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20 Dec 2004

Volume 85, Issue 25, pp. 6083-6293

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 6281 (2004); http://dx.doi.org/10.1063/1.1834720 (3 pages)

M. P. Rao, M. F. Aimi, and N. C. MacDonald
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Electron-irradiation enhanced photoluminescence from GaInNAs∕GaAs quantum wells subject to thermal annealing

E.-M. Pavelescu, A. Gheorghiu, M. Dumitrescu, A. Tukiainen, T. Jouhti, T. Hakkarainen, R. Kudrawiec, J. Andrzejewski, J. Misiewicz, N. Tkachenko, V. D. S. Dhaka, H. Lemmetyinen, and M. Pessa

Appl. Phys. Lett. 85, 6158 (2004); http://dx.doi.org/10.1063/1.1834997 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2004

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Electron irradiation of a 1.3‐μm‐GaInNAs∕GaAs multi-quantum-well heterostructure, grown by molecular beam epitaxy and subsequently rapid-thermal annealed, is found to induce much stronger photoluminescence than what is observed for an identical as-grown sample upon annealing. Annealing of the irradiated sample also causes a small additional spectral blueshift and reduces alloy potential energy fluctuations at the conduction band minimum. These irradiation-related phenomena are accompanied by small but discernable changes in x-ray diffraction features upon annealing, which indicate compositional and∕or structural changes in the quantum wells.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Determination of elastic properties of a film-substrate system by using the neural networks

Baiqiang Xu, Zhonghua Shen, Xiaowu Ni, Jijun Wang, Jianfei Guan, and Jian Lu

Appl. Phys. Lett. 85, 6161 (2004); http://dx.doi.org/10.1063/1.1841472 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2004

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An inverse method based on artificial neural network (ANN) is presented to determine the elastic properties of films from laser-genrated surface waves. The surface displacement responses are used as the inputs for the ANN model; the outputs of the ANN are the Young’s modulus, density, Poisson’s ratio, and thickness of the film. The finite element method is used to calculate the surface displacement responses in a film-substrate system. Levenberg Marquardt algorithm is used as numerical optimization to speed up the training process for the ANN model. In this method, the materials parameters are not recovered from the dispersion curves but rather directly from the transient surface displacement. We have also found that this procedure is very efficient for determining the materials parameters of layered systems.
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81.05.Bx Metals, semimetals, and alloys
07.05.Mh Neural networks, fuzzy logic, artificial intelligence
68.60.Bs Mechanical and acoustical properties
02.60.Pn Numerical optimization
43.60.Np Acoustic signal processing techniques for neural nets and learning systems
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
02.70.Dh Finite-element and Galerkin methods
02.30.Zz Inverse problems

In situ measurements of the critical thickness for strain relaxation in AlGaN∕GaN heterostructures

S. R. Lee, D. D. Koleske, K. C. Cross, J. A. Floro, K. E. Waldrip, A. T. Wise, and S. Mahajan

Appl. Phys. Lett. 85, 6164 (2004); http://dx.doi.org/10.1063/1.1840111 (3 pages) | Cited 33 times

Online Publication Date: 15 December 2004

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Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1−xN∕GaN heterostructures with 0.14⩽x⩽1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocation glide suggests that the onset of strain relaxation occurs by surface fracture for all compositions. Misfit-dislocations follow initial fracture, with slip-system selection occurring under the influence of composition-dependent changes in surface morphology.
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81.05.Ea III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.37.Ps Atomic force microscopy (AFM)
68.60.Bs Mechanical and acoustical properties
62.20.M- Structural failure of materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Optical characteristics of arsenic-doped ZnO nanowires

Woong Lee, Min-Chang Jeong, and Jae-Min Myoung

Appl. Phys. Lett. 85, 6167 (2004); http://dx.doi.org/10.1063/1.1840124 (3 pages) | Cited 34 times

