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1 Jan 2009

Volume 105, Issue 1, Articles (01xxxx)

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Metallic slit aperture as a near-field optical head for heat-assisted magnetic recording

Satoshi Omodani, Toshiharu Saiki, and Minoru Obara

J. Appl. Phys. 105, 013101 (2009); http://dx.doi.org/10.1063/1.3054363 (5 pages)

Online Publication Date: 6 January 2009

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Heat assisted magnetic recording (HAMR) technique requires an optical head that can efficiently generate a subwavelength optical spot. The results of finite difference time domain simulation shows that two subwavelength rectangular holes adjacent to a metallic slit aperture make an optical spot from the slit smaller and its peak intensity higher. A subwavelength spot of 82×46 nm2 (full width at half maximum) in the recording medium is obtainable when a pair of rectangular holes is flanked adjacent to the slit aperture with a much smaller distance than the optical wavelength. This configuration provides a high transmittance of the slit aperture and a high expectation for a high controllability of both a thickness of the slit and a distance between the slit and the rectangular hole by the use of the planar process. By using a plasmon waveguide to guide light into the metallic slit aperture, a thin and efficient optical head for HAMR is achieved.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Ag Apertures, collimators
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
42.82.Et Waveguides, couplers, and arrays

Nanosilver enhanced upconversion fluorescence of erbium ions in Er3+: Ag-antimony glass nanocomposites

Tirtha Som and Basudeb Karmakar

J. Appl. Phys. 105, 013102 (2009); http://dx.doi.org/10.1063/1.3054918 (8 pages) | Cited 25 times

Online Publication Date: 6 January 2009

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Er3+:Ag-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix K2O–B2O3–Sb2O3 by a single-step melt-quench technique involving selective thermochemical reduction. The UV-vis-near-infrared absorption spectra show typical surface plasmon resonance (SPR) band of Ag0 nanoparticles (NPs) in addition to the distinctive absorption peaks of Er3+ ion. X-ray diffraction and selected area electron diffraction results indicate formation of Ag0 NPs along the (200) plane direction. The transmission electron microscopic image reveals the formation of spherical, fractal, and rod-shaped Ag0 NPs having maximum size ∼ 31 nm. The rod-shaped Ag0 NPs have aspect ratio ∼ 2.4. The field emission scanning electron microscopic image shows development of three dimensional cornlike microstructures. Photoluminescent upconversion under excitation at 798 nm exhibit two prominent emission bands of Er3+ ions centered at 536 (green) and 645 (red) nm due to 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions, respectively. Both the bands undergo a maximum of three- and eightfold intensity enhancement, respectively, at Ag0 concentration of 0.007 wt % (1.8×1018 atoms/cm3). Local field enhancement induced by Ag0 SPR is found to be responsible for enhancement while energy transfer from Er3+→Ag0 and optical reabsorption due to Ag0 SPR for quenching.
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78.55.Qr Amorphous materials; glasses and other disordered solids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Pg Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
73.22.Lp Collective excitations

Carrier localization degree of In0.2Ga0.8N/GaN multiple quantum wells grown on vicinal sapphire substrates

Zhen-Yu Li, Ming-Hua Lo, Ching-Hua Chiu, Po-Chun Lin, Tien-Chang Lu, Hao-Chung Kuo, and Shing-Chung Wang

J. Appl. Phys. 105, 013103 (2009); http://dx.doi.org/10.1063/1.3055264 (7 pages) | Cited 1 time

Online Publication Date: 6 January 2009

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In this work, we have grown In0.2Ga0.8N/GaN multiple quantum well (MQWs) epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the In0.2Ga0.8N/GaN MQWs grown on 0.2°-off sapphire substrate exhibited the smallest carrier localization degree and more ordered In0.2Ga0.8N/GaN MQW structure. In addition, mechanisms for carrier localization in In0.2Ga0.8N/GaN MQWs grown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaN epitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of In0.2Ga0.8N/GaN MQWs grown on 0.2° vicinal sapphire substrate at the bottom of n-GaN layer was about 9.4×108 cm−2 and reduced to 3.0×108 cm−2 at the top of n-GaN layer. We also obtained the TDD of 5.6×107 cm−2 in the MQW region and only 1.0×107 cm−2 in the p-GaN region. Based on the results mentioned above, 0.2°-off substrate can offer In0.2Ga0.8N/GaN MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree.
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78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
73.21.Fg Quantum wells

