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7 Jan 2008

Volume 92, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 92, 011101 (2008); http://dx.doi.org/10.1063/1.2828458 (3 pages)

F. Pedaci, S. Barland, E. Caboche, P. Genevet, M. Giudici, J. R. Tredicce, T. Ackemann, A. J. Scroggie, W. J. Firth, G.-L. Oppo, G. Tissoni, and R. Jäger
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Impact of different defects on the kinetics of negative bias temperature instability of hafnium stacks

J. F. Zhang, C. Z. Zhao, M. H. Chang, M. B. Zahid, A. R. Peaker, S. Hall, G. Groeseneken, L. Pantisano, S. De Gendt, and M. Heyns

Appl. Phys. Lett. 92, 013501 (2008); http://dx.doi.org/10.1063/1.2828697 (3 pages) | Cited 5 times

Online Publication Date: 2 January 2008

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For SiO2 or SiON, negative bias temperature instability (NBTI) generally follows a power law. There is less information available for the NBTI of Hf stacks and it will be studied and compared with that of SiO2 in this work. We found that the power factor for Hf stacks was substantially smaller and the NBTI kinetics has a “flat-then-rise” feature. The flat region at short stress time originates from the preexisting cyclic positive charge in Hf stacks, which is different from the defect responsible for the rising part at longer time and leads to the smaller power factor for Hf stacks.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
72.80.Sk Insulators

Combinatorial study of zinc tin oxide thin-film transistors

M. G. McDowell, R. J. Sanderson, and I. G. Hill

Appl. Phys. Lett. 92, 013502 (2008); http://dx.doi.org/10.1063/1.2828862 (3 pages) | Cited 23 times

Online Publication Date: 2 January 2008

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Groups of thin-film transistors using a zinc tin oxide semiconductor layer have been fabricated via a combinatorial rf sputtering technique. The ZnO:SnO2 ratio of the film varies as a function of position on the sample, from pure ZnO to SnO2, allowing for a study of zinc tin oxide transistor performance as a function of channel stoichiometry. The devices were found to have mobilities ranging from 2 to 12 cm2/V s, with two peaks in mobility in devices at ZnO fractions of 0.80±0.03 and 0.25±0.05, and on/off ratios as high as 107. Transistors composed predominantly of SnO2 were found to exhibit light sensitivity which affected both the on/off ratios and threshold voltages of these devices.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

Erasing characteristics of Cu2O metal-insulator-metal resistive switching memory

A. Chen, S. Haddad, Y. C. Wu, T. N. Fang, S. Kaza, and Z. Lan

Appl. Phys. Lett. 92, 013503 (2008); http://dx.doi.org/10.1063/1.2828864 (3 pages) | Cited 26 times

Online Publication Date: 2 January 2008

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The erasing characteristics of Cu2O metal-insulator-metal resistive switching memory were measured on a 64 Kb memory test array. The erasing yield reaches the maximum at an optimal erasing voltage. Effective erasing requires a threshold current compliance that is higher for shorter pulse width. The erasing current and erasing power both depend strongly on the on-state before erasing, while the erasing voltage is essentially unaffected. Erasing appears to be a power-driven process, which may be related to the thermal effect of power dissipation. The experimental data and analysis suggest that erasing can be explained by field-assisted thermal emission of trapped charges.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

Anthony J. Morfa, Kathy L. Rowlen, Thomas H. Reilly, III, Manuel J. Romero, and Jao van de Lagemaat

Appl. Phys. Lett. 92, 013504 (2008); http://dx.doi.org/10.1063/1.2823578 (3 pages) | Cited 127 times

Online Publication Date: 3 January 2008

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Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle layers were fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase in optical electrical field inside the photoactive layer, the inclusion of such particle films lead to increased optical absorption and consequently increased photoconversion at solar-conversion relevant wavelengths. The resulting solar energy conversion efficiency for a bulk heterojunction photovoltaic device of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester was found to increase from 1.3%±0.2% to 2.2%±0.1% for devices employing thin plasmon-active layers. Based on six measurements, the improvement factor of 1.7 was demonstrated to be statistically significant.
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84.60.Jt Photoelectric conversion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials

Two-dimensional eccentric elliptic electromagnetic cloaks

Do-Hoon Kwon and Douglas H. Werner

Appl. Phys. Lett. 92, 013505 (2008); http://dx.doi.org/10.1063/1.2830698 (3 pages) | Cited 86 times

