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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Scanning electron microscopy of dopant distribution in semiconductors

P. G. Merli, V. Morandi, G. Savini, M. Ferroni, and G. Sberveglieri

Appl. Phys. Lett. 86, 101916 (2005); http://dx.doi.org/10.1063/1.1883708 (3 pages) | Cited 4 times

Online Publication Date: 4 March 2005

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We show that, in scanning electron microscopy, it is possible to use the secondary electrons produced by the backscattered electrons to obtain chemical information on the dopant distribution in Sb-implanted silicon. Theoretical investigations and experimental data concur to point out that the resolution of the method is defined by the probe size—values of 1 nm or even lower are possible in the present instruments—while the contrast depends on the electron range and on the boundary conditions. A proper choice of beam energy and boundaries of the doped layer may allow a sensitivity below 1%, suitable to characterize the high-dose near-surface region of the ultrashallow junctions in cross-sectioned bulk specimens.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.72.S- Impurities in crystals
79.20.Hx Electron impact: secondary emission
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Monte Carlo simulation of the effects of vacuum-ultraviolet radiation on dielectric materials

G. S. Upadhyaya, J. L. Shohet, and J. L. Lauer

Appl. Phys. Lett. 86, 102101 (2005); http://dx.doi.org/10.1063/1.1879100 (3 pages) | Cited 10 times

Online Publication Date: 1 March 2005

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Radiation-induced damage during plasma processing of semiconductor materials can adversely affect device reliability. However, it has been shown that vacuum ultraviolet (VUV) radiation (8–20 eV) can beneficially deplete previously deposited charge on the surface of dielectrics by temporarily increasing their conductivity. Incident VUV photons can cause photoemission and form electron-hole pairs in the dielectric thus producing the desired increased conductivity. To verify this, statistical information obtained from a Monte Carlo simulation is used to model VUV exposure of dielectrics. The simulation calculates the surface potential on the dielectric produced by electron photoemission, which compares favorably with experimental surface-potential measurements made using a Kelvin probe.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
72.40.+w Photoconduction and photovoltaic effects

High transparency of Ag/Zn–Ni solid–solution ohmic contacts for GaN-based ultraviolet light-emitting diodes

Dong-Seok Leem, June-O Song, Woong-Ki Hong, Jeong-Tae Maeng, J. S. Kwak, Y. Park, and Tae-Yeon Seong

Appl. Phys. Lett. 86, 102102 (2005); http://dx.doi.org/10.1063/1.1879084 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2005

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Ag/Zn–Ni solid–solution scheme has been investigated to produce transparent ohmic contacts for ultraviolet (UV) light-emitting diodes (LEDs). The Ag/Zn–Ni solid–solution contacts annealed at 430 °C for 1 min in air show high transmittance of 67%–69% at 340 nm, which is much better than that (53%) of the conventional Ni/Au contact. The annealed contacts give specific contact resistance of 8.2×10−5 and 4.8×10−5 Ω cm2. Further, near UV LEDs (300×300 μm2) made with the annealed contact layers produce a forward-bias voltage of 3.32–3.46 V at 20 mA. Possible explanations are given to describe the annealing-induced improvement of the ohmic behaviors of the Ag/Zn–Ni solid–solution contacts.
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85.60.Jb Light-emitting devices
78.66.Bz Metals and metallic alloys
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
78.40.Kc Metals, semimetals, and alloys

Time-resolved photocurrent spectroscopy of the evolution of the electric field in optically excited superlattices and the prospects for Bloch gain

Alvydas Lisauskas, Claudia Blöser, Robert Sachs, Hartmut G. Roskos, Aušrius Juozapavičius, Gintaras Valušis, and Klaus Köhler

Appl. Phys. Lett. 86, 102103 (2005); http://dx.doi.org/10.1063/1.1867552 (3 pages) | Cited 5 times

