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27 Jun 2011

Volume 98, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 98, 263101 (2011); http://dx.doi.org/10.1063/1.3587576 (3 pages)

Jing Ye, Yu Zhao, Libin Tang, Li-Miao Chen, C. M. Luk, S. F. Yu, S. T. Lee, and S. P. Lau
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Dramatic enhancement of thermoelectric power factor in PbTe:Cr co-doped with iodine

Biplab Paul, P. K. Rawat, and P. Banerji

Appl. Phys. Lett. 98, 262101 (2011); http://dx.doi.org/10.1063/1.3603962 (3 pages) | Cited 1 time

Online Publication Date: 27 June 2011

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We report thermoelectric properties of PbTe doubly doped with chromium (Cr) and iodine (I). Cr is found to create a local enhancement of density of states (DOS) in the conduction band of PbTe, and I is found to tune the position of the Fermi level. The coincidence of the Fermi level with the enhanced DOS is found to produce up to 135% enhancement in thermopower leading to a high power factor (PF) of 56.16 × 10−4 Wm−1K−2 at 500 K. Such high value of power factor can produce thermoelectric figure of merit (ZT) above 2.
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72.20.Pa Thermoelectric and thermomagnetic effects
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Electrical spin accumulation with improved bias voltage dependence in a crystalline CoFe/MgO/Si system

Kun-Rok Jeon, Byoung-Chul Min, Il-Jae Shin, Chang-Yup Park, Hun-Sung Lee, Young-Hun Jo, and Sung-Chul Shin

Appl. Phys. Lett. 98, 262102 (2011); http://dx.doi.org/10.1063/1.3600787 (3 pages) | Cited 11 times

Online Publication Date: 27 June 2011

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We report the electrical spin accumulation with enhanced bias voltage dependence in n-type Si, employing a crystalline CoFe/MgO tunnel contact. A sizable spin signal of ∼4.8 kΩμm2, a spin lifetime of ∼155 ps, and a spin diffusion length of ∼220 nm were obtained at 300 K. The spin signal and lifetime obtained in this system show consistent behavior with the temperature variation irrespective of the bias voltage. Notably, the spin signal exhibits nearly symmetric dependence with respect to the bias polarity, which is ascribed to the improved bias dependence of tunnel spin polarization.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.25.-b Spin polarized transport

Chemical vapor deposition-assembled graphene field-effect transistor on hexagonal boron nitride

Edwin Kim, Tianhua Yu, Eui Sang Song, and Bin Yu

Appl. Phys. Lett. 98, 262103 (2011); http://dx.doi.org/10.1063/1.3604012 (3 pages) | Cited 2 times

Online Publication Date: 28 June 2011

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We investigate key electrical properties of monolayer graphene assembled by chemical vapor deposition (CVD). Graphene field-effect transistors (GFETs) were fabricated with carbon channel placing directly on hexagonal boron nitride (h-BN) and SiO2. Small-signal transconductance (gm) and effective carrier mobility (μeff) are improved by 8.5 and 4 times on h-BN, respectively, as compared with that on SiO2. Compared with GFET with exfoliated graphene on SiO2, gm and μeff measured from device with CVD graphene on h-BN substrate exhibit comparable values. The experiment demonstrates the potential of employing h-BN as a platform material for large-area carbon electronics.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

The metallic interface between the two band insulators LaGaO3 and SrTiO3

S. Nazir, N. Singh, and U. Schwingenschlögl

Appl. Phys. Lett. 98, 262104 (2011); http://dx.doi.org/10.1063/1.3604020 (3 pages) | Cited 3 times

Online Publication Date: 28 June 2011

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The formation of metallic interface states between the two band insulators LaGaO3 and SrTiO3 is studied by the full-potential linearized augmented plane-wave method based on density functional theory. Structural optimization of the atomic positions points to only small changes of the chemical bonding at the interface. The n-type (LaO/TiO2) and p-type (GaO2/SrO) interfaces turn out to be metallic. Reduction of the O content increases the conductivity of the n-type interface, while the p-type interface can be turned gradually from a hole doped into an electron doped state.
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73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Characterization of a microwave frequency resonator via a nearby quantum dot

T. Frey, P. J. Leek, M. Beck, K. Ensslin, A. Wallraff, and T. Ihn

Appl. Phys. Lett. 98, 262105 (2011); http://dx.doi.org/10.1063/1.3604784 (3 pages)

Online Publication Date: 28 June 2011

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We present measurements of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined on a GaAs heterostructure. The two subsystems are separately characterized and their interaction is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong microwave field in the resonator is found to reduce the resonant conductance through the quantum dot and is attributed to electron heating and modulation of the dot potential. We use this interaction to demonstrate a measurement of the resonator transmission spectrum using the quantum dot.
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84.40.Az Waveguides, transmission lines, striplines

Formation of a semi-insulating layer in n-type 4H-SiC by electron irradiation

Hiromi Kaneko and Tsunenobu Kimoto

Appl. Phys. Lett. 98, 262106 (2011); http://dx.doi.org/10.1063/1.3604795 (3 pages) | Cited 2 times

Online Publication Date: 29 June 2011

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Electron irradiation has been applied to the formation of a semi-insulating 4H-SiC(0001) layer. The resistivity of the semi-insulating layer, which was irradiated with a fluence of 1.9 × 1018 cm−2 at 400 keV, exceeded 1010 Ω cm at room temperature. From capacitance-voltage characteristics of Schottky structure, the depth of the semi-insulating layer was estimated to be 10 μm, indicating that the whole region of lightly-doped n-type epilayer was converted to the semi-insulating layer by electron irradiation. The semi-insulating property can be ascribed to electron trapping at the Z1/2 and EH6/7 centers generated by electron irradiation. The threshold energy for the generation of Z1/2 center was about 100 keV.
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68.55.ag Semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.30.+y Surface double layers, Schottky barriers, and work functions
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
73.61.Le Other inorganic semiconductors

Trigonal distortion of topologically confined channels in bilayer graphene

A. S. Núñez, E. Suárez Morell, and P. Vargas

Appl. Phys. Lett. 98, 262107 (2011); http://dx.doi.org/10.1063/1.3605568 (3 pages) | Cited 1 time

Online Publication Date: 29 June 2011

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In this work, we show that the trigonal warping of the electronic bands in bilayer graphene dramatically modifies the behavior of the topologically confined one-dimensional modes due to an inhomogeneous bias that changes sign across a channel. Up to four zero modes are present, depending on the orientation of the channel, these zero modes are related to a fractionalization of the topological charge due to the trigonal warping.
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81.05.ue Graphene
73.22.Pr Electronic structure of graphene

On the effect of Ti on the stability of amorphous indium zinc oxide used in thin film transistor applications

Sunghwan Lee and David C. Paine

Appl. Phys. Lett. 98, 262108 (2011); http://dx.doi.org/10.1063/1.3605589 (3 pages) | Cited 3 times

Online Publication Date: 30 June 2011

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In2O3-based amorphous oxide channel materials are of increasing interest for thin film transisitor applications due, in part, to the remarkable stability of this class of materials amorphous structure and electronic properties. We report that this stability is degraded in the presence of Ti, which is widely used as a contact and/or adhesion layer. A cross-sectional transmission electron microscopy analysis, supported by glancing incident angle x-ray and selected area diffraction examination, shows that amorphous indium zinc oxide in contact with Ti undergoes crystallization to the bixbyite phase and reacts to form the rutile phase of TiO2 at a temperature of 200 °C. A basic thermodynamic analysis is presented and forms the basis of a model that describes both the crystallization and the resistivity decrease.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
88.05.De Thermodynamic constraints on energy production
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