Online Publication Date: 4 January 2008

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A spatial transformation technique is applied to an important class of two-dimensional electromagnetic cloaks that do not possess rotational symmetry around the longitudinal axis. These cloaks are based on an eccentric elliptic annular geometry, which represents a generalization of previously published cloaking configurations. The required material properties of the cloak are derived in terms of the geometrical parameters and the coordinates in the transformed system. The validity of the cloak parameters is verified by a full-wave finite-element simulation of plane wave scattering from uncloaked and cloaked perfectly conducting cylinders with elliptic cross section.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
02.70.Dh Finite-element and Galerkin methods

Flexible-foam-based capacitive sensor arrays for object detection at low cost

Christian Metzger, Elgar Fleisch, Jan Meyer, Mario Dansachmüller, Ingrid Graz, Martin Kaltenbrunner, Christoph Keplinger, Reinhard Schwödiauer, and Siegfried Bauer

Appl. Phys. Lett. 92, 013506 (2008); http://dx.doi.org/10.1063/1.2830815 (3 pages) | Cited 7 times

Online Publication Date: 4 January 2008

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Polymer foams are used in the automotive and construction industries for thermal insulation, vibration attenuation, and pressure absorption, due to their lightweight structure, thermal characteristics and low manufacturing costs. These foams have higher elasticity in their cross sections than bulk polymers, which makes them the preferred mount for capacitive sensor arrays. The authors describe a flexible pressure-sensitive surface mounted on packaging foam. The elastic properties of the foam are presented along with the sensor array’s weight sensitivity. The authors illustrate an inventory management application where objects on display can be detected through their weights.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
82.70.Rr Aerosols and foams

Cascade single-chip phosphor-free white light-emitting diodes

X. Guo, G. D. Shen, B. L. Guan, X. L. Gu, D. Wu, and Y. B. Li

Appl. Phys. Lett. 92, 013507 (2008); http://dx.doi.org/10.1063/1.2830991 (3 pages) | Cited 8 times

Online Publication Date: 4 January 2008

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In order to resolve the problems existing in the conventional phosphor-converted light-emitting-diodes (LEDs) and red-green-blue LEDs, the cascade single-chip phosphor-free white LED was proposed with GaAs/GaN heterojunction direct wafer bonding. Corresponding to the color-matching calculation, the white LED demonstrated the CIE chromaticity coordinates of about (0.3, 0.3) at 20 mA, which was very close to the ideal white light position (1/3, 1/3) on the chromaticity diagram. The fabrication and the electrical and optical performances of such white LEDs were described.
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85.60.Jb Light-emitting devices

Close-packed arrays of transition-edge x-ray microcalorimeters with high spectral resolution at 5.9 keV

N. Iyomoto, S. R. Bandler, R. P. Brekosky, A.-D. Brown, J. A. Chervenak, F. M. Finkbeiner, R. L. Kelley, C. A. Kilbourne, F. S. Porter, J. E. Sadleir, S. J. Smith, and E. Figueroa-Feliciano

Appl. Phys. Lett. 92, 013508 (2008); http://dx.doi.org/10.1063/1.2830665 (3 pages) | Cited 10 times

Online Publication Date: 7 January 2008

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We present measurements of high fill-factor arrays of superconducting transition-edge x-ray microcalorimeters designed to provide rapid thermalization of the x-ray energy. We designed an x-ray absorber that is cantilevered over the sensitive part of the thermometer itself, making contact only at normal-metal features. With absorbers made of electroplated gold, we have demonstrated an energy resolution between 2.4 and 3.1 eV at 5.9 keV on 13 separate pixels. We have determined the thermal and electrical parameters of the devices throughout the superconducting transition and, using these parameters, have modeled all aspects of the detector performance.
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07.85.-m X- and γ-ray instruments
07.20.Fw Calorimeters
85.25.Am Superconducting device characterization, design, and modeling

Pull-in instability of parallel-plate electrostatic microactuators under a combined variable charge and voltage configuration

C. Son and B. Ziaie

Appl. Phys. Lett. 92, 013509 (2008); http://dx.doi.org/10.1063/1.2832770 (3 pages) | Cited 2 times

Online Publication Date: 8 January 2008

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In this letter, we present a theoretical analysis of pull-in instability of parallel-plate electrostatic microactuators under a combined variable charge and voltage configuration. This occurs in parallel plate capacitors partially filled with a charged dielectric (electret) where the plates are connected together through an impedance. Our results demonstrate the possibility of achieving full range motion under certain conditions. For Teflon® electrets much thinner than the air gap; the maximum traveling distance is similar to the voltage controlled electrostatic actuators (gap/3), whereas for electrets four times thicker than the initial gap the maximum traveling distance can approach 100% of the gap.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
77.22.Jp Dielectric breakdown and space-charge effects

