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28 Jun 2010

Volume 96, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 96, 261101 (2010); http://dx.doi.org/10.1063/1.3456618 (3 pages)

I. V. Konoplev, L. Fisher, A. W. Cross, A. D. R. Phelps, K. Ronald, and C. W. Robertson
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Self-aligned imprint lithography for top-gate amorphous silicon thin-film transistor fabrication

E. Lausecker, Y. Huang, T. Fromherz, J. C. Sturm, and S. Wagner

Appl. Phys. Lett. 96, 263501 (2010); http://dx.doi.org/10.1063/1.3457446 (3 pages) | Cited 7 times

Online Publication Date: 28 June 2010

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We developed self-aligned imprint lithography (SAIL) for top-gate amorphous silicon (a-Si) thin-film transistors (TFTs). Our SAIL process enables a device pattern definition in a single imprint step that uses a three-level mold. The various levels of the mold are defined by a stepwise opening of a chromium hardmask and subsequent dry-etching. For TFT fabrication we imprint, and consecutively etch the imprint resist levels and device layers. The imprinted top-gate a-Si TFTs have nickel silicide source/drain self-aligned to the gate with mobilities of ∼ 0.4 cm2/V s.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Acoustic far-field focusing effect for two-dimensional graded negative refractive-index sonic crystals

Shasha Peng, Zhaojian He, Han Jia, Anqi Zhang, Chunyin Qiu, Manzhu Ke, and Zhengyou Liu

Appl. Phys. Lett. 96, 263502 (2010); http://dx.doi.org/10.1063/1.3457447 (3 pages) | Cited 10 times

Online Publication Date: 28 June 2010

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Focusing effect is experimentally observed for acoustic plane wave normally incident onto a two-dimensional sonic crystal with gradient negative refractive index. The gradual refractive-index is achieved by gradual modification of the lattice spacing both along the transverse and longitudinal directions. It is found that the focal length is controllable by modulation of the lattice spacing. The experiment results are in excellent agreement with theoretical calculation by a multiple scattering theory method.
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43.20.-f General linear acoustics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Mechanism for excess noise in mixed tunneling and avalanche breakdown of silicon

Andrew Pan, Dee-Son Pan, and Chi On Chui

Appl. Phys. Lett. 96, 263503 (2010); http://dx.doi.org/10.1063/1.3457468 (3 pages)

Online Publication Date: 28 June 2010

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We propose a mechanism to explain the excess noise observed in silicon p-n junctions biased at the onset of mixed tunneling and avalanche breakdown. Electrons tunneling into different conduction valleys are treated as separate reaction channels with different impact ionization rates, due to different initial energies, that contribute excess noise. This noise contribution is regulated by the biasing circuit to prevent runaway. We have analyzed data from past measurements and shown higher conduction valley carrier channels can adequately account for the observed excess noise. The proposed framework provides an explanation of the excess noise data without any fitting parameters.
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77.22.Jp Dielectric breakdown and space-charge effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ht High-field and nonlinear effects

Electrical nanocharacterization of copper tetracyanoquinodimethane layers dedicated to resistive random access memories

Damien Deleruyelle, Christophe Muller, Julien Amouroux, and Robert Müller

Appl. Phys. Lett. 96, 263504 (2010); http://dx.doi.org/10.1063/1.3458596 (3 pages) | Cited 4 times

Online Publication Date: 28 June 2010

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The local electrical properties of copper tetracyanoquinodimethane (CuTCNQ)/HfO2/Pt stacks were investigated thanks to conductive-atomic force microscopy (AFM) measurements. Local I-V and I-t spectroscopy evidenced repeatable and reversible bipolar electrical switching (SET and RESET operations) at the nanometer scale beneath the AFM tip. Experimental results suggest that resistive switching is due to the creation/dissolution of conductive filaments bridging the CuTCNQ surface to the AFM tip. A physical model based on the migration of Cu+ ions within a nanogap and the growth of a conductive filament shows an excellent agreement with the experimental results during SET operation achieved at nanoscale.
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84.30.Sk Pulse and digital circuits
73.63.-b Electronic transport in nanoscale materials and structures

