bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Elastic Mid-IR-Laser-Light Scattering for Non-Destructive Inspection in Microelectronics
Authors: Kalinushkin Victor P. , Yuryev Vladimir A. , Astafiev Oleg V. , Buzynin Alexander N. , Bletskan Nikolay I.
Published: April 2011

Some possible applications of the low-angle mid-IR-light scattering technique and some recently developed on its basis methods for non-destructive inspection and investigation of semiconductor materials and structures are discussed in the paper. The conclusion is made that the techniques in question might be very useful for solving a large number of problems regarding defect investigations and quality monitoring both in research laboratories and the industry of microelectronics.
Characterization of MOS Devices Fabricated on Carbon Implanted Silicon Substrates
Authors: Ban Ibrahim , Öztürk Mehmet C. , Christensen Kim , Maher Dennis M.
Published: April 2011

In this study, we present characterization of Metal-Oxide-Semiconductor (MOS) capacitors fabricated on carbon (C14) implanted silicon substrates. Carbon was implanted at an energy of 50 keV with doses ranging from 1 × 1012 cm−2 to 4.1×1015 cm−2. Metal-Oxide-Silicon (MOS) capacitors were fabricated and used to determine the MOS capacitance-voltage (C-V) and capacitance-time (C-t) behavior. These measurements revealed a strong correlation between carrier lifetime and the carbon dose. Degradation in lifetime was observed for carbon dose levels as low as 4 × l012 cm−2. At carbon doses equal to and above 6.4 × l013 cm−2, extremely low generation lifetimes were obtained (∼ 10−7 sec). On the other hand, degradation in C-V characteristics was observed only for carbon doses above 2.7 × l014 cm−2. Below this dose, both flatband voltage and interface trap density of the carbon implanted samples were comparable to those of the monitors. Analysis of the samples by cross sectional transmission electron microscopy revealed the absence of extended defects even in samples with high carbon dose levels.
Comparative Study of Experimental Techniques for Boron Profiling at Poly-Si/SiO2 Interface
Authors: Furtsch M. , Bevk J. , Bude J. , Downey S. W. , Krisch K. S. , Moriya N. , Silverman P. J. , Luftman H. S.
Published: April 2011

Electrical characterization of MOS structures and device modeling require accurate information about dopant concentration, particularly at the poly-Si/SiO2 interface. We compare four experimental techniques (secondary ion mass spectrometry SIMS, resonant ion mass spectrometry RIMS, differential Hall effect profiling, and spreading resistance analysis) to measure boron and free carrier concentrations in poly-Si, SiO2 and crystalline Si. We find that no single technique completely characterizes the entire MOS structure, and that spreading resistance analysis in particular substantially underestimates the free carrier concentration at the poly-Si/SiO2 interface. We conclude that in most cases of technological interest the magnitude of the poly depletion effect scales with the average carrier concentration at some distance away from the interface and that the interfacial effects, such as dopant segregation, are of only secondary importance. These findings are supported by theoretical modeling of capacitance-voltage behavior of boron-doped MOS capacitors.
Magnetic Exchange Coupling in Asymmetric Trilayers of Co/Cr/Fe
Authors: Theis-BrÖhl K. , Scheidt R. , Zeidler TH. , Schreiber F. , Zabel H. , Mathieu TH. , Mathieu CH. , Hillebrands B.
Published: April 2011

We present first results of anisotropy and exchange coupling studies of a system with two different magnetic layers (Fe and Co) separated by a nonmagnetic Cr spacer. For the magnetic measurements we used the longitudinal magneto-optical Kerr effect and ferromagnetic resonance. The hysteresis data obtained from the trilayer were fit to a theoretical model which contains both bilinear and biquadratic coupling. The in-plane anisotropy was found to be four-fold with the same easy-axis orientation for both the Fe and the Co layers. An analysis of the easy-axishysteresis loops indicates long period oscillatory coupling and also suggests a short period coupling.
Magnetism of Bct Iron Grown In (001) FeIr Superlattices
Authors: Andrieu Stéphane , Bauer Philippe , Lahatra-Razafindramisa Fils , Hennet Louis , Snoeck Etienne , Brunel Michel , Piecuch Michel
Published: April 2011

In this paper, we show that iron can be grown by MBE in a body centered tetragonal structure in (001) FeIr superlattices. The growth, structure and morphology of these superlattices are briefly resumed. A variation of the BCT Fe magnetic moment depending on the Jr thickness is observed. This variation is demonstrated to come from a variation of the BCT Fe atomic volume, due to the competition of the Fe and Ir stresses. A magnetic transition from a non-magnetic to a low spin ferromagnetic state depending on the atomic volume is thus observed.
Structural Studies and Magnetotransport Properties of Sputtered Ni/Co Multilayers
Authors: Freitag J.M. , Bian X. , Altounian Z. , Ström-Olsen J.O. , Cochrane R.W.
Published: April 2011

Ferromagnetic/ferromagnetic Ni/Co multilayers were prepared by DC-magnetron sputtering with component layer thicknesses ranging from 40 Å down to 5 Å. Structural characterizations by x-ray diffractometry show a well-defined compositional modulation along the film growth direction and a preferred (111) crystalline orientation. A longitudinal magnetoresistance ΔR/R over 2.7% with a sensitivity of ~0.11%/Oe was measured at room temperature in small fields less than 20 Oe. The highest room temperature sensitivity obtained in this system was 0.16%/Oe. Magnetoresistive sensitivity was found to vary inversely with the number of bilayers in the multilayers. The magnetic anisotropy of the films as determined by MOKE magnetometry is correlated to the magnetoresistance and indicative of an AMR effect.
(100) Epitaxial and (111) Polycrystalline Spin Valve Heterostructures on si (100): Magnetotransport and the Importance of Interface Mixing in Ion Beam Sputtering
Authors: Joo Hyun S. , Hashim Imran , Atwater Harry A. , Watson Thomas J.
Published: April 2011

