bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observation of Rheed Intensity Oscillations During PbSe/CaF2/Si(111) MBE
Authors: Liu W. K. , Fang X. M. , McCann P. J. , Santos M. B. 
Published: April 2011

AbstractRHEED intensity oscillations observed during MBE growth of CaF2 on Si(111) and PbSe on CaF2/Si(111) are presented. The effects of substrate temperature and initial nucleation procedure are investigated. Strong temporal oscillations of the specular beam intensity are found to be most readily observed at temperatures below 200°C for both CaF2 and PbSe. Growth rates measured as a function of cell temperatures exhibit Arrhenius behavior with activation energies of 5.0 eV and 1.93 eV for CaF2 and PbSe, respectively. The relatively high activation energy obtained for CaF2 is consistent with the high melting point and sublimation energy of ionic fluorides.
Pulsed Laser Deposition of Barium Zirconate Thin Films for Neutral Imaging Applications
Authors: Leuchtner R. , Yanochko R. , Krzanowski J. , Brock W. , Quinn J. 
Published: April 2011

AbstractLow work function surfaces offer great promise as thermionic converters and neutral conversion surfaces due to the relative ease with which electrons may be removed. BaZrO3 surfaces were prepared using pulsed laser deposition (PLD) and their materials properties evaluated for potential use as a neutral conversion surface for space applications. Single layer films were fabricated at temperatures ranging from 110°C to 600°C, and as a function of background ambient pressure. The degree of crystallinity of the resulting films was measured using x-ray diffraction (XRD) and the surface morphology evaluated with atomic force microscopy (AFM). The film quality was found to be directly related to substrate temperature: an increase in grain size from ˜ 10 nm to >50 nm and improved crystal orientation with respect to the substrate were observed as the deposition temperature was increased from 110°C to 600°C.
In-Situ Optical Diagnostics During Pulsed-Laser Deposition of Magnetoresistive La-Ca-Mn-O Films on Silicon Substrates
Authors: Kung P.-J. , Cosgrove J. E. , Kinsella K. , Hamblen D. G. 
Published: April 2011

AbstractDuring pulsed-laser deposition of La0.67Ca0.33MnO3 films on silicon substrates, a system that consists of visible optical-emission spectroscopy (OES) and Fourier transform infrared (FT-IR) spectroscopy is employed to perform in-situ diagnosis of the laser-induced plume and to monitor the substrate temperature and the film thickness. The effects of oxygen pressure, laser fluence, and distance from the target surface on emission spectra were studied. In FT-IR measurements, the slopes of the reflectance versus wavenumber curves were observed to increase with film thickness and hence with time, which provides end-point detection during the film growth. La0.67Ca0.33MnO3 films with (100), (110), and mixed orientations, depending on the substrate temperature, were deposited on yttria-stabilized zirconia (YSZ) buffered Si(100) and Si(111) substrates. In a magnetic field of 5 T, the maximum magnetoresistance (MR) values of 250% at 195 K and 164% at 140 K were observed in the as-deposited (110) and (100) films, respectively.
Estimation of Minimum Liquidus Free Energy Concentration for Silicide and Germanide Systems
Authors: Nam H. G. , Cho N.-I. 
Published: April 2011

AbstractThermodynamic functions of Co-Si and Au-Si systems were studied. The validity of these functions were confirmed by successfully calculating phase diagrams. It was revealed that the composition of the first nucleated compound is close to the concentration of the minimum free energy of the liquid alloy with respect to the two solid components (ΔG) of the binary systems. In addition, the minimum ΔG concentration was found to be located by interpolating the portion of the liquidus, where the liquid alloy is in equilibrium with the two solid constituents, into the central region of the diagram where compounds exist. The minimum ΔG concentration of other silicide and germanide systems were estimated by the suggested interpolation method. A new model for predicting the first nucleated compound in silicide as well as germanide systems was proposed based on the findings.
Van Der Waals Epitaxy of Transition Metal Dichalcogenides Using Metal Organic Precursors (Movdwe)
Authors: Tiefenbacher S. , Pettenkofer C. , Jaegermann W. 
Published: April 2011

AbstractEpitaxial WS2 films have been grown on MoTe2 (0001) van der Waals faces using W(CO)6 and SnS2 as precursors. Despite a lattice mismatch of 10.3 % the film shows high crystalline quality. The interface is atomically abrupt and shows no interface dangling bonds as deduced from photoemission results (XPS, UPS). The growing overlayer nucleates on the flat (0001) terraces and not on steps as suggested from STM-measurements. For thin epilayers Moiré superstructures in LEED have been measured for the first time in semiconductor heteroepitaxy. From the intensity variation of the LEED spots with energy a corrugation of the overlayer film can be deduced. Based on these results a mechanism of van der Waals epitaxy is suggested.
New Silicon-Carbon Materials Incorporating Si4C Building Blocks
Authors: Chandrasekhar D. , Kouvetakis J. , Murran J. Mc , Todd M. , Smith David J. 
Published: April 2011

