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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

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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Ge2Sb2Te5 phase-change films on polyimide substrates by pulsed laser deposition

Hongbing Lu, Erik Thelander, Jürgen W. Gerlach, Dietmar Hirsch, Ulrich Decker, and Bernd Rauschenbach

Appl. Phys. Lett. 101, 031905 (2012); http://dx.doi.org/10.1063/1.4737410 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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Growth of Ge2Sb2Te5 phase-change films on flexible polyimide substrates by pulsed laser deposition (PLD) is demonstrated. The effect of annealing temperature on the crystalline nature of the films was studied. A decrease of (200) lattice plane distance with the increase of annealing temperature was revealed for the films grown on both polyimide and Si substrates, which was related to tensile stress in the crystallized films. Optical reflectivity measurements showed a high reflectivity contrast between full crystalline and amorphous films. The results indicate an excellent potential for applications of these PLD-deposited Ge2Sb2Te5 films on flexible polyimide substrates in optical data storage.
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78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology

Type-II GaSb/GaAs coupled quantum rings: Room-temperature luminescence enhancement and recombination lifetime elongation for device applications

Wei-Hsun Lin, Kai-Wei Wang, Shu-Wei Chang, Min-Hsiung Shih, and Shih-Yen Lin

Appl. Phys. Lett. 101, 031906 (2012); http://dx.doi.org/10.1063/1.4737443 (4 pages) | Cited 2 times

Online Publication Date: 18 July 2012

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Type-II GaSb/GaAs coupled quantum rings have exhibited two-order-of-magnitude luminescence enhancement and ten-times elongation of recombination lifetime at room temperature as compared with regular rings. The longer lifetime suggests that a significant amount of electrons are confined in coupled rings rather than simply leaking away. These phenomena indicate that type-II nanostructures can be potentially utilized for room-temperature luminescence and carrier storage applications.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Kv Quantum dots

Light amplification in zero-index metamaterial with gain inserts

Weiren Zhu, Ivan D. Rukhlenko, and Malin Premaratne

Appl. Phys. Lett. 101, 031907 (2012); http://dx.doi.org/10.1063/1.4737643 (4 pages) | Cited 6 times

Online Publication Date: 18 July 2012

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The concept of light amplification in a system of zero-index metamaterial with gain inserts is studied. We demonstrate that the radiation from a point source embedded in the system can be effectively amplified and the net gain is independent of the positions of gain inserts and the source. We further investigate how the net gain grows with the imaginary part of the inserts’ permittivities and find that it saturates when the imaginary part is sufficiently large. It is also shown that the efficiency of amplification is significantly reduced when lossy inserts are introduced into the system.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Longitudinal optical phonon-plasmon coupled modes of degenerate Al-doped ZnO films

K. Ding, Q. C. Hu, W. W. Lin, J. K. Huang, and F. Huang

Appl. Phys. Lett. 101, 031908 (2012); http://dx.doi.org/10.1063/1.4737647 (5 pages)

Online Publication Date: 18 July 2012

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We have investigated the interaction between carriers and polar phonons by using Raman scattering spectroscopy in highly conductive Al-doped ZnO films grown by metalorganic chemical vapor deposition. Different from the longitudinal optical phonon-plasmon coupled modes (LOPPCM) observed in nondegenerate ZnO, an A1(LO)-like mode appears at the low frequency side of the uncoupled A1(LO) mode, and it monotonically shifts to higher frequencies and approaches to the uncoupled A1(LO) mode as Al composition increases. Based on line shape calculations, the A1(LO)-like mode is assigned to the large wave-vector LOPPCM arising from nonconserving scattering dominated by the Al impurity-induced Fröhlich mechanism. Benefiting from the nonmonotonic Al composition dependence of the electron density, it is revealed that the LOPPCM depends mainly on the doping level but not the carrier concentration.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.uj III-V and II-VI semiconductors

Electrical and thermoelectric properties of single-wall carbon nanotube doped Bi2Te3

Y. Zhang, X. L. Wang, W. K. Yeoh, R. K. Zheng, and C. Zhang

Appl. Phys. Lett. 101, 031909 (2012); http://dx.doi.org/10.1063/1.4737898 (4 pages)

