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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages)

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng
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Improved memory characteristics by NH3-nitrided GdO as charge storage layer for nonvolatile memory applications

L. Liu, J. P. Xu, F. Ji, J. X. Chen, and P. T. Lai

Appl. Phys. Lett. 101, 033501 (2012); http://dx.doi.org/10.1063/1.4737158 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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Charge-trapping memory capacitor with nitrided gadolinium oxide (GdO) as charge storage layer (CSL) is fabricated, and the influence of post-deposition annealing in NH3 on its memory characteristics is investigated. Transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction are used to analyze the cross-section and interface quality, composition, and crystallinity of the stack gate dielectric, respectively. It is found that nitrogen incorporation can improve the memory window and achieve a good trade-off among the memory properties due to NH3-annealing-induced reasonable distribution profile of a large quantity of deep-level bulk traps created in the nitrided GdO film and reduction of shallow traps near the CSL/SiO2 interface.
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81.20.-n Methods of materials synthesis and materials processing
81.40.Gh Other heat and thermomechanical treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
84.32.Tt Capacitors
71.55.Ht Other nonmetals
79.60.-i Photoemission and photoelectron spectra

Cantilever driving low frequency piezoelectric energy harvester using single crystal material 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3

Chundong Xu, Bo Ren, Wenning Di, Zhu Liang, Jie Jiao, Lingying Li, Long Li, Xiangyong Zhao, Haosu Luo, and Dong Wang

Appl. Phys. Lett. 101, 033502 (2012); http://dx.doi.org/10.1063/1.4737170 (4 pages) | Cited 1 time

Online Publication Date: 16 July 2012

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We present a high performance piezoelectric energy harvester CANtilever Driving Low frequency Energy harvester (CANDLE) consisting of cantilever beam and cymbal transducers based on piezoelectric single crystal 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3. Electrical properties of CANDLE under different proof masses, excitation frequencies, and load resistances are studied systematically. Under an acceleration of 3.2g (g = 9.8 m/s2), a peak voltage of 38 V, a maximum power of 3.7 mW were measured at 102 Hz with a proof mass of 4.2 g. Low resonance frequency and high power output performance demonstrate the promise of the device in energy harvesting for wireless sensors and low-power electronics.
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84.60.-h Direct energy conversion and storage
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Modeling of a vertical tunneling graphene heterojunction field-effect transistor

S. Bala Kumar, Gyungseon Seol, and Jing Guo

Appl. Phys. Lett. 101, 033503 (2012); http://dx.doi.org/10.1063/1.4737394 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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Vertical tunneling field-effect-transistor (FET) based on graphene heterojunctions with layers of hBN is simulated by self-consistent quantum transport simulations. It is found that the asymmetric p-type and n-type conduction is due to work function difference between the graphene contact and the tunneling channel material. Modulation of the bottom-graphene-contact plays an important role in determining the switching characteristic of the device. Due to the electrostatic short-channel-effects stemming from the vertical-FET structure, the output I-V characteristics do not saturate. The scaling behaviors the vertical-FET as a function of the gate insulator thickness and the thickness of the tunneling channel material are examined.
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85.30.Tv Field effect devices
85.65.+h Molecular electronic devices
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Selective mode suppression in a W-band second harmonic coaxial-waveguide gyrotron backward-wave oscillator

C. L. Hung, M. F. Syu, M. T. Yang, and K. L. Chen

Appl. Phys. Lett. 101, 033504 (2012); http://dx.doi.org/10.1063/1.4737398 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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A gyrotron backward-wave oscillator (gyro-BWO) encounters increasingly severe mode competition problems during development toward the goal of higher power at high frequencies. A coaxial interaction waveguide with distributed losses is proposed to enhance the stability and frequency tunability of a W-band second harmonic gyro-BWO. The losses of the inner and outer cylinders complement each other and effectively stabilize all of the competing modes while having minor effects on the operating mode. Under stable operating conditions, the W-band second harmonic coaxial gyro-BWO has a predicted peak output power of 71 kW with a magnetic tuning bandwidth of 1.0 GHz.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

Very high thermoelectric power factor in a Fe3O4/SiO2/p-type Si(100) heterostructure

Z. Viskadourakis, M. L. Paramês, O. Conde, M. Zervos, and J. Giapintzakis

Appl. Phys. Lett. 101, 033505 (2012); http://dx.doi.org/10.1063/1.4737409 (4 pages)

