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27 Aug 2007

Volume 91, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 093110 (2007); http://dx.doi.org/10.1063/1.2775801 (3 pages)

M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, G. J. Salamo, D. Grigoriev, P. Schäfer, R. Köhler, and M. Hanke
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Atomic scale nitrogen depth profile control during plasma enhanced atomic layer deposition of high k dielectrics

W. J. Maeng and H. Kim

Appl. Phys. Lett. 91, 092901 (2007); http://dx.doi.org/10.1063/1.2776350 (3 pages) | Cited 10 times

Online Publication Date: 27 August 2007

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Nitrogen incorporation produces several benefits in the performance of high k gate oxides. However, since too much nitrogen incorporation at the interface of gate dielectric can result in device degradation, the atomic scale control of nitrogen depth profile is desirable. In this study, the authors have improved electrical properties and interface properties by depth profile control of in situ nitrogen incorporation during plasma enhanced atomic layer deposition. The best electrical properties in terms of hysteresis, equivalent oxide thickness, and interface states were obtained when the nitrogen is incorporated in the middle of the thin film, which has not been achievable by other techniques.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.20.At Surface states, band structure, electron density of states

Prediction of polar ordered oxynitride perovskites

Razvan Caracas and R. E. Cohen

Appl. Phys. Lett. 91, 092902 (2007); http://dx.doi.org/10.1063/1.2776370 (3 pages) | Cited 2 times

Online Publication Date: 27 August 2007

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Using a materials by design approach, the authors find a class of ordered oxynitride piezoelectrics with perovskite structure. They predict that ordered YSiO2N and YGeO2N are characterized by large nonlinear optic responses and by some of the largest polarizations known to date.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
42.65.-k Nonlinear optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effect of low fluence laser annealing on ultrathin Lu2O3 high-k dielectric

P. Darmawan, P. S. Lee, Y. Setiawan, J. Ma, and T. Osipowicz

Appl. Phys. Lett. 91, 092903 (2007); http://dx.doi.org/10.1063/1.2771065 (3 pages) | Cited 10 times

Online Publication Date: 27 August 2007

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The effect of low fluence single pulse laser annealing on a pulsed laser deposited high-k dielectric, Lu2O3 is reported. With low fluence laser irradiation, high “k” of 45 is achieved with an equivalent oxide thickness of 0.39 nm, without taking into account the quantum mechanical tunneling effect. High-resolution transmission electron microscopy micrograph revealed well-ordered epitaxial-like interfacial layer. High-resolution Rutherford backscattering confirmed the presence of Lu-based silicate layer at the interface. It was proposed that the high dielectric constant was caused by the increased ionic polarizability in the film, thereby increasing the ionic contribution of the dielectric constant.

Stability of photovoltage and trap of light-induced charges in ferroelectric WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 thin films

Meng Qin, Kui Yao, Yung C. Liang, and Bee Keen Gan

Appl. Phys. Lett. 91, 092904 (2007); http://dx.doi.org/10.1063/1.2776855 (3 pages) | Cited 14 times

Online Publication Date: 27 August 2007

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The stability of photovoltage in WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLWZT) ferroelectric thin films was investigated. For in-plane polarized configuration, with a greatly enhanced electrode gap, the reduction ratio of photovoltage during multicycle UV illumination was significantly smaller and stability of photovoltage was greatly improved over the sandwich capacitor configuration. The ferroelectric-metal interfacial effects including Schottky barriers and polarization screening due to the trap of photoinduced charges at interfaces were found to determine the magnitude, stability, and even the polarity of the photovoltage, particularly for the electrode-sandwiched PLWZT thin films.
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73.61.Ng Insulators
73.40.Rw Metal-insulator-metal structures
73.50.Pz Photoconduction and photovoltaic effects
73.30.+y Surface double layers, Schottky barriers, and work functions
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization

Large polarization and enhanced magnetic properties in BiFeO3 ceramic prepared by high-pressure synthesis

