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1 Jun 2009

Volume 94, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 94, 221101 (2009); http://dx.doi.org/10.1063/1.3143652 (3 pages)

Gangyi Xu, Virginie Moreau, Yannick Chassagneux, Adel Bousseksou, Raffaele Colombelli, G. Patriarche, G. Beaudoin, and I. Sagnes
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Horizontal position analysis of single acceptors in Si nanoscale field-effect transistors

M. A. H. Khalafalla, Y. Ono, K. Nishiguchi, and A. Fujiwara

Appl. Phys. Lett. 94, 223501 (2009); http://dx.doi.org/10.1063/1.3147209 (3 pages) | Cited 2 times

Online Publication Date: 1 June 2009

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The authors performed conductance measurements to identify the horizontal position of single boron acceptors in silicon-on-insulator nanoscale field-effect transistors at a temperature of 6 K. The horizontal position, i.e., how far the acceptor is from the source or drain terminal, is qualitatively obtained, and it is shown, on the level of single dopants, that the acceptor near the source significantly affects the subthreshold nature of the transistor.
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85.30.Tv Field effect devices

Fermi edge singularity observed in GaN/AlGaN heterointerfaces

N. Akopian, A. Vardi, G. Bahir, V. Garber, E. Ehrenfreund, D. Gershoni, C. Poblenz, C. R. Elsass, I. P. Smorchkova, and J. S. Speck

Appl. Phys. Lett. 94, 223502 (2009); http://dx.doi.org/10.1063/1.3147869 (3 pages) | Cited 2 times

Online Publication Date: 1 June 2009

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We observe sharp spectral lines, at energies which are higher than the bulk GaN band gap, in the photoluminescence and photoluminescence excitation spectra of GaN/AlGaN heterointerfaces grown by molecular beam epitaxy. The spectra and their temperature dependence are in accord with the Fermi edge singularity expected for two dimensional electron gas systems. The associated localized hole energy in the AlGaN interface side was extracted directly from the spectra.
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78.66.Fd III-V semiconductors
68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Sensing of atomized liquids through field effects of polarization and ionization induced by nanostructures

Zhongyu Hou, Bingchu Cai, and Hai Liu

Appl. Phys. Lett. 94, 223503 (2009); http://dx.doi.org/10.1063/1.3138122 (3 pages)

Online Publication Date: 1 June 2009

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The mechanism and instrumentation of an atomized liquid sensing system is presented, characterizing the dynamic polarization and ionization processes of liquid droplets in an electric field converged by one dimensional nanostructures. The microarchitecture implementing the mechanism is realized by microlithography technology. It is shown that the current amplitude is a function of both droplets’ flow rate and its chemistry; thus, one of them can be differentiated when the other is a constant. Further, the current-time spectrum responding to the vaporization and diffusion processes can enhance the differentiability. The methodology can be applied to atomized liquid sensing or liquid chemistry differentiation.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
47.55.D- Drops and bubbles
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight

Wolfgang Guter, Jan Schöne, Simon P. Philipps, Marc Steiner, Gerald Siefer, Alexander Wekkeli, Elke Welser, Eduard Oliva, Andreas W. Bett, and Frank Dimroth

Appl. Phys. Lett. 94, 223504 (2009); http://dx.doi.org/10.1063/1.3148341 (3 pages) | Cited 125 times

Online Publication Date: 1 June 2009

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A metamorphic Ga0.35In0.65P/Ga0.83In0.17As/Ge triple-junction solar cell is shown to provide current-matching of all three subcells and thus composes a device structure with virtually ideal band gap combination. We demonstrate that the key for the realization of this device is the improvement of material quality of the lattice-mismatched layers as well as the development of a highly relaxed Ga1−yInyAs buffer structure between the Ge substrate and the middle cell. This allows the metamorphic growth with low dislocation densities below 106 cm−2. The performance of the approach has been demonstrated by a conversion efficiency of 41.1% at 454 suns (454 kW/m2, AM1.5d ASTM G173–03).
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84.60.Jt Photoelectric conversion

