Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H41: Dielectric, Ferroelectric, and Piezoelectric Oxides I |
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Sponsoring Units: DMP Chair: Eugene Tsiper, Naval Research Laboratory Room: Baltimore Convention Center 344 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H41.00001: Constrained polarization study of ferroelectric KNO$_3$ Oswaldo Di\'eguez, David Vanderbilt Potassium nitrate has an interesting phase diagram that includes a reentrant ferroelectric phase (phase III, {\em R3m}), and it has been proposed as a promising material to be used in random-access memory devices.\footnote{J.~F.~Scott, M.~S.~Zhang, R.~B.~Godfrey, C.~Araujo, and L.~McMillan, Phys. Rev. B {\bf 35}, 4044 (1987).} Recently, we have developed a method to compute the ground-state of an insulator under a fixed value of its polarization\footnote{See: cond-mat/0511711 (www.arXiv.org).} that can be used to gain insight into the properties of polar materials. In this talk we show the results of applying this method to study the structural behavior of potassium nitrate under polarization reversal, describing an unusual mechanism in which the reversal is accompanied by a rotation of the NO$_3$ unit by 60$^\circ$. We also use our calculations as a basis for constructing first-principles based models that can be used to gain a deeper understanding of the switching behavior of this material. [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H41.00002: Surface passivation of III-V compound semiconductors using atomic-layer-deposition grown Al2O3 M.L. Huang, M. Hong, Y.C. Chang, C.H. Chang, Y.J. Lee, P. Chang, T.B. Wu, J. Kwo Al2O3 was deposited on In0.15Ga0.85As/GaAs using atomic layer deposition (ALD). Without any surface preparation or post thermal treatment, excellent electrical properties of Al2O3/InGaAs/GaAs heterostructures were obtained, in terms of low electrical leakage current density (10-8 to 10-9 A/cm2) and low interfacial density of states (Dit) in the range of 1012 cm-2eV-1. The interfacial reaction and structural properties studied by HRXPS and HRTEM. The depth profile of HRXPS, using synchrotron radiation beam and low energy Ar+ sputtering, exhibited no residual arsenic oxides and elemental arsenic at interface. The removal of the arsenic oxides from Al2O3/InGaAs heterostructures during ALD process ensures the Fermi level unpinning, which was observed in the C-V measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor. The bandgap of ALD grown Al2O3 was measured by O 1s core level loss spectra as 6.55 eV, and valence band offset was 3.78 eV between Al2O3 and In0.15Ga0.85As layers. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H41.00003: Electronic and vibrational properties of tungsten-bronze niobates Marco Fornari We investigated the electronic and vibrational properties of complex niobates with tetragonal tungsten-bronze structure. Our first principles results show that, in PbNb$_2$O$_6$, the largest contribution to the polarization is from the four 15-coordinates Pb sites (A$^{XV}$). The interaction between these sites favors the orthorhombic ground-state. The substitution of Ba on the A$^{XV}$ site drives the system to a tetragonal phase forming a morphotropic phase boundary. Replacing Ba with Pb breaks the cooperative behavior a the origin of the orthorhombic phase. Octahedral rotations do not seem to play a significant role even if they influence the energetic of the position of Pb in the A$^{XV}$ cage. Chemical substitutions are tried to explore novel ferroelectric materials. [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:03PM |
H41.00004: Cubic HfO2 Doped with Y2O3 for Advanced Gate Dielectrics by MBE. ZhiKai Yang, W.C. Lee, Pen Chang, MoLin Huang, Yi Lin Huang, Minghwei Hong, C.M. Huang, C.H. Hsu, Raynien Kwo High $\kappa $ HfO$_{2}$ ($\kappa $ =20) is currently employed as an alternative gate dielectric replacing SiO$_{2}$ in CMOS scaling. There are three known crystal structures of HfO$_{2}$, monoclinic, cubic, and tetragonal with varying dielectric constants [1]. Recently we showed HfO$_{2}$ films epitaxially grown on GaAs(100) formed the stable monoclinic phase ($\alpha =\gamma $ = 90° and $\beta \quad \sim $ 99°) with the $a$ and $b$ axes aligned with the in-plane GaAs{\{}100{\}}axes resulting in four equivalent domains. This work demonstrates the successful alteration of the crystal structure of HfO$_{2 }$from the lower $\kappa $ monoclinic phase to the higher $\kappa $ ($\kappa $ =30) cubic phase stabilized through epitaxy on GaAs(100) and Si(100) with the aid of Y$_{2}$O$_{3}$ doping ($\sim $ 20{\%} based on XPS). X-ray diffraction scans on these films clearly indicated the cubic symmetry. Doping Y$_{2}$O$_{3}$ is also to enhance the thermal stability of amorphous HfO$_{2}$. Y$_{2}$O$_{3 }$doping was shown to help raise the re-crystallization temperature of HfO$_{2 }$to be$_{ }$compatible with high temperature processing. [1] X. Zhao et al, PRB \textbf{65}, 233106, (2002). [Preview Abstract] |
