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1 Nov 2010

Volume 108, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 091101 (2010); http://dx.doi.org/10.1063/1.3489943 (28 pages)

S. O. Kucheyev and A. V. Hamza
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Condensed hydrogen for thermonuclear fusion

S. O. Kucheyev and A. V. Hamza

J. Appl. Phys. 108, 091101 (2010); http://dx.doi.org/10.1063/1.3489943 (28 pages) | Cited 1 time

Online Publication Date: 3 November 2010

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Inertial confinement fusion (ICF) power, in either pure fusion or fission-fusion hybrid reactors, is a possible solution for future world’s energy demands. Formation of uniform layers of a condensed hydrogen fuel in ICF targets has been a long standing materials physics challenge. Here, we review the progress in this field. After a brief discussion of the major ICF target designs and the basic properties of condensed hydrogens, we review both liquid and solid layering methods, physical mechanisms causing layer nonuniformity, growth of hydrogen single crystals, attempts to prepare amorphous and nanostructured hydrogens, and mechanical deformation behavior. Emphasis is given to current challenges defining future research areas in the field of condensed hydrogens for fusion energy applications.
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28.52.-s Fusion reactors
28.52.Fa Materials
28.52.Av Theory, design, and computerized simulation
52.58.-c Other confinement methods
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back to top Lasers, Optics, and Optoelectronics

Laser properties of the diode-pumped Nd3+-doped La2CaB10O19 crystal

A. Brenier, Y. Wu, J. Zhang, Y. Wu, and P. Fu

J. Appl. Phys. 108, 093101 (2010); http://dx.doi.org/10.1063/1.3503237 (5 pages)

Online Publication Date: 1 November 2010

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We have determined the angular distribution of the fluorescence at 1051 nm wavelength of the Nd3+-doped monoclinic La2CaB10O19 crystal, originating from Nd3+ ions located in the regular La3+ sites, for extraordinary polarization in the XZ principal plane. We have found that the highest emission intensity does not occurs the Z-axis direction but in a −7.1° around the Y = b-axis rotated direction. With a one-pump cavity we obtained simultaneous lasing at 1051 and 1069 nm in X and Z-polarizations from Nd3+ ions located in La3+ and Ca2+ sites, respectively. In the active Q-switch regime the two laser pulses are always simultaneous. With a two-pump setup based on an optical bifurcated fiber we obtained also simultaneous lasing at 1051 and 1069 nm. The relative power of the two laser channels is tuneable with the help of a beam-splitter. An adequate value of the relative pump power of the two channels leads to simultaneous pulses in the active Q-switch regime.
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42.55.Rz Doped-insulator lasers and other solid state lasers
78.55.Hx Other solid inorganic materials
42.55.Px Semiconductor lasers; laser diodes
42.79.Fm Reflectors, beam splitters, and deflectors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Noise temperature and beam pattern of an NbN hot electron bolometer mixer at 5.25 THz

W. Zhang, P. Khosropanah, J. R. Gao, T. Bansal, T. M. Klapwijk, W. Miao, and S. C. Shi

J. Appl. Phys. 108, 093102 (2010); http://dx.doi.org/10.1063/1.3503279 (7 pages)

Online Publication Date: 1 November 2010

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We report the measured sensitivities of a superconducting NbN hot electron bolometer (HEB) heterodyne receiver at 5.25 THz. Terahertz (THz) radiation is quasioptically coupled to a HEB mixer with a lens and a spiral antenna. Using a measurement setup with black body calibration sources and a beam splitter in vacuo, and an antireflection coated Si lens, we obtained a double sideband (DSB) receiver noise temperature (TrecDSB) of 1150 K, which is nine times hν/2k, where h is the Planck constant, ν the frequency, and k the Boltzmann constant. In addition, the measured far field beam patterns of the integrated lens antenna show nearly collimated beams from 2.5 to 5.3 THz that allow reliable measurement of TrecDSB using the vacuum setup. Our experimental results in combination with an antenna-to-bolometer coupling simulation suggest that the HEB mixer can work well at least up to 6 THz, making it suitable for next generation of high-resolution spectroscopic space telescopes and, in particular, for the detection of the neutral atomic oxygen line at 4.7 THz.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Refractive index change in ion-implanted LiNbO3 waveguides calculated from lattice damage ratio

