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13 Dec 2004

Volume 85, Issue 24, pp. 5819-6053

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 5968 (2004); http://dx.doi.org/10.1063/1.1830083 (3 pages)

A. Urbieta, P. Fernández, and J. Piqueras
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Near room temperature droplet epitaxy for fabrication of InAs quantum dots

Jong Su Kim and Nobuyuki Koguchi

Appl. Phys. Lett. 85, 5893 (2004); http://dx.doi.org/10.1063/1.1839642 (3 pages) | Cited 37 times

Online Publication Date: 9 December 2004

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By using the droplet epitaxy method, we succeed in fabricating the InAs quantum dots (QDs) with the spatial density of 4×1010∕cm2 and an average lateral size of 20 nm on GaAs (001) at the droplets deposition temperature of 50 °C and subsequent annealing process under As4 flux. These QDs shows the intense photoluminescence even at room temperature indicating that high-quality InAs QDs can be fabricated by near room temperature droplets deposition and crystallization process by 400 °C in situ annealing.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
64.70.K- Solid-solid transitions
68.35.B- Structure of clean surfaces (and surface reconstruction)

Wave-shaped Si crystal wafers obtained by plastic deformation and preparation of their solar cells

Kazuo Nakajima, Kozo Fujiwara, and Wugen Pan

Appl. Phys. Lett. 85, 5896 (2004); http://dx.doi.org/10.1063/1.1834719 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2004

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We can prepare wave-shaped crystal wafers by the plastic deformation of Si crystal wafers, and we report on the characteristics of solar cells fabricated using the wave-shaped Si wafers, in order to demonstrate whether the shaped wafers are of high quality to be used in the preparation of devices or not. To obtain wave-shaped Si wafers, graphite dies were used. The diameter of the convex and concave waves formed in the dies is 4 mm. The Si wafers were pressed by an overload of 200 N. A thickness versus temperature region for obtaining well wave-shaped Si wafers by plastic deformation was determined. Solar cells were prepared using wave-shaped wafers pressed at 1100 and 1200 °C. The wafers were annealed at 1109 and 1209 °C, respectively, for 1 h in a hydrogen atmosphere. The conversion efficiency of the wave-shaped solar cells is 6.0%–10.1%. Thus, it is clarified that the wave-shaped wafers are of high quality to be used in the preparation of devices. The quality of the wafers can be significantly improved by suitable thermal treatments.
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84.60.Jt Photoelectric conversion
81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
61.72.Cc Kinetics of defect formation and annealing
62.20.F- Deformation and plasticity

Patterned nanoclusters in the indium-doped SrTiO3 films

M. Zhang, X. L. Ma, D. X. Li, H. B. Lu, Z. H. Chen, and G. Z. Yang

Appl. Phys. Lett. 85, 5899 (2004); http://dx.doi.org/10.1063/1.1836879 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Highly dense, dimensionally uniform, and self-organized nanoclusters have been formed in the indium-doped SrTiO3 film, which was grown by computer-controlled laser molecular-beam epitaxy on SrTiO3 substrate. On the basis of transmission electron microscopy and three-dimensional strain mapping from a high-resolution lattice image, it is found that the nanoclusters exhibit a dome-shaped structure with a flat bottom, whose diameter distribution ranges from 1.6 nm to 6.4 nm. Nanobeam composition analysis shows that the nanoclusters are rich of doping element compared with their surrounding medium.
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61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Chemical ordering in ilmenite-hematite bulk ceramics through proton irradiation

D. M. Allen, L. Navarrete, J. Dou, R. Schad, P. Padmini, P. Kale, R. K. Pandey, S. Shojah-Ardalan, and R. Wilkins

Appl. Phys. Lett. 85, 5902 (2004); http://dx.doi.org/10.1063/1.1834989 (3 pages) | Cited 7 times

Online Publication Date: 9 December 2004

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We demonstrated the capability of MeV proton irradiation to promote chemical ordering processes in a solid at low temperature. We used the ilmenite–hematite solid solution system which allows estimation of the degree of ordering through measurement of its magnetization. Normally, ordering through diffusion would require high temperature annealing. At high temperatures, however, the equilibrium state would be less ordered and thus the achievable ordering incomplete. High energetic protons continuously transfer energy to the sample through electronic interaction which locally deposits large quantities of energy without a general increase of the sample temperature. This promotes diffusion processes which allow the system to relax towards the ordered equilibrium state.
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81.05.Mh Cermets, ceramic and refractory composites
61.80.Jh Ion radiation effects
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
61.82.Ms Insulators
66.30.Ny Chemical interdiffusion; diffusion barriers
64.70.K- Solid-solid transitions

