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1 Dec 2010

Volume 108, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 111101 (2010); http://dx.doi.org/10.1063/1.3503495 (21 pages)

R. C. Runkle, A. Bernstein, and P. E. Vanier
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back to top Lasers, Optics, and Optoelectronics

Effects of the intermediate SiO2 layer on polarized output of a light-emitting diode with surface plasmon coupling

Kun-Ching Shen, Che-Hao Liao, Zan-Yao Yu, Jyh-Yang Wang, Cheng-Hung Lin, Yean-Woei Kiang, and C. C. Yang

J. Appl. Phys. 108, 113101 (2010); http://dx.doi.org/10.1063/1.3517082 (8 pages) | Cited 6 times

Online Publication Date: 1 December 2010

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The variation behaviors of the output intensity and polarization ratio of InGaN/GaN quantum well (QW) light-emitting diodes (LEDs) with surface plasmon (SP) coupling by inserting SiO2 intermediate layers between the p-GaN layers and surface Ag grating structures are demonstrated. The insertion of the SiO2 layer is expected to reduce the metal dissipation of SP energy and extend the near-field distribution range of the induced SP for generating more favored SP-QW coupling effects. The Ag grating period for optimizing SP-QW coupling is increased when a SiO2 layer is added to the device, which is consistent with the simulation results of the momentum matching of SP polariton and the resonance behavior of localized SP. The almost unpolarized outputs from other LED samples fabricated with an epitaxial structure of thicker p-GaN layer, which leads to weak SP-QW coupling, indicate that the observed polarization ratios are due to near-field SP-QW coupling, instead of far-field diffraction.
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85.60.Jb Light-emitting devices
78.67.De Quantum wells
73.21.Fg Quantum wells

Polarized edge emission from GaN-based light-emitting diodes sandwiched by dielectric/metal hybrid reflectors

L. J. Yan, J. K. Sheu, F. W. Huang, and M. L. Lee

J. Appl. Phys. 108, 113102 (2010); http://dx.doi.org/10.1063/1.3516472 (5 pages)

Online Publication Date: 1 December 2010

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Edge-emitting c-plane GaN/sapphire-based light-emitting diodes (LEDs) sandwiched by two dielectric/metal hybrid reflectors on both sapphire and GaN surfaces were studied to determine their light emission polarization. The hybrid reflectors comprised dielectric multiple thin films and a metal layer. The metal layers of Au or Ag used in this study were designed to enhance the polarization ratio from S-polarization (transverse electric wave, TE) to P-polarization (transverse magnetic wave, TM). The two sets of optimized dielectric multi thin films served as matching layers for wide-angle incident light on both sapphire and GaN surfaces. To determine which reflector scheme would achieve a higher polarization ratio, simulations of the reflectance at the hybrid reflectors on sapphire (or GaN) interface were performed before the fabrication of experimental LEDs. Compared with conventional c-plane InGaN/GaN/sapphire LEDs without dielectric/metal hybrid reflectors, the experimental LEDs exhibited higher polarization ratio (ITE-max/ITM-max) with r = 2.174 ( ∼ 3.37 dB) at a wavelength of 460 nm. In contrast, the original polarized light (without dielectric/metal hybrid reflectors) was partially contributed (r = 1.398) by C-HH or C-LH (C band to the heavy-hole sub-band or C band to the crystal-field split-off sub-band) transitions along the a-plane or m-plane direction.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors

High transmittance of a twisted-vertical aligned liquid crystal display

Cheng-Chung Peng, Kuei-Chu Hsu, Jin-Jei Wu, Shih-Hung Fan, Hsin-Ta Lee, and Yuhren Shen

J. Appl. Phys. 108, 113103 (2010); http://dx.doi.org/10.1063/1.3516478 (5 pages) | Cited 1 time

Online Publication Date: 2 December 2010

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A high transmittance continuum domain twisted-vertical alignment (CDTVA) liquid crystal display (LCD) without domain walls defect and complex fabrication process has been developed. The CDTVA mode has no optical schlieren pattern occurring in the TVA cell. The optimum conditions for liquid crystal phase retardation (Γ) and cell gap-to-helical pitch ratio (d/p) were studied using three-dimensional finite element simulation, which showed good agreement with the experimental results. The results indicate that the maximum transmittance of the proposed CDTVA cell is similar to that of the twisted nematic mode thin-film-transistor LCD. Thus, CDTVA cell has potential applications for wide-viewing angle LCDs.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Wedge mode of spoof surface plasmon polaritons at terahertz frequencies

