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24 Jan 2011

Volume 98, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 043101 (2011); http://dx.doi.org/10.1063/1.3536475 (3 pages)

Zhichao Ruan and Shanhui Fan
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Single-crystalline (100) Ge networks on insulators by rapid-melting growth along hexagonal mesh-pattern

Kaoru Toko, Yasuharu Ohta, Takashi Sakane, Taizoh Sadoh, Ichiro Mizushima, and Masanobu Miyao

Appl. Phys. Lett. 98, 042101 (2011); http://dx.doi.org/10.1063/1.3544057 (3 pages) | Cited 5 times

Online Publication Date: 24 January 2011

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Single-crystalline-Ge (c-Ge) networks on insulator films formed on Si substrates are essential for integrating high-speed and multifunctional devices onto the Si-platform. Rapid-melting-growth of mesh-patterned amorphous-Ge is examined over large areas (500×250 μm2). For squared-mesh-pattern, polycrystalline-Ge forms throughout most of the mesh, though c-Ge is obtained near (<100 μm) Si-seed. Based on the consideration of geometric-effects, mesh-patterns are changed to hexagonal. This realizes c-Ge networks over the entire insulator area. These results indicate that Ge growth initiated from Si-seed propagates laterally over the hexagonal-mesh-pattern though bending and branching. These unique c-Ge-networks on insulators facilitate Ge-based advanced-devices on the Si-platform.
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81.10.Fq Growth from melts; zone melting and refining
81.05.Cy Elemental semiconductors
64.70.dj Melting of specific substances
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Effect of vacancy-type oxygen deficiency on electronic structure in amorphous alumina

Hiroyoshi Momida, Seisuke Nigo, Giyuu Kido, and Takahisa Ohno

Appl. Phys. Lett. 98, 042102 (2011); http://dx.doi.org/10.1063/1.3548549 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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Electronic and atomic structures associated with a vacancy-type oxygen deficiency in an amorphous alumina model are studied by first-principles calculations. The energy levels of the oxygen defects significantly shift depending on their charge states because of remarkable changes of local atomic structures. That is different in character from the α crystal case. We discuss a possibility of the oxygen defects as a conductive path and present an atomistic mechanism of the resistive switching effects in the memory devices.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Top-down fabrication of AlGaN/GaN nanoribbons

M. Azize and T. Palacios

Appl. Phys. Lett. 98, 042103 (2011); http://dx.doi.org/10.1063/1.3544048 (3 pages) | Cited 2 times

Online Publication Date: 25 January 2011

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Lateral AlGaN/GaN nanoribbons (NRs) have been fabricated through a top-down technology on planar AlGaN/GaN samples grown on a silicon substrate. Electron-beam lithography and Cl2-based dry etching were used to define the NRs with widths in the 70–145 nm range. The electrical and structural properties of the AlGaN/GaN NRs have been measured and compared to standard planar structures fabricated on the same chip. External mechanical stress and adequate surface passivation have an important effect on the NR’s performance. A 50% improvement in the current density of SixNy passivated AlGaN/GaN NRs was obtained with respect to planar samples.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
81.65.Rv Passivation
85.30.Tv Field effect devices
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors

Mg doped InN and confirmation of free holes in InN

K. Wang, N. Miller, R. Iwamoto, T. Yamaguchi, M. A. Mayer, T. Araki, Y. Nanishi, K. M. Yu, E. E. Haller, W. Walukiewicz, and J. W. Ager, III

Appl. Phys. Lett. 98, 042104 (2011); http://dx.doi.org/10.1063/1.3543625 (3 pages) | Cited 16 times

Online Publication Date: 25 January 2011

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We report a systematic investigation on Mg doped InN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy. Electrolyte capacitance voltage (ECV) combined with thermopower measurements find p-type conduction over an Mg concentration range. For InN:Mg in this p-type “window” the Seebeck coefficients dramatically change their signs from negative to positive when the thickness of undoped InN interlayer decreases to zero. This notable sign change of Seebeck coefficient explains the previous inconsistency between ECV and thermopower results and confirms the existence of mobile holes in the InN:Mg. Taking into account the undoped InN interlayer, the hole density and mobility are extracted.
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73.61.Ey III-V semiconductors
73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

Gd-doping effect on performance of HfO2 based resistive switching memory devices using implantation approach

Haowei Zhang, Lifeng Liu, Bin Gao, Yuanjun Qiu, Xiaoyan Liu, Jing Lu, Ruqi Han, Jinfeng Kang, and Bin Yu

Appl. Phys. Lett. 98, 042105 (2011); http://dx.doi.org/10.1063/1.3543837 (3 pages) | Cited 16 times