X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment

B. Abendroth, R. Gago, F. Eichhorn, and W. Möller

Appl. Phys. Lett. 85, 5905 (2004); http://dx.doi.org/10.1063/1.1836868 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2–10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress–release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.82.Ms Insulators
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.A- Nucleation and growth
61.80.Jh Ion radiation effects
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
81.40.Gh Other heat and thermomechanical treatments

Columnar [001]-oriented nitrogen order in Ga(NAs) and (GaIn)(NAs) alloys

O. Rubel, K. Volz, T. Torunski, S. D. Baranovskii, F. Grosse, and W. Stolz

Appl. Phys. Lett. 85, 5908 (2004); http://dx.doi.org/10.1063/1.1829801 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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By calculations in the framework of the valence force field method, we show that nitrogen atoms in diluted GaAs1−xNx tend to align along the [001] direction. In quaternary alloys Ga1−yInyAs1−xNx this tendency is observed only in “as-grown” samples, while in the annealed samples nitrogen atoms build more energetically favorable bonds with indium. Experimentally observed inhomogeneous strain profiles in these material systems, as well as their dissolution upon annealing, agree qualitatively with results of the calculations.
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61.50.-f Structure of bulk crystals
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
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Room-temperature operations of memory devices based on self-assembled InAs quantum dot structures

C. Balocco, A. M. Song, and M. Missous

Appl. Phys. Lett. 85, 5911 (2004); http://dx.doi.org/10.1063/1.1831558 (3 pages) | Cited 28 times

Online Publication Date: 9 December 2004

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Memory devices have been fabricated in high-electron-mobility transistors with embedded InAs quantum dots (QDs). We show that memory operations can be fully controlled by gate biases at room temperature, without the need for light excitations to erase memory states. Real-time measurements indicate a charge retention time of a few minutes. Neither such retention time nor the self-consistent simulations can justify the picture that the memory effect is due to charging/discharging of intrinsic QD states. Experiments at a series of gate biases point to the presence of deep levels coexisting in the QD layer(s), which are responsible for the memory effect.
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85.30.Tv Field effect devices
73.63.Kv Quantum dots
73.21.La Quantum dots
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Spin-polarized tunneling in room-temperature mesoscopic spin valves

S. O. Valenzuela and M. Tinkham

Appl. Phys. Lett. 85, 5914 (2004); http://dx.doi.org/10.1063/1.1830685 (3 pages) | Cited 47 times

Online Publication Date: 9 December 2004

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We study optimization of spin injection and detection both at 4.2 K and at room temperature using a metallic mesoscopic spin valve structure with tunneling interfaces between the ferromagnetic electrodes (CoFe or NiFe) and the central metallic conductor (Al). We investigate the influence of the barrier transparency on the spin polarization of the tunneling electrons by varying the O2 exposure of the Al film before depositing the ferromagnetic electrodes. An increase of the polarization from ∼10% to 16% (25% at 4.2 K) is observed as the resistance of the junction is increased from 100 to 700 Ωμm2. A spin transresistance as high as 2.5 Ω is obtained at 4.2 K.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.At Metal and metallic alloys
85.75.Mm Spin polarized resonant tunnel junctions
68.55.-a Thin film structure and morphology

Band alignment between (100)Si and complex rare earth∕transition metal oxides

V. V. Afanas’ev, A. Stesmans, C. Zhao, M. Caymax, T. Heeg, J. Schubert, Y. Jia, D. G. Schlom, and G. Lucovsky

Appl. Phys. Lett. 85, 5917 (2004); http://dx.doi.org/10.1063/1.1829781 (3 pages) | Cited 62 times

Online Publication Date: 9 December 2004

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The electron energy band alignment between (100)Si and several complex transition∕rare earth (RE) metal oxides (LaScO3, GdScO3, DyScO3, and LaAlO3, all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides (5.6–5.7 eV) yielding the conduction and valence band offsets at the Si∕oxide interface of 2.0±0.1 and 2.5±0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states.
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71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Ht Disordered structures
72.40.+w Photoconduction and photovoltaic effects