Analytic modal solution to transmission and collimation of light by one-dimensional nanostructured subwavelength metallic slits

Yi-Lei Hua and Zhi-Yuan Li

J. Appl. Phys. 105, 013104 (2009); http://dx.doi.org/10.1063/1.3043885 (8 pages) | Cited 5 times

Online Publication Date: 6 January 2009

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Light transmitting through a subwavelength slit on an ordinary metal plate is diffracted to all directions but if the exit plane of the slit is patterned with periodical nanostructures, the diffracted light may be compressed into a collimated beam within a small angle. In this paper, we develop a rigorous theoretical method for solving the surface wave induced beam collimation in nanostructured subwavelength metallic slits. The method combines the analytical modal expansion method, the supercell technique, the transfer-matrix method, and the conventional Kirchhoff’s diffraction theory. It allows for quantitative investigation of coupling of the incident light into the guided wave of the slit and coupling of the guided wave out of the nanostructured exit plane. We have used the method to examine light transmission through the nanostructured metallic slit and the corresponding diffraction and beam collimation behaviors. We have extensively analyzed the angular transmission spectrum as a function of the nanostructure period and the incident light wavelength and revealed the condition at which good beam collimation can take place. The result shows that the beam collimation is caused by the excitation of the surface waves supported on the periodical nanostructured pattern and subsequent coupling into the radiation light. Several scattering channels can coexist for coupling the surface waves into the observed diffraction waves and they can act constructively to create one or more collimation beams with excellent directionality and high brightness. The diffraction field patterns in the large area confirm the angular spectrum analysis.
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42.25.Fx Diffraction and scattering
42.79.Dj Gratings
78.66.-w Optical properties of specific thin films

Investigation of Förster-type energy transfer in organic light-emitting devices with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)-4H-pyran doped cohost emitting layer

Li-Zhen Yu, Xue-Yin Jiang, Zhi-Lin Zhang, Li-Ren Lou, and Ching-Ting Lee

J. Appl. Phys. 105, 013105 (2009); http://dx.doi.org/10.1063/1.3039412 (4 pages) | Cited 12 times

Online Publication Date: 7 January 2009

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Organic light-emitting devices (OLEDs) with cohosted emitter, which is composed of 9,10-di(2-naphthyl)anthracene (ADN) and tris(8-hydroxy-quinolinato) aluminum (Alq3) and doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)-4H-pyran (DCJTB), were fabricated and studied. The efficiency of OLEDs with a cohost emitter was higher than that with a single host emitter. For the cohost emitter with ADN/Alq3 weight ratio of 75:25, the 3.4 cd/A efficiency of the resulted OLEDs was obtained. It is found that the absorption spectra of DCJTB and the emission spectra of Alq3 changed with the composition of the emitter. This phenomenon is attributed to the polarization effect. On the basis of the Förster’s theory, the resulted overlap integral exhibits the highest value for this cohost emitter. The experimental results reveal that the cascade energy transfer plays an important role in the luminance efficiency enhancement of the cohost emitter in OLEDs.
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85.60.Jb Light-emitting devices

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

S. N. Danilov, B. Wittmann, P. Olbrich, W. Eder, W. Prettl, L. E. Golub, E. V. Beregulin, Z. D. Kvon, N. N. Mikhailov, S. A. Dvoretsky, V. A. Shalygin, N. Q. Vinh, A. F. G. van der Meer, B. Murdin, and S. D. Ganichev

J. Appl. Phys. 105, 013106 (2009); http://dx.doi.org/10.1063/1.3056393 (6 pages) | Cited 9 times

Online Publication Date: 8 January 2009

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We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.
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68.65.Fg Quantum wells
81.07.St Quantum wells
41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.05.Ea III-V semiconductors

Microstructure and luminescent properties of novel InGaP alloys on relaxed GaAsP substrates

