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14 Jan 2013

Volume 102, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 023901 (2013); http://dx.doi.org/10.1063/1.4773526 (4 pages)

Yoshihiro Gohda and Shinji Tsuneyuki
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Field-effect-based chemical sensing using nanowire-nanoparticle hybrids: The ion-sensitive metal-semiconductor field-effect transistor

Vivek Pachauri, Klaus Kern, and Kannan Balasubramanian

Appl. Phys. Lett. 102, 023501 (2013); http://dx.doi.org/10.1063/1.4775579 (5 pages)

Online Publication Date: 15 January 2013

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A new class of nanoscale devices called ion-sensitive metal-semiconductor field-effect transistors (nano-IS-MESFET) for sensing applications is reported. Nanoparticle-nanowire hybrids with active metal-semiconductor regions are operated as ion-sensitive field-effect transistors (ISFETs) in liquids, where 0D metal gates induce quasi-spherical charge depletion regions in 1D transport channel producing stronger field-effects. As a proof-of-concept, we present ZnO nanowire-Pd/Au nanoparticle IS-MESFETs that show increased transconductance in comparison to ZnO nanowire ISFETs. As demonstrated further, ISMESFETs may also provide strategies for site-specific immobilization of receptor molecules paving way towards a novel electrical biosensing platform operable at low voltages with improved selectivity and sensitivity.
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85.30.Tv Field effect devices
82.80.-d Chemical analysis and related physical methods of analysis

How does external feedback cause AlGaAs-based diode lasers to degrade?

Martin Hempel, Mingjun Chi, Paul M. Petersen, Ute Zeimer, and Jens W. Tomm

Appl. Phys. Lett. 102, 023502 (2013); http://dx.doi.org/10.1063/1.4775681 (4 pages)

Online Publication Date: 15 January 2013

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The effect of external feedback on the degradation of 808 nm emitting AlGaAs-based high-power broad-area diode lasers is studied. For this purpose, early stages of gradual degradation are induced by accelerated aging at high power levels. While the quantum well that actually experiences the highest total optical load remains unaffected, severe impact by point defects is observed on the cladding layers and the waveguide. Extended defects such as dislocations, however, are not observed in such early stages of degradation, which are accompanied by gradual power loss of a few percent only.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High current stress effects in amorphous-InGaZnO4 thin-film transistors

Mallory Mativenga, Sejin Hong, and Jin Jang

Appl. Phys. Lett. 102, 023503 (2013); http://dx.doi.org/10.1063/1.4775694 (4 pages)

Online Publication Date: 15 January 2013

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Amorphous-InGaZnO4 (a-IGZO) thin-film transistors (TFTs) on glass undergo large positive threshold voltage shifts (ΔVTH) under high current stress (HCS)—a consequence of Joule heating of the active-layer. Here, we show that when the active layer is split into smaller parts, HCS induces negligible ΔVTH. When the active layer heats up during HCS, conducting electrons in the channel gain enough energy to surmount the energy barrier at the active-layer/gate-insulator interface and become trapped into deep states inside the gate-insulator. Splitting the active-layer into smaller parts increases the surface area for heat dissipation, resulting in the elimination of these self-heating effects.
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85.30.Tv Field effect devices

A digital miniature x-ray tube with a high-density triode carbon nanotube field emitter

Jin-Woo Jeong, Jun-Tae Kang, Sungyoul Choi, Jae-Woo Kim, Seungjoon Ahn, and Yoon-Ho Song

Appl. Phys. Lett. 102, 023504 (2013); http://dx.doi.org/10.1063/1.4776222 (4 pages)

Online Publication Date: 15 January 2013

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We have fabricated a digital miniature x-ray tube (6 mm in diameter and 32 mm in length) with a high-density triode carbon nanotube (CNT) field emitter for special x-ray applications. The triode CNT emitter was densely formed within a diameter of below 4 mm with the focusing-functional gate. The brazing process enables us to obtain and maintain a desired vacuum level for the reliable electron emission from the CNT emitters after the vacuum packaging. The miniature x-ray tube exhibited a stable and reliable operation over 250 h in a pulse mode at an anode voltage of above 25 kV.
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07.85.-m X- and γ-ray instruments
84.47.+w Vacuum tubes
85.35.Kt Nanotube devices