Electric field distribution in GaN/AlGaN/GaN heterostructures with two-dimensional electron and hole gas

C. Buchheim, R. Goldhahn, G. Gobsch, K. Tonisch, V. Cimalla, F. Niebelschütz, and O. Ambacher

Appl. Phys. Lett. 92, 013510 (2008); http://dx.doi.org/10.1063/1.2830836 (3 pages) | Cited 4 times

Online Publication Date: 8 January 2008

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Ga-face GaN/AlGaN/GaN heterostructures with different cap thicknesses are investigated by electroreflectance spectroscopy (ER). The voltage dependent electric field strengths of the barrier and cap layers are determined. The AlGaN electric field amounts of up to −2.6 MV/cm, whereas the GaN electric field is always below 700 kV/cm. The two electric fields have opposite signs. Characteristic features in the voltage maps of the ER spectra are assigned to the formation/depletion of a two-dimensional electron gas below and a two-dimensional hole gas above the AlGaN barrier. Between −6.5 and 0 V, both carrier gases coexist.
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73.21.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Jq Electro-optical effects

Self-assembled monolayers of protonated poly(amidoamine) dendrimers on indium tin oxide

Gianluca Latini, Michael Wykes, Robert Schlapak, Stefan Howorka, and Franco Cacialli

Appl. Phys. Lett. 92, 013511 (2008); http://dx.doi.org/10.1063/1.2829387 (3 pages) | Cited 9 times

Online Publication Date: 8 January 2008

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We have investigated the change of work function of indium tin oxide (ITO) anodes induced by adsorption of positively charged poly(amidoamine) (PAMAM) dendrimers. Kelvin probe characterization of the functionalized ITO films and electroabsorption measurements on polymer light-emitting diodes incorporating poly(9,9-dioctylfluorene) active layers revealed an abrupt (0.55 eV) lowering of the effective work function upon addition of the adsorbed layer and a weak dependence on the PAMAM generation. We interpret our results with an electrostatic model accounting for both positively charged amines and for possible contaminations providing compensating negative charges.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.Mn Adsorption kinetics
78.20.Jq Electro-optical effects
85.60.Jb Light-emitting devices

Memory characteristics of cobalt-silicide nanocrystals embedded in HfO2 gate oxide for nonvolatile nanocrystal flash devices

JooHyung Kim, JungYup Yang, JunSeok Lee, and JinPyo Hong

Appl. Phys. Lett. 92, 013512 (2008); http://dx.doi.org/10.1063/1.2831667 (3 pages) | Cited 18 times

Online Publication Date: 8 January 2008

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Cobalt-silicide (CoSi2) nanocrystals (NCs) were investigated for use in charge storage for metal oxide semiconductor (MOS) devices with thin HfO2 tunneling and control oxide layers. CoSi2 NCs were synthesized by exposure of Co/Si/HfO2 tunneling oxide/Si stacks to an external UV laser. Observations from transmission electron microscopy and x-ray photoelectron spectroscopy clearly confirm the formation of CoSi2 NCs and the values of Co–Si bonding energies that are shifted 0.3 eV from original values, respectively. The CoSi2 NCs in MOS devices exhibited a large memory window of 3.4 V as well as efficient programming/erasing speeds, good retention, and endurance times.
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81.07.Bc Nanocrystalline materials
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Evidence of hot electrons generated from an AlN/GaN high electron mobility transistor

Suvranta K. Tripathy, Guibao Xu, Xiaodong Mu, Yujie J. Ding, Kejia Wang, Yu Cao, Debdeep Jena, and Jacob B. Khurgin

Appl. Phys. Lett. 92, 013513 (2008); http://dx.doi.org/10.1063/1.2830834 (3 pages) | Cited 5 times

Online Publication Date: 11 January 2008

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We have observed that the temperature of the electrons drifting under a relatively high electric field in an AlN/GaN-based high-electron-mobility transistor is significantly higher than the lattice temperature (i.e., the hot electrons are generated). These hot electrons are produced through the Fröhlich interaction between the drifting electrons and long-lived longitudinal-optical phonons. By fitting electric field versus electron temperature deduced from the measurements of photoluminescence spectra to a theoretical model, we have deduced the longitudinal-optical-phonon emission time for each electron is to be on the order of 100 fs.
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85.30.Tv Field effect devices
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