M. J. Mori and E. A. Fitzgerald

J. Appl. Phys. 105, 013107 (2009); http://dx.doi.org/10.1063/1.3037240 (10 pages) | Cited 5 times

Online Publication Date: 9 January 2009

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We present a metal organic chemical vapor deposition (MOCVD) growth study of unconventional alloys of InGaP (with In fraction of 0.2–0.4) grown on fully relaxed GaAsP virtual substrates for the application of high performance visible light emitting diodes (LEDs) and lasers in the green to red range of the visible spectrum. Several defects which are harmful to optical performance were identified, characterized, and removed. These include CuPt–B order (which lowers band gap), phase separation or short range order (which contributes to leakage currents and reduces luminescence) and undulation of the virtual substrate surface (which prevents high quality epitaxial growth). Each of these defects is understood through a two-step growth model which describes the formation and subsequent randomization of defects during growth. Through control of MOCVD parameters including growth temperature, V/III ratio, growth rate, and surfactant we demonstrate growth of extremely high quality InGaP heterostructures which hold promise for fabrication of light emitting devices.
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78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Influence of nitrogen on the growth and luminescence of silicon nanocrystals embedded in silica

M. Bolduc, G. Genard, M. Yedji, D. Barba, F. Martin, G. Terwagne, and G. G. Ross

J. Appl. Phys. 105, 013108 (2009); http://dx.doi.org/10.1063/1.3054561 (5 pages) | Cited 9 times

Online Publication Date: 9 January 2009

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Silicon nanocrystals (Si-ncs) have been produced by implantation of Si+ in excess into SiO2 followed by both annealing and passivation using argon or nitrogen. Nitrogen increases the photoluminescence (PL) emission and shifts the spectra toward the blue. The measured Si-nc diameter is 4.3 and 3.8 nm after annealing performed under Ar and N2, respectively. A significant quantity of nitrogen atoms has been detected in all samples by resonant nuclear reaction analysis (RNRA). The nitrogen concentration is significantly higher when the annealing and passivation are performed in a nitrogen environment, in agreement with a larger Si–N vibration signal on the Raman spectra. The depth profiles of nitrogen are very similar to those of Si-nc, suggesting that the N2 molecules may diffuse in the SiO2 during the annealing and then are trapped in proximity to the Si-nc. In addition to Si+, the implantation of N2+ to concentrations of 3 and 6 at. % produced a decrease in the PL intensity (accentuated at the higher concentration) and an increase in the Raman signal associated to Si–N vibrations. These results suggest that a relatively low nitrogen atomic fraction enhances the PL emission, since a large nitrogen concentration impedes the formation of Si-nc thus significantly decreasing the PL intensity.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.uf Ge and Si
78.30.Am Elemental semiconductors and insulators

Dynamic measurements of ultraviolet-enhanced silica contamination by photoluminescence-based diagnostic

Alexandre Pereira, Etienne Quesnel, and Maryse Reymermier

J. Appl. Phys. 105, 013109 (2009); http://dx.doi.org/10.1063/1.3056390 (9 pages)

Online Publication Date: 9 January 2009

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The ultraviolet-enhanced (UV-enhanced) contamination of optical components leads to an untimely aging of sealed laser systems, photolithography, and synchrotron installations. The laser-induced deposition of organic films on silica substrates and coatings significantly reduces their transmission and degrades their optical functions. In this paper, measurements of organic contaminant films growth under 213 nm laser irradiation performed on silica Corning 7980 grade ArF are reported. We present an in situ contaminant layer growth diagnostic based on silica photoluminescence measurements. The purpose was to determine the photodeposition kinetics as a function of controlled environmental conditions and fluence and to find out the experimental conditions in which the growth of contamination films was significantly reduced. We then demonstrated that with a low partial pressure of oxygen, the growth of carbonaceous films is drastically reduced during UV laser irradiation whereas with water and nitrogen it was not the case. We also proposed a physical modeling of the UV-enhanced silica contamination processes.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.15.Fg Pulsed laser ablation deposition
42.62.-b Laser applications
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Simultaneous measurement of substrate temperature and thin-film thickness on SiO2/Si wafer using optical-fiber-type low-coherence interferometry

