts, Dries VanThourhout, and Marc Schaekers

Appl. Phys. Lett. 97, 071120 (2010); http://dx.doi.org/10.1063/1.3479918 (3 pages)

Online Publication Date: 20 August 2010

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Deposited silicon and, in particular, hydrogenated amorphous silicon forms an attractive alternative platform for realizing compact photonic integrated circuits. In this paper we report on trimming (toward lower wavelengths) and tuning (toward higher wavelengths) of photonic devices through a suitable thermal treatment. The former is achieved by a material density change, the latter through the thermo-optic effect. By using Fourier transform infrared spectroscopy, a change in the hydrogen content is identified as the source of the density change. A total wavelength tuning range of 24.6 nm is achievable, which can be used for compensating fabrication imperfections.
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42.79.-e Optical elements, devices, and systems
78.30.-j Infrared and Raman spectra
78.20.N- Thermo-optic effects
81.65.-b Surface treatments
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
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Nonthermal and screening effects on the Thomson scattering in Lorentzian plasmas

Dae-Han Ki and Young-Dae Jung

Appl. Phys. Lett. 97, 071501 (2010); http://dx.doi.org/10.1063/1.3482941 (3 pages) | Cited 5 times

Online Publication Date: 20 August 2010

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The nonthermal and screening effects on the Thompson scattering process are investigated in generalized Lorentzian electron plasmas. The Thompson scattering cross section is obtained as a function of the spectral index, wave number, and Debye length. It is shown that the nonthermal effect suppresses the Thompson scattering process in Lorentzian plasmas. It is also shown that the nonthermal effects on the forward scatterings are more significant than those on the backward scatterings. In addition, the nonthermal effects are found to be more significant in the intermediate domain of the wave number.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Mq Dielectric properties
52.25.Gj Fluctuation and chaos phenomena
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Indium induced step transformation during InGaN growth on GaN

D. D. Koleske, S. R. Lee, G. Thaler, M. H. Crawford, M. E. Coltrin, and K. C. Cross

Appl. Phys. Lett. 97, 071901 (2010); http://dx.doi.org/10.1063/1.3479414 (3 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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The surface-step evolution of InGaN quantum-wells (QWs) was studied on GaN (0001). While the GaN template is dominated by single-monolayer steps the frequency of multiple-layer steps increases significantly when InGaN/GaN single- or multiple-QWs are grown. It is proposed that the InGaN multiple-layer step structure arises to partially accommodate the in-plane film strain which is insufficient to trigger bulk InGaN relaxation. This intrinsic multiple-layer step restructuring, when coupled with the strong piezoelectric fields present in the wurtzite group III-nitrides, could explain the enhanced carrier localization in InGaN QWs.
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81.07.St Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Microscale oscillating crack propagation in silicon nitride thin films

Donghyun Kim, Prashanth Makaram, and Carl V. Thompson

Appl. Phys. Lett. 97, 071902 (2010); http://dx.doi.org/10.1063/1.3480408 (3 pages)

Online Publication Date: 16 August 2010

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Controlled microscale (<50 μm) wavy cracks in silicon nitride thin films have been produced through a simple heating process. The crack paths were controlled by metal patterns under the silicon nitride thin films. Wavy crack characteristics were investigated by changing the metal, metal linewidths, metal thickness, and silicon nitride thickness. We discuss the differences in the characteristics and mechanisms of propagation of wavy cracks formed due to differential thermal expansion and those that result from thermal gradients.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.mt Cracks
65.40.De Thermal expansion; thermomechanical effects
68.60.Bs Mechanical and acoustical properties
81.40.Gh Other heat and thermomechanical treatments

Molecular beam epitaxy of N-polar InGaN

Digbijoy N. Nath, Emre Gür, Steven A. Ringel, and Siddharth Rajan

Appl. Phys. Lett. 97, 071903 (2010); http://dx.doi.org/10.1063/1.3478226 (3 pages) | Cited 9 times

Online Publication Date: 17 August 2010

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We report on the growth of N-polar InxGa1−xN by N2 plasma-assisted molecular beam epitaxy. Ga-polar and N-polar InGaN films were grown at different growth temperatures and the composition was estimated by photoluminescence (PL) measurements. A growth model that incorporates the incoming and desorbing atomic fluxes is proposed to explain the compositional dependence of InGaN on the flux of incoming atomic species and growth temperature. The growth model is found to be in agreement with the experimental data. The peak PL intensity for N-face samples is found to exhibit a two order of magnitude increase for a 100 °C increase in growth temperature. Besides, at 600 nm, the N-face sample shows more than 100 times higher PL intensity than Ga-face sample at comparable wavelengths indicating its superior optical quality. The understanding of growth kinetics of InGaN presented here will guide the growth of N-polar InGaN in a wide range of growth temperatures.
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81.05.Ea III-V semiconductors
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Mechanisms of complex morphological evolution during solid-state dewetting of single-crystal nickel thin films

Jongpil Ye and Carl V. Thompson

Appl. Phys. Lett. 97, 071904 (2010); http://dx.doi.org/10.1063/1.3480419 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2010

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We report studies of complex morphological evolution during solid-state dewetting of 120 nm thick single-crystal Ni(100) and Ni(110) thin films on MgO(100) and MgO(110) substrates. During dewetting, holes that form in the Ni films evolve to complex shapes that depend on the crystallographic orientation of the films and annealing ambient. We characterize the origins of hole, line, and particle morphologies that develop during the dewetting process, and identify a sequence of instabilities that control the morphological evolution. This study provides mechanistic insights for control of dewetting to produce specific ordered structures.
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68.55.-a Thin film structure and morphology
68.55.J- Morphology of films
68.08.Bc Wetting
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Cc Kinetics of defect formation and annealing
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