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12 Sep 2011

Volume 99, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 99, 113501 (2011); http://dx.doi.org/10.1063/1.3634072 (3 pages)

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan, Ramamoorthy Ramesh, and Sayeef Salahuddin
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Experimental evidence of ferroelectric negative capacitance in nanoscale heterostructures

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan, Ramamoorthy Ramesh, and Sayeef Salahuddin

Appl. Phys. Lett. 99, 113501 (2011); http://dx.doi.org/10.1063/1.3634072 (3 pages) | Cited 7 times

Online Publication Date: 12 September 2011

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We report a proof-of-concept demonstration of negative capacitance effect in a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of ferroelectric Pb(Zr0.2Ti0.8)O3 and dielectric SrTiO3, the composite capacitance was observed to be larger than the constituent SrTiO3 capacitance, indicating an effective negative capacitance of the constituent Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning parameter for the ferroelectric negative capacitance and the degree of capacitance enhancement in the heterostructure. Landau’s mean field theory based calculations show qualitative agreement with observed effects. This work underpins the possibility that by replacing gate oxides by ferroelectrics in nanoscale transistors, the sub threshold slope can be lowered below the classical limit (60 mV/decade).
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Cg PZT ceramics and other titanates
61.46.-w Structure of nanoscale materials

Graphene microwave transistors on sapphire substrates

E. Pallecchi, C. Benz, A. C. Betz, H. v. Löhneysen, B. Plaçais, and R. Danneau

Appl. Phys. Lett. 99, 113502 (2011); http://dx.doi.org/10.1063/1.3633105 (3 pages) | Cited 5 times

Online Publication Date: 12 September 2011

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We have developed metal-oxide graphene field-effect transistors (MOGFETs) on sapphire substrates working at microwave frequencies. For monolayers, we obtain a transit frequency up to ∼80 GHz for a gate length of 200 nm and a maximum oscillation frequency of about ∼3 GHz for this specific sample. Given the strongly reduced charge noise for nanostructures on sapphire, the high stability and high performance of this material at low temperature, our MOGFETs on sapphire are well suited for a cryogenic broadband low-noise amplifier.
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85.30.Tv Field effect devices

Effect of metal-doping in TiO2 on fill factor of dye-sensitized solar cells

Xi Zhang, Shu-Tao Wang, and Zhong-Sheng Wang

Appl. Phys. Lett. 99, 113503 (2011); http://dx.doi.org/10.1063/1.3635788 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2011

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In the study of dye-sensitized solar cells (DSSCs), we find that fill factor (FF) increases with the doping amount of Zn(II) but decreases with the doping amount of W(VI) in TiO2. A single-diode model is established to analyze the dependence of FF on open-circuit voltage (Voc) and ideal factor (m). This model well explains the changes of FF caused by the doping element and amount, that is, FF increases with the ratio of Voc/m. This study will shed light on the influencing factors of FF and guide the design of new materials towards high FF for DSSCs.
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88.40.hj Efficiency and performance of solar cells
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.up Other materials

Dual in-plane-gate oxide-based thin-film transistors with tunable threshold voltage

Jie Jiang, Jia Sun, Liqiang Zhu, Guodong Wu, and Qing Wan

Appl. Phys. Lett. 99, 113504 (2011); http://dx.doi.org/10.1063/1.3636404 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2011

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Dual in-plane-gate oxide-based thin-film transistors (TFTs) are self-assembled on SiO2-based solid-electrolytes by only one shadow mask. The unique feature of such TFTs is that indium-tin-oxide (ITO) channel and four ITO electrodes can be deposited simultaneously. Threshold voltage can be effectively tuned from −0.55 V to 0.76 V when the second in-plane gate bias switches from 3.0 V to −2.0 V. Such dual-gate TFTs exhibit a large current on/off ratio (>106) and a small subthreshold swing (<200 mV/decade). A model based on three gate capacitors is proposed to further understand the operation mechanism of such devices.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Insight into low frequency noise induced by gate leakage current in AlGaAs/GaAs high electron mobility transistors at 4.2 K

Y. X. Liang, Q. Dong, M. C. Cheng, U. Gennser, A. Cavanna, and Y. Jin

Appl. Phys. Lett. 99, 113505 (2011); http://dx.doi.org/10.1063/1.3637054 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2011