Qing Huang, Jin-Hua Zhao, Peng Liu, Jing Guan, and Xue-Lin Wang

J. Appl. Phys. 108, 093103 (2010); http://dx.doi.org/10.1063/1.3503414 (5 pages)

Online Publication Date: 2 November 2010

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We related the refractive index change in ion-implanted LiNbO3 crystals to the lattice damage ratio using a quadratic polynomial relationship. We used this relationship to calculate the refractive index profiles of z-cut LiNbO3 crystals implanted with oxygen ions using different energies, fluences, and annealing treatments. A highly damaged surface layer with a decreased refractive index was caused by electronic excitations in LiNbO3 crystals implanted with 4.0 MeV oxygen ions at a fluence of 2×1015 ions/cm2, which buried the optical modes inside the crystals. This relationship was also used for the estimation of the lattice damage in ion-implanted LiNbO3 crystals. It could make a quick estimate which was basically agree with the measured damage level.
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42.79.Gn Optical waveguides and couplers
61.72.up Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Tv Optical and dielectric properties related to treatment conditions
42.82.Et Waveguides, couplers, and arrays

Design and fabrication technology for high performance electrical pumped terahertz photonic crystal band edge lasers with complete photonic band gap

Hua Zhang (张华), Giacomo Scalari, Jérôme Faist, L. Andrea Dunbar, and Romuald Houdré

J. Appl. Phys. 108, 093104 (2010); http://dx.doi.org/10.1063/1.3476565 (6 pages)

Online Publication Date: 2 November 2010

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We detail the design and fabrication technology of two-dimensional photonic crystal (PhC) band edge emitting quantum cascade lasers (QCLs) operating at terahertz frequencies ( ∼ 3.3 THz). The entire QCL active layer has been deeply etched to form a triangular lattice PhC, in which a complete in-plane photonic band gap for TM polarized light exists. Strong vertical optical confinement is provided by metal-metal plasmon waveguide fabricated with thermocompression bonding and planarization. Benzocyclobutene is employed as a low loss medium to planarize the PhC structure. By tailoring the top metal contact on the planarized PhC structures, electrical current injection pad can also be defined. The lasing properties can be controlled by engineering the photonic band structure. Broad band continuous single mode tuning over 30 GHz was observed; while lower current threshold density and higher operation temperature compared to Fabry–Perot (FP) asers were obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.55.Tv Photonic crystal lasers and coherent effects
42.82.Cr Fabrication techniques; lithography, pattern transfer

Extend the omnidirectional zero-average-index photonic band gap using the band edge formalism: Application to the metamaterial with Drude dispersion

Yuanjiang Xiang, Shuangchun Wen, Xiaoyu Dai, Zhixiang Tang, and Dianyuan Fan

J. Appl. Phys. 108, 093105 (2010); http://dx.doi.org/10.1063/1.3499657 (9 pages)

Online Publication Date: 3 November 2010

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The band edge formalism of zero-average-index photonic band gap for the one-dimensional photonic crystals containing dispersion negative-index metamaterial is obtained. By adopting the band edge formalism, the upper and lower frequencies limits of the zero-average-index band gap are analyzed, and the results are in complete agreement with the results got by the projected band structure method. It is shown that the width and the band edge of the zero-average-index photonic band gap are significantly affected by the each constitutive parameter of the component materials of the one-dimensional photonic crystals. Based on the band edge formalism, new method of extending the zero-average-index photonic band gap has been presented by tuning the constitutive parameter of the component materials. Moreover, the conditions for zero width zero-average-index band gap are obtained. The realizability of tuning the constitutive parameter of the Drude dispersion metamaterial constructed by the nonresonant composite right/left-handed transmission structures is also discussed.
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42.70.Qs Photonic bandgap materials
42.25.Bs Wave propagation, transmission and absorption

