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30 Apr 2012

Volume 100, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 181901 (2012); http://dx.doi.org/10.1063/1.4705414 (4 pages)

Etienne Brasselet, Arnaud Royon, and Lionel Canioni
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Thermal nonlinearity in silicon microcylindrical resonators

Natasha Vukovic, Noel Healy, Priyanth Mehta, Todd D. Day, Pier J. A. Sazio, John V. Badding, and Anna C. Peacock

Appl. Phys. Lett. 100, 181101 (2012); http://dx.doi.org/10.1063/1.4709424 (4 pages)

Online Publication Date: 30 April 2012

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We explore the thermally induced nonlinearity in hydrogenated amorphous silicon microcylindrical resonators that are fabricated from the silicon optical fiber platform. In particular, we use a pump-probe technique to experimentally demonstrate thermally induced optical modulation and determine the response time. Through characterization of the thermal properties and the associated resonance wavelength shifts, we will show that it is possible to infer the material absorption coefficient for a range of whispering gallery mode resonators.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.40.Az Waveguides, transmission lines, striplines
07.10.Cm Micromechanical devices and systems

Vertically integrated double-layer on-chip silicon membranes for 1-to-12 waveguide fanouts

Yang Zhang, Amir Hosseini, Jaehyun Ahn, David N. Kwong, Babak Fallahazad, Emanuel Tutuc, and Ray T. Chen

Appl. Phys. Lett. 100, 181102 (2012); http://dx.doi.org/10.1063/1.4709489 (4 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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We present an on-chip vertically integrated three-dimensional photonic integrated circuit. Double-layer 1 × 12 multimode interference (MMI) couplers are fabricated on silicon membranes using double-bonded silicon-on-insulator wafers. The input light is transverse electric polarized, operating at 1550 nm. The top layer MMI coupler has an excess loss of 0.48 dB and an uniformity within 1.1 dB. The bottom layer MMI coupler has an excess loss of 2.9 dB and an uniformity within 1.7 dB.
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42.82.Et Waveguides, couplers, and arrays

Two-color GaN/AlGaN quantum cascade detector at short infrared wavelengths of 1 and 1.7 μm

S. Sakr, E. Giraud, A. Dussaigne, M. Tchernycheva, N. Grandjean, and F. H. Julien

Appl. Phys. Lett. 100, 181103 (2012); http://dx.doi.org/10.1063/1.4707904 (3 pages) | Cited 5 times

Online Publication Date: 30 April 2012

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A two-color GaN-based quantum cascade detector is demonstrated. This photodetector operates simultaneously at a peak wavelength of 1.7 and 1 μm at room temperature without any external voltage. These peaks correspond, respectively, to the e1e2 and e1e3 intersubband absorption of the active GaN quantum well. The extractor has been designed to allow for efficient transfer of electrons from both the e2 and e3 states to the next period. The 1 μm detected wavelength is the shortest value reported for an intersubband semiconductor based detector.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

A normal incident quantum cascade detector enhanced by surface plasmons

Shen-Qiang Zhai, Jun-Qi Liu, Feng-Qi Liu, and Zhan-Guo Wang

Appl. Phys. Lett. 100, 181104 (2012); http://dx.doi.org/10.1063/1.4710523 (4 pages) | Cited 2 times

Online Publication Date: 1 May 2012

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We demonstrate a normal incident quantum cascade detector excited by surface plasmons resonance using an Au two-dimensional hole array integrated on top of the detector absorption region. With normal incidence, the device has a maximal responsivity value of 8.4 mA/W at 160 K and can work up to room temperature with a responsivity of 1.02 mA/W. Compared with the 45° polished edge coupling device, the two-dimensional hole array can lead to quantum efficiency enhancement at most measured temperatures, and at 140 K the quantum efficiency is enhanced most strongly by 69%.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.55.Px Semiconductor lasers; laser diodes

Broadband Purcell effect: Radiative decay engineering with metamaterials

Zubin Jacob, Igor I. Smolyaninov, and Evgenii E. Narimanov

Appl. Phys. Lett. 100, 181105 (2012); http://dx.doi.org/10.1063/1.4710548 (4 pages) | Cited 15 times