Online Publication Date: 2 March 2005

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We report on photocurrent spectroscopy on undoped GaAs/AlGaAs semiconductor superlattices subjected to femtosecond optical excitation. The evolution of the carrier-drift-induced inhomogeneity of the electric field is studied by tracing the shifting and broadening of Wannier–Stark transitions as a function of delay time and bias field. Based on experimental data and results of numerical simulations, we find that the superlattice rapidly splits into two moving field regions, one with strong field gradient and low electron density, the other with partially screened field at low gradient and high electron density. Concerning future Bloch-gain measurements, we find that gain is expected in spite of the inhomogeneous field if the electron-rich region is not heavily screened. The time window during which Bloch gain exists is determined by the sweep out of the electrons (10–30 ps).
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68.65.Cd Superlattices
73.63.-b Electronic transport in nanoscale materials and structures
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance
78.47.-p Spectroscopy of solid state dynamics

Effect of inductively coupled plasma damage on performance of GaN–InGaN multiquantum-well light-emitting diodes

Hyuck Soo Yang, Sang Youn Han, K. H. Baik, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 86, 102104 (2005); http://dx.doi.org/10.1063/1.1882749 (3 pages) | Cited 9 times

Online Publication Date: 3 March 2005

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InGaN multiquantum-well light-emitting diodes (LEDs) in the form of unpackaged die with emission wavelengths from 420 to 505 nm were exposed to either Ar or H2 inductively coupled plasmas as a function of both rf chuck power (controlling incident ion energy) and source power (controlling ion flux). The forward turn-on voltage is increased by both types of plasma exposure and is a function of both the incident ion energy and flux. The reverse bias current in the LEDs is much larger in the case of H2 plasma exposure, indicating that preferential loss of nitrogen leads to increased surface leakage. The current transport in the LEDs is dominated by generation-recombination (ideality factor ∼ 2) both before and after the plasma exposures.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Pressure-dependent thermopower of individual Bi nanowires

D. Gitsu, L. Konopko, A. Nikolaeva, and T. E. Huber

Appl. Phys. Lett. 86, 102105 (2005); http://dx.doi.org/10.1063/1.1873045 (3 pages) | Cited 10 times

Online Publication Date: 3 March 2005

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The 240–620 nm diameter nanowires were freely suspended and thermopower measurements were carried out over the temperature range 4–300 K and for stresses as high as 1 GPa. The peaks of up to 80 μV/K that are observed around 40 K are interpreted in terms of a model of diffusion thermopower under strong electron and hole-boundary scattering. The partial Seebeck coefficients are calculated from the stress-dependent carrier Fermi energies obtained from magnetoresistance measurements. The prospect of Bi nanowire arrays achieving high thermoelectric figure of merit is discussed.
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73.63.Bd Nanocrystalline materials
73.50.Lw Thermoelectric effects
75.47.Np Metals and alloys
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.40.Rs Electrical and magnetic properties related to treatment conditions

High mobility two-dimensional electron gas in AlGaN/GaN heterostructures grown on bulk GaN by plasma assisted molecular beam epitaxy

C. Skierbiszewski, K. Dybko, W. Knap, M. Siekacz, W. Krupczyński, G. Nowak, M. Boćkowski, J. Łusakowski, Z. R. Wasilewski, D. Maude, T. Suski, and S. Porowski

Appl. Phys. Lett. 86, 102106 (2005); http://dx.doi.org/10.1063/1.1873056 (3 pages) | Cited 19 times

Online Publication Date: 3 March 2005

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The results on growth and magnetotransport characterization of AlGaN/GaN heterostructures obtained by plasma assisted molecular beam epitaxy on dislocation-free (below 100 cm−2) GaN high pressure synthesized bulk substrates are presented. The record mobilities of the two dimensional electron gas (2DEG) exceeding 100 000 cm2/V s at liquid helium temperature and 2 500 cm2/V s at room temperature are reported. An analysis of the high field conductivity tensor components allowed us to discuss the main electron scattering mechanisms and to confirm unambiguously the 2DEG room temperature mobility values.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Fq High-field and nonlinear effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.63.-b Electronic transport in nanoscale materials and structures

Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As/GaAs heterostructures

X. Y. Dong, C. Adelmann, J. Q. Xie, C. J. Palmstrøm, X. Lou, J. Strand, P. A. Crowell, J.-P. Barnes, and A. K. Petford-Long

Appl. Phys. Lett. 86, 102107 (2005); http://dx.doi.org/10.1063/1.1881789 (3 pages) | Cited 66 times

Online Publication Date: 4 March 2005

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Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-n Al0.1Ga0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.
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85.60.Jb Light-emitting devices
75.70.Ak Magnetic properties of monolayers and thin films
72.25.Mk Spin transport through interfaces
72.25.Dc Spin polarized transport in semiconductors
72.25.Ba Spin polarized transport in metals
73.40.Ns Metal-nonmetal contacts
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.60.Fi Electroluminescence

Activation of shallow boron acceptor in C/B coimplanted silicon carbide: A theoretical study

A. Gali, T. Hornos, P. Deák, N. T. Son, E. Janzén, and W. J. Choyke

Appl. Phys. Lett. 86, 102108 (2005); http://dx.doi.org/10.1063/1.1883745 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2005

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Ab initio supercell calculations have been carried out to investigate the complexes of boron acceptors with carbon self-interstitials in cubic silicon carbide. Based on the calculated binding energies, the complex formation of carbon interstitials with shallow boron acceptor and boron interstitial is energetically favored in silicon carbide. These bistable boron defects possess deep, negative-U occupation levels in the band gap. The theoretical results can explain the observed activation rates in carbon-boron coimplantation experiments.
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61.72.up Other materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.72.J- Point defects and defect clusters
71.20.Nr Semiconductor compounds
71.15.Nc Total energy and cohesive energy calculations
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Transport and magnetic Jc of MgB2 strands and small helical coils

M. D. Sumption, M. Bhatia, M. Rindfleisch, M. Tomsic, and E. W. Collings

Appl. Phys. Lett. 86, 102501 (2005); http://dx.doi.org/10.1063/1.1875753 (3 pages) | Cited 11 times

Online Publication Date: 1 March 2005

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The critical current densities of MgB2 monofilamentary strands with and without SiC additions were measured at 4.2 K. Additionally, magnetic Jc at B = 1 T was measured from 4.2 to 40 K. Various heat treatment times and temperatures were investigated for both short samples and small helical coils. SiC additions were seen to improve high field transport Jc at 4.2 K, but improvements were not evident at 1 T at any temperature. Transport results were relatively insensitive to heat treatment times and temperatures for both short samples and coils in the 700–900 °C range.
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84.71.Ba Superconducting magnets; magnetic levitation devices
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.40.Gh Other heat and thermomechanical treatments

Soft x-ray resonant Kerr rotation measurement and simulation of element-resolved and interface-sensitive magnetization reversals in a NiFe/FeMn/Co trilayer structure

Sang-Koog Kim, Ki-Suk Lee, J. B. Kortright, and Sung-Chul Shin

Appl. Phys. Lett. 86, 102502 (2005); http://dx.doi.org/10.1063/1.1873047 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2005

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We report experimental observations of element- and buried interface-resolved magnetization reversals in an oppositely exchange-biased NiFe/FeMn/Co trilayer structure by soft x-ray resonant Kerr rotation measurements. Not only Co-, Ni-, Fe-specific exchange-biased loops but also interfacial uncompensated (UC) Fe reversal loops coupled to the individual Co and NiFe layers are separately observed. From the experimental results interpreted with the help of the model simulations of soft x-ray resonant Kerr rotation, the effective thicknesses of interfacial UC regions at the buried interfaces of both FeMn/Co and NiFe/FeMn are found to be tUC = 13±2 Å and 6±4 Å, respectively. The depth sensitivity as well as element specificity of the x-ray resonant Kerr effect offer an elegant way into the investigations of element- and depth-resolved magnetization reversals of ferromagnetic ultrathin regions at buried interfaces in multicomponent multilayer films.
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75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.30.Et Exchange and superexchange interactions
78.20.Ls Magneto-optical effects
68.55.-a Thin film structure and morphology