Takayuki Ohta, Chishio Koshimizu, Kanta Kawasaki, Keigo Takeda, and Masafumi Ito

J. Appl. Phys. 105, 013110 (2009); http://dx.doi.org/10.1063/1.3058592 (7 pages) | Cited 3 times

Online Publication Date: 13 January 2009

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This paper proposes a technique for simultaneously monitoring the thickness of a SiO2 thin film and the temperature of a Si substrate. This technique uses low-coherence interferometry and has the potential to be used for online monitoring of semiconductor manufacturing processes. In low-coherence interferometry, when the optical path length of a layer is shorter than the coherence length of the light source, the two interference at the top and bottom interfaces of the layer overlap each other. In this case the detected peak position of the interference is shifted from the actual interface, resulting in an error in the temperature measurement, since the temperature is derived from the optical path length of the layer. To improve the accuracy of the temperature measurement, the effect of the overlapping interference was compensated by measuring the SiO2 thickness. The thickness of the Si substrate was 750 μm and the thickness of the SiO2 film was varied between 0 and 2 μm. The SiO2 thickness, which is shorter than the coherence length of the light source, was measured from the ratio of interference intensities of two superluminescent diodes (wavelengths: 1.55 and 1.31 μm). The measured ratio corresponded well with the theoretical one for SiO2 film thicknesses between 0 and 2 μm, and the error was less than 25 nm. The Si temperature was measured from the optical path length. In order to compensate for the overlapping interference, the shift in the peak position of the interference at the SiO2/Si interface was estimated from the measurement results of the SiO2 thickness. This improved the accuracy of the temperature measurement from 5.3 to 3.5 °C.
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68.60.-p Physical properties of thin films, nonelectronic
78.66.Nk Insulators

Interference in wave-front-division-based spectrometers illuminated with ultrafast pulses of light

L. Grave de Peralta

J. Appl. Phys. 105, 013111 (2009); http://dx.doi.org/10.1063/1.3062150 (6 pages) | Cited 2 times

Online Publication Date: 13 January 2009

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Visually appealing simulations of the ultrafast response of an integrated-optics spectrometer reveal how interference occurs inside of the device and before the light arrives to the external measurement instrument. The device was especially designed for having no more than one pulse at a time in the common path of the spectrometer. Simulations are in excellent agreement with recent experiments involving arrayed waveguide grating pulse shapers.
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42.82.Et Waveguides, couplers, and arrays
07.60.Rd Visible and ultraviolet spectrometers
42.79.Dj Gratings
42.82.Bq Design and performance testing of integrated-optical systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Optical characteristics of III-nitride quantum wells with different crystallographic orientations

Mikhail V. Kisin, Robert G. W. Brown, and Hussein S. El-Ghoroury

J. Appl. Phys. 105, 013112 (2009); http://dx.doi.org/10.1063/1.3053049 (5 pages) | Cited 6 times

Online Publication Date: 13 January 2009

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This article presents a direct comparison of calculated optical characteristics of polar, nonpolar, and semipolar III-nitride quantum wells. We show that the advantage of using wider quantum wells offered by nonpolar/semipolar technology is severely limited by narrower valence subband separation, thermal hole redistribution, and resulting optical gain degradation in wider wells. However, we emphasize the importance of using wider quantum wells to prevent electron leakage. We also show that gain characteristics of laser structures grown in nonpolar/semipolar orientations are less vulnerable to detrimental effect of nonradiative recombination.
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78.67.De Quantum wells
68.65.Fg Quantum wells

Time-resolved spectroscopy on GaN nanocolumns grown by plasma assisted molecular beam epitaxy on Si substrates

