bluuebunny/crossref_metadata_2025 huggingface dataset:
Substrate-Induced Anomalous Electrical Transport and Magnetic Transitions in Epitaxial La0.66Sr0.33MnO3 Films Grown on (001) BaTiO3 Substrates
Authors: Nath T.K. , Lee M.K. , Eom C.B. , Smoak M. , Ryan P.A. , Tsui F.
Published: April 2011

Effects of drastic change of 3-dimensional films' lattice strain by substrate structural transformations on the transport and magnetic properties of tensile strained epitaxial La0.66Sr0.33MnO3 thin films were studied using (001) BaTiO3 as the templates. These films exhibit dramatic jumps in electrical resistance and magnetization at temperatures very close to different crystallographic structural change of BaTiO3 substrate. Application of high magnetic field (50 kOe) suppresses both the electrical transport and magnetization jumps. The observed low-field sharp transitions correspond sudden changes in magnetic anisotropy, caused by the structural transformation of the substrate. The magnetic easy axis lies in the film plane along [100] direction having a strong correlation with the substrate-induced 3-dimensional strain states as determined by the normal and grazing incidence x-ray diffraction. The sudden substrate structural transformations imposes an additional drastic sharp change of the film strain which is found to reorient the magnetic easy axis within the film plane.
Structural and Magnetic States in Layered Manganites: An Expanding View of the Phase Diagram
Authors: Mitchell J.F. , Millburn J.E. , Ling C. , Argyriou D.N. , Bordallo H. N.
Published: April 2011

Colossal magnetoresistive (CMR) manganites display a spectacular range of structural, magnetic, and electronic phases as a function of hole concentration, temperature, magnetic field, etc. Although the bulk of research has concentrated on the 3-D perovskite manganites, the ability to study anisotropic magnetic and electronic interactions made available in reduced dimensions has accelerated interest in the layered Ruddlesden-Popper (R-P) phases of the manganite class. The quest for understanding the coupling among lattice, spin, and electronic degrees of freedom (and dimensionality) is driven by the availability of high quality materials. In this talk, we will present recent results on synthesis and magnetic properties of layered manganites from the La2−2xSr1+2xMn2O7 series in the Mn4+-rich regime x > 0.5. This region of the composition diagram is populated by antiferromagnetic structures that evolve from the A-type layered order to G-type “rocksalt” order as x increases. Between these two regimes is a wide region (0.7 < x < 0.9) where an incommensurate magnetic structure is observed. The IC structure joins spin canting and phase separation as a mode for mixed-valent manganites to accommodate FM/AF competition. Transport in these materials is dominated by highly insulating behavior, although a region close to x = 0.5 exhibits metal-nonmetal transitions and an extreme sensitivity to oxygen content. We suggest two possible explanations for this transport behavior at doping just above x=0.5: localization by oxygen defects or charge ordering of Mn3+/Mn4+ sites.
Cation Ordering Structure in La0.8Ca0.2MnO3 Thin Films by Pulsed Laser Deposition
Authors: Li Y. H. , Rajeswari M. , Biswasl A. , Kang D. J. , Sehmen C. , Salamanca-Riba L. , Ramesh R. , Venkatesan T.
Published: April 2011

A careful analysis of high-resolution transmission electron microscopy images from La0.8Ca0.2MnO3 thin films indicates that the images can not explained based on either the classical Pnma structure or its monoclinic distortion. A cation ordered structure is proposed which could be responsible for the significantly higher Tc of the film (298K) compared with the bulk material of the same composition (190K).
Magnetotransport in Epitaxial Trilayer Junctions Fabricated from 90° Off-Axis Sputtered Manganite Films
Authors: Noh J. S. , Nath T. K. , Sun J. Z. , Eom C. B.
Published: April 2011

We report studies on La1−xSrxMnO3 /SrTiO3/ La1−xSrxMnO3 (x=0.33) trilayer junctions made using 90° off-axis sputtering. Both (110) NdGaO3 and (001) (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) are used for substrates. Optical lithography is used for junction formation. These sputtered trilayers show improved junction resistance uniformity over trilayers made using laser ablation. A magnetoresistance of ∼100% is observed for junctions on LSAT with 30 Å barrier at 13 K and around 100 Oe. The shape of junction magnetoresistance vs. field depends both on barrier thickness and on substrate type, suggesting that both inter-layer coupling and substrateinduced-strain play a role in determining the junction's micromagnetic state. These results indicate better junction interfaces can be obtained for manganite trilayer junctions by 90° off-axis sputtering.
30 GHz Electronically Steerable Antennas Using BaxSr1−xTiO3-Based Room-Temperature Phase Shifters
Authors: Carlson C. M. , Rivkin T. V. , Parilla P. A. , Perkins J. D. , Ginley D. S. , Kozyrev A. B. , Oshadchy V. N. , Pavlov A. S. , Golovkov A. , Sugak M. , Kalinikos D. , Sengupta L. C. , Chiu L. , Zhang X. , Zhu Y. , Sengupta S.
Published: April 2011

