bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum-Confined Stark Effect and Recombination Dynamics of Spatially Indirect Excitons in Mbe-Grown GaN-AlGaN Quantum Wells
Authors: Lefebvre Pierre , Gil Bernard , Allègre Jacques , Mathieu Henry , Grandjean Nicolas , Leroux Mathieu , Massies Jean , Bigenwald Pierre 
Published: April 2011

AbstractWe analyze the low-temperature photoluminescence decay times, for a series of MBE-grown samples embedding GaN-AlGaN quantum wells. We investigate a variety of configurations in terms of well widths, barrier widths and overall strain states. We find that not only the wells but also the barriers are submitted to large built-in electric fields. In the case of narrow barriers (5 um), these fields favor the nonradiative escape of carriers from narrow wells into wider wells. When all wells have the same width, the field in such narrow barriers allow us to observe the recombination of long-lived “inter-well” excitons at energies close to those of the short-lived “intra-well” excitons. Our results also prove that the energies and the dynamics of excitonic recombinations depend on the parameters of the heterostructures in a complicated way, due to the interplay of piezoelectric and spontaneous polarizations.
Studies on Carbon as Alternative P-Type Dopant for Gallium Nitride
Authors: Birkle U. , Fehrer M. , Kirchner V. , Einfeldt S. , Hommel D. , Strauf S. , Michler P. , Gutowski J. 
Published: April 2011

AbstractGaN layers were grown by molecular beam epitaxy and doped with carbon of nominal concentrations ranging from 1016 cm-1 to 10 20 cm-1. The incorporation of carbon leads to a reduction of the background electron concentration by one order of magnitude but the material remains n-type. For high carbon concentrations a re-increase of the carrier concentration is observed which is related to selfcompensation. Investigations of the donor-acceptor-pair luminescence show that doping with carbon is accompanied by the generation of a new donor exhibiting a thermal activation energy of about 55 meV. Layers grown by atomic layer epitaxy are marked by an increased intensity of the donor-acceptor-pair band luminescence which is attributed to the enforced incorporation of carbon onto the nitrogen sublattice. The yellow luminescence is found to be a typical feature of all carbon doped layers in contrast to nominally undoped samples.
Control of the Polarity and Surface Morphology of GaN Films Deposited on C-Plane Sapphire
Authors: Sumiya M. , Ohnishi T. , Tanaka M. , Ohtomo A. , Kawasaki M. , Yoshimoto M. , Koinuma H. , Ohtsuka K. , Fuke S. 
Published: April 2011

AbstractControl of the polarity of GaN films deposited by metalorganic chemical vapor deposition was achieved by substrate nitridation and subsequent annealing of a buffer layer. The surface morphology and optical properties of 1.2μm GaN films were influenced by the different growth mode due to the polar direction. Coaxial impact collision ion scattering spectroscopy revealed that the polarity composition of a buffer layer on nitrided sapphire varied by annealing in a H2 atmosphere. It was considered that the systematic variation of the surface morphology was caused by the polarity composition of the buffer layer.
Electrical Characterization of MOVPE-GROWN P-Type GaN:Mg Against Annealing Temperature
Authors: Fujita Shizuo , Funato Mitsuru , Park Doo-Cheol , Ikenaga Yoshifumi , Fujita Shigeo 
Published: April 2011

AbstractHall effect measurements have been applied for the electrical characterization of p-type Mg-doped GaN grown by metalorganic vapor-phase epitaxy on sapphire substrates in terms of annealing temperature for dehydrogenation (N2 annealing) and hydrogenation (H2 annealing) of the acceptors. With the N2 annealing temperature from 600 to 900°C for dehydrogenation, both hole concentration and mobility increases, showing more activation of acceptors and less incorporation of unfavorable scattering centers probably originating from Mg-H bondings. The N2 annealing at higher than the growth temperature results in reduced hole concentration, but the mobility gets higher. Some defects compensating acceptors may be induced at high temperature annealing, but they seem to be no scattering centers and be inactivated by successive hydrogenation and re-dehydrogenation at the optimum dehydrogenation temperature 900°C. The electrical degradation of GaN due to thermal damage is not very destructive and can be well recovered by annealing treatments.
Dynamic Crack Propagation in Single-Crystalline Silicon
Authors: Cramer T. , Wanner A. , Gumbsch P. 
Published: April 2011