Performance analysis of statistical samples of graphene nanoribbon tunneling transistors with line edge roughness

Mathieu Luisier and Gerhard Klimeck

Appl. Phys. Lett. 94, 223505 (2009); http://dx.doi.org/10.1063/1.3140505 (3 pages) | Cited 13 times

Online Publication Date: 2 June 2009

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Using a three-dimensional, atomistic quantum transport simulator based on the tight-binding method, we investigate statistical samples of single-gate graphene nanoribbon (GNR) tunneling field-effect transistors (TFETs) with different line edge roughness probabilities. We find that as the nanoribbon edges become rougher, the device OFF-current drastically increases due to a reduction of the graphene band gap and an enhancement of source-to-drain tunneling leakage through the gate potential barrier. At the same time, the ON-current remains almost constant. This leads to a deterioration of the transistor subthreshold slopes and to unacceptably low ON/OFF current ratios limiting the switching performances of GNR TFETs.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
85.35.-p Nanoelectronic devices
85.30.De Semiconductor-device characterization, design, and modeling

Demonstration of midinfrared type-II InAs/GaSb superlattice photodiodes grown on GaAs substrate

Binh-Minh Nguyen, Darin Hoffman, Edward Kwei-wei Huang, Simeon Bogdanov, Pierre-Yves Delaunay, Manijeh Razeghi, and Meimei Z. Tidrow

Appl. Phys. Lett. 94, 223506 (2009); http://dx.doi.org/10.1063/1.3148326 (3 pages) | Cited 11 times

Online Publication Date: 2 June 2009

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We report the growth and characterization of type-II InAs/GaSb superlattice photodiodes grown on a GaAs substrate. Through a low nucleation temperature and a reduced growth rate, a smooth GaSb surface was obtained on the GaAs substrate with clear atomic steps and low roughness morphology. On the top of the GaSb buffer, a p+-i-n+ type-II InAs/GaSb superlattice photodiode was grown with a designed cutoff wavelength of 4 μm. The detector exhibited a differential resistance at zero bias (R0A) in excess of 1600 Ω cm2 and a quantum efficiency of 36.4% at 77 K, providing a specific detectivity of 6×1011 cmmath/W and a background limited operating temperature of 100 K with a 300 K background. Uncooled detectors showed similar performance to those grown on GaSb substrates with a carrier lifetime of 110 ns and a detectivity of 6×108 cmmath/W.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Dw Photodiodes; phototransistors; photoresistors

Vertical alignment of liquid crystals on a fully oxidized HfO2 surface by ion bombardment

Won-Kyu Lee, Byeong-Yun Oh, Ji-Hun Lim, Hong-gyu Park, Byoung-Yong Kim, Hyun-Jae Na, and Dae-Shik Seo

Appl. Phys. Lett. 94, 223507 (2009); http://dx.doi.org/10.1063/1.3126961 (3 pages) | Cited 11 times

Online Publication Date: 3 June 2009

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High-performance liquid crystals (LCs) driven at a 0.9 V threshold were demonstrated on very thin HfO2 films with vertical (homeotropic) alignment by ion bombardment. Atomic layer deposition was used to obtain LC orientation on ultrathin high-quality films of double-layer HfO2/Al2O3. X-ray photoelectron spectroscopy indicated that full oxidization of HfO2 film surfaces was induced by ion bombardment, shifting the Hf 4f spectra to lower binding energies. The increased intensities of the Hf 4f peaks after ion bombardment confirmed that nonstoichiometric HfOx was converted to the fully oxidized HfO2 surfaces.
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61.30.-v Liquid crystals
77.55.-g Dielectric thin films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Determination of the electrostatic lever arm of carbon nanotube field effect transistors using Kelvin force microscopy

David Brunel, Dominique Deresmes, and Thierry Mélin

Appl. Phys. Lett. 94, 223508 (2009); http://dx.doi.org/10.1063/1.3148364 (3 pages) | Cited 9 times