We have investigated magnetoresistance properties of (100) epitaxial, (11) textured and polycrystalline spin valve heterostructures of the form Ni80Fe20/Cu/NiNi80Fe20/Fe50Mn50 on (100) Si substrates by ultra high vacuum (UHV) ion beam sputtering at room temperature. Magnetoresistance was measured as a function of Cu interlayer thickness (ti) with 10 Å ≤ti ≤ 100 Å and the maximum was found at 20 Å in the case of (100) epitaxial spin valves. Highly (11) textured spin valves with heterostructure configurations similar to the (100) spin valves were found to have a slightly lower magnetoresistance than the (100) heterostructures, but the functional dependence of the magnetoresistance on ti was very similar.

Interface mixing during the sputtering process by energetic neutral bombardment was found to significantly affect the magnetoresistance. Samples were made under various sputtering conditions (gas pressure, ion beam energy, target and substrate configuration) that could enhance or suppress high energy neutral bombardment of the growing film surface. Samples made under the conditions that suppressed neutral bombardment showed higher magnetoresistance and more abrupt interfaces as confirmed by small angle X-ray diffraction analysis of interface mixing by energetic neutral bombardment during sputter deposition.
Microstructure and Magnetic Properties of Nanocrystalline Fe93-x-yZr7B,xCuy Alloys
Authors: Kopcewicz M. , Grabias A. , Nowicki P.
Published: April 2011

An unconventional technique combining Mossbauer spectroscopy with the effects induced by magnetic radio-frequency fields (if collapse and if sidebands) is employed to study the microstructure and magnetic properties of nanocrystalline clusters of bcc Fe formed by annealing amorphous Fe93-x-yZr7B,xCuy (x=6, 8, 12, y=0, 2) alloys at 500-600°C. The rf-Mössbauer experiments allow us to distinguish magnetically soft nanoclusters from magnetically harder microcrystalline phases. The dependence of the bcc Fe phase formation on the alloy composition is discussed. The Mössbauer results are supplemented by DSC measurements.
Bonding and Penetration at Metal/Self-Assembled Organic Monolayer Interfaces
Authors: Jung D. R. , Czanderna A. W. , Herdt G. C.
Published: April 2011

The purpose of research on metals (M) deposited onto self-assembled monolayers (SAMs) is to understand the interactions between the metal and eventually metal oxide overlayers on well-ordered organic substrates. Applications of M/SAM and inorganic/SAM research results to the understanding of real inorganic/organic interfaces in vacuum and under environmental conditions can potentially play a key role in the development of advanced devices with stable interfacial properties. The results of selected M/SAM studies to date are reviewed, and MISAM combinations ranked according to reactivity and penetration. Specific examples of reactive interfaces (Cu/COOH, Cr/several groups) and nonreactive interfaces with penetration (Ag/CH3, Ag/COOH) are used to illustrate the extremes.
Adhesive Systems Based on Functionalized Block Copolymers
Authors: Saunders Randall S. , Kent Michael S.
Published: April 2011

Functionalized block copolymers were synthesized as adhesion promoters using Ring-Opening Metathesis Polymerization (ROMP). They were designed for glass/epoxy and copper/epoxy interfaces. The former contained triethoxysilane groups in the first block and secondary amine groups in the second. The latter contained imidazole groups in the first and amine groups in the second block. These block copolymers were shown to form ordered monolayers on the respective glass and copper surfaces using neutron reflectivity. Adhesion measurements showed an enhancement of adhesion after application of these block copolymers.
Cleaning of SiO2: Differences Between Thermal and Deposited Oxides
Authors: Ravkin M. , Farber J. J. , Malik I. J. , Zhang J. , Jensen A. J. , de Larios J. M. , Krusell W. C.
Published: April 2011

The effects described in this paper are specific to cleaning with mechanical brush scrubbing. Oxides, both thermally grown and deposited are common cleaning applications for mechanical brush scrubbing. Thermally grown oxides present higher final defect counts after scrubbing with deionized water compared to deposited oxides. In this paper we present our results on the cleaning of unpolished and polished oxide surfaces and show differences in these results to be dependent on the chemistry used for cleaning and the degree of hydrophilicity of the wafer surface.
Studies of the Relationship between Megasonics, Surface Etching, and Particle Removal in SC-1 Solutions
Authors: Cohen S. L. , Rath D. , Lee G. , Furman B. , Pope K. R. , Tsai R. , Syverson W. , Gow C. , Liehr M.
Published: April 2011

Wafer cleaning studies have been performed so as to understand the influence of acoustic (megasonic) energy on particle removal in dilute SC-1 solutions. Surface etching alone (up to 60Å) has been found to be insufficient to completely remove silicon nitride surface particles from native oxide surfaces in the absence of megasonics. For megasonic cleaning processes the minimum surface etching required for complete nitride particle removal is significantly lower (between 3–12Å) than for a non-megasonic process. The exact 'threshold' for surface etching will depend on the chemical nature of the particle/surface and the megasonics power. Megasonics energy does not appear to enhance chemical etching of the substrate, at least for silicon oxide substrates, however, it significantly improves particle removal. This data suggests that the particle removal process can benefit from both a thermally activated component (etching) as well as an acoustic component (cavitation/ acoustic streaming).
Measuring Diffusion Lengths in Epitaxial Silicon by Surface Photovoltage
Authors: Lowell John , Wenner Valerie , Debusk Damon
Published: April 2011

