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31 Mar 2008

Volume 92, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 92, 133501 (2008); http://dx.doi.org/10.1063/1.2901684 (3 pages)

Eric Akmansoy, Emmanuel Centeno, Kevin Vynck, David Cassagne, and Jean-Michel Lourtioz
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Graded photonic crystals curve the flow of light: An experimental demonstration by the mirage effect

Eric Akmansoy, Emmanuel Centeno, Kevin Vynck, David Cassagne, and Jean-Michel Lourtioz

Appl. Phys. Lett. 92, 133501 (2008); http://dx.doi.org/10.1063/1.2901684 (3 pages) | Cited 20 times

Online Publication Date: 31 March 2008

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We report the experimental demonstration of a beam curvature in graded photonic crystals via a spectacular mirage effect. A two-dimensional structure of metallic rods is constructed to produce this effect in the microwave domain near 10 GHz. Experimental results are in excellent agreement with theoretical predictions, thus, proving the versatility of graded photonic crystals in view of their integration in future photonic circuits.
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42.70.Qs Photonic bandgap materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

ZnO/SiO2 microcavity modulator on silicon

P. D. Batista, B. Drescher, W. Seidel, J. Rudolph, S. Jiao, and P. V. Santos

Appl. Phys. Lett. 92, 133502 (2008); http://dx.doi.org/10.1063/1.2905276 (3 pages) | Cited 2 times

Online Publication Date: 1 April 2008

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We demonstrate a monolithic acousto-optic light modulator on silicon consisting of a piezoelectric ZnO/SiO2 microcavity (MC) excited by a surface acoustic wave (SAW). The modulation of the MC optical resonance by the SAW creates an optical grating on the MC, which efficiently diffracts light beams impinging at the Bragg angle.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
42.79.Jq Acousto-optical devices
42.79.Hp Optical processors, correlators, and modulators
68.60.Bs Mechanical and acoustical properties

Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states

Hsing-Hung Hsieh, Toshio Kamiya, Kenji Nomura, Hideo Hosono, and Chung-Chih Wu

Appl. Phys. Lett. 92, 133503 (2008); http://dx.doi.org/10.1063/1.2857463 (3 pages) | Cited 85 times

Online Publication Date: 1 April 2008

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We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO4 (a-IGZO) for device simulation of a-IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Impact of the strained SiGe source/drain on hot carrier reliability for 45 nm p-type metal-oxide-semiconductor field-effect transistors

C. Y. Cheng, Y. K. Fang, J. C. Hsieh, H. Hsia, W. M. Chen, S. S. Lin, and C. S. Hou

Appl. Phys. Lett. 92, 133504 (2008); http://dx.doi.org/10.1063/1.2904647 (3 pages) | Cited 5 times

Online Publication Date: 1 April 2008

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In this letter, the impact of the uniaxial strain SiGe source/drain (S/D) on hot carrier reliability in 45 nm p-type metal-oxide-semiconductor field-effect transistor is investigated in detail. We find that the extra mechanical stress deteriorates the gate oxide and/or generates interface states significantly, resulting in the hot carrier degradation dominantly driven by the drain avalanche hot carrier stress (Vg = 1/2Vd), as opposed to the channel hot electron stress (Vg = Vd), the well-known dominant mechanism for hot carrier degradation in the conventional deep submicron devices. A model to explain the mechanism of these observations is proposed.
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85.30.Tv Field effect devices

Nanowire sensor response to reactive gas environment

Uroš Cvelbar, Kostya (Ken) Ostrikov, Aleksander Drenik, and Miran Mozetic

Appl. Phys. Lett. 92, 133505 (2008); http://dx.doi.org/10.1063/1.2905265 (3 pages) | Cited 57 times

Online Publication Date: 2 April 2008

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The response of an originally developed catalytic sensor with a Nb2O5 nanowire array at its outer surface to the varying density of O atoms is experimentally and numerically studied. This technique can be used to measure one order of magnitude lower densities of O atoms and achieve a stable linear response in a significantly broader pressure range compared to conventional catalytic probes with a flat surface. The nanostructured outer surface also acts as a thermal barrier against sensor overheating. This approach is generic and can be used for reactive species detection in other reactive gas environments.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Nanoscale epitaxial cobalt salicide bitlines for charge trapping memory cells

C. A. Kleint, T. Mueller, S. Teichert, C. Fitz, N. Nagel, and K. H. Kuesters

Appl. Phys. Lett. 92, 133506 (2008); http://dx.doi.org/10.1063/1.2906366 (3 pages)