Stochastic base doping and quantum-well enhancement of recombination in an n-p-n light-emitting transistor or transistor laser

H. W. Then, C. H. Wu, M. Feng, N. Holonyak, Jr., and G. Walter

Appl. Phys. Lett. 96, 263505 (2010); http://dx.doi.org/10.1063/1.3458708 (3 pages)

Online Publication Date: 28 June 2010

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Data and analysis are presented showing that heavy p-type stochastic doping of the base barrier region of an n-p-n quantum-well (QW) light-emitting transistor (LET) or transistor laser (TL), the acceptors within tunneling range of the QW and perturbing the QW, enhances the LET or TL base recombination (base current) and the device speed (bandwidth). A relationship between the spontaneous recombination rate (1/lifetime, 1/τ) and the base current density is derived by considering (stochastic-doping) modified rate balance equations involving the spontaneous, A21, and stimulated recombination coefficients, B21 = B12, and is verified with experimental optical microwave modulation (bandwidth) data obtained on QW-LETs.
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42.55.Px Semiconductor lasers; laser diodes
85.30.Pq Bipolar transistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells

Ching-Chun Chang, Chi-Feng Lin, Jian-Ming Chiou, Tzung-Han Ho, Yian Tai, Jiun-Haw Lee, Yang-Fang Chen, Juen-Kai Wang, Li-Chyong Chen, and Kuei-Hsien Chen

Appl. Phys. Lett. 96, 263506 (2010); http://dx.doi.org/10.1063/1.3456530 (3 pages) | Cited 8 times

Online Publication Date: 28 June 2010

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The effects of cathode buffer layers on the bulk-heterojunction solar cells are investigated. Comparing with the device without buffer layer, obvious enhancements of Voc from 0.38 to 0.65 V and fill factor from 44% to 63% have been achieved by using 2 nm bathocuproine layer, which make the efficiency of the devices improved from 1.63% to 4.11%. Alternatively, lithium fluoride and/or tris(8-hydroxyquinolinato) aluminum were also introduced for clarification purpose. X-ray photoelectron spectroscopy study indicates that the degradation caused by the outer diffusion of carbon from active layers plays a crucial role in the device performance.
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88.40.H- Solar cells (photovoltaics)

Back-junction back-contact n-type silicon solar cells with screen-printed aluminum-alloyed emitter

Robert Bock, Susanne Mau, Jan Schmidt, and Rolf Brendel

Appl. Phys. Lett. 96, 263507 (2010); http://dx.doi.org/10.1063/1.3456536 (3 pages) | Cited 7 times

Online Publication Date: 28 June 2010

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We introduce an n-type Si back-junction back-contact solar cell based on an Al-doped p+ rear emitter fabricated by means of screen-printing and firing instead of the commonly applied high-temperature boron diffusion. In order to demonstrate the applicability of this easy-to-fabricate p+ emitter to a back-junction back-contact solar cell we present experimental results showing 19.0% cell efficiency. The structuring of the cell is performed by laser processing omitting any photolithography. Using two-dimensional device simulation we determine a realistic efficiency limit of 21.6% for this cell type.
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88.40.jj Silicon solar cells
42.62.-b Laser applications
88.40.hj Efficiency and performance of solar cells

Nonequilibrium carrier distribution in semiconductor photodetectors: Surface leakage channel under illumination

Hao Yin, Tian-xin Li, Wei-da Hu, Wen-juan Wang, Ning Li, Xiao-shuang Chen, and Wei Lu

Appl. Phys. Lett. 96, 263508 (2010); http://dx.doi.org/10.1063/1.3457872 (3 pages) | Cited 1 time

