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6 Feb 2012

Volume 100, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 061101 (2012); http://dx.doi.org/10.1063/1.3665180 (3 pages)

I. E. Khodasevych, C. M. Shah, S. Sriram, M. Bhaskaran, W. Withayachumnankul, B. S. Y. Ung, H. Lin, W. S. T. Rowe, D. Abbott, and A. Mitchell
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Spontaneous induction of the uniform lying helix alignment in bimesogenic liquid crystals for the flexoelectro-optic effect

Damian J. Gardiner, Stephen M. Morris, Philip J. W. Hands, Flynn Castles, Malik M. Qasim, Wook-Sung Kim, Su Seok Choi, Timothy D. Wilkinson, and Harry J. Coles

Appl. Phys. Lett. 100, 063501 (2012); http://dx.doi.org/10.1063/1.3682305 (4 pages) | Cited 3 times

Online Publication Date: 6 February 2012

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Using in-plane electric fields, the electrical induction of the uniform lying helix (ULH) alignment in chiral nematic liquid crystals is reported. This process permits spontaneous induction of the ULH alignment to give an in-plane optic axis, without the need for complex processing. Flexoelectro-optic switching is subsequently obtained by holding the in-plane electrodes at a common voltage and addressing via a third, plane-parallel electrode on a second, or upper, substrate to give a field across the device in the viewing direction. For this device, in optimized bimesogenic materials, we demonstrate full intensity modulation and sub-millisecond response times at typical device temperatures.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects

Deformable transparent all-carbon-nanotube transistors

Shinya Aikawa, Erik Einarsson, Theerapol Thurakitseree, Shohei Chiashi, Eiichi Nishikawa, and Shigeo Maruyama

Appl. Phys. Lett. 100, 063502 (2012); http://dx.doi.org/10.1063/1.3683517 (4 pages) | Cited 3 times

Online Publication Date: 7 February 2012

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We fabricated polymer-laminated, transparent, all-carbon-nanotube field-effect transistors (CNT-FETs), making use of the flexible yet robust nature of single-walled carbon nanotubes (SWNTs). All components of the FET (active channel, electrodes, dielectric layer, and substrate) consist of carbon-based materials. The use of a plastic substrate that is considerably thinner than those used in other flexible CNT-FETs allowed our devices to be highly deformable without degradation of electrical properties. Using this approach, flexible, transparent CNT-FET devices able to withstand a 1 mm bending radius were realized.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices

Superconducting low-inductance undulatory galvanometer microwave amplifier

D. Hover, Y.-F. Chen, G. J. Ribeill, S. Zhu, S. Sendelbach, and R. McDermott

Appl. Phys. Lett. 100, 063503 (2012); http://dx.doi.org/10.1063/1.3682309 (3 pages) | Cited 3 times

Online Publication Date: 7 February 2012

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We describe a microwave amplifier based on the superconducting low-inductance undulatory galvanometer (SLUG). The SLUG is embedded in a microstrip resonator, and the signal current is injected directly into the device loop. Measurements at 30 mK show gains of 25 dB at 3 GHz and 15 dB at 9 GHz. Amplifier performance is well described by a simple numerical model based on the Josephson junction phase dynamics. We expect optimized devices based on high critical current junctions to achieve gain greater than 15 dB, bandwidth of several hundred MHz, and added noise of order one quantum in the frequency range of 5-10 GHz.
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85.25.Cp Josephson devices
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
84.30.Le Amplifiers
84.40.Az Waveguides, transmission lines, striplines

Full band atomistic modeling of homo-junction InGaAs band-to-band tunneling diodes including band gap narrowing

Woo-Suhl Cho, Mathieu Luisier, Dheeraj Mohata, Suman Datta, David Pawlik, Sean L. Rommel, and Gerhard Klimeck

Appl. Phys. Lett. 100, 063504 (2012); http://dx.doi.org/10.1063/1.3682506 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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A homo-junction In0.53Ga0.47As tunneling diode is investigated using full-band, atomistic quantum transport approach based on a tight-binding model (TB) and the non-equilibrium Green’s function formalism. Band gap narrowing (BGN) is included in TB by altering its parameters using the Jain-Roulston model [S. C. Jain and D. J. Roulston, Solid-State Electron. 34, 453 (1991)]. BGN is found to be critical in the determination of the current peak and the second turn-on in the forward bias region. Empirical excess current that mimics additional recombination paths must be added to the calculation to model the diode behavior in the valley current region. Overall, the presented model reproduces experimental data well.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Kk Junction diodes