Design of optical cloaks and illusion devices along a circumferential direction in curvilinear coordinates

Tungyang Chen and Shang-Ru Yu

J. Appl. Phys. 108, 093106 (2010); http://dx.doi.org/10.1063/1.3501103 (7 pages)

Online Publication Date: 4 November 2010

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We propose a cloaking and illusion device of circumferential topology based on the concept of transformation optics. The device is capable to cloak an object and/or simultaneously generate illusion images along a circumferential direction in curvilinear orthogonal coordinates. This feature allows us to construct multiple illusions in different ways, irrespective of the profile and direction of incident wave. Particularly when the device is served as a building brick of a larger device, one can generate a circumferential array of illusions in a periodic or any preferred pattern. We demonstrate the effectiveness of the proposed illusion devices by carrying out full wave simulations based on finite element calculations.
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42.79.-e Optical elements, devices, and systems
42.15.Eq Optical system design

Optical performances of InAs/GaSb/InSb short-period superlattice laser diode for mid-infrared emission

S. Ben Rejeb, M. Debbichi, M. Said, A. Gassenq, E. Tournié, and P. Christol

J. Appl. Phys. 108, 093107 (2010); http://dx.doi.org/10.1063/1.3503513 (6 pages)

Online Publication Date: 4 November 2010

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An antimonide-based InAs/GaSb/InSb short-period superlattice (SPSL) laser diode on GaSb substrate for mid-infrared emission has been modeled by an accurate eight-band k.p model. By using a realistic graded and asymmetric interface profile, calculated energy gap between the electron and heavy-hole miniband shows good agreement with our experimental data. Optical gain and threshold current density are then presented and compared with experimental results of SPSL laser diodes operating in pulsed regime. Analysis of the optical performances obtained at room temperature is made.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.72.Ai Infrared sources

Influence of exponential-doping structure on photoemission capability of transmission-mode GaAs photocathodes

Yijun Zhang, Jun Niu, Jing Zhao, Jijun Zou, Benkang Chang, Feng Shi, and Hongchang Cheng

J. Appl. Phys. 108, 093108 (2010); http://dx.doi.org/10.1063/1.3504193 (6 pages) | Cited 2 times

Online Publication Date: 4 November 2010

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In order to verify the actual effect of an exponential-doping structure on cathode performance, an exponential-doping structure has been applied to the preparation of the transmission-mode GaAs photocathode via molecular beam epitaxy technique. Compared with the uniform-doping photocathode, the activation and spectral response results show that the exponential-doping photocathode can achieve a higher photoemission capability. In addition, based on the revised uniform-doping and exponential-doping transmission-mode quantum yield equations, the cathode performance parameters such as electron average transport length and electron escape probability of the exponential-doping photocathode are obtained, which are greater than those of the uniform-doping one. The improvement in the cathode performance is attributed to the built-in electric field arising from this special doping structure, which effectively increases the electron transport efficiency and escape probability.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Design and operation of distributed feedback transistor lasers

F. Dixon, M. Feng, and N. Holonyak, Jr.

J. Appl. Phys. 108, 093109 (2010); http://dx.doi.org/10.1063/1.3504608 (6 pages)

Online Publication Date: 4 November 2010

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The design and fabrication methods utilizing soft photocurable nanoimprint lithography to realize single longitudinal mode distributed feedback transistor lasers are investigated. Coupled-mode theory and the effective index method are used to determine accurately the periodic dimensions necessary to integrate a surface grating in the top emitter AlGaAs confining layers of an InGaP/GaAs/InGaAs heterojunction bipolar transistor laser. Electrical and optical device data confirm the design methods. The distributed feedback device produces continuous wave laser operation with a peak wavelength λ = 959.75 nm and threshold current IB = 13 mA operating at −70 °C. For devices with cleaved ends a side mode suppression ratio >25 dB has been achieved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.30.Pq Bipolar transistors
42.79.Dj Gratings

