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14 May 2012

Volume 100, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 203104 (2012); http://dx.doi.org/10.1063/1.3701731 (4 pages)

Z. Y. Jiang, X. X. Jiang, S. Su, X. P. Wei, S. T. Lee, and Y. He
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Columnar thermoelectric elements of linked spheres for miniature electric generation modules

Kenta Takagi, Kimihiro Ozaki, Yasuhiro Kawaguchi, and Hideki Yumi

Appl. Phys. Lett. 100, 203501 (2012); http://dx.doi.org/10.1063/1.4718526 (3 pages)

Online Publication Date: 14 May 2012

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Thermoelectric elements that were formed from vertically aligned microspheres were fabricated from 500-µm monosized spherical particles of Fe2VAl alloys with a particle assembly that used pulsed current micro-welding. P-n pairs of the elements consisting of three particles generated relatively large temperature differences ΔT despite being 1.5 mm tall. At ΔT = 19 K, the five pairs generated a voltage of 21 mV and a maximum generation power of 40 µW, which converted to 0.21 V/cm2 voltage per unit area and 0.4 mW/cm2 power density, respectively. Moreover, we demonstrated the feasibility of building a massive array with 100 elements.
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials

High-power, stable Ka/V dual-band gyrotron traveling-wave tube amplifier

Chien-Lun Hung

Appl. Phys. Lett. 100, 203502 (2012); http://dx.doi.org/10.1063/1.4719076 (4 pages)

Online Publication Date: 14 May 2012

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A dual-band amplifier can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. This study proposes and theoretically investigates a gyrotron traveling-wave tube (gyro-TWT) amplifier capable of dual-band operation. Possible oscillations in the coaxial interaction waveguide are stabilized by the lossy inner cylinder. Under stable operating conditions, the gyro-TWT is predicted to provide a peak power of 375 kW with 71 dB saturated gain and 3.8 GHz bandwidth in the Ka-band and a peak power of 150 kW with 35 dB saturated gain and 1.7 GHz bandwidth in the V-band.
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84.30.Le Amplifiers
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Az Waveguides, transmission lines, striplines

Interface trap generation and recovery mechanisms during and after positive bias stress in metal-oxide-semiconductor structures

Piyas Samanta, Heng-Sheng Huang, Shuang-Yuan Chen, Tsung-Jian Tzeng, and Mu-Chun Wang

Appl. Phys. Lett. 100, 203503 (2012); http://dx.doi.org/10.1063/1.4711216 (4 pages)

Online Publication Date: 14 May 2012

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Interface trap (Nit) generation and their partial recovery during and after cessation of the positive bias-temperature stress (PBTS) in n-type metal-oxide-semiconductor capacitors have been investigated. The analysis of experimental results indicates that Nit creation is caused by the depassivation of Si3 ≡ Si-H bonds at the Si/SiO2 interface by the atomic neutral hydrogen (H0) cracked via electron impact at or near gate/oxide interface during electron injection from the substrate. Nit recovery after interruption of the stress is due to back diffusion of H2 species toward the Si/SiO2 interface and repassivation of Si3 ≡ Si• dangling bonds. We propose that in absence of holes, a modified one dimensional reaction-diffusion (R-D) model following three step degradation sequences can qualitatively explain the generation and the recovery of Nit during and after PBTS.
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73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
73.40.Ns Metal-nonmetal contacts

Terahertz current oscillations in a gated two-dimensional electron gas with antenna integrated at the channel ends

Alessandra Di Gaspare, Roberto Casini, Vittorio Foglietti, Valeria Giliberti, Ennio Giovine, and Michele Ortolani

Appl. Phys. Lett. 100, 203504 (2012); http://dx.doi.org/10.1063/1.4717464 (5 pages) | Cited 2 times

Online Publication Date: 14 May 2012

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We studied terahertz current oscillations induced by a frequency-tunable radiation source in a AlGaAs/InGaAs/AlGaAs heterostructure field effect transistor channel. A planar antenna was integrated on-chip, and a substrate lens was used for broadband coupling of free-space radiation at 0.18–0.72 THz to the channel ends. Through spectral analysis of the detection signal, we identified two different mixing mechanisms: one related to channel current oscillations and the other to modulation of the gate-to-channel potential. Depending on gate bias and radiation frequency, the two mechanisms either compete or cooperate, leading to responsivity up to 300 V/W and noise equivalent power of 1 nW/Hz0.5
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85.30.Tv Field effect devices
84.40.Ba Antennas: theory, components and accessories