Online Publication Date: 3 June 2009

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We use Kelvin force microscopy (KFM) to study the electrostatic properties of single-walled carbon nanotube field effect transistor devices (CNTFETs) with backgate geometry at room temperature. We show that KFM maps recorded as a function of the device backgate polarization enable a complete phenomenological determination of the averaging effects associated with the KFM probe side capacitances, and thus, to obtain KFM measurements with quantitative character. The value of the electrostatic lever arm of the CNTFET is determined from KFM measurements and found in agreement with transport measurements based on Coulomb blockade.
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85.35.Kt Nanotube devices
07.79.-v Scanning probe microscopes and components
68.37.Ps Atomic force microscopy (AFM)

Aluminum/polyaniline/GaAs metal-insulator-semiconductor solar cell: Effect of tunneling on device performance

Sutanu Mangal, Sarbani Adhikari, and P. Banerji

Appl. Phys. Lett. 94, 223509 (2009); http://dx.doi.org/10.1063/1.3149703 (3 pages) | Cited 7 times

Online Publication Date: 4 June 2009

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We report fabrication of GaAs based metal-insulator-semiconductor solar cell with polyaniline, a polymeric material, as an insulator. The photovoltaic response of Aluminum/Polyaniline/GaAs metal-insulator-semiconductor diode was measured in the air mass (AM) 1.0 and 1.5. The values of the open circuit voltage, short circuit current and the series resistance at AM 1.0 are measured to be 0.45 mA, 1.07 V and 26 Ω, respectively. It is found that the thickness of the polyaniline layer plays a crucial role in determining various properties of the device. The findings are explained on the basis of the tunneling probability.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Kk Junction diodes

A spin-wave frequency doubler by domain wall oscillation

Sebastian J. Hermsdoerfer, Helmut Schultheiss, Christopher Rausch, Sebastian Schäfer, Britta Leven, Sang-Koog Kim, and Burkard Hillebrands

Appl. Phys. Lett. 94, 223510 (2009); http://dx.doi.org/10.1063/1.3143225 (3 pages) | Cited 7 times

Online Publication Date: 4 June 2009

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We present a mechanism for spin-wave excitation using a pinned domain wall, which is forced to oscillate at its eigenfrequency and radiates spin waves. The domain wall acts as a frequency doubler as the excited spin waves have twice the frequency of the domain wall oscillation. The investigations have been carried out using micromagnetic simulations and enable the determination of the main characteristics of the excited spin waves such as frequency, wavelength, and velocity. This behavior is understood by the oscillation in the perpendicular magnetization, which shows two antinodes oscillating out of phase with respect to each other.
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75.60.Ch Domain walls and domain structure
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Characterization of diamond ultraviolet detectors fabricated with high-quality single-crystalline chemical vapor deposition films

Y. Iwakaji, M. Kanasugi, O. Maida, and T. Ito

Appl. Phys. Lett. 94, 223511 (2009); http://dx.doi.org/10.1063/1.3143621 (3 pages) | Cited 8 times

Online Publication Date: 4 June 2009

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We have fabricated high-performance ultraviolet (UV) detectors with high-quality undoped and B-doped homoepitaxial diamond layers which were sequentially grown on a high-pressure/high-temperature-synthesized (HPHT) type-Ib (100) substrate by means of a high-power microwave-plasma chemical vapor deposition method. The detector performance measured had large quantum efficiencies due to an effective built-in current amplification function, fast temporal responses, and high UV/visible sensing ratios although the HPHT substrate used had considerable amounts of various defects inducing visible light absorptions and slow detector responses. The usefulness of the bilayer detector structure employed is discussed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
62.50.-p High-pressure effects in solids and liquids
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.U- Carbon/carbon-based materials
68.55.jd Thickness

Characterization of AlGaN/GaN metal-oxide-semiconductor field-effect transistors by frequency dependent conductance analysis

