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13 Sep 2010

Volume 97, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages)

Sarah E. Baker, Michael D. Pocha, Allan S. P. Chang, Donald J. Sirbuly, Stefano Cabrini, Scott D. Dhuey, Tiziana C. Bond, and Sonia E. Létant
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Effective reduction of interfacial traps in Al2O3/GaAs (001) gate stacks using surface engineering and thermal annealing

Y. C. Chang, C. Merckling, J. Penaud, C. Y. Lu, W.-E. Wang, J. Dekoster, M. Meuris, M. Caymax, M. Heyns, J. Kwo, and M. Hong

Appl. Phys. Lett. 97, 112901 (2010); http://dx.doi.org/10.1063/1.3488813 (3 pages) | Cited 29 times

Online Publication Date: 13 September 2010

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To effectively passivate the technologically important GaAs (001) surfaces, in situ deposition of Al2O3 was carried out with molecular beam epitaxy. The impacts of initial GaAs surface reconstruction and post-deposition annealing have been systematically investigated. The corresponding interfacial state density (Dit) were derived by applying the conductance method at 25 and 150 °C on both p-type and n-type GaAs metal-oxide-semiconductor capacitors to establish the Dit spectra in proximity of the critical midgap region. We show that significant reduction of Dit near the midgap is achieved by applying an optimized thermal annealing on samples grown on a Ga-rich (4×6) reconstructed surface.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
81.65.Rv Passivation
81.40.Gh Other heat and thermomechanical treatments
81.05.Ea III-V semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Increased electromechanical coupling in w−ScxAl1−xN

Gunilla Wingqvist, Ferenc Tasnádi, Agne Zukauskaite, Jens Birch, Hans Arwin, and Lars Hultman

Appl. Phys. Lett. 97, 112902 (2010); http://dx.doi.org/10.1063/1.3489939 (3 pages) | Cited 7 times

Online Publication Date: 14 September 2010

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AlN is challenged as the material choice in important thin film electroacoustic devices for modern wireless communication applications. We present the promise of superior electromechanical coupling (kt2), in w−ScxAl1−xN by studying its dielectric properties. w−ScxAl1−xN (0 ≤ x ≤ 0.3) thin films grown by dual reactive magnetron sputtering exhibited low dielectric losses along with minor increased dielectric constant (ε). Ellipsometry measurements of the high frequency ε showed good agreement with density function perturbation calculations. Our data show that kt2 will improve from 7% to 10% by alloying AlN with up to 20 mol % ScN.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.hn Other piezoelectric or electrostrictive films
77.65.Bn Piezoelectric and electrostrictive constants
68.55.at Other materials
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Probing mixed tetragonal/rhombohedral-like monoclinic phases in strained bismuth ferrite films by optical second harmonic generation

Amit Kumar, Sava Denev, Robert J. Zeches, Eftihia Vlahos, Nikolas J. Podraza, Alexander Melville, Darrell G. Schlom, R. Ramesh, and Venkatraman Gopalan

Appl. Phys. Lett. 97, 112903 (2010); http://dx.doi.org/10.1063/1.3483923 (3 pages) | Cited 6 times

Online Publication Date: 14 September 2010

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Epitaxial strain can induce the formation of morphotropic phase boundary in lead free ferroelectrics like bismuth ferrite, thereby enabling the coexistence of tetragonal and rhombohedral phases in the same film. The relative ratio of these phases is governed by the film thickness and theoretical studies suggest that there exists a monoclinic distortion of both the tetragonal as well as the rhombohedral unit cells due to imposed epitaxial strain. In this work we show that optical second harmonic generation can distinguish the tetragonal-like phase from the rhombohedral-like phase and enable detection of monoclinic distortion in only a pure tetragonal-like phase.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
77.80.-e Ferroelectricity and antiferroelectricity
75.50.Gg Ferrimagnetics

Magnetoelectric effects in ferromagnetic cobalt/ferroelectric copolymer multilayer films

A. Mardana, Mengjun Bai, A. Baruth, Stephen Ducharme, and S. Adenwalla

Appl. Phys. Lett. 97, 112904 (2010); http://dx.doi.org/10.1063/1.3488814 (3 pages) | Cited 3 times