Mapping return currents in laser-generated Z-pinch plasmas using proton deflectometry

M. J.-E. Manuel, N. Sinenian, F. H. Séguin, C. K. Li, J. A. Frenje, H. G. Rinderknecht, D. T. Casey, A. B. Zylstra, R. D. Petrasso, and F. N. Beg

Appl. Phys. Lett. 100, 203505 (2012); http://dx.doi.org/10.1063/1.4718425 (4 pages) | Cited 2 times

Online Publication Date: 15 May 2012

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Dynamic return currents and electromagnetic field structure in laser-generated Z-pinch plasmas have been measured using proton deflectometry. Experiments were modeled to accurately interpret deflections observed in proton radiographs. Current flow is shown to begin on axis and migrate outwards with the expanding coronal plasma. Magnetic field strengths of ∼1 T are generated by currents that increase from ∼2 kA to ∼7 kA over the course of the laser pulse. Proton deflectometry has been demonstrated to be a practical alternative to other magnetic field diagnostics for these types of plasmas.
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52.25.Fi Transport properties
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.80.Hc Glow; corona
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Theoretical study of Si-based ionic switch

Takashi Yamauchi, Moon Young Yang, Katsumasa Kamiya, Kenji Shiraishi, and Takashi Nakayama

Appl. Phys. Lett. 100, 203506 (2012); http://dx.doi.org/10.1063/1.4718758 (4 pages)

Online Publication Date: 15 May 2012

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We studied the formation/dissolution of a silver (Ag) filament in a silicon (Si) layer through the first-principles calculations. We found these processes take place reversibly by switching the polarity of the bias voltage, bringing about the large resistance change of the Si layer. Furthermore, we developed a model to describe the current-voltage (I-V) characteristics for the Ag(electrode)/Si(electrolyte)/p-Si(electrode) switch device and analyzed the experimental result [S. H. Jo and W. Lu, Nano Lett. 8, 392 (2008)] in the case of using an amorphous Si(a-Si) layer as the electrolyte. It was suggested from the simulated results that dendritic Ag filaments with a fractal dimension of 1.6 are formed in the a-Si layer.
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84.32.Dd Connectors, relays, and switches
85.30.-z Semiconductor devices

Mesoscopic resistor as a self-calibrating quantum noise source

N. Bergeal, F. Schackert, L. Frunzio, D. E. Prober, and M. H. Devoret

Appl. Phys. Lett. 100, 203507 (2012); http://dx.doi.org/10.1063/1.4717462 (4 pages)

Online Publication Date: 15 May 2012

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We present a method for the measurement of the noise of microwave amplifiers operating at the single photon level. It is based on the shot noise produced by a nanowire resistor in the hot electron regime. This noise source is simply controlled by a dc current and offers the advantage of being self-calibrating. After testing the noise source with a cryogenic high electron mobility transistor amplifier, we demonstrate its usefulness by calibrating a Josephson parametric amplifier operating near the quantum limit.
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84.30.Le Amplifiers
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.40.Dc Microwave circuits

Metamaterial metal-based bolometers

F. B. P. Niesler, J. K. Gansel, S. Fischbach, and M. Wegener

Appl. Phys. Lett. 100, 203508 (2012); http://dx.doi.org/10.1063/1.4714741 (3 pages) | Cited 6 times

Online Publication Date: 16 May 2012

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We demonstrate metamaterial metal-based bolometers, which take advantage of resonant absorption in that a spectral and/or polarization filter can be built into the bolometer. Our proof-of-principle gold-nanostructure-based devices operate around 1.5 μm wavelength and exhibit room-temperature time constants of about 134 μs. The ultimate detectivity is limited by Johnson noise, enabling room-temperature detection of 1 nW light levels within 1 Hz bandwidth. Graded bolometer arrays might allow for integrated spectrometers with several octaves bandwidth without the need for gratings or prisms and for integrated polarization analysis without external polarization optics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Improved performance of non-volatile memory with Au-Al2O3 core-shell nanocrystals embedded in HfO2 matrix

Zhongguang Xu, Chenxin Zhu, Zongliang Huo, Yanxiang Cui, Yumei Wang, Fanghua Li, and Ming Liu

Appl. Phys. Lett. 100, 203509 (2012); http://dx.doi.org/10.1063/1.4720085 (4 pages)