Mechanism for ohmic contact formation of Ni∕Ag contacts on p-type GaN

Ho Won Jang and Jong-Lam Lee

Appl. Phys. Lett. 85, 5920 (2004); http://dx.doi.org/10.1063/1.1835535 (3 pages) | Cited 33 times

Online Publication Date: 9 December 2004

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The mechanism for ohmic contact formation of Ni∕Ag contacts on p-type GaN was investigated using synchrotron photoemission spectroscopy. A low contact resistivity of 6.6×10−5 Ω cm2 was obtained from Ni(50 math)∕Ag(1200 math) contact after annealing at 500°C in O2 ambient. Ni out-diffused to form a NiO and Ag in-diffused into the contact interface during the oxidation annealing. Out-diffused Ga atoms from GaN could dissolve in the Ag layer to form Ag–Ga solid solutions, leaving Ga vacancies below the contact. Ga vacancies could increase the net hole concentration and reduce the surface band bending, resulting in the ohmic contact formation.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Cg Contact resistance, contact potential
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters

ZnO nanowire field-effect transistor and oxygen sensing property

Zhiyong Fan, Dawei Wang, Pai-Chun Chang, Wei-Yu Tseng, and Jia G. Lu

Appl. Phys. Lett. 85, 5923 (2004); http://dx.doi.org/10.1063/1.1836870 (3 pages) | Cited 269 times

Online Publication Date: 9 December 2004

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Single-crystal ZnO nanowires are synthesized using a vapor trapping chemical vapor deposition method and configured as field-effect transistors. Electrical transport studies show n-type semiconducting behavior with a carrier concentration of ∼107 cm−1 and an electron mobility of ∼17 cm2∕V s. The contact Schottky barrier between the Au/Ni electrode and nanowire is determined from the temperature dependence of the conductance. Thermionic emission is found to dominate the transport mechanism. The effect of oxygen adsorption on electron transport through the nanowires is investigated. The sensitivity to oxygen is demonstrated to be higher with smaller radii nanowires. Moreover, the oxygen detection sensitivity can be modulated by the gate voltage. These results indicate that ZnO holds high potential for nanoscale sensing applications.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Dn Low-field transport and mobility; piezoresistance
79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
68.43.Mn Adsorption kinetics
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

290 fs switching time of Fe-doped quantum well saturable absorbers in a microcavity in 1.55 μm range

M. Gicquel-Guézo, S. Loualiche, J. Even, C. Labbé, O. Dehaese, A. Le Corre, H. Folliot, and Y. Pellan

Appl. Phys. Lett. 85, 5926 (2004); http://dx.doi.org/10.1063/1.1804239 (3 pages) | Cited 10 times

Online Publication Date: 9 December 2004

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Ultrafast all-optical switch has been demonstrated by inserting Fe-doped multiple quantum wells (MQWs) in asymmetric Fabry-Perot microcavities. Heavy Fe doping during the InGaAs∕InP MQW epitaxial growth is a well-controlled technique to reach subpicosecond optical time constants. An asymmetric Fabry-Perot microcavity using gold metal as a back mirror and air/InP interface as a front mirror is realized. Pump-probe experiments using a conventional scheme on such switching devices are investigated. The device reveals an ultrafast response time, as low as 290 fs, for an iron concentration of 2×1019 cm−3, a contrast ratio of 8 dB, a threshold switching fluence of 3.5 μJ∕cm−2, and a 37-nm 3-dB bandwidth in the 1.55-μm telecommunication spectral range.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.07.St Quantum wells
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Current-induced spin polarization at a single heterojunction

A. Yu. Silov, P. A. Blajnov, J. H. Wolter, R. Hey, K. H. Ploog, and N. S. Averkiev

Appl. Phys. Lett. 85, 5929 (2004); http://dx.doi.org/10.1063/1.1833565 (3 pages) | Cited 17 times

Online Publication Date: 9 December 2004

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We have experimentally achieved spin polarization by a lateral current in a single nonmagnetic semiconductor heterojunction. The effect does not require an applied magnetic field. The current-induced spin orientation can be seen as the inverse of the circular photogalvanic effect (also often referred to as spin photocurrents): the nonequilibrium spin changes its sign as the current reverses.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.25.Dc Spin polarized transport in semiconductors
78.55.Cr III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