We report the performance of 16-element phased array antennas operating at 30 GHz and ambient temperature. These antennas use BaxSr1−xTiO3(BST)-based phase shifters to produce the beam steering. Ferroelectric phase shifters offer advantages over current semiconductor and ferrite devices including faster switching speeds and lower costs. Also, ferroelectric phase shifters offer higher power handling capability than semiconductor devices and also have high radiation resistance. We made phase shifters from laser-ablated epitaxial BST films as well as from polycrystalline BST-oxide composite films. Although neither the devices nor the materials themselves are fully optimized, phase shifters have shown > 360° of phase shift with < 350 V DC bias (E < 9 V/µm) and ∼8 dB insertion loss. With ferroelectric phase shifters incorporated, antennas show radiation patterns with central-lobe half-power widths of ∼13° and side lobe intensities down by more than 10 dB. Using the phase shifters, the central lobe can be shifted, or “steered,” by ±18° in either direction. These results demonstrate a first step toward a prototype steerable antenna for 20–30 GHz satellite communications as well as other applications.
Near-Field Imaging of the Microwave Dielectric Properties of Single-Crystal PbTiO3 and Thin-Film Sr1−xBxTiO3
Authors: Wang Y.G. , Reeves M.E. , Chang W. , Horwitz J.S. , Kim W.
Published: April 2011

A PbTiO3 crystal and Sr1−xBaxTiO3 films have been studied by near-field scanning microwave microscopy (SMM). In the PbTiO3 crystal, dielectric properties and topography are obtained simultaneously. In Sr1−xBaxTiO3 films, local variations and sample-to-sample differences are observed. To quantitatively determine local dielectric permittivity and loss, we also carry out theoretical calculations on dependence of resonant frequency and quality factor on dielectric constants of bulk samples and thin films. Good agreements between experimental and theoretical results are obtained.
Tunable Dielectric Thin Films for HTS Microwave Applications
Authors: Moeckly B. H. , Zhang Y. M.
Published: April 2011

SrTiO3 (STO) thin films are promising for a variety of applications requiring tunability. We describe the growth and characterization of STO thin films including their dielectric properties. We also present attempts at reducing the loss tangent of these films, and we discuss their integration with high-temperature superconductor (HTS) microwave filters for trimming purposes.
Ferrites for Tunable RF and Microwave Devices
Authors: Dionne Gerald F.
Published: April 2011

Microwave systems for communications and radar require control of propagation of the rf signal. Devices that accomplish this function include phase shifters, isolators and circulators, and tunable filters. In many instances, these devices are magnetic and are based on the variable permeability of electrically insulating ferrimagnetic oxides (ferrites). Recent advances in microwave ferrite devices have featured superconductor circuitry that promises to virtually eliminate insertion losses due to rf surface resistance. Lower conduction losses allow the use of small lightweight microstrip configurations in place of traditional bulky waveguide structures. For operation at cryogenic temperatures ferrimagnetic spinels and garnets will require chemical alteration to realize the full potential of these devices. Challenges include the reduction of magnetocrystalline anisotropy to optimize switching energies and speeds, and the elimination of fast-relaxing impurities in the magnetic garnets that can increase magnetic losses and degrade resonator Q factors at low temperatures.
The Influence of the Initial Supersaturation of Si Interstitial Atoms on the Relative Thermal Stability of Dislocation Loops in Silicon
Authors: Cristiano F. , Colombeau B. , Mauduit B. de , Giles F. , Omri M. , Claverie A.
Published: April 2011

In this work, we have studied the relative stability of perfect (PDLs) and faulted (FDLs) dislocation loops formed during annealing of preamorphised silicon. In particular, we have investigated the effect of the initial supersaturation of Si interstitial atoms (Si(int)s) created by the implantation process on their thermal evolution. Transmission Electron Microscopy analysis shows that in samples with a low Si interstitial supersaturation, FDLs are the dominant defects while PDLs appear as the most stable defects in highly supersaturated samples. We have calculated the formation energies of both types of dislocation loops and found that, for defects of the same size, FDLs are more energetically stable than PDLs, if their diameter is smaller than 80 nm and viceversa. The application of these calculations to the samples studied in this work indicates that a direct correspondence exists between the formation energy of the two defect families and the number of atoms bound to them. Moreover, we have shown that the relative stability of FDLs and PDLs depends on the initial supersaturation of Si(int)s created during the implantation process.
Ultra-shallow Junction Formation via GeB- ion Implantation of Si
Authors: Lu Xinming , Shao Lin , Jin Jianyue , Li Qinmian , Rusakova I. , Chen Q. Y. , Liu Jiarui , Chu Wei-Kan , Ling Peiching
Published: April 2011

GeB− Cluster ions have been used to effectively produce 0.65-2keV boron for low energy ion implantation. We have generated the GeB− cluster ions using the SNICS ion source (source of negative ion by cesium sputtering). Shallow junctions have been made by the GeB− cluster ions implanting into Si substrates at 15keV, 1×1015/cm2 and 5keV, 5×1014/cm2. The junction depth as small as 37nm has been achieved by rapid thermal annealing of the 5 keV sample at 1000°C for 1 second. A two-step annealing was also performed to study the diffusion of B in the GeB− ion cluster implanted Si by annealing the 15 keV implanted sample at 550°C/300sec+1000°C/10sec. We found that the junction depth of the two-step annealed sample was only half of the one-step annealed sample. TEM (transmission electron microscopy) showed clear recrystallization of the amorphized layer with no observable residual defects. We briefly discussed the role of Ge in regards to reduction of the junction depth.
Dopant - Extended Defects Interactions: The Case of Aluminum
Authors: Ortiz Ch. , Mathiot D. , Dubois Ch. , Alquier D. , Jérisian R.
Published: April 2011

We studied the Al redistribution in the vicinity of a well-defined EOR band formed by Ge pre-amorphization. Aluminum was implanted in Si at 3 MeV to a low dose before the preamorphization step in order to localize the as-implanted Al peak away from the EOR band. Rapid thermal annealings were performed in the temperature range [900-1000°C] for times varying from 20 s up to 200 s. The results of this study evidence a clear accumulation of the dopant on the extended defects, indicating a direct trapping mechanism of the dopant by the EOR.
Diffusion Engineering by Carbon in Silicon
Authors: Goesele Ulrich , Laveant Pierre , Scholz Rene , Engler Norbert , Werner Peter
Published: April 2011