AbstractTensile tests on notched plates of single-crystalline silicon were carried out at high overloads. Cracks were forced to propagate on {110} planes in a <110> direction. The dynamics of the fracture process was measured using the potential drop technique and correlated with the fracture surface morphology. Crack propagation velocity did not exceed a terminal velocity of v = 3800 m/s, which corresponds to 83%7 of the Rayleigh wave velocity vR. Specimens fractured at low stresses exhibited crystallographic cleavage whereas a transition from mirror-like smooth regions to rougher hackle zones was observed in case of the specimens fractured at high stresses. Inspection of the mirror zone at high magnification revealed a deviation of the {110} plane onto {111} crystallographic facets.
Molecular Dynamics Study of Copper and Aluminum under Mechanical Strain
Authors: Heino P. , Häkkinen H. , Perondi L. , Kaski K. 
Published: April 2011

AbstractMechanical properties of copper and aluminum have been studied using finite temperature molecular dynamics simulations. Atomic interactions have been described by a many-atom effective medium potential, which takes into account interactions up to third neighbors. The computed elastic constants showed good agreement with experimental data. Encouraged by these results the model was applied to study fracture in copper. Systems with a grain boundary and an initial cut serving as a crack seed have been studied. In the first case, crack nucleation and propagation took place exclusively at the grain boundary. In the second case, dislocation propagation was observed in one of the <110> directions, with a speed of about 60% of the longitudinal speed of sound. For thin systems crack propagation occurred through micro-void coalescence with a speed of about 30% of the Rayleigh wave speed in copper.
Finite Element Analysis of Thermal-Mechanical Stress Induced Failure in Interconnects
Authors: Yu X. , Weide K. 
Published: April 2011

AbstractIn this work a study of the nature as well as an evalution of the thermal-mechanical stress in aluminum interconnects was carried out. A theoretical model discribes the atom flux which can be induced by the relaxation of the stress. Based on this theory an algorithm has been developed and integrated into the finite element simulation software. This algorithm allows the calculation of the mass flux divergence and prediction of the failure location before the damage occurs. For the verification of this algorithm an aluminum pad structure sputtered on thermal oxide layer was used. The failure location was correlated with in situ observation during the long term stress tests. Experimental results confirm that the observed structure degradations correspond with the simulations very well.
Effect of Crack Blunting on the Ductile-Brittle Response of Crystalline Materials
Authors: Lipkin D.M. , Beltz G.E. , Fischer L.L. 
Published: April 2011

AbstractWe propose a self-consistent criterion for crack propagation versus dislocation emission, taking into account the effects of crack-tip blunting. Continuum concepts are used to evaluate the evolving competition between crack advance and dislocation nucleation as a function of crack- tip curvature. This framework is used to classify crystals as intrinsically ductile or brittle in terms of the unstable stacking energy, the surface energy, and the peak cohesive stresses achieved during opening and shear of the atomic planes. We find that ductile-brittle criteria based on the assumption that the crack is ideally sharp capture only two of the four possible fracture regimes. One implication of the present analysis is that a crack may initially emit dislocations, only to reinitiate cleavage upon reaching a sufficiently blunted crack-tip geometry.
Chemical Vapor Deposition (CVD) of Iridium and Platinum Films and Gas-Phase Chemical Etching of Iridium Thin Films
Authors: Xu Chongying , Dimeo Frank , Baum Thomas H. , Russell Michael 
Published: April 2011

AbstractChemical vapor deposition (CVD) of noble metal thin-films is increasingly important for future memory storage applications. Integration of ferroelectric perovskites and/or high permittivity oxides requires specialized metal interconnect technologies. Platinum and iridium are two preferred metal electrode materials being explored since they are highly resistant to corrosion and exhibit excellent stability at high temperatures. Further, the formation of stable oxides (IrO2) provides a mechanism for decreased inter-diffusion of oxygen and elemental film constituents, and provides improved reliability in silicon-based devices. CVD provides conformal electrode films that are required to achieve high-densities; high purity films of both platinum and iridium were deposited in this research, using (β-diketonate)Ir(I)L and (MeCp)Me3Pt(IV) as the precursors.Concurrently, chemical etching of these metals is highly desirable for creating patterns of the electrical contacts and for CVD reactor cleaning. To date, etching of noble metal electrodes has relied upon physical sputtering or chemically assisted etching. In this paper, we also report the first chemical etching of iridium films under ambient conditions, such as room temperature.
Nonlinear Dielectric Relaxation of Mn Doped Polycrystalline (Ba,Sr)TiO3 Thin Films Over the Temperature Range of 4.2 - 473 K
Authors: Baniecki J.D. , Laibowitz R.B. , Shaw T.M. , Duncombe P.R. , Kotecki D.E , Shen H. , Lian J. , Mat Q.Y. 
Published: April 2011