AbstractNovel precursor chemistry and ultrahigh-vacuum chemical vapor deposition have been used to deposit Si1-yCyth in films on (001) Si substrates. Films with carbon compositions ranging up to 20 at. % were deposited at substrate temperatures of 600–750°C using interactions of C(SiH3)4 or C(SiH2Cl)4 (C-H free precursors incorporating Si4C tetrahedra) and SiH4 gas mixtures. The composition of the resulting materials was obtained by Rutherford backscattering spectrometry including carbon resonance analysis. Cross-sectional transmission electron microscopy and infrared spectroscopy were used to provide microstructural and bonding information respectively. The effect of precursor chemistry on the composition and structure of the materials is discussed.
Cross-Sectional Transmission Electron Microscopy of Si-Based Nanostructures
Authors: Sidorov Maxim V. , Smith David J. 
Published: April 2011

AbstractThis work demonstrates the successful application of the precision cross-sectioning technique to the characterization of two types of Si-based nanostructures. Careful wedge-polishing of an array of metal-coated poly-Si microlines gave electron transparency over areas as broad as 1.5 mm across. A single, specific, SET (Single Electron Transistor), having dimensions of 4 × 4 μm2, was cross-sectioned for examination using conventional and high-resolution TEM imaging.
GaxIn1-xP/GaP Heterostructures on Si(001) Substrate
Authors: Sukidi N. , Dietz N. , Rossow U. , Bachmann K. J. 
Published: April 2011

AbstractIn this contribution we report on the real-time monitoring of low temperature growth of epitaxial GaxIn1-xP/GaP heterostructures on Si(100) by pulse chemical beam epitaxy, using tertiary butylphosphine (TBP), triethylgallium (TEG), and trimethylindium (TMI) as source materials. Both step-graded and continuously graded heterostructures have been investigated. The composition of the GaxIn1-xP epilayers has been analyzed by various techniques including X-ray diffraction, Rutherford backscattering, Auger, and Raman spectroscopy. Good correlation has been found between X-ray diffraction, RBS, and Vegard's law compositional analysis. We used Ppolarized Reflectance Spectroscopy (PRS) and Laser Light Scattering (LLS) to monitor the growth rate and surface morphology during growth. The information gained by these techniques has been utilized in the improvement of the surface preconditioning as well as to optimize the initial heteroepitaxial nucleation and overgrowth process. We studied the optical response to the compositional changes in the surface reaction layer (SRL) during the exposure of the surface to either sequential or synchronous pulses of TEG and TMI. The cross sectional TEM analysis indicates that the synchronous exposure results in an abrupt GaxIn1-xP/GaP interface while the sequential exposure does not which may suggest a compositionally graded interlayer formation. For heteroepitaxial GaxIn1-xP films on Si, a buffer layer of GaP is found to be necessary for optimum uniformity of the GaxIn1-xP layer. The selective growth of GaxIn1-xP on Si(001) is accessed.
Composite Materials with Adjustable Thermal Expansion for Electronic Applications
Authors: Shi J. D. , Pu Z. J. , Wu K. ‐H. , Larkins G. 
Published: April 2011

AbstractIn this paper, we discuss a newly characterized compound, ZrW2Og, that has been introduced into the composite materials with an adjustable and low thermal expansion for electronic applications. Offering a negative coefficient of thermal expansion (CTE) of approximate ‐9xlO–6/°C in a large temperature range, ZrW2Og was used as a particle filler in polymer‐matrix composites. The paper presents two kinds of composites, that is, polyester and epoxy with various volume fractions of ZrW20g. The CTEs of the polyester/ZrW2Og and epoxy/ZrW2Og composites have been proven adjustable in the ranges of 94 to 56x10–6 /°C and 54 to 18х 10–6 /°C, respectively, with ZrW2Og filler from 0 to 30 vol%. In addition, the analysis about the interfaces between the matrices and filler indicated that the interfaces may be beneficial to reduce the overall thermal expansion of the composites. The methods to further decrease composite CTEs are also discussed.
Technique to Measure Thermodynamic Adhesion of Copper-Polyimide Interfaces
Authors: Menezes Marlon E. , Roberton I.M. , Birnbaum H.K. 
Published: April 2011

AbstractA contact angle measurement technique has been used to determine the thermodynamic adhesive strength between nano-sized copper clusters and polyimide. The copper clusters are formed under UHV conditions by using ∼ mono-layer per minute deposition rates to assist equilibrium cluster formation. Temperatures of the polyimide substrate during the deposition process are maintained below Tg, which ensures no diffusion of the copper atoms into the polyimide matrix. Values of the strength of adhesion from these contact angle measurements are in reasonable agreement with predictions made using Fowkes’ theory of non-polar interfacial adhesion, but are at least one order of magnitude less than the value obtained by mechanical tests. The limitations of this technique due to deformation at the polyimide surface, as well as kinetic factors constraining equilibrium cluster formation will be discussed.
Spalling of Cu-Sn Compound Spheroids in Solder Joints on Si Wafers
Authors: Kim H.K. , Tu K.N. 
Published: April 2011