One-dimensional bigyrotropic magnetic photonic crystals

I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, E. A. Shapovalov, A. Lakhtakia, and Th. Rasing

Appl. Phys. Lett. 85, 5932 (2004); http://dx.doi.org/10.1063/1.1825060 (3 pages) | Cited 16 times

Online Publication Date: 9 December 2004

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Electromagnetic wave propagation in a one-dimensional magnetic photonic crystal (MPC) made of bigyrotropic magnetic yttrium–iron garnet and nonmagnetic gadolinium–gallium garnet is theoretically investigated using the 4×4 transfer matrix method. Band gaps in the electromagnetic spectrum are numerically obtained and appear to depend on the helicity and direction of light propagation through the MPC.
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42.70.Qs Photonic bandgap materials
73.21.Ac Multilayers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Piezoresistive detection-based ferromagnetic resonance force microscopy of microfabricated exchange bias systems

A. Volodin, D. Buntinx, S. Brems, and C. Van Haesendonck

Appl. Phys. Lett. 85, 5935 (2004); http://dx.doi.org/10.1063/1.1836866 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2004

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Ferromagnetic resonance measurements were performed on CoO∕Co exchange biased microstructures with a low-temperature magnetic resonance force microscope (MRFM). The MRFM instrument relies on piezoresistive force detection, and the magnetic tip attached to the cantilever acts as a field gradient source. These features extend the applicability of the MRFM that can also be used as a conventional magnetic force microscope. Spatial variations of the MRFM signal, which are induced by a spatially modulated exchange bias, are monitored with a lateral resolution of about 5 μm.
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75.50.Cc Other ferromagnetic metals and alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.37.Rt Magnetic force microscopy (MFM)
75.30.Et Exchange and superexchange interactions

Microscopic analysis of low-frequency flux noise in YBa2Cu3O7 direct current superconducting quantum interference devices

D. Doenitz, R. Straub, R. Kleiner, and D. Koelle

Appl. Phys. Lett. 85, 5938 (2004); http://dx.doi.org/10.1063/1.1839273 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2004

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We use low-temperature scanning electron microscopy combined with superconducting quantum interference device (SQUID) detection of magnetic flux to image vortices and to investigate low-frequency flux noise in YBa2Cu3O7 thin film SQUIDs. The low-frequency flux noise shows a nonlinear increase with magnetic cooling field up to 60 μT. This effect is explained by the surface potential barrier at the SQUID hole. By correlating flux noise data with the spatial distribution of vortices, we obtain information on spatial fluctuations of vortices on a microscopic scale, e.g., an average vortex hopping length of ∼10 nm.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

The subgap current in Nb∕AlOx∕Nb tunnel junctions

F. P. Milliken, R. H. Koch, J. R. Kirtley, and J. R. Rozen

Appl. Phys. Lett. 85, 5941 (2004); http://dx.doi.org/10.1063/1.1836016 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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We have measured the subgap current at 0.8 K in several hysteretic 1.5×1.6 and 2.6×2.6 μm2 Nb∕AlOx∕Nb tunnel junctions. In zero magnetic field, the critical current Ic∼8 μA and the subgap resistance R∼0.3 MΩ. When we apply a magnetic field, Ic can be as low as 1 nA, and R is larger than 1 GΩ. This means that in a superconducting qubit made using Nb tunnel junctions, the decoherence rate from the quasiparticle conductance may be as low as 1∕(100 μs).
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Sv Critical currents

Magnetic properties arising from two additive contributions in soft magnetic nanocrystalline alloys

J. González

Appl. Phys. Lett. 85, 5944 (2004); http://dx.doi.org/10.1063/1.1833583 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2004

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The behavior of different magnetic properties (saturation magnetization and magnetostriction) of Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy exhibiting a biphase character has been assumed to be the algebraic sum of the contributions arising from the partial volume of both phases is investigated. Experimental results of the mentioned properties obtained in the classical mentioned nanocrystalline alloys seem to indicate the validity of the two volumetric contributions, although some discrepancies could suggest the relevance of another contribution coming from the surface region of the nanograins.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.80.+q Magnetomechanical effects, magnetostriction
81.07.Bc Nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Complex capacitance spectroscopy as a probe for oxidation process of AlOx-based magnetic tunnel junctions