AbstractWe have investigated the dielectric relaxation currents of Mn doped polycrystalline Ba0.7Sr0.3TiO3 (BSTO) thin films as a function of applied electric field and temperature (4.2 - 473 K). The dielectric relaxation currents followed a power law time dependence, J(t) = Jot-n, over the entire temperature range. Plots of log(Jo) vs. reciprocal temperature were not linear and showed slopes approaching values of 0.35 eV at high temperatures which rapidly decreased to 0.25 meV at lower temperatures. The relaxation currents were found to be nonlinear with applied field. The observed nonlinearity of the field dependence of the relaxation currents can be understood in terms of the nonlinear relaxation component of the total capacitance. An equivalent circuit model for a paraelectric BSTO thin film capacitor is presented and possible polarization mechanisms are briefly discussed.
Correlations Between Composition, Texture, and Polarization in SrxBiyTa2O5+x+3y/2 Thin Films Deposited by MOCVD
Authors: Hendrix Bryan C. , Hintermaieri Frank , Desrochers Debra A. , Roeder Jeffrey F. , Baum Thomas H. , Dehm Christine , Nagel Nikolas , Honlein Wolfgang , Mazure Carlos 
Published: April 2011

AbstractSrxBiyTa2O5+x+3y/2 (SBT) is a promising material for ferroelectric random access memories (FeRAM's) because of its inherently high resistance to fatigue and imprint. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformal SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise control of film stoichiometry and thickness. In this study, wavelength dispersive x-ray fluorescence and x-ray diffractometry have been used to survey composition and preferred crystallographic orientation (texture) relationships. It is shown that as-deposited film composition can be used to influence the texture of the Aurivillius phase in the annealed film. The polarization of the films increases with increasing (115) and (200)/(020) peak intensity due to the relationship of the electric field direction with the polarization direction in the film. The highest values of polarization are found with Sr content, x<0.8 and Bi content, 2.1 <y<2.6.
Ultra-Thin PZT Films for Low-Voltage Ferroelectric Non-Volatile Memories
Authors: Wouters D.J. , Norga G.J. , Maes H.E. 
Published: April 2011

AbstractFor the possible application of PZT thin films in ferroelectric non-volatile memories, the potential of low-voltage switching is a major requirement. By straightforward thickness scaling down to 75nm, operation voltage can be reduced to 1.5V without degradation of the hysteresis properties. However, interface effects increase the coercive field for thinner films, so that operation voltage does not scale linearly with thickness. In view of the large difference in coercive field between bulk and thin-films, on the other hand, material (and interface) optimization may constitute an interesting alternative route for further voltage scaling. By optimizing the composition and stoichiometry, less than 1.5V switching has indeed been obtained even for 150nm films. It is argued that an important material parameter affecting low-voltage switching behavior is the ferroelectric domain configuration and presence/absence of mobile domain walls in the PZT film.
Study of Rf-Sputtered Ba(ZrxTi1−x)O3 Thin Films for Ulsi Dram Application
Authors: Lee Jian-Hung , Chen Tung-Sheng , Balu Venkatasubramani , Han Jeong , Mohammedali Razak , Gopalan Sundar , Wong Chun-Hui , Lee Jack C. 
Published: April 2011

AbstractBarium zirconate-titanate (Ba(ZrxTi1−x)O3, BZT) films with thickness around 60 nm were deposited on Ir substrates using RF magnetron sputtering. The effect of zirconium atomic fraction (x = 0.14 to 0.7), substrate temperature (380 °C to 550 °C) and oxygen partial pressure (0 to 5 mTorr with total pressure 30 mTorr) on leakage current, dielectric constant and dielectric dispersion (capacitance reduction with increasing frequency) was studied. We found that the Zr/Ti ratio played a crucial role in determining the dielectric constant and dispersion. The dielectric constant varies from 26 to 168 while dispersion ranges from 0.80 to 2.58 % loss in capacitance (dielectric constant) per decade of frequency. Low leakage currents (< 1× 10−7 A/cm2) were observed.
PMN Based Thin Film Capacitor for Decoupling Applications in High Speed Digital Circuits
Authors: Fukumaru F. , Nagakari S. , Konushi S. , Nishikawa H. , Kamigaki K. , Nambu S. 
Published: April 2011