Online Publication Date: 1 May 2012

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We show that metamaterials with hyperbolic dispersion support a large number of electromagnetic states that can couple to quantum emitters leading to a broadband Purcell effect. The proposed approach of radiative decay engineering, useful for applications such as single photon sources, fluorescence imaging, biosensing, and single molecule detection, also opens up the possibility of using hyperbolic metamaterials to probe the spontaneous emission properties of atoms and artificial atoms such as quantum dots.
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42.70.-a Optical materials

Magnetic assembly of gold core-shell necklace resonators

Kanna Aoki, Kentaro Furusawa, and Takuo Tanaka

Appl. Phys. Lett. 100, 181106 (2012); http://dx.doi.org/10.1063/1.4706254 (4 pages)

Online Publication Date: 2 May 2012

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Gold core-shell necklace structures are assembled by inducing magnetic moments of gold-coated paramagnetic microspheres and a diamagnetic sphere using an external magnetic field. Sphere numbers in a necklace structure was tuned solely by controlling magnetic permeability of background medium. A necklace structure consisting of evenly spaced metal spheres or disks is known to be a good medium for a plasmonic resonance. Therefore, their optical properties were numerically studied. The electric field enhancement by a factor of 1800 was estimated in the gaps between adjacent spheres at a resonant wavelength. The wavelength-scaling strategies of our structures to visible wavelength are also discussed.
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07.10.Cm Micromechanical devices and systems

Phase matching for surface plasmon enhanced second harmonic generation in a gold grating slab

Ngoc Luong, Cheng-Wen Cheng, Min-Hsiung Shih, and Wan Kuang

Appl. Phys. Lett. 100, 181107 (2012); http://dx.doi.org/10.1063/1.4710546 (3 pages)

Online Publication Date: 2 May 2012

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Surface plasmon enhanced second harmonic generation in gold grating slabs was investigated. The efficiency is analyzed with respect to the phase matching at the fundamental and the second harmonic frequencies. A classical electromagnetic model was developed under the weak nonlinearity approximation and solved by the finite element method. The measured zeroth order transmitted second harmonic intensity was found to be in quantitative agreement with numerical results. It is shown experimentally and numerically that proper phase matching at both frequencies improves the second harmonic efficiency.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Enhancement in light emission efficiency of Si nanocrystal light-emitting diodes by a surface plasmon coupling

Chul Huh, Chel-Jong Choi, Wanjoong Kim, Bong Kyu Kim, Byoung-Jun Park, Eun-Hye Jang, Sang-Hyeob Kim, and Gun Yong Sung

Appl. Phys. Lett. 100, 181108 (2012); http://dx.doi.org/10.1063/1.4711033 (5 pages) | Cited 4 times

Online Publication Date: 2 May 2012

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We report an enhancement in light emission efficiency form Si nanocrystal (NC) light-emitting diodes (LEDs) via surface plasmons (SPs) by employing Au nanoparticles (NPs). Photoluminescence intensity of Si NCs with Au NPs was enhanced by 2 factors of magnitude due to the strong coupling of Si NCs and SP resonance modes of Au NPs. The electrical characteristics of Si NC LED were significantly improved, which was attributed to an increase in an electron injection into the Si NCs due to the formation of inhomogeneous Schottky barrier at the SiC-indium tin oxide interface. Moreover, light output power from the Si NC LED was enhanced by 50% due to both SP coupling and improved electrical properties. The results presented here can provide a very promising way to significantly enhance the performance of Si NC LED.
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85.60.Jb Light-emitting devices

Nonlinear graphene metamaterial

Andrey E. Nikolaenko, Nikitas Papasimakis, Evangelos Atmatzakis, Zhiqiang Luo, Ze Xiang Shen, Francesco De Angelis, Stuart A. Boden, Enzo Di Fabrizio, and Nikolay I. Zheludev

Appl. Phys. Lett. 100, 181109 (2012); http://dx.doi.org/10.1063/1.4711044 (3 pages) | Cited 6 times