Online Publication Date: 15 December 2004

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The effect of arsenic doping on optical characteristics of ZnO nanowires was investigated by photoluminescence spectroscopy carried out at 13–290 K. In as-grown nanowires, emission due to acceptor-bound excitons predominated at low temperatures; as temperatures increased, emission due to recombination of free excitons prevailed. Arsenic-doped nanowires exhibited emission due to acceptor-bound excitons with no free exciton emission in the whole temperature range, indicating the formation of the acceptor level within the ZnO nanowire by arsenic doping.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
73.22.Lp Collective excitations

Microstructural change near the martensitic transformation in a ferromagnetic shape memory alloy Ni51Fe22Ga27 studied by electron holography

Y. Murakami, D. Shindo, K. Oikawa, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 85, 6170 (2004); http://dx.doi.org/10.1063/1.1841471 (3 pages) | Cited 16 times

Online Publication Date: 15 December 2004

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Temperature dependence of the magnetic microstructure in a ferromagnetic shape memory alloy Ni51Fe22Ga27 has been studied by electron holography, by which the distribution of magnetic flux is clearly imaged. Although the magnetic flux is quite even in the parent phase near room temperature, it undergoes considerable modulation when the temperature approaches Ms (martensitic transformation start temperature). The magnetization distribution in the martensite appears to be inherited from that in the parent phase. The observations shed further light on the precursor phenomenon of martensitic transformations.
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81.05.Bx Metals, semimetals, and alloys
75.50.Bb Fe and its alloys
81.30.Kf Martensitic transformations
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
64.70.K- Solid-solid transitions

A simple approach to determine five thermomechanical properties of thin ductile films on an elastic substrate

W. M. Huang, Y. Y. Hu, and L. An

Appl. Phys. Lett. 85, 6173 (2004); http://dx.doi.org/10.1063/1.1840125 (3 pages) | Cited 8 times

Online Publication Date: 15 December 2004

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We present a simple approach to determine five thermomechanical properties of linear strain hardening thin films, namely, the Young’s modulus, coefficient of thermal expansion, yield start stress, strain hardening, and Poisson’s ratio. The approach is based on the conventional curvature test on bilayer structures upon temperature variation. Three tests, which result in three curvature versus temperature curves, are enough to determine the values of these properties. Both the closed-form solutions and estimations are obtained.
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65.40.De Thermal expansion; thermomechanical effects
68.60.Bs Mechanical and acoustical properties
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
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Band tail hopping conduction mechanism in highly conductive amorphous carbon nitride thin films

G. Lazar, K. Zellama, M. Clin, and C. Godet

Appl. Phys. Lett. 85, 6176 (2004); http://dx.doi.org/10.1063/1.1839649 (3 pages) | Cited 10 times

Online Publication Date: 15 December 2004

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Nitrogenated amorphous carbon (a-C:N) films have been synthesized by radio frequency (rf) magnetron sputtering at various substrate temperatures and rf discharge powers. The temperature dependence of the electrical conductivity has been measured in order to identify the dominant conduction mechanism. The conductivity was found to increase over ten orders of magnitude with increasing growth temperature and discharge power. In the ohmic regime, the conductivity of the investigated a-C:N films is likely dominated by hopping conduction, in good agreement with a model for hopping in localized bandtail states, rather than by extended states band conduction.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth
73.20.At Surface states, band structure, electron density of states
71.55.Jv Disordered structures; amorphous and glassy solids

Atomic strings of group IV, III–V, and II–VI elements

S. Tongay, E. Durgun, and S. Ciraci

Appl. Phys. Lett. 85, 6179 (2004); http://dx.doi.org/10.1063/1.1839647 (3 pages) | Cited 12 times