Thermally stable, sub-nanometer equivalent oxide thickness gate stack for gate-first In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors

M. El Kazzi, L. Czornomaz, C. Rossel, C. Gerl, D. Caimi, H. Siegwart, J. Fompeyrine, and C. Marchiori

Appl. Phys. Lett. 100, 063505 (2012); http://dx.doi.org/10.1063/1.3683472 (3 pages) | Cited 1 time

Online Publication Date: 8 February 2012

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Metal-oxide-semiconductor (MOS) capacitors were fabricated by depositing composite 2 nm HfO2/1 nm Al2O3/1 nm a-Si gate stacks on p-In0.53Ga0.47As/InP (001) substrates. Thanks to the presence of the Al2O3 barrier layer, a minimum amount of the a-Si passivating layer is oxidized during the whole fabrication process. The capacitors exhibit excellent electrical characteristics with scaled equivalent oxide thickness (EOT) of 0.89 nm and mid-gap interface state density of 5 × 1011 eV−1 cm−2 upon post-metallization anneal up to 550 °C. Gate-first, self-aligned MOS field-effect-transistors were fabricated with a similar 5 nm HfO2/1 nm Al2O3/1 nm a-Si gate stack and raised source and drain (600 °C for 30 min). Owing to the excellent thermal stability of the stack, no degradation of the gate stack/semiconductor interface is observed, as demonstrated by the excellent capacitance vs voltage characteristics and the good mobility values (peak at 1030 cm2 V−1 s−1 and 740 cm2 V−1 s−1 at carrier density of 6.5 × 1012 cm−2) for a 1.3 nm EOT.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
81.40.Gh Other heat and thermomechanical treatments
68.60.Dv Thermal stability; thermal effects

High mobility thin film transistors with indium oxide/gallium oxide bi-layer structures

S.-L. Wang, J.-W. Yu, P.-C. Yeh, H.-W. Kuo, L.-H. Peng, A. A. Fedyanin, E. D. Mishina, and A. S. Sigov

Appl. Phys. Lett. 100, 063506 (2012); http://dx.doi.org/10.1063/1.3683518 (4 pages)

Online Publication Date: 9 February 2012

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We investigate the transport properties of thin-film transistors using indium oxide (In2O3)/gallium oxide (Ga2O3) bi-layer stacks as the channel material. At low gate bias, we observe the transistor field-effect mobility increases with the film resistivity to μFE = 51.3 cm2/Vs and ON/OFF current ratio to 108 due to combinatorial layer thickness modulation. With the Ga2O3 layer thickness ratio increase to R = 14.35%, these observations are accompanied with one-order-of-magnitude reduction in the transistor subthreshold swing to 0.38 V/decade and suggest a trap-limited conduction mechanism upon which the reduced scattering centers due to annihilation of subgap states improve the device electric characteristics without post-growth annealing.
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85.30.Tv Field effect devices

Electron gas dimensionality engineering in AlGaN/GaN high electron mobility transistors using polarization

Pil Sung Park, Digbijoy N. Nath, Sriram Krishnamoorthy, and Siddharth Rajan

Appl. Phys. Lett. 100, 063507 (2012); http://dx.doi.org/10.1063/1.3685483 (3 pages)

Online Publication Date: 9 February 2012

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We propose and demonstrate a two dimensional/three dimensional hybrid channel AlGaN/GaN high electron mobility transistor (HEMT) structure with a flat transconductance profile using polarization-induced channel engineering. A quasi three dimensional electron gas profile with 5–6 nm of vertical channel depth was formed by grading the channel region linearly from GaN to Al0.15Ga0.85 N over 50 Å. We demonstrate a flat gm profile in an AlGaN/GaN HEMT with high current density of 1 A/mm and peak gm of 168 mS/mm over 85% of the input bias range under dc conditions. This approach simultaneously enables vertical device scaling and transconductance engineering in a HEMT structure.
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85.30.Tv Field effect devices