In CMOS, the use of epitaxial layers for prevention of latch-up in logic technologies is well-known and pervasive. One of the crucial parameters is the amount of metallic contamination due to transition metals such as Fe in the epi since this phenomena effects both device performance and quality. However, the ability to measure this parameter on product material is not generally available due to inherent problems with most known methods. The limitation of traditional surface photovoltage is that the deep optical penetration of over a hundred microns is well-beyond the depth of most epitaxial layers and does not accurately profile the epitaxial region [1]. In this paper we report on the application of optical surface photovoltage (SPV) using a set of ultra-shallow optical filters to both quantify and qualify as-grown epitaxial layers on CZ P-type silicon. We believe that a non-contact, SPV measurement of Fe concentration and diffusion lengths within an epitaxial region has not been previously reported.
Analyzing Atomic Force Micrographs Using Spectral Methods
Authors: Halepete Sameer D. , Lin H. C. , Fang Simon J. , Helms C. R.
Published: April 2011

Microroughness is a critical parameter in ULSI device interface reliability and has been shown to effect several critical MOS electrical properties. The atomic force microscope (AFM) has become the instrument of choice for silicon surface microroughness analysis. The parameters usually specified to characterize roughness are average and root mean square roughness. However, these parameters are spatial averages and can have the same value for two significantly different surfaces. Spectral analysis using the Fast Fourier Transform (FFT) has been applied as a powerful tool to analyze AFM data by looking at roughness as a function of spatial wavelength. The Fast Hartley Transform, being a real transform, is faster than the FFT and is better suited for this analysis. It has been used here to derive spectral information from the AFM height data. Before evaluating the transform, cancellation of any tilt or warp in the AFM data is done to remove frequency components which interfere with other spectral information. A PC-based computer program to determine the transform and its magnitude will be described. The application of this method to analyze data from Si and SiO2 surfaces as a function of pre-oxidation cleaning chemistry will be presented. Significantly better insight into the spatial distribution of roughness is obtained, when compared to previous implementations.
Removal of Metallic Contaminants and Native Oxide from Silicon Wafer Surface by Pure Water Containing a Little Dissolved Oxygen
Authors: Hayami Yuka , Suzuki Miki T. , Okui Yoshiko , Ogawa Hiroki , Fujimura Shuzo
Published: April 2011

Cleaning effects of pure water containing dissolved oxygen of very low concentration (LDO water) to metallic contaminants on silicon wafer surface were confirmed. To maintain the concentration of the dissolved oxygen in water, experiments were performed in a glove box in which ambience was controlled so as to satisfy Henry's law between the water and the ambient gas. In the experiment using intensionally contaminated wafers, residual metal contaminants except copper on Si-surface decreased from 1014atoms/cm2to 1011atoms/cm2after the 1ppb hot LDO treatment at boiling point. This effect depended on the concentration of dissolve oxygen, treatment temperature, and rinsing time. Contact angle of the wafer surface increased gradually from about 10 [deg] with decrease in the residual metals and jumped up to about 90 [deg]. when the amount of residual metals reached to minimum. Then absorption peak of Si-O bonds in FT-IR-RAS spectra also disappeared. These results therefore show that hot LDO water removed metal contaminants from the wafer surface with etching of the native oxide.
Pulsed-Laser Deposition of Titanium Nitride
Authors: Jiang Wenbiao , Grant Norton M. , Thomas Dickinson J. , EVANS N.D.
Published: April 2011

The pulsed-laser deposition technique has been used to form thin films of TiN on (100)-oriented single crystal substrates of silicon and rocksalt. Using atomic force microscopy, it was revealed that TiN films grown on silicon at substrate temperatures ranging from 50°C to 500°C were extremely smooth—the mean roughness being ~ 0.2 nm. Thin TiN films deposited on freshly cleaved NaCl were found to be epitaxial at substrate temperatures as low as 50°C. Epitaxy in this latter system is believed to be due to the structural similarity between film and substrate and the almost exact 4:3 coincident site lattice.
On- and Off-AXIS Large-Area Pulsed Laser Deposition
Authors: Greer James A. , Tabat M. D.
Published: April 2011

Over the past few years Pulsed Laser Deposition (PLD) has become a popular technique for the deposition of a wide variety of thin films, and PLD systems are currently found in numerous industrial, government, university, and military laboratories. At present, it is estimated that well over 200 different materials have been deposited by PLD and the list keeps growing. However, even with all the interest in laser deposition the technique has not yet emerged as an industrial process. At the moment, industry still prefers standard thin film growth techniques such as magnetron and ion beam sputtering, chemical vapor deposition, and electron beam evaporation for production applications. These processes have been in use for decades and have demonstrated the ability to deposit films of most materials over large areas with excellent uniformity at reasonable cost and deposition rates. Furthermore, an entire infrastructure has been built up to support these processes including standardization of deposition rate monitors, power sources, target and crucible sizes, etc. On the other hand, laser-deposition is still an emerging technology, and relatively little infrastructure exists to adequately support either research or industrial applications. Since there are several materials which are difficult if not impossible to grow in thin-film form by more conventional techniques, it is expected that as pulsed laser-deposition matures this unique process will take its rightful place on the manufacturing line.
Growth and Properties of Carbon Nitride Thin Films
Authors: John Zhang Z. , Yang Peidong , Lieber Charles M.
Published: April 2011