The superluminal propagation in an organic nonlinear optical glass at room temperature

Qiu-Yun Ouyang, Yun-Dong Zhang, He Tian, Da-Jun Liu, Ping Yuan, and Ying-Lin Song

J. Appl. Phys. 108, 093110 (2010); http://dx.doi.org/10.1063/1.3493116 (5 pages)

Online Publication Date: 5 November 2010

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We investigated the light propagation in an organic glass with phthalocyanine gallium (GaPc) dispersed in polymethyl methacrylate (PMMA) fabricated by injection molding. The GaPc/PMMA organic glass is a reverse saturation absorption medium. We observed the superluminal propagation in this organic glass by using the technique of coherent population oscillations at room temperature. The largest time advancement is 2.21 ms and the corresponding group velocity is −0.90 m/s at the wavelength of 532 nm and with the input power of 89 mW. The density matrix theory with four-level model was used to analyze the experimental data. The theoretical simulations showed that the time advancement not only depends on the modulation frequency but also on the lifetime of the first triplet-state of the GaPc. We compared the time advancements between the GaPc/PMMA organic glass and the C60/toluene solution. Although the value of the former is smaller, it is more suitable for practical applications such as optical information processing than the latter.
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42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
42.70.Jk Polymers and organics

Monte Carlo simulation of carrier dynamics in terahertz quantum cascade lasers

Y. J. Han and J. C. Cao

J. Appl. Phys. 108, 093111 (2010); http://dx.doi.org/10.1063/1.3505675 (5 pages) | Cited 1 time

Online Publication Date: 8 November 2010

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We employ a Monte Carlo method to investigate the carrier dynamics in the terahertz quantum cascade lasers with vertical and diagonal radiative transition designs. Electron-electron and electron-phonon scattering are included in the calculations and their effects on the temperature dependence of electron transport are evaluated. The simulation shows that the degradation of temperature performance is mainly due to the rapid electron relaxation from upper to lower laser levels, in which the electron-phonon interaction is the dominant scattering mechanism. The parasitic coupling between laser levels is weakened in the diagonal design, resulting in better device performance such as lower current density, higher operating temperature, and less hot electron effects. The calculations are in good agreement with experimental results.
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42.55.Px Semiconductor lasers; laser diodes
02.70.Ss Quantum Monte Carlo methods

Distortion analysis of pulsed terahertz signal measured with spectral-encoding technique

Xiao-Yu Peng, Jing-Hua Teng, Xin-Hai Zhang, and Yong-Lim Foo

J. Appl. Phys. 108, 093112 (2010); http://dx.doi.org/10.1063/1.3499639 (10 pages) | Cited 1 time

Online Publication Date: 9 November 2010

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The principle of the spectral-encoding technique, one of the single-shot techniques for measurement of arbitrary pulsed terahertz (THz) signals, or T-rays, is demonstrated theoretically and through simulation. For single-cycle input THz pulse (bipolar wave form), THz signal could be retrieved faithfully under certain conditions, while for the multicycle input case, the THz signal cannot be retrieved without any distortion. However, there is an optimal length of the chirped-probe-pulse, corresponding to the characteristic time of the multicycle THz field, to minimize the distortion in the retrieved THz signal. Three main possible sources of distortions from both bipolar and multicycle THz signals are analyzed systematically. The first distortion originates from the mismatch of the optimal duration Tco of the chirped-probe-pulse and the T-ray length T. The second one is relevant to the spectrum bandwidth of the probe pulse. The third one occurs when the modulation depth k⪡1 is not satisfied. It comes from the neglect of the quadratic term of the modulation depth k, which reflects the strength of the THz signal in the retrieving process. Possible strategies are proposed to reduce these distortions.
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84.40.-x Radiowave and microwave (including millimeter wave) technology

Optical studies of degradation of AlGaN quantum well based deep ultraviolet light emitting diodes