Operation of transition edge sensors in a resistance locked loop

J. van der Kuur and M. Kiviranta

Appl. Phys. Lett. 102, 023505 (2013); http://dx.doi.org/10.1063/1.4788683 (4 pages)

Online Publication Date: 16 January 2013

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We propose to operate a superconducting transition edge sensor (TES) using a different type of biasing, in which the resistance of the TES is kept constant by means of feedback on the bias voltage and is independent of the incoming signal power. By combining a large negative electrothermal feedback with a load independent resistance, this approach can significantly linearise the response of the detector in the large signal limit. The electrothermal feedback is enhanced in comparison with the commonly applied voltage biasing, which further increases the speed of the detector. Furthermore, in frequency domain multiplexed readout, the sinusoidal bias voltages for each TES can be generated cryogenically with the readout SQUIDs.
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85.25.Am Superconducting device characterization, design, and modeling
85.25.Dq Superconducting quantum interference devices (SQUIDs)
29.40.-n Radiation detectors

Single-shot 35 fs temporal resolution electron shadowgraphy

C. M. Scoby, R. K. Li, E. Threlkeld, H. To, and P. Musumeci

Appl. Phys. Lett. 102, 023506 (2013); http://dx.doi.org/10.1063/1.4776686 (4 pages)

Online Publication Date: 16 January 2013

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We obtain single-shot time-resolved shadowgraph images of the electromagnetic fields resulting from the interaction of a high intensity ultrashort laser pulse with a metal surface. Using a high brightness relativistic electron beam and a high streaking speed radiofrequency deflector, we report <35 fs temporal resolution enabling a direct visualization of the retarded-time dominated field evolution which follows the laser-induced charge emission. A model including the finite signal propagation speed well reproduces the data and yields measurements of fundamental parameters in short pulse laser-matter interaction such as the amount of emitted charge and the emission time scale.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Fm Reflectors, beam splitters, and deflectors
79.20.Ds Laser-beam impact phenomena
41.75.Ht Relativistic electron and positron beams

Transient characterization of the electroforming process in TiO2 based resistive switching devices

Mohammad Noman, Abhishek A. Sharma, Yi Meng Lu, Marek Skowronski, Paul A. Salvador, and James A. Bain

Appl. Phys. Lett. 102, 023507 (2013); http://dx.doi.org/10.1063/1.4776693 (4 pages) | Cited 1 time

Online Publication Date: 16 January 2013

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The transient electroforming process of TiO2-based resistive switching devices is investigated using a pulsed voltage method, and the electroforming time is found to vary from 10−8 s to 10−1 s as function of pulse magnitude (3–8 V) and ambient temperature (25–100 °C). Pulsed experiments and thermal simulations reveal that Joule self-heating has a significant effect on the electroforming dynamics, specially for electroforming voltages above 5.5 V where there is little dependence on ambient temperature and the electroforming time (10–100 ns) is much shorter than the device thermal time constant (≈2 μs).
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81.10.Fq Growth from melts; zone melting and refining
72.60.+g Mixed conductivity and conductivity transitions

Controllable low-bias negative differential resistance and rectifying behaviors induced by symmetry breaking

Zhi-Qiang Fan, Zhen-Hua Zhang, Xiao-Qing Deng, Gui-Ping Tang, and Ke-Qiu Chen

Appl. Phys. Lett. 102, 023508 (2013); http://dx.doi.org/10.1063/1.4788691 (5 pages)

Online Publication Date: 17 January 2013

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Incorporating the characteristic of pyramidal electrode and symmetry breaking of molecular structure, we theoretically design a molecular device to perform negative differential resistance and rectifying behaviors simultaneously. The calculated results reveal that low-bias negative differential resistance behaviors can appear symmetrically when tetraphenyl molecule connects to pyramidal gold electrodes. However, as one phenyl of tetraphenyl molecule is replaced by a pyrimidyl, the symmetry breaking on the molecule will break the symmetry of negative differential resistance behavior. The peak-to-valley ratio on negative bias region is larger than that on positive bias region to perform a low-bias rectifying behavior. More importantly, increasing the symmetry breaking can further weaken these two behaviors which propose an effective way to modulate them.
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85.65.+h Molecular electronic devices

