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7 Jun 2010

Volume 96, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages)

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi
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Modeling of flexoelectric effect on capacitor-voltage and memory window of metal-ferroelectric-insulator-silicon capacitor

Y. Q. Chen, X. J. Zheng, and W. Li

Appl. Phys. Lett. 96, 233501 (2010); http://dx.doi.org/10.1063/1.3446890 (3 pages)

Online Publication Date: 7 June 2010

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The flexoelectric effect on electrical behaviors of metal-ferroelectric-insulator-silicon (MFIS) capacitor was investigated by considering stress gradient in Landau–Khalatnikov theory. In the presence of flexoelectric coupling, the compressive stress shifts capacitor-voltage (C-V) loop of MFIS capacitor to the negative voltage axis and enlarges memory window, however, the tensile stress shifts C-V loop to the positive voltage axis and compresses memory window. The magnitudes of stress, flexoelectric coefficient, and characteristic length of stress distribution have a significant influence on C-V characteristic and memory window of MFIS capacitor. The results show stress gradient should be avoided to prevent failure of MFIS capacitor.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.65.-j Piezoelectricity and electromechanical effects

Frequency dependent rotation and translation of nanowires in liquid environment

Marcin Marczak, Djamila Hourlier, Thierry Mélin, Leszek Adamowicz, and Heinrich Diesinger

Appl. Phys. Lett. 96, 233502 (2010); http://dx.doi.org/10.1063/1.3430738 (3 pages)

Online Publication Date: 7 June 2010

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In this paper, an approach of aligning and handling silicon nanowires in liquid environment on the large scale is presented. Traveling dielectrophoresis was used to simultaneously pump a weakly ionic nanowire suspension and to rotate nanowires in a plane perpendicular to the electrodes. The pumping force on the solution was maximized by monitoring the cell impedance using impedance spectroscopy and by matching the frequency of the supply voltage to the impedance crossover. At frequencies above or below impedance crossover, trapping or rotation of nanowires was observed which is explained by means of a competition between stationary and drag forces.
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82.45.-h Electrochemistry and electrophoresis
47.65.-d Magnetohydrodynamics and electrohydrodynamics

An infrared invisibility cloak composed of glass

Elena Semouchkina, Douglas H. Werner, George B. Semouchkin, and Carlo Pantano

Appl. Phys. Lett. 96, 233503 (2010); http://dx.doi.org/10.1063/1.3447794 (3 pages) | Cited 6 times

Online Publication Date: 7 June 2010

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We propose to implement a nonmetallic low-loss cloak for the infrared range from identical chalcogenide glass resonators. Based on transformation optics for cylindrical objects, our approach does not require metamaterial response to be homogeneous and accounts for the discrete nature of elementary responses governed by resonator shape, illumination angle, and inter-resonator coupling. Air fractions are employed to obtain the desired distribution of the cloak effective parameters. The effect of cloaking is verified by full-wave simulations of the true multiresonator structure. The feasibility of cloak fabrication is demonstrated by prototyping glass grating structures with the dimensions characteristic for the cloak resonators.
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42.70.-a Optical materials
42.79.-e Optical elements, devices, and systems
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
42.79.Dj Gratings

Electrode oxygen-affinity influence on voltage nonlinearities in high-k metal-insulator-metal capacitors

C. Vallée, P. Gonon, C. Jorel, and F. El Kamel

Appl. Phys. Lett. 96, 233504 (2010); http://dx.doi.org/10.1063/1.3447795 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2010

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This work highlights the influence of the oxygen affinity of the metal electrodes used in high-k metal-insulator-metal capacitors. Several metallic electrodes are tested in order to investigate the role of the metal work function, and the role of the electrode oxygen-affinity in nonlinear behavior of HfO2 and BaTiO3 capacitors. It is shown that the magnitude of the quadratic coefficient of nonlinearity is better explained by the electrode oxygen-affinity rather than by its work function. It is thought that electrode oxidation increases the number of oxygen vacancies at the electrode/dielectric interface, and so increases the magnitude of nonlinearity.
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85.30.Tv Field effect devices
84.32.Tt Capacitors

Collimation of horizontally polarized shear waves by means of ridge grating supported Love modes

J. Christensen, L. Martín-Moreno, and F. J. García-Vidal

Appl. Phys. Lett. 96, 233505 (2010); http://dx.doi.org/10.1063/1.3447929 (3 pages) | Cited 1 time

