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28 Jul 2008

Volume 93, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 043101 (2008); http://dx.doi.org/10.1063/1.2963352 (3 pages)

Xin Fu, Jun Jiang, Wenzheng Zhang, and Jun Yuan
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Measurement and validation of PbS nanocrystal energy levels

D. M. N. M. Dissanayake, T. Lutz, R. J. Curry, and S. R. P. Silva

Appl. Phys. Lett. 93, 043501 (2008); http://dx.doi.org/10.1063/1.2964203 (3 pages) | Cited 9 times

Online Publication Date: 28 July 2008

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Cyclic voltammetry was used to measure PbS nanocrystal (PbS-NC) energy levels. Accuracy of these measurements was justified by electron transfer experiments, with well known fullerene derivatives, which included photoluminescence quenching experiments and current density-voltage measurements of hybrid photovoltaic devices. It is believed that these energy level measurements, carried out on PbS-NCs under ambient conditions, would provide valuable information for the design and fabrication of optimized hybrid nanoelectronic devices.
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85.60.Bt Optoelectronic device characterization, design, and modeling
73.63.Bd Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
82.80.Fk Electrochemical methods
81.05.Hd Other semiconductors

Reverse-bias-induced bipolar resistance switching in Pt/TiO2/SrTi0.99Nb0.01O3/Pt devices

S. X. Wu, L. M. Xu, X. J. Xing, S. M. Chen, Y. B. Yuan, Y. J. Liu, Y. P. Yu, X. Y. Li, and S. W. Li

Appl. Phys. Lett. 93, 043502 (2008); http://dx.doi.org/10.1063/1.2965469 (3 pages) | Cited 24 times

Online Publication Date: 28 July 2008

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Stoichiometric single-crystalline TiO2 thin films were grown on SrTi0.99Nb0.01O3 (Nb:STO) substrates by oxygen plasma-assisted molecular beam epitaxy. The Pt/TiO2/Nb:STO/Pt devices showed extremely weak resistance switching hysteresis without applying reverse bias. However, when the reverse bias increased above −2 V, the hysteresis became more and more prominent. Further, it was found that the low (high) resistance state can be set by applying sufficient reverse (forward) bias. The origin of the reverse-bias-induced bipolar switching behavior should be attributed to the modulation of Schottky-like barrier width by electrochemical migration of oxygen vacancies.
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84.32.Dd Connectors, relays, and switches
73.30.+y Surface double layers, Schottky barriers, and work functions
66.30.Qa Electromigration
61.72.jd Vacancies

Optical reduction of low frequency noise in cryogenic GaAs junction field effect transistor

M. Fujiwara, H. Nagata, H. Matsuo, and M. Sasaki

Appl. Phys. Lett. 93, 043503 (2008); http://dx.doi.org/10.1063/1.2961034 (3 pages) | Cited 2 times

Online Publication Date: 29 July 2008

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We demonstrated optical low frequency noise reduction in a n-type SONY GaAs junction field effect transistor (JFET) (gate width: 5 μm; length: 1 μm) operating at 4.2 K. At 1 Hz, a 6 dB decrease and a 10 dB increase in noise were observed when the JFET (band gap: 1.51 eV) was illuminated by light with wavelengths of 1650 and 1550 nm, respectively, for a drain voltage of 0.5 V and drain current of 0.25 μA. When the drain current was 0.5 μA, 1650 nm illumination increased the noise; moreover, hysteretic behavior in response to the illumination was also observed. These results show that deep level trapped charges apparently affect low frequency noise, which can be controlled by illumination using photons whose energies are below the band gap energy at cryogenic temperatures.
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85.30.Tv Field effect devices
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Photovoltaic cells fabricated by electrophoretic deposition of CdSe nanocrystals

Nathanael J. Smith, Kevin J. Emmett, and Sandra J. Rosenthal

Appl. Phys. Lett. 93, 043504 (2008); http://dx.doi.org/10.1063/1.2965464 (3 pages) | Cited 11 times

Online Publication Date: 29 July 2008

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Electrophoretic deposition was used to deposit CdSe nanocrystals on TiO2 for use in photovoltaic cells. The deposition current underwent a simple exponential decay, consistent with the current being comprised of charge transfer from charged nanocrystals to the electrodes. Rutherford backscattering spectroscopy showed the composition of the deposited films depended on the polarity of the electrode on which the film formed. A solar cell constructed using electrophoretic deposition exhibited a photovoltaic response from the region in which nanocrystals were deposited, with an efficiency of ∼ 10−6%. The low efficiency was primarily due to the planar geometry employed for the TiO2 subsrate.
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84.60.Jt Photoelectric conversion

