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17 Sep 2012

Volume 101, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 101, 123901 (2012); http://dx.doi.org/10.1063/1.4751469 (4 pages)

Chin-An Lin, K. P. Huang, S. T. Ho, Mei-Wen Huang, and Jr-Hau He
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Unipolar behavior of asymmetrically doped strained Si0.5Ge0.5 tunneling field-effect transistors

M. Schmidt, R. A. Minamisawa, S. Richter, A. Schäfer, D. Buca, J. M. Hartmann, Q.-T. Zhao, and S. Mantl

Appl. Phys. Lett. 101, 123501 (2012); http://dx.doi.org/10.1063/1.4751356 (4 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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We investigate here the impact of the dopant concentration in the source and drain regions on the ambipolar behavior of band-to-band tunneling field-effect transistors with compressively strained Si0.5Ge0.5 channels grown on Si on insulator. Source and drain areas were formed by BF2+ and As+ ion implantation to doses of 1 × 1013, 1 × 1014, and 1 × 1015 cm−2. We show that the dopant concentration impacts the energy band alignment of source/drain and the channel region, and thus influences the tunneling current. The ambipolar device behavior is strongly reduced toward unipolar for source-to-drain implantation dose ratio of 100, but at the expense of the on-current, as compared to symmetric implanted devices. Moreover, our results indicate that for SiGe devices, the change of the B doping concentration has a greater impact on the tunneling currents than the variation of the As concentration.
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85.30.Tv Field effect devices

Light/negative bias stress instabilities in indium gallium zinc oxide thin film transistors explained by creation of a double donor

Piero Migliorato, Md Delwar Hossain Chowdhury, Jae Gwang Um, Manju Seok, and Jin Jang

Appl. Phys. Lett. 101, 123502 (2012); http://dx.doi.org/10.1063/1.4752238 (5 pages) | Cited 1 time

Online Publication Date: 17 September 2012

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The analysis of current-voltage (I-V) and capacitance-voltage (C-V) characteristics for amorphous indium gallium zinc oxide Thin film transistors as a function of active layer thickness shows that negative bias under illumination stress (NBIS) is quantitatively explained by creation of a bulk double donor, with a shallow singly ionized state ε(0/+) > EC-0.073 eV and a deep doubly ionized state ε(++/+) < EC-0.3 eV. The gap density of states, extracted from the capacitance-voltage curves, shows a broad peak between EC–E = 0.3 eV and 1.0 eV, which increases in height with NBIS stress time and corresponds to the broadened transition energy between singly and doubly ionized states. We propose that the center responsible is an oxygen vacancy and that the presence of a stable singly ionized state, necessary to explain our experimental results, could be due to the defect environment provided by the amorphous network.
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85.30.Tv Field effect devices

Coherent terahertz radiation from high-harmonic component of modulated free-electron beam in a tapered two-asymmetric grating structure

Ya-Xin Zhang, Yu-Cong Zhou, Liang Dong, and Sheng-Gang Liu

Appl. Phys. Lett. 101, 123503 (2012); http://dx.doi.org/10.1063/1.4752730 (4 pages) | Cited 1 time

Online Publication Date: 18 September 2012

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Based on the mechanism of incoherent diffraction radiation excited by an electron bunch in a waveguide with periodic structure, this paper presents the concept of coherent terahertz (THz) radiation from the high-harmonic component of a modulated free-electron beam in a tapered two-asymmetric grating structure. The results show that in this mechanism 0.43 THz radiation can be generated with 10 A/cm2 current density, and the efficiency can reach 0.5%. Because of the low required current density and relative high efficiency, this concept shows the application potential for electron-beam-driven terahertz sources.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.Dj Gratings
41.75.Fr Electron and positron beams
84.40.Az Waveguides, transmission lines, striplines

Recovery improvement of graphene-based gas sensors functionalized with nanoscale heterojunctions

Il-Suk Kang, Hye-Mi So, Gyeong-Sook Bang, Jun-Hyuk Kwak, Jeong-O Lee, and Chi Won Ahn

Appl. Phys. Lett. 101, 123504 (2012); http://dx.doi.org/10.1063/1.4753974 (4 pages)

Online Publication Date: 18 September 2012

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We report a development of reduced graphene oxide (rGO)-based gas sensors with a practical recovery by facile functionalization with tin dioxide nanoclusters. Upon the introduction of UV illumination to this nanostructure, the reaction on surfaces of tin dioxide nanoclusters was activated and thereby the nanoscale heterojunction barriers between the rGO sheet and the nanoclusters were developed. This lowered the conductance to quickly recover, which was intensified as the cluster density has reached to the percolation threshold. However, after the formation of the cluster percolating network, the sensor response has totally changed into a deterioration of the sensitivity as well as the recovery.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.ue Graphene

High field carrier transport in graphene: Insights from fast current transient

Kausik Majumdar, Sangeeth Kallatt, and Navakanta Bhat

Appl. Phys. Lett. 101, 123505 (2012); http://dx.doi.org/10.1063/1.4754103 (4 pages) | Cited 2 times

