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3 Sep 2012

Volume 101, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages)

Massimo Cuscunà, Annalisa Convertino, Emiliano Zampetti, Antonella Macagnano, Alessandro Pecora, Guglielmo Fortunato, Laura Felisari, Giuseppe Nicotra, Corrado Spinella, and Faustino Martelli
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Conduction mechanisms of epitaxial EuTiO3 thin films

R. Zhao, W. W. Li, L. Chen, Q. Q. Meng, J. Yang, H. Wang, Y. Q. Wang, R. J. Tang, and H. Yang

Appl. Phys. Lett. 101, 102901 (2012); http://dx.doi.org/10.1063/1.4750073 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2012

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To investigate leakage current density versus electric field characteristics, epitaxial EuTiO3 thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition and were post-annealed in a reducing atmosphere. This investigation found that conduction mechanisms are strongly related to temperature and voltage polarity. It was determined that from 50 to 150 K, the dominant conduction mechanism was a space-charge-limited current under both negative and positive biases. From 200 to 300 K, the conduction mechanism shows Schottky emission and Fowler-Nordheim tunneling behaviors for the negative and positive biases, respectively. This work demonstrates that Eu3+ is one source of leakage current in EuTiO3 thin films.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
68.55.at Other materials
81.15.Fg Pulsed laser ablation deposition
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity

Piezoelectric force microscopy of crystalline oxide-semiconductor heterostructures

M. S. J. Marshall, D. P. Kumah, J. W. Reiner, A. P. Baddorf, C. H. Ahn, and F. J. Walker

Appl. Phys. Lett. 101, 102902 (2012); http://dx.doi.org/10.1063/1.4750243 (4 pages)

Online Publication Date: 5 September 2012

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Thin films of epitaxial SrTiO3 grown on silicon exhibit compressive in-plane strain that may stabilize ferroelectricity in this normally non-ferroelectric material. We investigate this possibility by using an ultra-high vacuum atomic force microscope to measure the local force response of coherently strained SrTiO3 films on silicon to an applied ac electric field. The observed cantilever response is different in regions that were previously written with positive and negative voltages, but the frequency dependence of this response indicates that the dominant forces are related to electrostatic charging rather than ferroelectricity.
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77.55.hn Other piezoelectric or electrostrictive films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.55.ag Semiconductors
77.84.Cg PZT ceramics and other titanates

Prediction of stable ferroelectricity in epitaxial BaTiO3 on Si

H. L. Yu, H. B. Zhang, X. F. Jiang, and G. W. Yang

Appl. Phys. Lett. 101, 102903 (2012); http://dx.doi.org/10.1063/1.4751848 (4 pages)

Online Publication Date: 6 September 2012

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We show theoretically that stable ferroelectricity can be realized in a BaTiO3/Si heterojunction using first-principles calculations. Interfacial ferroelectric behavior is sensitive to the interface structure. Strong ferroelectric-semiconductor interactions would produce a fixed interface polarization and dominate the oxide film polarization properties. Weak interface interaction would be beneficial for preservation of ferroelectricity in the oxide films. The charge transfer between the ferroelectric and the semiconductor, the potential barrier, and the depolarizing field of the ferroelectric also play important roles in heterojunction ferroelectric stability. These findings are useful for silicon-based functional oxide device design.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Cg PZT ceramics and other titanates
77.55.fe BaTiO3-based films
77.22.Ej Polarization and depolarization
68.35.Ct Interface structure and roughness
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Electron spin resonance signature of the oxygen vacancy in HfO2

R. Gillen, J. Robertson, and S. J. Clark

Appl. Phys. Lett. 101, 102904 (2012); http://dx.doi.org/10.1063/1.4751110 (4 pages) | Cited 3 times

Online Publication Date: 6 September 2012

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The oxygen vacancy has been inferred to be the critical defect in HfO2, responsible for charge trapping, gate threshold voltage instability, and Fermi level pinning for high work function gates, but it has never been conclusively identified. Here, the electron spin resonance g tensor parameters of the oxygen vacancy are calculated, using methods that do not over-estimate the delocalization of the defect wave function, to be gxx = 1.918, gyy = 1.926, gzz = 1.944, and are consistent with an observed spectrum. The defect undergoes a symmetry lowering polaron distortion to be localized mainly on a single adjacent Hf ion.
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76.30.Mi Color centers and other defects
61.72.jd Vacancies
71.38.-k Polarons and electron-phonon interactions
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals

Fixed charge in high-k/GaN metal-oxide-semiconductor capacitor structures

Junwoo Son, Varistha Chobpattana, Brian M. McSkimming, and Susanne Stemmer

Appl. Phys. Lett. 101, 102905 (2012); http://dx.doi.org/10.1063/1.4751466 (3 pages) | Cited 1 time

Online Publication Date: 7 September 2012

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The location and nature of fixed charge states in high-k/GaN metal-oxide-semiconductor capacitor structures are characterized by analyzing flatband voltage shifts in high-frequency capacitance-voltage measurements. It is shown that a significant fixed, positive sheet charge forms at Al2O3/GaN interfaces, but not at HfO2/GaN interfaces. Furthermore, an interface dipole is created at HfO2/Al2O3 interfaces, which causes an abrupt shift in the flat band voltage as HfO2 is introduced to form HfO2/Al2O3 bilayer dielectrics. The observed dependence of the flatband voltage shift on the relative thicknesses of the dielectrics comprising the bilayer dielectrics is discussed.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
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