Tuesday, March 14, 2006 12:03PM - 12:15PM |
H41.00005: Hydrogen bistability in non-magnetic oxides Jacob Gavartin, Alexander Shluger, Marshall Stoneham, Steve Cox Recent extensive muonium spectroscopy measurements ($\mu $SR) [1] suggest a general correlation between stable muonium (Mu) forms in non magnetic oxides and their band gap, E$_{g}$: in the materials with Eg$<$4 eV, Mu is, as a rule, fully ionized; in the oxides with Eg$>$7 eV, most of the Mu exists in the atomic form, while both ionized and atomic forms of Mu coexist in the oxides with the band gap in the interval 4$<$Eg$<$7 eV. Based on the analogy between muonium and hydrogen, we propose a general model which may explain such a correlation and makes important predictions about hydrogen behavior in non-magnetic oxides. As an example, we use ab initio calculations to extract the parameters for this model to explain difference in hydrogen behavior in HfO$_{2}$, ZrO$_{2}$ films and in their silicates at low hydrogen concentrations [2]. We further discuss the role of hydrogen in mechanisms of tetragonal to a monoclinic phase transformations in ZrO$_{2}$ and HfO$_{2}$. 1. S.F.J. Cox, J.L. Gavartin, J.S. Lord et al. J. Phys.~: Condens. Matter, 2006 (in press). 2. R.P. Pezzi, L. Miotti, K.P. Bastos \textit{et al}. \textit{Appl. Phys. Lett.} \textbf{85} 3540 (2004). [Preview Abstract] |
Tuesday, March 14, 2006 12:15PM - 12:27PM |
H41.00006: Growth of highly oriented monoclinic HfO$_{2}$ thin films after Co and Fe doping by pulsed laser deposition S. Dhar, M.S.R. Rao, S.B. Ogale, D.C. Kundaliya, S.R. Shinde, T. Venkatesan, S.J. Welz, R. Erni, N.D. Browning Above room-temperature ferromagnetism in undoped and Co doped high-k dielectric HfO$_{2 }$thin films opens up the possibility for using spin functionality in various new electronic devices. In the present work, we report on the growth of high quality epitaxial HfO$_{2}$ thin films stabilized in monoclinic phase after 5{\%} Co or Fe doping at 700-800$^{o }$C in an oxygen partial pressure of 10$^{-4}$ torr on (001) yttria stabilized zirconia and (001) Si substrates by pulsed laser deposition. On the one hand, pure HfO$_{2}$ film did not grow epitaxally under various deposition conditions. On the other hand, the formation of single crystalline phase after Co or Fe doping was confirmed by X-ray analysis. Ion channeling analysis in Co and Fe doped films showed 8-24{\%} minimum yield indicating highly oriented film growth, whereas, a very poor minimum yield was observed in the undoped case. Angular scans showed the HfO$_{2}$ to grow in a monoclinic phase with a 9.1 degree tilt with respect to the substrate. High resolution transmission electron microscopy showed very sharp interface while Electron energy loss spectroscopy revealed that Co is in 2+ state indicating the substitution of Co in ionic form into the HfO$_{2 }$lattice. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 12:39PM |
H41.00007: Anomalous behavior of the dielectric constant of hafnium silicates Carlo Antonio Pignedoli, Alessandro Curioni, Wanda Andreoni Hafnium silicates (HfSiO) are among the materials most frequently investigated in the search for a replacement of silicon dioxide as gate dielectric in CMOS devices. Measurements of the dielectric constant as a function of the relative concentration of the two binary oxides exhibit an anomalous behavior. Large-scale DFT-based calculations reveal that this is due to the change of the relative stability of different structures with composition and their strong influence on the permittivity. These results also help to rationalize the wide scatter in the experimental data for the dielectric constant for some concentrations and suggest ways to optimize the integration of these materials in the device. [Preview Abstract] |
Tuesday, March 14, 2006 12:39PM - 12:51PM |
H41.00008: Nucleation and Growth of ALD Hafnium Oxide High-k Dielectric Films by GISAXS. Andrew Allen, Martin Green Atomic layer deposition (ALD) is an important film growth technique that enables accurate growth of ultrathin layers for high-k gate dielectrics. Results will be presented of grazing incidence small angle x-ray scattering (GISAXS) studies of the nucleation and growth of ALD hafnium oxide films. The scattering is related to surface roughness and internal interfaces within the films, resulting from film coalescence of the nuclei. Films grown on H-terminated Si are rough and nonplanar, exhibit greater scattering, and have greater internal surface area than films grown on chemically oxidized Si. These films have 5 times the internal surface area of films grown on chemically oxidized Si, and may be significantly porous. The characteristic scattering features are the film nuclei, which coalesce and become inherited features of the films. The nuclei size is about 2 nm, consistent with TEM observations. Films grown on chemically oxidized Si reach coalescence at about 25 cycles, or 1.3 nm thickness, consistent with electrical data. Implications arising from the different film morphologies discussed. [Preview Abstract] |