The possibility to suppress undesirable diffusion of the base dopant boron in siliconbased bipolar transistor structures by the incorporation of a high concentration of carbon has lead to renewed interest in the behavior of carbon in crystalline silicon. The present paper will review essential features of carbon in silicon including solubility, diffusion mechanisms and precipitation behavior. Based on this information the possibilities to use carbon to influence diffusion of dopants in silicon by the introduction of non-equilibrium concentrations of intrinsic point defects will be discussed as well as the reason for the relatively high resilience against carbon precipitation. Interactions between carbon and oxygen will be mentioned, especially in the context of an as yet unexplained fast out-diffusion of carbon close to the surface.
Clustering Equilibrium and Deactivation Kinetics in As doped Si
Authors: Nobili Dario , Solmi Sandro , Shao Jenta , Merli Marco
Published: April 2011

Clustering equilibrium was studied on silicon on insulator specimens uniformly doped with As at concentrations CAs up to 7.6 × 1020 cm−3. Values of the carrier density n* after equilibration at 700, 800 and 900°C are reported. It is shown that both the concentration and the temperature dependence of n* can be accurately simulated by a simple cluster model detailed in the Appendix. The analysis of the clustering kinetics of these compositions was performed at temperatures in the range 550 to 800°C. It is found that at 800°C the kinetics accurately complies with the rate equation:

-dn/ dt = A{exp[-(E-αn)/kT] - (n0- n)/( n0- n*) exp[-(E-αn*)/kT]

which is the one reported in Ref.[14] complemented by the second term on the right to account for the declustering process. Deviations leading to rates lower than predicted by the above equation are observed by annealing at lower temperatures. The dependence of this phenomenon on composition and temperature is reported.
Quantitative Depth Profiles of Vacancy Cluster Defects Produced by MeV Ion Implantation in Si: Species and dose Dependence
Authors: Kalyanaraman R. , Haynes T.E. , Jacobson D.C. , Gossmann H.-J. , Rafferty C.S.
Published: April 2011

Monte Carlo simulation codes such as TRIM or MARLOWE show a net displacement of interstitials with respect to vacancies from the Frenkel pairs produced in implant cascades. As a result, defect profiles after recombination have an excess of vacancies (Vex) in the shallow region of these implants, with excess interstitials near the projected range Rp. Typically, accurate estimates of the Vex distribution are computer intensive as the complete history of each damage cascade must be recorded. In this work we introduce a method for fast estimation of the Vex profile based on the derivative of the recoil distribution obtained from binary collision simulations using the Kinchen-Pease approximation for damage production. Also, Au labeling has been used to quantitatively analyze and compare the experimental depth profiles of Vex produced by implants of B, Si, and Ge into Si for a range of doses. Specific conditions like matching of the projected range of the implanted ions and matching of the number of Frenkel pairs created have been compared. This detailed study and comparison with simulation provides the first systematic, quantitative measurements of the Vex concentrations over such a range of species and doses. In analogy to the “+ number” for excess interstitials from ion implantation, we determine the range of “minus (-) numbers”, that is the number of excess vacancies per implanted ion for the different species. For Si it is constant in the dose range studied at -0.05, while for B it is -0.001 to -0.004 and for Ge, -0.1 to -0.2. The general shapes of the Vex profiles are similar to those obtained from simulation. Evidence is presented that one significant difference, namely an experimentally observed vacancy depletion near the surface, may be due to the diffusion and annihilation of vacancies at the surface. In addition, an increased nucleation probability of vacancy defects close to Rp may account for the growth of excess vacancies from close to Rp towards the surface with increasing implant dose.
Epitaxial CoSi2 formation by a Cr or Mo interlayer
Authors: Detavernier C. , Van Meirhaeghe R.L. , Cardon F. , Maex K. , Brijs B. , Vandervorst W.
Published: April 2011

We have studied CoSi2 formation in the presence of a Cr or Mo interlayer or capping layer. We shall show that, contrary to what was previously reported, Cr and Mo may be used as interlayers to grow epitaxial CoSi2. However, unlike for Ti, the thickness of the interlayer is very important. If the Cr or Mo interlayer is too thick (> 5 nm), polycrystalline CrSi2 or MoSi2 are formed first and epitaxial growth of CoSi2 becomes impossible. However, both XRD and random/channeling RBS results indicate that for a 2-3 nm interlayer of Cr or Mo, CoSi2 forms epitaxially on Si(100). For thinner interlayers, there is a preferential (220) and (400) orientation. This can be explained by the presence of Cr or Mo on the CoSi grain boundaries, which will affect the heterogeneous nucleation of CoSi2.
A Closer “Look” at Modern Gate Oxides
Authors: Baumann Frieder H. , Chang C.-P. , Grazul John L. , Kamgar Avid , Liu C. T. , Muller David A.
Published: April 2011

Using high resolution TEM (HRTEM), we identified some process induced ‘weak spots’ in SiO2 layers: First, we observed thinning in the periphery of the transistor, i. e. near the boundary to the shallow trench isolation. At the boundary to the shallow trench, the Si substrate gradually changes its orientation from <100> to <110>, which results in an unexpected oxidation behavior in this region. Secondly, we observed the intrusion of poly-Si grains from the gate into the gate oxide, resulting in local thinning of the dielectric. Using image simulations, we show that conventional high resolution TEM can reveal the interface roughness only to a very limited extend.
A Two-Step Spacer Etch for High-Aspect-Ratio Gate Stack Process
Authors: Yu Chien , Wise Rich , Domenicucci Anthony
Published: April 2011