Fabrication and uniaxial magnetic anisotropy of Co nanowires on a Pd(110) surface

L. Yan, M. Przybylski, Yafeng Lu, W. H. Wang, J. Barthel, and J. Kirschner

Appl. Phys. Lett. 86, 102503 (2005); http://dx.doi.org/10.1063/1.1870127 (3 pages) | Cited 13 times

Online Publication Date: 3 March 2005

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We have fabricated Co atomic chains and nanowires on a Pd(110) surface oriented along the [1-10] direction. This is possible due to high diffusion anisotropy of the Co adatom on the Pd(110) surface. The Co nanowires on Pd(110) exhibit a strong uniaxial in-plane magnetic anisotropy, in which the easy axis is along [1-10], i.e., nanowire direction.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.75.-c Magnetic properties of nanostructures
68.35.Fx Diffusion; interface formation
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of doping on the magnetic properties of GaMnN: Fermi level engineering

M. J. Reed, F. E. Arkun, E. A. Berkman, N. A. Elmasry, J. Zavada, M. O. Luen, M. L. Reed, and S. M. Bedair

Appl. Phys. Lett. 86, 102504 (2005); http://dx.doi.org/10.1063/1.1881786 (3 pages) | Cited 39 times

Online Publication Date: 3 March 2005

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GaMnN dilute magnetic semiconductor samples, prepared by metalorganic chemical vapor deposition, are shown to exhibit ferromagnetism or even paramagnetism depending upon the type and concentration of extrinsic impurity present in the film. In addition, GaMnN deposited using growth parameters normally yielding a nonferromagnetic film becomes strongly ferromagnetic with the addition of magnesium, an acceptor dopant. Based upon these observations, it seems that ferromagnetism in this material system depends on the relative position of the Mn energy band and the Fermi level within the GaMnN band gap. Only when the Fermi level closely coincides with the Mn-energy level is ferromagnetism achieved. By actively engineering the Fermi energy to be within or near the Mn energy band, room temperature ferromagnetism is realized.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.uj III-V and II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
71.55.Eq III-V semiconductors
75.20.Ck Nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.20.At Surface states, band structure, electron density of states
61.72.S- Impurities in crystals

Emissivity — a remote sensor of giant magnetoresistance

S. M. Stirk, S. M. Thompson, and J. A. D. Matthew

Appl. Phys. Lett. 86, 102505 (2005); http://dx.doi.org/10.1063/1.1880437 (3 pages) | Cited 15 times

Online Publication Date: 3 March 2005

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The link between emissivity in the mid-to-far-infrared regime and electrical conductivity is used to probe magnetoresistance. A direct relationship between the change in radiated flux and giant magnetoresistance is confirmed by experiment. The potential for spatially resolved measurements is also considered.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Bias-voltage dependence of magnetoresistance in magnetic tunnel junctions grown on Al2O3 (0001) substrates

Sung-Jin Ahn, Takeharu Kato, Hitoshi Kubota, Yasuo Ando, and Terunobu Miyazaki

Appl. Phys. Lett. 86, 102506 (2005); http://dx.doi.org/10.1063/1.1870104 (3 pages) | Cited 6 times