Online Publication Date: 19 September 2012

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In this work, we observe gate tunable negative differential conductance (NDC) and current saturation in single layer and bilayer graphene transistor at high source-drain field, which arise due to the interplay among (1) self-heating, (2) hot carrier injection, and (3) drain induced minority carrier injection. The magnitude of the NDC is found to be reduced for a bilayer, in agreement with its weaker carrier-optical phonon coupling and less efficient hot carrier injection. The contributions of different mechanisms to the observed results are decoupled through fast transient measurements with nanosecond resolution. The findings provide insights into high field transport in graphene.
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72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.30.Tv Field effect devices
81.05.ue Graphene

Single charge detection in capacitively coupled integrated single electron transistors based on single-walled carbon nanotubes

Xin Zhou and Koji Ishibashi

Appl. Phys. Lett. 101, 123506 (2012); http://dx.doi.org/10.1063/1.4752240 (4 pages) | Cited 1 time

Online Publication Date: 19 September 2012

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Single charge detection is demonstrated in the capacitively coupled integrated single electron transistors (SETs) in single-walled carbon nanotubes (SWCNTs) quantum dots. Two SETs are fabricated based on two different SWCNTs aligned in parallel, by taking advantage of the aligned growth of SWCNTs and subsequent transfer-printed techniques. In order to make both two SETs be capacitively coupled, a metal finger is fabricated on the top of them. The charge sensing is proved by the response of a detector current in one SWCNT-SET when the number of electrons in the other SWCNT-SET is changed by sweeping the corresponding gate voltages. In this integrated device, shifts of Coulomb oscillation peaks due to the single electron event are also observed.
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85.35.Gv Single electron devices
85.35.Kt Nanotube devices

Heat flow control in thermo-magnetic convective systems using engineered magnetic fields

Jaewook Lee, Tsuyoshi Nomura, and Ercan M. Dede

Appl. Phys. Lett. 101, 123507 (2012); http://dx.doi.org/10.1063/1.4754119 (4 pages)

Online Publication Date: 19 September 2012

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We present the design of a magnetically controlled convective heat transfer system. The underlying thermo-magnetic instability phenomenon is described, and enhanced convective fluid flow patterns are determined using non-linear programming techniques plus a design sensitivity analysis. Specifically, the magnetic fluid body force is computed by finding the optimal distribution and magnetization direction of a magnetic field source, where the objective is to minimize the maximum temperature of a closed loop heat transfer system. Sizeable fluid recirculation zones are induced by arranging magnetic field generation elements in configurations similar to Halbach arrays. Applications include improved heat flow control for electromechanical systems.
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47.85.L- Flow control
47.27.te Turbulent convective heat transfer
47.65.Cb Magnetic fluids and ferrofluids

White light emission with red-green-blue lasing action in a disordered system of nanoparticles

Shujing Chen, Xiaoye Zhao, Yanrong Wang, Jinwei Shi, and Dahe Liu

Appl. Phys. Lett. 101, 123508 (2012); http://dx.doi.org/10.1063/1.4754286 (4 pages)

Online Publication Date: 20 September 2012

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White light emission from a disordered system with intensity feedback is investigated. The gain material is an ethanol solution with three laser dyes (Coumarin 440, Coumarin 6, Oxazine), and titanium dioxide (TiO2) nanoparticles to provide feedback. A single pulsed laser beam at 355 nm with 8 ns pulse duration is used to pump the dyes. Coumarin 440 and Coumarin 6 are excited first by the pump beam, and part of the Coumarin 6 peak pumps Oxazine. Bright white light emission is obtained by combining blue, green, and red beams with a threshold effect. The working properties and system emission characteristics are discussed.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Hj Laser materials
78.55.Bq Liquids
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Electro-optic polymer/TiO2 multilayer slot waveguide modulators

Y. Enami, B. Yuan, M. Tanaka, J. Luo, and A. K.-Y. Jen

Appl. Phys. Lett. 101, 123509 (2012); http://dx.doi.org/10.1063/1.4754597 (4 pages)

Online Publication Date: 21 September 2012

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We report an all-dielectric electro-optic (EO) polymer/TiO2 multilayer slot waveguide modulator with low optical insertion loss for high-speed operations. The EO polymer is sandwiched between thin TiO2 slot waveguide films to improve mode confinement in the EO polymer. The structure increased the mode confinement in the TiO2 and EO polymer slot layers and reduced the electrode distance between the Au electrodes without introducing optical loss from the metal electrodes. The half-wave voltage of the modulator was 6.5 V for a 5-mm-long electrode at a wavelength of 1550 nm. The half-wave voltage and length product was 3.25 V·cm.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers

Dislocation-limited open circuit voltage in film crystal silicon solar cells

Kirstin Alberi, Howard M. Branz, Harvey Guthrey, Manuel J. Romero, Ina T. Martin, Charles W. Teplin, Paul Stradins, and David L. Young

Appl. Phys. Lett. 101, 123510 (2012); http://dx.doi.org/10.1063/1.4754142 (4 pages)

Online Publication Date: 21 September 2012

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Carrier recombination at dislocations is a major source of efficiency loss in epitaxial film Si solar cells and significantly affects the open circuit voltage, VOC. We develop a simple empirical model that yields a logarithmic relationship between VOC and the dislocation density, which fits well to our data. Straightforward evaluation of device performance with this model provides qualitative information about the recombination activity at dislocations.
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88.40.jj Silicon solar cells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
88.40.hj Efficiency and performance of solar cells
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