bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectric Thin Films Via Sol-Gel Processing of Singlesource Precursors
Authors: Chandler C.D. , Hampden-Smith M.J. , Schwartz R.W.
Published: March 2011

The use of single-source mixed metal-organic precursors specifically designed for the formation of crystalline perovskite phase mixed metal oxide powders has been investigated. Pyridine solutions of divalent metal α-hydroxycarboxylates of general empirical formula A(O2CCMe2OH)2 where A = Pb, Ca, Sr, Ba; Me = methyl, were designed to react with metal alkoxides, for example, Ti(O-i-Pr)4, with the elimination of two equivalents of alcohol to form species with fixed A:B stoichiometry of 1:1 according to the equation: A(O2CCMe2OH)2 + B(OR)4 → A(O2CCMe2O)2B(OR)2 + 2HOR. Hydrolysis of these compounds in pyridine produces clear solutions which on removal of the solvent in vacuo, yield yellow powders. These powders readily dissolve in ethanol to give solutions from which thin films can be formed either by dip-coating or spin coating. The crystallization behavior, composition and ferroelectric properties of these films is discussed. The crystallization of the films generally required substantially higher temperatures compared to powders obtained from the same precursor solutions.
Transmission Electron Microscopy of Pzt Thin-Films Prepared by A Sol-Gel Technique
Authors: Seraphin Supapan , Zhou Dan , Teowee G. , Boulton J.M. , Uhlmann D.R.
Published: March 2011

The microstructure of lead zirconate titanate (PZT) thin films prepared by a sol-gel technique was investigated using transmission electron microscopy (TEM) and transmission electron diffraction. We investigated the microstructure of three sets of thin films with different chemical compositions: PZT 53/47 films with no excess PbO; with excess PbO; and PZT 65/35 with no excess PbO. All samples were fired for 30 minutes at temperatures ranging from 400C to 700C. Incorporation of excess PbO in the 53/47 film fired at 450C resulted in polycrystalline perovskite grains with an average grain size of less than 0.1 μm. Grain boundaries are decorated by 5-10 nm diameter precipitates possibly caused by the segregation of remnant pyrochlore or excess PbO. The films have high values of dielectric constant (up to 2500) when fired at 700C. PZT 65/35 fired at 700C consists of two distinct phases: a fine-grained matrix of pyrochlore, and 10-μm diameter rosettes of perovskite. The correlations between the compositions, the microstructure of the films, and their processing conditions on the one hand, and ferroelectric properties on the other are discussed.
Piezoelectric and Capacitative Microactuators and Devices
Authors: Sayer M. , Barrow D. , Zou L. , Kumar C.V.R. Vasant , Noteboom R. , Knapik D.A. , Schindel D.W. , Hutchins D.A.
Published: March 2011

Ultrasonic transducers, microactuators and resonators using sol gel PZT films, polymer membranes and silicon machining techniques can take the form of cantilevers, membranes, and array sensors. Static deflections in simple electrode configurations for PZT films supported on silicon or silicon nitride membranes are of the order of 1 μm, while larger deflections can be developed under ac and resonant excitation. High frequency acoustic actuators using capacitative excitation of polymer films have been used to evaluate the performance of piezoelectric sensors.
Current Status of and Recent Results on Group 2 Source Compounds for Vapor Phase Epitaxy of Ferroelectric Thin Films
Authors: Rees William S. , Luten Henry A. , Carris Michael W. , Caballero Celia R. , Hesse Werner , Goedken Virgil L.
Published: March 2011

Much interest in the area of ferroelectric thin films has been generated by the recent developments in unique property observation for these materials. As deposition methods move toward potential commercialization, the importance of chemically and thermally stable at use temperature, high vapor pressure and purity, readily available and economically competitive sources for the requisite group 2 elements will emerge. This presentation entails an initial overview of the presently utilized compounds, their advantages and disadvantages. New group 2 CVD precursors have been developed based both on inter- and intramolecular stabilization of cyclopentadienides, alkoxides and β-diketonates. Recent results on the coordination environment around the central metal atom have offered insight into the next generation of polydentate, monoanionic ligand design. Specific details are discussed for the metal complexes of “scorpion-tail” β-diketoethers. Results of comparison studies between these new precursors and earlier compounds are presented as a model for designing future sources.
The Defect Structure of BaTiO3 Thin Films
Authors: Wills L.A. , Wessels B.W.
Published: March 2011

The defect structure of BaTiO3 thin films grown on (100) Si was examined using transient photocapacitance spectroscopy. The concentration, optical cross section and associated energy levels of both native and impurity defects in as-grown and annealed BaTiO3 films were evaluated. Deep level defects withpeak energies of Ev+1.8, Ev+2.4, Ev+2.7, Ev+3.0-3.1 and Ev+3.2-3.3 eV were observed in the as-grown films. Upon vacuum annealing, the concentration of the traps at Ev+3.0 and Ev+3.2 eV increased while the concentration of the traps at Ev+ 1.8 and Ev+2.4 eV decreased. The levels at Ev+3.0-3.1 and Ev+3.2-3.3 eV are attributed to oxygen vacancies. The other levels are tentatively ascribed to Fe and Fe related defects.
A Model of The Metal-Ferroelectric-Metal Capacitor
Authors: Teowee G. , Uhlmann D.R.
Published: March 2011

Ferroelectric (FE) films, especially PZT films, have received increasing attention for microelectronic applications such as ferroelectric memory and high density DRAM. There has been significant progress in the preparation of high quality PZT films involving wet chemical and physical vapor deposition techniques. Metal-FE-metal structures, typified by Pt-PZT-Pt capacitors, are the basic building blocks for the ferroelectric devices. The leakage currents of the capacitors are known to be non-ohmic and exhibit an exponential dependence on applied voltage.