W. N. Su, D. H. Wang, Q. Q. Cao, Z. D. Han, J. Yin, J. R. Zhang, and Y. W. Du

Appl. Phys. Lett. 91, 092905 (2007); http://dx.doi.org/10.1063/1.2776864 (3 pages) | Cited 21 times

Online Publication Date: 27 August 2007

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The BiFeO3 ceramics were prepared by sol-gel method (BFO-1) and high-pressure synthesis (BFO-2). X-ray diffraction showed that these ceramics are almost of single phase. It is difficult to observe a ferroelectric loop of BFO-1 even at an electric field of 6 kV/cm. Compared to BFO-1, the high-pressure synthesized one has higher resistivity, higher density, and better crystallization. Under an applied electric field of 120 kV/cm, the values of remanent polarization and the coercive field are 46 μC/cm2 and 73 kV/cm, respectively. At room temperature, a magnetic hysteresis loop with enhanced magnetization can be observed in BFO-2.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Dd Nonmetallic ferromagnetic materials
62.50.-p High-pressure effects in solids and liquids

Evaluation of microwave dielectric properties of giant permittivity materials by a modified resonant cavity method

Lei Li, Xiang Ming Chen, Lei Ni, and Mao Sen Fu

Appl. Phys. Lett. 91, 092906 (2007); http://dx.doi.org/10.1063/1.2775091 (3 pages) | Cited 2 times

Online Publication Date: 27 August 2007

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A modified resonant cavity method was developed to evaluate the microwave dielectric properties of giant permittivity materials, which were difficult to determine accurately using previous methods. A small-sized sample was used for measurement in the present work, and the microwave dielectric properties could be measured accurately over a wide frequency range with the aid of low-loss reference ceramics. The measurement was conducted on CaCu3Ti4O12 ceramics from 3.38 to 10.16 GHz. The permittivity of CaCu3Ti4O12 ceramics was around 84 over the above frequency range and decreased slightly with increasing frequency, while the dielectric loss decreased significantly from 0.17 to 0.055.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)

First principles phase diagram calculations for the system NaNbO3–KNbO3: Can spinodal decomposition generate relaxor ferroelectricity?

B. P. Burton and Takeshi Nishimatsu

Appl. Phys. Lett. 91, 092907 (2007); http://dx.doi.org/10.1063/1.2775308 (3 pages) | Cited 4 times

Online Publication Date: 27 August 2007

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First principles based phase diagram calculations were performed for the system (1−X) NaNbO3–(X) KNbO3. Plane wave pseudopotential calculations of formation energies were used as a basis for fitting a cluster expansion Hamiltonian, and a phase diagram was calculated. The predicted phase diagram has an unusual asymmetric miscibility gap, which suggests that it might be possible to synthesize a lead-free compositionally modulated sample with bulk composition X ≈ 0.23; such a sample is likely to exhibit relaxor characteristics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.-e Ferroelectricity and antiferroelectricity
64.75.-g Phase equilibria

Piezoelectricity and ferroelectric cluster size in relaxor ferroelectrics

L.-F. Wang and J.-M. Liu

Appl. Phys. Lett. 91, 092908 (2007); http://dx.doi.org/10.1063/1.2775309 (3 pages) | Cited 3 times

Online Publication Date: 27 August 2007

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The dipole configuration and electromechanical behaviors of dipole-disorder induced relaxor ferroelectrics (RFs) are investigated using a phenomenological model. In comparison to normal ferroelectric lattice, the RF lattice shows spatially inhomogeneous cluster configuration but no breaking of the dipole orientation symmetry is identified. A clean relationship between the piezoelectric response and the characteristic size of the ferroelectric clusters is established, which predicts a broad peak of the piezoelectric coefficient in response to the dipole disorder degree.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.65.Bn Piezoelectric and electrostrictive constants
77.80.-e Ferroelectricity and antiferroelectricity

Dopant position in Ti-doped high-temperature phase Ta2O5: First principles study

R. Z. Zhang, C. L. Wang, J. C. Li, J. L. Zhang, K. Yang, C. Zhang, and H. M. Chen

Appl. Phys. Lett. 91, 092909 (2007); http://dx.doi.org/10.1063/1.2775324 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2007

