bluuebunny/crossref_metadata_2025 huggingface dataset:
Defects in Low-Temperature-Grown MBE GaAs as Studied by a Variation of TSC Spectroscopy
Authors: Fang Z-Q , Look D. C.
Published: March 2011

A zero-bias thermally stimulated current (TSC) spectroscopy under both optical (1.96eV) and electrical excitation using samples with a Schottky contact on the top was applied to annealed LTMBE GaAs grown at different temperatures, and bulk SI GaAs with different stoichiometries. The results show that: 1) the new TSC technique is capable of revealing the traps at 235K<T<380K and is effective in indicating the crystal stoichiometry of bulk SI GaAs; 2) the driving force for the currents under a zero-bias comes from the builtin surface field as well as a thermal gradient; 3) the trap species in the annealed LTMBE GaAs samples and the annealed control SI GaAs sample are similar, especially for TA(0.79eV), Ta (0.33eV), T4 (0.29eV), and T6*(0.16eV); and 4) the trap densities in LTMBE samples are higher than those in the control samples and are dependent on the MBE growth temperature.
Growth Technique For Large Area Mosaic Diamond Films†
Authors: Pryor R. W. , Geis M. W. , Clark H. R.
Published: March 2011

A new technique has been developed to grow semiconductor grade diamond substrates with dimensions comparable to those of currently available Si wafers. Previously, the synthetic single crystal diamond that could be grown measured only a few millimeters across, compared with single crystal Si substrates which typically are 10 to 15 cm in diameter. In the technique described, an array of features is first etched in a Si substrate. The shape of the features matches that of inexpensive, synthetic faceted diamond seeds. A diamond mosaic is then formed by allowing the diamond seeds to settle out of a slurry onto the substrate, where they become fixed and oriented in the etched features. For the experiments reported, the mosaic consists of seeds ∼ 100 μm across on 100 μm centers. A mosaic film is obtained by chemical vapor deposition of homoepitaxial diamond until the individual seeds grow together. Although these films contain low angle (<1°) grain boundaries, smooth, continuous diamond films have been obtained with electronic properties substantially better than those of polycrystalline diamond films and equivalent to those of homoepitaxial single crystal diamond films. The influence of growth conditions and seeding procedures on the crystallographic and electronic properties of these mosaic diamond films is discussed.
Polycrystalline Diamond Film Resistors
Authors: Edwards L. M. , Davidson J. L.
Published: March 2011

The technology to fabricate polycrystalline diamond film resistors has been initiated using modified thick film patterning techniques andin situsolid source doping.

Doping of polycrystalline diamond films in microwave plasma CVD systems has been achieved historically through use of diborane gas, which may contaminate the deposition system causing all diamond films thereafter to be doped p-type. We have attempted noncontaminatingin situdoping utilizing two solid source dopants, and have met with preliminary success.

The more effective source (B2O3) produces a fairly even dopant concentration across the substrate, with sheet resistances ranging from 800 ohms per square to 4500 ohms per square. The other source (BN) showed significant doping in a narrow band surrounding the source, but the doping concentration decreased rapidly with distance from the source. Films grown afterwards with no doping were evaluated through resistance measurements; no evidence of doping contamination was observed.
Growth and Characterization of ZnSe/ZnCdSe Diode Structures on (In, Ga)As Buffer Layers
Authors: Hua G. C. , Otsuka N. , Xie W. , Grillo D. C. , Kobayashi M. , Gunshor R. L.
Published: March 2011

ZnSe/ZnCdSe diode structures were grown on (In, Ga)As buffer layers by molecular beam epitaxy. Lattice distortions and defect distributions in buffer layers and diode structures were examined by X-ray diffraction and transmission electron microscopy. Diode structrues with low dislocation densities were obtained by the growth on tetragonally distorted In0.043 Ga0.957 buffer layers, the lattice spacing of which is slightly smaller than that of ZnSe.
MBE Growth and Properties of Wide Band-Gap II-VI Strained-Layer Superlattice
Authors: Wang Hailong , Cui Jie , Shen Aidong , Xu Liang , Chen Yunliang , Shen Yuhua
Published: March 2011

The (ZnSe) /(ZnS ), strained layer super-lattices (SLSs) on (100) GaAs and (ZnTe)/(ZnSe) SLSs on (100) InP have been grown by molecular beam epitaxy (MBE) and atomic layer epitaxy (ALE). The structural characteristics of these SLSs were investigated in situ RHEED observation, low-angle X-ray diffraction spectra, TED image and AES analysis. The optical properties of the SLSs, such as refractive index of superlattice materials, photoluminescence (PL) spectra, transient PL spectra, Raman spectra, far-infrared reflectivity spectra and Optical nonlinear have been studied.
Excimer Laser Melting of MBE-ZnSe
Authors: Padmapani Nallan C. , Yi G. -J. , Neumark G. F. , Lu Z. , Chang C. C. , Tamaargo M. C.
Published: March 2011

It has. generally been concluded that good doping in wide-gap semiconductors is best accomplished by non-equilibrium means. Excimer lasers, because of their high intensity and short pulses, are ideal for this. Our earlier laser annealing work on bulk ZnSe resulted in complications due to increased twinning of the sample. Our present work shows that twinning can be eliminated by the use of originally untwinned MBE material. The MBE samples had the additional advantage, over bulk, of a far smoother surface, which simplified the investigation of melting and evaporation. Use of power levels of 10, 20, and 35 MW/cm2 showed no melting at 10 MW/cm2, melting and no detectable evaporation at 20 MW/cm2, and evaporation at 35 MW/cm2. Combined ion beam cratering and SEM examination showed a depth of the melted layer, at 20 MW/cm2, of - 0.5 μm. Moreover, AES analysis showed minimal decomposition of the 20 MW/cm2 sample.
On the Burste In-Moss Shift in Quantum Confined Wide-Band Gap Semiconductors
Authors: Ghatak Kamakhya P. , De Badal
Published: March 2011

