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8 Aug 2011

Volume 99, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 063701 (2011); http://dx.doi.org/10.1063/1.3622631 (3 pages)

Bomi Gweon, Mina Kim, Dan Bee Kim, Daeyeon Kim, Hyeonyu Kim, Heesoo Jung, Jennifer H. Shin, and Wonho Choe
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Thermally assisted resistive switching in Pr0.7Ca0.3MnO3/Ti/Ge2Sb2Te5 stack for nonvolatile memory applications

Manzar Siddik, Seungjae Jung, Jubong Park, Wootae Lee, Seonghyun Kim, Joonmyoung Lee, Jungho Shin, Sangsu Park, Daeseok Lee, Insung Kim, and Hyunsang Hwang

Appl. Phys. Lett. 99, 063501 (2011); http://dx.doi.org/10.1063/1.3622656 (3 pages) | Cited 1 time

Online Publication Date: 8 August 2011

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We propose a low power, high-performance nanoscale (φ = 150 nm) resistive memory device having a Ge2Sb2Te5/Ti/Pr0.7Ca0.3MnO3 (GST/Ti/PCMO) structure. As a thermoelectric heater and/or thermal barrier, GST accelerates the Ti/PCMO interfacial redox process thermally by enhancing the mobility of oxygen ions and minimizes the loss of local heat. Improvement of the memory performances and voltage-time dilemma issue is achieved by adopting this type of thermally assisted process.
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84.30.Sk Pulse and digital circuits
85.80.Fi Thermoelectric devices

The plasmonic resonant absorption in GaN double-channel high electron mobility transistors

Lin Wang, Xiao-Shuang Chen, Wei-Da Hu, Jun Wang, Jian Wang, Xiao-Dong Wang, and Wei Lu

Appl. Phys. Lett. 99, 063502 (2011); http://dx.doi.org/10.1063/1.3619842 (3 pages) | Cited 10 times

Online Publication Date: 8 August 2011

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We have investigated the plasmonic oscillations in GaN double-channel (DC) high electron mobility transistors (HEMTs). It is shown that the absorption peaks of DC-HEMT can exist in wider frequency regions than that of single channel HEMT. These absorption peaks appear as a result of excitation of elementary plasmon modes supported by separate channels and can be tuned for the entire terahertz domain. Significant resonant enhancement is also observed after varying the two-dimensional electron gas density in DC-HEMTs. These promising properties indicate that DC-HEMTs can have important applications as voltage tunable broadband terahertz detectors, intensity modulators, and filters.
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81.05.Ea III-V semiconductors
85.30.Tv Field effect devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Modelling the resistive state in a transition edge sensor

A. Kozorezov, A. A. Golubov, D. D. E. Martin, P. A. J. de Korte, M. A. Lindeman, R. A. Hijmering, J. van der Kuur, H. F. C. Hoevers, L. Gottardi, M. Yu. Kupriyanov, and J. K. Wigmore

Appl. Phys. Lett. 99, 063503 (2011); http://dx.doi.org/10.1063/1.3621829 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2011

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We have developed a model for the resistive transition in a transition edge sensor (TES) based on the model of a resistively and capacitively shunted junction, taking into account phase-slips of a superconducting system across the barriers of the tilted washing board potential. We obtained analytical expressions for the resistance of the TES, R(T, I), and its partial logarithmic derivatives αI and βI as functions of temperature and current. We have shown that all the major parameters describing the resistive state of the TES are determined by the dependence on temperature of the Josephson critical current, rather than by intrinsic properties of the S-N transition. The complex impedance of a pristine TES exhibits two-pole behaviour due to its own intrinsic reactance.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.25.-j Superconducting devices

Towards a high efficiency amorphous silicon solar cell using molybdenum oxide as a window layer instead of conventional p-type amorphous silicon carbide

Sang Il Park, Seung Jae Baik, Jong-San Im, Liang Fang, Jin-Wan Jeon, and Koeng Su Lim

Appl. Phys. Lett. 99, 063504 (2011); http://dx.doi.org/10.1063/1.3624591 (3 pages)

