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25 Apr 2011

Volume 98, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 98, 171102 (2011); http://dx.doi.org/10.1063/1.3582035 (3 pages)

Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa
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Depletion of the In2O3(001) and (111) surface electron accumulation by an oxygen plasma surface treatment

Oliver Bierwagen, James S. Speck, Takahiro Nagata, Toyohiro Chikyow, Yoshiyuki Yamashita, Hideki Yoshikawa, and Keisuke Kobayashi

Appl. Phys. Lett. 98, 172101 (2011); http://dx.doi.org/10.1063/1.3583446 (3 pages) | Cited 6 times

Online Publication Date: 25 April 2011

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Using x-ray photoemission spectroscopy (XPS) and current-voltage (I-V) measurements of Hg contacts we show that the surface electron accumulation layer of In2O3 can be removed by an oxygen plasma treatment. For the untreated sample, XPS measured a downward band bending toward the surface and a conduction band peak, and the I-V curve was linear which indicated the presence of a surface accumulation layer. After the treatment an upward bending, the absence of the conduction band peak, and a nonlinear I-V curve indicated the absence of the surface accumulation layer. The sheet resistance of the surface accumulation layer of >45 kΩ was deduced from the increase of the total sheet resistance upon the treatment. The removal of the surface electron accumulation layer opens up the possibility to use Schottky contacts for electrical characterization and device applications of semiconducting In2O3.
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73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Nr Semiconductor compounds
72.80.Jc Other crystalline inorganic semiconductors
73.40.Ns Metal-nonmetal contacts

Tuning Fano-type resonances in coupled quantum point contacts by applying asymmetric voltages

Rubén C. Villarreal, Francisco Mireles, Ernesto E. Marinero, and Bruce A. Gurney

Appl. Phys. Lett. 98, 172102 (2011); http://dx.doi.org/10.1063/1.3579538 (3 pages)

Online Publication Date: 26 April 2011

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We study the ballistic magnetotransport in a double quantum point contact (QPC) device consisting of a quasi-one-dimensional quantum wire with an embedded islandlike impurity-etched nanohole as in a recently published experiment { J. C. Chen et al., [Appl. Phys. Lett. 94, 012105 (2009)] }. We reproduce the zero field quantized conductance, the interference phenomenon induced by the coupled QPCs, as well as the Ramsauer-like resonances observed in the experiments. At finite magnetic fields Fano-type resonances arises in the conductance due to the formation of localized states at the impurity periphery and to an interedge state resonant coupling effect. It is predicted that the Fano-type resonances can be controlled by an asymmetric confinement of the QPCs.
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85.35.Ds Quantum interference devices
73.23.Ad Ballistic transport
73.63.Rt Nanoscale contacts

Effects of interwall interaction on the electrical conductance at the junction between a double-walled carbon nanotube and copper electrodes

Feng Gao, Jianmin Qu, and Matthew Yao

Appl. Phys. Lett. 98, 172103 (2011); http://dx.doi.org/10.1063/1.3582242 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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Considered in this letter are the effects of interwall interaction on the electrical conductance at the junction of a double-walled carbon nanotube (DWCNT) between two copper electrodes. In the end-contact configuration, the effect of interwall interaction on the electrical conductance is rather weak, and both walls of DWCNT contribute to the electronic transport almost as if they are parallel connectors. In the side-contact configuration, not only the inner tube does not contribute to the overall electrical conductance, its presence hinders the electronic transport of the outer wall by causing significant localization of density of states near the Fermi level.
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73.63.Fg Nanotubes
73.20.At Surface states, band structure, electron density of states
61.46.Fg Nanotubes

High-temperature thermoelectric properties of Cu2Ga4Te7 with defect zinc-blende structure

Theerayuth Plirdpring, Ken Kurosaki, Atsuko Kosuga, Manabu Ishimaru, Adul Harnwunggmoung, Tohru Sugahara, Yuji Ohishi, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 98, 172104 (2011); http://dx.doi.org/10.1063/1.3583662 (3 pages) | Cited 7 times

Online Publication Date: 27 April 2011

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Here we show the high-temperature thermoelectric (TE) properties of Cu2Ga4Te7 with the defect zinc-blende structure in which one-seventh of the cation sites are structural vacancies. Cu2Ga4Te7 exhibited relatively low electrical resistivity (ρ) and thermal conductivity (κ) and moderate positive Seebeck coefficient (S) at high temperatures, making this compound a promising high-performance p-type TE material. At 940 K, the S, ρ, and κ were +215 μV K−1, 10.1×10−5 Ω m, and 0.67 Wm−1 K−1, respectively, which resulted in the maximum dimensionless figure of merit ZT ( = S2T/ρ/κ, where T is the absolute temperature) of 0.64.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.jd Vacancies
72.80.Sk Insulators

Quantum magnetoresistance of the PrFeAsO oxypnictide

D. Bhoi, P. Mandal, P. Choudhury, S. Pandya, and V. Ganesan

Appl. Phys. Lett. 98, 172105 (2011); http://dx.doi.org/10.1063/1.3584023 (3 pages) | Cited 2 times

Online Publication Date: 28 April 2011

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We report the observation of an unusual B dependence of transverse magnetoresistance (MR) in the PrFeAsO, one of the parent compound of pnictide superconductors. Below the spin density wave transition, MR is large, positive and increases with decreasing temperature. At low temperatures, MR increases linearly with B up to 14 T. For T ≥ 40 K, MR versus B curve develops a weak curvature in the low-field region which indicates a crossover from B linear to B2 dependence as B→0. The B linear MR originates from the Dirac cone states and has been explained by the quantum mechanical model proposed by Abrikosov.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Xa Pnictides and chalcogenides
75.30.Ds Spin waves
75.47.Lx Magnetic oxides

Schottky barrier height reduction for metal/n-GaSb contact by inserting TiO2 interfacial layer with low tunneling resistance

Ze Yuan, Aneesh Nainani, Yun Sun, J.-Y. Jason Lin, Piero Pianetta, and Krishna C. Saraswat

Appl. Phys. Lett. 98, 172106 (2011); http://dx.doi.org/10.1063/1.3584862 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2011

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Fermi level pinning near GaSb valence band edge leads to high Schottky barrier height for metal/n-type GaSb contacts. However, this effect can be alleviated by depinning of the Fermi level with the introduction of thin interfacial dielectric. In this paper, the use of TiO2 allows depinning of the Fermi level without introducing excessive tunneling resistance due to the low conduction band offset, estimated by synchrotron radiation photoemission spectroscopy. It is shown the insertion of TiO2 results in reduction in Schottky barrier height and greater than four orders of magnitude increase in current density for metal contacts on n-type GaSb.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
71.20.Nr Semiconductor compounds

Rectifying behavior in La2/3Sr1/3MnO3/MgO/SrRuO3 magnetic tunnel junctions

Hongguang Cheng, Zuli Liu, and Kailun Yao

Appl. Phys. Lett. 98, 172107 (2011); http://dx.doi.org/10.1063/1.3586242 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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We report first principles calculations of transport properties of the all-oxide La2/3Sr1/3MnO3/MgO/SrRuO3 magnetic tunnel junctions. A sizeable rectifying behavior which can be enhanced by increasing the MgO barrier thickness is predicted theoretically. For the device with 13 layers of MgO barrier, the positive current is about two orders of magnitude larger than the reverse leakage current. The rectifying behavior arises from the symmetry-filtering properties of the MgO barrier. This rectifying effect which is totally dominated by quantum tunneling could be used to design faster quantum devices such as tunnel diode and tunnel transistor.
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73.40.Ei Rectification
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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