P. Kordoš, R. Stoklas, D. Gregušová, and J. Novák

Appl. Phys. Lett. 94, 223512 (2009); http://dx.doi.org/10.1063/1.3148830 (3 pages) | Cited 12 times

Online Publication Date: 5 June 2009

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We report on the frequency dependent conductance measurements of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). The properties of the devices with as-deposited and annealed 9-nm-thick Al2O3 gate oxide were investigated. The trap density in the range of 1011 cm−2 eV−1 was evaluated for the nonannealed devices. However, the conductance versus frequency peaks were significantly broader than those expected from theory, which indicates a surface potential fluctuation due to nonuniformities in the oxide charge and interface traps. Additionally, the dependence of the trap state time constant on gate voltage showed a deviation from the expected exponential function. However, the annealed devices (680 °C, 5 min) yielded a slightly lower ( ∼ 75%) trap density. Moreover, the conductance versus frequency data and the time constant versus gate voltage dependence of the annealed devices were in full agreement with the theoretical ones. The results show that the frequency dependent conductance analysis can be a useful tool for the characterization of AlGaN/GaN MOSHFETs.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Conceal an entrance by means of superscatterer

Xudong Luo, Tao Yang, Yongwei Gu, Huanyang Chen, and Hongru Ma

Appl. Phys. Lett. 94, 223513 (2009); http://dx.doi.org/10.1063/1.3149694 (3 pages) | Cited 12 times

Online Publication Date: 5 June 2009

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Based on the fact that superscatterer can look like a scatterer bigger than its geometric size, we propose a design of hidden portal in which an entrance is concealed from the electromagnetic wave detection. Such a superscatterer is realized by coating a negative index material shell on a perfect electrical conductor rectangle cylinder. The results are numerically confirmed by full-wave simulations both in the far field and near field.
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42.70.-a Optical materials
42.79.Wc Optical coatings
02.60.-x Numerical approximation and analysis
41.20.Jb Electromagnetic wave propagation; radiowave propagation

The effective quality factor at low temperatures in dynamic force microscopes with Fabry–Pérot interferometer detection

Hendrik Hölscher, Peter Milde, Ulrich Zerweck, Lukas M. Eng, and Regina Hoffmann

Appl. Phys. Lett. 94, 223514 (2009); http://dx.doi.org/10.1063/1.3149700 (3 pages) | Cited 7 times

Online Publication Date: 5 June 2009

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The oscillation of a cantilever in ultrahigh vacuum dynamic force microscopy is sometimes measured with the help of a Fabry–Pérot interferometer. We show that the photoinduced forces present in such an interferometer can artificially increase or decrease the effective quality factor of the cantilever. We examine this effect on the basis of a PtIr-coated rectangular silicon cantilever at temperatures between 7.7 and 30 K. By measuring resonance curves we demonstrate that the magnitude of the effective quality factor changes with cantilever-fiber distance, laser power, and temperature.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.60.Ly Interferometers
84.30.-r Electronic circuits

Impact of field-enhanced band-traps-band tunneling on the dark current generation in germanium p-i-n photodetector

Kah-Wee Ang, Joseph Weisheng Ng, Guo-Qiang Lo, and Dim-Lee Kwong

Appl. Phys. Lett. 94, 223515 (2009); http://dx.doi.org/10.1063/1.3151913 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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This letter investigates the impact of field-enhanced band-traps-band tunneling on the dark current generation in germanium (Ge) p-i-n photodetector. We show that the existence of defect-induced traps within the forbidden gap forms the underlying leakage mechanism. Enhancing the electric field intensity is found to reduce the activation energy that governs the leakage generation rates. In the presence of enlarged band-bending, the dark current generation is further aggravated by the enhancement in electrons and holes tunneling from the resulting deep levels into the conduction and valence bands, respectively. Such field-enhanced band tunneling effect becomes increasingly prominent with a downsizing of the detector’s depletion width, which imposes a design trade-off between leakage generation and bandwidth enhancement.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Bt Optoelectronic device characterization, design, and modeling
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