A highly selective nitride etch was developed for gate stack spacer process in advanced memory programs. Based on methyl fluoride chemistry with better than 8:1 selectivity of nitride:oxide, this process exhibits minimal erosion to the underlying RTO thermal oxide for consistent diffusion ion-implant control. As the groundrule changed to 0.175um and below, a two-step etch scheme was employed to maintain the profile control in high-aspect-ratio structures. The stability and repeatability of the process is demonstrated in the SPC chart of the post etch FTA site measurement.
Formation and Electrical Transport Properties of Nickel Silicide Synthesized by Metal Vapor Vacuum Arc Ion Implantation
Authors: Zhang X. W. , Wong S. P. , Cheung W. Y. , Zhang F.
Published: April 2011

Nickel disilicide layers were prepared by nickel ion implantation into silicon substrates using a metal vapor vacuum arc ion source at various beam current densities to an ion dose of 6×1017 cm−2. Characterization of the as-implanted and annealed samples was performed using Rutherford backscattering spectrometry, x-ray diffraction, electrical resistivity and Hall effect measurements. The temperature dependence of the sheet resistivity and the Hall mobility from 30 to 400 K showed peculiar peak and valley features varying from sample to sample. A two-band model was proposed to explain the observed electrical transport properties.
A Low-Cost BiCMOS Process with Metal Gates
Authors: van Zeijl H.W. , Nanver L.K.
Published: April 2011

A low-complexity and low-cost double-metal BiCMOS process is proposed with only 13 mask steps. By decoupling the source-drain thermal budget from gate-stack formation, metal gates are realizable.
Using Wafer-Scale Patterns for CMP Analysis
Authors: Lee Brian , Gan Terence , Boning Duane S. , David Jeffrey , Bonner Benjamin A. , McKeever Peter , Osterheld Thomas H.
Published: April 2011

A new set of wafer-scale patterns has been designed for analysis and modeling of key CMP effects. In particular, the goal of this work is to develop methods to characterize the planarization capability of a CMP process using simple measurements on wafer scale patterns. We examine means to pattern large trenches (e.g. 1 to 15 mm wide and 15 mm tall) or circles across 4” and 8” wafers, and present oxide polish results using both stacked and solo pads in conventional polish processes. We find that large separation (15 mm) between trenches enables cleaner measurement and analysis. Examination of oxide removal in the center of the trench as a function of trench width shows a saturation at a length comparable to the planarization length extracted from earlier studies of small-scale oxide patterns. Increase in polish pressure is observed to decrease this saturation point. Such wafer scale patterns may provide information on pad flexing limits in addition to planarization length, and promise to be useful in both patterned wafer CMP modeling and studies of wafer scale CMP dependencies such as nanotopography.
Fundamental Studies on the Mechanisms of Oxide CMP
Authors: Mahajan Uday , Lee Seung-Mahn , Singh Rajiv K.
Published: April 2011

In this paper, results of studies on the addition of salt to a polishing slurry, in terms of its effect on slurry stability, SiO2 polishing rate and surface roughness of the polished surface are presented. Three salts, viz. LiCl, NaCl and KCl were selected, and three concentrations were tested. Polishing rate measurements using these slurries show that adding salt leads to increased removal rate without affecting surface roughness significantly. Based on these results, we can say that the agglomerates formed by adding salt to the slurry are fairly soft and easily broken during the polishing process. In addition, turbidity and particle size measurements show that significant coagulation of the particles in the slurry occurs only at the highest salt concentration, and is fastest for LiCl and NaCl, with KCl showing the slowest coagulation. From these results, it can be concluded that the enhancement in polish rate is due to increased contact at the wafer-pad-slurry interface, and not due to formation of larger agglomerated particles in the slurry. This is because of reduced electrostatic repulsion between these three surfaces, due to the screening of their negative surface charge by the metal ions in solution, resulting in a higher wear rate.
Chemical Wear of Cu CMP
Authors: Liang Hong
Published: April 2011

In this work, we used surface analysis techniques, such as a field-emission highresolution analytical TEM, X-ray spectroscopy, and XPS to analyze abrasive particles after polishing. Results showed evidence of copper oxide (Cu2O) in the polished slurry. However, there was no metallic crystalline copper detected. After comparing these data with the results obtained from our electro-chemical experiments, we propose two possible chemical wear mechanisms in Cu CMP.
A Novel Single Step Lapping and Chemo-Mechanical Polishing Scheme for Antimonide Based Semiconductors Using 1 µm Agglomerate-Free Alumina Slurry
Authors: Dutta P.S. , Gutmann R.J. , Keller D. , Sweet L.
Published: April 2011

A novel approach for a single step lapping and chemical-mechanical polishing of antimonide-based III-V compounds using agglomerate-free alumina slurries is presented. Relatively high removal rates, minimal scratching, and low surface roughness have been obtained. The effects of slurry preparation cycle on the slurry properties and chemomechanical polishing results are discussed.
An Image Analysis Technique For Assessing Particle Size And Agglomeration Tendency Of Slurries
Authors: Machinski Susan R. , Richardson Kathleen A. , Dogariu Aristide
Published: April 2011

Understanding the time-dependent behavior and size of particulate systems, specifically, particles in abrasive slurries, is a key part of chemical mechanical polishing (CMP). Microscopy and image analysis enables both qualitative and quantitative analysis of particle interaction behavior in diluted samples of such particulate suspensions. A technique using microscopy and image analysis has been developed specific to the analysis of suspensions of, micron size or larger, abrasive particle slurry systems. This technique has been applied to aluminum oxide (Al2O3) slurries and measurements of particle size and stability have been obtained with good accuracy and precision.
Removal Rate, Uniformity and Defectivity Studies of Chemical Mechanical Polishing of BPSG Films
Authors: Bonner Benjamin A. , Fishkin Boris , David Jeffrey , Garretson Chad , Osterheld Thomas H.
Published: April 2011