Online Publication Date: 2 April 2008

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An epitaxial CoSi2 process is presented, which allows the self-aligned formation of bitlines with only a few tens of nanometer width for Twin Flash memory cells in the 63 nm generation. The bitlines show a good thermal stability and low resistance for widths down to 35 nm, where polycrystalline CoSi2 is known to exhibit a strong narrow linewidth effect. Transmission electron microscopy studies revealed a cube-on-cube epitaxy with only a few twins depending on the annealing conditions. The low bitline resistance results in a linear drain voltage dependence of the programing characteristics and a suppression of secondary electron injection during programing.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.40.Gh Other heat and thermomechanical treatments
84.30.Sk Pulse and digital circuits
73.61.Le Other inorganic semiconductors

ZnO nanorods for solar cells: Hydrothermal growth versus vapor deposition

Y. F. Hsu, Y. Y. Xi, A. B. Djurišić, and W. K. Chan

Appl. Phys. Lett. 92, 133507 (2008); http://dx.doi.org/10.1063/1.2906370 (3 pages) | Cited 43 times

Online Publication Date: 2 April 2008

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Performance of dye-sensitized solar cells (DSSCs) based on ZnO nanorods prepared by hydrothermal and vapor-deposition methods has been investigated. In spite of their inferior optical properties, DSSCs based on hydrothermally grown rods exhibit higher power conversion efficiency, which can be attributed to the higher dye adsorption. Hydrothermally grown and vapor deposited nanorods also exhibit different dependence of photovoltaic performance on the annealing conditions of the rods, indicating significant effect of the native defects on the achievable photocurrent and power conversion efficiency. Efficiency of 0.22% is obtained for both as grown hydrothermally grown nanorods and vapor deposited nanorods annealed in oxygen at 200 °C.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
73.63.-b Electronic transport in nanoscale materials and structures
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Dynamic bias temperature instability-like behaviors under Fowler–Nordheim program/erase stress in nanoscale silicon-oxide-nitride-oxide-silicon memories

Seung Hwan Seo, Gu-Cheol Kang, Kang Seob Roh, Kwan Young Kim, Sunyeong Lee, Kwan-Jae Song, Chang Min Choi, So Ra Park, Kichan Jeon, Jun-Hyun Park, Byung-Gook Park, Jong Duk Lee, Dong Myong Kim, and Dae Hwan Kim

Appl. Phys. Lett. 92, 133508 (2008); http://dx.doi.org/10.1063/1.2905272 (3 pages) | Cited 2 times

Online Publication Date: 3 April 2008

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Bias temperature-dependent characteristics of nanoscale silicon-oxide-nitride-oxide-silicon memories are investigated under program/erase (P/E) Fowler–Nordheim (FN) stresses. In the erased cell, FN stress time evolution is found to be a similar physical process to the recovery of interface traps (NIT) that takes place under the dynamic negative bias temperature instability stress. In addition, anode hole injection induced holes are trapped in the bottom oxide, both in the erase and in the read conditions of the erased cell, and make significant roles in the reverse hysteresis and higher power-law exponent n at higher temperature in P/E cycled erased cells. While the temperature-independent n = 0.3 is observed in the programed cell, the temperature-sensitive n = 0.36–0.66 is observed in the erased cell.
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84.30.Sk Pulse and digital circuits

Asymmetric double two-dimensional electron gas structures for electrical quantum metrology

K. Pierz, G. Hein, E. Pesel, B. Schumacher, H. W. Schumacher, and U. Siegner

Appl. Phys. Lett. 92, 133509 (2008); http://dx.doi.org/10.1063/1.2906377 (3 pages) | Cited 3 times

Online Publication Date: 3 April 2008

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We study growth and low temperature magnetotransport of Ga(Al)As based asymmetric double two-dimensional electron gas (2DEG) structures consisting of a quantum well stacked on top of a heterojunction. These structures allow for matching the electron densities in the two parallel 2DEGs by variation of a single growth parameter without the appearance of any parasitic transport channel. At filling factor 2, we observe a 2 T wide quantum Hall plateau of metrological quality with a quantized resistance of one quarter of the resistance quantum. Such structures can be used for electrical quantum metrology and to fabricate vertically integrated circuits.
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73.61.Ey III-V semiconductors
73.21.Fg Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Bistable resistive states of amorphous SrRuO3 thin films

J. Y. Son, Y.-H. Shin, and C. S. Park

Appl. Phys. Lett. 92, 133510 (2008); http://dx.doi.org/10.1063/1.2897306 (3 pages) | Cited 6 times