Online Publication Date: 15 December 2004

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A systematic first-principles study of atomic strings made by group IV, III–V, and II–VI elements has revealed interesting mechanical, electronic, and transport properties. The double bond structure underlies their unusual properties. We found that linear chain of C, Si, Ge, SiGe, GaAs, InSb, and CdTe are stable and good conductor, although their parent diamond (zincblende) crystals are covalent (polar) semiconductors but, compounds SiC, BN, AlP, and ZnSe are semiconductors. First row elements do not form zigzag structures.
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71.20.Mq Elemental semiconductors
71.20.Nr Semiconductor compounds
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.15.Nc Total energy and cohesive energy calculations

Effects of n-type 4H-SiC epitaxial wafer quality on reliability of thermal oxides

Junji Senzaki, Kazutoshi Kojima, and Kenji Fukuda

Appl. Phys. Lett. 85, 6182 (2004); http://dx.doi.org/10.1063/1.1839279 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2004

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The reliability of thermal oxides was investigated on n-type 4H-SiC(0001) epitaxial wafers with different metal impurity concentrations and surface roughness. Time-zero dielectric breakdown measurements showed that almost all of the thermal oxides ruptured at a field-to-breakdown (EBD) of 10 MV∕cm, and that the maximum EBD was 11 MV∕cm, despite the influence of the epitaxial wafer. On the other hand, time-dependent dielectric breakdown measurements indicated that the charge-to-breakdown (QBD) of the thermal oxides was influenced by the epitaxial wafer. This suggests that two types of oxide breakdown regimes exist under a high-stress field: one resulting from wafer influences, and the other intrinsic.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.22.Jp Dielectric breakdown and space-charge effects

The influence of the time-of-flight mobility on the efficiency of solid-state dye-sensitized TiO2 solar cells

C. Jäger, D. Haarer, B. Peng, and M. Thelakkat

Appl. Phys. Lett. 85, 6185 (2004); http://dx.doi.org/10.1063/1.1834717 (3 pages) | Cited 7 times

Online Publication Date: 15 December 2004

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The dependence of zero field charge carrier mobilities obtained from time-of-flight (TOF) measurements for a series of doped triphenyldiamines on trap depth and concentration were determined. The influence of these mobilities on the solar cell characteristics have been studied by measuring I–V characteristics and IPCE values using the same doped hole conductors in solid-state dye-sensitized TiO2 solar cells. The traps exhibit only a weak influence on the solar cell characteristics, because the traps which are responsible for low charge transport mobilities in the TOF experiment are filled under steady state illumination conditions. In consequence the effective mobility is raised almost to that of the pristine hole conductor, thus allowing the use of doped hole conductor systems in solar cells without any adverse effects.
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84.60.Jt Photoelectric conversion
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.20.Jq Electro-optical effects
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals

Drive current enhancement in p-type metal–oxide–semiconductor field-effect transistors under shear uniaxial stress

L. Shifren, X. Wang, P. Matagne, B. Obradovic, C. Auth, S. Cea, T. Ghani, J. He, T. Hoffman, R. Kotlyar, Z. Ma, K. Mistry, R. Nagisetty, R. Shaheed, M. Stettler, et al.

Appl. Phys. Lett. 85, 6188 (2004); http://dx.doi.org/10.1063/1.1841452 (3 pages) | Cited 10 times

Online Publication Date: 15 December 2004

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Recent attention has been given to metal–oxide–semiconductor field-effect transistor (MOSFET) device designs that utilize stress to achieve performance gain in both n-type MOSFETs (NMOS) and p-type MOSFETs (PMOS). The physics behind NMOS gain is better understood than that of PMOS gain, which has received less attention. In this letter, we describe the warping phenomena which is responsible for the gain seen in [110] uniaxially stressed PMOS devices on [100] orientated wafers. We also demonstrate that shear uniaxial stress in PMOS is better suited to MOSFET applications than biaxial stress as it is able to maintain gain at high vertical and lateral fields.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Low-resistivity and transparent indium-oxide-doped ZnO ohmic contact to p-type GaN

Jae-Hong Lim, Dae-Kue Hwang, Hyun-Sik Kim, Jin-Yong Oh, Jin-Ho Yang, R. Navamathavan, and Seong-Ju Park