Self-assembly of orthogonal three-axis sensors

J. H. Cho, S. Hu, and D. H. Gracias

Appl. Phys. Lett. 93, 043505 (2008); http://dx.doi.org/10.1063/1.2965616 (3 pages) | Cited 5 times

Online Publication Date: 29 July 2008

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Conventional planar microfabrication is widely utilized to construct sensors for the measurement of physical or chemical properties. However, in these devices, the information component measured is typically restricted to only one vectorial axis. Here, we describe a self-assembling strategy that can be utilized to construct three dimensional (3D) cubic devices that facilitate measurement along three axes. This 3D measurement is achieved by arranging sensing elements orthogonally; any sensing element that can be lithographically patterned can be utilized. The 3D arrangement of sensors allows for the measurement of angular and orientation parameters. As an example, we describe a three-axis cantilever based sensor and demonstrate measurement of an evaporated analyte using resonant frequency shifts of cantilevers in each of the x, y, and z axes.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Enhanced optical responsivity of InAlAs/InGaAs metamorphic high mobility electron mobility using indium tin oxide transparent gate technology

Hsien-Chin Chiu, Che-Kai Lin, Chao-Wei Lin, and Ming-Yang Chen

Appl. Phys. Lett. 93, 043506 (2008); http://dx.doi.org/10.1063/1.2965808 (3 pages) | Cited 1 time

Online Publication Date: 29 July 2008

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The high optical responsivity of a transparent gate metamorphic high electron mobility transistor (TG-MHEMT) on GaAs substrate is demonstrated. The transmittance of a 1.3 μm emission wavelength for sputtered indium tin oxide TG-MHEMT gate fingers was 90% after 2 min of annealing at 300 °C and the sheet resistance was 31.3 Ω mm. Compared to the back side illumination of a MHEMT phototransistor, which is beneficial for improving photoresponse, the TG-MHEMT can avoid the inconvenient back side thin-down and polish processes. Experimental results demonstrate that TG-MHEMT has good optical performance at a wavelength of λ = 1.3 μm and comparable to that of the conventional metal gate MHEMT. The increase in drain current and decrease in threshold voltage caused by the illumination can be explained by the photovoltaic effect beneath the transparent gate. The responsivity of TG-MHEMT is roughly 20.6 A/W for a wavelength of λ = 1.3 μm.
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85.30.Tv Field effect devices
85.60.Dw Photodiodes; phototransistors; photoresistors

Broadband electro-optic polymer modulators with high electro-optic activity and low poling induced optical loss

H. Chen, B. Chen, D. Huang, D. Jin, J. D. Luo, A. K.-Y. Jen, and R. Dinu

Appl. Phys. Lett. 93, 043507 (2008); http://dx.doi.org/10.1063/1.2965809 (3 pages) | Cited 15 times

Online Publication Date: 29 July 2008

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A screening method is reported for electro-optic (EO) polymers with an emphasis on broadband device suitability. The method is based on comparing the signal from second harmonic generation (SHG) and the leak through current (LTC) during poling. Plots of the SHG and LTC are used to define high EO activity-low current poling windows that are critical for low driving voltage, broadband devices with relatively low optical loss. The screening procedure was used to select an EO polymer core that resulted in a 40 Gbits/s broadband modulator with a driving voltage of 1.3 V and an insertion loss of <8 dB.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Strong dependence of tunneling transport properties on overdriving voltage for room-temperature-operating single electron/hole transistors formed with ultranarrow [100] silicon nanowire channel

Sejoon Lee and Toshiro Hiramoto

Appl. Phys. Lett. 93, 043508 (2008); http://dx.doi.org/10.1063/1.2958224 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2008

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The single electron/hole transistor (SET/SHT) consisting of a Si nanowire channel with a self-assembled Si quantum dot showed a strong dependence of Coulomb blockade (CB) characteristics on the overdriving voltage (Vover). The SET/SHT requiring a low Vover due to the moderate dot size compared to the nanowire size showed good device performances, for example, very sharp CB oscillation and long extension of blockade regime. However, the SET/SHT requiring a high Vover due to the unduly shrunken of size, which leads to an increase in the valence band offset between the dot and the nanowire, showed the drastic degradation of the device performances.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
73.23.Hk Coulomb blockade; single-electron tunneling