The present paper presents a model based on totally depleted back-to-back Shottky barriers. Predictions based on the model can provide significant new understanding of the FE behavior of thin films. For example, the assumption of total depletion leads to the presence of a built-in field within the film which can explain the ubiquitously higher values of coercive field in FE films than found in bulk ceramics. It will be shown that the agreement between model predictions and actual device I-V characteristics of Pt-PZT-Pt capacitors is very close. Further, the model can also explain the observed hysteresis loop asymmetry and low dielectric constants of films of relaxor FE's, whose dielectric constants are much smaller than those of bulk materials.
Effect of Zr/Ti Ratio on The Fatigue and Retention Behavior of Sol-Gel Derived Pzt Films
Authors: Teowee G. , Boulton J.M. , Orr M.N. , Baertlein C.D. , Wade R.K. , Birnie D.P. , Uhlmann D.R.
Published: March 2011

A series of sol-gel derived PZT films with various Zr/Ti ratios - namely PT, 0/100 - 20/80, 35/65, 53/47, 65/35, 80/20, 94/6 and PZ, 100/0 - were prepared on platinized Si wafers. Excess PbO was added to the precursor chemistries to compensate for eventual PbO loss and also to aid in obtaining the desired perovskite phase.

It was found that the phase assembly, namely the presence of tetragonal or rhombohedral perovskite phases, plays an important role in determining the fatigue and retention behavior. PT-rich (or tetragonal) films offer better retention characteristics than those observed in PZ-rich (or rhombohedral) or PZT 53/47 films. Films with PZrich compositions tend to exhibit superior fatigue behavior compared with PT-rich films.
A Novel Method for Determining the Curie Temperature of Ferroelectric Films
Authors: Kwok Chi Kong , Desu Seshu B.
Published: March 2011

A novel technique to measure the Curie temperature of ferroelectric thin films has been developed. The method is based on identifying changes in slope of film stress vs temperature plot. At the Curie temperature, ferroelectric films undergo a phase transition from ferroelectric phase to paraelectric phase. Due to this phase transformation, physical properties of films such as elastic constants and coefficients of thermal expansion also change at the Curie temperature. Consequently, at this temperature the temperature coefficient of film stress changes since it is related to elastic constants and thermal expansion coefficient. Thus, by measuring the film stress as a function of temperature, the Curie temperature can be determined. The Curie temperatures measured by this method are in good agreement with the literature values. Small discrepancies that were observed can be attributed to the intrinsic stresses present in the films.
Tunable Dielectric and Piezoelectric Characteristics of Lead Magnesium Niobate Titanate Relaxor Thin Films
Authors: Chen J. , Zhang Q. , Cross L.E.
Published: March 2011

Ferroelectric relaxor thin films Pb[(Mg1/3Nb2/3)0.9Ti0.1]O3 (90PMNIOPT) have been fabricated by the sol-gel technique. The dielectric, piezoelectric and electrostrictive characteristics have been investigated. Experimental results show that the dielectric permittivity and effective piezoelectric coefficients of the films can be tuned by varying dc bias fields which offers the useful features in designing smart micro transducer and actuator systems. Dielectric constants of the films are in the range of 5000 to 6000. The electric field induced strain is on the order of 10−3, and the maximum effective d33 coefficient of 90PMINI0PT films is as large as 265 pC/N at 31 kV/cm. The electrostrictive coefficient Q11 is on the order of 1.2 c×10−2 m4/C2 and M11 is 3.5 c×10−16 m2/V2.
Ultra-Thin Sputtered Pzt Films for Ulsi Drams
Authors: Kim Jiyoung , Sudhama C. , Khamankar Rajesh , Lee Jack
Published: March 2011

In this work, a high-temperature deposition technique has been developed for ultra-thin sputtered PZT films for ULSI DRAM (<256Mb) storage capacitor applications. In contrast to the previously developed low-temperature (200°C) deposition, deposition at high-temperature (400°C) yields a desirable reduction in grain size of the perovskite phase. The thickness of PZT films has been reduced to less than 30nm with high charge storage density (∼30μC/cm2) and low leakage current density. An optimized 65nm PZT thin film was found to have an equivalent SiO2 thickness of 1.9Å and a leakage current density of less than 10−6 A/cm2 under 2V operation.
Pyroelectric Properties of Lead Based Ferroelectric thin Films
Authors: Patel A. , Tossell D.A. , Shorrocks N.M. , Whatmore R. W. , Watton R.
Published: March 2011

Lead based thin ferroelectric films have been prepared using both sol-gel and dual ion beam sputtering (DIBS) processes. Material compositions within the PbTiO3 and PLZT system have been deposited by both techniques onto metallised silicon. By using a standard sol-gel prepared solution, modified with acetylacetone and spin-coating, lµm thick fully perovskite layers, were obtained at low temperature (450°) with some preferred orientation. The grain size was in the range 0.2-0.4µm. A dielectric constant of 400 and a reversible pyroelectric coefficient of 1.2 × 10−4Cm−2K−1 were obtained. In contrast, a range of capping layers (SiO2, A12O3, BPSG) on silicon have been investigated using the DIBS process. Highly crystalline (100) and (111) films were readily produced at temperatures in excess of 550°, at a growth rate of 0.3µm/hour. Control of stoichiometry has also been studied in detail, by sputtering of a composite metal-ceramic target with a high energy Kr beam and by bombarding the growing film with a low energy oxygen ion-beam. Dielectric constants of 200-300, losses below 0.015 and resistivities above 1010Ωm have been achieved. A pyroelectric coefficient of the order of 2.5 × 10−4Cm−2K-1, pre-poled for a La-doped film on BPSG capped Si was obtained, which did not increase significantly on poling.
Materials Characterization of Nondestructive Readout Nonvolatile Memory Devices
Authors: Tuttle Bruce A. , McIntyre Dale C. , Seager Carleton H. , Garino Terry J. , Warren William L , Evans Joseph T. , Waldman Robert W.
Published: March 2011