We study the Burstein-Moss shift (BMS) in quantum wiies and quantum dots of wide-gap semiconductors, taking Ge as an example, it is found that the BMS increases with increasing electron concentration in a ladder like manner. The numerical values of the BMS is greatest in quantum dots and least in quantum wells. The theoretical analysis is in agreement with the experimental results as given elsewhere.
Characterization of AlXGa1-xN Grown by MOCVD at Low Temperatures
Authors: Yu Z. J. , Sywe B. S. , Edgar J. H.
Published: March 2011

The low temperature deposition (400–650° C) of AlxGa1-xN films by metalorganic chemical vapor deposition (MOCVD) was characterized. Triethylgallium (TEG), trimethylaluminum (TMA), and ammonia (NH3) served as the precursors and both sapphire and silicon as the substrates with helium as the carrier gas. The deposition was operated at the atmospheric pressure. The crystallinity was improved even at low temperatures when AlxGal-xN was grown on a thin buffer layer of A1N at 400° C. With an AlxGa1-xN/AIN layered structure, epitaxial growth of AlxGa1-xN was obtained at 650° C on sapphire substrates. Auger results showed that the Al fraction x was less than 0.1. X-ray diffraction indicated a strong peak at 2θ =34.9 degrees for the (0002) planes from the film on sapphire substrates. The electron channelling pattern (ECP) of the film produced at 650° C revealed a 6 fold symmetry contrast pattern indicating the epitaxial growth of the film. Photoluminescence (PL) showed a dominant emission at 353 nm for the film on sapphire substrate. Surface morphology examined by SEM was featureless for the film produced at 500° C, while a relatively rough surface can be seen on the film produced at 650° C (5, 000x). The band gap was measured as 3.56 eV. The Al mole fraction x in the alloy was observed to be lower than that in the gas phase.
Low Temperature Preparation of Gallium Nitride Thin Films
Authors: Gordon Roy G. , Hoffman David M. , Riaz Umar
Published: March 2011

Gallium nitride thin films were prepared by atmospheric pressure chemical vapor deposition from hexakis(dimethylamido)digallium, Ga2(NMe2)6, and ammonia precursors at substrate temperatures of 100–400 °C with growth rates up to 1000 Å/min. The films were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry and forward recoil spectrometry. The N/Ga ratio varied from 1.05 for films deposited at 400 °C to 1.5 at 100 °C. The hydrogen concentration increased from 10 atom % for films deposited at 400 °C to 24 atom % at 100 °C. Films deposited at 100 °C were amorphous but films deposited at higher temperatures were polycrystalline. Bandgaps of the films varied from 3.8 eV for films deposited at 400 °C to 4.2 eV at 100 °C.
An Investigation of Light Induced Defects in Aluminum Nitride Ceramics
Authors: Harris J. H. , Youngman R. A.
Published: March 2011

It has been observed that aluminum nitride (AIN) ceramics exhibit a significant photo-darkening when exposed to UV or X-ray radiation, though the origin of this effect has never been understood. In this study, the optical character of these defects is investigated utilizing a UV-pump, visible-probe arrangement, where very large changes ΔT in the probe transmission T (induced absorption) are observed after excitation (Δ/T-0.60). These experiments reveal that the photo-darkening is due to the creation of light induced defects, with an energy level deep in the AIN bandgap. Utilizing these results, a light induced defect formation model is proposed which is consistent with the known defect chemistry of this material.
Crystalline Growth of Wurtzite GaN on (111) GaAs
Authors: Ross J. , Rubin M. , Gustafson T. K.
Published: March 2011

Gallium Nitride films were grown on (111) Gallium Arsenide substrates using reactive rf magnetron sputtering. Despite a 20% lattice mismatch and different crystal structure, wurtzite GaN films grew epitaxially in basal orientation on (111) GaAs substrates. Heteroepitaxy was observed for growth temperatures between 550–600°C. X-ray diffraction patterns revealed (0002) GaN peak with a full-width-half-maximum (FWHM) as narrow as 0.17°. Possible surface reconstructions to explain the epitaxial growth are presented.
Structrual Characterization and Raman Scattering of Epitaxial Aluminum Nitride Thin Films on Si(111)
Authors: Meng W. J. , Perry T. A. , Heremans J. , Cheng Y. T.
Published: March 2011

Thin films of aluminum nitride were grown epitaxially on Si(111) by ultra-high-vacuum dc magnetron reactive sputter deposition. Epitaxy was achieved at substrate temperatures of 600° C or above. We report results of film characterization by x-ray diffraction, transmission electron microscopy, and Raman scattering.
Tem Study of Dislocations in Plastically Deformed AlN
Authors: Audurier V. , Demenet J. L. , Rabier J.
Published: March 2011

AlN ceramics were plastically deformed using uniaxial compression under hydrostatic pressure between room temperature (RT) and 800°C. Deformation microstructures have been studied by Transmission Electron Microscopy (TEM) using the weak beam technique. The deformation substructure at RT is characterized by perfect glide loops with 1/3<1120> Burgers vector in (0001) elongated in the screw direction. When deformation temperature increases, the screw character is associated to cross slip events and dislocation dipolesare found. In the investigated temperature range, slip of dislocations with 1/3<1120> Burgers vector is also evidenced on prismatic planes. Weak beam observations failed to evidence any dislocation splitting. Some of these dislocation properties, similar to those of III-V compound semiconductors, suggest that electronic doping effects could be used to control plastic behaviour of covalent ceramics.
Temperature Dependence of Optical Properties of AlAs, Studied by In Situ Spectroscopic Ellipsometry
Authors: Yao Huade , Snyder Paul G. , Stair Kathleen , Bird Thomas
Published: March 2011