Tuesday, March 14, 2006 12:51PM - 1:03PM |
H41.00009: Self-interaction corrected extrinsic levels of oxygen vacancies in hafnia Giorgia M. Lopez, Vincenzo Fiorentini, Alessio Filippetti To identify fixed-charge (generally negative) centers in thin hafnia layers on silicon, the position and nature of the electronic levels of candidate defects should be known accurately. Due to the DFT gap problem, this is still a controversial issue in ab initio calculations, especially for high-gap insulators and near-conduction states. Here we apply a self-interaction corrected DFT method, which dealt successfully with a variety of systems dominated by localized and correlated states, to study the electronic structure of oxygen vacancies in monoclinic hafnium oxide in various charge states. We set the position of the extrinsic levels within the gap, and relative to the Si gap position as determined by interface band offsets. In the positive states, the partially filled levels are well below the Si gap, hence the Fermi level, and play a minor role. For the neutral vacancy, a filled extrinsic state sits within the Si gap and may tend to pin the Fermi level. A negative center may be realized upon occupation of a near-conduction shallow state, which would occur under typical device operation bias. While a conclusive identification of fixed-charge centers remains an open issue, the nature of this level is compatible with the experimentally observed kinetics of trapping and detrapping. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H41.00010: A Novel Template Approach by MBE for ALD Growth of High k Dielectrics K.Y. Lee, W.C. Lee, M.L. Hung, Y.C. Lee, C.H. Chang, Y.K. Chiou, M. Hong, J. Kwo Although growth of high k dielectrics by ALD on H-Si is feasible, it undergoes an incubation period during which the formation of SiO2 layer seems inevitable. Recently we showed the MBE growth of HfO2 on Si produced atomically abrupt interfaces, and achieved excellent electrical performance. Here we employed the MBE-grown high k dielectrics thin film as a template to suppress the interfacial layer formation during the ALD growth, and to improve the electrical properties of ALD films. The first demonstration is a bi-layer composite made of a lower HfO2 (MBE) layer 2.5nm thick, and an upper Al2O3 (ALD) film 4.0nm thick. The electrical properties are consistent with the two capacitors in series from two individual dielectric layers. The second demonstration is an MBE and ALD composite Al2O3 6.6nm thick. Studies are underway for the third structure of Al2O3 (MBE) and HfO2 (ALD) composite, which offers dual advantages of interfacial layer suppression and leakage current reduction during HfO2 recrystalization. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H41.00011: Dielectric Relaxation of CaCu$_3$Ti$_4$O$_{12}$ synthesized from a pyrolysis method Jianjun Liu, W. N. Mei, R. W. Smith, J. R. Hardy Giant dielectric constant material CaCu$_3$Ti$_4$O$_{12}$ has been synthesized by using a pyrolysis method. A stable solution was made by dissolving calcium nitrate, copper nitrate, and titanium isopropoxide in 2-methoxyethanol; the solution was then heated at 500 and 700 $^o$C for 2 hours to obtain a pure phase of CaCu$_3$Ti$_4$O$_{12}$. The frequency and temperature dependences of dielectric permittivity were examined in the ranges of 10$^{-1}$$\sim$10$^{6}$ Hz and -150$\sim$200 $^o$C. We found that the dielectric properties of the sample were the same as those made from solid state reaction. Specifically, there is a Debye-like relaxation at low temperature and its giant dielectric constant about 11000 is independent of the temperature and frequency over a wide range. [Preview Abstract] |
Tuesday, March 14, 2006 1:27PM - 1:39PM |