Prototype ferroelectric thin film, nonvolatile memory, nondestructive readout (NDRO), semiconductor devices have been fabricated. The “1” and “0” logic states of these prototype devices are in principle determined by the modulation of the conductivity of a semiconductor film channel by the polarization state of the underlying ferroelectric thin film layer. Programmed resistance ratios of the two logic states of 5:1 are demonstrated. While the best performance to date has been achieved for devices that have a 40 nm ln2O3 film covering a 300 nm thick PZT 20/80 layer, we also develop criteria for selecting semiconductor films that will improve performance for this NDRO device design. Among the other semiconductor films that are characterized with respect to this criteria are boron doped Ge, ZnO and aluminum doped ZnO. It is demonstrated that by appropriate donor doping of ZnO films the effects of intrinsic defects are masked and that process temperatures can be extended by 300×C.
Integrated Pyroelectric Infrared Sensor Using Pvdf thin Film Deposited by Electro-Spray Method
Authors: Asahi Ryouji , Sakata Jiro , Tabata Osamu , Mochizuki Midori , Sugiyama Susumu , Taga Yasunori
Published: March 2011

A pyroelectric infrared sensor using a poly(vinylidene fluoride) (PVDF) thin film has been integrated with a read-out circuit on a silicon substrate. The PVDF thin film with a thickness of 1-2 µm was deposited on the sensing area by an electro-spray (ESP) method. A form I crystal and a large pyroelectric coefficient of 4 nCcm−2K−1 were observed just after the deposition without any poling treatments. The fabrication process of the sensor was based on a standard MOS LSI process and a polysilicon sacrificial layer etching technique. In order to reduce the heat capacitance and the thermal conduction, the PVDF thin film was supported on a thin Si3N4 membrane structure formed by etching a part of the silicon substrate under the sensing area. The sensor with a sensing area of 400x400 µm2 had a responsivity of 98 V/W, a detectivity of l.4× 107 cmHz1/2W−1, an NEP of 2.9× 10−99 Hz1/2W at a frequency of 100 Hz and a time constant of 1.3 msec.
Photo-Induced and Electrooptic Properties of (Pb,La)(Zr,Ti)O3 Films
Authors: Dimos D. , Warren W.L. , Tuttle B.A.
Published: March 2011

Photo-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)03 (PLZT) films have been characterized. The film photosensitivity has been evaluated with respect to the magnitude of the effects, the time response and the spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge (∼3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.
Effect of Elastic Stress on Phase Selection in a Binary System
Authors: Huh Joo-Youl , Johnson William C.
Published: March 2011

Elastic stress arising from differences in lattice parameters between phases is known to alter both qualitatively and quantitatively the characteristics of phase equilibria in coherent systems. One important consequence of misfit or epitaxial strain is the possible existence of several linearly stable equilibrium states: For a given composition, temperature and applied stress, different combinations of volume fraction and corresponding phase compositions render the free energy of the system a minimum. Here, we examine how epitaxial stresses influence phase equilibria in a binary alloy when the system can select from three different phases. In particular, we show the existence of several equilibrium states with different combinations of phases that minimize the system free energy.
The Formation of Epitaxial Eutectic Modulated Structures
Authors: Roytburd Alexander L. , Sung Gisuk
Published: March 2011

The thermodynamics of the formation of a coherent epitaxial two-phase modulated structures from a liquid solution is considered. It is shown that elastic interactions in the epitaxial system change the topologic features of the eutectic phase diagram. As a consequence an eutectic point splits into two eutectic points or it is transformed into a consolute point.
Analysis of Structural Transformations in High Fluence Nitrogen Ion Implanted Aluminium
Authors: Calvo L. , Perez-Rodriguez A. , Romano-Rodriguez A. , Moranteand J.J. , Montserrat J.
Published: March 2011

The structural analysis of Al layers on Si obtained by sputtering at different conditions and implanted with nitrogen (with doses of 2.5×10'17 and 5×1017 N2+ ions/cm2, energy 150 keV, room temperature) is performed by SRP, SIMS and TEM measurements. The correlation between these measurements shows the formation of AIN crystalline precipitates already at the substoichiometric dose. SRP and TEM reveal the presence of a buried layer with resistivity higher than the Al matrix, with a high concentration of AIN precipitates. The morphology of this layer is affected by surface roughness. For the higher dose, a buried continuous AIN polycrystalline dielectric layer is formed. Moreover, the SIMS measurements suggest a gettering effect of Si in the buried layer.
Amorphization of Fe/Zr Multilayers by Ar-Ion-Beam-Mixing
Authors: Kopcewicz M. , Jagielski J. , Stobiecki T. , Stobiecki F. , RÖLL K.
Published: March 2011