Zhen Gao, Xufeng Zhang, and Linfang Shen

J. Appl. Phys. 108, 113104 (2010); http://dx.doi.org/10.1063/1.3517059 (4 pages) | Cited 6 times

Online Publication Date: 2 December 2010

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Surface plasmon polaritons (SPPs) propagating along a structure consisting of a single row of metallic wedges periodically protruding out of a planar metallic surface are investigated theoretically. It is shown that such a structure can sustain a mode of spoof SPPs in the terahertz region, whose fields are highly confined in the transverse plane. The guiding mode in the structure possesses excellent properties such as good modal shape, large propagation length, and low bending loss, making it a promising candidate for routing terahertz radiation in highly integrated circuits.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.70.Gq Microwave and radio-frequency interactions

Flare coupled metal parallel-plate waveguides for high resolution terahertz time-domain spectroscopy

Michael Theuer, S. Sree Harsha, and D. Grischkowsky

J. Appl. Phys. 108, 113105 (2010); http://dx.doi.org/10.1063/1.3516307 (6 pages) | Cited 9 times

Online Publication Date: 3 December 2010

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We report on a new coupling scheme for high resolution terahertz spectroscopy of microcrystalline films using parallel-plate waveguides. Metal flares are used to couple the terahertz radiation into and out of the waveguide. Very good coupling ratios as high as 35% at 1 THz from a collimated free-space beam into a subwavelength gap are obtained. This microwave approach is compared in terms of coupling ratio and spectral characteristics to the established technique of quasioptic coupling to parallel-plate waveguides using silicon lenses. Various samples at room and cryogenic temperatures are measured to show the capabilities of flare coupling for high resolution terahertz spectroscopy.
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78.70.Gq Microwave and radio-frequency interactions
78.66.Bz Metals and metallic alloys
84.40.Az Waveguides, transmission lines, striplines
78.47.D- Time resolved spectroscopy (>1 psec)

Spatial filtering using dielectric photonic crystals at beam-type excitation

Evrim Colak, Atilla Ozgur Cakmak, Andriy E. Serebryannikov, and Ekmel Ozbay

J. Appl. Phys. 108, 113106 (2010); http://dx.doi.org/10.1063/1.3498810 (8 pages) | Cited 3 times

Online Publication Date: 6 December 2010

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Spatial filtering is demonstrated at beam-type excitations by utilizing finite thickness slabs of two-dimensional dielectric photonic crystals (PCs) showing exotic Fabry–Perot resonances that are preserved over a wide range of variation of the incidence angle. Bandstop and dual-bandpass filtering effects are illustrated theoretically and the corresponding filters are validated in the microwave experiments by using square-lattice PCs. It is shown that the basic transmission features that were observed earlier for a plane-wave illumination are also recognizable at beam-type excitations. The proposed spatial filtering mechanism exhibits directional beaming. The desired widths and the locations of the passbands and stopbands are attainable in the angle domain with a proper choice of the operating frequency for the given excitation characteristics.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Influence of polarization-induced electric fields on coherent electron tunneling in AlN/GaN coupled double quantum wells

L. B. Cen, B. Shen, C. C. Huang, F. J. Xu, Z. X. Qin, G. Y. Zhang, X. S. Chen, and W. Lu

J. Appl. Phys. 108, 113107 (2010); http://dx.doi.org/10.1063/1.3517067 (4 pages)

Online Publication Date: 6 December 2010

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The influence of polarization-induced electric fields on the coherent electron tunneling probability in AlN/GaN coupled double quantum wells (CDQWs) has been performed by solving Schrödinger and Poisson equations self-consistently. It is found that when the first excited state (E2) and the second excited state (E3) resonate in AlN/GaN CDQWs, the coherent electron tunneling probability is 16 times higher than that in AlN/GaN single quantum well, which is attributed to the Fabry–Perot quantum interference mechanism in AlN/GaN CDQWs. However, the coherent electron tunneling probability decreases rapidly with the polarization-induced electric fields increasing, which is attributed to the resonance between the E2 and E3 subbands weakening with the polarization-induced electric fields increasing in AlN/GaN CDQWs.
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73.23.-b Electronic transport in mesoscopic systems
78.67.De Quantum wells
73.63.Hs Quantum wells
81.07.St Quantum wells
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors

Coupled surface plasmon interference lithography based on a metal-bounded dielectric structure

Xiaowei Guo and Qiming Dong

J. Appl. Phys. 108, 113108 (2010); http://dx.doi.org/10.1063/1.3517793 (4 pages) | Cited 5 times

Online Publication Date: 6 December 2010

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We propose a coupled surface plasmon (SP) interference lithography based on a metal-bounded dielectric structure. The long and short range SP interferences at different dielectric thicknesses in the structure are analyzed. The interference in Kretschmann structure under the same conditions is also compared. Numerical results show the coupled SP interference offers better lithography performance as compared with the Kretschmann SP interference. This proposed technique provides potential for fabrication of periodic nanostructures.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.16.Nd Micro- and nanolithography
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Finite difference method for solving the Schrödinger equation with band nonparabolicity in mid-infrared quantum cascade lasers

J. D. Cooper, A. Valavanis, Z. Ikonić, P. Harrison, and J. E. Cunningham

J. Appl. Phys. 108, 113109 (2010); http://dx.doi.org/10.1063/1.3512981 (5 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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The nonparabolic Schrödinger equation for electrons in quantum cascade lasers (QCLs) is a cubic eigenvalue problem (EVP) which cannot be solved directly. While a method for linearizing this cubic EVP has been proposed in principle for quantum dots [ Hwang et al., Math. Comput. Modell., 40, 519 (2004) ] it was deemed too computationally expensive because of the three-dimensional geometry under consideration. We adapt this linearization approach to the one-dimensional geometry of QCLs, and arrive at a direct and exact solution to the cubic EVP. The method is then compared with the well established shooting method, and it is shown to be more accurate and reliable for calculating the bandstructure of mid-infrared QCLs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
03.65.Ge Solutions of wave equations: bound states
02.10.Ud Linear algebra

High-speed microjet particles measurement using in-line pulsed holography

Zuoyou Li, Zhenxiong Luo, Zhenqing Liu, Yan Ye, Zeren Li, Jie Zhong, and Jun Li

J. Appl. Phys. 108, 113110 (2010); http://dx.doi.org/10.1063/1.3506537 (6 pages)

Online Publication Date: 6 December 2010

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Transient in-line holographic imaging system is optimized for recording the holograms of detonation loaded microjet particles with a velocity higher than 5 km/s. Then an adaptive multithreshold image segmentation method is developed to improve the measurement precision of particle size and number. The measured size of ejected particles is from several microns to over ten microns, and the processing errors of particle number and size are less than 5% and 15%, respectively. The statistical results also show that the size, number, and velocity of microjet particles vary depending on the surface conditions of the Al metal debris. Compared with a uniform metal sample, the nonuniform metal sample with cone-shaped hole exhibits more ejected particles, larger particle size, and higher velocity.
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47.80.Jk Flow visualization and imaging
47.40.Rs Detonation waves
47.15.Uv Laminar jets
42.40.My Applications
42.30.Va Image forming and processing

Exciton diffusion length analysis of mixed donor materials in organic solar cells by doping with phosphorescent iridium complex

Junsheng Yu (于军胜), Jiang Huang (黃江), Hui Lin (林慧), and Yadong Jiang (蒋亚东)

J. Appl. Phys. 108, 113111 (2010); http://dx.doi.org/10.1063/1.3514545 (6 pages) | Cited 6 times

Online Publication Date: 6 December 2010

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In this paper, the photovoltaic characteristics of ITO/(t-bt)2Ir(acac):CuPc (mixed ratio R by weight)/C60/BCP/Ag organic solar cells (OSCs) are analyzed in detail. The intrinsic properties of a (t-bt)2Ir(acac):CuPc doped layer on device performance are discussed based on theoretical analysis of the experimental OSCs. By studying the photoluminescence densities of pure (t-bt)2Ir(acac) film and mixed films with R = 0.75, 0.9, the key exciton diffusion lengths LD were calculated to be 28.3±5.0 nm, 31.7±5.0 nm, and 33.0±2.0 nm, respectively. A new method is then proposed to calculate LD for films with R<0.75. The analysis gives an exciton diffusion length of LD = 17.4±2.5 nm for a mixed film with R = 0.25, an improvement of 74% in comparison to a pure CuPc layer. Moreover, the exciton diffusion efficiency ηED of an OSC with R = 0.25 is obviously improved with the assistance of an increased exciton diffusion length. Finally, to reveal the influence of the dopant (t-bt)2Ir(acac) on charge carrier collection H(V), device energy loss is analyzed and discussed.
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88.40.jr Organic photovoltaics
81.05.Fb Organic semiconductors
71.35.-y Excitons and related phenomena
78.55.-m Photoluminescence, properties and materials
61.72.U- Doping and impurity implantation