A. Pinos, S. Marcinkevičius, J. Yang, R. Gaska, M. Shatalov, and M. S. Shur

J. Appl. Phys. 108, 093113 (2010); http://dx.doi.org/10.1063/1.3506697 (6 pages) | Cited 2 times

Online Publication Date: 10 November 2010

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Aging under high current stress of AlGaN quantum well based light emitting diodes with high and low Al content in the wells emitting at 270 nm and 335 nm, respectively, has been studied by scanning near field optical spectroscopy and far field electroluminescence, photoluminescence and time-resolved photoluminescence. In the high Al content devices emission band related to optical transitions in the cladding involving nitrogen vacancies has been found. Evolution of this band during aging suggests that the role of N vacancies is crucial in the aging process by aiding defect generation and formation of high conductivity channels.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors
61.72.jd Vacancies

Effects of the impurity–host interactions on the nonradiative processes in ZnS:Cr

C. Tablero

J. Appl. Phys. 108, 093114 (2010); http://dx.doi.org/10.1063/1.3506705 (7 pages)

Online Publication Date: 10 November 2010

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There is a great deal of controversy about whether the behavior of an intermediate band in the gap of semiconductors is similar or not to the deep-gap levels. It can have significant consequences, for example, on the nonradiative recombination. In order to analyze the behavior of an intermediate band, we have considered the effect of the inward and outward displacements corresponding to breathing and longitudinal modes of Cr-doped ZnS and on the charge density for different processes involved in the nonradiative recombination using first-principles. This metal-doped zinc chalcogenide has a partially filled band within the host semiconductor gap. In contrast to the properties exhibited by deep-gap levels in other systems, we find small variations in the equilibrium configurations, forces, and electronic density around the Cr when the nonradiative recombination mechanisms modify the intermediate band charge. The charge density around the impurity is equilibrated in response to the perturbations in the equilibrium nuclear configuration and the charge of the intermediate band. The equilibration follows a Le Chatelier principle through the modification of the contribution from the impurity to the intermediate band and to the valence band. The intermediate band introduced by Cr in ZnS for the concentrations analyzed makes the electronic capture difficult and later multiphonon emission in the charge-transfer processes, in accordance with experimental results.
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81.05.Dz II-VI semiconductors
71.55.Gs II-VI semiconductors
71.28.+d Narrow-band systems; intermediate-valence solids
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations

New model for assessing dose, dose rate, and temperature sensitivity of radiation-induced absorption in glasses

Olivier Gilard, Matthieu Caussanel, Hervé Duval, Gianandrea Quadri, and François Reynaud

J. Appl. Phys. 108, 093115 (2010); http://dx.doi.org/10.1063/1.3503370 (5 pages)

Online Publication Date: 10 November 2010

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A new theoretical approach is proposed to explain the dose, dose rate and temperature sensitivity of the radiation-induced absorption (RIA) in glasses. In this paper, a βth-order dispersive kinetic model is used to simulate the growth of the density of color centers in irradiated glasses. This model yields an explanation for the power-law dependence on dose and dose rate usually observed for the RIA in optical fibers. It also leads to an Arrhenius-like relationship between the RIA and the glass temperature during irradiation. With a very limited number of adjustable parameters, the model succeeds in explaining, with a good agreement, the RIA growth of two different optical fiber references over wide ranges of dose, dose rate and temperature.
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61.72.jn Color centers
61.82.Ms Insulators
61.80.Ed γ-ray effects
42.70.Ce Glasses, quartz
42.81.-i Fiber optics

Improved hole confinement in GaInAsN–GaAsSbN thin double-layer quantum-well structure for telecom-wavelength lasers