Online Publication Date: 14 September 2010

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Interactions between a ferromagnet, cobalt, and a ferroelectric copolymer, poly(vinylidene fluoride with trifluoroethylene) in thin film heterostructures result in a 5% change in the ferroelectric polarization on application of a perpendicular 6 kG magnetic field corresponding to a magnetoelectric coupling coefficient of α = 5.45 V/cm Oe. The effect disappears on magnetic saturation, ruling out conventional strain coupling. A simple model posits that the ferroelectric film develops in-plane strain gradients, a consequence of the coupling to strain gradients present at the domain walls in the multidomain Co layer, resulting in the measured polarization change via the flexoelectric effect.
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77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics
75.50.Cc Other ferromagnetic metals and alloys
77.80.-e Ferroelectricity and antiferroelectricity
77.55.F- High-permittivity capacitive films
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Implementing TiO2 as gate dielectric for Ge-channel complementary metal-oxide-semiconductor devices by using HfO2/GeO2 interlayer

Qi Xie, Davy Deduytsche, Marc Schaekers, Matty Caymax, Annelies Delabie, Xin-Ping Qu, and Christophe Detavernier

Appl. Phys. Lett. 97, 112905 (2010); http://dx.doi.org/10.1063/1.3490710 (3 pages) | Cited 12 times

Online Publication Date: 16 September 2010

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The electrical properties of plasma-enhanced atomic-layer-deposited (PE-ALD) TiO2 as gate dielectric were investigated for germanium-channel complementary metal-oxide-semiconductor capacitors by using ultrathin in situ HfO2/GeO2 interlayers. TiO2 grown by PE-ALD exhibited a k value of 50±5. An equivalent oxide thickness of 0.9 nm was obtained for the TiO2(3 nm)/HfO2(1.2 nm)/GeO2(0.7 nm)/Ge capacitor with very low leakage current density of 2×10−7 A/cm2 at VFB±1 V. Capacitance-voltage hysteresis was below 30 mV for the TiO2/HfO2/GeO2/Ge capacitors. Relatively low minimum density of interface states, Dit ∼ 5×1011 eV−1 cm−2 was obtained, suggesting the potential of HfO2/GeO2 passivation layer for the application of TiO2 as gate dielectric for both p- and n-type Ge channels.
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84.32.Tt Capacitors

Kinetics controlled aging effect of ferroelectricity in Al-doped and Ga-doped BaTiO3

Y. Y. Guo, M. H. Qin, T. Wei, K. F. Wang, and J.-M. Liu

Appl. Phys. Lett. 97, 112906 (2010); http://dx.doi.org/10.1063/1.3490700 (3 pages) | Cited 4 times

Online Publication Date: 17 September 2010

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Our experiments on ferroelectric aging of Al3+- and Ga3+-doped BaTiO3 ceramics reveal the crucial role of migration kinetics of point defects (oxygen vacancies) besides the thermodynamic driving force based on the symmetry conforming short-range ordering scenario. The doping with Ga3+ or tiny Al3+ ions shows the clear aging effect, while the high-level Al3+-doping suppresses the aging effect. The suppression is mainly attributed to the kinetically limited migration of oxygen vacancies due to the lattice shrinkage, while the other mechanisms may also make sense.
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77.84.Cg PZT ceramics and other titanates
77.80.bg Compositional effects
61.72.jd Vacancies

Three-dimensional ferroelectric domain imaging of epitaxial BiFeO3 thin films using angle-resolved piezoresponse force microscopy

Moonkyu Park, Seungbum Hong, Jeffrey A. Klug, Michael J. Bedzyk, Orlando Auciello, Kwangsoo No, and Amanda Petford-Long

Appl. Phys. Lett. 97, 112907 (2010); http://dx.doi.org/10.1063/1.3487933 (3 pages) | Cited 7 times

Online Publication Date: 17 September 2010

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Here we introduce angle-resolved piezoresponse force microscopy (AR-PFM), whereby the sample is rotated by 30° increments around the surface normal vector and the in-plane PFM phase signals are collected at each angle. We obtained the AR-PFM images of BaTiO3 single crystal and cube-on-cube epitaxial (001) BiFeO3 (BFO) thin film on SrRuO3/SrTiO3 substrate, and confirmed that the AR-PFM provides more unambiguous information on the in-plane polarization directions than the conventional PFM method. Moreover, we found eight additional in-plane polarization variants in epitaxial BFO thin films, which are formed to mitigate highly unstable charged domain boundaries.
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77.80.Dj Domain structure; hysteresis
77.55.Px Epitaxial and superlattice films
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
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