Nanoscale size dependence on pulsed laser sintering of hydroxyapatite/titanium particles on metal implants

Martin Yi Zhang and Gary J. Cheng

J. Appl. Phys. 108, 113112 (2010); http://dx.doi.org/10.1063/1.3504612 (9 pages) | Cited 3 times

Online Publication Date: 7 December 2010

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Nanoscale size effects on pulsed laser coating of hydroxyapatite/titanium nanoparticles (nanoTi) on metal substrate is discussed in this article. Laser coating method has recently been developed to coat bioceramics material on Ti–6Al–4V substrate. Laser-coated bioceramics implants have several advantages due to the use of nanosized materials: strong interfacial bonding strength, good biocompatibility and potentially longer lifetime cycle. These advantages benefit from intrinsic properties of nanoparticles. Size effects on melting point, heat capacity, thermal, and electrical conductivities have been discussed. Multiphysics model is built to reveal the mechanism of laser coating process. Two submodules are included in the model: electromagnetic module to represent the laser-nanoparticle interactions and heat transfer module to simulate the heat conduction. Both simulation and experimental results showed that nanoTi, functioning as nanoheaters, effectively enhances the laser coating sinterability. For large nanoTi (>100 nm), sinterability enhancement mainly attributes to the stronger laser-particle interactions due to higher plasmon resonance; for small nanoparticles (<100 nm), not only stronger laser-nanoparticle interactions, reduction on melting point also contributes to sinterability enhancement.
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87.85.Rs Nanotechnologies-applications
87.85.J- Biomaterials
81.16.Mk Laser-assisted deposition
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Highly efficient white organic light-emitting diodes based on fluorescent blue emitters

Thomas C. Rosenow, Mauro Furno, Sebastian Reineke, Selina Olthof, Björn Lüssem, and Karl Leo

J. Appl. Phys. 108, 113113 (2010); http://dx.doi.org/10.1063/1.3516481 (5 pages) | Cited 21 times

Online Publication Date: 9 December 2010

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Beside inorganic LEDs and fluorescent lamps, organic light-emitting diodes (OLEDs) are evolving into a serious alternative to incandescent lamps. Up to now, it was assumed that all-phosphorescent OLEDs are required for reaching sufficiently high efficiencies. However, the stability of phosphorescent blue emitters is a major challenge. We present a novel approach to achieve highly efficient (up to 90 lm/W at 1000 cd/m2 using a macroextractor) white light emission from OLEDs. The here presented combination of a fluorescent blue and a phosphorescent red emitter simultaneously allows for a strong blue emission and efficient triplet transfer to the phosphor. The spectrum is extended in the green and yellow region by a full phosphorescent unit stacked on top of the triplet harvesting device. This superposition of four different emitters results in color coordinates close to illuminant A and a color rendering index of 80. Furthermore, color stability is given with respect to varying driving conditions and estimations of the electrical and optical efficiencies are provided.
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85.60.Jb Light-emitting devices
78.55.Kz Solid organic materials

Effect of annealing and Nd concentration on the photoluminescence of Nd3+ ions coupled with silicon nanoparticles