The Ar-ion-beam-mixing of the FeZr multilayer system is studied by conversion electron Mdssbauer spectroscopy. The dependence of the amorphization process on the layer thickness and ion dose is studied in detail for samples with Fe to Zr ratio of 1 and 0.5 and modulation wavelength of 5 to 90 nm.
Temperature Dependence of Ion Beam Mixing of Ingaas Marker Layers in GaAs
Authors: Forbes D.D. , Coleman J.J. , Klatt J.J. , Averback R.R.
Published: March 2011

Ion beam mixing of In0.20Ga0.80As quantum well marker layers in GaAs following 1 MeV Kr ion irradiation has been measured as a function of irradiation temperature and fluence. Secondary Ion Mass Spectrometry (SIMS) was used to measure the diffusion of the In0.20Ga0.80As layer following irradiation at various temperatures. Rutherford Backscattering (RBS) and channeling methods were used to determine the extent of the amorphization as a result of the implantation. The mixing parameter of the In0.20Ga0.80As in the GaAs matrix increased from σ120 Å5/eV at 77K to σ160Å5/eV in the temperature range of 300K–450K, but decreased somewhat at 573K. This behavior of In0.20Ga0.80As marker layers will be compared to AlAs marker layers which show similar temperature dependence. These results are interpreted on the basis of thermal spikes and crystal structure.
Ion Bombardment Effects on the Growth of Rutile Phase of Reactively Sputtered TiO2 Thin Films
Authors: Wicaksana D. , Tsujikawa T. , Kobayashi A. , Ono K. , Kinbara A.
Published: March 2011

Titania thin films grown by reactive bias sputtering were characterized. In order to investigate the role of energetic ion on the growth of crystalline phases of TiO2 thin films, we applied substrate biases during deposition. The structural properties were analyzed using X-ray diffractometry (XRD), and related to the optical properties of the films. The atomic composition was determined using Rutherford backscattening spectrometry (RBS).

Negative substrate bias, Vb, showed a significant influence on the phase formed composition and microstructure: Vb in the range of 15 and 60 V enhanced the growth of crystalline phases and the rutile dominated the phase composition. However, the quantity of rutile decreased when Vb was raised to 100 V. The excess of oxygen was shown in the films by RBS.
Phase Transformation of Co Silicidation in the Co/Ti- and Ti/Co-Si(100) Systems
Authors: Hong Feng , Patnaik Bijoy K. , Li Bingzong , Liu Ping , Sun Zen , Rozgonyi George A.
Published: March 2011

Co silicide formed via selective diffusion of Co through a Ti interfacial layer has been reported by several groups. In this report, phase identification of the silicide has been further studied for both Co/Ti and Ti/Co multi- and bilayers deposited on p(100)-Si substrates. The samples were either vacuum furnace or RTA annealed from 550°C to 900°C. The Co silicide formation sequence in the Co/Ti-Si systems follows CoSi2→Co2Si→CoSi→CoSi2 with the formation temperature increasing for each phase. The Co/Ti bilayer CoSi to CoSi2 transformation temperature was lower than that for the six layer Co/Ti system. For the multilayer sample with Co as the first layer in contact with the Si substrate, CoSi2 formed at 550°C and then CoSi was observed at higher temperatures due to the effect of Co supply on disilicide phase instability. Epitaxial CoSi2 growth occured at higher temperatures after the removal of the unreacted upper layers. A 15 μΩ-cm film resistivity was obtained from 50 nm epitaxial CoSi2.
Variations Of Fractal Dimension During the Phase Transformation To The Silucide Nucleation in Thin Film Systems
Authors: Cho Nam-Lhn , Nam H. Gin
Published: March 2011

Detailed relationship between the fractal dimension and the excess noise frequency exponent has been considered for metal-silicon interfacial structures during the phase transformation to the initial compound phase formation in thin film systems. In the estimation of the fractal dimension of the thin film structures, a technique has been used, which basically employs a digital image processing of highly magnified micrographs of the structures. Previously measured frequency exponent data of the excess noise power spectral density for the same thin film systems has been interpreted by introducing a multiplication process which combines the fractal dimension variations and cluster interactions of the interfaces. It has been assumed that the fractal dimension plays a role as a multiplication factor in the multiplication process.
Microstructure of Si Films Deposited on Si(100) Surfaces by Remote Plasma-Enhanced Chemicalvapor Deposition, Rpecvd: Dependence on Process Pressure and Substrate Temperature
Authors: Habermehl S. , He S. S. , Chen Y. L. , Lucovsky G.
Published: March 2011

The microstructure of Si thin films, deposited on in-situ cleaned Si(100) surfaces by remote plasma-enhanced chemical-vapor deposition (RPECVD), is dependent on the process pressure, substrate temperature and H2 flow rate. Surface characterization by on-line low energy electron diffraction, LEED, has been used to detect changes in the character of the deposited films which can either be amorphous, microcrystalline or crystalline, hereafter designated as a-Si, Sμc-Si, and c-Si, respectively. We have used these results to generate phase diagrams for the Si microstructure as a function of the process pressure and substrate temperature, including the flow rate of H2 as an additional deposition parameter.
Laser Induced Phase Transformations in Thin Insb Films
Authors: Chou L.L. , Kuo M.M.
Published: March 2011