Recent research on carbon nitride thin films grown using pulsed laser deposition combined with atomic beam techniques is reviewed. the composition, growth mechanism and phases of these films have been systematically investigated. the nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 nm and 248 nm wavelengths. Time of flight mass spectroscopy investigations of the ablation products have shown that the fluence variations affect primarily the yield of the carbon reactant. these experiments demonstrate that the overall film growth rate determines the average nitrogen composition, and furthermore, suggest that a key step in the growth mechanism involves a surface reaction between carbon and nitrogen. INfrared spectroscopy has been used to assess the phases present in the carbon nitride thin films as a function of the overall nitrogen content. these measurements have shown that a cyanogen-like impurity occurs in films with nitrogen compositions greater than 30%. Studies of thermal annealing have shown, however, that this impurity phase can be eliminated to yield a single phase C2N material. IN addition, systematic studies of the electrical resistivity and thermal conductivity of the carbon nitride films are discussed.
Fabrication of a Free-Standing, Synthetic, Single Crystal Diamond Plate Using Ion Implantation and Plasma-Enhanced Chemical Vapor Deposition
Authors: Posthill J.B. , Malta D.P. , Humphreys T.P. , Hudson G.C. , Thomas R.E. , Rudder R.A. , Markunas R.J.
Published: April 2011

Using a specific combination of energetic and chemical processes we have grown homoepitaxial diamond on and lifted it off of a type Ia natural C(100) crystal. Before growth, the C(100) crystal is exposed to a self implant of 190keV energy and dose of 1E16 cm-2. Low temperature (~600°C) homoepitaxial diamond growth conditions were used that are based on water-alcohol source chemistries. To achieve layer separation (lift-off), samples were annealed to a temperature sufficient to graphitize the buried implant-damaged region. Contactless electrochemical etching was found to remove the graphite, and a transparent synthetic (100) single crystal diamond plate of 17.5μm thickness was lifted off. This free-standing diamond single crystal plate was characterized and found to be comparable to homoepitaxial films grown on unimplanted single crystal diamond.
Competitive Oxidation During Buried Oxide Formation Using Separation by Plasma Implantation of Oxygen (Spimox)
Authors: Liu Jingbao , Sundar Kumar Iyer S. , Min Jing , Chu Paul , Gronsky Ron , Hu Chenming , Cheung Nathan W.
Published: April 2011

We have recently demonstrated a new implantation technique called SPIMOX (separation by plasma implantation of oxygen) to synthesize silicon-on-insulator structures using plasma immersion ion implantation (PIII) process. the implantation is performed by applying a large negative bias to a Si wafer immersed in an oxygen plasma created by an ECR source. Since the technique has no mass analysis, coexistence of O+ and O2+ ions in oxygen plasma can cause a non-Gaussian profile of the as-implanted oxygen distribution. We observed that during post-implantation annealing, the ripening process of the oxide precipitates depends on depth and concentration of the oxygen peaks. IN addition, implanted oxygen can migrate towards the Si surface during annealing, preventing a continuous buried oxide layer formation. IN this paper, we report our observation on the effect of the implantation profile on the competitions between internal oxidation at different depths and between internal and surface oxidation processes. With an additional He implantation, we demonstrate that the nucleation of oxide precipitation can be enhanced.
Epitaxial Multilayers of (Sr,Ba)Nb2O6 and Conducting Films on (001) Mgo Substrates
Authors: Huang T. F. , Youden K. E. , Schwyn Thöny S. , Hesselink L. , Harris J. S.
Published: April 2011

(Sr,Ba)Nb2O6 (SBN) is a very promising material for nonlinear optical applications because of its high electro-optic and nonlinear optical coefficients. For these applications, SBN requires ferroelectric poling along the optical axis. Conducting layers such as Pt or YBCO must therefore be deposited to provide electrodes above and below the SBN film.

We have investigated the epitaxial growth of multilayers of Sr0.61Ba0.39Nb2O6/Pt and Sr0.61Ba0.39Nb2O6/YBCO thin films on (001) MgO substrates by pulsed laser deposition. X-ray diffraction 2θ scans indicate epitaxial growth of SBN/Pt/MgO and SBN/YBCO/MgO heterostructures with their c-axes perpendicular to the substrate plane. X-ray phi scans indicate single crystal Pt and YBCO growth with one in plane orientation. atomic Force Microscopy shows surface roughness of 2.19 nm, and no evidence of particles is observed.
High-Performance Thermoplastics for Rigid-Flex Printed Circuit Boards
Authors: Lin Wendy W. , Savrun Ender
Published: April 2011

Adhesive failure of rigid-flex printed circuit boards (RF-PCBs) during use has degraded the performance of military avionics systems. Adhesive failure is often caused by differences in the coefficient of thermal expansion (CTE) between the materials used in RF-PCBs and by moisture absorption by the adhesives and polyimide (PI) films. High-performance thermoplastics were investigated to replace the epoxies, PIs, and adhesives currently used in RF-PCBs. Because thermoplastic materials are remeltable, adhesive bonding may be replaced by fusion bonding to join RF-PCBs. Fusion bonding would eliminate problems with material compatibility and differences in the CTE encountered with adhesive bonding. Industries that would benefit from this research are manufacturers of aerospace instrumentation, medical equipment, automotive systems, computers, telecommunications equipment, industrial instrumentation and controls, and consumer products, such as stereo systems and calculators.