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The ab initio calculation and bond valence model (BVM) are employed to investigate dopant occupancy in the Ti-doped high-temperature phase Ta2O5. In this structure, there are two types of Ta atoms, which the authors denote as Ta1 locating inside oxygen octahedral and Ta2 locating inside oxygen decahedral. The 5d state electron configuration of Ta1 and Ta2 is different, the hybridization between Ta1 5d state and O 2p state is stronger than that between Ta2 and O. The chemical bonding between Ta and oxygen ions is mainly covalent. However, there is an increase of the covalent character in going from Ta1–O bond to Ta2–O bond. Both total energy method and BVM indicate that Ti substituting Ta1 is energy favorable, and this maybe due to different electronic structures of Ta1 and Ta2.
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71.20.Ps Other inorganic compounds
71.15.Nc Total energy and cohesive energy calculations
61.72.up Other materials
61.72.S- Impurities in crystals
61.50.Lt Crystal binding; cohesive energy

Effect of crystallinity and nonstoichiometric region on dielectric properties of SrTiO3 films formed on Ru

Ja-Yong Kim, Ji-Hoon Ahn, Sang-Won Kang, Jin-Hyock Kim, and Jae-Sung Roh

Appl. Phys. Lett. 91, 092910 (2007); http://dx.doi.org/10.1063/1.2775325 (3 pages) | Cited 7 times

Online Publication Date: 28 August 2007

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The dielectric constant depending on the film thickness for SrTiO3 films formed on Ru was investigated after an annealing step at 600 °C, which shows that the dielectric constant increased abruptly with the film thickness up to 20 nm and then increased slightly, remaining relatively constant at a value of about 65. The abrupt increase was due to the crystallinity of SrTiO3 films. On the other hand, the slight increase was related to the existence of nonstoichiometric region near the interface of SrTiO3 film and Ru, which was intermixed with SrTiO3 and Ti–O phases having an equivalent oxide thickness over 0.32 nm.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition

Vertical organic light emitting transistor

Zheng Xu, Sheng-Han Li, Liping Ma, Gang Li, and Yang Yang

Appl. Phys. Lett. 91, 092911 (2007); http://dx.doi.org/10.1063/1.2778751 (3 pages) | Cited 13 times

Online Publication Date: 30 August 2007

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The authors demonstrate a vertical organic light emitting transistor achieved by stacking a capacitor on top of an organic light emitting diode (OLED). This unique device has dual functions, emitting light as an OLED and switching current as a transistor. When the capacitor is under bias, the storage charges on the thin electrode shared by two cells modulate the charge injection of the OLED active cell, hence controlling the current flow and subsequently tuning the light emission. Due to the vertical integration, this device can be operated at low voltage, which provides a solution for OLED display applications.
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85.60.Jb Light-emitting devices
85.30.-z Semiconductor devices

Dielectric relaxations of yttrium iron garnet ceramics over a broad temperature range

Y. J. Wu, Y. Gao, and X. M. Chen

Appl. Phys. Lett. 91, 092912 (2007); http://dx.doi.org/10.1063/1.2780116 (3 pages) | Cited 13 times

Online Publication Date: 31 August 2007

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Dielectric response of Y3Fe5O12 ceramics was investigated over broad temperature and frequency ranges. Three dielectric relaxations were identified in the temperature range from 125 to 620 K. A Debye-type dielectric relaxation at low temperatures (125–320 K) with an activation energy of 0.29 eV is shown to originate from the carrier hopping process between Fe2+ and Fe3+. In a higher temperature range (320–620 K), a low frequency (f≦10 kHz) dielectric relaxation with an activation energy of 0.84 eV most likely arises from the inhomogeneous structure, such as grain boundaries. Another dielectric relaxation in a wider frequency range has a similar activation energy with conduction (Ea = 1.00 eV) suggests that it can be attributed to the conduction.
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77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Mm Grain and twin boundaries
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