Thin In46Sb54 films have been prepared on glass substrates by flash evaporation. Films of 1000 Å were deposited at room temperature. After 7 mins' thermal annealing at 450ºC, an average grain size increased from 20 nm to 200 nm. Under exposure to a Fraunhofer diffracted pulsed Nd-YAG laser beam, the films showed different microstructures for different applied laser power. In general, five regions are identified: ablation region, regions with grain sizes less than 20 nm, grain sizes ranging from 400 to 1000 nm, grain sizes ranging from 200 to 400 nm and unchanged region. The previous five regions are counted from the center of the exposed area outward. The pulse duration is 16 ns. In this paper, an atomic migration mechanism is proposed to explain the power dependent microstructures changes. Transmission electron microscopy was mainly used to characterize the films. The application of this type of phase transformations in the phase change optical storage is also discussed.
The Reactivity of Thin Titanium Films Towards Aluminum and the N-O-N Insulator Stack, and its Effects on the Composition and Properties of Voltage Programmable Links
Authors: Gleason Edward F. , Cohen Simon S. , Wyatit Peter W.
Published: March 2011

A metal-insulator-metal (MIM) voltage programmable link (VPL) has been fabricated that relies on the breakdown of a thin nitride - oxide - nitride (N-O-N) plasma deposited insulator stack. The metal electrodes were prepared by depositing a titanium layer (400 Å) on top (or bottom) of 7500 Å Al ( 1% Si). The resulting metallization resists hillock formation during thermal anneal steps and thus preserves the integrity of the thin link dielectric. The breakdown voltage is typically 10 volts for a 100 Å-150 A-100 Å NON stack. Sintering at temperatures up to 425°C results in a negligible increase in breakdown voltage. After sinter at 455°C, the breakdown voltage drops to 6 volts and continues to decrease with further sintering. Auger depth profiles of the as-deposited sample indicate the N-O-N stack is intact and the titanium has also not reacted with the aluminum film. After sinter at 455°C no distinct interfaces are observed in the auger depth profile. Angle-resolved x-ray photoelectron spectroscopy (ARXPS) of the nitride film after deposition and sinter indicate that the nitride film reacts with the titanium to form titanium nitride or titanium silicide. Angle resolved measurements indicate the titanium concentration has increased by a factor of 5 throughout the film as compared to the as-deposited sample. These results explain the observed drop in breakdown voltage since the insulator is being consumed and being converted into conducting titanium nitride or titanium silicide.
Grain Boundary Diffusion Controlled Precipitation as a Model For thin Film Reactions
Authors: Barmak K. , Coffey K.K.
Published: March 2011

In order to arrive at a model for nucleation in the reaction of polycrystalline thin films, we have made use of a transport model that combines atom transport across interface reaction barriers with transport along grain boundaries. Through this transport model, the boundary chemical potential, μIi, and a characteristic length Li for each specie are defined. Li and the ratio of grain size to Li determine the spatial variation and the time evolution of the boundary chemical potential respectively. Nucleation of the product phase is modeled as a process whose driving force is determined by these position dependent (and time dependent) boundary chemical potentials. Thus thin film reactions become similar to precipitation from bulk homogeneous supersaturated solid solutions. Numerical calculations, however, show that boundary diffusion results in low “effective” driving forces for nucleation which can lead to heterogeneous nucleation of even the first phase. The model provides a new approach to phase selection by re-evaluation of the driving force and considers the effect of product and reactant grain structure to be fundamental to the reaction process.
Mechanisms of Transition Metal Diffusion into Semiconductor Film
Authors: Goldiner M. G. , Vaysleyb A. V.
Published: March 2011

Descriptions of metal (Me) diffusion into semiconductor (Se) film by diffusion-kinetic and purely kinetic methods were compared. To analyze thin film diffusion, thin film surfaces were considered as a substantial source/sink of point defects. Conditions of transition from one Me diffusion transport mechanism/regime to another, when Se sample thickness is changed, were found to be practically the same in both considerations. Critical Se film size, dislocation density, and temperature of diffusion mechanisms and regimes coincide, providing a correct interpretation of the experimental results in terms of the corresponding diffusion mechanism.
Evolution of Gd Thin Film Structure Due to Amorphization by Co Deposition
Authors: Hufnagel T.T. , Bertero G.G. , Sinclair R. , Clemens B.B.
Published: March 2011

Multilayers of Gd/Co produced by sputter deposition are observed to be amorphous for a wide range of bilayer periods. This structure is largely the result of an amorphization reaction during the deposition between crystalline Gd and newly arriving Co atoms. We explore this reaction by producing multilayers of Gd/Co/Cr, and examining the resulting microstructure. We observe both interfacial disordering due to a layer thickening mechanism and evidence for growth of the amorphous phase from Gd grain boundaries. The reaction is enhanced by the presence of a large number of crystalline defects in the Gd layers.
Interface Quality and Interdiffusion in Si-Ge Heterostructures
Authors: Baribeau J.-M. , Lockwood D. J. , Aers G. C. , Dharma-Wardana M. W. C.
Published: March 2011

The evolution of interfaces of short-period (SimGen)p superlattices upon annealing has been studied by x-ray reflectometry and Raman scattering spectroscopy. Isothermal annealing treatments at 700° C resulted in a significant material redistribution as evidenced by a strong decay of the superlattice x-ray satellites and by the decay of longitudinal acoustic modes and changes in the optical mode intensity ratios in Raman scattering. Interdiffusion was more pronounced in superlattices of short periodicity. This may possibly be explained by the strong composition dependence of the diffusivity of Ge atoms in Sil-xGex alloys and the degree of preexisting interfacial mixing. This composition dependence of the diffusion may favor atomic displacement parallel to the interfaces leading to an initial smoothing of the interfaces
The Dynamical Transition to Step-Flow Growth During Homoepitaxy of GaAs (001)
Authors: Orr B. G. , Sudijono J. , Johnson M. D.
Published: March 2011