Wafers where deposited with BPSG films having phosphorus concentration varying from 3.65 to 6.25% and boron concentration varying from 4 to 5.7%. These wafers were polished using CMP and the rates were found to depend on dopant concentrations. A fit to the data indicated that removal rates were more than 3 times as sensitive to boron concentration compared to phosphorus concentration. For a constant phosphorus concentration of 5%, each percent increase in boron increases CMP removal rate by 340 Å/min. For a constant boron concentration of 5%, each percent increase in phosphorus increases CMP removal rate by 96 Å/min.
Dry Etching of MRAM Structures
Authors: Pearton S.J. , Cho H. , Jung K.B. , Childress J.R. , Sharifi F. , Marburger J.
Published: April 2011

A wide variety of GMR and CMR materials have been patterned by high density plasma etching in both corrosive (Cl2-based) and non-corrosive (CO/NH3) plasma chemistries. The former produce much higher etch rates but require careful in-situ or ex-situ, post-etch cleaning to prevent corrosion of the metallic multilayers. The former may have application for shallow etching of NiFe-based structures, but there is little chemical contribution to the etch mechanism and mask erosion can be a problem. The magnetic performance of patterned MRAM elements is stable over long periods (>1 year) after etching in Cl2 plasmas, provided a suitable cleaning protocol is followed. It is also clear that high ion energies during patterning of magnetic materials can have a significant influence on their coercivity. The effects of ion energy, ion flux and process temperature are discussed.
Selective Area Chemical Vapor Deposition of Chromium Oxides
Authors: Cheng Ruihua , Borca C.N. , Dowben P.A.
Published: April 2011

We demonstrate that two-phase CrO2 and Cr2O3 thin films can be grown by using selective organometallic chemical vapor deposition through the oxidation of Cr(CO)6 in an oxygen environment. While the magnetization measurements show that both chromium oxides are present, the relative weight of each phase depends on the oxygen partial pressure. Changes of the Curie temperature, Tc, and the saturation magnetization field may be possible by controlling the stoichiometry.
TEM to Support Magnetic Media Development in YR2000
Authors: MoberlyChan Warren J. , Dorsey Paul , Nolan Tom , Alex Michael , Yamashita Tom
Published: April 2011

TEM provides fast and statistical support for magnetic recording media development. Turn-around time including sample preparation, data collection and computer analysis is reduced to ∼3 hours. Rapid, systematic TEM analysis is shown to accurately measure crystallographic Orientation Ratio (OR) on mechanically textured media by diffraction analysis; elucidate grain separation by Weak Beam Dark Field Imaging; and determine the crystallographic relationship between cubic-NiAl seed layers and hexagonal cobalt-alloy (Co) layers. Novel evidence for reduction of the number of preferred orientations in sequentially grown epitaxial films is presented, which explains the “2-&-1/4-D isotropic” growth orientation and the high magnetic squareness of Co media grown on nearly randomly oriented “3D-isotropic” NiAl underlayers.
Microstructures and Soft Magnetic Properties of High Saturation Magnetization Fe-Co-N alloy Thin Films
Authors: Sun N. X. , Wang S. X. , Hung Chin-Ya , Chien Chester X. , Tong Hua-Ching
Published: April 2011

High saturation magnetization soft magnetic materials are required for future high-density recording heads as well as high frequency inductors. In this work, (Fe0.7Co0.3)1−xNx (or in short FeCoN) alloy films were synthesized with a high saturation magnetization of 24.5 kG, a hard axis coercivity of 5 Oe, an easy axis coercivity of 18 Oe, and a resistivity of 55 μΩcm. The FeCoN film sandwiched between two permalloy layers (5 nm) shows very good magnetic softness, a low hard axis coercivity of 0.6 Oe, an easy axis coercivity of 7.8 Oe, an excellent in-plane uniaxial anisotropy with an anisotropy of about 20 Oe, an initial permeability of 1000, and a roll-off frequency of 1.5 GHz. In order to understand the effect of the permalloy layers on the FeCoN layer, we fabricated four film structures: single layer FeCoN film; FeCoN film sandwiched between two permalloy layers on both sides; FeCoN film with one permalloy layer as the underlayer; and FeCoN film with one permalloy layer as caplayer. All these film structures were both magnetically and structurally characterized and compared. Structural characterization shows that there is no significant difference in the grain size of the FeCoN single layer and the FeCoN layer sandwiched between two permalloy layers. The four film structures have almost the same amount of compressive stress, about −300 MPa; and their saturation magnetostriction constants are also very close, in the range of 39.6×10−6 to 44.3×10−6. Difference in the crystallographic textures was observed in the pole figures for the FeCoN single layer and FeCoN film with permalloy underlayer.
Structural and Elastic Response of Mo/Ni Multilayers to Ion Irradiation
Authors: Pacaud Jérôme , Martin Franck , Michel Anny , Jaouen Christiane , Djemia Philippe , Ganot François
Published: April 2011

Mo/Ni multilayers are investigated by x-ray diffraction and Brillouin light scattering before and after ion induced stress relaxation and mixing. Study of the evolution of interplanar distances in both layers as a function of the period exhibits a strong anomaly of the Mo (110) distance (in the growth direction) that can be correlated with the elastic anomaly. The very low interplanar distance in the molybdenum layers found after stress relaxation seems to favor an explanation of this behavior based on the diffusion of Ni in the Mo layers during the growth.
Lateral and Vertical Ordering of PbSe Self-Assembled Quantum Dots in PbSe/PbEuTe Superlattices
Authors: Holý V. , Stangl J. , Springholz G. , Pinczolits M. , Bauer G.
Published: April 2011