J. C. A. Huang and C. Y. Hsu

Appl. Phys. Lett. 85, 5947 (2004); http://dx.doi.org/10.1063/1.1835534 (3 pages) | Cited 9 times

Online Publication Date: 9 December 2004

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Proper as well as under- and over-oxided CoFe−AlOx−CoFe magnetic tunnel junctions (MTJs) have been systematically investigated in a frequency range from 102 to 108 Hz by complex capacitance spectroscopy. The dielectric relaxation behavior of the MTJs remarkably disobeys the typical Cole–Cole arc law probably due to the existence of imperfectly blocked Schottky barrier in the metal-insulator interface. The dielectric relaxation response can be successfully modeled on the basis of Debye relaxation by incorporating an interfacial dielectric contribution. In addition, complex capacitance spectroscopy demonstrates significant sensitivity to the oxidation process of metallic Al layers, i.e., almost a fingerprint of under, proper, and over oxidation. This technique provides a fast and simple method to inspect the AlOx barrier quality of MTJs.
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75.50.Bb Fe and its alloys
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.65.Mq Oxidation
81.05.Bx Metals, semimetals, and alloys
77.22.Gm Dielectric loss and relaxation
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Pq Other materials
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Characteristics of metal-insulator-semiconductor capacitors based on high-k HfAlO dielectric films obtained by low-temperature electron-beam gun evaporation

V. Mikhelashvili, R. Brener, O. Kreinin, B. Meyler, J. Shneider, and G. Eisenstein

Appl. Phys. Lett. 85, 5950 (2004); http://dx.doi.org/10.1063/1.1836875 (3 pages) | Cited 14 times

Online Publication Date: 9 December 2004

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We describe the characteristics of thin HfAlO films deposited at low temperature by electron beam gun evaporation. As-deposited films thinner than 6 nm exhibit an effective dielectric constant (keff) of 9–11.5. The minimum quantum mechanical corrected effective oxide thickness is ∼1.45 nm and the leakage currents are very low. Rapid thermal annealing in a N2 environment improves the leakage further and up to 750 °C does not affect keff. Higher annealing temperatures reduce keff, but even at 950 °C, it has a value of 6.5. These HfAlO films have the potential to serve as a substitute for SiO2 in small-scale metal-insulator-semiconductor structures.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
61.72.Cc Kinetics of defect formation and annealing
73.61.Ng Insulators
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures

Comparison between atomic-layer-deposited HfO2 films using O3 or H2O oxidant and Hf[N(CH3)2]4 precursor

Moonju Cho, Doo Seok Jeong, Jaehoo Park, Hong Bae Park, Suk Woo Lee, Tae Joo Park, Cheol Seong Hwang, Gi Hoon Jang, and Jaehack Jeong

Appl. Phys. Lett. 85, 5953 (2004); http://dx.doi.org/10.1063/1.1829773 (3 pages) | Cited 42 times

Online Publication Date: 9 December 2004

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The dielectric properties of HfO2 thin films, which were deposited on Si wafers by an atomic layer deposition (ALD) technique at a wafer temperature of 300 °C using a N-containing, tetrakis dimethylamido hafnium precursor (Hf[N(CH3)2]4), were highly improved by adopting O3 as the oxidant during the ALD instead of H2O. The films contained a much smaller carbon impurity concentration and were of more amorphous nature compared to the films grown using H2O as oxidant. Temperature-dependent leakage current analysis showed that the films grown using O3 as oxidant had a higher interfacial potential barrier for tunneling and the leakage current densities of the as-deposited film were three orders of magnitude smaller than that of the films grown using H2O. The dielectric constant of the HfO2 film was 24.4 and the leakage current density was 1.6×10−7 A∕cm2 when the capacitance equivalent thickness was 1.49 nm.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.22.Ch Permittivity (dielectric function)
81.65.Mq Oxidation
61.72.S- Impurities in crystals
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Directional growth by low electric-field-controlled crystallization of bulk amorphous lithium tetraborate