An extensive survey of high-performance-engineering thermoplastic materials was performed, and samples of the more promising materials (both films and chopped fiber reinforced) were obtained for preliminary screening tests. The tests performed were chemical resistance, water absorption, tensile strength, flexibility, and solder resistance of bare dielectric. From these tests, a glass-filled liquid crystal polymer film made by Hoescht Celanese Performance Films best met the performance criteria compared with the thermoplastics tested.
Corrosion Behaviour of Aluminum Metallization During Aqueous Exposure
Authors: Koo Y. C. , Walzak T. L. , Davidson R. D.
Published: April 2011

It is known that aluminum will readily form aluminum hydroxide during aqueous exposures. Thick oxide layers with a typical pseudoboehmite (fibre-like network) structure and bayerite crystals were observed on the aluminum metallization after the aqueous cleaning process. The study investigated the effect of a deionized (DI) water cleaning process (recently implemented to replace CFC-based cleaning technology) on the surface chemistry and corrosion behaviour of aluminum wire bond pads. The study also correlated the wire bond yield and oxide thickness with various water cleaning process parameters. The wire bond yield and reliability issues are discussed briefly.
Material Science and the Electronic Packaging Roadmap
Authors: Steidel C. A. , Sundahl R. C. , Grayeli N.
Published: April 2011

The National Technology Roadmap forecasts significant increases in performance for silicon devices over the next several years continuing the pace of the last 25 years. As the complexity and performance of the silicon have increased, so has the cost to manufacture the supporting packages. However, continued growth of the industry demands that package costs be held under control. A requirement of the Roadmap is a need for a significant lowering of cost over the period. On a per lead basis: for example, for cost/performance products in 1995 the range in per pin cost is 1.4–8 cents. These costs must move to 1–3 cents per lead over the next 15 years, while lead count increases from a few hundred to a few thousand. These costs will not be achievable unless we change how materials are developed and deployed to the market.
Determination of the Adhesive Strength of Film-Substrate Interfaces Using the Constant Depth Scratch Test
Authors: Dutta I. , Campbell J. C.
Published: April 2011

A constant depth scratch test (CDST) has been recently developed to quantify the shear strength of film-substrate interfaces. This test is capable of measuring interfacial adhesion as a function of position on the sample surface during a continuous scratch. Unlike many of the currently available tests which are applicable to a limited array of materials systems, or are experimentally complex, this test is quite versatile, and is relatively straightforward to conduct and interpret because of the constant depth geometry. The theoretical basis and the experimental set-up for the test have been previously presented. In this paper, extensions of the theoretical formulation to account for different debonding behaviors of different film-substrate systems are discussed. Experimental results generated with a number of systems, including chromium on glass, gold on aluminum nitride, gold on aluminum nitride with a chromium inter-layer, and polycrystalline diamond on aluminum nitride are presented.
Stability and Performance Issues for Nonlinear Optical Chromophores, Polymers and Devices
Authors: Twieg R. J. , Burland D. M. , Jurich M. , Lee V. Y. , Miller R. D. , Moylan C. R. , Siemens R. , Skumanich A. , Thackara J. I. , Verbeist T. , Volksen W. , Knoesen A. , Hill R. A. , Yankelevich D.
Published: April 2011

In the course of development of any new technology the issues of device stability and reliability are inevitably encountered and must be summarily dealt with. The development of organic and polymeric nonlinear optical media has been no exception and has now evolved to a stage wherein solutions to a few performance issues are of crucial importance. Discussions here focus on just two of these critical problems. First, we describe a preliminary study intended to identify some of the variables involved in optical damage. The goal here is to identify suitable photochemically stable chromophores and polymers and to elucidate any processing and environmental influences which contribute to damage. Second, the thermal stability of nonlinear optical chromophores has already attracted much attention and significant progress has been made in enhancing the thermal stability of many systems. Our most recent effort has concentrated on chromophores with a variety of different configurations and combinations of nitrile acceptor groups, some of which possess both large nonlinearities and excellent thermal stability. Some newer aspects of a thermal stability screening protocol which are particularly useful for these thermally stable chromophores and polymers are also described.
Ferroelectric Thin Films and Their Applications
Authors: Neurgaonkar R. R. , Oliver J. R. , Nelson J. G. , Santha I. S.
Published: April 2011

Ferroelectric morphotropic phase boundary (MPB) materials based on Pb2+ - containing compositions are potentially important for optical and electronic applications because they exhibit high switchable polarization near this boundary with superior electro-optic and piezoelectric properties. In this paper we discuss these MPB materials, substrate issues, and the growth of MPB film compositions based on the PZT and PSKNN systems.
Degradation, Structure and Properties of Fibrous Nonwoven Poly(Glycolic Acid) Scaffolds for Tissue Engineering
Authors: Ma Peter X. , Langer Robert
Published: April 2011

Biodegradable polymer scaffolds have been used to engineer new tissues or organs by culturing cells on them. The degradation, structure and properties of fibrous nonwoven poly(glycolic acid) (PGA) scaffolds (2 mm thick and 10 mm in diameter) were studied over 9 weeks in tissue culture medium at 37°C under mixing condition. After 3 days of in vitro culture, the mass of the scaffolds increased slightly (5.6%) due to hydration and/or adsorption, but it decreased thereafter. After 9 weeks, only 12.5% of the mass were retained. The melting point of the scaffolds decreased from 218.1°C to 186.0°C in the first 3 weeks, as measured with differential scanning calorimetry (DSC). No melting peak could be identified for later times (6 weeks and 9 weeks). The crystallinity of the scaffolds doubled over the first 11 days, but decreased thereafter. The glass transition temperature of the degrading scaffolds (36–39°C) was lower than that of the dry starting scaffolds (40°C) presumably due to the plasticizing effect of absorbed water and other low molecular weight molecules. The PGA scaffolds without cells lost their structural integrity and mechanical strength completely in 2 to 3 weeks. In contrast, the neocartilage constructs regenerated from the PGA scaffolds and bovine chondrocytes kept their structural integrity throughout the in vitro culture study. After 12 weeks of in vitro culture, the biomechanical properties of the neocartilage constructs reached the same orders of magnitude as those of normal bovine cartilage.
The Effect of a GaN Nucleation Layer on GaN Film Properties Grown by Metalorganic Chemical Vapor Deposition
Authors: Van Der Stricht W. , Moerman I. , Demeester P. , Crawley J.A , Thrush E.J. , Middleton P.G. , Trager Cowan C. , O'donnell K.P.
Published: April 2011