The evolution of surface morphology of molecular-beam-epitaxy-grown GaAs (001) has been studied by scanning tunneling microscope. Images show that in the early stages of deposition the morphology oscillates between one -with twodimensional nucleation and coalescing islands, i.e. flat terraces. After the initial oscillatory regime, the system evolves to a dynamical steady state. This state is characterized by a constant step density. As such, the growth mode can be called a generalized step flow. Comparison with RHEED shows that there is a direct correspondence between the surface step density and the RHEED specular intensity. An increase in step density results in a decrease in specular intensity. Additionally, further deposition beyond 120 monolayers (up to 1450 monolayers) display a slowly increasing surface roughness.
Crystal Quality of III-V Substrate Wafers and Epitaxial Layers Studied by X-Ray Topography
Authors: Bassignana I. C. , Macquistan D. A.
Published: March 2011

The crystal quality of III-V substrates was studied by x-ray asymmetric crystal topography (ACT). An extensive study of device-quality GaAs (LEC SI, LEC n-type, VGF and VB) and InP (LEC n-type (S) and SI (Fe) ) wafers reveals that they can contain various defects: low angle grain boundaries, dislocation cell structure, slip, swirl and included mosaic structure.

The high angular resolution of ACT was used to non-destructively study both the epitaxial layer and the substrate. Topographs of the substrate and the epitaxial layers of AlGaAs/GaAs layers grown by MBE and MOCVD are compared. The quality of the substrate has direct implications for the quality of the epitaxial growth. For coherent layers, both the large scale and small scale defects observed in the substrates were exactly reproduced in the epitaxial layers grown by both techniques.
Evolution of Roughness on InP Layers Observed by Scanning Force Microscopy
Authors: Cotta M. A , Hamm R. A , Chu S. N. G , Staley T. W , Harriott L. R , Panish M. B , Temkin H.
Published: March 2011

The evolution of surface roughness with increasing thickness of (100) InP layersgrown by metalorganic molecular beam epitaxy has been observed by scanningforce microscopy. The process of roughening gives rise to periodic elongatedfeatures on the surface aligned in the [011] direction, reflecting the surfaceanisotropy. The morphology eventually evolves to a grain-like surface. Theroughening is dependent on both the group III and V flux, and the growthtemperature, indicating that this phenomenon is kinetically controlled by surfacediffusion activation. For each set of parameters chosen for the growth, there is aminimum temperature where smooth, two-dimensional growth can be obtained.Below that temperature the roughening shows two distinct power law regimesdependent on the epitaxial layer thickness.
Low Temperature Growth Mechanisms for Rheed Oscillations
Authors: Biswas R. , Roos K. , Tringides M. C.
Published: March 2011

Low temperature (T<150 K) RHEED oscillations during the growth of ultrathin films suggest the presence of substantial adatom mobility. In most systems thermal diffusion can not account for the observed oscillations, and the origin of the oscillations is an open question. Experiments on Ag/Si(111) at 150 K demonstrate the absence of thermal diffusion due to the observed scaling in the RHEED intensity for different flux rates. We have performed molecular dynamics simulations to understand the mechanisms of RHEED oscillations at low temperature. Classical two- and three-body Si potentials were used together with an adatom mass that is 3.84 times the Si mass to account for the Ag/Si mass ratio. Results indicate that the landing site for the adatom is very important to predict whether a particular adatom will display lateral motion or not. A fraction of the adatoms incident near a maximum of the potential energy surface display significant lateral motion. The substrate stiffness for Ag/Si results in an energy transfer process which is much slower than that in fcc/fcc systems.
Hopping Barriers at Step Edges
Authors: Šmilauer Pavel , Wilby Mark R. , Vvedensky Dimitri D.
Published: March 2011

The recent discovery of reentrant layer-by-layer growth in metal homoepitaxy has stimulated considerable interest in the role played by barriers to hopping down descending steps. However, the existence of step-edge barriers for semiconductors is far from being clearly established. We have investigated the effects of step-edge barriers for epitaxial growth and the “inverse” process of low-energy ion sputtering on metal surfaces using Monte Carlo simulations of a solid-on-solid model. Our results are in good agreement with available experimental data and provide new insights into the microscopic origins of the evolution of surface morphology during these processes. Our simulations also suggest that such step-edge barriers can explain the observed temperature and time dependence of the reflection high-energy electron diffraction intensity during post-growth recovery on GaAs(001), which sheds new light on this controversial subject.
Common Features of Epitaxial Growth on Vicinal GaAs(001), AlAs(001) and InAs(001) Surfaces
Authors: Shitara T. , Vvedensky D. D. , Neave J. H. , Joyce B. A.
Published: March 2011

We have carried out RHEED measurements and Monte Carlo simulations of the growth on GaAs(001), AlAs(001) grown on GaAs(001), and InAs(001) to address the common features of the growth near the transition to step flow. For a fixed V/IIl ratio, the cation flux and misorientation-angle dependencies of the transition temperature on AlAs(001) and InAs(001) follow the same pattern as on GaAs(001). The same anisotropic behavior was also obtained, in that the transition temperature on a surface misoriented toward [110] is higher than that on a surface misoriented toward [110]. Unlike the case of GaAs(001), however, the surface reconstruction could not be kept constant near the growth mode transition for AlAs(001) and InAs(001). Therefore, we cannot compare simulations with experiments in as much detail as we have done for GaAs(001). Nevertheless, we can still estimate the effective surface migration barrier for Al adatoms on AlAs(001) as approximately 1.74eV and for In adatoms on InAs(001) as at most 1.23eV. This value should be compared with the value of 1.58eV obtained for GaAs(001).
In-Situ Observation of The Initial Stages of Co (0001) Epitaxy on Pt (111) Using Grazing Incidence X-Ray Diffraction
Authors: Bain James A. , Clemens Bruce M. , Brennan Sean
Published: March 2011