P. Corfdir, P. Lefebvre, J. Ristić, P. Valvin, E. Calleja, A. Trampert, J.-D. Ganière, and B. Deveaud-Plédran

J. Appl. Phys. 105, 013113 (2009); http://dx.doi.org/10.1063/1.3062742 (8 pages) | Cited 14 times

Online Publication Date: 13 January 2009

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A detailed study of excitons in unstrained GaN nanocolumns grown by plasma assisted molecular beam epitaxy on silicon substrates is presented. The time-integrated and time-resolved photoluminescence spectra do not depend significantly on the (111) or (001) Si surface used. However, an unusually high relative intensity of the two-electron satellite peak of the dominant donor-bound exciton line is systematically observed. We correlate this observation with the nanocolumn morphology determined by scanning electron microscopy, and therefore propose an interpretation based on the alteration of wave functions of excitonic complexes and of donor states by the proximity of the semiconductor surface. This explanation is supported by a model that qualitatively accounts for both relative intensities and time decays of the photoluminescence lines.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
71.55.Eq III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
78.47.jd Time resolved luminescence
78.55.Cr III-V semiconductors

A two-dimensional lattice ion trap for quantum simulation

Robert J. Clark, Tongyan Lin, Kenneth R. Brown, and Isaac L. Chuang

J. Appl. Phys. 105, 013114 (2009); http://dx.doi.org/10.1063/1.3056227 (8 pages) | Cited 13 times

Online Publication Date: 13 January 2009

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Quantum simulations of spin systems could enable the solution of problems that otherwise require infeasible classical resources. Such a simulation may be implemented using a well-controlled system of effective spins, such as a two-dimensional lattice of locally interacting ions. We propose here a layered planar rf trap design that can be used to create arbitrary two-dimensional lattices of ions. The design also leads naturally to ease of microfabrication. As a first experimental demonstration, we confine 88Sr+ ions in a millimeter-scale lattice trap and verify numerical models of the trap by measuring the motional frequencies. We also confine 440 nm diameter charged microspheres and observe ion-ion repulsion between ions in neighboring lattice sites. Our design, when scaled to smaller ion-ion distances, is appropriate for quantum simulation schemes, e.g., that of Porras and Cirac [Phys. Rev. Lett. 92, 207901 (2004)] . We note, however, that in practical realizations of the trap, an increase in the secular frequency with decreasing ion spacing may make a coupling rate that is large relative to the decoherence rate in such a trap difficult to achieve.
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29.25.-t Particle sources and targets
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Midinfrared absorption by InAs/GaSb type-II superlattices

L. L. Li, W. Xu, J. Zhang, and Y. L. Shi

J. Appl. Phys. 105, 013115 (2009); http://dx.doi.org/10.1063/1.3058692 (7 pages) | Cited 4 times

Online Publication Date: 14 January 2009

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We present a systematic theoretical study on optical properties of short-period InAs/GaSb type-II superlattices (SLs) which can serve for midinfrared (MIR) detection. Using the standard Kronig–Penney model we calculate the miniband structure of such SLs. The obtained band-gap energies are in line with those realized experimentally. On the basis of the energy-balance equation derived from the Boltzmann equation we develop a simple approach to calculate the optical absorption coefficient for the corresponding SL systems. Our results agree with recent experimental findings. Moreover, the dependence of MIR absorption in InAs/GaSb type-II SLs on temperature and well width are examined. This study is pertinent to the application of InAs/GaSb type-II SLs as MIR photodetectors working in the ambient condition.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.21.Cd Superlattices
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Thermal links for the implementation of an optical refrigerator

John Parker, David Mar, Steven Von der Porten, John Hankinson, Kevin Byram, Chris Lee, Michael K. Mayeda, Richard Haskell, Qimin Yang, Scott Greenfield, and Richard Epstein