Online Publication Date: 8 August 2011

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A thermally evaporated molybdenum oxide (MoO3) film was used as a window layer of a hydrogenated amorphous silicon (a-Si:H) solar cell instead of the conventional p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) film. The short circuit current density (JSC) and fill factor were increased due to the wide optical band gap and high conductivity of the MoO3 film. As a result, the conversion efficiency of the fabricated MoO3 solar cell was increased to 6.21% compared to the typical a-Si:H solar cell (5.97%).
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88.40.jj Silicon solar cells

Degradation in InAlN/AlN/GaN heterostructure field-effect transistors as monitored by low-frequency noise measurements: Hot phonon effects

C. Kayis, R. A. Ferreyra, M. Wu, X. Li, Ü. Özgür, A. Matulionis, and H. Morkoç

Appl. Phys. Lett. 99, 063505 (2011); http://dx.doi.org/10.1063/1.3624702 (3 pages) | Cited 6 times

Online Publication Date: 9 August 2011

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Low-frequency noise technique was applied to analyze performance of nearly lattice-matched InAlN/AlN/GaN heterostructure field-effect transistors and their degradation caused by electrical stress. Nearly identical devices from the same wafer have undergone a 7 h DC electrical stress at a fixed DC drain bias of VDS = 20 V and different gate biases. We noted up to 32 dB/Hz higher low-frequency noise for stressed devices over the entire frequency range of 1 Hz-100 kHz. The measurements showed the minimum degradation at a gate-controlled two-dimensional electron gas density of 9.4 × 1012 cm−2. This result is in good agreement with the reported stress effect on drain-current degradation and current-gain-cutoff-frequency measurements and consistent with the ultrafast decay of hot-phonons due to the phonon–plasmon coupling.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

One-dimensional model of the programming kinetics of conductive-bridge memory cells

John R. Jameson, Nad Gilbert, Foroozan Koushan, Juan Saenz, Janet Wang, Shane Hollmer, and Michael N. Kozicki

Appl. Phys. Lett. 99, 063506 (2011); http://dx.doi.org/10.1063/1.3623485 (3 pages) | Cited 11 times

Online Publication Date: 9 August 2011

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A one-dimensional model of filament growth in conductive-bridge memory cells is presented, in which ions are thermally excited from the anode surface into the electrolyte, pulled by the electric field through a periodic series of wells and reduced at the cathode to form a metallic filament. The voltage, temperature, and thickness dependencies of the time required to program a cell are calculated, and material parameters for Ag/GeS2/W cells are obtained by comparison to experiment. The relation of the model to recent observations of quantized conductance is highlighted, as is the need for further study of the Ag/GeS2 interface.
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84.30.Sk Pulse and digital circuits
82.45.Fk Electrodes
82.45.Gj Electrolytes

Conduction mechanism of TiN/HfOx/Pt resistive switching memory: A trap-assisted-tunneling model

Shimeng Yu, Ximeng Guan, and H.-S. Philip Wong

Appl. Phys. Lett. 99, 063507 (2011); http://dx.doi.org/10.1063/1.3624472 (3 pages) | Cited 14 times

Online Publication Date: 9 August 2011

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The conduction mechanism of metal oxide resistive switching memory is debated in the literature. We measured the I-V characteristics below the switching voltages through TiN/HfOx/Pt memory stack and found the conduction cannot be described by the commonly used Poole-Frenkel model, because the fitted dielectric constant and the trap energy are unreasonable as compared to their known values. Therefore, we provide an alternate viewpoint based on a trap-assisted-tunneling model. Agreement of the bias polarity/temperature/resistance state-dependent conduction behavior was achieved between this model and experimental data. And insights for the multilevel capability due to the control of tunneling distance were obtained.
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84.30.Sk Pulse and digital circuits
73.40.Gk Tunneling
77.22.Ch Permittivity (dielectric function)

Voltage dependent photocurrent of thin film hematite electrodes

Benjamin M. Klahr and Thomas W. Hamann

Appl. Phys. Lett. 99, 063508 (2011); http://dx.doi.org/10.1063/1.3622130 (3 pages) | Cited 7 times

Online Publication Date: 9 August 2011

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The current density (J) vs. applied voltage (V) curves of thin-film hematite electrodes under illumination exhibit non-ideal behavior; as a result, very poor fill factors and photocurrent densities are generally observed. A simple model is presented to describe the photocurrent density behavior of hematite photoelectrodes, which assumes only drift collection of holes in a uniform electric field. Excellent agreement is found between the model and experimental results. Use of this model provides important insight into the limitations of hematite electrodes as well as strategies to achieve improved efficiency.
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72.40.+w Photoconduction and photovoltaic effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.aj Insulators