Online Publication Date: 18 July 2012

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The effects of single-wall carbon nanotube (SWCNT) doping in n-type Bi2Te3 bulk samples on the electrical and thermal transport properties have been studied. Bi2Te3 samples doped with 0–5 wt. % SWCNTs were fabricated using solid state reaction and investigated using x-ray diffraction, transmission electron microscopy, and magneto transport measurements. Results show that the 0.5% doping results in the significant enhancement of the Seebeck coefficience to as high as −231.8 μV/K, giant magneto resistance of up to 110%, reduction of thermal conductivity, and change of sign of the Seebeck coefficient from n to p type depending on the doping level and temperature. The figure of merit, ZT, of the optimum SWCNT doped Bi2Te3 was increased by 25%–40% over a wide temperature range compared to the undoped sample.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.up Other materials
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.66.Fn Inorganic compounds
72.20.My Galvanomagnetic and other magnetotransport effects

A realistic design of three-dimensional full cloak at terahertz frequencies

Yongjun Bao, Cheng He, Fan Zhou, Colin Stuart, and Cheng Sun

Appl. Phys. Lett. 101, 031910 (2012); http://dx.doi.org/10.1063/1.4735133 (4 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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This paper presents a realistic design of a three-dimensional invisibility full cloak device at Terahertz frequency, consisting of radially arranged polymer slabs covered with III-V semiconductor materials featuring Drude-like resonance. By applying high order optical transformation, it is possible to constrain the semiconductor layer of constant thickness for the convenience in practical fabrication. The anisotropic and spatially variant material constants are realized by adjusting the filling ratio of the polymer slabs. Such a structure can be readily fabricated using high-aspect ratio three-dimensional microfabrication of polymeric slabs in combine with conformal deposition of the semiconductor cladding layer.
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42.70.Jk Polymers and organics
42.79.-e Optical elements, devices, and systems

Plasmonic mediated nucleation of resonant nano-cavities

V. G. Karpov, M. Nardone, and A. V. Subashiev

Appl. Phys. Lett. 101, 031911 (2012); http://dx.doi.org/10.1063/1.4737654 (4 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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We show that the energy required for nucleation can be efficiently supplied by the electromagnetic field in resonance with plasmonic oscillations of a nucleus, and the field frequency dictates its strongly anisotropic resonant shape. The predicted effect is especially strong for nucleation of pancake shaped nano-cavities in skin depth metallic layers. This significant modification of nucleation physics can have important implications in nano-photonics and optical recording.
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42.79.-e Optical elements, devices, and systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
41.20.-q Applied classical electromagnetism

Realization of compressively strained GaN films grown on Si(110) substrates by inserting a thin AlN/GaN superlattice interlayer

X. Q. Shen, T. Takahashi, H. Kawashima, T. Ide, and M. Shimizu

Appl. Phys. Lett. 101, 031912 (2012); http://dx.doi.org/10.1063/1.4737874 (4 pages)

Online Publication Date: 19 July 2012

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We investigate the strain properties of GaN films grown by plasma-assisted molecular beam epitaxy on Si(110) substrates. It is found that the strain of the GaN film can be converted from a tensile to a compressive state simply by inserting a thin AlN/GaN superlattice structure (SLs) within the GaN film. The GaN layers seperated by the SLs can have different strain states, which indicates that the SLs plays a key role in the strain modulation during the growth and the cooling down processes. Using this simple technique, we grow a crack-free GaN film exceeding 2-μm-thick. The realization of the compressively strained GaN film makes it possible to grow thick GaN films without crack generation on Si substrates for optic and electronic device applications.
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68.55.ag Semiconductors
52.77.-j Plasma applications
68.65.Cd Superlattices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Substrate effect on the room-temperature ferromagnetism in un-doped ZnO films

Peng Zhan, Weipeng Wang, Zheng Xie, Zhengcao Li, Zhengjun Zhang, Peng Zhang, Baoyi Wang, and Xingzhong Cao

Appl. Phys. Lett. 101, 031913 (2012); http://dx.doi.org/10.1063/1.4737881 (4 pages) | Cited 2 times

Online Publication Date: 19 July 2012

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Room-temperature ferromagnetism was achieved in un-doped ZnO films on silicon and quartz substrates. Photoluminescence measurement and positron annihilation analysis suggested that the ferromagnetism was originated from singly occupied oxygen vacancies (roughly estimated as ∼0.55 μB/vacancy), created in ZnO films by annealing in argon. The saturated magnetization of ZnO films was enhanced from ∼0.44 emu/g (on quartz) to ∼1.18 emu/g (on silicon) after annealing at 600 °C, as silicon acted as oxygen getter and created more oxygen vacancies in ZnO films. This study clarified the origin of ferromagnetism in un-doped ZnO and provides an idea to enhance the ferromagnetism.
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75.70.Ak Magnetic properties of monolayers and thin films
78.55.Et II-VI semiconductors
78.70.Bj Positron annihilation
81.40.Gh Other heat and thermomechanical treatments
75.50.Dd Nonmetallic ferromagnetic materials
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Bipolar conductivity in nanocrystallized TiO2