Online Publication Date: 29 June 2010

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The nonequilibrium carrier distribution in an InGaAs/InP avalanche photodiode under light illumination is obtained by cross-sectional scanning capacitance microscopy combined with numerical simulation. The sheet density of negative surface charge is determined to be 1.85×1010 cm−2 on the native-oxidized InGaAs (110) face. This surface charge is found responsible for the accumulation of minority holes, which leads to an inversion layer at the sidewall surface of device in the absorption region under illumination exceeding 0.1 mW/cm2. The inversion depth increases up to 200 nm along with the enhancement of excitation intensity. This work suggests that a surface leakage channel may form in semiconductor photodetectors through detection light excitation.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Three-dimensionally stacked flexible integrated circuit: Amorphous oxide/polymer hybrid complementary inverter using n-type a-In–Ga–Zn–O and p-type poly-(9,9-dioctylfluorene-co-bithiophene) thin-film transistors

Kenji Nomura, Takashi Aoki, Kiyoshi Nakamura, Toshio Kamiya, Takashi Nakanishi, Takayuki Hasegawa, Mutsumi Kimura, Takeo Kawase, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 96, 263509 (2010); http://dx.doi.org/10.1063/1.3458799 (3 pages) | Cited 13 times

Online Publication Date: 30 June 2010

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A three-dimensional vertically-stacked flexible integrated circuit is demonstrated based on hybrid complementary inverters made of n-type In–Ga–Zn–O (a-IGZO) amorphous oxide thin-film transistors (TFTs) and p-type poly-(9,9-dioctylfluorene-co-bithiophene) (F8T2) polymer TFTs, where all the fabrication processes were performed at temperatures ≤ 120 °C. Saturation mobilities of the a-IGZO TFT and the F8T2 TFT are ∼ 3.2 and ∼ 1.7×10−3 cm2 V−1 s−1, respectively, from which we chose the appropriate dimensions of the TFTs so as to obtain a good balance for the inverter operation. The maximum voltage gain is ∼ 67, which is better than those reported for organic/oxide hybrid complementary inverters.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Tv Field effect devices

Wigner crystallization due to electrons localized at deep traps in two-dimensional amorphous dielectric

S. S. Shaimeev, V. A. Gritsenko, and Hei Wong

Appl. Phys. Lett. 96, 263510 (2010); http://dx.doi.org/10.1063/1.3458832 (3 pages)

Online Publication Date: 30 June 2010

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We calculated the spatial distribution of electrons localized at deep neutral traps in some amorphous dielectric films based on some fundamental physics in order to explain the phenomena such as space ordering of electrons. We showed that when the surface density of traps (Ns) is much larger than that of the trapped electrons (ns), e.g., ns/Ns ≤ 0.001, Wigner crystallization occurs due to the Coulomb repulsion of trapped electrons and a two-dimensional quasiperiodic hexagonal lattice or Wigner glass can be formed.
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71.55.Jv Disordered structures; amorphous and glassy solids
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.55.-g Dielectric thin films

High-speed phonon imaging using frequency-multiplexed kinetic inductance detectors

L. J. Swenson, A. Cruciani, A. Benoit, M. Roesch, C. S. Yung, A. Bideaud, and A. Monfardini

Appl. Phys. Lett. 96, 263511 (2010); http://dx.doi.org/10.1063/1.3459142 (3 pages) | Cited 8 times

Online Publication Date: 1 July 2010

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We present a measurement of phonon propagation in a silicon wafer utilizing an array of frequency-multiplexed superconducting resonators coupled to a single transmission line. The electronic readout permits fully synchronous array sampling with a per-resonator bandwidth of 1.2 MHz, allowing submicrosecond array imaging. This technological achievement is potentially vital in a variety of low-temperature applications, including single-photon counting, quantum-computing, and dark-matter searches.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
06.60.Jn High-speed techniques (microsecond to femtosecond)

Correlation between kink and cathodoluminescence spectra in AlGaN/GaN high electron mobility transistors

G. Meneghesso, F. Rossi, G. Salviati, M. J. Uren, E. Muñoz, and E. Zanoni

Appl. Phys. Lett. 96, 263512 (2010); http://dx.doi.org/10.1063/1.3459968 (3 pages) | Cited 8 times