In this paper GaN films are examined, which are grown on basal plane (0001) sapphire substrates. Growth is performed in a novel type of vertical rotating disk reactor. Results on the effect of a GaN nucleation layer on the properties of the overgrown GaN epilayer are presented. Characterisation includes surface morphology studies, DC X-ray diffraction and optical characterisation. Best film quality so far has a double crystal X-ray half width of 85 arcsec at approximately 1 μm thickness.
Halide Vapor Phase Epitaxy of Gallium Nitride Films on Sapphire and Silicon Substrates
Authors: Perkins N.R. , Horton M.N. , Bandic Z.Z. , McGill T.C. , Kuech T.F.
Published: April 2011

A major limitation of the current technology for GaN epitaxy is the availability of suitable substrates matched in both lattice constant and thermal expansion coefficient. One alternative for the development of GaN substrates rests in the application of halide vapor phase epitaxy (HVPE) to produce GaN films at high growth rates. In this paper, we describe the growth of thick GaN films via the HVPE technique on (0001) sapphire and (111) Si substrates. At a temperature of 1030°C, films are grown at rates between 70 and 90 μm/hr, yielding total thicknesses exceeding 200 μm on sapphire. DCXRD measurements of GaN/sapphire indicate FWHM values less than 220 arcsec on 180 μm thick films. Room temperature PL measurements of GaN/sapphire indicate strong emission at 3.41 eV, with a FWHM value of 65 meV. Moreover, no detectable deep level emission was found in room temperature PL measurement. Under optimized conditions, films are morphologically smooth and optically clear. The GaN morphology appears to be a strong function of the initial nucleation conditions, which in turn are strongly affected by the partial pressure of GaCl. HVPE growth on (111) Si substrates is accomplished using an AlN MOVPE buffer layer.
Supersonic Jet Epitaxy: An Improved Method for Nitride Deposition
Authors: Norris Peter E. , Zhu Long D. , Paul Maruska H. , HO Wilson , Ustin Scott , Lauhon L.
Published: April 2011

GaN was grown by supersonic jet epitaxy(SSJE), seeding triethylgallium in helium carrier gas. Activated nitrogen was supplied by a microwave plasma source. Single crystalline GaN films were deposited on the Si-face 6H-SiC and the c-plane sapphire substrates at 600–670°C. A cubic SiC buffer layer was grown onSi(111) at 800°C by SSJE using dichlorosilane, acetylene, and a high quality GaN crystal was grown on this template at 630°C. The materials high quality was proved by hard rectifying characteristics of a diode with an N-GaN/β-SiC/P-Si(111) structure.
XPS Measurement of the SiC/AlN Band-Offset at the (0001) Interface
Authors: King Sean W. , Benjamin Mark C. , Nemanich Robert J. , Davis Robert F. , Lambrecht Walter R. L.
Published: April 2011

X-ray photoelectron spectroscopy is used to determine the band-offset at the SiC/AIN (0001) interface. First, the valence band spectra are determined for bulk materials and analyzed with the help of calculated densities of states. Core levels are then measured across the interface for a thin film of 2H-AIN on 6H-SiC and allow us to extract a band offset of 1.4 ±0.3 eV. The analysis of the discrepancies between measured peak positions and densities of states obtained within the local density approximation provides information on self-energy corrections in good agreement with independent calculations of the latter.
Lattice-Matching Growth of InGaAIN Systems
Authors: Matsuoka Takashi
Published: April 2011

The development and device applications of the InGaAIN system have progressed dramatically with improvements in crystalline quality by achieved through a buffer layer, the realization of p-type doping, and the growth of ternary alloys. As a substrate, sapphire is mainly used for epitaxial growth because of the lack of a GaN bulk crystal. However, many cracks in GaN film can still be observed and its X-ray rocking curve width is less than 100 arc seconds. This is are thought to be due to the lattice constants and thermal expansion coefficients of GaN and sapphire differ by 13.8% and by -34.2%, respectively. These values are extremely large in comparison with the corresponding values for InP and GaAs. Lattice-matching growth thus remains a basic problem in growing the high-quality epitaxial films necessary for high-performance devices.

This paper reviews attempts at lattice-matching growth. Lattice-matching growth of InGaN on a house-made ZnO substrate and near-lattice-matching growth of GaN on SiC and NdGaO3 substrates have been proposed and performed, and the effects of lattice-matching have been confirmed. Various types of surface planes commercially available sapphire substrates are also discussed.
The Role of Impurities in LP-MOCVD Grown Gallium Nitride
Authors: Hwang C.Y. , Li Y. , Schurman M. J. , Mayo W. E. , Lu Y. , Stall R. A.
Published: April 2011