D. R. Islamov, V. A. Gritsenko, C. H. Cheng, and A. Chin

Appl. Phys. Lett. 101, 032101 (2012); http://dx.doi.org/10.1063/1.4737016 (2 pages)

Online Publication Date: 16 July 2012

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This study calculated the contribution of electrons and holes to TiO2 conductivity in Si/TiO2/Ni structures by conducting experiments on the injection of minority carriers from n- and p-type silicon. Results show that electrons and holes contribute to the conductivity of TiO2, enabling two-band conductivity.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-efficiency heterojunction solar cells on crystalline germanium substrates

Bahman Hekmatshoar, Davood Shahrjerdi, Marinus Hopstaken, Keith Fogel, and Devendra K. Sadana

Appl. Phys. Lett. 101, 032102 (2012); http://dx.doi.org/10.1063/1.4737166 (4 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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We report stand-alone heterojunction (HJ) solar cells with conversion efficiencies of 5.9% and 7.2% on n-type and p-type crystalline germanium (c-Ge) substrates, respectively. The emitter of the HJ solar cells is formed by growing thin layers of highly doped hydrogenated microcrystalline silicon using plasma-enhanced chemical vapor deposition at temperatures close to 200 °C. The conversion efficiencies of the HJ solar cells are well-comparable with conventional devices fabricated at temperatures as high as 600 °C. We also study the surface passivation of c-Ge with hydrogenated amorphous and microcrystalline Si and correlate the passivation quality with the electrical performance of the HJ solar cells.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells

Nitrogen-polar core-shell GaN light-emitting diodes grown by selective area metalorganic vapor phase epitaxy

Shunfeng Li, Xue Wang, Sönke Fündling, Milena Erenburg, Johannes Ledig, Jiandong Wei, Hergo H. Wehmann, Andreas Waag, Werner Bergbauer, Martin Mandl, Martin Strassburg, Achim Trampert, Uwe Jahn, Henning Riechert, Holger Jönen, et al.

Appl. Phys. Lett. 101, 032103 (2012); http://dx.doi.org/10.1063/1.4737395 (4 pages) | Cited 3 times

Online Publication Date: 17 July 2012

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Homogeneous nitrogen-polar GaN core-shell light emitting diode (LED) arrays were fabricated by selective area growth on patterned substrates. Transmission electron microscopy measurements prove the core-shell structure of the rod LEDs. Depending on the growth facets, the InGaN/GaN multi-quantum wells (MQWs) show different dimensions and morphology. Cathodoluminescence (CL) measurements reveal a MQWs emission centered at about 415 nm on sidewalls and another emission at 460 nm from top surfaces. CL line scans on cleaved rod also indicate the core-shell morphology. Finally, an internal quantum efficiency of about 28% at room temperature was determined by an all-optical method on a LED array.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Growth direction dependence of the electron spin dynamics in {111} GaAs quantum wells

H. Q. Ye, G. Wang, B. L. Liu, Z. W. Shi, W. X. Wang, C. Fontaine, A. Balocchi, T. Amand, D. Lagarde, P. Renucci, and X. Marie

Appl. Phys. Lett. 101, 032104 (2012); http://dx.doi.org/10.1063/1.4737007 (5 pages) | Cited 1 time

Online Publication Date: 17 July 2012

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The electron spin dynamics is studied by time-resolved Kerr rotation in GaAs/AlGaAs quantum wells embedded in NIP structures grown on (111)A or (111)B-oriented substrates. In both cases the spin lifetimes are significantly increased by applying an external electric field, but this field has to point along the growth direction for structures grown on (111)A and opposite to it for the ones grown on (111)B. This extended electron spin lifetime is the result of the suppression of the D’yakonov-Perel spin relaxation mechanism [Sov. Phys. Solid State 13, 3023 (1972)] due to the cancellation effect of the internal Dresselhaus term [Phys. Rev. 100, 580 (1955)] with the external electric field induced Rashba one [J. Phys. C 17, 6039 (1984)], both governing the conduction band spin-orbit splitting. These results demonstrate the key role played by the growth direction in the design of spintronic devices.
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73.21.Fg Quantum wells
78.20.Jq Electro-optical effects
78.67.De Quantum wells
68.65.Fg Quantum wells