Asaf Albo, Gad Bahir, and Dan Fekete

J. Appl. Phys. 108, 093116 (2010); http://dx.doi.org/10.1063/1.3503435 (6 pages) | Cited 2 times

Online Publication Date: 10 November 2010

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In this work we demonstrated increased hole confinement in a bilayer quantum well that consists of two thin layers of GaInAsN/GaAsSbN confined by GaAs barriers. Comparison between the temperature dependence of photoluminescence intensity of the bilayer and GaInAsN quantum wells indicated that electrons rather than holes are the less confined carriers in the bilayer structure. This structure enables independent control of the band gap energy, band offsets and reduces the temperature sensitivity of laser performance. The calculations showed that a bilayer based short-period superlattice would provide a high optical gain at 1.3–1.55 μm due to increased electron-hole wave functions overlap.
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78.55.-m Photoluminescence, properties and materials

One-dimensional photonic crystal with a complex defect containing an ultrathin superconducting sublayer

N. N. Dadoenkova, A. E. Zabolotin, I. L. Lyubchanskii, Y. P. Lee, and Th. Rasing

J. Appl. Phys. 108, 093117 (2010); http://dx.doi.org/10.1063/1.3494034 (7 pages) | Cited 1 time

Online Publication Date: 11 November 2010

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The influence of the variation in the incidence angle on the photonic band gap spectra of a one-dimensional dielectric photonic crystal with a complex defect layer, consisting of ultrathin superconducting and dielectric sublayers, was theoretically investigated. The behavior of the defect modes with different polarizations as a function of the incidence angle variation is studied numerically for different thicknesses of the superconducting sublayer. The pronounced contrast in behavior of TE- and TM-polarized modes was demonstrated. The intensity of the TE-polarized defect mode decreases with increasing incidence angle, whereas the intensity of the TM-polarized defect mode increases. The increase in the superconducting defect sublayer thickness leads to a shift in the defect mode of TM-polarization to higher frequencies.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
74.78.Fk Multilayers, superlattices, heterostructures

Theoretical simulations of the effects of the indium content, thickness, and defect density of the i-layer on the performance of p-i-n InGaN single homojunction solar cells

Shih-Wei Feng, Chih-Ming Lai, Chien-Hsun Chen, Wen-Ching Sun, and Li-Wei Tu

J. Appl. Phys. 108, 093118 (2010); http://dx.doi.org/10.1063/1.3484040 (7 pages) | Cited 1 time

Online Publication Date: 11 November 2010

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In this study, we conducted numerical simulations with the consideration of microelectronic and photonic structures to determine the feasibility of and to design the device structure for the optimized performance of InGaN p-i-n single homojunction solar cells. Operation mechanisms of InGaN p-i-n single homojunction solar cells were explored through the calculation of the characteristic parameters such as the absorption, collection efficiency (χ), open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF). Simulation results show that the characteristic parameters of InGaN solar cells strongly depend on the indium content, thickness, and defect density of the i-layer. As the indium content in the cell increases, Jsc and absorption increase while χ, Voc, and FF decrease. The combined effects of the absorption, χ, Voc, Jsc, and FF lead to a higher conversion efficiency in the high-indium-content solar cell. A high-quality In0.75Ga0.25N solar cell with a 4 μm i-layer thickness can exhibit as high a conversion efficiency as ∼ 23%. In addition, the similar trend of conversion efficiency to that of Jsc shows that Jsc is a dominant factor to determine the performance of p-i-n InGaN solar cells. Furthermore, compared with the previous simulation results without the consideration of defect density, the lower calculated conversion efficiency verifies that the sample quality has a great effect on the performance of a solar cell and a high-quality InGaN alloy is necessary for the device fabrication. Simulation results help us to better understand the electro-optical characteristics of InGaN solar cells and can be utilized for efficiency enhancement through optimization of the device structure.
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88.40.hj Efficiency and performance of solar cells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
02.60.-x Numerical approximation and analysis
88.40.J- Types of solar cells
42.79.-e Optical elements, devices, and systems
back to top Plasmas and Electrical Discharges

Growth and characteristics of tantalum oxide thin films deposited using thermionic vacuum arc technology

Rodica Vladoiu, Victor Ciupina, Aurelia Mandes, Virginia Dinca, Madalina Prodan, and Geavit Musa