O. Debieu, D. Bréard, A. Podhorodecki, G. Zatryb, J. Misiewicz, C. Labbé, J. Cardin, and F. Gourbilleau

J. Appl. Phys. 108, 113114 (2010); http://dx.doi.org/10.1063/1.3510521 (6 pages) | Cited 6 times

Online Publication Date: 9 December 2010

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We report on the microstructure and photoluminescence (PL) properties of Nd-doped SiO2 thin films containing silicon nanoparticles (Si-np) as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing due to the agglomeration of the Si excess resulting in the formation of Si-np. Besides, after annealing, the films exhibit PL from excitonic states confined in Si-np. We showed that the intensity of the PL of Nd3+ ions that occurs at ∼ 0.92, 1.06, and 1.4 μm is maximal at low Nd concentration and while well-passivated Si-np are formed. FTIR and x-ray measurements showed that the increase in the Nd incorporation has detrimental effects on the PL of Nd3+ because of the formation of Nd2O3 nanocrystals and inherent disorder in the SiO2 host matrix. PL excitation measurements demonstrate that the PL of Nd3+ ions is nonresonant and follows the excitation of Si-np giving new evidence of the energy transfer from Si-np toward the rare earth ions.
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78.66.Nk Insulators
81.40.Gh Other heat and thermomechanical treatments
78.55.Hx Other solid inorganic materials
68.55.A- Nucleation and growth
78.30.Hv Other nonmetallic inorganics
81.15.Cd Deposition by sputtering

Optoelectronic and all-optical multiple memory states in vanadium dioxide

Horacio Coy, Rafmag Cabrera, Nelson Sepúlveda, and Félix E. Fernández

J. Appl. Phys. 108, 113115 (2010); http://dx.doi.org/10.1063/1.3518508 (6 pages) | Cited 10 times

Online Publication Date: 9 December 2010

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Vanadium dioxide exhibits a well-known insulator-to-metal transition during which several of its physical properties change significantly. A hysteresis loop develops for each of them as the material is heated and then cooled through the transition. In this work VO2/SiO2 samples were maintained—by heat sinking—at a selected temperature within the heating branch of the hysteresis loops for resistance and near-infrared transmittance, while brief thermal excursions of the VO2 film were caused by either voltage pulses applied to the film or laser light pulses irradiating the film. These pulses had durations from milliseconds to a few seconds and the resulting drops in resistance or transmittance were easily and repeatably measurable without appreciably affecting their new values. A sequence of equal-duration pulses (for either equal-voltage or equal-irradiation pulses) caused the resistance and infrared transmittance to continue to drop, each time by a smaller amount, and larger energy pulses were required in order to cause drops comparable with the initial one. The ability of the film to change the values of the measurands in this manner with additional pulses was maintained up to a limit defined by the outer hysteresis curve for the measurand in question. The results presented show that a plurality of memory “states” in VO2 can be established or “written” either by voltage pulses or by light pulses applied to the material, and queried or “read” by resistance or transmittance readings, or both. These states were found to remain stable for at least several hours, as long as temperature was kept constant, and are expected to persist indefinitely under this condition. In the all-optical case, if the same light beam is used for writing and reading the memory state, the device is an optical analog of a memristor.
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73.61.Ng Insulators
78.66.Nk Insulators
78.20.Jq Electro-optical effects
73.50.Pz Photoconduction and photovoltaic effects
71.30.+h Metal-insulator transitions and other electronic transitions
81.40.Gh Other heat and thermomechanical treatments

Improved photoluminescence properties of sol-gel derived Er3+ doped silica films

Sudipto Pal, Abhijit Mandal, Goutam De, Enrico Trave, Valentina Bello, Giovanni Mattei, Paolo Mazzoldi, and Cinzia Sada

J. Appl. Phys. 108, 113116 (2010); http://dx.doi.org/10.1063/1.3518515 (8 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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Silica films (amorphous and crystalline) doped with erbium were fabricated on silica glass substrate and characterized. The inorganic-organic hybrid sol-gel method was used to prepare the films and the Na codoping induced the crystallization of silica film. Photoluminescence (PL) measurements revealed that the Er3+ ions can be excited from the ground state through an energy transfer process mediated by active defective sites in SiO2 film matrix. The annealing temperature and atmospheres have large effects on the local environment of Er3+ and the 1.54 μm PL intensity can be improved significantly by suitable heating treatments. We could correlate Er3+ sensitization effect due to the presence of carbon related species in the films. The PL intensity at nonresonant (476.5 nm) condition can be made as intense as the resonant (488 nm) one, for particular annealing conditions. Noticeable changes in PL emission intensities have not been observed whether the matrix silica film is amorphous or crystalline in nature; however, the defect-related luminescence is almost vanished in case of crystalline silica films.
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78.66.Nk Insulators
68.55.aj Insulators
61.43.Er Other amorphous solids
78.55.Qr Amorphous materials; glasses and other disordered solids
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials

InAlN/GaN Bragg reflectors grown by plasma-assisted molecular beam epitaxy

Ž. Gačević, S. Fernández-Garrido, D. Hosseini, S. Estradé, F. Peiró, and E. Calleja

J. Appl. Phys. 108, 113117 (2010); http://dx.doi.org/10.1063/1.3517138 (7 pages) | Cited 9 times

Online Publication Date: 13 December 2010

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We report on molecular beam epitaxy growth and characterization of ten-period lattice-matched InAlN/GaN distributed Bragg reflectors (DBRs), with peak reflectivity centered around 400 nm. Thanks to the well tuned ternary alloy composition, crack-free surfaces have been obtained, as confirmed by both optical and transmission electron microscopy (TEM). Their good periodicity and well-defined interfaces have been confirmed by both x-ray diffraction and TEM measurements. Peak reflectivity values as high as 60% with stop bands of 30 nm have been demonstrated. Optical measurements revealed that discrepancy between the obtained (60%) and the theoretically expected ( ∼ 75%) reflectivity is a consequence of significant residual absorption ( ∼ 35%). TEM measurements revealed the coexistence of zinc-blende and wurtzite phases, as well as planar defects, mainly in GaN. These defects are suggested as the potential source of the undesired absorption and/or scattering effects that lowered the DBRs’ peak reflectivity.
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42.79.Dj Gratings
42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Effect of n-p-n heterostructures on interface recombination and semiconductor laser cooling

G. Rupper, N. H. Kwong, R. Binder, Ch.-Y. Li, and M. Sheik-Bahae

J. Appl. Phys. 108, 113118 (2010); http://dx.doi.org/10.1063/1.3517144 (9 pages) | Cited 3 times

Online Publication Date: 13 December 2010

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The design of doped n-p-n semiconductor heterostructures has a significant influence on the structures’ nonradiative decay and can also affect their photoluminescence characteristics. Such structures have recently been explored in the context of semiconductor laser cooling. We present a theoretical analysis of optically excited n-p-n structures, focusing mainly on the influence of the layer thicknesses and doping concentrations on nonradiative interface recombination. We find that high levels of n-doping (1019 cm−3) can reduce the minority-carrier density at the interface and increase the nonradiative lifetime. We calculate time-dependent luminescence decay and find them to be in good agreement with experiment for temperatures >120 K, which is the temperature range in which our model assumptions are expected to be valid. A theoretical analysis of the cooling characteristics of n-p-n structures elucidates the interplay of nonradiative, radiative, and Auger recombination processes. We show that at high optical excitation densities, which are necessary for cooling, the undesired nonradiative interface recombination rates for moderate (1017 cm−3) n-doping concentrations are drastically increased, which may be a major hindrance in the observation of laser cooling of semiconductors. On the other hand, high n-doping concentrations are found to alleviate the problem of increased nonradiative rates at high excitation densities, and for the model parameters used in the calculation we find positive cooling efficiencies over a wide range of excitation densities.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Influence of crystal phase and transparent substrates on electro-optic properties of lead zirconate titanate films

M. M. Zhu, Z. H. Du, and J. Ma

J. Appl. Phys. 108, 113119 (2010); http://dx.doi.org/10.1063/1.3520459 (4 pages) | Cited 2 times

Online Publication Date: 14 December 2010

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Pb(ZrxTi1−x)O3 [x = 0.52, PZT(52) near morphotropic phase boundary], tetragonal PZT(65), and rhombohedral PZT(20) thin films have been fabricated on different transparent substrates by radio frequency sputtering. The optical studies show that the band gap energies and refractive indices of the PZT thin films are crystal phase dependent. The largest electro-optic (EO) coefficient of 219.6 pm/V has been achieved by controlling the crystal phase of the PZT thin films. The linear EO coefficients of PZT(52) films on the (Pb0.86La0.14)TiO3-coated glass, indium tin oxides, and MgO substrates are also studied. Such study could contribute to the crystal phase and substrate dependent PZT films for electro-optic devices and multifunctional integrated circuits.
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78.20.Jq Electro-optical effects
81.15.Cd Deposition by sputtering
71.20.Ps Other inorganic compounds
68.60.-p Physical properties of thin films, nonelectronic
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.aj Insulators
back to top Plasmas and Electrical Discharges