J. Appl. Phys. 105, 013116 (2009); http://dx.doi.org/10.1063/1.3062522 (11 pages) | Cited 2 times

Online Publication Date: 14 January 2009

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Optical refrigeration has been demonstrated by several groups of researchers, but the cooling elements have not been thermally linked to realistic heat loads in ways that achieve the desired temperatures. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. We have designed thermal links that minimize the absorption of fluoresced photons by the heat load using multiple mirrors and geometric shapes including a hemisphere, a kinked waveguide, and a tapered waveguide. While total link performance is dependent on additional factors, we have observed net transmission of photons with the tapered link as low as 0.04%. Our optical tests have been performed with a surrogate source that operates at 625 nm and mimics the angular distribution of light emitted from the cooling element of the Los Alamos solid state optical refrigerator. We have confirmed the optical performance of our various link geometries with computer simulations using CODE V optical modeling software. In addition we have used the thermal modeling tool in COMSOL MULTIPHYSICS to investigate other heating factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a nonabsorptive dielectric trapping mirror, the three dominant heating factors are (1) absorption of fluoresced photons transmitted through the thermal link, (2) blackbody radiation from the surrounding environment, and (3) conductive heat transfer through mechanical supports. Modeling results show that a 1 cm3 load can be chilled to 107 K with a 100 W pump laser. We have used the simulated steady-state cooling temperatures of the heat load to compare link designs and system configurations.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.79.Bh Lenses, prisms and mirrors
42.79.Gn Optical waveguides and couplers
42.87.-d Optical testing techniques
42.55.Rz Doped-insulator lasers and other solid state lasers
07.05.Tp Computer modeling and simulation

Electronic and optical properties of InGaN quantum dot based light emitters for solid state lighting

Yuh-Renn Wu, Yih-Yin Lin, Hung-Hsun Huang, and Jasprit Singh

J. Appl. Phys. 105, 013117 (2009); http://dx.doi.org/10.1063/1.3065274 (7 pages) | Cited 32 times

Online Publication Date: 15 January 2009

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In this paper, we have made a systematic study of the electronic and optical properties of InGaN based quantum dot light emitters. The valence force field model and 6×6k⋅p method have been applied to study the band structures in InGaN or InN quantum dot devices. Piezoelectric and spontaneous polarization effects are included. A comparison with InGaN quantum wells shows that InGaN quantum dots can provide better electron-hole overlap and reduce radiative lifetime. We also find that variation in dot sizes can lead to emission spectrum that can cover the whole visible light range. For high carrier density injection conditions, a self-consistent method for solving quantum dot devices is applied for better estimation of device performance. Consequences of variations in dot sizes, shapes, and composition have been studied in this paper. The results suggest that InGaN quantum dots would have superior performance in white light emitters.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.72.-g Optical sources and standards

Tuning the Er3+ sensitization by Si nanoparticles in nanostructured as-grown Al2O3 films

S. Núñez-Sánchez, R. Serna, J. García López, A. K. Petford-Long, M. Tanase, and B. Kabius

J. Appl. Phys. 105, 013118 (2009); http://dx.doi.org/10.1063/1.3065520 (5 pages) | Cited 4 times

Online Publication Date: 15 January 2009

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Nanostructured films consisting of single Si nanoparticles (NPs) and Er3+ ions layers separated by nanometer-scale Al2O3 layers of controlled thickness have been prepared in order to tune the energy transfer between Si NPs and Er3+ ions. The amorphous Si NPs with an effective diameter of ∼ 4.5 nm are formed during growth and are able to sensitize the Er3+ ions efficiently with no postannealing treatments. The characteristic distance for energy transfer from Si NPs to Er3+ ions in Al2O3 is found to be in the 1 nm range. It is shown that in the nanostructured films, it is possible to achieve an optimized configuration in which almost all the Er3+ ions have the potential to be excited by the Si NPs. This result stresses the importance of controlling the dopant distribution at the nanoscale to achieve improved device performance.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.sh Impurity distribution
61.43.Dq Amorphous semiconductors, metals, and alloys
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Quenching of He-induced intensity enhancement effect in H and D emission produced by Nd-doped yttrium aluminum garnet laser irradiation on solid targets in low pressure helium gas

Koo Hendrik Kurniawan, Tjung Jie Lie, Maria Margaretha Suliyanti, Marincan Pardede, Syahrun Nur Abdulmadjid, Kiichiro Kagawa, and May On Tjia