The dielectric functions ε = ε1+iε2 of AlAs were determined from 1.5 eV to 5.0 eV, by spectroscopie ellipsometry (SE), from room temperature (RT) to ∼577 °C in an ultrahigh vacuum (UHV) chamber. Molecular beam epitaxy (MBE)-grown AlAs was covered by a thin GaAs layer, which was passivated by arsenic capping to prevent oxidation. The arsenic cap was desorbed inside the UHV chamber. SE measurements of the unoxidized sample were made, at various temperatures. Temperature dependent optical constants of AlAs were obtained by mathematically removing the effects of the GaAs cap and substrate. Quantitative analyses of the variations of critical-point energies with temperature, by using the harmonic oscillator approximation (HOA), indicate that the E1 and E1+Δ1 energies decrease -350 meV as temperature increases from RT to 500 °C.
Epitaxial Monocrystalline SiC Films Grown on Si by Low-Pressure Chemical Vapor Deposition at 750°C
Authors: Golecki I. , Reidinger F. , Marti J.
Published: March 2011

Monocrystalline, epitaxial cubic (100) SiC films have been grown on monocrystalline (100) Si substrates at 750°C, the lowest epitaxial growth temperature reported to date. The films were grown by low-pressure chemical vapor deposition, using methylsilane, SiCH3H3, a single precursor with a Si:C ratio of 1:1, and H2. The films were characterized by means of transmission electron microscopy, single- and double-crystal X-ray diffraction, infra-red absorption, ellipsometry, thickness measurements, four-point probe measurements, and other methods. Based on X-ray diffractometry, the crystalline quality of our films is equivalent to that of commercial films of similar thickness. We describe the novel growth apparatus used in this study and the properties of the films.
Evaluation of Silicon Carbide Formed with a Single Precursor of Di-Tert-Butylsilane
Authors: Tay Sing-Pin , Ellul J. P. , Hewitt Susan B. , Tarr N. G. , Boothroyd A. R.
Published: March 2011

A low temperature process of silicon carbide deposition using the pyrolysis of di-tert-butylsilane has been explored for formation of emitter structures in silicon heterojunction bipolar transistors. Near stoichiometric amorphous silicon carbide films were achieved at 775°C. Doping and annealing of these films resulted in resistivity as low as 0.02 ohm-cm.
Stress-Induced Polytypic Transformation in Sic
Authors: Yang J. W. , Suzuki T. , Pirouz P. , Powell J. A. , Iseki T.
Published: March 2011

Deformation experiments were carried out on 6H-SiC single crystals and the deformed samples were examined by electron-optical techniques to verify any evidence for stress-induced polytypic transformation.
Heteroepitaxial Growth of Cubic Boron Nitride on Silicon
Authors: Doll G. L. , Perry T. A. , Sell J. A. , TAYLORS C. A. , Clarke R.
Published: March 2011

New x-ray diffraction measurements performed on bonm nitride films deposited by pulsed excimer laser deposition are presented. The x-ray data, taken with both a molybdenum rotating anode source and synchrotron radiation, indicate that the epitaxial cBN films are ≤ 200 Å thick. We also report the successful growth of oriented crystalline diamond on the (001) surface of cBN/Si substrates using the method of pulsed laser deposition. X-ray diffraction measurements indicate that the diamond layer is 200 Å thick with a lattice constant of 3.56 Å. The structures of metastable films (cBN and diamond) are very sensitive to growth conditions: we present evidence that an epitaxial-crystalline to incoherent phase transition occurs when the thickness of the films exceeds a critical value (∼ 200 Å for our present growth conditions).
Pulsed Excimer Laser Ablation Deposition of Boron Nitride on Si (100) Substrates
Authors: Friedmann T. A. , McCarty K. F. , Klaus E. J. , Boehme D. , Clift W. M. , Johnsen H. A. , Mills M. J. , Ottesen D. B. , Stulen R. H.
Published: March 2011

We are studying the boron nitride system by using a pulsed excimer laser to ablate from hexagonal BN (hBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (600°C) silicon (100) surfaces in a flowing (0- 10 sccm) ambient background gas of either NH3 or N2 of varying partial pressure (0–100 m Torr). Infrared (IR) reflection spectroscopy indicates the films have short-range hexagonal order. Some films grown at low laser energy densities have shown the cubic phase in IR transmission. Auger electron spectroscopy (AES) indicates the films are nitrogen deficient, which is linked to changes in the target stoichiometry with increasing laser fluence. Raman spectroscopy on the films shows only a strong background luminescence suggesting a high concentration of defects associated with the nitrogen vacancies. Atomic force microscopy (AFM) of the films shows a surface morphology that roughens as the growth rate increases. In order to improve the film stoichiometry it was necessary to actively enhance the nitrogen content of the films. It was found that bombarding films during growth with ions from an ion gun filled with NH3 gas increased the N/B ratio but did not enhance the cubic phase. RF biasing the substrate gave films which showed both cubic and hexagonal features in IR reflection. High resolution transmission electron microscopy (TEM) confirms the presence of cBN grains of ∼ 200Å size in films grown with an RF bias.
Growth of Tetrahedral Phases of Boron Nitride thin Films by Reactive Sputtering
Authors: Moustakas T.D. , Lei T. , Molnar R. J. , Fountzoulas C. , Oles E.J.
Published: March 2011