Online Publication Date: 3 May 2012

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We demonstrate that the broadband nonlinear optical response of graphene can be resonantly enhanced by more than an order of magnitude through hybridization with a plasmonic metamaterial, while retaining an ultrafast nonlinear response time of ∼ 1 ps. Transmission modulation close to ∼ 1% is seen at a pump fluence of ∼ 30 μJ/cm2 at the wavelength of ∼ 1.6 μm. This approach allows to engineer and enhance graphene’s nonlinearity within a broad wavelength range enabling applications in optical switching, mode-locking, and pulse shaping.
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78.67.Wj Optical properties of graphene
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Partially disordered photonic-crystal thin films for enhanced and robust photovoltaics

Ardavan Oskooi, Pedro A. Favuzzi, Yoshinori Tanaka, Hiroaki Shigeta, Yoichi Kawakami, and Susumu Noda

Appl. Phys. Lett. 100, 181110 (2012); http://dx.doi.org/10.1063/1.4711144 (4 pages) | Cited 6 times

Online Publication Date: 3 May 2012

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We present a general framework for the design of thin-film photovoltaics based on a partially disordered photonic crystal that has both enhanced absorption for light trapping and reduced sensitivity to the angle and polarization of incident radiation. The absorption characteristics of different lattice structures are investigated as an initial periodic structure is gradually perturbed. We find that an optimal amount of disorder controllably introduced into a multi-lattice photonic crystal causes the characteristic narrow-band, resonant peaks to be broadened resulting in a device with enhanced and robust performance ideal for typical operating conditions of photovoltaic applications.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.50.Pz Photoconduction and photovoltaic effects
78.66.Db Elemental semiconductors and insulators
78.40.Fy Semiconductors

Optically recorded tunable microlenses based on dye-doped liquid crystal cells

Liana Lucchetti and Jordanka Tasseva

Appl. Phys. Lett. 100, 181111 (2012); http://dx.doi.org/10.1063/1.4711203 (3 pages)

Online Publication Date: 4 May 2012

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We report on optically recorded microlenses in conventional liquid crystal cells doped with the azo-dye methyl-red. The focal length can be tuned electrically and changed in a wide range with just a small variation of the applied dc voltage. No patterned electrodes, built-in polymeric lens, or patterned molecular reorientation are required.
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42.79.Bh Lenses, prisms and mirrors
42.65.-k Nonlinear optics
42.70.Df Liquid crystals

Tesla coil discharges guided by femtosecond laser filaments in air

Yohann Brelet, Aurélien Houard, Leonid Arantchouk, Benjamin Forestier, Yi Liu, Bernard Prade, Jérôme Carbonnel, Yves-Bernard André, and André Mysyrowicz

Appl. Phys. Lett. 100, 181112 (2012); http://dx.doi.org/10.1063/1.4711208 (3 pages) | Cited 1 time

Online Publication Date: 4 May 2012

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A Tesla coil generator was designed to produce high voltage pulses oscillating at 100 kHz synchronisable with a nanosecond temporal jitter. Using this compact high voltage generator, we demonstrate reproducible meter long discharges in air at a repetition rate of 1 Hz. Triggering and guiding of the discharges are performed in air by femtosecond laser filaments.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
52.50.Dg Plasma sources
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
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Ripple formation on a nickel electrode during a glow discharge in a solution

Genki Saito, Sou Hosokai, Masakatsu Tsubota, and Tomohiro Akiyama

Appl. Phys. Lett. 100, 181601 (2012); http://dx.doi.org/10.1063/1.4709491 (4 pages)

Online Publication Date: 30 April 2012

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We investigated ripple formation on a nickel electrode during a glow discharge in a solution. A nickel wire was partially melted to produce nanoparticles during glow discharge electrolysis. When the electrolysis time was over 30 min, a ripple pattern was formed on the electrode surface, and particle size increased. In this study, we investigated the relationship between the ripple formation and crystal orientation of the electrode. As a result, the ripple patterns were formed on all planes, except (111)- and (100)-oriented planes; their direction was [001].
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82.45.Fk Electrodes
82.45.Hk Electrolysis
82.45.Yz Nanostructured materials in electrochemistry
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing

Band bending and surface defects in β-Ga2O3

T. C. Lovejoy, Renyu Chen, X. Zheng, E. G. Villora, K. Shimamura, H. Yoshikawa, Y. Yamashita, S. Ueda, K. Kobayashi, S. T. Dunham, F. S. Ohuchi, and M. A. Olmstead

Appl. Phys. Lett. 100, 181602 (2012); http://dx.doi.org/10.1063/1.4711014 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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Surface band bending and surface defects on the UV-transparent conducting oxide β-Ga2O3 (100) are studied with hard x-ray photoemission spectroscopy and scanning tunneling microscopy. Highly doped β-Ga2O3 shows flat bands near the surface, while the bands on nominally undoped (but still n-type), air-cleaved β-Ga2O3 are bent upwards by ≳0.5 eV. Negatively charged surface defects are observed on vacuum annealed β-Ga2O3, which also shows upward band bending. Density functional calculations show oxygen vacancies are not likely to be ionized in the bulk, but could be activated by surface band bending. The large band bending may also hinder formation of ohmic contacts.
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81.40.Lm Deformation, plasticity, and creep
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.72.jd Vacancies
62.20.F- Deformation and plasticity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Contactless electroreflectance studies of Fermi level position on c-plane GaN surface grown by molecular beam epitaxy and metalorganic vapor phase epitaxy

R. Kudrawiec, M. Gladysiewicz, L. Janicki, J. Misiewicz, G. Cywinski, C. Chèze, P. Wolny, P. Prystawko, and C. Skierbiszewski

Appl. Phys. Lett. 100, 181603 (2012); http://dx.doi.org/10.1063/1.4707386 (4 pages) | Cited 4 times

Online Publication Date: 2 May 2012

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Contactless electroreflectance (CER) has been applied to study the Fermi-level position on c-plane GaN surface in Van Hoof structures grown by molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). A clear CER resonance followed by strong Franz-Keldysh oscillation (FKO) of various periods was clearly observed for the series of samples of different thicknesses (30, 50, and 70 nm) of undoped GaN layer. The built-in electric field in this layer has been determined from the period of GaN-related FKO. A good agreement between the calculated and measured electric fields has been found for the Fermi-level located ∼0.4 and ∼0.3 eV below the conduction band for the MBE and MOVPE samples, respectively.
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78.20.Jq Electro-optical effects
73.20.At Surface states, band structure, electron density of states
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.20.Nr Semiconductor compounds

Viable thermionic emission from graphene-covered metals

E. Starodub, N. C. Bartelt, and K. F. McCarty

Appl. Phys. Lett. 100, 181604 (2012); http://dx.doi.org/10.1063/1.4711212 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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Thermionic emission from monolayer graphene grown on representative transition metals, Ir and Ru, is characterized by low-energy electron microscopy. Work functions were determined from the temperature dependence of the emission current and from the electron energy spectrum of emitted electrons. The high-temperature work function of the strongly interacting system graphene/Ru(0001) is sufficiently low, 3.3 ± 0.1 eV, to have technological potential for large-area emitters that are spatially uniform, efficient, and chemically inert. The thermionic work functions of the less strongly interacting system graphene/Ir(111) are over 1 eV larger and vary substantially (0.4 eV) between graphene orientations rotated by 30°.
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79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
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Dense arrays of microscopic optical vortex generators from femtosecond direct laser writing of radial birefringence in glass

Etienne Brasselet, Arnaud Royon, and Lionel Canioni

Appl. Phys. Lett. 100, 181901 (2012); http://dx.doi.org/10.1063/1.4705414 (4 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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We report on the generation of permanent singular light mode converters at the microscale using femtosecond direct laser writing in photo-thermo-refractive glass. It relies on the irreversible light-induced radial birefringence in the bulk of the material. The ability of such birefringence pattern to convert the spin angular momentum of light into orbital optical angular momentum is exploited to demonstrate the production of large arrays of optical vortex generators with surface densities up to 104cm-2.
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42.62.-b Laser applications
42.70.Ce Glasses, quartz
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.20.Fm Birefringence
78.20.nb Photothermal effects

Electron transport in suspended semiconductor structures with two-dimensional electron gas