Microdroplet target synthesis for kilohertz ultrafast lasers

Pavel Chvykov, Wise Ongg, James Easter, Bixue Hou, John Nees, and Karl Krushelnick

J. Appl. Phys. 108, 113301 (2010); http://dx.doi.org/10.1063/1.3516158 (3 pages)

Online Publication Date: 1 December 2010

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We have developed a method for producing spatially stable micron-scale liquid targets of flexible shapes at kilohertz repetition rate for use in air and vacuum, by perturbing 5 and 30 μm diameter streams with femtosecond laser pulses and monitoring the temporal development of the perturbation. Using water, we have produced features such as 2.1 μm diameter droplet and 1.3 μm diameter neck with less than ±0.3 μm shot-to-shot variation, with prospects for further reduction in size and variability. The use of such micron-scale targets can be expected to prevent conductive heat dissipation, enhance field strength for ion acceleration and allow spatially-deterministic laser-cluster experiments.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
78.47.J- Ultrafast spectroscopy (<1 psec)

Multidiagnostic analysis of ultrafast laser ablation of metals with pulse pair irradiation

S. Amoruso, R. Bruzzese, X. Wang, G. O’Connell, and J. G. Lunney

J. Appl. Phys. 108, 113302 (2010); http://dx.doi.org/10.1063/1.3516491 (10 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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Copper targets are irradiated in the ablation regime by pairs of equal, time-delayed collinear laser pulses separated on a timescale going from ≈2 ps to ≈2 ns. The ablation plume is characterized by ion probe diagnostic, fast imaging, and temporally and spatially resolved optical emission spectroscopy. The variation in the ablation efficiency with the delay between the pulses is analyzed by measuring the ablation crater profile with a contact profilometer. The second laser pulse modifies the characteristics of the plasma plume produced by the first pulse and the ablation efficiency. The different mechanisms involved in double pulse ultrafast laser ablation are identified and discussed. The experimental findings are interpreted in the frame of a simple model of the interaction of the second pulse with the nascent ablation plume produced by the first pulse. This model yields consistent and quantitative agreement with the experimental findings predicting the observed experimental trends of the ablation depth reduction and ion yield increase with the delay between the pulses, as well as the characteristic timescale of the observed changes. The possibility of controlling the characteristics of the plumes produced during ultrafast laser ablation via an efficient coupling of the energy of the second pulse to the various ablation components produced by the first pulse is of particular interest in ultrafast pulsed laser deposition and microprobe analyses of materials.
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79.20.Eb Laser ablation
52.38.Mf Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.80.-d Chemical analysis and related physical methods of analysis
78.47.J- Ultrafast spectroscopy (<1 psec)
61.82.Bg Metals and alloys

Choosing optimum method for the efficient design of a relativistic magnetron with diffraction output

Wei Li and Yong-gui Liu

J. Appl. Phys. 108, 113303 (2010); http://dx.doi.org/10.1063/1.3520219 (5 pages) | Cited 7 times

Online Publication Date: 8 December 2010

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The relativistic magnetron with diffraction output (MDO) is promising to be the most compact narrow band high power microwave source. In this paper, based on the theory of S-parameters, a method named “choosing optimum” is proposed for the efficient design of the MDO in any wave band. By means of S-parameters, the π-TE31 mode conversion efficiencies of an S band MDO are calculated and then verified by three-dimensional particle-in-cell simulations. In order to illustrate the advantage of the choosing optimum method, the S-parameters of another L-band MDO are computed in a wide range of structure parameters and two results are chosen with detail information. Compared with the conventional method, the choosing optimum method is not only a shortcut, but also a convenient and easy way for choosing the high efficient MDOs in any wave band to meet the needs of different applications.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Experimental study on dielectric barrier discharge actuators operating in pulse mode