Online Publication Date: 3 April 2008

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We fabricated amorphous SrRuO3 thin films which exhibited the electronic transport behavior of an insulator that showed a three-dimensional hopping transport. Depending on the polarity of a sweep bias, bistable resistive states were observed in the capacitor consisted of an amorphous SrRuO3 thin film and Pt electrodes, which gives the opportunity for nonvolatile memory applications. From electric transport and optical conductivity data, we indirectly confirmed a probability of the mixed phase of SrO and RuO2 in the amorphous SrRuO3 thin film. This supports the applicability of a filament model as a mechanism for the bistable resistive states.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ng Insulators
84.32.Tt Capacitors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators

Influence of carrier confinement on the subthreshold swing of multigate silicon-on-insulator transistors

Jean-Pierre Colinge, Aryan Afzalian, Chi-Woo Lee, Ran Yan, and Nima Dehdashti Akhavan

Appl. Phys. Lett. 92, 133511 (2008); http://dx.doi.org/10.1063/1.2907330 (3 pages) | Cited 1 time

Online Publication Date: 3 April 2008

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The minimum energy of the first conduction subband varies with gate voltage in trigate silicon-on-insulator metal-oxide-silicon field-effect transistors (MOSFETs) in subthreshold operation. In an inversion-mode trigate device, the energy level of the lowest subband increases with electron concentration, while it decreases under the same conditions in some accumulation-mode devices. As a result of this quantum effect, the subthreshold swing of accumulation-mode trigate FETs is smaller than predicted by classical theory. This effect is not observed in fin-shaped FETs and gate-all-around MOSFETs and can be amplified by modifying the device cross section.
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85.30.Tv Field effect devices

Trap densities in amorphous-InGaZnO4 thin-film transistors

Mutsumi Kimura, Takashi Nakanishi, Kenji Nomura, Toshio Kamiya, and Hideo Hosono

Appl. Phys. Lett. 92, 133512 (2008); http://dx.doi.org/10.1063/1.2904704 (3 pages) | Cited 74 times

Online Publication Date: 3 April 2008

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Trap densities in amorphous-InGaZnO4 (α-IGZO) are extracted directly from the capacitance-voltage characteristics of thin-film transistors at low frequencies. It is found that the trap densities are flat in the energy gap, and are 1.7×1016 cm−3 eV−1 in the deep energy far from the conduction band edge (Ec), but become larger near Ec. Moreover, postannealing reduces the trap density near Ec, which is associated with the reduction of the hysteresis in the current-voltage characteristics. The annealed α-IGZO does not have a Gaussian-type state and has fewer tail states than amorphous Si.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

III-nitride heterostructure field-effect transistors grown on semi-insulating GaN substrate without regrowth interface charge

J. P. Liu, J.-H. Ryou, D. Yoo, Y. Zhang, J. Limb, C. A. Horne, S.-C. Shen, R. D. Dupuis, A. D. Hanser, E. A. Preble, and K. R. Evans

Appl. Phys. Lett. 92, 133513 (2008); http://dx.doi.org/10.1063/1.2906372 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2008

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Charge is observed at the regrowth interface for heterostructure field-effect transistors (HFETs) grown on semi-insulating (SI) bulk GaN substrates, even with Fe doping in the regrown buffer layer for reduction of the interface charge. Ultraviolet photoenhanced chemical (PEC) etching is used to treat the surface of SI bulk GaN substrates. Employing optimized etching conditions, a very smooth surface is achieved for the bulk GaN substrate after the etching. The charge at the regrowth interface is eliminated for HFETs grown on etched SI GaN substrates. Secondary ion mass spectrometry measurements show that the Si impurity concentration at the regrowth interface for HFETs grown on etched SI GaN substrates is much lower than that for HFETs grown on unetched SI GaN substrates, which suggests that the charge-containing layer on the SI substrate is removed by PEC etching and that the effects of the reduced charge layer near the regrowth interface can be eliminated by Fe doping for HFETs grown on etched SI substrates.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning
61.72.U- Doping and impurity implantation

Unified retention model for localized charge trapping nonvolatile memory device

Asia Shapira, Yael Shur, Yosi Shacham-Diamand, Assaf Shappir, and Boaz Eitan

Appl. Phys. Lett. 92, 133514 (2008); http://dx.doi.org/10.1063/1.2906895 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2008

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Retention after cycling in an NROM nonvolatile memory cell is investigated. Electrical characterizations combined with two-dimensional simulations were employed. By combining subthreshold current characterizations with gate-induced drain leakage measurements, the retention loss mechanisms are quantified and differentiated. A unified retention model for the NROM technology is proposed, incorporating both lateral charge transport in the nitride layer and hot carrier-induced interface-states formation. The fabrication conditions in the various studies reported in the literature and the resultant impact on interface-states formation are most likely the cause of the formally nonresolved debate regarding the origin of retention loss in NROM technology.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits
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