The shape and the positions of self-organized PbSe quantum dots embedded in PbEuTe are studied by means of grazing-incidence small angle x-ray scattering and x-ray diffraction. Using a detailed numerical analysis of the measured x-ray data, we have determined a truncated pyramidal shape of the free-standing dots. The type of the lateral dot ordering depends substantially on the period of the PbSe/PbEuTe superlattice. In the case of smaller periods, the lateral ordering of the dots obeys a short-range order model and we have determined the statistical properties of the dot arrangement. For intermediate spacer thicknesses the dots form a hexagonal lattice. For larger periods, the dots are completely uncorrelated and their distribution can be described as a two-dimensional ideal gas. From coplanar x-ray diffraction we have determined additionally the vertical correlation of the dot positions changes from a mere vertical correlation for small superlattice periods, to a distorted trigonal lattice for the intermediate periods. For the largest period, no vertical correlation of dot positions is observed.
InGaAs/GaAs Quantum Dot Interdiffusion Induced by Cap Layer Overgrowth
Authors: Jasinski J. , Babinski A. , Czeczott M. , Bozek R.
Published: April 2011

The effect of thermal treatment during and after growth of InGaAs/GaAs quantum dot (QD) structures was studied. Transmission electron microscopy and atomic force microscopy confirmed the presence of interacting QDs, as was expected from analysis of temperature dependence of QD photoluminescence (PL) peak. The results indicate that the effect of post-growth annealing can be similar to the effect of elevated temperature of capping layer growth. Both, these thermal treatments can lead to a similar In and Ga interdiffiusion resulting in a similar blue-shift of QD PL peak.
Optoelectronic Device Applications of Self-Organized In(Ga,Al)As/Ga(Al)As Quantum Dots
Authors: Bhatiacharya P. , Krishna S. , Zhu D. , Phillips J. , Klotzkin D. , Qasaimeh O. , Zhou W. D. , Singh J. , Mccann P. J. , Namjou K.
Published: April 2011

Self-organized growth of strained semiconductor heterostructures has enabled the realization of ordered arrays of quantum dots that can be incorporated into the active region of electronic and optoelectronic devices. Highly uniform In(Ga)As/Ga(Al)As with greatly reduced photoluminescence linewidths (FWHM=19 meV, T=17K) have been grown and characterized. Various aspects of carrier dynamics in these dots, such as measurement of carrier relaxation times and the modulation bandwidths of quantum dot lasers, estimation of the tunneling time in vertically coupled dots along with tuning of the intersubband electronic energy levels have also been studied. The favorable relaxation times can be exploited to realize far infrared emission and detection based on intersubband transitions in the dots. The optoelectronic properties of the dots and the dynamics of carriers therein are also extremely attractive for high-speed wavelength switching and the design of electro-optic modulators. The electro-optic coefficients in the quantum dots have been measured and the linear E-O coefficient, r1 =2.6 ×10−11m/V, is found to be comparable to that in LiNbO3
Formation of Continuous Nanometer PtSi Thin Film on Si by Pulsed Laser Deposition (PLD)
Authors: Li Meicheng , Chen Xuekang , Wang Jing , Yang Jianping , Lei Zhanxu , Wu Gan , Zhao Liancheng
Published: April 2011

Metal-based silicides on silicon substrates are a widely used material system for infrared detection. PtSi/p-Si infrared Schottky barrier detectors (IRSBD) have become one of the most successful photoemisive infrared detectors. Till now, most of the efforts have been focused on the design of two dimensional PtSi-SBD arrays for the infrared (IR) camera. In this paper, we discussed the formation conditions of PtSi. Qualities are compared for PtSi films prepared at different conditions including different annealing sequences, annealing time, film thickness, and annealing ambient using pulsed laser deposition on various temperature substrates. Film structures and compositions, phase's formation using different processes are analyzed. By studying the kinetics of PtSi formation during various annealing processing, preferable preparing conditions are proposed to form the continuous PtSi ultra-thin film on Si substrate by PLD.
Effect of Copper-Induced Recrystallization on the Piezoresistivity of Germanium Films
Authors: Khakifirooz A. , Mohajerzadeh S. S. , Haji S. , Soleimani E. Asl
Published: April 2011

Effect of copper-induced recrystallization on the piezoresistivity of germanium films is reported. SEM and XRD are used to study the crystalline structure of the films, while RBS, PIXE, and EDX are utilized to investigate their composition. Significant grain growth is observed in Ge films, upon annealing a Cu/Ge bilayer at 400°C for 30 minutes. Also a dominant orientation of Ge(111) is observable when amorphous precursor films are used. Hall measurements and cantilever beam bending show a considerable increase in hole mobility and longitudinal gauge factor, respectively
Formation of Self-Assembled Nanometer-Scale InP Islands on Silicon Substrates
Authors: Bakin A.S. , Piester D. , Wehmann H.-H. , Ivanov A.A. , Schlachetzki A. , Becker K.D.
Published: April 2011