H41.00012: Cathodoluminescence Studies of Rare Earth Ions in LiNbO$_3$ and GaN S. Tafon Penn, Zack Fleischmann, G.S. Cargill, V. Dierolf In most host materials, rare earth ions have intra-atomic transitions that exhibit a sensitivity to the local environment through the crystal field splitting of their Stark sub-levels and the modification of the free ion parameters (e.g.: Slater parameters). Moreover, in crystals that lack inversions symmetry the transitions exhibit linear Stark shifts that makes them good probes for local electric fields that are created for instance by local charging and a ferroelectric domain inversion. We present cathodoluminescence emission spectra of Eu$^{3+}$ ions and Er$^{3+}$ in two host materials (LiNbO$_3$ and GaN) for a temperature range between 12 and 300K using the electron beam in JEOL JSM-6400 SEM with a voltage of 10keV, various beam currents and beam scanning modes. We observe a pronounced saturation effect in the emission of the rare earth ions that depends on details of the scan mode, the electron beam deflection frequency, and magnification. The saturation effect is absent in the intrinsic emission of GaN that is recorded simultaneously. We will present an interpretation of the effect that takes into account charging effects and the excitation and relaxation dynamics of the free carriers and the rare earth ions. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 1:51PM |
H41.00013: Electronic Structure Calculations of BiFeO3 David Sulock, Lucas K. Wagner, Lubos Mitas Bismuth Ferrite (BiFeO3) is a potentially useful material because it exhibits both ferroelectricity and antiferromagnetism, providing a link between magnetic and ferroelectric action in the same material. Experimentally BiFeO3 has been reported to have a spontaneous polarization ranging from .06 C/m2 to 1.50 C/m2, possibly indicating a large dependence on experimental setup. Theoretical efforts thus far within Density Functional Theory in the LDA approximation have settled on a value of around 0.95 C/m2; however, it is not clear that LDA provides a sufficient description of the material as it predicts a lattice constant in error by ~.2 angstroms and zero band gap for some parts of the ferroelectric distortion. To check the results provided by LDA we use Quantum Monte Carlo (QMC), which allows us to treat the system in a fully correlated way. We use the Reptation Monte Carlo algorithm of Moroni and Baroni to calculate the polarization and other properties, allowing us to then evaluate the accuracy of QMC versus LDA. [Preview Abstract] |
Tuesday, March 14, 2006 1:51PM - 2:03PM |
H41.00014: Calculated polarizations and piezoelectric constants of wurtzite ZnO, CdO and MgO Priya Gopal The macroscopic polarization in wurtzite crystal structures such as GaN and ZnO has a strong influence on the electrical and optical properties. This property has been exploited in GaN/AlGaN heterostructures, where the difference in the polarizations between layers induces an electric field at the interface forming a high mobility two-dimensional electron gas (2DEG)~\footnote[1]{U. K. Mishra,Y. Wu, B.P. Keller, S. Keller and S.P. Denbaars \textit{IEEE Transactions on Microwave theory and Techniques}, \textbf{46}, 6 (1998)}. . Here we calculate the polarization and the piezoelectric properties of the corresponding wurtzite-structure binary oxides ZnO, MgO and CdO. The knowledge of these properties is essential to explore the possibility of creating similar high mobility polarization induced 2DEGs in the ZnO-based material system. However, since wurtzite-structure MgO and CdO are not experimentally accessible, the values can be obtained computationally. We use the recently developed self-interaction corrected pseudopotential (pseudo-SIC) implementation~\footnote[2]{ A. Filippetti and N.A. Spaldin \textit{Phys. Rev. B} \textbf{67}, 125109 (2003).} of the density functional theory and the widely used Berry phase method~\footnote[3]{R. D. Kingsmith and D. Vanderbilt \textit{Phys. Rev. B} \textbf{49}, 5828 (1994).} for obtaining the polarization and piezoelectric constants. We find that the polarization gradients between the end-point compounds in the MgO-ZnO-CdO are larger~\footnote[4]{P. Gopal and N.A. Spaldin \textit{submitted}} than in the GaN analogues. [Preview Abstract] |
Tuesday, March 14, 2006 2:03PM - 2:15PM |
H41.00015: A More Accurate Generalized Gradient Approximation for Solids Zhigang Wu, Ronald E. Cohen We present a new nonempirical density functional generalized gradient approximation (GGA) based on a diffuse radial cutoff for the exchange-hole in real space and the analytic gradient expansion of the exchange energy for small gradients. There are no adjustable parameters, the constraining conditions of PBE are maintained, and the functional is easily implemented in existing codes. For the 18 testing solids including simple and transition metals, and ionic and covelent crystals, the new functional improves equilibrium lattice constants and bulk moduli significantly over the most popular Perdew-Burke-Ernzerhof (PBE) GGA and the local density approximation (LDA), and its accuracy for cohesive energies is similar to PBE. It also predicts highly accurate ground states of ferroelectrics, better metal surface energies and sublimation energy of ice than PBE and LDA, and correct ground states of magnetic iron and alpha quartz. [Preview Abstract] |
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