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The bias-cooling method—the gate being kept biased at Vgc during the cooling—has been used to investigate the low frequency noise (LFN) in an AlGaAs/GaAs two-dimensional electron gas high electron mobility transistor at 4.2 K. For a chosen working point (i.e., a chosen drain bias/current), its gate bias Vgs, gate leakage current Igs, and LFN depend on Vgc. With the help of the heterostructure band diagram simulation for each Vgc, the relation between Igs and the LFN can be elucidated by the gate Fermi level with regard to the heterostructure band diagram. The LFN originated from Igs is caused by its sequential tunnelling component.
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85.30.Tv Field effect devices

Electroforming and endurance behavior of Al/Pr0.7Ca0.3MnO3/Pt devices

Zhaoliang Liao, Peng Gao, Yang Meng, Hongwu Zhao, Xuedong Bai, Jiandi Zhang, and Dongmin Chen

Appl. Phys. Lett. 99, 113506 (2011); http://dx.doi.org/10.1063/1.3638059 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2011

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We have investigated the electroforming (EF) and resistive switching (RS) of Al/Pr0.7Ca0.3MnO3 (PCMO)/Pt devices by using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy combined with transport measurement. The device prefers EF with positive bias with respect to Pt electrode and their endurance is enhanced with the chemically reactive Al electrode. The presence of an Al2O3−δ layer in Al/PCMO junction indicates that the oxidization and reduction near the Al/PCMO interface play a key role in the RS.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Minimizing quasiparticle generation from stray infrared light in superconducting quantum circuits

R. Barends, J. Wenner, M. Lenander, Y. Chen, R. C. Bialczak, J. Kelly, E. Lucero, P. O’Malley, M. Mariantoni, D. Sank, H. Wang, T. C. White, Y. Yin, J. Zhao, A. N. Cleland, et al.

Appl. Phys. Lett. 99, 113507 (2011); http://dx.doi.org/10.1063/1.3638063 (3 pages) | Cited 19 times

Online Publication Date: 13 September 2011

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We find that quasiparticle generation from stray infrared light creates a significant loss mechanism in superconducting resonators and qubits. We show that resonator quality factors and qubit energy relaxation times are limited by a quasiparticle density of approximately 200 μm−3, induced by 4 K blackbody radiation from the environment. We demonstrate how this influence can be fully removed by isolating the devices from the radiative environment using multistage shielding.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
03.65.-w Quantum mechanics
03.65.Yz Decoherence; open systems; quantum statistical methods
03.67.Lx Quantum computation architectures and implementations
85.25.-j Superconducting devices

Amorphous HgCdTe infrared photoconductive detector with high detectivity above 200 K

Jun Wang, Xiaoshuang Chen, Weida Hu, Lin Wang, Wei Lu, Faqiang Xu, Jun Zhao, Yanli Shi, and Rongbin Ji

Appl. Phys. Lett. 99, 113508 (2011); http://dx.doi.org/10.1063/1.3638459 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2011

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Temperature dependence of dark current (Id) and photocurrent (Iph) is reported for Si-based amorphous HgCdTe (a-MCT) infrared photoconductive detector at 80-300 K. It is indicated that an uncooled a-MCT infrared detector can be fabricated based on the Si-based a-MCT. To describe the transport process, the Mott and Davis model [Davis and Mott, Philos. Mag. 22, 903 (1970)] is proposed as the conducting model originally developed for amorphous silicon. A possible mechanism of the carrier transports is shown in the a-MCT materials. The transport transition between the localized and extended carriers leads to the maximal Iph/Id above 200 K.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
85.30.De Semiconductor-device characterization, design, and modeling

Forming-free resistive switching behavior in Nd2O3, Dy2O3, and Er2O3 films fabricated in full room temperature

Tung-Ming Pan and Chih-Hung Lu

Appl. Phys. Lett. 99, 113509 (2011); http://dx.doi.org/10.1063/1.3638490 (3 pages) | Cited 10 times

Online Publication Date: 13 September 2011

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In this study, we reported the forming-free resistive switching behavior in the Ru/RE2O3/TaN (RE = Nd, Dy, and Er) memory devices using thin Nd2O3, Dy2O3, and Er2O3 films fabricated with full room temperature process. The dominant conduction mechanisms of the Ru/RE2O3/TaN devices in the low-resistance state and high-resistance state are Ohmic behavior. The Ru/Dy2O3/TaN memory device exhibited high resistance ratio, nondestructive readout, reliable data retention, and good endurance. Ru/Dy2O3/TaN memory device has a great potential for the application in nonvolatile resistive switching memory.
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84.32.Dd Connectors, relays, and switches