Appl. Phys. Lett. 85, 6191 (2004); http://dx.doi.org/10.1063/1.1826231 (3 pages) | Cited 25 times

Online Publication Date: 15 December 2004

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We report on the indium-oxide-doped ZnO (IZO) transparent ohmic contact to the p‐GaN. The IZO transparent ohmic contact layer was deposited on p‐GaN by e-beam evaporation. The transmittance of an IZO film with a thickness of 250 nm was 84%–92% for the light in the wavelength range of 400 and 600 nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4×10−4 Ω cm2 on p‐GaN when annealed at 600 °C for 5 min under a nitrogen ambient. Auger electron spectroscopy and x-ray photoemission spectroscopy analyses of the IZO and p‐GaN interface indicated that Ga atoms had out-diffused and an InN phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. The light output power of a light-emitting diode (LED) with an IZO ohmic contact layer was increased by 34% at 83 mW of electrical input power compared to that of a LED with a Ni∕Au ohmic contact layer.
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85.60.Jb Light-emitting devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
73.61.Ey III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.40.Cg Contact resistance, contact potential
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
79.60.Jv Interfaces; heterostructures; nanostructures

Current-induced electroresistive effect in mixed-phase La0.67Ca0.33MnO3 thin films

A. Masuno, T. Terashima, Y. Shimakawa, and M. Takano

Appl. Phys. Lett. 85, 6194 (2004); http://dx.doi.org/10.1063/1.1840114 (3 pages) | Cited 11 times

Online Publication Date: 15 December 2004

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We examined electroresistive effects of epitaxial thin films of La0.67Ca0.33MnO3 deposited on LaAlO3(100) substrates. To be noted here is that these oxides are considerably lattice-mismatched. Measurements of the resistivity, magnetoresistance effect, and current-voltage characteristics of these films revealed that they were inhomogeneous and composed of domains of the highly strained charge-ordered insulator (COI) and the less strained ferromagnetic metal (FMM). By using a microfabricating process, we obtained high current densities and observed a current-induced irreversible behavior at low temperature. The irreversibility became larger with increasing current density. Below the insulator-metal (ferromagnetic) transition temperature, spin-polarized electrons in the FMM domains were injected into the neighboring COI domains. There they forced antiferromagnetically ordered spins to align parallel, leading to a current-induced first-order transition from the COI to the FMM.
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75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials
71.45.-d Collective effects
75.70.Ak Magnetic properties of monolayers and thin films
71.30.+h Metal-insulator transitions and other electronic transitions
72.25.-b Spin polarized transport
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Superconducting properties of MgB2 films electroplated to stainless steel substrates

Hideki Abe, Kenji Nishida, Motoharu Imai, Hideaki Kitazawa, and Kenji Yoshii

Appl. Phys. Lett. 85, 6197 (2004); http://dx.doi.org/10.1063/1.1839644 (3 pages) | Cited 11 times

Online Publication Date: 15 December 2004

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Superconducting MgB2 films have been fabricated on stainless steel substrates by means of electroplating in a molten electrolyte composed of MgCl2, MgB2O4, NaCl, and KCl containing a fractional amount of CuCl2. Microscopic observation has revealed that the electroplated films and substrates are combined with each other through Cu-rich layers at the interfaces. Transport measurements have shown that the electroplated MgB2 films possess an upper critical field, Hc2(0), of 28 T, an irreversibility field, Hirr(0), of 13 T, and a critical current density, Jc(5 K,0 T), of 25 000 A∕cm2, which suggests that the electroplating in molten salts is a promising alternative to the powder-in-tube method for the fabrication of MgB2 tapes.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.Na Mesoscopic and nanoscale systems
74.25.F- Transport properties
81.15.Pq Electrodeposition, electroplating
74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
68.55.-a Thin film structure and morphology