Tetrahedrally coordinated phases of boron nitride (c-BN and w-BN) were produced by reactive sputtering. The structure of the films was investigated by XRD and TEM diffraction, and found to be poly cry stalline. Films with microhardness up to 3500kg/mm2 were deposited but some degradation over time has been observed. A model for the stabilization of the tetrahedral phases over the graphitic one is proposed.
ESR Characteristics of Cubic Boron Nitride Crystals
Authors: Zhang Fangqing , Chen Guanghua
Published: March 2011

Electron spin resonance (ESR) spectrum have been used to study undoped cubic boron nitride crystals. The results show that the peak-to-peak width of the ESR signal is 27×10-4 T and the g-value is 2.00248, the spin density N s is 2.8×1015 cm-3, it is considered that the ESR signal is originated from the nitrogen dangling bond. Raman spectrum measurements have been also carried out, the peak positions are at 1054 cm-1 and 1306 cm-1.
An Investigation into the Use of a Diffusion Barrier in the Microwave Plasma Assisted Chemical Vapor Deposition of Diamond on Iron Based Substrates
Authors: Weiser Paul S. , Prawer S. , Hoffman A. , Manory R. , Paterson P. J. K. , Stuart S-A.
Published: March 2011

The growth of CVD diamond onto iron based substrates is complicated by preferential soot formation and carbon diffusion into the substrate, leading to poor quality films and poor adhesion. One strategy to overcome these problems is the use of thin film barrier layers between the Fe substrate and the growing diamond film. The present investigation reports the growth of diamond films on Fe substrates coated with thin films of TiN. The effectiveness of the TiN layers in inhibiting C diffusion into the Fe substrate was investigated by Auger measurements of the C distribution within the TiN layer, through the interface and into the substrate both before and after diamond deposition.

The results show that a layer of TiN only 250Å thick is sufficient to inhibit soot formation and C diffusion into the Fe bulk, as well as providing nucleation sites for CVD diamond growth.
High-Quality Amorphous Silicon Carbide Prepared by a New Fabrication Method for a Window P-Layer of Solar Cells
Authors: Ninomiya K. , Haku H. , Tarui H. , Nakamura N. , Tanaka M. , Wakisaka K. , Tsuda S. , Nishiwaki H. , Nakano S. , Kuwano Y.
Published: March 2011

A total area conversion efficiency of 11.1% has been achieved for a 1Ocm×1Ocm integrated-type single-junction a-Si solar cell submodule using a high-quality wide-bandgap p-layer doped with B(CH3)3 and other advanced techniques. This is the highest conversion efficiency ever reported for an a-Si solar cell with an area of 100cm2. As for a multi-junction solar cell, 12.1% was obtained for a 1cm2 cell with a high-quality wide-bandgap a-Si i-layer. The layer was fabricated by a hydrogen dilution method at a low substrate temperature for a front active layer of an a-Si/a-Si/a-SiGe stacked solar cell.

For further improvement in conversion efficiency, a wider-bandgap a-SiC was developed using a novel plasma CVD method, called the CPM (Controlled Plasma Magnetron) method. From XPS and IR measurements, the resultant films were found to have high Si-C bond density and low Si-H bond density, p-type a-SiC was fabricated using the post-doping technique, and dark conductivity more than 10-5(Q. cm)-1 was obtained (Eopt3 ≥ 2eV; Eopt2 2.2eV), whereas that of conventional p-type a-SiC is less than 10-6(Ω·cm)-1. These properties are very promising for application to the p-layers of advanced a-Si solar cells.
Doped Amorphous and Microcrystalline Silicon Carbide as Wide Band-Gap Material
Authors: Demichelis F. , Pirri C.F. , Tresso E. , Rava P.
Published: March 2011

Amorphous and microcrystalline silicon carbide, undoped and doped, are promising materials as wide band gap semiconductors (Eg > 2 eV). In the present work results on nydrogenated and fluorinated a-SiC and uc-SiC films intrinsic, B or P doped are reported. Energy gap higher than 2 eV are obtained together with electrical dark conductivities in the range 10-12 -10-2 Ω-1cm-1
Wide-Gap Polysilane Produced by Plasma-Enhanced CVD at Cryogenic Temperatures
Authors: Miyazaki S. , Shin H. , Okamoto K. , Hirose M.
Published: March 2011

Polysilane thin films have been grown by the rf glow discharge decomposition of SiH4 at substrate temperatures ranging from -84 to -110°C. The infrared absorption spectra have shown that polysilane chains (SiH2)n are predominantly incorporated in the matrix together with SiH3 which terminates the chain. Also, the infrared absorption band at 2120∼2140 cm-1 and a distinct Raman peak at ∼430 cm-1indicates that fairly long chains (SiH2)n with n>11 are produced. Polysilane prepared at -110°C has an optical bandgap of about 3.1 eV and exhibits a visible luminescence around 2.75 eV at 100 K.
Optically Induced Paramagnetism in Amorphous Hydrogenated Silicon Nitride Thin Films
Authors: Warren W. L. , Kanicki J. , Rong F. C. , Buchwald W. R. , Harmatz M.
Published: March 2011

The creation mechanisms of Si and N dangling bond defect centers in amorphous hydrogenated silicon nitride thin films by ultra-violet (UV) illumination are investigated. The creation efficiency and density of Si centers in the N-rich films are independent of illumination temperature, strongly suggesting that the creation mechanism of the spins is electronic in nature, i.e., a charge transfer mechanism. However, our results suggest that the creation of the Si dangling bond in the Si-rich films are different. Last, we find that the creation of the N dangling-bond in N-rich films can be fit to a stretched exponential time dependence, which is characteristic of dispersive charge transport.
Selective Nucleation of Diamond Crystals on the Apex of Silicon Pyramids
Authors: Ramesham R. , Ellis C.
Published: March 2011