Silicon nanowire - poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) heterojunction solar cells

Baris Ozdemir, Mustafa Kulakci, Rasit Turan, and Husnu Emrah Unalan

Appl. Phys. Lett. 99, 113510 (2011); http://dx.doi.org/10.1063/1.3636385 (3 pages) | Cited 11 times

Online Publication Date: 14 September 2011

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Radial heterojunctions are known to exhibit magnificent anti-reflectivity and enhanced carrier collectivity due to short carrier diffusion distances. In this work, silicon nanowire-poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) radial heterojunction solar cells are presented. Both layers of the heterojunction are fabricated using simple and cost-effective methods. Radial heterojunctions showed remarkable improvements in solar cell characteristics compared to planar heterojunctions, fabricated under the same conditions. The highest solar cell efficiency of 5.30% is obtained. The cells exhibit external quantum efficiency of 77% at 500 nm wavelength and harvest light over the entire 300-1200 nm spectral bandwidth. The effect of nanowire length on device performance is also determined.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Low-frequency noise of unipolar nanorectifiers

Claudio Balocco, Shahrir R. Kasjoo, Linqing Q. Zhang, Yasaman Alimi, and Aimin M. Song

Appl. Phys. Lett. 99, 113511 (2011); http://dx.doi.org/10.1063/1.3636437 (3 pages)

Online Publication Date: 14 September 2011

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Unipolar nanodiodes, also known as self-switching devices, have recently been demonstrated as terahertz detectors at room temperature. Here, we study their low-frequency noise spectra and noise equivalent power and show that both performance parameters are comparable to those reported for state-of-the-art Schottky diodes. The truly planar nanodiode layout enables building structures with thousands of devices connected in parallel, which reduce low-frequency noise without affecting sensitivity. The observed 1/f noise can be described by Hooge’s mobility fluctuation theory.
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84.30.Jc Power electronics; power supply circuits
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.30.Kk Junction diodes

Innovative dual function nc-SiOx:H layer leading to a >16% efficient multi-junction thin-film silicon solar cell

Baojie Yan, Guozhen Yue, Laura Sivec, Jeffrey Yang, Subhendu Guha, and Chun-Sheng Jiang

Appl. Phys. Lett. 99, 113512 (2011); http://dx.doi.org/10.1063/1.3638068 (3 pages) | Cited 22 times

Online Publication Date: 14 September 2011

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We present our development of n-type nano-structured hydrogenated silicon oxide (nc-SiOx:H) as a dual-function layer in multi-junction solar cells. We optimized nc-SiOx:H and attained a conductivity suitable for a doped layer and optical property suitable for an inter-reflection layer. We tested the effectiveness of the dual-function nc-SiOx:H layer by replacing the normal n layer between the middle and the bottom cells in an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure. A significant gain in the middle cell current density of ∼1.0 mA/cm2 is achieved. We further optimized the component cells and the triple-junction structures and attained an initial active-area cell efficiency of 16.3%.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells

Surface loss simulations of superconducting coplanar waveguide resonators

J. Wenner, R. Barends, R. C. Bialczak, Yu Chen, J. Kelly, Erik Lucero, Matteo Mariantoni, A. Megrant, P. J. J. O’Malley, D. Sank, A. Vainsencher, H. Wang, T. C. White, Y. Yin, J. Zhao, et al.

Appl. Phys. Lett. 99, 113513 (2011); http://dx.doi.org/10.1063/1.3637047 (3 pages) | Cited 9 times

Online Publication Date: 15 September 2011

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Losses in superconducting planar resonators are presently assumed to predominantly arise from surface-oxide dissipation, due to experimental losses varying with choice of materials. We model and simulate the magnitude of the loss from interface surfaces in the resonator and investigate the dependence on power, resonator geometry, and dimensions. Surprisingly, the dominant surface loss is found to arise from the metal-substrate and substrate-air interfaces. This result will be useful in guiding device optimization, even with conventional materials.
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85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines

Quantum-dot-induced optical transition enhancement in InAs quantum-dot-embedded p–i–n GaAs solar cells