Distinguishing between dipoles and field effects in molecular gated transistors

O. Shaya, M. Shaked, A. Doron, A. Cohen, I. Levy, and Y. Rosenwaks

Appl. Phys. Lett. 93, 043509 (2008); http://dx.doi.org/10.1063/1.2958343 (3 pages) | Cited 6 times

Online Publication Date: 30 July 2008

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We combine Kelvin probe force microscopy and current-voltage measurements in order to characterize silicon-on-insulator bioFETs. The measurements were conducted on monolayer of (3-aminopropyl)-trimethoxysilane, which was deposited on ozone activated silicon oxide surface covering the transistor channel. The work function of the modified surface decreased by more than 2 eV, and the threshold voltage measured on the same devices showed a very large increase ( ∼ 10 V) following the chemical modification. A detailed analysis enables us to distinguish between electron affinity and field effects in such devices, and in molecular gated transistors in general.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices

Focused ion beam specimen preparation for off-axis electron holography using Si, Ga, and Au ions

David Cooper, Francois Bertin, Phillipe Salles, and Gerard Benassayag

Appl. Phys. Lett. 93, 043510 (2008); http://dx.doi.org/10.1063/1.2960351 (3 pages) | Cited 7 times

Online Publication Date: 30 July 2008

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Silicon specimens containing p-n junctions have been prepared by focused ion beam milling using gallium, silicon, and gold ion sources. The specimens have been examined using off-axis electron holography and the total thickness of the electrically ‘inactive’ layer has been measured as 80, 140, and 410±15 nm for the Au, Ga, and Si ions, respectively. We also show that the thickness of this damaged layer can be predicted using simulations.
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61.05.jp Electron holography
42.40.My Applications

High frequency and low frequency noise of AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors with gate insulator grown using photoelectrochemical oxidation method

Li-Hsien Huang, Su-Hao Yeh, and Ching-Ting Lee

Appl. Phys. Lett. 93, 043511 (2008); http://dx.doi.org/10.1063/1.2966142 (3 pages) | Cited 8 times

Online Publication Date: 30 July 2008

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The AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors, which are fabricated using gate insulators directly grown by photoelectrochemical oxidation method, were studied for rf and low frequency noise applications. The drain-source current in saturation (IDSS) and maximum extrinsic transconductance gm(max) are 580 mA/mm and 76.72 mS/mm, respectively. The unity gain cutoff frequency (fT) and maximum frequency of oscillation (fmax) are 5.6 and 10.6 GHz, respectively. Furthermore, the low frequency noise in saturation region is measured and fitted well by 1/f law up to 10 kHz.
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85.30.Tv Field effect devices
81.65.Mq Oxidation

Interfacial electronic structures in an organic double-heterostructure photovoltaic cell

J. X. Tang, Y. C. Zhou, Z. T. Liu, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 93, 043512 (2008); http://dx.doi.org/10.1063/1.2966155 (3 pages) | Cited 27 times

Online Publication Date: 30 July 2008

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The electronic structure of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline/fullerene/copper-phthalocyanine double heterostructure in a typical organic photovoltaic cell was studied by photoemission spectroscopy. The results show that the traditional vacuum energy level lineup is not valid for these organic heterojunctions, which suggests formation of interface dipole and energy level bending across the interface due to charge transfer. Based on the measured energy levels using x-ray and ultraviolet photoemission spectroscopies, important parameters such as the theoretical maximum of the open circuit voltage are extracted, and their impacts on charge photogeneration process are discussed.
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85.60.-q Optoelectronic devices
79.60.-i Photoemission and photoelectron spectra

Magnetic field tuning of coplanar waveguide resonators

J. E. Healey, T. Lindström, M. S. Colclough, C. M. Muirhead, and A. Ya. Tzalenchuk

Appl. Phys. Lett. 93, 043513 (2008); http://dx.doi.org/10.1063/1.2959824 (3 pages) | Cited 9 times

Online Publication Date: 31 July 2008

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We describe measurements on microwave coplanar resonators designed for quantum bit experiments. Resonators have been patterned onto sapphire and silicon substrates, and quality factors in excess of a million have been observed. The resonant frequency shows a high sensitivity to magnetic field applied perpendicular to the plane of the film, with a quadratic dependence for the fundamental, second, and third harmonics. Frequency shift of hundreds of linewidths can be obtained with no change in the quality factor.
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84.40.Az Waveguides, transmission lines, striplines