Diamond crystals have been selectively grown on the apex of anisotropically chemically etched silicon pyramids. A novel process sequence is developed which exposes patterned sharp apex of silicon pyramids surrounded by thermally grown silicon dioxide to a high pressure microwave plasma-assisted chemical vapor deposition (HPMACVD) process where the reactant feed gases are methane and hydrogen. Nucleation rate of diamond is very high on the sharp edge of a silicon mesa structure or an apex of a silicon pyramid as anticipated. Selective growth of diamond particles on the apex of silicon pyramids fabricated using various approaches were analyzed by scanning electron microscopy.
Observation of Gas Flow Patterns In A CVD Reactor For Wide Band Gap Semiconductor Thin Film Deposition
Authors: Atsumi Kinya , Ueno Yoshiki , Hattori Tadashi , Hamakawa Yoshihiro
Published: March 2011

A new method for the direct observation of two-dimensional gas flow patterns in a CVD reactor has been developed by combining a laser scanning technique with generating micron-sized TiO2 particles. With this specially developed technology, the size of generated TiO2 particles are quite uniform, and of high density by the use of hydrolysis of Ti-alkoxide in the ceramic honeycomb at the top inlet of the model chamber. In this system, vertical cross sections of the gas flow patterns can be visualized by illuminated TiO2 particles in a He-Ne laser light sheet. Using this technique, detailed gas flow patterns can be clearly identified in the reaction chamber. Changes in the gas flow patterns with the various growth conditions, such as gas flow rate and pressure, have been measured. In this presentation, GaAs thin film growth by the MOCVD method will be reported as an example.

This gas flow visualization method could be a useful tool to identify the mechanism of CVD reactions to give better understanding about carrier gas transport and thin film growth for wide band gap semiconductors such as GaN, a-SiC, SiNx, etc.
Electronic Transition-Related Optical Absorption in Vanadia Films
Authors: Abuhadba Nada M. , Aita Carolyn R.
Published: March 2011

Vanadium pentoxide (vanadia) is a wide band gap semiconductor. Its layered orthorhombic structure consists of alternating sublayers of V+O atoms and O atoms (vanadyl O) alone aligned perpendicular to the b-axis. This unique structure makes vanadia a useful host for alkali atom intercalation for electrochromic applications, and therefore, an understanding of its optical properties is important. Here, we study the optical absorption characteristics of vanadia in the incident photon energy range E=2.5–6.0 eV (λ=490–200 nm). The material is in the form of 0.1μm thick films sputter deposited in Ne/O2 discharges. Two types of films were studied: single-oriented films with the b-axis perpendicular to the substrate, and amorphous films with an oxygen deficiency. The optical absorption coefficient, α(E), was determined and interpreted in terms of the structure of the V 3d conduction band. Amorphous, O-deficient vanadia were examined for room temperature aging and were found to oxidize and increase in transmittance in the photon energy range studied.
ZnO on Si3N4 Bimorphs with Large Deflections
Authors: Choi Wai-Shing , Smits Jan G.
Published: March 2011

Piezoelectric bimorphs and piezoelectric strain sensors based on sputtered ZnO films were fabricated on Si3N4 cantilever beams to form tactile sensors. The sensors were used to determine object positions. Deflections of the bimorphs showed a quadratic dependence on the applied voltages. Deflection as large as 1166 μm were registered for a bimorph of 2980 μm long. The apparent d33 of ZnO under a bias of -4 volts was - 103 × 1O-12 m/V, which was approximately 20 times larger than the previously reported values of -5.12 × 10-12m/V. The large deflections of the bimorphs were due to the quadratic effect under strong electric field.
Nanometer Size Lead Iodide Particles
Authors: Mehrotra Vivek , Rodeghiero Eric , OTTO Jens W. , Giannelis Emmanuel P.
Published: March 2011

Nanometer size lead iodide particles have been synthesized in the porous network of a cross-linked polymer matrix. The optical band gap of the nanocrystals is shifted towards higher energy as compared to the bulk value. This shift is attributed to the quantum size effect on excitons. Intercalation with aniline leads to a further shift in the band gap which depends on the dipole moment of the intercalated guest species. Differential scanning calorimetry and high temperature x-ray diffraction have been used to analyze the ferroelectric transition in Pbl2.
Diamond as a Material in Solid State Electronics
Authors: Vavilov Victor S. , Lebedev P.N.
Published: March 2011

Present state of the work devoted to the control of properties of diamond is analyzed, with emphasis on the results obtained in USSR, including the data on ion implantation and several types of devices. Future possibilities of the work with single crystals, films and diamond ceramics are discussed and typical difficulties indicated.
Investigation of Cvd-Grown Diamond by Cathodoluminescence in TEM
Authors: Graham R.J.
Published: March 2011

High resolution cathodoluminescence (CL) spectroscopy and imaging have been performed in transmission electron microscopy (TEM) to analyze defects and impurities in polycrystalline diamond films grown by chemical vapor deposition (CVD) using a variety of gas mixtures, and oxyacetylene combustion flame synthesis (CFS). The combination of CL and TEM allows a direct correlation of film microstructure with the electronic structure due to defects. The CL was found to be very nonuniformly distributed on a submicron scale reflecting different spatial distributions of N, B and Si impurities and their correlations with microstructure. Band A CL due to closely-spaced donor-acceptor (D-A) pairs was correlated with dislocations in both CVD-grown and CFS material whereas band A from widely-separated D-A pairs was uniformly distributed in the films. CL from several different N-related point-type defects was observed and found to depend on the growth gases used, although no correlation with microstructure has been observed so far. A di-Si interstitial impurity, believed to arise from the Si substrate and reactor walls, was not correlated with any microstructure but varied greatly in concentration from grain to grain and from film to Film. In addition, both highly faulted and defect-free grains were found to emit no visible CL due to mid gap states.
Effect of Electrode Materials on the Microstructure of Sol-Gel Derived Pzt Ferroelectric Thin Films
Authors: Myers Sharon A. , Myers Edward R.
Published: March 2011

A wide range of electrode materials have been investigated for use in ferroelectric-silicon CMOS technology. Numerous metal and metal-oxide films were deposited on silicon substrates and coated with sol-gel derived ferroelectric thin films. The films were sintered in either a diffusion furnace or by rapid thermal processing. Transmission electron microscopy was used to investigate the evolution of the resulting ferroelectric thin film microstructure and ferroelectric / electrode material interactions.