J. Appl. Phys. 108, 093301 (2010); http://dx.doi.org/10.1063/1.3503278 (5 pages)

Online Publication Date: 1 November 2010

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Tantalum pentoxide (Ta2O5) thin films were synthesized using thermionic vacuum arc (TVA) technology. TVA is an original deposition method using a combination of anodic arc and electron gun system for the growth of thin films from solid precursors under vacuum of 10−6 Torr. The properties of the deposited Ta2O5 thin films were investigated in terms of wettability, refractive index, morphology, and structure. The surface free energy was determined by means of surface energy evaluation system indicating a hydrophilic character and the refractive index was measured by Filmetrics F20 device. The morphology was determined from bright field transmission electron microscopy (TEM) image performed by Philips CM 120 ST TEM system. It exhibits nanoparticles of 3–6 nm diameter smoothly distributed. Selected area electron diffraction pattern revealed the contrast fringes given by complex polycrystalline particles included in the amorphous film. The measured fringes could be indexed using monoclinic structure of Ta2O5.
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68.55.-a Thin film structure and morphology
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.08.Bc Wetting
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Plasma diagnostics for investigating extreme ultraviolet light sources

P. Yeates, J. White, and E. T. Kennedy

J. Appl. Phys. 108, 093302 (2010); http://dx.doi.org/10.1063/1.3486220 (11 pages) | Cited 1 time

Online Publication Date: 3 November 2010

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Plasma temperature and density diagnostics are crucial for lithographic applications of extreme ultraviolet light sources. One widely used technique employs line intensity ratios of successively charged ion states to determine the ion temperature (Tionz). This work comprises a detailed “stress-test” of the applied technique, where space and time resolved emission in laser-produced plasmas were studied, using a Nd:yttrium aluminum garnet laser pulse incident on an aluminum target in the 26.5–32.5 nm range. Detailed hydrodynamic simulations also investigate the dependency of ion temperature on electron density and the charge states for various line combinations (Al VI/V, Al VII/VI, Al VIII/VII, Al IX/VIII, and Al X/IX).
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

High-current diode with ferroelectric plasma source-assisted hollow anode

V. Vekselman, J. Z. Gleizer, S. Yatom, V. Tz. Gurovich, and Ya. E. Krasik

J. Appl. Phys. 108, 093303 (2010); http://dx.doi.org/10.1063/1.3486450 (8 pages)

Online Publication Date: 3 November 2010

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The operation of a ferroelectric plasma source-assisted hollow anode (HA) electron source in a vacuum diode powered by an ∼ 200 kV and ∼ 400 ns pulsed generator was studied using time- and space-resolved laser induced fluorescence diagnostics. It was found that the plasma ion “temperature” in the vicinity of the HA output grid increases up to ∼ 15 eV during the accelerating pulse, which is consistent with a model of the potential screening of the grid by the randomly moving ions [ Phys. Plasmas 13, 073506 (2006) ]. Also it was shown that the increase in the HA plasma potential up to several kilovolts because of the appearance of a noncompensated ion charge in the HA bulk plasma due to electrons fast extraction, leads to explosive emission centers being generated at the HA grid and to nonuniformity in the cross-sectional electron beam current density. Finally, the plasma prefilled mode of diode operation was studied using a simple one-dimensional model of the plasma erosion and the HA plasma electron heating by energetic ions was considered.
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52.59.Mv High-voltage diodes
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Dg Plasma sources
52.25.Tx Emission, absorption, and scattering of particles

Angular ion emission characteristics of a laser triggered tin vacuum arc as light source for extreme ultraviolet lithography