Online Publication Date: 25 January 2011

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An implantation doping approach is implemented to fabricate Gd-doped HfO2 resistive random access memory (RRAM) devices. The significantly enhanced performances are achieved in the Gd-doped HfO2 RRAM devices including improved uniformity of switching parameters, enlarged ON/OFF ratio, and increased switching speed without obvious reliability degradation. This performance improvement in the Gd-doped HfO2 RRAM devices is clarified to the suppressed randomicity of oxygen vacancy filaments’ formation and the reduced oxygen ion migration barrier induced by trivalent Gd-doping effect. The achieved results also demonstrate the validity of implantation doping approach for the fabrication of RRAM devices.
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84.30.Sk Pulse and digital circuits

Niobium substitution in Zr0.5Hf0.5NiSn based Heusler compounds for high power factors

Michael Schwall and Benjamin Balke

Appl. Phys. Lett. 98, 042106 (2011); http://dx.doi.org/10.1063/1.3548867 (3 pages) | Cited 6 times

Online Publication Date: 26 January 2011

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This work reports on the structural and physical properties of the Heusler alloy (Zr0.5Hf0.5)1−xNbxNiSn with varying Nb concentrations. The structure of the (Zr0.5Hf0.5)1−xNbxNiSn solid solution was investigated by means of X-ray diffraction. It is found that the alloys exhibit the C1b structure for all Nb concentrations. The physical properties were studied using the physical properties measurement system from low temperature to room temperature. It was shown that the thermoelectric properties like the dimensionless Figure of Merit are increased five times by substituting (Zr0.5Hf0.5) with Nb to 0.09 at 300 K and the Powerfactor is increased 10 times to 1.8 mW/K2 m at 300 K.
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72.15.Jf Thermoelectric and thermomagnetic effects
61.50.-f Structure of bulk crystals

Subgap optical conductivity in semihydrogenated graphene

Yee Sin Ang and C. Zhang

Appl. Phys. Lett. 98, 042107 (2011); http://dx.doi.org/10.1063/1.3549201 (3 pages) | Cited 2 times

Online Publication Date: 27 January 2011

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We report that for graphene with a finite band gap (such as semihydrogenated graphene or graphene with spin-orbit coupling), there exists a strong nonlinear optical response for energies lower than the band gap where the linear response is forbidden. At low temperatures, the nonlinear current in graphene with a gap is much stronger than that in gapless graphene. Our result suggests that semihydrogenated graphene can have a unique potential as a two-color nonlinear material in the terahertz frequency region. The relative intensity of the two colors can be tuned with the electric field.
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81.05.ue Graphene
78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.22.Pr Electronic structure of graphene

Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide

K. Buchholt, R. Ghandi, M. Domeij, C.-M. Zetterling, J. Lu, P. Eklund, L. Hultman, and A. Lloyd Spetz

Appl. Phys. Lett. 98, 042108 (2011); http://dx.doi.org/10.1063/1.3549198 (3 pages) | Cited 7 times

Online Publication Date: 28 January 2011

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Epitaxial Ti3SiC2 (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 °C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10−4 Ω cm2. Transmission electron microscopy shows that the interface between Ti3SiC2 and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing.
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68.55.ag Semiconductors
68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
61.72.Cc Kinetics of defect formation and annealing
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Thermal oxidation of silicon carbide: A comparison of n-type and p-type doped epitaxial layers

Xiao-An Fu, Kenji Okino, and Mehran Mehregany

Appl. Phys. Lett. 98, 042109 (2011); http://dx.doi.org/10.1063/1.3549294 (3 pages)

Online Publication Date: 28 January 2011

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The kinetics of wet thermal oxidation of both n-type and p-type doped 6H-SiC epitaxial layers grown on p-type 6H-SiC wafers has been investigated. The oxidation rates are affected significantly by doping concentration. The kinetics of wet thermal oxidation abides by the Deal–Grove model B. E. Deal and A. S. Grove, [J. Appl. Phys. 36, 3770 (1965)] . The linear oxidation rate constant B/A and the parabolic oxidation rate constant B are obtained by fitting the measured data to the Deal–Grove model.
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81.05.Hd Other semiconductors
81.65.Mq Oxidation
61.72.up Other materials

Thermoelectric effect of multiferroic oxide interfaces

Chenglong Jia and Jamal Berakdar

Appl. Phys. Lett. 98, 042110 (2011); http://dx.doi.org/10.1063/1.3549863 (3 pages) | Cited 1 time

Online Publication Date: 28 January 2011

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We investigate the thermoelectric properties of electrons at the interface of an oxide heterostructure and in the presence of a multiferroic oxide with spiral spin order. We find that there is no (spin) Hall current generated by the temperature gradient. A Seebeck effect is, however, present. Due to the magnetoelectric coupling, the charge and thermal conductivities are electrically controllable via the spin spiral helicity. Moreover, the thermopower exhibits a sign change when tuning the carrier density electro-statically.
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72.20.Pa Thermoelectric and thermomagnetic effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
75.85.+t Magnetoelectric effects, multiferroics
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
73.40.-c Electronic transport in interface structures
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