We have investigated the relationship of the Hall electron mobility to the background carrier concentration in low pressure MOCVD grown GaN. The highest electron mobility (400 cm2 /V•s) of the unintentionally doped GaN was obtained at a carrier concentration of 1×1017 cm−3 and samples with carrier concentrations lower than this exhibited lower mobilities. SIMS analysis shows C and O concentrations in the range of 2–3×1016 cm−3 and H in the 2–3×1017 cm−3 range. Structural defects, stoichiometry and impurities in the GaN films grown under different conditions are investigated to understand their relationship to the electron Hall mobilities. In particular, different growth temperatures and pressures were used to grow undoped GaN and modify the background doping effect of the impurities.
Optical Properties of Wurtzite-and Zincblende-GaN Films Grown by RF Plasma-MBE
Authors: Semendy F. , Bambha N. , Kim J.G. , Liu H. , Park R.M.
Published: April 2011

Both wurtzite-and zincblende-GaN films have been grown on sapphire and MgO substrates, respectively, and examined by photoluminescence and x-ray analysis. GaN films were grown on suitably prepared Al2O3 and MgO substrates by molecular beam epitaxy employing a rf plasma discharge, nitrogen free radical source. The wurtzite-and zincblende-GaN films exhibited dominant near band-edge emission, the nature of which will be compared and contrasted for both phases in this paper. X-ray diffraction data for both phases will also be discussed.
Dielectric Functions of Wurtzite and Zincblende Structure GaN
Authors: Wang R. , Ruden P.P. , Kolnik J. , Oguzman I. , Brennan K.F.
Published: April 2011

We present calculated longitudinal frequency and wavevector dependent dielectric functions of zincblende and wurtzite structure GaN using band energies and wavefunctions generated in the framework of the empirical pseudopotential method. We discuss the anisotropy of the static dielectric function and find that our results are in satisfactory agreement with experimental data for |q| ₒ 0.
Detection of Magnetic Resonance on Shallow Donor - Shallow Acceptor and Deep (2.2 eV) Recombination from GaN Films Grown on 6H-SiC
Authors: Glaser E.R. , Kennedy T.A. , Brown S.W. , Freitas J.A. , Perry W.G. , Bremser M.D. , Weeks T.W. , Davis R.F.
Published: April 2011

Photoluminescence (PL) and optically-detected magnetic resonance (ODMR) experiments have been performed on undoped GaN epitaxial layers grown on 6H-SiC substrates. The defects observed in these films are compared with those found from previous ODMR studies of undoped GaN layers grown on sapphire substrates. Strong, sharp donor-bound exciton bands at 3.46 -3.47 eV and weak, broad emission bands at 2.2 eV were observed from several 0.7 and 2.6 μm-thick films. In addition, fairly strong shallow donor - shallow acceptor (SD-SA) recombination with a zero-phonon-line at 3.27 eV was found for GaN layers less than 1 μm-thick. The first observation of magnetic resonance on this SD-SA recombination from undoped GaN is reported in this work. Two magnetic resonance features attributed to effective-mass (EM) and deep-donor (DD) states were detected on the 2.2 eV emission bands from all the GaN/6H-SiC films. These resonances were observed previously on similar emission from undoped GaN layers grown on sapphire substrates. The same EM donor resonance, though much weaker, was also found on the SD-SA recombination. However, a resonance associated with shallow acceptor states was not observed on this emission. The weakness of the donor resonance arises from the weak spin-dependence of the recombination mechanism involving spin-thermalized shallow acceptors. The absence of an EM acceptor is due to the broadening of the resonance through the spreading of the acceptor g-values by random strains in these films.
Role of C, O and H in III-V Nitrides
Authors: Abernathy C. R. , Pearton S. J. , MacKenzie J. D. , Lee J. W. , Vartuli C. B. , Wilson R. G. , Shul R. J. , Zolper J. C. , Zavada J. M.
Published: April 2011

The light ion impurities C, O and H have been implanted or diffused into GaN and related compounds and their effect on the electrical properties of these materials measured by Hall, C-V and SIMS as a function of annealing temperatures from 300-1100ºC. While C in as-grown GaN appears to create an acceptor under MOMBE conditions, implanted C shows no measurable activity. Similarly, implanted O does not show any shallow donor activity after annealing at ≤ 700°C, but can create high resistivity regions (106 Ω/□) in GaN, AlInN and InGaN for device isolation when annealed at 500–700°C. Finally, hydrogen is found to passivate shallow donor and acceptor states in GaN, InN, InAIN and InGaN, with dissociation of the neutral complexes at >450°C. The liberated hydrogen does not leave the nitride films until much higher annealing temperatures (>800°C). Typical reactivation energies are ∼2.0eV for impurity-hydrogen complexes.
Infrared Absorption and Electron Spin Resonance Studies of Nanocrystalline Cubic Boron Nitride/Amorphous Hydrogenated Boron Nitride Mixed Phase Thin Films
Authors: Lin Shu-han , Brown Ian M. , Feldman Bernard J.
Published: April 2011

Both infrared absorption (IR) and electron spin resonance (ESR) spectroscopies have been used to investigate the complicated structure of nanocrystalline cubic boron nitride/amorphous hydro-genated boron nitride thin films. The ESR spectra from this material consist of a component with a four-line hyperfine structure and/or a component with a ten-line hyperfine structure superimposed upon a broad central line. The hyperfine structures are associated with defect centers located in the nanocrystalline phase, whereas the broad line is attributed to dangling bonds in the amorphous phase. The IR spectra consist of three lines around 1400 cm−1: the lines at 1263 and 1505 cm−1 originate in a boron-poor amorphous hydrogenated boron nitride region; the line at 1371 cm−1, in a boron-rich amorphous hydrogenated boron nitride region. These results, together with previously reported electron diffraction spectra, suggest the following picture: small (2.5 nm) nanocrys-tallites of cubic boron nitride (about 5% of the material) are imbedded in a mixed amorphous phase. The amorphous region can be approximated by a mixture of boron-rich and boron-poor amorphous hydrogenated boron nitride.
Magneto-Optic Studies of GaN Films and GaN/AlGaN Heterostructures
Authors: Wang Y.J. , Ng H.K. , Kaplan R. , Doverspike K. , Gaskill D.K. , Ikedo T. , Amano H. , Akasaki I.
Published: April 2011