Three-dimensional islands of InP have been reproducibly grown in the Stranski-Krastanow growth mode on Si (001) and (111) by using metal-organic vapor phase epitaxy in order to obtain nanometer-scale quantum dots. Atomic-force microscopy was used to determine the morphology of the samples and to evaluate the dimensions of the islands. Formation of three-dimensional islands with densities as high as 2.5×1010 cm−2 and small sizes have been observed. The evolution of island morphology is explained in terms of strain-relaxing mechanisms at the first stages of InP/Si heteroepitaxy.
X-ray Photoelectron Spectroscopy Evaluation on Surface Chemical States of GaN, InGaN and AlGaN Heteroepitaxial Thin Films Grown on Sapphire by MOCVD
Authors: Li K. , Wee A.T.S. , Lin J. , Feng Z. C. , Chua S.J.
Published: April 2011

The surface chemical states of MOCVD grown GaN, AlGaN and InGaN, and the influence of different dopants have been studied with x-ray photoelectron spectroscopy (XPS). The results show that for most of the samples the N 1s peak can be fitted with a dominant GaN peak at the binding energy of 397.2 ± 0.2 eV and a small N-H peak at the binding energy of 398.5 ± 0.2 eV, while Ga 3d can be deconvoluted into three peaks, i.e., elemental Ga at 18.5 ± 0.1 eV, GaN at 19.7 ± 0.1 eV, and Ga2O3 at 20.4 ± 0.1 eV. Si-doping appears to have small influence on the surface chemical states of GaN. Compared with Si-doping, the influence of Mg-doping appears -to be larger. In addition to a change in the component intensities, Mg-doping also causes the N ls and Ga 3d peaks to broaden. The ternary AlxGa1−xN (x ∼ 0.025) sample shows aluminum surface segregation, while the undoped InxGa1−xN(x ∼0.12) shows indium surface deficiency
New Tools to Control Morphology of Self-Organized Quantum Dot Nanostructures
Authors: Shchukina V.A. , Ledentsova N.N. , Ustinov V.M. , Musikhin Yu.G. , Volovik V.B. , Schliwa A. , Stier O. , Heitz R. , Bimberg D.
Published: April 2011

We consider several approaches to control morphology of self-organized quantum dot (QD) nanostructures. (i) We study effects of temperature and of temperature ramping on formation of QD arrays. The theory of equilibrium distribution of island volumes is developed predicting an entropy-driven decrease of island volume at higher temperatures. Experiments on InAs/GaAs(001) obtained both at submonolayer deposition and in Stranski-Krastanow (SK) growth mode reveal the decrease of island volume with temperature increase that agrees with the thermodynamic picture of island formation. (ii) We show a reversibility of temperature-driven changes in island volume, shape, and density for SK InAs/GaAs(001) islands and a new possibility to control QDs. (iii) We consider an advanced way of formation of complex QD structures. For multisheet arrays of strained islands a transition between correlation and anticorrelation driven by the spacer thickness is predicted theoretically and confirmed experimentally. (iv) The overgrowth of InAs/GaAs islands by an InGa(Al)As alloy leads to alloy phase separation in the capping layer and an effective increase of both the lateral size and the height of the QDs. These complex growth approaches enable us to tune efficiently electronic spectra of the QD systems.
The Effect of Magnesium Oxide Buffer on the Epitaxial Growth of Zinc Oxide on Sapphire
Authors: Chen Y.F. , Ko H.J. , Hong S.K. , Hanada T. , Yao T. , Segawa Y.
Published: April 2011

ZnO single crystal thin film is grown on Al2O3(0001) substrate by plasma-assisted molecular beam epitaxy employing a thin MgO buffer layer. Using reflection high-energy electron diffraction (RHEED), we investigated the surface morphology evolution during the buffer and ZnO growth. We found that a few nanometers thick MgO layer deposited on Al2O3(0001) substrate strongly influences the subsequent growth of ZnO by promoting lateral epitaxial growth, which eventually leads to an atomically flat surface. As a result, (3×3) surface reconstruction of ZnO is observed and RHEED intensity oscillations are recorded. Structural investigations indicate that MgO with rock-salt crystallographic structure forms on the Al2O3(0001) surface as a template between the substrate and ZnO epilayer. Above that, the ZnO epilayer grows with little strain. The mosaicity in the ZnO film is suppressed by more than two orders as indicated by both symmetric and asymmetric X-ray rocking curves. The twin defect with a 30° in-plane crystal orientation difference is completely eliminated. Free exciton emissions at 3.3774 eV (XA) and 3.383 eV (XB) are observed in photoluminescence at 4.2 K further indicating the high quality of the resulting ZnO epilayers.
Kinetic Roughening of Multilayer Ag/Ag(100) Films: Complex Temperature-Dependence in a Simple System
Authors: Stoldt C.R. , Caspersen K.J. , Bartelt M.C. , Jenks C.J. , Evans J.W. , Thiel P.A.
Published: April 2011

Metal(100) homoepitaxial systems constitute perhaps the simplest class of systems in which to study thin film growth. Yet, our Variable-Temperature Scanning Tunneling Microscopy (VTSTM) analysis of Ag/Ag(100) homoepitaxy reveals that the variation of roughness with temperature is extraordinarily complex. As the deposition temperature is reduced from 300K to 50K, the roughness of 25 monolayer films first increases, then decreases, and then increases again. Furthermore, a transition from mound formation to self-affine (semi-fractal) growth occurs at around 135K. We postulate that the following the atomistic mechanisms underly this behavior: the existence of a small step-edge barrier inhibiting diffusive downward transport; “downward funneling” of atoms deposited at step edges and microprotrusions towards lower four-fold hollow adsorption sites; and statistically significant deviations from “complete” downward funneling at lower temperatures, where deposited atoms instead become trapped on the sides of (the more prevalent) small steep microprotrusions. To support these postulates, we employ kinetic Monte Carlo simulations to show that atomistic (lattice-gas) models for epitaxial growth, which incorporate these mechanisms, reproduce the experimental data quantitatively.
Microscopical Study of the Structural Evolution of Sol-Gel Derived Buffer Layers for the Integration of YBCO on Biaxially Textured Nickel
Authors: Dobberstein H. , Schwartz R. W. , Clem P. G. , Carroll D. L. , Czerw R.
Published: April 2011