Magnetic shielding of walls from the unmagnetized ion beam in a Hall thruster

Ioannis G. Mikellides, Ira Katz, Richard R. Hofer, and Dan M. Goebel

Appl. Phys. Lett. 102, 023509 (2013); http://dx.doi.org/10.1063/1.4776192 (5 pages)

Online Publication Date: 17 January 2013

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We demonstrate by numerical simulations and experiments that the unmagnetized ion beam formed in a Hall thruster can be controlled by an applied magnetic field in a manner that reduces by 2–3 orders of magnitude deleterious ion bombardment of the containing walls. The suppression of wall erosion in Hall thrusters to such low levels has remained elusive for decades.
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52.75.-d Plasma devices
02.60.Cb Numerical simulation; solution of equations
41.75.Ak Positive-ion beams
52.65.-y Plasma simulation
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Origin of InGaN light-emitting diode efficiency improvements using chirped AlGaN multi-quantum barriers

Joachim Piprek and Z. M. Simon Li

Appl. Phys. Lett. 102, 023510 (2013); http://dx.doi.org/10.1063/1.4776739 (4 pages) | Cited 3 times

Online Publication Date: 17 January 2013

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We analyze efficiency droop reductions in InGaN/GaN light-emitting diodes caused by a chirped AlGaN/GaN multi-quantum barrier (MQB). Such electron barriers are expected to create an additional forbidden energy range above the natural conduction band edge, which reduces the electron leakage current. Advanced numerical device simulations reveal that energy band bending practically eliminates this MQB effect. Instead, we find that the measured efficiency improvement has its origin in enhanced hole injection, which can be more easily accomplished using a single thin AlGaN layer.
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85.60.Jb Light-emitting devices

Gate traps inducing band-bending fluctuations on AlGaN/GaN heterojunction transistors

A. Pérez-Tomás, A. Fontserè, S. Sánchez, M. R. Jennings, P. M. Gammon, and Y. Cordier

Appl. Phys. Lett. 102, 023511 (2013); http://dx.doi.org/10.1063/1.4788722 (4 pages)

Online Publication Date: 18 January 2013

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Here, using a frequency dependent conductance analysis, we map the parallel conductance vs gate bias/frequency and further analyze the slow and fast traps as a function of the Fermi level for different gate architectures of analogous AlGaN/GaN heterojunction transistors with Schottky and SiNx metal-insulator-semiconductor (MIS) gate. The density of interface traps (Dit)-MIS reducing Dit-, the characteristic trap constant and the variance of the band-bending (σs) have been investigated for slow and fast traps. Additional gate stress appears to have a notable effect on the MIS fast trap profile with σs increasing up to 2.5 kT/q.
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85.30.Tv Field effect devices

Study of beam optics and beam halo by integrated modeling of negative ion beams from plasma meniscus formation to beam acceleration

K. Miyamoto, S. Okuda, A. Hatayama, M. Hanada, and A. Kojima

Appl. Phys. Lett. 102, 023512 (2013); http://dx.doi.org/10.1063/1.4788725 (4 pages)

Online Publication Date: 18 January 2013

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To understand the physical mechanism of the beam halo formation in negative ion beams, a two-dimensional particle-in-cell code for simulating the trajectories of negative ions created via surface production has been developed. The simulation code reproduces a beam halo observed in an actual negative ion beam. The negative ions extracted from the periphery of the plasma meniscus (an electro-static lens in a source plasma) are over-focused in the extractor due to large curvature of the meniscus.
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52.50.Dg Plasma sources
52.65.Rr Particle-in-cell method
41.75.Cn Negative-ion beams
41.85.Ar Particle beam extraction, beam injection
52.25.Fi Transport properties
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