AbstractA new type of Pb(Mgl1/3Nb2/3)O3 (PMN) based thin film decoupling capacitor for high speed digital circuits is presented. The thin film capacitor fabricated on a ceramic Al2O3 substrate with Ball Grid Array (BGA) terminations showed low impedance and low inductance characteristics in the 100MHz – 1GHz range. The sol-gel derived Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) thin film showed a high dielectric constant (k=3000) with broad temperature dependence. The capacitor consists of a PMN-PT thin film (0.8 µm thickness), Au electrodes, and solder balls mounted on the upper electrode as terminals. Numerical simulations based on the Partial Element Equivalent Circuit (PEEC) model were conducted for the design of electrodes, which gives low inductance of the capacitor. It was shown that the thin film 1.2mm × 1.2mm capacitor mounted on a board exhibits high capacitance of 20 nF, low ESR of 100 mΩ, and low inductance of 135 pH. These values are in good agreement with the results of numerical simulations.
Investigation of PZT//LSCO/IPT//Aerogel Thin Film Composites for Uncooled Pyroelectric Ir Detectors
Authors: Clem P.G. , Tuttle B.A. , Ruffner J.A. , Brinker C.J. , Schwartz R.W. , Rodriguez M. , Warren W.L. 
Published: April 2011

AbstractA monolithic thin film structure for uncooled pyroelectric infrared detector arrays was developed to integrate thermally isolated Pb(Zr,Ti)O3-based thin films on silicon, with a low thermal conductivity, aerogel thin film interlayer. Aerogel thin films of 0.4-1.2μm thickness and 70-85% porosity were deposited on silicon substrates by dip coating to form a thermal isolation layer. 200-400nm thick Pb(Zr0.4Ti0.6)O3 films deposited on (La,Sr)CoO3[LSCO]//Pt electrodes atop these aerogel films displayed a remanent polarization Pr = 28μ C/cm2, pyroelectric coefficient p = 30 nC/cm2K, and calculated noise equivalent temperature difference NETD = 0.07°C. Processing of Pb(Zr,Ti)O3 thin films atop the aerogel interlayer structure required modifications to deposition and heat treatment methods to minimize tensile stress accumulation. Effects of thermal processing and thin film stress state on ferroelectric properties are also reported.
Epitaxial Giant Magnetoresistive/Ferroelectric La0.7Ca0.3MnO.3/PbZr0.52Ti0.48O3 Thin Film Heterostructures
Authors: Grishin A. , Khartsev S. , Johnsson P. , Maneikis A. 
Published: April 2011

AbstractRecently, doped rare-earth manganates exhibiting colossal magnetoresistivity have been proposed to be used as the semiconductor channel material for a Ferrolectric Field Effect Transistor. Although the feasibility of epitaxial magnetoresistive/ferroelectric heterostructures have been demonstrated, the leakage in the ferrolectric layer and the strain induced degradation of the magnetoresitive layer remain a principal problem. We present results on fabrication and characterization of epitaxial giant magnetoresistive/ferrolectric La0.7Ca0.3MnO3(LCMO)/PbZr0.52TiO.48O3(PZT) heterostructures. The films have been prepared in situ by a KrF pulsed laser deposition technique on single crystal LaAlO3 substrates from stoichiometric LCMO and PZT targets. The main processing parameters have been optimized to preserve the existence of giant magnetoresitivity in the LCMO films after deposition of the top ferrolectric layer. A high degree of c-axis orientation and a strong in-plane texture coherent with the substrate both in template LCMO and PZT layers, high dielectric permittivity of 1800, remanent polarization of 0.2 C/m2 and a magnetoresistivity of 28% at H=0.5 T indicate excellent characteristics of coexisting magnetoresistive and ferroelectric properties.
Pulsed Laser Deposition of BaxSr1−xTiO3 Films on MgO, LaAlO3 and SrTiO3 for Tunable Microwave Applications
Authors: Chang Wontae , Horwitz James S. , Kim Won-Jeong , Pond Jeffrey M. , Kirchoefer Steven W. , Gilmore Charles M. , Qadri Syed B. , Chrisey Douglas B. 
Published: April 2011