Epitaxial buffer layers of Ho2O3 on biaxially textured nickel were fabricated using a chelate (acetic acid) solution route as an alternative to the 2-methoxyethanol solution approach, which has demonstrated good texturing characteristics. Plan-view SEM studies of the films as a function of heat treatment temperature have shown that the holmium oxide film pyrolyzes into an open structure with a high level of interconnected porosity before densification, without significant film shrinkage in the thickness direction. Consolidation of the film started around 900°C along the backbone of the open structure and sintering to a dense film of uniform small crystallites (∼25 nm) was observed at higher temperature. The as-received nickel tapes displayed significant surface damage with a roughness on the order of 1000 Å. Electron backscattering analysis suggests that only 65% of the nickel grains were aligned along the (100) axis within 5°. Finally, STM studies of the nickel substrate have shown that small nickel oxide crystallites were formed on the surface when the substrate is in contact with air.
Control of Variants in Heteroepitaxy by Substrate Miscut
Authors: Flynn C P , Bonham S M , Eades J A , Ondrejcek M , Swiech W , Zhou G L
Published: April 2011

This paper discusses variants that occur in heteroepitaxy when the substrate possesses symmetries that are absent from the epilayer. Variants are enumerated in terms of 2-D symmetries of the substrate and epilayer, as they exist terminated at their interface. In this formulation, all possible cases can be presented in a single table. The role of miscut in controlling otherwise equal variants proportions is discussed with a view to eliminating unwanted variants and thereby improving the translational invariance of the materials. We summarize an experimental study of a (3m) symmetry epilayer growing on a (2mm) substrate, specifically Cu3Au (111) grown by molecular beam epitaxy on Nb (110), for which the two variants predicted from symmetry are stacking twins. Miscuts of about 1° along the indicated azimuth are sufficient to eliminate all except ∼ 0.1% of the less favored variant. This has interesting consequences in the context of the theory. A detailed understanding of the mechanisms for this example requires information about nanostructures that develop on the miscut Nb (011) surface. State-of-the-art information about novel substrate nanostructures, derived from scanning probe and low energy electron microscopies, is presented, and the prospects for a predictive science of variant control in heteroepitaxial growth are assessed.
AlGaN-Based Microwave Transmit and Receive Modules
Authors: Zolper John C.
Published: April 2011

AlGaN High Electron Mobility Transistors (HEMTs) have made great progress for solid state power amplifiers with the demonstration of an X-band power density up to 9.8 W/mm. This high power density is the result of the high current and voltage capability of this material system. Recently, it has also been shown that these devices can achieve low microwave added noise figures (NF = 0.6 dB at 10 GHz) while maintaining a large breakdown voltage (>60 V) and hence a large dynamic range. These results imply that AlGaN HEMTs can be used to perform the active transmit and receive functions in more robust, higher dynamic range modules. In this paper, the progress in AlGaN microwave HEMTs is reviewed and the issues related to AlGaN transmit and receive (T/R) modules are described.
A comparative study of AlGaN- and GaN-based lasing structures for near- and deep-UV applications
Authors: Bidnyk Sergiy , Lam Jack B. , Gainer Gordon G. , Little Brian D. , Kwon Yong-Hwan , Song Jin-Joo , Bulman Gary E. , Kong Hua-Shuang
Published: April 2011

We report a comprehensive study on the optical properties of GaN- and AlGaN-based lasing structures at high-levels of optical excitation (carrier densities of 1017−1020 cm−3) and identify critical issues necessary for the development of near- and deep-UV light emitting devices. We successfully achieved room temperature stimulated emission (SE) with emission wavelengths ranging from 351 nm to 373 nm in a variety of samples. Through an analysis of the temperature-dependent lasing characteristics, combined with absorption and time-resolved photoluminescence measurements, we estimated the carrier density required to achieve the SE threshold in GaN epilayers. We found that in AlGaN epilayers, the onset of SE (∼1019 cm−3) occurs at carrier densities one order of magnitude higher than in thick GaN epilayers, indicating that an electron-hole plasma is the dominant gain mechanism over the entire temperature range studied (10 K to 300 K). A remarkably low lasing threshold was observed in GaN/AlGaN heterostructures over the temperature range of 10 K to 300 K. Our experimental results indicate that GaN/AlGaN heterostructures could be used to efficiently generate laser emission with wavelengths shorter than 373 nm. The implications of this study on the development of UV laser diodes is discussed.
Lateral polarity heterostructures by overgrowth of patterned AlxGa1-xN nucleation layers
Authors: Dimitrov R. , Tilak V. , Murphy M. , Schaff W.J. , Eastman L.F. , Lima A.P. , Miskysa C. , Ambacher O. , Stutzmann M.
Published: April 2011

In this study thin AlxGa1−xN nucleation layers on sapphire were patterned and overgrown by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic chemical vapor deposition (MOCVD) to obtain adjacent regions of GaN and AlGaN/GaN heterostructures with different polarities. The role of polarity on the structural and electrical properties of epitaxial layers and AlGaN/GaN heterostructures was investigated for samples grown on patterned AlN or GaN nucleation layers. Epitaxial GaN and AlGaN/GaN heterostructures grown on Al-face AlN or N- face GaN nucleation layers were found to be Ga-face or N-face, respectively, independent of the technique used for the overgrowth.