The origin of signal-to-noise ratio improvements in laminated recording media

D. T. Margulies, M. E. Schabes, N. Supper, H. Do, A. Berger, A. Moser, P. M. Rice, P. Arnett, M. Madison, B. Lengsfield, H. Rosen, and Eric E. Fullerton

Appl. Phys. Lett. 85, 6200 (2004); http://dx.doi.org/10.1063/1.1831571 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2004

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We report an experimental and theoretical study of laminated recording media made of two CoPtCrB magnetic layers separated by a Ru spacer layer. We find that a 4 math Ru spacer layer is sufficient to decorrelate the noise of the magnetic transitions in the two layers, thus producing improved media signal-to-noise ratios. This result is surprising given that the layers remain structurally correlated due to their epitaxial growth, and therefore the noise in the layers would be expected to be correlated as well. Experiments suggest that the reduced transition noise is produced by a slight shift between the transition locations in the layers. This shift is on the order of the grain size and allows the transitions to sample a different microstructure causing the noise associated with the transitions to be uncorrelated.
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75.50.Ss Magnetic recording materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials

Giant Zeeman effect of excitons in a hybrid nanostructure of diluted magnetic semiconductor quantum well sandwiched in Co wires

M. Sakuma, K. Hyomi, I. Souma, A. Murayama, and Y. Oka

Appl. Phys. Lett. 85, 6203 (2004); http://dx.doi.org/10.1063/1.1841480 (3 pages) | Cited 6 times

Online Publication Date: 15 December 2004

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Giant Zeeman effects of excitons in a hybrid nanostructure of diluted magnetic semiconductor (DMS) quantum well (QW) with ferromagnetic Co have been demonstrated, where the DMS-QW wire with the width of 200 nm is sandwiched in the Co wires and magnetic fields nearly perpendicular to the well plane can efficiently be applied from the Co wires to all of the DMS QW. The spectral shape of excitonic photoluminescence and the field dependence show clearly that the microscopic perpendicular fields generated from the Co wires induce the giant Zeeman shifts of excitons in the DMS QW.
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75.50.Pp Magnetic semiconductors
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
78.67.De Quantum wells
73.21.Fg Quantum wells
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Focused-ion-beam-induced deposition of superconducting nanowires

E. S. Sadki, S. Ooi, and K. Hirata

Appl. Phys. Lett. 85, 6206 (2004); http://dx.doi.org/10.1063/1.1842367 (3 pages) | Cited 34 times

Online Publication Date: 15 December 2004

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Superconducting nanowires, with a critical temperature of 5.2 K, have been synthesized using an ion-beam-induced deposition, with a gallium focused ion beam and tungsten carboxyl, W(CO)6, as precursor. The films are amorphous, with atomic concentrations of about 40%, 40%, and 20% for W, C, and Ga, respectively, 0 K values of the upper critical field and coherence length of 9.5 T and 5.9 nm, respectively, are deduced from the resistivity data at different applied magnetic fields. The critical current density is Jc=1.5×105 A∕cm2 at 3 K. This technique can be used as a template-free fabrication method for superconducting devices.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Jj Ion and electron beam-assisted deposition; ion plating
74.25.Sv Critical currents
74.25.Op Mixed states, critical fields, and surface sheaths
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.46.-w Structure of nanoscale materials
84.71.Mn Superconducting wires, fibers, and tapes

Charge and spin distribution in ferromagnetic Mn-doped InGaAs∕GaAs multilayers

G. M. Sipahi, S. C. P. Rodrigues, L. M. R. Scolfaro, and I. C. da Cunha Lima

Appl. Phys. Lett. 85, 6209 (2004); http://dx.doi.org/10.1063/1.1840121 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2004

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The search for materials tailored for spintronic devices led recently to the study of III–V diluted magnetic semiconductors (DMS). These materials are found to be closer to room-temperature ferromagnetism than their II–VI counterparts. Following this pathway, heterostructures based on III–V DMS were found to have higher Curie temperature. In this work, we propose geometrical arrangements that maximize spin separation combining strained and DMS III–V layers.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Room temperature ferromagnetism in anatase Ti0.95Cr0.05O2 thin films: Clusters or not?