Online Publication Date: 4 March 2005

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Magnetic tunnel junctions with the structure of Al2O3 (0001)/Pt (111) 20 nm/Ni80Fe20 (111) 50 nm/Al 1.6 nm–O/Co75Fe25 4 nm/Ir22Mn78 10 nm/Ni80Fe20 30 nm were fabricated using UHV sputtering and photolithography process. As the annealing temperature increased up to 250 °C, tunnel magnetoresistance (TMR) ratio at 1 mV bias increased from 28% to 43% for tox = 180 s plasma oxidation and the V±1/2, at which the zero bias TMR value is halved, is +640 mV and−650 mV for positive and negative bias voltages, respectively. The bias-voltage dependence of TMR could be explained in terms of the relationship with V±1/2 and the interface of the ferromagnetic electrode and the Al–O insulating layer. V+1/2, which reflects the bottom ferromagnetic electrode-barrier interface state, changes with plasma oxidation time, while V−1/2, which corresponds to top ferromagnetic electrode-barrier interface, hardly changes.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Np Metals and alloys
81.65.Mq Oxidation
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering
73.63.-b Electronic transport in nanoscale materials and structures
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.B- Structure of clean surfaces (and surface reconstruction)

Brillouin light scattering from pumped uniform-precession and low-k magnons in Ni81Fe19

Ward L. Johnson, Sudook A. Kim, Stephen E. Russek, and Pavel Kabos

Appl. Phys. Lett. 86, 102507 (2005); http://dx.doi.org/10.1063/1.1882754 (3 pages) | Cited 5 times

Online Publication Date: 4 March 2005

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A method is presented for performing Brillouin-light-scattering measurements on uniform-precession and low-wave-number (low-k) magnons excited by a microwave magnetic field in opaque magnetic specimens. The optical configuration is similar to that employed in conventional 180° backscattering measurements, except that the incident and specularly reflected beams pass through the collection lens along different parallel paths. Examples of spectra from a Ni81Fe19 film are presented that include separate detection of light scattered from low-k magnons with the same frequency as the uniform precession.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
78.35.+c Brillouin and Rayleigh scattering; other light scattering
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Ds Spin waves

Change of the barrier potential shape in magnetic tunnel junctions due to an anneal treatment

P. H. P. Koller, H. J. M. Swagten, W. J. M. de Jonge, and R. Coehoorn

Appl. Phys. Lett. 86, 102508 (2005); http://dx.doi.org/10.1063/1.1883324 (3 pages)

Online Publication Date: 4 March 2005

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A very important process step in the fabrication of magnetic tunnel junctions (MTJs) is the application of a modest anneal step in the presence of a high magnetic field. Roughly, a doubling of the magnetoresistance (MR) ratio is commonly observed. We show that both AlOx as well as TaOx MTJs with Co90Fe10 electrodes have similar oxidation time and anneal temperature dependencies of the MR ratios. In both cases, the maximum MR ratio shifts to higher oxidation times with annealing. TaOx MTJs are, in this sense, good model systems. From photoconductance experiments we find that for TaOx MTJs, this shift in maximum MR is accompanied by a similar shift of the zero crossing of the oxidation time dependent barrier asymmetry. This directly supports the point of view that for obtaining the highest MR ratio one should anneal MTJs that would be characterized as “slightly overoxidized” in the as-deposited state. We argue that this result can be understood by a homogenization of the oxygen distribution in the barrier, and∕or a change of the bottom barrier-electrode interface.
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75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Pz Photoconduction and photovoltaic effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.65.Mq Oxidation
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Extremely low frequency response of magnetoelectric multilayer composites

Shuxiang Dong, Junyi Zhai, Zhengping Xing, Jie-Fang Li, and D. Viehland

Appl. Phys. Lett. 86, 102901 (2005); http://dx.doi.org/10.1063/1.1881784 (3 pages) | Cited 37 times