A higher-k tetragonal HfO2 formed by chlorine plasma treatment at interfacial layer for metal-oxide-semiconductor devices

Chung-Hao Fu, Kuei-Shu Chang-Liao, Chen-Chien Li, Zong-Hao Ye, Fang-Ming Hsu, Tien-Ko Wang, Yao-Jen Lee, and Ming-Jinn Tsai

Appl. Phys. Lett. 101, 032105 (2012); http://dx.doi.org/10.1063/1.4737393 (4 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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A tetragonal HfO2 (t-HfO2) with higher-k value and large band gap is investigated in this work. X-ray diffraction analysis shows a t-HfO2 can be formed by using Cl2 plasma treatment at the HfO2/Si interface after a post deposition annealing at 650 °C. The mechanisms of t-HfO2 formation can be attributed to the Si diffusion and oxygen vacancy generation which are formed by Cl2 plasma treatment. From the cross-sectional transmission electron microscope and capacitance-voltage measurement, the k value of this t-HfO2 is estimated to be about 35. The optical band gap value for t-HfO2 is similar to that of the monoclinic.
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84.32.Tt Capacitors

Solitary acoustic pulses in quantum semiconductor plasmas

W. M. Moslem, I. Zeba, and P. K. Shukla

Appl. Phys. Lett. 101, 032106 (2012); http://dx.doi.org/10.1063/1.4736726 (5 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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We report properties of solitary acoustic pulses that propagate in electron-hole quantum semiconductor plasmas. We show that the dynamics of nonlinear acoustic pulses is governed by the Korteweg–de Vries equation, which includes contributions of the electron and hole quantum recoil effects, quantum statistical pressures of the plasma species, as well as exchange and correlation effects. Typical values for GaAs, GaSb, GaN, and InP semiconductors are used to estimate the speed and profiles of solitary acoustic pulses. The nonlinear solitary pulses depict intrinsic localization of electrostatic wave energies in semiconductor plasmas.
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72.30.+q High-frequency effects; plasma effects

Room temperature sub-bandgap photoluminescence from silicon containing oxide precipitates

K. Bothe, R. J. Falster, and J. D. Murphy

Appl. Phys. Lett. 101, 032107 (2012); http://dx.doi.org/10.1063/1.4737175 (4 pages) | Cited 2 times

Online Publication Date: 19 July 2012

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Room temperature photoluminescence was measured from p-type Czochralski silicon processed to contain oxide precipitates. No detectable luminescence was associated with unstrained oxide precipitates. Strained oxide precipitates gave rise to a broad luminescence peak centred at ∼1600 nm. The intensity of the peak increased with the density of strained precipitates, with band-to-band luminescence being reduced correspondingly. Dislocations and stacking faults around the strained precipitates were found to introduce competing non-radiative recombination centres which reduced the sub-bandgap photoluminescence. A mechanism is proposed for the sub-bandgap luminescence due to strained precipitates in terms of a transition between defect bands.
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78.55.-m Photoluminescence, properties and materials
81.05.Cy Elemental semiconductors
81.10.Fq Growth from melts; zone melting and refining
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Applicability of continuum absorption in semiconductor quantum wells to absolute absorption-strength standards

Masahiro Yoshita, Kenji Kamide, Hidekatsu Suzuura, and Hidefumi Akiyama

Appl. Phys. Lett. 101, 032108 (2012); http://dx.doi.org/10.1063/1.4737900 (4 pages) | Cited 1 time

Online Publication Date: 19 July 2012

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The absolute strength of two-dimensional continuum absorption in semiconductor quantum wells (QWs) was investigated for application to an absorption-strength standard. We presented an equation for the continuum-state absorbance in a QW, showing that the absorbance near the band edge is essentially described by a universal value proportional to the fine-structure constant with correction terms for band-mixing effects and Coulomb enhancement effects. By using k·p equations with the established band parameters, we calculated the absorbance with quantitative estimations of the correction terms in typical semiconductor QWs. The results indicate that the absorbance of the QW is applicable to an absorption-strength standard.
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78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors

Ultra-low resistance ohmic contacts to GaN with high Si doping concentrations grown by molecular beam epitaxy