Online Publication Date: 7 June 2010

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In this paper a theoretical study on transmission phenomena of horizontally polarized shear waves propagating through a subwavelength solid probe surrounded by ridges is presented. In this context, the resonant components responsible for enhanced transmission and elastic beaming are identified as Fabry–Perot resonances inside the probe, and ridge induced Love waves. Apart from the fundamental interest, it is envisaged that the ability to enhance elastic vibrations through subwavelength channels and to focus the emerged field, will give rise to improved ultrasonic devices for sensing and testing applications.
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46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
42.79.Dj Gratings

Metal-oxide-semiconductor tunneling photodiodes with enhanced deep depletion at edge by high-k material

Jen-Yuan Cheng, Hui-Ting Lu, and Jenn-Gwo Hwu

Appl. Phys. Lett. 96, 233506 (2010); http://dx.doi.org/10.1063/1.3449128 (3 pages) | Cited 3 times

Online Publication Date: 7 June 2010

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Metal-oxide-semiconductor (MOS) photodetector with the high-k material enhanced deep depletion at edge was demonstrated. The mechanism of saturated substrate injection current in MOS capacitor was adopted. By building HfO2 based devices that with the direct observation of the enhanced edge charge collection efficiency due to fringing field effect in inversion, we are able to show a photodetector with 3000 times (ratio of photocurrent to dark current) improvement in sensitivity than the conventional SiO2 based tunneling photodiodes (approximate 100 times) in the visible.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Accumulation capacitance of narrow band gap metal-oxide-semiconductor capacitors

Erik Lind, Yann-Michel Niquet, Hector Mera, and Lars-Erik Wernersson

Appl. Phys. Lett. 96, 233507 (2010); http://dx.doi.org/10.1063/1.3449559 (3 pages) | Cited 8 times

Online Publication Date: 9 June 2010

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We have investigated the accumulation capacitance-voltage characteristics for capacitors with narrow band gap materials using modeling and experiments. The capacitance for InAs and In0.53Ga0.47As capacitors with a HfO2 oxide layer has been calculated using atomistic tight-binding, effective mass, and semiclassical nonparabolic models. The simulations show that band structure effects have a strong influence on the accumulation capacitance, and are essential for the description of narrow band gap capacitors. The calculated tight binding data compare well with measurements on n-type InAs HfO2 capacitors on (100) and (111)B substrates, highlighting the nonparabolicity as the main origin for the large accumulation capacitance.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
73.40.Ty Semiconductor-insulator-semiconductor structures

Impact of secondary gas-phase reactions on microcrystalline silicon solar cells deposited at high rate

G. Parascandolo, R. Bartlome, G. Bugnon, T. Söderström, B. Strahm, A. Feltrin, and C. Ballif

Appl. Phys. Lett. 96, 233508 (2010); http://dx.doi.org/10.1063/1.3449571 (3 pages) | Cited 4 times

Online Publication Date: 9 June 2010

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The role of secondary gas-phase reactions during plasma-enhanced chemical vapor deposition of microcrystalline silicon is a controversial subject. In this paper, we show that the enhancement of such reactions is associated with the improvement of material properties of absorber layers deposited at high constant rate. We detect powder, a product of secondary gas-phase reactions, via infrared laser absorption spectroscopy, laser light scattering, and optical emission spectroscopy. As the powder formation is increased, we measure a systematic improvement of device performance. This demonstrates that secondary gas-phase reactions are not detrimental to the material quality of microcrystalline silicon deposited at high rate.
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88.40.H- Solar cells (photovoltaics)
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Am Elemental semiconductors and insulators

Evolution of structural defects associated with electrical degradation in AlGaN/GaN high electron mobility transistors

Prashanth Makaram, Jungwoo Joh, Jesús A. del Alamo, Tomás Palacios, and Carl V. Thompson

Appl. Phys. Lett. 96, 233509 (2010); http://dx.doi.org/10.1063/1.3446869 (3 pages) | Cited 21 times