J. Appl. Phys. 105, 013301 (2009); http://dx.doi.org/10.1063/1.3058670 (7 pages) | Cited 3 times

Online Publication Date: 6 January 2009

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An experimental study was performed on the N2-induced quenching of He-induced intensity enhancement effect in reduced-pressure plasma emission produced by Nd-YAG irradiation on solid zircaloy and porous fossil samples. The spatial distributions and temporal variations in the emission intensities show pronounced intensity quenching effects on the He I 667.9 nm, H I 656.2 nm, and D I 656.1 nm emission lines in both samples when a tiny amount (5% by volume) of nitrogen was added to helium gas, while leaving the spatial and temporal intensity profiles of the heavier Zr and Ca atoms virtually unaffected. In both cases of different ambient gases, the spatial and temporal variations in the He, H, and D emission intensities exhibit distinct features and changes, which are clearly distinguishable from those observed on the Zr and Ca emission lines, which were mainly produced by the shock-wave induced thermal excitation process. The analysis of these data unambiguously revealed the presence of an additional and distinct “He-assisted” excitation mechanism in the He plasma, which was further suggested to be related to the He metastable excited state. The quenching effect was therefore explained as a consequence of energy depletion of the He metastable excited state triggered by the Penning ionization process induced by the presence of nitrogen. This also explains the relatively insensitive response of the Zr and Ca emission intensity profiles to nitrogen addition despite the increased plasma electron density resulting from the ionization process.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments

Experimental study of femtosecond laser-stimulated electrical discharges in small gaps and surface modifications

J. Chen, D. F. Farson, and S. I. Rokhlin

J. Appl. Phys. 105, 013302 (2009); http://dx.doi.org/10.1063/1.3055361 (8 pages) | Cited 2 times

Online Publication Date: 6 January 2009

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Femtosecond laser-stimulated discharges in nanoscale and microscale gaps between etched nanoprobe tip cathodes and gold film anodes with applied dc potential were experimentally studied to define parameter ranges for their controlled formation and resulting surface modifications. For appropriate values of gap length, applied potential, and laser irradiance, breakdown discharges could be reliably stimulated by femtosecond laser pulses and the mean breakdown field was approximately an order of magnitude smaller than for breakdown without laser stimulation. For 500 nm gaps, discharges were observed for applied potentials as small as 20 V and controllable gold film surface melting was detected for applied potential of 27.5 V. Minor cathode tip ablation could be observed for femtosecond laser pulses that reliably stimulated discharges, suggesting that cathode material played an important role in stimulation of breakdown discharges in nanoscale gaps. Surface melting produced features as small as 60 nm on gold film when discharge current was limited by 1 MΩ series resistor.
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52.80.-s Electric discharges
64.70.dj Melting of specific substances
81.65.Cf Surface cleaning, etching, patterning
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
77.22.Jp Dielectric breakdown and space-charge effects

Effect of a magnetic field in simulating the plume field of an anode layer Hall thruster

Yongjun Choi, Iain D. Boyd, and Michael Keidar

J. Appl. Phys. 105, 013303 (2009); http://dx.doi.org/10.1063/1.3055399 (9 pages)

Online Publication Date: 6 January 2009

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In this study, we present axisymmetric simulations of xenon plasma plume flow fields from a D55 anode layer Hall thruster. A hybrid particle-fluid method is used for the simulations. The magnetic field surrounding the Hall thruster exit is included in the calculation. The plasma properties obtained from a hydrodynamic model are used as boundary conditions for the simulations. The electron properties are calculated using the Boltzmann model and a detailed fluid model, collisions of heavy particle are modeled with the direct simulation Monte Carlo method, and ion transport in the electric field uses the particle-in-cell technique. The accuracy of the simulation is assessed through comparison with various measured data. It is found that a magnetic field significantly affects the profile of the plasma in the detailed model. The plasma has a potential of 80 V at 10 mm from the thruster exit in the case of zero magnetic field, which decreases to 60 V when the magnetic field is included. Results predicted by the detailed model with the magnetic field are found to be in better agreement with experimental data.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.75.Di Ion and plasma propulsion
52.65.Kj Magnetohydrodynamic and fluid equation
52.65.Pp Monte Carlo methods
52.65.Rr Particle-in-cell method
52.65.Ww Hybrid methods