Numerical investigation into the switchable diode effect in metal-ferroelectric-metal structures

Chen Ge, Kui-Juan Jin, Can Wang, Hui-Bin Lu, Cong Wang, and Guo-Zhen Yang

Appl. Phys. Lett. 99, 063509 (2011); http://dx.doi.org/10.1063/1.3624849 (3 pages) | Cited 11 times

Online Publication Date: 10 August 2011

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A self-consistent numerical model, particularly including the incomplete screening effect of metal electrodes, is introduced to reveal the mechanism of the switchable diode characteristics in metal/ferroelectric/metal structures. The calculated results are in good agreement with recent experimental data, theoretically demonstrating the important role played by the polarization-modulated barrier. Our calculations confirm that electrodes with a smaller permittivity, such as noble metals, are better choices to obtain a more pronounced switchable diode effect, and the barrier height variation as a function of the polarization will deviate from the linear relationship if the carrier concentration induced by the polarization becomes sufficiently high.
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77.80.Fm Switching phenomena
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.40.Ei Rectification
73.40.Sx Metal-semiconductor-metal structures

Impulse absorption using small, hard panels of embedded cylinders with granular alignments

Alexander Breindel, Diankang Sun, and Surajit Sen

Appl. Phys. Lett. 99, 063510 (2011); http://dx.doi.org/10.1063/1.3624466 (3 pages)

Online Publication Date: 10 August 2011

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Sustained ability to absorb impulses at varied temperatures using light, hard materials and at length scales of few centimeters has been a challenge. The tapered chains while effective have been difficult to construct for applications. Here we build on Hong’s granular protector concept to show that strong inertial mismatches due to alternate sets of few massive and light grains in elastically matched monosized granular alignments seem promising in absorbing impulses across millisecond time scales within a few centimeters. We propose a system which could find applications in the context of the construction and automobile industries, in combat, and elsewhere.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
89.40.Bb Land transportation

Functional electroless gold Ohmic contacts in light emitting diodes

P. Y. Chen, H. C. Wong, S. F. Hu, C. Y. Huang, and R. S. Liu

Appl. Phys. Lett. 99, 063511 (2011); http://dx.doi.org/10.1063/1.3624831 (3 pages)

Online Publication Date: 11 August 2011

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Conducting gold pads on light-emitting diodes chips are synthesized by electroless chemical deposition and exhibit no color difference, reliable ability of wire bonding, and high electrical conductivity. A plating electrolyte with a long life time and high stability is developed. The hardness of pads formed by electroless plating is three times softer than those formed by evaporation and the force gauge of the p- and n-pads yields of approximately 55 g. The mechanism of electroless gold plating is elucidated and the functions of chemical reagents are explained using the proposed model. The industrial application of electroless gold plating is feasible.
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85.60.Jb Light-emitting devices

Air stability of TiO2/PbS colloidal nanoparticle solar cells and its impact on power efficiency

Guangmei Zhai, Anna Bezryadina, Alison J. Breeze, Daoli Zhang, Glenn B. Alers, and Sue A. Carter

Appl. Phys. Lett. 99, 063512 (2011); http://dx.doi.org/10.1063/1.3617469 (3 pages) | Cited 5 times

Online Publication Date: 12 August 2011

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The short-term (less than 1 hour) exposure of TiO2/PbS quantum dot photovoltaics to air increases the open circuit voltage (Voc) and fill factor (FF) while slightly decreasing the short circuit current density (Jsc), leading to a power conversion efficiency above 4% and a peak external quantum efficiency over 80% for 1.1 eV PbS. The resulting Jsc, Voc, and FF under 100 mW/cm2 AM1.5 are 18.6 mA/cm2, 0.517 V, and 42% for 1.1 eV PbS and 8.03 mA/cm2, 0.655 V, and 35% for 1.7 eV PbS, respectively. Long-term air exposures result in much lower conductivities. Furthermore, short-term air exposure effects are fully reversible upon removal from air, and longer-term effects are mostly reversible through soaking in 1,2-ethanedithiol.
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88.40.H- Solar cells (photovoltaics)
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