Understanding on the current-induced crystallization process and faster set write operation thereof in non-volatile phase change memory

Dae-Hwan Kang, Nan Young Kim, Hongsik Jeong, and Byung-ki Cheong

Appl. Phys. Lett. 100, 063508 (2012); http://dx.doi.org/10.1063/1.3684245 (3 pages) | Cited 1 time

Online Publication Date: 9 February 2012

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We experimentally demonstrate that the crystallization process of Ge-Sb-Te crystallites during the set operation in non-volatile phase change memory commences after threshold switching event. It is also shown that the nucleation and growth rates have opposite behaviors with the increase of set operation power: the incubation time in nucleation stage can be minimized at higher power, whereas the percolation time in growth stage is smaller at lower power. Based on these results, we introduce a two-step set pulse of high-power nucleation and low-power growth making the set write operation much faster than conventional simple rectangular or slow-quenched form.
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81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.40.Gh Other heat and thermomechanical treatments
82.60.Nh Thermodynamics of nucleation

The mechanism of the asymmetric SET and RESET speed of graphene oxide based flexible resistive switching memories

Lu-Hao Wang, Wen Yang, Qing-Qing Sun, Peng Zhou, Hong-Liang Lu, Shi-Jin Ding, and David Wei Zhang

Appl. Phys. Lett. 100, 063509 (2012); http://dx.doi.org/10.1063/1.3681366 (4 pages) | Cited 5 times

Online Publication Date: 10 February 2012

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Oxygen migration is reported as key factors of resistive switching in graphene oxide (GO) based memories by different groups. A flexible nonvolatile resistive switching memory based on GO was fabricated through a spin-coating process. The speed of the SET and RESET operations of the GO memories was found to be significant asymmetric. The RESET speed is in the order of 100 ns under a −5 V voltage while the SET speed is three orders of magnitude slower (100 μs) under a 5 V bias. The behavior of resistive switching speed difference is elucidated by voltage modulated oxygen diffusion barrier change.
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84.30.Sk Pulse and digital circuits
85.65.+h Molecular electronic devices

Suppression of microwave rectification effects in electrically detected magnetic resonance measurements

C. C. Lo, F. R. Bradbury, A. M. Tyryshkin, C. D. Weis, J. Bokor, T. Schenkel, and S. A. Lyon

Appl. Phys. Lett. 100, 063510 (2012); http://dx.doi.org/10.1063/1.3684247 (3 pages)

Online Publication Date: 10 February 2012

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Spin-dependent transport properties of micro- and nano-scale electronic devices are commonly studied by electrically detected magnetic resonance (EDMR). However, the applied microwave fields in EDMR experiments can induce large rectification effects and result in perturbations of the device bias conditions and excessive noise in the EDMR spectra. Here we examine rectification effects of silicon metal-oxide-semiconductor field-effect transistors exposed to X-band microwave irradiation and show that the rectification effects can be effectively suppressed by incorporating a global capacitive shunt covering the device. We demonstrate that the signal-to-noise ratio in the EDMR spectra improves by over a factor of ten in the shunted devices.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
84.30.Jc Power electronics; power supply circuits
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Epitaxial NiO gate dielectric on AlGaN/GaN heterostructures

Fabrizio Roccaforte, Giuseppe Greco, Patrick Fiorenza, Vito Raineri, Graziella Malandrino, and Raffaella Lo Nigro

Appl. Phys. Lett. 100, 063511 (2012); http://dx.doi.org/10.1063/1.3684625 (4 pages) | Cited 2 times

Online Publication Date: 10 February 2012

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This letter reports on epitaxial nickel oxide (NiO) films grown by metal-organic chemichal vapor deposition on AlGaN/GaN heterostructures. The grown material was epitaxial, free from voids and exhibited a permittivity of 11.7, close to bulk NiO. This approach is advantageous with respect other methods such as the thermal oxidation of Ni films due to a better reproducibility and film quality. A reduction of the leakage current in Schottky diodes with an interfacial NiO layer has been observed and described using the metal-insulator-semiconductor Schottky model. The results indicate that these films are promising as gate dielectric for AlGaN/GaN transistors technology.
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73.61.Ng Insulators
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ch Permittivity (dielectric function)
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