The heteropitaxial growth of (111) Pt on (0001) sapphire and of (0001) Co on (111) Pt on (0001) sapphire has been observed in-situ using grazing incidence x-ray scattering (GIXS). The in-plane lattice parameters of the Pt and Co phases have been measured as a function of film thickness in the regime from two monolayers to 200 monolayers, Relaxation of elastic strain with thickness has been quantified. X-ray reflections consistent with stacking faults in the Co films have been observed and monitored as a function of thickness, giving a measure of the stacking fault density. A distinct Co phase was observed at two monolayers of Co on a thick Pt layer, indicating an incoherent interface between the Co and Pt, even at this very early stage of deposition.
Atomic Structure of The α-A12O3(0001)(√31×31)R±9° Reconstruction
Authors: Renaud G. , Villette B.
Published: March 2011

The atomic structure of the α-A12O3 (0001)(√31×√31)R±9° reconstruction has been solved by Grazing Incidence X-ray Diffraction. The surface structure is found to be perfectly commensurable with the underlying bulk lattice, with exponential correlation length ∼500 Å. It consists of hexagonal zones of two nearly perfect closed-packed Al(111) planes, separated by a defect of hexagonal periodicity with parameter 26.5 Å. This structure may explain why the reconstruction can be obtained at lower temperature by deposition of a few aluminum layers, and why Al/Al2O3 multilayers remain coherent, with aluminum of (111) orientation.
Natural Patterning of High-Index Gaas Surfaces
Authors: Nötzel Richard , Ploog Klaus H.
Published: March 2011

We present new methods to directly syntesize III-V semiconductor quantum-wire and dot structures based on the evolution of well ordered surface corrugations on non-(100)- oriented substrates and on the controlled step bunching during MBE growth. The distinct electronic properties of these novel structures highlight their potential for fundamental research and advanced device concepts.
Migration Enhanced Epitaxy of GaAs Studied by Reflection High Energy Electron Diffraction and Scanning Tunneling Microscopy
Authors: Fu Jianming , Miller D. L. , Kim J. , Gallagher M. C. , Willis R. F.
Published: March 2011

Migration enhanced epitaxy (MEE) of GaAs on (001) GaAs substrates was studied by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). In MEE, Ga and As species are alternately deposited on the growing surface. Ga adatom migration can be enhanced by the low arsenic pressure environment. The STM study was performed ex-situ by the arsenic capping and decapping procedure. We have demonstrated the correlation between the peak RHEED specular intensity during MEE growth and the variation of the lateral step density on the surface, even though the surface stoichiometry changes repetitively during MEE. The peak RHEED intensity during MEE is inversely dependent on the surface step density. The MEE surface exhibited a lower step density than the MBE surface, as shown by both RHEED and STM. However, the MEE surface still exhibited a much higher step density than a well-annealed surface. Consequently we believe that to achieve an atomically flat interface, annealing at high temperature in an arsenic flux is still necessary even if MEE is employed.
A Comparison of Two Epitaxial Formation Mechanisms in the SiGe System
Authors: Prokes S. M. , Rai A. K.
Published: March 2011

Two epitaxial growth mechanisms and the resulting defect generation have been examined. The first involves standard growth by molecular beam epitaxy (MBE), while the second employs wet oxidation to form a Ge-rich epilayer from an initially amorphous film. The MBE-grown high Ge content layers evolve by island coalescence, while the oxidationproduced high Ge content layers form by a Ge exchange mechanism below a contamination layer, which results in a more uniform epitaxial layer. Thus, the resulting threading dislocation, stacking fault and twin densities, along with the surface roughness can be quite different. Results also indicate a high misfit dislocation density limited to the Si/SiGe interface and a strain redistribution into the Si substrate for the oxidation-produced epilayers.
Surface Ordering of MBE Grown 001 Ga0.5Al0.5As – a Theoretical Study
Authors: Trivedi Rita , Venkatasubramanian R. , Dorsey Donald L.
Published: March 2011

The surface kinetics of MBE growth of (100) Ga0.5 Al0.5As are studied theoretically using a stochastic model which is based on master equation with random distribution approximation. The kinetic processes considered are: adsorption and inter- and intra-layer migrations for Ga, Al and As. Both monoatomic and diatomic As molecular species are considered. The model parameters such as the atomic pair interaction energies, migrational requency and activation energy were obtained from available experimental and theoretical data. The surface ordering kinetics are studied as a function of the fluxes (2Å/sec. for cations), flux ratio (1 : 10, 1 : 20 and 1 : 30 for cation to anion) and substrate temperature (775° – 923°K). Degree of ordering was obtained in terms of a short range order (SRO) parameter. The order-disorder temperature defined as the temperature of maximum order (above and below which the order parameter decreases) was obtained for flux ratios of 1 : 10 and 1 : 20. Both As and As2 species were considered. The order-disorder temperature was found to increase as the flux ratio was changed from 1 : 10 to 1 : 30, while the maximum degree of ordering decreased slightly. The results are in good qualitative agreement with experiments. The surface ordering kinetics observed can be described in terms of effective surface migration rates of the cations as follows. Lower temperature and higher flux ratio yield smaller effective surface migration rates for cation, which results in lesser degree of ordering. Beyond the transition temperature, the thermal energy is large enough to thermally randomize the atom pair bonds, thereby decreasing the degree of ordering. The higher transition temperature for higher flux ratios is attributed to lower effective migration rate.
Defect Engineering and Characterization in Oxide Surfaces using Electron Beam Irradiation
Authors: Doering D. L. , Siek K. H. , Xiong-Skiba P. , Carroll D. L.
Published: March 2011