X.-J. Shang, J.-F. He, M.-F. Li, F. Zhan, H.-Q. Ni, Z.-C. Niu, H. Pettersson, and Y. Fu

Appl. Phys. Lett. 99, 113514 (2011); http://dx.doi.org/10.1063/1.3638488 (3 pages) | Cited 8 times

Online Publication Date: 15 September 2011

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Photocurrents (PCs) of three p–i–n GaAs solar cells, sample A with InAs quantum dots (QDs) embedded in the depletion region, B with QDs in the n region, and C without QDs, were studied experimentally and theoretically. Above GaAs bandgap, the PC of A is increased, while B is decreased with respect to C, since in A, the QD-induced reflection of hole wave function increases its overlap with electron wave function so that the optical transition rate is enhanced, while carrier mobility in B is reduced due to QD-induced potential variations. Moreover, A and B have increased PCs in the sub-GaAs-bandgap range due to QD optical absorptions.
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88.40.hj Efficiency and performance of solar cells

Better than Bragg: Optimizing the quality factor of resonators with aperiodic dielectric reflectors

Jonathan Breeze, Mark Oxborrow, and Neil McN Alford

Appl. Phys. Lett. 99, 113515 (2011); http://dx.doi.org/10.1063/1.3639271 (3 pages)

Online Publication Date: 16 September 2011

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Periodic dielectric structures, such as Bragg reflectors and photonic band-gap crystals, are used to localize electromagnetic modes. A key parameter for electromagnetic resonators is the quality factor, Q. For conventional Bragg reflectors, losses occur predominantly in the first few reflectors and one of the materials usually has a low dielectric loss tangent. By varying the individual dimensions of the reflecting elements, a significant improvement in the Q-factor can be obtained. We verify this by constructing and measuring proof-of-principle microwave resonators.
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42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials

An insulating liquid environment for reducing adhesion in a microelectromechanical system

Seung-Deok Ko, Jeong Oen Lee, Hyun-Ho Yang, Min-Wu Kim, Yong-Ha Song, and Jun-Bo Yoon

Appl. Phys. Lett. 99, 113516 (2011); http://dx.doi.org/10.1063/1.3640228 (3 pages) | Cited 1 time

Online Publication Date: 16 September 2011

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Stiction has been one of the major failure problems in microelectromechanical systems (MEMS). As a solution for stiction failure, we investigated an insulating liquid environment for MEMS to eliminate adhesion force. We speculated that three forces—capillary, solid-solid contact, and van der Waals (vdW) forces decrease when the devices are operated in an insulating liquid environment. In the experiment, the adhesion force of the devices was measured to be 42.8 μN on average in air, whereas it decreased to 2.52 μN on average in the insulating liquid, corresponding to a remarkable 94.1% decrement.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Coaxial cable Bragg grating

Tao Wei, Songping Wu, Jie Huang, Hai Xiao, and Jun Fan

Appl. Phys. Lett. 99, 113517 (2011); http://dx.doi.org/10.1063/1.3636406 (3 pages)

Online Publication Date: 16 September 2011

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This paper reports a coaxial cable Bragg grating (CCBG) fabricated by drilling holes into the cable at periodic distances along the axial direction. Resonances were observed at discrete frequencies in both transmission and reflection spectra. The analogy of the CCBG with a fiber Bragg grating is shown. The grating was tested for the potential application as a strain-sensing device.
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42.81.Bm Fabrication, cladding, and splicing
84.32.Hh Inductors and coils; wiring
42.79.Dj Gratings

Parallel memristive filaments model applicable to bipolar and filamentary resistive switching

Xinjun Liu (蘇東榆), Kuyyadi P. Biju, Joonmyoung Lee, Jubong Park, Seonghyun Kim, Sangsu Park, Jungho Shin, Sharif Md. Sadaf, and Hyunsang Hwang

Appl. Phys. Lett. 99, 113518 (2011); http://dx.doi.org/10.1063/1.3638486 (3 pages) | Cited 3 times

Online Publication Date: 16 September 2011

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The concept of memristive filaments (MFs) is introduced, which is based on the memristors developed by the Hewlett–Packard group. The effects of key parameters on electrical properties are elucidated. The current–voltage features of bipolar and filamentary resistive switching are reproduced by using a parallel MF model with dynamic growth and rupture of multiple MFs. This model can be extended and adapted to most nanosized transition metal oxide memristors.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
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