Faiza Afroz Faria, Jia Guo, Pei Zhao, Guowang Li, Prem Kumar Kandaswamy, Mark Wistey, Huili (Grace) Xing, and Debdeep Jena

Appl. Phys. Lett. 101, 032109 (2012); http://dx.doi.org/10.1063/1.4738768 (4 pages)

Online Publication Date: 20 July 2012

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Ti/Al/Ni/Au ohmic contacts were formed on heavily doped n+ metal-polar GaN samples with various Si doping concentrations grown by molecular beam epitaxy. The contact resistivity (RC) and sheet resistance (Rsh) as a function of corresponding GaN free carrier concentration (n) were measured. Very low RC values (<0.09 Ω mm) were obtained, with a minimum RC of 0.035 Ω mm on a sample with a room temperature carrier concentration of ∼5 × 1019 cm−3. Based on the systematic study, the role of RC and Rsh is discussed in the context of regrown n+ GaN ohmic contacts for GaN based high electron mobility transistors.
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73.40.Ns Metal-nonmetal contacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
73.40.Cg Contact resistance, contact potential
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Variation of magnetic domain structure during martensite variants rearrangement in ferromagnetic shape memory alloys

Xingzhe Wang and Fang Li

Appl. Phys. Lett. 101, 032401 (2012); http://dx.doi.org/10.1063/1.4737172 (4 pages)

Online Publication Date: 16 July 2012

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Studies of magnetic domain and anisotropy in ferromagnetic shape memory alloys (FSMAs) are crucial for both understanding their ferromagnetism and engineering in applications. The experimental measurements showed that magnetization rotations and domain-wall motions exhibit distinct characteristics in the field-preferred variants and stress-preferred variants of FSMAs [Y. W. Lai, N. Scheerbaum, D. Hinz, O. Gutfleisch, R. Schäfer, L. Schultz, and J. McCord, Appl. Phys. Lett. 90, 192504 (2007)]. Aiming at characterization of formation and variation of the complex magnetic microstructure in FSMAs, we present an analytical approach based on the energy minimization theory and Boltzmann relation on magnetic domains. The magnetic domain behavior during the martensite variants rearrangement is captured to show a good agreement with the experimental observations.
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81.05.Bx Metals, semimetals, and alloys
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetoresistance effect in L10-MnGa/MgO/CoFeB perpendicular magnetic tunnel junctions with Co interlayer

Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, H. Naganuma, M. Oogane, Y. Ando, and T. Miyazaki

Appl. Phys. Lett. 101, 032402 (2012); http://dx.doi.org/10.1063/1.4737000 (4 pages) | Cited 3 times

Online Publication Date: 16 July 2012

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The fully perpendicular magnetic tunnel junctions (p-MTJs) based on L10-MnGa and thin CoFeB electrodes with MgO barrier were reported in this letter. A thin Co layer was introduced between the MnGa layer and the MgO barrier layer to investigate interfacial effect on the device’s magnetic and transport properties. The magnetoresistance ratio improved significantly due to the Co insertion, and reached 40% at room temperature (80% at 5 K) when the Co thickness was 1.5 nm. Moreover, the junctions with Co interlayer exhibited four low-resistance states in one full cycle rather than two in normal MTJs. The physical origin was discussed by considering the coupling between MnGa and Co layers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.47.Pq Other materials

Precessional reversal in orthogonal spin transfer magnetic random access memory devices

H. Liu, D. Bedau, D. Backes, J. A. Katine, and A. D. Kent

Appl. Phys. Lett. 101, 032403 (2012); http://dx.doi.org/10.1063/1.4737010 (4 pages) | Cited 2 times

Online Publication Date: 18 July 2012

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Single-shot time-resolved resistance measurements have been used to determine the magnetization reversal mechanisms of orthogonal spin transfer magnetic random access memory (OST-MRAM) devices at nanosecond time scales. There is a strong asymmetry between antiparallel (AP) to parallel (P) and P to AP transitions under the same pulse conditions. P to AP transitions are shown to occur by precession of the free layer magnetization, while the AP to P transition is typically direct, occurring in less than 200 ps. We associate the asymmetry with spin torques perpendicular to the plane of the free layer, an important characteristic of OST-MRAM bit cells that can be used to optimize device performance.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Electrical characterization of all-epitaxial Fe/GaN(0001) Schottky tunnel contacts

Sergio Fernández-Garrido, Kai U. Ubben, Jens Herfort, Cunxu Gao, and Oliver Brandt