A. G. Pogosov, M. V. Budantsev, E. Yu. Zhdanov, D. A. Pokhabov, A. K. Bakarov, and A. I. Toropov

Appl. Phys. Lett. 100, 181902 (2012); http://dx.doi.org/10.1063/1.4709485 (3 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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We study electron transport in suspended semiconductor microstructures fabricated from AlAs/GaAs membranes containing a high mobility two-dimensional electron gas. In quantizing magnetic fields, a reflection of edge current channels from the border of suspended area is observed resulting in the absence of vanishing magnetoresistance in the quantum Hall effect (QHE) regime. Relocation of this border out of the Hall bar revives the QHE. We have also found that the critical current of the breakdown of QHE in suspended samples is three times lower than in non-suspended samples due to the peculiarity of heat transport in the membranes.
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73.63.-b Electronic transport in nanoscale materials and structures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance

Screened hybrid density functional study on Sr2Nb2O7 for visible light photocatalysis

J. Nisar, B. Pathak, and R. Ahuja

Appl. Phys. Lett. 100, 181903 (2012); http://dx.doi.org/10.1063/1.4709486 (5 pages) | Cited 1 time

Online Publication Date: 30 April 2012

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The electronic structure of pure Sr2Nb2O7 and its electronic band position are being aligned with respect to the water oxidation/reduction potential level using hybrid functional (HSE06) theory. The experimental band gap (3.90 eV) of pure Sr2Nb2O7 can be reproduced (3.92 eV) using this level of theory. The cationic-anionic co-doping (Mo-N) in layered perovskite Sr2Nb2O7 structure reduces the band gap significantly, and its electronic band position is excellent for the visible-light photocatalysis. The respective cationic and anionic mono-doped systems create an occupied or unoccupied impurity states in the band gap, which can reduce the efficiency of the photocatalysis.
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71.20.Ps Other inorganic compounds
61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Stress-relaxed growth of n-GaN epilayers

J. H. Ryu, Y. S. Katharria, H. Y. Kim, H. K. Kim, K. B. Ko, N. Han, J. H. Kang, Y. J. Park, E.-K. Suh, and C.-H. Hong

Appl. Phys. Lett. 100, 181904 (2012); http://dx.doi.org/10.1063/1.4710561 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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A significant stress-relaxation was observed in GaN epilayers by integrating a heavily Si-doped GaN (n+-GaN) sacrificial layer in the undoped GaN templates grown on sapphire substrates by metal-organic chemical vapor deposition. Selective GaN growth and electrochemical etching were exploited to achieve embedded air-gaps. Stress-relaxation and its local variations were probed by Raman mapping of high-frequency transverse-optical E2 (high) phonon mode of GaN. Enhanced In incorporation and improved light emission were observed in InGaN/GaN multi-quantum well visible light emitting diode structures fabricated on stress-relaxed GaN-epilayers with embedded air-gaps. Relevant sources for stress reduction and improved optical emission have been discussed.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors

The influence of silicon nanoclusters on the optical properties of a-SiNx samples: A theoretical study

Roberto Guerra, Mariella Ippolito, Simone Meloni, and Stefano Ossicini

Appl. Phys. Lett. 100, 181905 (2012); http://dx.doi.org/10.1063/1.4711017 (4 pages) | Cited 3 times

Online Publication Date: 2 May 2012

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By means of ab-initio calculations, we investigate the optical properties of pure a-SiNx samples, with x∈[0.4,1.8], and samples embedding silicon nanoclusters (NCs) of diameter 0.5 ≤ d ≤ 1.0 nm. In the pure samples, the optical absorption gap and the radiative recombination rate vary according to the concentration of Si-N bonds. In the presence of NCs, the radiative rate of the samples is barely affected, indicating that the intense photoluminescence of experimental samples is mostly due to the matrix itself rather than to the NCs. Besides, we evidence an important role of Si-N-Si bonds at the NC/matrix interface in the observed photoluminescence trend.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Dynamic observations of dislocation behavior in SrTiO3 by in situ nanoindentation in a transmission electron microscope

Shun Kondo, Naoya Shibata, Tasuku Mitsuma, Eita Tochigi, and Yuichi Ikuhara

Appl. Phys. Lett. 100, 181906 (2012); http://dx.doi.org/10.1063/1.4710558 (4 pages) | Cited 1 time