Surface radicals in silane/hydrogen discharges

Peter Horvath and Alan Gallagher

J. Appl. Phys. 105, 013304 (2009); http://dx.doi.org/10.1063/1.3050331 (10 pages) | Cited 6 times

Online Publication Date: 7 January 2009

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Using threshold ionization mass spectrometry, radical densities have been measured at the substrate surface of a radio frequency discharge in silane plus hydrogen vapor. The conditions are 100–300 Pa pressure and a ratio (R) of hydrogen flow/silane flow typical of discharges used to produce large area amorphous (R = 20) and microcrystalline (R = 40) silicon. For comparison, we include measurements in pure-silane vapor. The neutral radicals observed in the mixed gases are H, SiH3, Si2H2, and Si2H5, with decreasing flux in that order. (Si2H4 is also seen in pure silane and SiH2 for R = 20.) The H flux is sufficient for major film etching and restructuring, particularly for R = 40. The ion-bombardment species were also measured, establishing that SiyHn+ (y = 1–3) ion flux is much larger than the Hn+ (n = 1–3) flux. The ion flux provides 15±4% of the total Si flux to the film for R = 20 and 37±10% for R = 40. This is larger than in pure-silane discharges, and it may be very important to film properties due to the impact energy.
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52.80.Pi High-frequency and RF discharges
52.70.Nc Particle measurements

Current drive by helicon waves

Manash Kumar Paul and Dhiraj Bora

J. Appl. Phys. 105, 013305 (2009); http://dx.doi.org/10.1063/1.3041637 (9 pages) | Cited 2 times

Online Publication Date: 7 January 2009

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Helicity in the dynamo field components of helicon wave is examined during the novel study of wave induced helicity current drive. Strong poloidal asymmetry in the wave magnetic field components is observed during helicon discharges formed in a toroidal vacuum chamber of small aspect ratio. High frequency regime is chosen to increase the phase velocity of helicon waves which in turn minimizes the resonant wave-particle interactions and enhances the contribution of the nonresonant current drive mechanisms. Owing to the strong poloidal asymmetry in the wave magnetic field structures, plasma current is driven mostly by the dynamo-electric-field, which arise due to the wave helicity injection by helicon waves. Small, yet finite contribution from the suppressed wave-particle resonance cannot be ruled out in the operational regime examined. A brief discussion on the parametric dependence of plasma current along with numerical estimations of nonresonant components is presented. A close agreement between the numerical estimation and measured plasma current magnitude is obtained during the present investigation.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Wq Current drive; helicity injection

Spectroscopic study of hydrogen Balmer lines in a microwave-induced discharge

S. Jovićević, N. Sakan, M. Ivković, and N. Konjević

J. Appl. Phys. 105, 013306 (2009); http://dx.doi.org/10.1063/1.3046587 (6 pages) | Cited 4 times

Online Publication Date: 9 January 2009

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We present the results of a spectroscopic study of hydrogen Balmer line shapes and intensities in a microwave-induced discharge generated in an Evenson resonant cavity at 2.45 GHz in pure hydrogen and hydrogen-argon and hydrogen-helium gas mixtures. The Balmer line shapes do not show signs of excessive Doppler broadening. The discharge parameters—Doppler temperature (980 K), electron excitation temperature (1460–1790 K), and electron density of about 8×1011 cm−3—point to a typical microwave-induced discharge.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
32.30.Jc Visible and ultraviolet spectra
32.70.Jz Line shapes, widths, and shifts
32.70.-n Intensities and shapes of atomic spectral lines
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources
52.75.Hn Plasma torches
84.40.-x Radiowave and microwave (including millimeter wave) technology

Stimulated Brillouin scattering of laser radiation in a piezoelectric semiconductor: Quantum effect

Ch. Uzma, I. Zeba, H. A. Shah, and M. Salimullah

J. Appl. Phys. 105, 013307 (2009); http://dx.doi.org/10.1063/1.3050340 (5 pages) | Cited 2 times

Online Publication Date: 9 January 2009

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Using quantum-hydrodynamic model, the phenomenon of the stimulated Brillouin scattering of a laser radiation in an unmagnetized piezoelectric semiconductor has been examined in detail. It is noticed that the Bohm potential in the electron dynamics of the semiconductor plasma enhances drastically the growth rate of the stimulated Brillouin scattering at higher values of the electron number density of the semiconductor plasma and the wave number of the electron-acoustic wave in the semiconductor.
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52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
03.65.-w Quantum mechanics
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
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