Magneto-studies have been carried out for several MOCVD grown GaN thin films and GaN/AlGaN heterostructures at magnetic fields up to 30 T and at temperatures between 4.2 K to 100 K. Electron cyclotron resonance was observed in two heterostructures with high mobilities (μ > 2000 cm2/V-s), the effective mass obtained from the cyclotron resonance measurement is 0.23±0.01 m0, where m0 is the mass of free electron. For Si-doped thin film GaN there was no sign of electron cyclotron resonance even when samples were heated up to 100 K. However, a Is to 2p+ absorption line was observed for Si-doped GaN samples. A binding energy of 29 meV and low frequency dielectric constant of 10.4 is obtained.
Deep States in GaN Studied by Thermally Stimulated Current Spectroscopy
Authors: Huang Z.C. , Chen J.C. , Mott D.B.
Published: April 2011

Deep levels in insulating GaN grown by metalorganic chemical vapor deposition have been studied using thermally stimulated current (TSC) and photocurrent (PC) spectroscopies. Five main traps were observed by TSC measurement in the as-grown undoped GaN in the range of 0-0.75 eV below the conduction band edge or above the valence band edge. Their activation energies were 0.11, 0.24, 0.36, 0.53 and 0.62 eV, respectively. PC measurements showed three deep levels located within the bandgap at 1.32, 1.70 and 2.36 eV, respectively. Furnace annealing was carried out on GaN for identifying all the observed deep levels. We have found that the 0.24, 0.36 and 0.53 eV traps were eliminated by annealing at 1000°C under N2for six hours, whereas the 0.62 eV trap density increased after annealing. The three deep levels detected by the PC measurement were not affected by annealing. The 1.70 eV trap, which is located at the midgap, does not seem to compensate with narrow donors. We attribute the 0.11 eV trap to surface states, and the 0.62 eV trap to nitrogen vacancies.
Plasma Chemistry Dependent ECR Etching of GaN
Authors: Shul R. J. , Ashby C. I. H. , Rieger D. J. , Howard A. J. , Pearton S. J. , Abernathy C. R. , Vartuli C. B. , Barnes P. A. , Davis P.
Published: April 2011

Electron cyclotron resonance (ECR) etching of GaN in Cl2/H2/Ar, Cl2/SF6/Ar, BCl3/H2Ar and BCl3/SF6/Ar plasmas is reported as a function of percent H2 and SF6. GaN etch rates were found to be 2 to 3 times greater in Cl2/H2/Ar discharges than in BCl3/H2/Ar discharges independent of the H2 concentration. In both discharges, the etch rates decreased as the H2 concentration increased above 10%. When SF6 was substituted for H2, the GaN etch rates in BCl3-based plasmas were greater than those for the Cl2-based discharges as the SF6 concentration increased. GaN etch rates were greater in Cl2/H2/Ar discharges as compared to Cl2/SF6/Ar discharges whereas the opposite trend was observed for BCl3,-based discharges. Variations in surface morphology and near-surface stoichiometry due to plasma chemistries were also investigated using atomic force microscopy and Auger spectroscopy, respectively.
Light-Emitting Devices Based on Gallium Nitride and Related Compound Semiconductors
Authors: Koike M. , Shibata N. , Yamasaki S. , Nagai S. , Asami S. , Kato H. , Koide N. , Amano H. , Akasaki I.
Published: April 2011

Asymmetric double heterostructures (ADH) of AlGaN/GaInN/GaN blue light emitting diodes (LEDs) and GaInN/GaN multiple quantum well (MQW) LEDs were fabricated by metalorganic vapor phase epitaxy (MOVPE). The ADH LEDs had spectral emissions peaking at 450 nm and the luminous intensify was 2.5 cd at 20 mA The output power was 3.6 mW at 20mA and the external quantum efficiency was as high as 5.1 % at 20 mA. The GaInN/GaN MQW structure was grown successfully by MOVPE. Fine multi-layer structures 7 – 9 nm thick were detected by secondary ion mass spectroscopy and transmission electron microscopy (TEM). The dislocation density in the MQW was as high as 0.5–2×109 cm−2 by TEM The optical efficiency of the MQW layer was higher than that of a bulk GalnN layer. The intensity of UV emission from MQW LEDs was greater than that of blue light from ADH blue LEDs. The UV emission increased as a super-linear function of injection current at -100°C.
AlGaN/GaN/AlGaN double-heterojunction blue LEDs on 6H-SiC substrates
Authors: Kong Hua-Shuang , Leonard Michelle , Bulman Gary , Negley Gerry , Edmond John
Published: April 2011

Blue LEDs with double-heterojunction (DH) have been produced in AIN-GaN system grown on n-type 6H-SiC substrates via metalorganic chemical vapor deposition (MOCVD). These devices employ a GaN active layer bordered by Mg doped p-type Al0.1Ga0.9N and Si doped n-type Al0.1Ga0.9N. A vertical device design was utilized with a p-type Au contact centered on the chip top side for wire bonding. The backside contact to the SiC is Ni. The peak emission from these devices is 430 nm with a FWHM of 65 nm, producing a deep blue color. The output power is 1.7 mW at 20 mA which corresponds to an external quantum efficiency of 3%.