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15 Jul 2011

Volume 110, Issue 2, Articles (02xxxx)

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J. Appl. Phys. 110, 021101 (2011); http://dx.doi.org/10.1063/1.3583536 (14 pages)

Farzan A. Ghavanini, Peter Enoksson, Stefan Bengtsson, and Per Lundgren

Vertically aligned carbon based varactors

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back to top Lasers, Optics, and Optoelectronics

Modular PbSrS/PbS mid-infrared vertical external cavity surface emitting laser on Si

A. Khiar, M. Rahim, M. Fill, F. Felder, H. Zogg, D. Cao, S. Kobayashi, T. Yokoyama, and A. Ishida

J. Appl. Phys. 110, 023101 (2011); http://dx.doi.org/10.1063/1.3610407 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2011

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A mid-infrared vertical external cavity surface emitting laser (VECSEL) based on undoped PbS is described herein. A 200 nm-thick PbS active layer embedded between PbSrS cladding layers forms a double heterostructure. The layers are grown on a lattice and thermal expansion mismatched Si-substrate. The substrate is placed onto a flat bottom Bragg mirror again grown on a Si substrate, and the VECSEL is completed with a curved top mirror. Pumping is done optically with a 1.55 μm laser diode. This leads to an extremely simple modular fabrication process. Lasing wavelengths range from 3–3.8 μm at 100–260 K heat sink temperature. The lowest threshold power is ∼210 mWp and highest output power is ∼250 mWp. The influence of the different recombination mechanism as well as free carrier absorption on the threshold power is modeled.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.72.Ai Infrared sources

Three dimensional optical modeling of amorphous silicon thin film solar cells using the finite-difference time-domain method including real randomly surface topographies

Jürgen Lacombe, Oleg Sergeev, Kambulakwao Chakanga, Karsten von Maydell, and Carsten Agert

J. Appl. Phys. 110, 023102 (2011); http://dx.doi.org/10.1063/1.3610516 (6 pages) | Cited 2 times

Online Publication Date: 19 July 2011

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In this paper, modeling of light propagation in silicon thin film solar cells without using any fitting parameter is presented. The aim is to create a realistic view of the light trapping effects and of the resulting optical generation rate in the absorbing semiconductor layers. The focus is on real three dimensional systems. Our software Sentaurus tcad, developed by Synopsys, has the ability to import real topography measurements and to model the light propagation using the finite-difference time-domain method. To verify the simulation, we compared the measured and simulated angular distribution functions of a glass/SnO2:F transparent conducting oxide system for different wavelengths. The optical generation rate of charge carriers in amorphous silicon thin film solar cells including rough interfaces is calculated. The distribution of the optical generation rate is correlated with the shape of the interface, and the external quantum efficiencies are calculated and compared to experimental data.
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88.40.H- Solar cells (photovoltaics)
88.40.jj Silicon solar cells
02.70.Bf Finite-difference methods

Polarization sensitive near-complete reflection from photonic crystal slab in centered rectangular lattice

Simon Padron, Kris Ohlinger, Karen Lozano, and Yuankun Lin

J. Appl. Phys. 110, 023103 (2011); http://dx.doi.org/10.1063/1.3610518 (4 pages)

Online Publication Date: 19 July 2011

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In this study, reflective properties have been systematically calculated for two-dimensional photonic crystal slabs in centered rectangular lattices with elliptical patterns for transverse electric polarization along perpendicular x- and y-directions. The slab structures can be geometrically optimized for a near-complete reflection over a broad wavelength range. The reflection from the photonic crystal slabs is polarization selective, allowing a complete reflection for one polarization and complete transmission for the other polarization, which could be useful for a laser cavity mirror without using Brewster windows. The dependence of the reflection on the slab thickness and the structural parameters demonstrates the effect of guided-mode resonances on the reflection.
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42.70.Qs Photonic bandgap materials
42.25.Gy Edge and boundary effects; reflection and refraction
42.25.Ja Polarization

Spectroscopic analysis of Eu3+ in single-crystal hexagonal phase AlN

John B. Gruber, Ulrich Vetter, Takashi Taniguchi, Gary W. Burdick, Hans Hofsäss, Sreerenjini Chandra, and Dhiraj K. Sardar