AbstractSingle phase BaxSr1−xTiO3 (BST) films (∼0.5-7 μm thick) have been deposited onto single crystal substrates (MgO, LaAlO3, SrTiO3) by pulsed laser deposition. Silver interdigitated electrodes were deposited on top of the ferroelectric film. The room temperature capacitance and dielectric Q (1/tanδ) of the film have been measured as a function of electric field (≤80 kV/cm) at 1 - 20 GHz. The dielectric properties of the film are observed to strongly depend on substrate type and post-deposition processing. After annealing (≤1000° C), it was observed that the dielectric constant and % tuning decreased and the dielectric Q increased for films deposited onto MgO, and the opposite effect was observed for films deposited onto LaA1O3. Presumably, this change in dielectric properties is due to the changes in film stress. Very thin (∼50 Å) amorphous BST films were successfully used as a stress-relief layer for the subsequently deposited crystalline BST (∼5000 Å) films to maximize % tuning and dielectric Q. Films have been deposited from stoichiometric targets and targets that have excess Ba and Sr. The additional Ba and Sr has been added to the target to compensate for deficiencies in Ba and Sr observed in the deposited BST (x=0.5) films. Films deposited from compensated targets have higher dielectric constants than films deposited from stoichiometric targets. Donor/acceptor dopants have also been added to the BST target (Mn, W, Fe ≤4 mol.%) to further improve the dielectric properties. The relationship between the dielectric constant, the dielectric Q, the change in dielectric constant with electric field is discussed.
Interconnect-Related Degradation of PZT Capacitor for FeRAM
Authors: Kobayashi S. , Amanuma K. , Hada H. 
Published: April 2011

AbstractFerroelectric properties of a Pb(Zr,Ti)O3 (PZT) thin film capacitor with a conventional Al/TiN/Ti interconnect are seriously degraded by annealing at around 400°C. The degradation of the PZT capacitor is reduced as the interconnects are narrowed while the total area of the interconnects on the capacitor is fixed. This result cannot be understood by supposing that Ti diffusion into PZT degrades the ferroelectric properties. A possible cause for the degradation is stress placed on the PZT film during the 400°C annealing.
Depth and Time Dependence of Polystyrene Chain Diffusion Near the Polystyrene/Silicon Interface
Authors: Trzhemechny Y. , Hapovalov V. , Hou K. G. , Chwarz S. A. , Sokolov J. , Rafailovich M. H. 
Published: April 2011

AbstractWe report on the results for the diffusion coefficient (D*) of polystyrene (PS) chains near the PS/Silicon interface. The present study employs secondary ion mass spectrometry (SIMS) to examine diffusion from a deuterated marker layer in thin PS films on silicon. The observed SIMS depth profiles are fit to numerical simulations of the diffusion process. The best fit is obtained for a super-linear dependence of D* vs. distance from the silicon wall. A non-trivial time dependence extending over tens of hours is observed for all the models tested.
Buckling Dynamics of Tethered Membranes
Authors: Moldovan Dorel , Golubovic Leonardo 
Published: April 2011

AbstractWe investigate the dynamics of the classical Euler buckling of compressed solid membranes. We relate the membrane buckling dynamics to phase ordering phenomena. Membrane develops a wavelike pattern whose wavelength grows, via coarsening, as a power of time. Evolving membrane is similar to rough growing surfaces (“growing interfaces”) whose roughness grows as a power of time. Membrane buckling dynamics is characterized by a distinct scaling behavior not found in other coarsening phenomena
Studies Of The Polymer Thin Film Glass Transition Temperature Monitored With The Complex Viscoelastic Cofficients
Authors: White C. C. , Wu W. L. 
Published: April 2011

AbstractIn integrated circuit manufacturing, the gaps between metal lines are a critical parameter, and polymer films are being evaluated as low k dielectric materials for VLSI. Desire to maximize the number of elements within a given area to increase clock speed and decrease power consumption have forced the gaps to become increasingly smaller. Currently, 0.25–0.18 micron line widths are the subject of much commercial interest. A line width of 0.25 microns is within a factor of 5 of the molecular dimension of most commercial polymers. Experiments have suggested polymer films slightly smaller than these dimensions may not have the expected bulk mechanical properties. This deviation from the expected behavior (i.e., Change in the glass transition temperature) would present significant technical challenges to the manufacturing and reliability of integrated circuits. These effects are extremely difficult to determine experimentally with requisite precision. Recently, an experimental technique, based on a highly modified quartz crystal microbalance, has been developed to study the mechanical properties of these ultra-thin polymer films with high precision. The experimental details and preliminary results from this recently developed state-of-the-art experimental technique will be presented.