Online Publication Date: 1 July 2010

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The “kink” effect in AlGaN/GaN high electron mobility transistor current-voltage characteristics is shown to be associated with the epitaxial growth and is unaffected by fabrication process or growth substrate in device wafers from two epitaxy sources and three foundries. We demonstrate that there is a direct correlation between the presence of the “kink” and the presence of a broad yellow cathodoluminescence band. On the basis of generally accepted models for yellow luminescence, we propose that the kink is due to the presence of deep levels in the GaN buffer layer which decrease the drain current when negatively charged.
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85.30.Tv Field effect devices
78.60.Hk Cathodoluminescence, ionoluminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.ag Semiconductors

Detection of mechanical resonance of a single-electron transistor by direct current

Yu. A. Pashkin, T. F. Li, J. P. Pekola, O. Astafiev, D. A. Knyazev, F. Hoehne, H. Im, Y. Nakamura, and J. S. Tsai

Appl. Phys. Lett. 96, 263513 (2010); http://dx.doi.org/10.1063/1.3455880 (3 pages) | Cited 6 times

Online Publication Date: 1 July 2010

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We have suspended an Al based single-electron transistor (SET) whose island can resonate freely between the source and drain leads forming the clamps. In addition to the regular side gate, a bottom gate with a larger capacitance to the SET island is placed underneath to increase the SET coupling to mechanical motion. The device can be considered as a doubly clamped Al beam that can transduce mechanical vibrations into variations in the SET current. Our simulations based on the orthodox model, with the SET parameters estimated from the experiment, reproduce the observed transport characteristics in detail.
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85.35.Gv Single electron devices

Comparison on the electroluminescence of Si-rich SiNx and SiOx based light-emitting diodes

Gong-Ru Lin, Yi-Hao Pai, Cheng-Tao Lin, and Chun-Chieh Chen

Appl. Phys. Lett. 96, 263514 (2010); http://dx.doi.org/10.1063/1.3459144 (3 pages) | Cited 12 times

Online Publication Date: 2 July 2010

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Electroluminescence (EL) of the metal-insulator-semiconductor light-emitting diodes (MISLEDs) made by Si-rich SiNx and SiOx films with buried Si nanocrystals are compared. The SiNx facilitates carrier transport and EL from MISLED with turn-on current and voltage of 4 μA and 12 V by reducing barrier heights at indium tin oxide /SiNx and SiNx/Si-nc interfaces. The SiNx MISLED exhibits larger charge loss rate of 12% within 200 s and shorter delay time of 3.86×10−4 sec than SiOx one, which limit its external EL quantum efficiency by strong carrier escaping effect due to the insufficient carrier confinement in Si nanocrystals with low interfacial barriers.
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85.60.Jb Light-emitting devices

Metal-related gate sinking due to interfacial oxygen layer in Ir/InAlN high electron mobility transistors

C. Ostermaier, G. Pozzovivo, B. Basnar, W. Schrenk, M. Schmid, L. Tóth, B. Pécz, J.-F. Carlin, M. Gonschorek, N. Grandjean, G. Strasser, D. Pogany, and J. Kuzmik

Appl. Phys. Lett. 96, 263515 (2010); http://dx.doi.org/10.1063/1.3458700 (3 pages) | Cited 4 times

Online Publication Date: 2 July 2010

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We report on an annealing-induced “gate sinking” effect in a 2-nm-thin In0.17Al0.83N/AlN barrier high electron mobility transistor with Ir gate. Investigations by transmission electron microscopy linked the effect to an oxygen containing interlayer between the gate metal and the InAlN layer and revealed diffusion of oxygen into iridium during annealing. Below 700 °C the diffusion is inhomogeneous and seems to occur along grain boundaries, which is consistent with the capacitance-voltage analysis. Annealing at 700 °C increased the gate capacitance over a factor 2, shifted the threshold voltage from +0.3 to +1 V and increased the transconductance from 400 to 640 mS/mm.
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85.30.Tv Field effect devices
81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.Mm Grain and twin boundaries
66.30.H- Self-diffusion and ionic conduction in nonmetals
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