Microstructural differences such as the volume fraction of the ferroelectric perovskite and pyrochlore phase, domains and grain structure are correlated with electrical results. A strong microstructural dependence on the substrate was found for the Cr, Zr, Hf and Ni electrode materials. In general, chromium and other metal-oxide films had high leakage currents and large volume fractions of the non-ferroelectric pyrochlore phase. Nickel electrodes displayed the best electrical results, but the microstructure is very different from the other ferroelectric films.
Crystallization of Sol Gel Pzt on Aluminium and Platinum Metallizations
Authors: Barrow D. , Vasant Kumar C.V.R. , Pascual R. , Sayer M.
Published: March 2011

Sol gel prepared PZT films from 0.3 - 1.0 μm in thickness can be crystallised at temperatures down to 520°C on aluminium substrates, but such films are often non-ferroelectric. Comparison with films made on Pt substrates suggests that reduced oxygen content at the interface nucleates a cubic non-ferroelectric PZT phase.
Analysis of Electric Fields, Space Charges, and Polarization of Thin-Film Ferroelectric Capacitors Based on Landau Theory
Authors: Brennan Ciaran J.
Published: March 2011

This paper describes a detailed physical analysis of the electric fields, space charges, and polarization of thin-film ferroelectric devices. The analysis is based on a previously developed model of the electric field dependent polarization, permittivity, and hysteresis of the thin-film polycrystalline ferroelectric, which was derived from the Landau-Devonshire theory. This paper includes the macroscopic effects related to device structure and composition, including potential barriers at contacts, domain relaxation, grain boundary surface charge, and interactions between the space charges and the non-linear polar displacement.
Microstructure and Electrical Properties of Very Thin Pzt Films Deposited byIn-SituIon Beam Sputtering.
Authors: Gifford Ken D. , Al-Shareef H.N. , Rou S.H. , Hren P.D. , Auciello O. , Kingon A.I.
Published: March 2011

PZT films < 700Å have been synthesized by in-situ ion beam sputter deposition on Pt/Ti/MgO and RuO2/SiO2/Si substrates using deposition temperatures ≤ 500°C. Films on Pt/Ti/MgO had a highly preferred (001) orientation, whereas, the films on RuO2/SiO2/Si were randomly oriented. The formation of perovskite vs. pyrochlore phases has been studied. In the case of heavily Sn doped samples, it appeared that the doping promoted the nucleation of pyrochlore. We believe this effect was caused by a substantial reduction in the A:B cation ratio which was the result of Sn contaminated Pb targets. Electrical characterization was performed using parallel-plate electrodes. Hysteresis measurements showed high polarization values and coercive fields for the highly oriented films, whereas, the randomly oriented films showed much lower values of polarization. Fatigue measurements on the highly oriented films showed a sharp drop in polarization at 105or 106cycles. A decrease in Pr with time has been observed and is discussed.
Preparation and Microstructural Characterization of Ferroelectric Thin Film PbTiO3 on Si, MgO, and Sapphire Deposited by DC Reactive Multitarget Co-Sputtering.
Authors: Kim K.Y. , Hwang H.I. , Lee J.Y. , Choo W.K.
Published: March 2011

PbTiO3 thin films on Si (100) plane were prepared by the DC reactive multitarget cosputtering technique. The film composition and structure were examined as a function of deposition parameters. The crystal structure and microstructure of PbTiO3 thin film deposited on Si at low substrate temperature of 200°C were examined as a fuction of post-annealing temperature by X-ray diffraction and transmission electron microscopy.The ferroelectric domain configurations were analyzed by plane-view TEM. The preferred orientation of PbTiO3 thin films deposited on MgO (100) and sapphire (1102) at high substrate temperature of 520°C were also examined.
Advances in Ferroelectric Thin Film Research at Nec and in Japan
Authors: Matsubara S. , Miyazaki S. , Sakuma T. , Miyasaka Y.
Published: March 2011

High dielectric constant thin film capacitors for integrated circuits were fabricated with an LSI process. The capacitors comprized AI/TiN top electrode, Si3N4 interlayer insulator, SrTiO3 dielectric and Pt/barrier-metal/Si bottom electrode. Two types of capacitor structure were discussed on the basis of dielectric property and fabrication process. The TiN layer played an important role in suppressing degradation of insulating properties at elevated temperature, which was caused by a reaction between Al and SrTiO3. Breakdown strength larger than 6.6 MV/cm was obtained for 0.001 mm2 area capacitors. However, the strength decreased with increasing capacitor area. The area dependence may be due to surface defects which were introduced during the processes subsequent to SrTiO3 film deposition. The capacitance density of about 9 fF/μm2 was obtained for 150nm thick film. Recent activities of ferroelectric thin film research in Japan was given as well.
Residual Stress in Pzt Thin Films and its Effect on Ferroelectric Properties
Authors: Garino Terry J. , Harrington Mark
Published: March 2011