Harald Verbraak, Felix Küpper, Jeroen Jonkers, and Klaus Bergmann

J. Appl. Phys. 108, 093304 (2010); http://dx.doi.org/10.1063/1.3499611 (6 pages)

Online Publication Date: 3 November 2010

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The angular resolved emission of tin ions from a laser triggered vacuum arc to be used as light source for extreme ultraviolet lithography is presented. Ion energies of more than 200 keV for emission angles up to 50° with respect to the optical axis are observed. The angular emission characteristic is strongly anisotropic with a pronounced peak for fast ions into a cone with an opening angle of roughly 10° at an angle of 35° with respect to the optical axis. These ions also exhibit a distinct energy distribution function compared to the more isotropic emitted bulk of ions, which can be referred to different mechanisms of production. Looking at the discharge current parameters, the production of the directed fast ions can be connected with a peaked increase in the impedance, which gives hint to a plasma instability as origin of those ions. The emission of isotropic emitted ions is in agreement with a model of plasma expansion into vacuum. The emission characteristic is also strongly dependent on the parameter of the trigger laser. It is shown that using a double trigger laser pulse the fast ion production can be suppressed by more than one order of magnitude.
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42.72.Bj Visible and ultraviolet sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Excitational energy transfer enhancing ionization and spatial-temporal evolution of air breakdown with UV laser radiation

Jason S. Hummelt and John E. Scharer

J. Appl. Phys. 108, 093305 (2010); http://dx.doi.org/10.1063/1.3504243 (8 pages) | Cited 1 time

Online Publication Date: 5 November 2010

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This paper examines the role multiphoton excitation of oxygen has on the ionization of nitrogen in laser air breakdown. Plasma is created by focusing a 193 nm ArF excimer laser using an 18 cm focal length lens, producing a cylindrical 540 μm wide spot of intensity 6.5 GW/cm2, well below the classical limit for collisional cascade (CC) breakdown. By spectroscopically monitoring the B 2Σu+ to X 2Σg+ transition at 391.4 nm of N2+ in N2 and O2 mixes, collisions between N2 and metastable O2 states that have undergone 1+1 absorption processes are shown to lower the degree of nonlinearity (i.e., the number of photons involved in the rate limiting multiphoton absorption process) in the ionization of N2. This process is also found to dominate the 2+1 resonant enhanced multiphoton ionization of N2 in air and be the primary source for ionization of N2 to the B 2Σu+ state. Plasma formation and evolution is also examined using a 1.3 cm focal length objective lens creating a 40 μm wide spot of intensity 1.25 TW/cm2, above the classical limit for breakdown. This plasma is imaged with a fast (1.2 ns) gating intensified charge coupled device camera. Early plasma formation is seen to be inhomogeneous in nature, and significant ion density is found to exist up to 20 μs after the laser pulse.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Spectroscopic, imaging, and probe diagnostics of laser plasma plumes expanding between confining surfaces

P. Yeates and E. T. Kennedy

J. Appl. Phys. 108, 093306 (2010); http://dx.doi.org/10.1063/1.3505801 (12 pages) | Cited 3 times

Online Publication Date: 9 November 2010

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Laser plasma plumes were generated in aluminum rectangular cavities of fixed depth (6 mm) and varying height (2.0, 1.5, and 1.0 mm). Space and time resolved visible emission spectroscopy, gated intensified visible imaging, and Langmuir probe diagnostics were utilized to diagnose the evolution of the confined plasma plumes in comparison to freely expanding plasma plume generated from ablation of a planar target. The constrained plasma behavior displayed a multiphase history. Early stage interactions (t<100 ns) resulted in enhanced continuum and line emission, shockwave formation and plasma plume rebound. Later phase, long duration plasma-surface interactions (t>160 ns) resulted in sustained “decay,” i.e., a rapid termination of continuum emission, in concert with decreases in peak electron density (Ne) and plasma temperature (T). This later phase originates from loss mechanisms which bleed the plasma plume of thermal energy and charged particles. These loss mechanisms increase in magnitude as the duration of the plasma-surface interaction increases. The transition from enhancement phase, originating from hydrodynamic containment, and plasma-surface collisions, to decay phase is described and occurs for each cavity at a different point in the space time history.
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52.30.-q Plasma dynamics and flow
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Dy General theory and basic studies of plasma lifetime, particle and heat loss, energy balance, field structure, etc.
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
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