Nguyen Hoa Hong, Antoine Ruyter, W. Prellier, and Joe Sakai

Appl. Phys. Lett. 85, 6212 (2004); http://dx.doi.org/10.1063/1.1841457 (3 pages) | Cited 14 times

Online Publication Date: 15 December 2004

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Laser ablated Cr-doped TiO2 thin films grown on LaAlO3 substrates are single phased anatase and room temperature ferromagnetic. The magnetic moment of Cr-doped TiO2 films is rather large, and it is consistent with the theoretical predictions. Magnetic force microscopy measurements certainly suggested that the strong ferromagnetism at high temperature in Cr-doped TiO2 films is intrinsic, and it must originate from the diluted magnetic matrix but not from any form of clusters.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Rt Magnetic force microscopy (MFM)

Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)

T. Slobodskyy, C. Rüster, R. Fiederling, D. Keller, C. Gould, W. Ossau, G. Schmidt, and L. W. Molenkamp

Appl. Phys. Lett. 85, 6215 (2004); http://dx.doi.org/10.1063/1.1841456 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2004

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We have investigated the growth by molecular-beam epitaxy of the II–VI diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates. The growth start has been optimized by using low-temperature epitaxy. Surface properties were assessed by Nomarski and scanning electron microscopy. Optical properties of (Zn,Mn)Se have been studied by photoluminescence and a giant Zeeman splitting of up to 30 meV has been observed. Our observations indicate a high crystalline quality of the epitaxial films.
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81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
75.70.Ak Magnetic properties of monolayers and thin films

Spin injection, diffusion, and detection in lateral spin-valves

Y. Ji, A. Hoffmann, J. S. Jiang, and S. D. Bader

Appl. Phys. Lett. 85, 6218 (2004); http://dx.doi.org/10.1063/1.1841455 (3 pages) | Cited 61 times

Online Publication Date: 15 December 2004

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We demonstrate the injection of spin-polarized electrons into paramagnetic Au nanowires by driving an electric current from a ferromagnetic permalloy (Py) electrode. The nonequilibrium spin accumulation in Au results in a difference between the chemical potentials for spin-up and spin-down electrons that is detected as a field-dependent voltage signal using a second Py electrode. The magnitude of the voltage contrast (>10%) and its coincidence with the magnetic switching of the Py electrodes attest to the spin-sensitive origin of the signals. By increasing the separation of the Py injector and detector, we observe an exponential decay of the spin signals. The measurements yield a spin-diffusion length of 63±15 nm and an injected spin polarization of 3% in Au at 10 K.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.75.-c Magnetic properties of nanostructures
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
75.20.En Metals and alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
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Orientation dependence of transverse piezoelectric properties of 0.70Pb(Mg1∕3Nb2∕3)O3-0.30PbTiO3 single crystals

Jue Peng, Hao-su Luo, Di Lin, Hai-qing Xu, Tian-hou He, and Wei-qing Jin

Appl. Phys. Lett. 85, 6221 (2004); http://dx.doi.org/10.1063/1.1839288 (3 pages) | Cited 45 times

Online Publication Date: 15 December 2004

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In this letter, we present our investigation of transverse piezoelectric performance in 0.70Pb(Mg1∕3Nb2∕3)O3-0.30PbTiO3 (0.70PMN-0.30PT) single crystals with different cuts using a resonance technique. We give the report on the finding of ultrahigh k31 and d31 values of 95.4% and −2517 pC∕N, respectively. However, this unusual transverse piezoelectric property is only obtained in crystals with the polarization (thickness) and vibration (length) directions along the 〈110〉 and 〈001〉 directions, respectively. The 0.70PMN-0.30PT crystal with this cut shows significantly great potential for applications in high-performance transverse-mode piezoelectric devices, such as medical array ultrasonic transducers and actuators.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ej Polarization and depolarization
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.80.Dj Domain structure; hysteresis
62.20.D- Elasticity
77.65.Ly Strain-induced piezoelectric fields