Electron beam irradiation at energies between 0.5 and 4 keV has been found to produce defects in oxide materials including SiO2, Al2O3 and ZrO2. These defects trap excess charge in the materials and affect their electronic and optical properties. Measurements of the thermally stimulated exoelectron emission following irradiation provides information on relative defect concentrations, defect creation mechanisms, electron trap binding energies, electron emission mechanisms and annealing properties of these materials. Electron emission during sample heating occurs via a variety of mechanisms including the thermionic emission of excess charge from defects at temperatures characteristic of each trap binding energy. By measuring relative trap concentrations as a function of beam parameters, we have identified electron beam energy thresholds for the creation of some types of defects which correlate with core level electronic transitions. Also, electron emission which occurs during defect annealing or diffusion to a surface shows the conditions for the elimination of defects. The ability to control and characterize defect formation and annihilation provides the possibility of engineering specific surface defect conditions. In addition, defect creation by electronic processes is very selective as compared with momentum transfer in ion beam damage of surfaces.
Structural Analysis of Silicon Doped by Plasma Source Ion Implantation
Authors: Matyi R.J. , Chapek D.L. , Conrad J.R. , Felch S.B.
Published: March 2011

We have used high resolution x-ray diffraction to analyze the structural changes that accompany boron doping of silicon by BF3 plasma source ion implantation (PSII). Triple crystal diffraction analysis of as-implanted PSII doped silicon showed little excess x-ray diffuse scattering, even when analyzed using the asymmetric (113) reflection for increased surface sensitivity. This result suggests that PSΠ is capable of providing high dose implantation with low damage. Annealing of the PSII-doped silicon showed the development of a compressive surface layer, indicated by enhanced x-ray scattering directed perpendicular to the surface. Virtually all of the scattering from the annealed samples was concentrated in the so-called “surface streak” which arises due to dynamical diffraction from the perfect crystal Si structure. Little if any diffuse scattering due to kinematic scattering from crystal defects was detected. These observations indicate that plasma source doping can be used to achieve both a shallow implant depth and an extremely uniform incorporation of boron into the silicon lattice.
Formation of Double-Height Si(001) Steps by Sputtering with Xe Ions - A Computer Simulation
Authors: Heinig K.-H. , Stock D. , Boettger H. , Zinovyev V.A. , Dvurechenskii A.V. , Aleksandrov L.N.
Published: March 2011

A study of the recently observed double-height Si(001) step formation by sputtering with low-energy Xe ions is presented. The modeling of the process has been separated in two stages: (i) Molecular dynamics (MD) simulations of the interaction of 225 eV Xe ions with Si(001) surfaces and (ii) calculation of the step kinetics by reaction-diffusion equations. It is found that a single Xe ion produces surface vacancies arranged in one cluster, some adatoms and on the average one sputtered atom. For adjacent terraces on a vicinal Si(001)-(2 × 1) surface separated by SA- and SB-steps, respectively, the adatom diffusion as well as their attachment and detachment at steps and vacancy clusters determines the kinetics of the steps and results in double-height Si(001) steps.
Reactive Ion Etching Processes for Amorphous Germanium Alloys
Authors: Kuo Yue
Published: March 2011

This paper presents results on reactive ion etching (RIE) processes of amorphous germanium (a-Ge:H), germanium silicon alloys (a-GeSix:H) and germanium oxide (GeOx). Their process characteristics are compared with those of the amorphous silicon (a-Si:H) and silicon nitride (SiNx). Various combinations of feeding gases, i.e., from CF4, CF2Cl2, CH3F, and O2, over a pressure range of 100 to 300 mTorr and a power range of 500 to 1500 W were used in this study. The following conclusions are drawn from the results: 1) the a-Ge:H and a-GeSix:H etch mechanisms are similar to that of a-Si:H, but the former have higher etch rates than the latter; 2) a-GeSix:H etch rate falls between those of a-Ge:H and a-Si:H; 3) the GeOx etch mechanism is similar to that of SiNx; 4) although plasma phase chemistry, ion bombardment energy, and surface reactions are all important to the etch process, the film component selectivity is greatly dependent on the feeding gas; 5) to obtain a high etch selectivity between a-GeSix:H and PECVD SiNx a chlorine-containing gas has to be used; 6) RIE plasma damage to a-Si:H TFT is decreased when it is covered with an a-GeSix:H layer.
High Resistivity in N-Type InP and InGaAsP by He+ Ion Induced Amorphization.
Authors: Sargunas V. , Comedi D. , Zhao J. , Jankowska K. , Thompson D.A. , Simmons J.G.
Published: March 2011

Changes in the resistivity of n-type InP and InGaAsP by He+ ion implantation have been investigated at implant temperatures of 60-523K. The highest resistivities are achieved at the lowest temperatures under the conditions where the dose is sufficient to render the implanted region amorphous, as indicated by Rutherford backscattering/channeling measurements. Anneal data indicates that the high resistivities achieved via amorphization are stable to higher temperatures than when the samples remain crystalline after implantation.