Online Publication Date: 28 February 2005

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A promising generation of extremely low frequency magnetic field sensors, based on multilayer composites (MLCs) of magnetostrictive Terfenol-D (Tb1−xDyxFe2−y) and piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3, has been developed. Our MLC magnetoelectric sensor presently shows a limit in (i) working frequency of ∼ 5×10−3 Hz; and (ii) magnetic field sensitivity of 10−7, 10−9, and 10−11 T for frequencies of f = 10−2, 1, and 102 Hz, respectively. The results open up possibilities for sensitive low frequency passive magnetic anomaly detection.
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07.55.Ge Magnetometers for magnetic field measurements
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
75.80.+q Magnetomechanical effects, magnetostriction

Real space imaging of the microscopic origins of the ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12

S. V. Kalinin, J. Shin, G. M. Veith, A. P. Baddorf, M. V. Lobanov, H. Runge, and M. Greenblatt

Appl. Phys. Lett. 86, 102902 (2005); http://dx.doi.org/10.1063/1.1880432 (3 pages) | Cited 34 times

Online Publication Date: 28 February 2005

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The origins of an ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 (CCTO) were studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM). Impedance spectra indicate that the transport properties in the 0.1 Hz–1 MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16 Hz. dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element. High frequency ac amplitude and phase distributions illustrate very weak grain boundary contrast in SPM, indicative of strong capacitive coupling across the interfaces. These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials is related to grain-boundary behavior.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
61.72.Mm Grain and twin boundaries

Correlation of nanochemistry and electrical properties in HfO2 films grown by metalorganic molecular-beam epitaxy

Tae-Hyoung Moon, Moon-Ho Ham, and Jae-Min Myoung

Appl. Phys. Lett. 86, 102903 (2005); http://dx.doi.org/10.1063/1.1873049 (3 pages) | Cited 8 times

Online Publication Date: 28 February 2005

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We present the annealing effects on nanochemistry and electrical properties in HfO2 dielectrics grown by metalorganic molecular-beam epitaxy. After the postannealing treatment of HfO2 films in the temperature range of 600–800 °C, the thicknesses and chemical states of the films were examined by high-resolution transmission electron microscopy and angle-resolved x-ray photoelectron spectroscopy. By comparing the line shapes of core-level spectra for the samples with different annealing temperatures, the concentrations of SiO and Hf-silicate with high dielectric constant are found to be highest for HfO2 film annealed at 700 °C. This result supports that the accumulation capacitance of the sample annealed at 700 °C is not deteriorated in spite of a steep increase in interfacial layer thickness compared with that of the sample annealed at 600 °C.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.-a Thin film structure and morphology
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Lp Transmission electron microscopy (TEM)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Piezoelectric–piezomagnetic multilayer with simultaneously negative permeability and permittivity

H. Liu, S. N. Zhu, Y. Y. Zhu, Y. F. Chen, N. B. Ming, and X. Zhang

Appl. Phys. Lett. 86, 102904 (2005); http://dx.doi.org/10.1063/1.1868073 (3 pages) | Cited 6 times

Online Publication Date: 1 March 2005

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We study the propagation of an electromagnetic (EM) wave in piezoelectric–piezomagnetic multilayers, in which the incident EM wave excites high frequency acoustic waves and couples strongly with them through piezoelectric and piezomagnetic effects, creating dielectric polariton and magnetic polariton simultaneously. The dispersion abnormality appears at some frequency ranges where simultaneous negative permittivity and permeability can be achieved. Theoretical analysis and numerical simulation proved that this structure forms a kind of “left-handed” material.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.50.Dd Nonmetallic ferromagnetic materials
75.80.+q Magnetomechanical effects, magnetostriction
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electron trap distribution in thin oxide after high-field stress

K. P. Cheung, D. Hits, and Y. Wang

Appl. Phys. Lett. 86, 102905 (2005); http://dx.doi.org/10.1063/1.1879088 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2005