M. Kotsonis and L. Veldhuis

J. Appl. Phys. 108, 113304 (2010); http://dx.doi.org/10.1063/1.3517453 (9 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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An experimental investigation is performed on the operation of dielectric barrier discharge plasma actuators used as manipulators of secondary and unsteady flow structures such as boundary layer instabilities or shedding vortices. The actuators are tested mainly in pulse mode. High sample rate hot-wire measurements of the induced velocity field downstream of the actuator are taken for the cases of pulse actuation in still air as well as in a laminar boundary layer. Complementary voltage and current measurements are taken to calculate power consumption. Additionally, a study on the influence of the pulse frequency and duty cycle of actuation is performed. Results show the effectiveness of plasma actuators in inducing fluctuating components of velocity when operated in pulse mode. Spectral analysis reveals the connection between the actuator driving signal and the induced flowfield. The magnitude as well as the consistency of the resulting fluctuating field are dependent on both the duty cycle and the pulse frequency. An empirical operational envelope based on phenomenological observations is proposed, for the use of the actuators at specific flow and operational conditions given in the paper.
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47.15.Fe Stability of laminar flows
47.32.cd Vortex stability and breakdown
47.15.Cb Laminar boundary layers
47.85.ld Boundary layer control
47.80.Cb Velocity measurements
52.75.-d Plasma devices

The effect of laser wavelength on emission and particle dynamics of Sn plasma

D. Campos, S. S. Harilal, and A. Hassanein

J. Appl. Phys. 108, 113305 (2010); http://dx.doi.org/10.1063/1.3493118 (7 pages) | Cited 14 times

Online Publication Date: 9 December 2010

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We investigated the effects of laser wavelength on the atomic, ionic, and radiative emission from laser-produced tin plasmas. For generating plasmas, planar tin targets were excited using either high intensity neodymium-doped yttrium aluminum garnet (Nd:YAG, 1.06 μm) or carbon dioxide (CO2, 10.6 μm) laser pulses; both are considered to be potential excitation lasers for an extreme ultraviolet (EUV) lithography laser-produced plasma light source. Various diagnostic tools were utilized for investigating ionic, neutral, and radiative emission from Sn plasmas including Faraday cup, witness plate in conjunction with x-ray photoelectron spectroscopy (XPS), EUV, and visible emission spectroscopy and photography. Atomic and ionic analysis showed that the amount of debris emitted by the Nd:YAG generated plasmas was considerably higher than the CO2 laser-produced plasmas. The angular distributions of both atomic and ionic debris were found to be more forward-centric for the 1.06 μm generated plasma while being much more uniform for the 10.6 μm heated plasma. EUV and visible emission images of the plasma also showed a forward-centric appearance for 1.06 μm heated plasmas. The strength of excited neutral emission was considerably lower for the case of the 10.6 μm plasma while the kinetic energies of ions debris were found to be much higher for CO2 generated plasmas. Surface analysis of the craters created by the lasers showed that the mass ablation rate is 3.6 times higher for Nd:YAG laser generated plasmas compared to CO2 generated plasmas at maximum EUV emission.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Tx Emission, absorption, and scattering of particles

450 mm dual frequency capacitively coupled plasma sources: Conventional, graded, and segmented electrodes

Yang Yang and Mark J. Kushner

J. Appl. Phys. 108, 113306 (2010); http://dx.doi.org/10.1063/1.3517104 (11 pages) | Cited 6 times

Online Publication Date: 10 December 2010

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Wafer diameters for microelectronics fabrication will soon transition from 300 to 450 mm at a time when excitation frequencies for capacitively coupled plasmas (CCPs) are increasing to 200 MHz or higher. Already for 300 mm tools, there is evidence that wave behavior (i.e., propagation, constructive, and destructive interference) affects the uniformity of processing. The increase in diameter to 450 mm is likely to exacerbate these effects, perhaps requiring nontraditional tool designs. This is particularly important in dual frequency (DF) CCP tools in which there are potential interactions between frequencies. In this paper, results from a two-dimensional computational investigation of Ar plasma properties in a 450 mm DF-CCP reactor, incorporating a full-wave solution of Maxwell’s equations, are discussed. As in 300 mm DF-CCP reactors, the electron density collapses toward the center of the reactor with increasing high frequency (HF), however, with more pronounced finite wavelength effects. Graded conductivity electrodes with multilayer of dielectrics are computationally demonstrated as a possible means to suppress wave effects thereby increasing plasma uniformity. Segmentation of the HF electrode also improves the plasma uniformity by making the electrical distance between the feeds and the sheath edges as uniform as possible.
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52.50.Dg Plasma sources
52.40.Hf Plasma-material interactions; boundary layer effects
52.40.Kh Plasma sheaths
52.77.Bn Etching and cleaning
52.25.Fi Transport properties
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