Online Publication Date: 3 May 2012

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The plastic deformation process of a SrTiO3 single crystal has been dynamically and microscopically observed by in situ nanoindentation in a transmission electron microscope. The plastic deformation of SrTiO3 was found to proceed by dislocation slips even at room temperatures under the present experimental condition, and the dynamic behavior of dislocations such as nucleation, propagation, and annihilation have been clearly captured. The detailed dislocation analyses revealed that the activated slip system is 〈110〉{1math0} type, which is consistent with the results of macroscopic deformation experiments reported so far. The mechanisms of dislocation behavior are discussed based on the experimentally obtained results.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Light-induced off-diagonal thermoelectric effect via indirect optical heating of incline-oriented CaxCoO2 thin film

Kouhei Takahashi, Tsutomu Kanno, Akihiro Sakai, Hideaki Adachi, and Yuka Yamada

Appl. Phys. Lett. 100, 181907 (2012); http://dx.doi.org/10.1063/1.4711020 (4 pages)

Online Publication Date: 3 May 2012

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Light-induced off-diagonal thermoelectric (ODTE) effect has been investigated in CaxCoO2 thin film coupled with a gold black light absorption layer. Increased light absorption at the gold black layer resulted in considerable enhancement of the steady-state thermoelectric voltage from the CaxCoO2 film upon continuous light heating. However, we found that the indirect optical heating process highly deteriorates the input thermal energy pulse in time-domain, and leads to significant reduction in the transient voltage generated upon pulsed light heating. The result manifests the importance of adequate thermal design of absorption layers for fabrication of light detection devices based on the ODTE effect.
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73.50.Lw Thermoelectric effects
78.66.Nk Insulators
78.20.nd Thermophotonic effects
68.60.Dv Thermal stability; thermal effects
72.20.Pa Thermoelectric and thermomagnetic effects

A liftoff process of GaN layers and devices through nanoporous transformation

Yu Zhang, Benjamin Leung, and Jung Han

Appl. Phys. Lett. 100, 181908 (2012); http://dx.doi.org/10.1063/1.4711218 (4 pages) | Cited 1 time

Online Publication Date: 4 May 2012

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A process to slice and separate GaN device layers for vertical light emitting diodes (LEDs) is presented through a developed electrochemical anodization process to create nanoporous (NP) GaN of designed porosity profiles. The NP GaN serves dual purposes of supporting subsequent overgrowth of LED structures while undergoing, during growth, shape transformation into a largely voided morphology. It is shown that this voided region decreases the lateral fracture resistance and enables large-area separation of the LED structures after appropriate wafer bonding. The separated LED layers are shown to have comparable material quality before and after the liftoff process. Blue emitting GaN LEDs are transferred to silicon substrates with vertical configuration by this unique process.
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81.65.-b Surface treatments
81.05.Ea III-V semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
85.60.Jb Light-emitting devices
61.43.Gt Powders, porous materials
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Enforced c-axis growth of ZnO epitaxial chemical vapor deposition films on a-plane sapphire

Yong Xie, Manfred Madel, Thilo Zoberbier, Anton Reiser, Wanqi Jie, Benjamin Neuschl, Johannes Biskupek, Ute Kaiser, Martin Feneberg, and Klaus Thonke

Appl. Phys. Lett. 100, 182101 (2012); http://dx.doi.org/10.1063/1.4709430 (4 pages) | Cited 2 times

Online Publication Date: 30 April 2012

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To enforce perfect c-axis orientation of ZnO epitaxial films grown on a-plane sapphire, we first grew perfectly perpendicularly aligned (i.e., c axis oriented) ZnO nanopillars on such sapphire substrates, and then over-grew these by a closed epitaxial film using a modified chemical vapor deposition process at atmospheric pressure. X-ray diffraction and low temperature photoluminescence measurements confirm the desired epitaxial relationship and very high crystalline quality. This growth scheme is an efficient method to suppress dislocations and polycrystalline growth of ZnO and could work equally well for other heteroepitaxial epilayer/substrate systems.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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