Appl. Phys. Lett. 101, 032404 (2012); http://dx.doi.org/10.1063/1.4737905 (4 pages)

Online Publication Date: 19 July 2012

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We analyze the properties of Fe Schottky contacts prepared in situ on n-type GaN(0001) by molecular beam epitaxy. In particular, we investigate the suitability of these epitaxial Fe layers for electrical spin injection. Current-voltage-temperature measurements demonstrate pure field emission for Fe/GaN:Si Schottky diodes with [Si] = 5×1018 cm−3. The Schottky barrier height of the clean, epitaxial Fe/GaN interface is determined by both current-voltage-temperature and capacitance-voltage techniques to be (1.47±0.09)eV.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Controllable spin-glass behavior and large magnetocaloric effect in Gd-Ni-Al bulk metallic glasses

Fang Yuan, Juan Du, and Baolong Shen

Appl. Phys. Lett. 101, 032405 (2012); http://dx.doi.org/10.1063/1.4738778 (4 pages) | Cited 1 time

Online Publication Date: 20 July 2012

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Glass-forming ability, spin-glass (SG) behavior, and magnetocaloric effect in Gd55NixAl45-x (x = 15, 20, 25, 30) metallic alloys were investigated. A ferromagnetic SG behavior was observed for glassy ribbons with compositions of x = 15, 20, and 25, but it disappeared for that of x = 30. Furthermore, the maximum magnetic entropy change (−ΔSmmax) increased with the increasing Ni/Al-ratio while the decrease of full width at half −ΔSmmax was almost negligible. Accordingly, −ΔSmmax of 9.25 J kg−1 K−1, adiabatic temperature change of 4.3 K and refrigeration capacity of 851 J kg−1 under 50 kOe were obtained for Gd55Ni30Al15 glassy alloy.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Lk Spin glasses and other random magnets
64.70.pe Metallic glasses
61.43.Fs Glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
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Tungsten silicide films for microwave kinetic inductance detectors

Thomas Cecil, Antonino Miceli, Orlando Quaranta, Chian Liu, Daniel Rosenmann, Sean McHugh, and Benjamin Mazin

Appl. Phys. Lett. 101, 032601 (2012); http://dx.doi.org/10.1063/1.4737408 (4 pages) | Cited 3 times

Online Publication Date: 18 July 2012

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Microwave kinetic inductance detectors provide highly multiplexed arrays of detectors that can be configured to operate from the sub-millimeter to the x-ray regime. We have examined two tungsten silicide alloys (W5Si3 and WSi2), which are dense alloys that provide a critical temperature tunable with composition, large kinetic inductance fraction, and high normal-state resistivity. We have fabricated superconducting resonators and provide measurement data on critical temperature, surface resistance, quality factor, noise, and quasiparticles lifetime. Tungsten silicide appears to be promising for microwave kinetic inductance detectors.
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73.61.At Metal and metallic alloys
85.25.Am Superconducting device characterization, design, and modeling
73.25.+i Surface conductivity and carrier phenomena
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Remarkably high-temperature stable piezoelectric properties of Bi(Mg0.5Ti0.5)O3 modified BiFeO3–BaTiO3 ceramics

Changrong Zhou, Antonio Feteira, Xu Shan, Huabin Yang, Qin Zhou, Jun Cheng, Weizhou Li, and Hua Wang

Appl. Phys. Lett. 101, 032901 (2012); http://dx.doi.org/10.1063/1.4736724 (4 pages) | Cited 9 times

Online Publication Date: 16 July 2012

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Show Abstract
Dense (1-y)BiFe1−x(Mg0.5Ti0.5)xO3 − yBaTiO3 (BFMT-BT, y = 0.29, x = 0-0.12) ceramics with a pseudocubic perovskite crystal structure exhibit remarkably high-temperature stable piezoelectric properties. In particular, x = 0.03 BFMT-BT ceramics, with a Curie temperature, Tc, of ∼425 °C, show a stable piezoelectric coefficient, d33, of ∼155 pC/N up to a depolarization temperature, Td, of ∼400 °C. This Td is higher than Tc for Pb(Zr,Ti)O3, therefore suggesting BFMT-BT ceramics to be promising high-temperature Pb-free piezoelectric materials.
Show PACS
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Cg PZT ceramics and other titanates
77.80.bg Compositional effects
61.66.Fn Inorganic compounds
77.22.Ej Polarization and depolarization
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