Online Publication Date: 17 May 2012

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In this paper, we demonstrate a charge trapping memory with Au-Al2O3 core-shell nanocrystals (NCs) embedded in HfO2 high-k dielectric. Transmission electron microscopy images clearly show the Au NCs surrounded by Al2O3 shells in the HfO2 matrix. Electrical measurements show a considerable memory window (3.6 V at ±8 V), low program/erase operation voltages, and good endurance. Particularly, data retention is improved both at room temperature and high temperature compared to the NC structure without shell. An energy band model is given for the improved retention characteristic. This Au-Al2O3 core-shell NCs memory device has a strong potential for future high-performance nonvolatile memory application.
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84.30.Sk Pulse and digital circuits
81.07.Bc Nanocrystalline materials

Vertically integrated submicron amorphous-In2Ga2ZnO7 thin film transistor using a low temperature process

Sang Ho Rha, Jisim Jung, Yoon Soo Jung, Yoon Jang Chung, Un Ki Kim, Eun Suk Hwang, Byoung Keon Park, Tae Joo Park, Jung-Hae Choi, and Cheol Seong Hwang

Appl. Phys. Lett. 100, 203510 (2012); http://dx.doi.org/10.1063/1.4717621 (5 pages) | Cited 1 time

Online Publication Date: 17 May 2012

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In this work, vertically integrated amorphous-In2Ga2ZnO7 (a-IGZO) thin film transistors (V-TFTs) with 310 nm channel length were fabricated using a low temperature process (<300  °C), and their device performance was evaluated. The fabricated V-TFTs show well behaved transfer characteristics with an Ion/Ioff current ratio greater than 104 and a threshold voltage of 1.7 V. The influence of the vertical structure on device performance was analyzed in detail. In addition, current polarity characteristics that arise from different metal/a-IGZO contacts were also examined. The non-optimum performance of the V-TFTs was attributed to the fringing-field effect, high defect density, and large source/drain contact resistance.
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85.30.Tv Field effect devices

Memory effects in electrochemically gated metallic point contacts

R. Maul, F.-Q. Xie, Ch. Obermair, G. Schön, Th. Schimmel, and W. Wenzel

Appl. Phys. Lett. 100, 203511 (2012); http://dx.doi.org/10.1063/1.4719207 (5 pages)

Online Publication Date: 18 May 2012

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Electrochemical gating permits the observation of few-atom processes in contact reconstruction. We monitor the junction conductance during the opening and closing of an atomic-scale metallic contact and use this as an instantaneous probe of the atomic-scale structural switching process. We observe clear correlations in the quantum conductance of a contact in subsequent switching events, demonstrating memory effects at the atomic scale. These experimental observations are supported by numerical simulations which show a conservation of the contact reconstruction process across several switching cycles. These results open a route to electrochemically control few-atom surface reconstruction events with present-day detection capabilities.
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73.40.-c Electronic transport in interface structures
85.30.Hi Surface barrier, boundary, and point contact devices
68.35.bd Metals and alloys
68.35.bg Semiconductors
02.60.-x Numerical approximation and analysis
68.35.Ct Interface structure and roughness

Ultra-low resistance ohmic contacts in graphene field effect transistors

J. S. Moon, M. Antcliffe, H. C. Seo, D. Curtis, S. Lin, A. Schmitz, I. Milosavljevic, A. A. Kiselev, R. S. Ross, D. K. Gaskill, P. M. Campbell, R. C. Fitch, K.-M. Lee, and P. Asbeck

Appl. Phys. Lett. 100, 203512 (2012); http://dx.doi.org/10.1063/1.4719579 (3 pages) | Cited 3 times

Online Publication Date: 18 May 2012

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We report on an experimental demonstration of graphene-metal ohmic contacts with contact resistance below 100 Ω µm. These have been fabricated on graphene wafers, both with and without hydrogen intercalation, and measured using the transmission line method. Specific contact resistivities of 3 × 10−7 to 1.2 × 10−8 Ω cm2 have been obtained. The ultra-low contact resistance yielded short-channel (source-drain distance of 0.45 µm) HfO2/graphene field effect transistors (FETs) with a low on-resistance (Ron) of 550 Ω µm and a high current density of 1.7 A/mm at a source-drain voltage of 1 V. These values represent state-of-the-art (SOA) performance in graphene-metal contacts and graphene FETs. This ohmic contact resistance is comparable to that of SOA high-speed III–V high electron mobility transistors.
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85.30.Tv Field effect devices
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