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The centroid of neutral electron trap distribution in 80 Å SiO2 film after high-field electrical stress is determined using trap-filling measurements that can eliminate the contributions from trapped holes and interface trapped charges—complications that introduce ambiguity in previous studies. The centroid is found to be roughly half way between the midpoint of the oxide and the injecting electrode, implying an extremely nonuniform distribution. Such a highly nonuniform distribution is at odds with the assumption used in most oxide breakdown models. The impact of a highly nonuniform neutral trap distribution on thin oxide reliability projection could be important.
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73.61.Ng Insulators
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Ht Other nonmetals
72.20.Ht High-field and nonlinear effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species
84.32.Tt Capacitors
85.30.Tv Field effect devices

Permittivity increase of yttrium-doped HfO2 through structural phase transformation

Koji Kita, Kentaro Kyuno, and Akira Toriumi

Appl. Phys. Lett. 86, 102906 (2005); http://dx.doi.org/10.1063/1.1880436 (3 pages) | Cited 50 times

Online Publication Date: 3 March 2005

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An approach to control the dielectric properties of hafnium-based oxide films with an intentional structural phase transformation was proposed and demonstrated. Yttrium serves effectively as a dopant to induce a phase transformation from the monoclinic to the cubic phase even at 600 °C. The yttrium-doped HfO2 films show higher permittivity than undoped HfO2, and the permittivity as high as 27 is obtained by 4 at. % yttrium doping. The permittivity enhancement by yttrium doping can be explained by the shrinkage of molar volume due to the structural phase transformation. The advantage of yttrium doping is more pronounced at higher temperatures, since the permittivity of undoped HfO2 is reduced significantly, whereas that of 17 at. % yttrium-doped film shows no change even at 1000 °C.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Tv Optical and dielectric properties related to treatment conditions

Critical thickness of ultrathin ferroelectric BaTiO3 films

Y. S. Kim, D. H. Kim, J. D. Kim, Y. J. Chang, T. W. Noh, J. H. Kong, K. Char, Y. D. Park, S. D. Bu, J.-G. Yoon, and J.-S. Chung

Appl. Phys. Lett. 86, 102907 (2005); http://dx.doi.org/10.1063/1.1880443 (3 pages) | Cited 71 times

Online Publication Date: 3 March 2005

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To investigate the critical thickness of ferroelectric BaTiO3 (BTO) films, we fabricated fully strained SrRuO3/BTO/SrRuO3 heterostructures on SrTiO3 substrates by pulsed laser deposition with in situ reflection high-energy electron diffraction. We varied the BTO layer thickness from 3 to 30 nm. By fabricating 10×10 μm2 capacitors, we could observe polarization versus electric-field hysteresis loops, which demonstrate the existence of ferroelectricity in BTO layers thicker than 5 nm. This observation provides an experimental upper bound of 5 nm for the critical thickness. The BTO thickness-dependent scaling of the remanent polarization agrees with the predictions of recent first-principle simulations [ J. Junquera and P. Ghosez, Nature 422, 506 (2003) ].
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.-a Thin film structure and morphology
84.32.Tt Capacitors
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Sensitivity of exciton spin relaxation in quantum dots to confining potential

S. Mackowski, T. Gurung, H. E. Jackson, L. M. Smith, W. Heiss, J. Kossut, and G. Karczewski

Appl. Phys. Lett. 86, 103101 (2005); http://dx.doi.org/10.1063/1.1875763 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2005

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We observe a strong dependence of the exciton spin relaxation in CdTe quantum dots on the average dot size and the depth of the confining potential. After rapid thermal annealing, which increases the average dot size and leads to weaker confinement, we measure the spin relaxation time of the quantum dot excitons to be 1.5 ns, as compared to 4.8 ns found previously for the as-grown CdTe quantum dots. The annealed CdTe quantum dots exhibit also smaller values of the absolute polarization of the quantum dot emission. This dramatic enhancement of the spin scattering efficiency upon annealing is attributed to increased mixing between different spin states in larger CdTe quantum dots.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
61.72.Cc Kinetics of defect formation and annealing
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