Online Publication Date: 17 July 2012

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The thermoelectric and transport properties of a Fe3O4/SiO2/p-Si(100) heterostructure have been investigated between 100 and 300 K. Both Hall and Seebeck coefficients change sign from negative to positive with increasing temperature while the resistivity drops sharply due to tunneling of carriers into the p-Si(100). The low resistivity and large Seebeck coefficient of Si give a very high thermoelectric power factor of 25.5 mW/K2m at 260 K which is an underestimated, lower limit value and is related to the density of states and difference in the work functions of Fe3O4 and Si(100) that create an accumulation of majority holes at the p-Si/SiO2 interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.40.Gk Tunneling

Carrier transport mechanism at metal/amorphous gallium indium zinc oxides interfaces

Seongjun Kim, Kyoung-Kook Kim, and Hyunsoo Kim

Appl. Phys. Lett. 101, 033506 (2012); http://dx.doi.org/10.1063/1.4737423 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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We report the carrier transport mechanism of Ni/Au Ohmic contacts to amorphous gallium indium zinc oxides. Despite the expected large barrier height, Ohmic contact could be achieved due to the trap-assisted tunneling associated with localized tail states. Upon thermal annealing, the specific contact resistance was further reduced to 3.28 × 10−4 Ωcm2, accompanied by a change in the predominant transport mechanism from trap-limited conduction to degenerate conduction. The Ohmic mechanism could be explained in terms of the thermionic field emission model, yielding a tunneling parameter of 49 meV, a Schottky barrier height of 0.63 eV, and a barrier width of 5.2 nm.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling

Seeding atomic layer deposition of high-k dielectric on graphene with ultrathin poly(4-vinylphenol) layer for enhanced device performance and reliability

Woo Cheol Shin, Taek Yong Kim, Onejae Sul, and Byung Jin Cho

Appl. Phys. Lett. 101, 033507 (2012); http://dx.doi.org/10.1063/1.4737645 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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We demonstrate that ultrathin poly(4-vinylphenol) (PVP) acts as an effective organic seeding layer for atomic layer deposition (ALD) of high-k dielectric on large-scale graphene fabricated by chemical vapor deposition (CVD). While identical ALD conditions result in incomplete and rough dielectric deposition on CVD graphene, the reactive groups provided by the PVP seeding layer yield conformal and pinhole-free dielectric films throughout the large-scale graphene. Top-gate graphene field effect transistors fabricated with the high quality, PVP-seeded Al2O3 gate dielectric show superior carrier mobility and enhanced reliability performance, which are desirable for graphene nanoelectronics.
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68.55.aj Insulators
77.55.D- High-permittivity gate dielectric films
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ng Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices

On the link between electroluminescence, gate current leakage, and surface defects in AlGaN/GaN high electron mobility transistors upon off-state stress

M. Montes Bajo, C. Hodges, M. J. Uren, and M. Kuball

Appl. Phys. Lett. 101, 033508 (2012); http://dx.doi.org/10.1063/1.4737904 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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The degradation of AlGaN/GaN high electron mobility transistors after off-state stress is studied by means of electroluminescence (EL) analysis, gate leakage current (Ig) monitoring, and atomic force microscopy (AFM) mapping of the semiconductor surface. It is found that the degradation of Ig upon stress is due to the combined effect of the individual defects underlying each of the EL spots, which contribute a few μA each to the total Ig. After removal of contacts and passivation, a direct one-to-one correspondence between EL spots and pits on the semiconductor surface is found. Reverse bias, conducting-tip AFM imaging showed that these surface pits do indeed act as leakage paths. Thus, the direct relationship between EL hot spots, surface pits, and gate current leakage is demonstrated. Discussion on the morphology of the surface pits and their possible origin is also provided.
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85.30.Tv Field effect devices

Scattering reduction for an acoustic sensor using a multilayered shell comprising a pair of homogeneous isotropic single-negative media

Tao Xu, Xue-Feng Zhu, Bin Liang, Yong Li, Xin-Ye Zou, and Jian-Chun Cheng

Appl. Phys. Lett. 101, 033509 (2012); http://dx.doi.org/10.1063/1.4737873 (4 pages) | Cited 3 times

Online Publication Date: 19 July 2012

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We have designed a cylindrical multilayered structure to reduce scattering for an acoustic sensor while allowing it to receive external information. The proposed structure consists of two alternately arranged complementary media with homogeneous isotropic single-negative parameters. Numerical results show that the acoustic scattering from the sensor is suppressed considerably when the number of bilayers is large enough and the thickness of each bilayer is much smaller than the incident wavelength. This may be particularly significant for practical applications where acoustic measurements would otherwise be disturbed by the insertion of sensors.
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43.58.-e Acoustical measurements and instrumentation
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.25.-x Nonlinear acoustics
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