J. Appl. Phys. 110, 023104 (2011); http://dx.doi.org/10.1063/1.3609076 (7 pages)

Online Publication Date: 21 July 2011

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A detailed spectroscopic analysis of the crystal-field splitting of the energy levels of Eu3+(4f6) in single crystals of hexagonal phase aluminum nitride is reported based on assignments made to the high-resolution cathodoluminescence spectra observed between 500 nm and 750 nm obtained at 11 K and room temperature. Single crystals doped with trivalent europium were grown by high pressure, high temperature technology, and the crystal structure was confirmed by x ray diffraction methods to be the hexagonal phase. The Eu3+ ions substitute for Al3+ ions in sites of C3v symmetry during crystal growth. More than 97% of the observed spectra are attributed to Eu3+ in the majority site. The spectra are identified as transitions from the excited 5D0 and 5D1multiplets of Eu3+ to the ground-state multiplets 7F0, 7F1, 7F2, 7F3,7F4, 7F5, and 7F6 split by the crystal field into energy (Stark) levels. A parameterized Hamiltonian defined to operate within the 4f6 electronic configuration of Eu3+ was used to model the experimental Stark levels and their symmetry assignments or irreducible representations (irreps). The crystal-field parameters were determined through use of a Monte Carlo method in which the six Bqk were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting, which involved 20 Stark levels and their irreps from 5D1, 5D0, and 7F0–4, resulted in a rms deviation of 6.7 cm−1. The predicted splitting of the 7F5 and 7F6 multiplets was used to assign the experimental splitting for these manifolds since the spectra involved are weak and broad, precluding detailed Stark-level assignments.
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78.60.Hk Cathodoluminescence, ionoluminescence
62.50.-p High-pressure effects in solids and liquids
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.40.Fy Semiconductors
61.66.-f Structure of specific crystalline solids
71.70.Ch Crystal and ligand fields

Study of Si-based three-dimensional photonic crystals infiltrated with liquid crystal within a one-dimensional effective model

L. Chang, C.-Z. Liao, and G. Y. Wu

J. Appl. Phys. 110, 023105 (2011); http://dx.doi.org/10.1063/1.3603008 (11 pages)

Online Publication Date: 25 July 2011

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In this work, we study Si-based three-dimensional photonic crystals infiltrated with liquid crystal (LC), within a one-dimensional effective medium model. Two specific systems of diamond crystal structure compatible with the mature Si technology are considered, namely, (i) diamond-1 which is composed of LC spheres embedded in the Si background, and (ii) diamond-2 which is the inverse of the foregoing structure, with Si spheres immersed in the LC background. For each system, the study is carried out with the LC being in the isotropic/nematic phase. The one-dimensional effective medium model employed in the study is an improved version of the conventional mean field theory (MFT). While retaining partially the typical advantage of MFT, e.g., physical transparency, analytical capability, and computational efficiency, it goes beyond the conventional MFT by taking into account the modulation of dielectric constant in the direction of wave propagation. As such, it improves greatly the poor numerical accuracy inherent in the MFT. We find a partial gap between the 2nd and 3rd bands, with the gap-to-midgap ratio being a few percents. Moreover, the edge of partial gap may be shifted by about 1% (in relative unit) when optical, thermal, or electrical means are applied to alter the phase of LC or rotate the axis of nematic molecules.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Thermo-optical control of dielectric loaded plasmonic racetrack resonators

K. Hassan, J.-C. Weeber, L. Markey, and A. Dereux

J. Appl. Phys. 110, 023106 (2011); http://dx.doi.org/10.1063/1.3609081 (7 pages) | Cited 3 times

Online Publication Date: 25 July 2011

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The optical properties of racetrack shaped dielectric loaded surface plasmon polariton resonators are studied experimentally for various radius, interaction lengths, and separation gaps between the resonator and the bus waveguide. Using radiation leakage microscopy, their power transmission spectra is recorded over the telecom frequency range and modeled by a notch filter made of a lossy bus waveguide coupled to a lossy resonator. For a typical separation gap around 250 nm, the optimum critical coupling condition is determined by a radius of 6 μm and an interaction length of 2.5 μm. Extinction ratios of the order of -30 dB are reported for resonators featuring quality factors that are found to be of the order of 110. The static thermo-optical control of such racetrack resonators produces a blueshift of the resonance frequency that can be as large as 4.5 nm for a temperature increase of 75 K. Extinction ratio of the order of 9 dB can be achieved between hot and cold states.
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84.40.Az Waveguides, transmission lines, striplines
84.40.Dc Microwave circuits
84.30.Vn Filters

Near infrared image sensor with integrated germanium photodiodes.

R. Kaufmann, G. Isella, A. Sanchez-Amores, S. Neukom, A. Neels, L. Neumann, A. Brenzikofer, A. Dommann, C. Urban, and H. von Känel

J. Appl. Phys. 110, 023107 (2011); http://dx.doi.org/10.1063/1.3608245 (6 pages) | Cited 1 time

Online Publication Date: 26 July 2011

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A near-infrared image sensor with monolithically integrated Ge photodiodes is demonstrated. The technology for the integration of the Ge photodiodes into the CMOS process is outlined, and the measurement results of test-diodes and the full imager are discussed in detail. The heterojunction-photodiodes show a quantum efficiency of about 30% up to a wavelength of 1500 nm. A tensile strain of 0.17% was measured in the epitaxial Ge layer, which is in good agreement with the optically measured direct bandgap absorption edge of 1580 nm. The image sensor can be operated at room temperature or with moderate cooling.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices

Fabrication and characterization of microlens arrays on soda-lime glass using a combination of laser direct-write and thermal reflow techniques