Chalcogenide thin-film transistors using oxygenated n-type and p-type phase change materials

Ki-Bong Song, Sung-Won Sohn, JunHo Kim, Kyung-Am Kim, and Kyuman Cho

Appl. Phys. Lett. 93, 043514 (2008); http://dx.doi.org/10.1063/1.2963401 (3 pages) | Cited 3 times

Online Publication Date: 31 July 2008

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A technique for chalcogenide thin-film transistors (ChG-TFT) using oxygenated (Ox) n-type and p-type phase change materials is developed. By the oxygen doping into Ge2Sb2Te5 (GST) in a range of 10%–35%, the oxygen impurities induced by destabilization of the electron killers in GST and resultantly n-type Ox-GST was realized. For a p-type Ox-GST, by GeTe deposition with GeTe/Ox-GST ratio more than 0.3 and subsequent thermal diffusion, the diffused film showed the p-type conductivity. With n-type and p-type Ox-GST films, the doped ChG-TFTs were developed. The rectification ratio was ∼ 103 at +5 V, and was increased by the p-n junction structure.
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85.30.Tv Field effect devices
73.40.Ei Rectification
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Jc Amorphous semiconductors; glasses
66.30.Xj Thermal diffusivity
84.30.Jc Power electronics; power supply circuits

Reconfigurable cloak for multiple operating frequencies

Dongxing Wang, Hongsheng Chen, Lixin Ran, Jiangtao Huangfu, Jin Au Kong, and Bae-Ian Wu

Appl. Phys. Lett. 93, 043515 (2008); http://dx.doi.org/10.1063/1.2964187 (3 pages) | Cited 7 times

Online Publication Date: 31 July 2008

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An invisible cloak based on active metamaterials whose permittivity can be controlled is proposed, and the performances of the cloak are verified in numerical simulations. Because of the tunability of the active metamaterials, the working frequency of the invisible cloak is reconfigurable, which is different from the traditional cloak designs based on passive metamaterials whose working frequencies are fixed.
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84.40.Xb Telemetry: remote control, remote sensing; radar

First-principles study on inversion layer properties of double-gate atomically thin silicon channels

Hiroyuki Kageshima and Akira Fujiwara

Appl. Phys. Lett. 93, 043516 (2008); http://dx.doi.org/10.1063/1.2964194 (3 pages) | Cited 2 times

Online Publication Date: 31 July 2008

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The inversion layer properties of double-gate atomically thin silicon channels are studied based on the first-principles enforced Fermi energy difference method. The calculated results indicate that the atomic-scale thickness of the channel significantly affects the inversion layer capacitance as well as the inversion layer carrier properties. They also indicate that the first-principles approach is essential and practical for studying the device physics of the field effect transistors with nanometer-scale channels.
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85.30.Tv Field effect devices

A percolation model for random telegraph signals in metal-oxide-silicon field effect transistor drain current

L. Forbes and D. A. Miller

Appl. Phys. Lett. 93, 043517 (2008); http://dx.doi.org/10.1063/1.2966157 (3 pages) | Cited 1 time

Online Publication Date: 1 August 2008

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Random telegraph signals (RTS) typically do not follow a simple model with uniform charge distributions and electron trapping causing a change in the average threshold voltage. Most often RTS with amplitudes greater than one electron are observed. These signals do not have a normal or Gaussian amplitude distribution. A model is presented here for RTS where electron trapping modulates preferential current paths in the device active region.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Tunable split-ring resonator for metamaterials using photocapacitance of semi-insulating GaAs

K. A. Boulais, D. W. Rule, S. Simmons, F. Santiago, V. Gehman, K. Long, and A. Rayms-Keller

Appl. Phys. Lett. 93, 043518 (2008); http://dx.doi.org/10.1063/1.2967192 (3 pages) | Cited 11 times

Online Publication Date: 1 August 2008

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We report a method for tuning a split-ring resonator (SRR) using infrared light. The SRR unit cells are commonly used in arrays to form a metamaterial that exhibits an effective negative permeability and are often used in negative-refractive-index materials. The region of negative permeability is generally limited to a narrow bandwidth at a fixed frequency. In this work, we use photocapacitance as observed in undoped semi-insulating GaAs to modify the gap capacitance of a SRR. We demonstrate a continuously tunable frequency over the range of 0.1–1.5 GHz using a 975 nm laser diode with a power range of 0–189 mW.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.-x Radiowave and microwave (including millimeter wave) technology
72.40.+w Photoconduction and photovoltaic effects
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