Online Publication Date: 9 June 2010

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We have investigated the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors using atomic force microscopy and scanning electron microscopy after removing the gate metallization by chemical etching. Changes in surface morphology were correlated with degradation in electrical characteristics. Linear grooves formed along the gate edges in the GaN cap layer for all electrically stressed devices. Beyond a critical voltage that corresponds to a sharp increase in the gate leakage current, pits formed on the surface at the gate edges. The density and size of the pits increase with stress voltage and time and correlate with degradation in the drain current and current collapse. We believe that high mechanical stress in the AlGaN layer due to high-voltage stressing is relieved by the formation of these defects which act as paths for gate leakage current and result in electron trapping and degradation in the transport properties of the channel underneath.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
85.40.Ls Metallization, contacts, interconnects; device isolation

Effects of the fluorine plasma treatment on the surface potential and Schottky barrier height of AlxGa1−xN/GaN heterostructures

Sen Huang, Hongwei Chen, and Kevin J. Chen

Appl. Phys. Lett. 96, 233510 (2010); http://dx.doi.org/10.1063/1.3446895 (3 pages) | Cited 6 times

Online Publication Date: 9 June 2010

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The variations in surface potential and the Schottky barrier height ϕB in fluorine-plasma-treated AlxGa1−xN/GaN heterostructures are systematically studied by x-ray photoelectron spectroscopy, providing insights to the mechanisms underlying the strong threshold voltage (Vth) modulation achieved by the F plasma treatment technology. It is found that a large amount of AlF3 appeared on the surface after the treatment, indicating a fluorinated surface. In addition, the surface potential of Al0.25Ga0.75N/GaN heterostructure was increased by ∼ 0.38 eV during the first 60 s of the treatment and then rises slowly with additional treatment. Annealing at 400 °C in N2 ambient for 10 min does not affect the surface potential, but results in quick reduction in AlF3, consistent with the relative poor thermal stability of AlF3 reported in literature. ϕB between Ni and F-plasma-treated Al0.25Ga0.75N surface was extrapolated from the shift in Ga 2p3/2 core-level and exhibits a small increase of 0.20 eV. The enhanced ϕB is much smaller than the positive shift in Vth observed from high electron mobility transistors fabricated with the same treatment conditions, suggesting that the primary factor responsible for the conversion from depletion-mode to enhancement-mode AlxGa1−xN/GaN by F plasma treatment is not the surface modifications but rather the negative fixed charges carried by F ions in AlxGa1−xN/GaN heterostructures.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions
47.85.M- Material processing flows; industrial applications

Frequency-dependence of the acoustic rectifying efficiency of an acoustic diode model

Bin Liang, Xin-ye Zou, Bo Yuan, and Jian-chun Cheng

Appl. Phys. Lett. 96, 233511 (2010); http://dx.doi.org/10.1063/1.3447361 (3 pages) | Cited 7 times

Online Publication Date: 9 June 2010

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For an acoustic diode (AD) model formed by coupling a superlattice with a nonlinear medium, the transmission of acoustic wave is investigated as a function of frequency in a numerical manner. The important phenomenon of rectifying effect of acoustic energy flux is identified in a series of frequency bands whose locations agree exactly with the analytical predictions. Within these frequency bands, the AD can exhibit extremely high rectifying efficiency and strong resistance to “reverse breakdown.” These results are particularly of practical significance for the potential design and application of ADs.
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43.25.Dc Nonlinear acoustics of solids

ZnO nanoparticle surface acoustic wave UV sensor

Venkata Chivukula, Daumantas Ciplys, Michael Shur, and Partha Dutta

Appl. Phys. Lett. 96, 233512 (2010); http://dx.doi.org/10.1063/1.3447932 (3 pages) | Cited 9 times

Online Publication Date: 9 June 2010

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The response to ultraviolet illumination of ZnO nanoparticles deposited on LiNbO3 substrate was investigated using surface acoustic waves (SAWs) in the wide range of UV wavelengths from 280 to 375 nm. Deposition of ZnO nanoparticles caused a SAW transmission loss of 27 dB at 64 MHz due to the acoustoelectric attenuation. Acoustoelectric change in the SAW velocity by 3.78×10−4 under 375 nm illumination led to downshift in transmitted SAW phase by 5.5° at UV power density of 691 μW/cm2. The spectral measurements show the peak response at 345 nm with corresponding sensitivity on the order of 2.8 ppm/(μW/cm2).
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43.58.-e Acoustical measurements and instrumentation
68.35.Iv Acoustical properties
85.60.Gz Photodetectors (including infrared and CCD detectors)
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