The residual stress in solution derived Pb(Zr.53Ti.47)o3, PZT 53:47, films was determined by measuring the bending of the substrate due to the stress. The substrate consisted of an oxidized (100) silicon wafer with 300 nm coating of platinum. In all cases the stress was tensile. Films fired at a temperature in the range where pyrochlore formation occurs (500° to 575°C) had the highest residual stresses, 200 to 350 MPa, whereas those fired at higher temperatures, 600° to 650°C, where the perovskite phase forms had stresses of 100 to 200 MPa. Stress measurements made during film firing indicate that the pyrochlore containing films had higher residual stress because their coefficient of thermal expansion was much larger than that of predominantly perovskite films. The effect of the amount of stress on ferroelectric properties was studied by making measurements on a film with and without the application of an external stress. The external stress was applied by bending a circular section of the substrate, which effectively lowered the amount of tensile stress in the film by ∼30%. Decreasing the stress in this manner was found to increase the remanent polarization by ∼11% and the dielectric constant by ∼2%.
Breakdown and Hysteresis in Thin Ferroelectric Polymer Films
Authors: Guy I. L , Tansley T. L. , Arafin P. , Moroney C. M.
Published: March 2011

Hysteresis loops obtained from sub-micron films of ferroelectric polymers show a maximum polarization which depends on the frequency of the driving field, the thickness of the film and the number of loops previously traversed (fatigue). We speculate that these effects result from changes in domain wall mobility. For films with thickness above 200nm, the hysteresis loops show no significant thickness dependence. This implies that the dimension of regions of field non-uniformity near the electrodes is less than 200 nm.

In ferroelectric polymers subject to a uniformly increasing field, the variation of breakdown strength with the field ramp-rate indicates that sample heating has a significant effect on the dielectric strength. At low ramp rates (below 100 MVm−1s−1) the heating in the sample is mainly due to Joule heating and the dielectric strength increases with increased ramp rate. At higher ramp rates the predominant heating mechanism is dipolar dielectric loss and the dielectric strength decreases with increased ramp rate. The two mechanisms combine to produce a maximum in the dielectric strength vs ramp-rate plot.
Ferroelectric Thin Films for Microactuator Applications
Authors: Chen Jiayu , Udayakumar K. R. , Brooks Keith G. , Cross L. Eric.
Published: March 2011

Ferroelectric thin films of PZT and PMN-PT were fabricated by the solgel spin-on technique. The films show high dielectric constants, polarization and breakdown strength values. Using a laser interferometer (ultradilatometer), the piezoelectric and electrostrictive coefficients of the films were measured. The results indicate that the sol-gel derived ferroelectric thin films have good electromechanical properties and can be used in rnicroactuator applications.
Role of Oxygen Vacancies on the Ferroelectric Properties of Pzt Thin Films
Authors: Kwok Chi Kong , Desu Seshu B.
Published: March 2011

The properties of ferroelectric thin films can be significantly influenced by the presence of point defects. The concentration of vacancies presented in these thin films is known to be one of the key parameters causing the degradation of these films when these films are subjected to polarization reversals.

To study the effects of the vacancy concentration on the ferroelectric properties, sol gel PZT films and powders were annealed in different oxygen partial pressures. For the PZT films, the reduction of oxides to pure metals was not observed even with films annealed at 2×10−5 atmosphere of oxygen partial pressure. Samples annealed at low oxygen partial pressure (for instance, 10−3 and 2×10−5 atmosphere), which has more Pb and O2 depletions and consequently has more Pb and O2 vacancies, cannot be switched easily. The ratios of coercive field after and before fatigue increase as the defect concentrations of the annealed samples increase.
Crystallographic Aspects of Ferroelectric Pzt Thin Films Prepared by Laser Deposition Technique
Authors: Wong-Ng Winnie , Huang Ting C. , Cook Lawrence P. , Schenck Peter K. , Vaudin M.D. , Chiang Chwan K. , Brody P.S.
Published: March 2011

X-ray diffraction techniques were used to study the crystallography of PZT thin films prepared by the laser deposition technique. This investigation included identification of phases formed during the annealing process and also the analysis of the profiles of selected diffraction peaks. The PZT films annealed below 800°C typically showed powder x-ray diffraction patterns corresponding to a cubic structure (i.e no peak splitting) instead of the tetragonal patterns characteristic of the target materials. The upper bound contribution of the macro and micro strain to the observed X-ray peak profile and positions was estimated. It was believed that the combined effect of small crystallite size together with residual strain, and possible local inhomogeneity gave rise to the broadening and displacement of the x-ray peaks, which subsequently masked off the splittings. At this stage the physical effect of high temperature annealing is not known. It is possible that as the annealing temperature increased, grain growth took place along with relaxation of residual strain, allowing peak splitting to be observed.
Undoped and Doped Perovskite Films: Sol-Gel Processing and Characterization
Authors: Klee Mareike , Waser Rainer
Published: March 2011

Thin undoped Pb(ZrxTi1−x)O3 (x=0.2-0.75), BaTiO3, SrTiO3 as well as acceptor (Mn, Ni) and donor (La, Ce) doped films with thicknesses of 0.2-1 μm have been deposited by a modified sol-gel process. The crystal structure and the morphology of the films as a function of the processing and composition were analyzed. The films were characterized with respect to their ferroelectric and dielectric properities e.g. permittivity, remanent polarization, coervice field strength, insulation resistance.
Lead Zirconate Titanate Stannate Thin Films for Large Strain Microactuator Applications
Authors: Brooks Keith G. , Chen Jiayu , Udayakumar K.R. , Cross L. Eric
Published: March 2011