Daniel Nieto, Justo Arines, Carlos Gomez-Reino, Gerard M. O’Connor, and M. Teresa Flores-Arias

J. Appl. Phys. 110, 023108 (2011); http://dx.doi.org/10.1063/1.3609085 (9 pages) | Cited 1 time

Online Publication Date: 26 July 2011

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We describe a hybrid technique for fabricating microlens arrays on soda-lime glass substrates composed by a direct-laser write and a post thermal treatment. In particular we use a nanosecond Q-Switch Nd: YVO4 laser and a mufla Heraeus furnace working in the range of 620 °C−670 °C. An improvement in the quality of the microlens arrays were obtained as temperature increases, reducing their optical aberrations, surface roughness and increasing their resemblance. In particular at 670 °C we obtain high quality microlens array with diameter 47.89 ± 6.65 μm; focal length 510 ± 10 μm; focal spot size 2.82 ± 0.02 μm; a root mean square of the total aberration λ/28 ± λ/77, strehl ratio 0.9475 ± 0.0352 and depth of focus 16.438 ± 5.762 μm. Our results show the reliability of the combination of the Laser-direct writing technique with thermal treatment for fabricating high quality microlens arrays.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.62.-b Laser applications

On- and off-axis second harmonic generation from an array of gold metallic nanocylinders

Ch. Awada, F. Kessi, Ch. Jonin, P. M. Adam, S. Kostcheev, R. Bachelot, P. Royer, I. Russier-Antoine, E. Benichou, G. Bachelier, and P. F. Brevet

J. Appl. Phys. 110, 023109 (2011); http://dx.doi.org/10.1063/1.3603007 (6 pages) | Cited 2 times

Online Publication Date: 27 July 2011

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The optical second harmonic (SH) response from gold metallic nanocylinders with diameters of 80 and 120 nm arranged in hexagonal arrays has been determined as a function of the input fundamental polarization angle for the on- and off-axis transmission geometries and crossed output polarization configurations. For the on-axis transmission geometry, the nonlinear response of the nanocylinders is shown to be mainly incoherent, of pure electric dipole nature and arising from the breaking of the centrosymmetric shape of the body of the cylinders in a plane parallel to the substrate surface. Small angle off-axis experiments however show that the coherent contribution to the nonlinear response is size dependent suggesting that, besides the out-of-plane nonlinearity, retardation effects may also play a nonnegligible role.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.46.-w Structure of nanoscale materials

Positive ion emission from oxidized aluminum during ultraviolet excimer laser irradiation

Enamul Khan, S. C. Langford, and J. T. Dickinson

J. Appl. Phys. 110, 023110 (2011); http://dx.doi.org/10.1063/1.3608152 (15 pages) | Cited 1 time

Online Publication Date: 27 July 2011

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We report quadrupole mass-selected time-of-flight measurements of positive ions from oxidized aluminum metal (and for comparison, single-crystal sapphire) during pulsed excimer laser irradiation at 193 and 248 nm. This work focuses on laser fluences well below onset of rapid etching or optical breakdown. By far the most intense emissions are due to Al+. On previously unexposed material, the ion kinetic energies are initially well above the photon energy, consistent with the ejection of Al+ sorbed at surface electron traps. During prolonged irradiation, the emission intensities and kinetic energies gradually fall. Emission from patches of oxide would account for previous reports of laser-induced Al+ emission from metallic aluminum surfaces cleaned by ion etching if patches of thin oxide were to survive the etching treatment.
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81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
61.82.Bg Metals and alloys
81.65.Mq Oxidation
77.22.Jp Dielectric breakdown and space-charge effects

High effective terahertz radiation from semi-insulating-GaAs photoconductive antennas with ohmic contact electrodes

Wei Shi (施卫), Lei Hou (侯磊), and Xinmei Wang (王馨梅)

J. Appl. Phys. 110, 023111 (2011); http://dx.doi.org/10.1063/1.3611397 (5 pages)

Online Publication Date: 28 July 2011

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Terahertz (THz) radiation efficiency of a photoconductive antenna with Schottky contact electrodes is low because the electrical field is limited to a narrow region close to the anode. However, the electrical field in the gap of an antenna with ohmic contact electrodes is more uniform, which contributes to improving THz generation efficiency. In this paper, the semi-insulating (SI)-GaAs antennas with ohmic contact electrodes and SI-GaAs antennas with Schottky contact electrodes were fabricated by using AuGeNi alloy electrodes and Ti/Au electrodes, respectively. The voltage-ampere characteristic and the distribution of electrical field of the two kinds of antennas were tested. At the same condition, the THz intensity from the antenna with ohmic contact electrodes was 3-8 times higher than that from the antenna with Schottky contact electrodes, and the larger gap antennas with ohmic contact electrodes have higher optical and electrical energy to THz intensity conversion efficiency.
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84.40.Ba Antennas: theory, components and accessories
85.60.-q Optoelectronic devices
84.32.Dd Connectors, relays, and switches
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