Dielectric response of the charge-ordered two-dimensional nickelate La1.5Sr0.5NiO4

J. Rivas, B. Rivas-Murias, A. Fondado, J. Mira, and M. A. Señarís-Rodríguez

Appl. Phys. Lett. 85, 6224 (2004); http://dx.doi.org/10.1063/1.1834998 (3 pages) | Cited 28 times

Online Publication Date: 15 December 2004

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We report the dielectric response of La1.5Sr0.5NiO4, a system that experiences charge ordering above room temperature (TCO=480 K) and a rearrangement of its charge-order pattern in the temperature region 160–200 K. A careful analysis of the role of the electrical contacts used, sample thickness, and grain size on the experimental data allows us to determine that this material exhibits a high intrinsic dielectric constant. In addition, the temperature dependence of the dielectric constant, that shows a maximum in the region of the rearrangement of the charge-order pattern, points to a link between the two phenomena.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)

Effect of the interfacial SiO2 layer thickness on the dominant carrier type in leakage currents through HfAlOx∕SiO2 gate dielectric films

Wataru Mizubayashi, Naoki Yasuda, Hirokazu Hisamatsu, Kunihiko Iwamoto, Koji Tominaga, Katsuhiko Yamamoto, Hiroyuki Ota, Tsuyoshi Horikawa, Toshihide Nabatame, and Akira Toriumi

Appl. Phys. Lett. 85, 6227 (2004); http://dx.doi.org/10.1063/1.1840120 (3 pages) | Cited 4 times

Online Publication Date: 15 December 2004

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The carrier conduction mechanism of leakage current in n+-gate p-channel metal-insulator-semiconductor field-effect-transistors with HfAlOx (Hf:60 at %,Al:40 at %)∕SiO2 dielectric layers has been investigated using the carrier separation method. Since the gate current depends on the substrate voltage and both electron and hole currents are independent of temperature in the range of 25–150 °C, the conduction mechanism for both currents is a tunneling process. It is shown that the dominant carrier in the leakage current depends on the structure of the high-k stack. When the interfacial SiO2 layer (IL) thickness increases at a fixed high-k thickness (Thigh‐k), the dominant carrier in the leakage current changes from hole to electron at ∼2.0–2.3‐nm-thick IL, because of asymmetric barrier height for electron and hole in the SiO2∕Si system. In contrast, for the case of a fixed IL thickness of 1.3 nm, the hole current dominates in the leakage current, regardless of Thigh‐k, due to symmetric barrier height of the conduction and valence bands in the HfAlOx∕Si system.
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85.30.Tv Field effect devices

Interfacial oxide formation from intrinsic oxygen in W–HfO2 gated silicon field-effect transistors

E. J. Preisler, S. Guha, M. Copel, N. A. Bojarczuk, M. C. Reuter, and E. Gusev

Appl. Phys. Lett. 85, 6230 (2004); http://dx.doi.org/10.1063/1.1834995 (3 pages) | Cited 20 times

Online Publication Date: 15 December 2004

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We report the effects of ultrahigh vacuum and nitrogen annealing on self-aligned W-gated HfO2 n-field-effect transistors. While rapid thermal annealing in a nitrogen ambient significantly improved the channel mobility, there is a corresponding increase in the gate dielectric thickness of up to 20 math. Here we show that this increase is due to the formation of interfacial oxides between the HfO2 and the silicon, caused by the diffusion of oxygen from the W gates. The results point to the importance of oxygen solubility in metals, which may be significant in many candidate gate electrodes.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
72.20.Fr Low-field transport and mobility; piezoresistance
68.35.Fx Diffusion; interface formation
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