Thin films of antiferroelectric tetragonal (Pb.97 La.02 )(Zr1-x-yTixSny)O3 have been synthesized from acetate and alkoxide precursors via a sol-gel process. A multiple layer spin coating procedure was used to prepare 0.4 gtm films on platinized silicon wafers. Crystallization of the films as confirmed by x-ray diffraction was achieved by rapid thermal annealing at 700°C for 20 seconds. Antiferroelectric to ferroelectric phase switching threshold fields were determined from P-E hysteresis curves. Longitudinal strain is reported as a function of applied electric field, with a maximum strain of 1.6×10-3 measured at an applied dc bias field of 120 kV/cm on a film of composition Pb.97 La.02 (Zr.60Ti.l0Sn.30 )O3. These films show promise for micromechanical actuator applications due to the high strain associated with field forced antiferroelectric to ferroelectric phase switching.
Chemical Vapor Deposition of Strontium-Barium-Niobate
Authors: Greenwald A. , Horenstein M. , Ruane M. , Clouser W. , Foresi J.
Published: March 2011

Spire Corporation has deposited strontium-barium-niobate by chemical vapor deposition at atmospheric pressure using Ba(TMHD), Sr(TMHD), and Nb ethoxide. Deposition temperature as 550°C in an isothermal furnace. Films were deposited upon silicon (precoated with silica), platinum, sapphire, and quartz. Materials were characterized by RBS, X-ray diffraction, EDS, electron, and optical microscopy. Electrical and optical properties were measured at Boston University.
Cross-Sectional Tem Studies of Barium Strontium Titanate Deposited on Silicon by Pulsed Laser Ablation
Authors: Pinizzotto Russell F. , Jacobs Elizabeth G. , Yang Hong , Summerfelt Scott R. , Gnade Bruce E.
Published: March 2011

Barium strontium titanate films were deposited onto silicon substrates using pulsed laser ablation deposition. The films were characterized using conventional and high resolution cross-sectional TEM. It was found that the grains were columnar with an average width of approximately 23 nm. An amorphous interfacial layer formed between the Si and BST in all cases. The interfacial layer thickness increased as the sample exposure to O2 increased. TiSi2 was also observed in all the films, although its location at the interface was not directly verified. There are no systematic effects of O2 overpressure on either the film thickness or film microstructure. However, the film which was fabricated with the greatest exposure to O2 may contain TixOy, and contains more equiaxed grains than the other samples. An interfacial layer was also observed at the Au-Pd/BST interface in a metal/ferroelectric/silicon capacitor. The significance of the results is the observation that BST may never come in direct contact with either capacitor electrode, which may explain why the fatigue behavior and electrical characteristics of ferroelectric capacitors depend so strongly on the interfaces.
Oxide Ferroelectric /Cuprate Superconductor Heterostructures: Growth and Properties
Authors: Ramesh R. , Chan W.K. , Gilchrist H. , Wilkens B. , Sands T. , Tarascon J.M. , Keramidas V.G. , Evans J.T. , Gealy F. Dan , Fork D.K.
Published: March 2011

Ferroelectric PbZr0.2Ti0.8O3/YBa2Cu3O7 heterostructures have been grown on single crystal LaAIO3 and on buffered [100] Si. The cuprate superconductors are used as metal-like bottom electrodes for the subsequent growth of the ferroelectric PZT thin film. Structural studies using x-ray diffraction, and transmission electron microscopy show that the PZT layer is free of large angle grain boundaries (i.e., single crystal-like). Rutherford backscattering studies reveal the composition of the PZT layer to be close to that of the target. Ferroelectric hysteresis measurements using both pulsed measurements and a variable frequency Sawyer-Tower circuit yield remnant polarization values (at 5V) in the range of 15-45μC/cm2 (depending on deposition conditions) with a coercive field in the range of 80-120kV/cm. At a cycling voltage of 5V, these heterostructures exhibit a fatigue lifetime of better than 2x1010 at 40kHz (the polarization decays by only 20% of the initial value). Pulsed poling experiments before and after show that the loss of polarization is reversible. These heterostructures also show excellent aging and logic state retention characteristics.
Piezoelectric Thin Film Ultrasonic Micromotors
Authors: Udayakumar K. R. , Chen J. , Brooks K. G. , Cross L. E. , Flynn A. M. , Ehrlich D. J.
Published: March 2011

Thin films of lead zirconate titanate have been fabricated for application to a new family of flexure-wave piezoelectric micromotors that are characterized by low speed and high torque. The high relative dielectric constant and breakdown strength of the films lead to high stored energy densities. Evaluation of the film as a bimorph yielded a value of -88 pC/N for the transverse piezoelectric strain coefficient, d31; the relevant electromechanical coupling factor, k31, calculated thereupon was 0.22. The development of the piezoelectric ultrasonic micromotors from the PZT thin films, and the architecture of the stator structure are described. Nonoptimized prototype micromotors show rotational velocities of 100-300 rpm at drives of 3-5 V.
Post-Processing of Pulsed Laser-Deposited Pzt Thin Films
Authors: Chiang C. K. , Wong-Ng W. , Cook L. P. , Schenck P. K. , Lee H. M. , Brody P. S. , Bennett K. W. , Rod B. J.
Published: March 2011

PZT thin films were prepared by pulsed laser deposition on unheated Ptcoated Si substrates. As deposited, the films were amorphous. Films crystallized at 550 - 600 °C to produce predominantly crystalline ferroelectric PZT. Crystallization of the amorphous material was accompanied by a linear shrinkage of ∼2 %, as manifested in development of cracks in the film. Spacing, width and morphology of larger cracks followed a regular progression with decreasing film thickness. For film thicknesses less than 500 runm, much of the shrinkage was taken up by small, closely-spaced cracks of local extent. Implications for measurement of PZT thin film ferroelectric properties and processing are discussed.