S. J. Kim, J. E. Kim, and Y. S. Yang

Appl. Phys. Lett. 85, 5956 (2004); http://dx.doi.org/10.1063/1.1825071 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2004

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Highly oriented rod-shaped crystals were grown during crystallization of bulk amorphous Li2B4O7 under a low ac electric field of ∼5 V∕mm. The crystal c axis that is the long direction of rods and perpendicular to the flat surface of the sample is parallel to the applied electric-field direction. The oriented crystals, with an alignment within a declined angle of ∼15°, are so long along the c direction compared with those of other directions that the geometrical structure of each rod is quasi-one-dimensional. The measured electromechanical coupling coefficient of kt=0.47 is comparable to that of single-crystal Li2B4O7.
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81.05.Pj Glass-based composites, vitroceramics
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
64.70.K- Solid-solid transitions
77.65.Bn Piezoelectric and electrostrictive constants
61.43.Fs Glasses
81.40.Gh Other heat and thermomechanical treatments

Chemical reaction and metallic cluster formation by annealing-temperature control in ZrO2 gate dielectrics on Si

J. Okabayashi, S. Toyoda, H. Kumigashira, M. Oshima, K. Usuda, M. Niwa, and G. L. Liu

Appl. Phys. Lett. 85, 5959 (2004); http://dx.doi.org/10.1063/1.1835001 (3 pages) | Cited 22 times

Online Publication Date: 9 December 2004

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Thermal stability of the ZrO2∕Zr–silicate∕Si structure and the Zr–silicide formation were investigated by photoemission spectroscopy depending on the annealing temperature in ultrahigh vacuum. By the annealing below 860 °C, the interfacial layer thickness of the Zr–silicate decreased although the ZrO2 top layer was not affected. The annealing at 860 °C caused the interfacial Zr–silicate layer to disappear. By the annealing above 860 °C, the metallic Zr components appeared and the metallic clusters were formed. High-resolution photoemission spectra have revealed that the clusters consist of a ZrSi2 layer. Valence-band spectra depending on the annealing temperature provide us with the information about the crystallization in the ZrO2 layer.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Nr Association, addition, insertion, cluster formation
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
73.20.At Surface states, band structure, electron density of states

Fatigue-free behavior of Bi3.25La0.75Ti3O12 thin films grown on several bottom eletrodes by the polymeric precursor method

A. Z. Simões, A. Ries, F. M. Filho, C. S. Riccardi, J. A. Varela, and E. Longo

Appl. Phys. Lett. 85, 5962 (2004); http://dx.doi.org/10.1063/1.1834999 (3 pages) | Cited 23 times

Online Publication Date: 9 December 2004

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Fatigue-free Bi3.25La0.75Ti3O12 (BLT) thin films were grown on LaNiO3,RuO2, and La0.5Sr0.5CoO3 bottom electrodes in a microwave furnace at 700 °C for 10 min. The remanent polarization (Pr) and the drive voltage (Vc) were in the range of 11–23 μC∕cm2 and 0.86–1.56 V, respectively, and are better than the values found in the literature. The BLT capacitors did not show any significant fatigue up to 1010 read∕write switching cycles.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
73.61.Ng Insulators
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Voltage-induced degradation in self-aligned polycrystalline silicon gate n-type field-effect transistors with HfO2 gate dielectrics

Jaehoo Park, Moonju Cho, Hong Bae Park, Tae Joo Park, Suk Woo Lee, Sug Hun Hong, Doo Seok Jeong, Chihoon Lee, and Cheol Seong Hwang

Appl. Phys. Lett. 85, 5965 (2004); http://dx.doi.org/10.1063/1.1834992 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2004

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The voltage-induced degradation in the threshold voltage of field-effect transistors using atomic layer deposited HfO2-gate dielectrics was studied. Si channel surfaces of some samples were in situ pretreated using O3 flow before HfO2 deposition, which formed a very thin SiO2 interfacial layer. This avoided a shift of the threshold voltage up to a stress time of 1000 s under inversion condition at +3 V gate voltage. The transistors without O3 pretreatment showed a serious change in the threshold voltage by electron trapping. A leakage current measurement under inversion condition showed that the leakage current was not the major factor that controlled the degradation. Instead, the interfacial traps resulting from the Si suboxide formation for the cases without O3 pretreatment appeared to constitute the major reason for the degradation.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
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