AbstractIn reacting eutectic SnPb solder with Ti/Cu and Cr/Cu/Au thin film metallization on Si wafers, we have observed spalling of Cu6Sn5 spheroids when the solder consumes the Cu. The formation of the spheroids is assisted by the ripening reaction among the compound grains. In addition we have observed an asymmetric spalling phenomenon using a sandwich structure, in which two wafers were soldered face-to-face. The spalling occurs predominantly at the interface below the solder joint. It suggests that gravity plays a role.
Structural Reliability of Direct-Chip-Attaches Bonded With Anisotropic Conductive Film
Authors: Lam D.C.C. , Shen C. , Karim JF Xie, Z. , Tong P. 
Published: April 2011

AbstractStructural reliability is a major concern in using anisotropic conductive films (ACF) in the electrical connection of chips or chip carriers to substrates. The relationship between electrical and structural failure is experimentally examined using a custom designed test chip. In-situ electrical measurements along with post failure microstructural examination revealed that electrical failure (open circuit) is caused by interfacial cracking of ACF/bump interface. An engineering analysis of the influence of assembly geometry revealed that tall relative bump height and large underbump adhesive thickness decrease the driving force for interfacial cracking. However, when relative bump height is increased and underbump adhesive thickness is reduced, increased compression from increased relative bump height dominate over increased shear resulting in a net decrease in crack propagation driving force. In general, tall relative bump height can reduce the potential for electrical failure in ACF interconnect when the ACF/bump interfacial fracture is the dominant failure mode.
Comparison of ICl and IBr for Dry Etching of III-Nitrides
Authors: Vartuli C. B. , Lee J. W. , MacKenzie J. D. , Pearton S. J. , Abernathy C. R. , Shul R. J. 
Published: April 2011

ABSTRACTICl/Ar ECR discharges provide the fastest dry etch rates reported for GaN, 1.3 µm/min. These rates are much higher than with Cl2/Ar, CH4/H2/Ar or other plasma chemistries. InN etch rates up to 1.15 µm/min and 0.7 µm/min for In0.5Ga0.5N are obtained, with selectivities up to 5 with no preferential loss of N at low rf powers and no significant residues remaining. The rates are much lower with IBr/Ar, ranging from 0.15 µm/min for GaN to 0.3 µm/min for InN. There is little dependence on microwave power for either chemistry because of the weakly bound nature of IC1 and IBr. In all cases the etch rates are limited by the initial bond breaking that must precede etch product formation and there is a good correlation between materials bond energy and etch rate. The fact that low microwave power can be employed is beneficial from the viewpoint that photoresist masks are stable under these conditions, and there is no need for use of silicon nitride or silicon dioxide. Selectivities for GaN over A1N with IC1 and IBr are still lower than with Cl2- only.
Wide Bandgap Semiconductors for Cold Cathodes: A Theoretical Analysis
Authors: Lerner Peter , Cutler P. H. , Miskovsky N. M. 
Published: April 2011

ABSTRACTIn this paper we describe the field emission from wide band-gap semiconductor thin film electron sources as a three-step process. Internal field emission is the mechanism for electron injection at the metal-semiconductor cathode interface. Under an internal field, electrons injected into the conduction band can propagate quasi-ballistically through the thin semiconductor film. At the vacuum interface, they are field emitted across a PEA or NEA surface. Consistent with the electron injection mechanism we have done molecular dynamics simulations for GaN films with an initial energy distribution corresponding to a Fowler-Nordheim (FN) spectrum. Results demonstrate quasi-ballistic propagation and approximate preservation of the FN energy distribution. Furthermore, high levels of n-doping in GaN (∼ 1017cm−3) do not inhibit transport in thin films (<0.1 μm).
Degradation of Single-Quantum Well InGaN Green Light Emitting Diodes Under High Electrical Stress
Authors: Osiński Marek , Perlin Piotr , Eliseev Ptr G , Liu Gungtan , Barton Daniel L 
Published: April 2011

ABSTRACTWe performed a degradation study of high-brightness Nichia single-quantum well AlGaN/InGaN/GaN green light-emitting diodes (LEDs). The devices were subjected to high current electrical stress with current pulse amplitudes between 1 A and 7 A and voltages between 10 V and 70 V with a pulse length of 100 ns and a repetition rate of 1 kHz. The study showed that when the current amplitude was increased to the 6 A - 7.5 A range, a fast (about 1 s) degradation occurred, with a visible discharge between the p and n-type electrodes. Subsequent failure analysis revealed severe damage to metal contacts which lead to the formation of shorts in the surface plane of diode. For currents smaller than 6 A, a slow degradation was observed as a decrease in optical power and an increase in the reverse current leakage. After between 24 and 100 hours however, a rapid degradation occurred which was similar to the rapid degradation observed at higher currents. Failure analysis results suggest that carbonization of the plastic encapsulation material on the diode surface leads to the discharge which destroys the diode.
Degradation of InGaN/AlGaN LED on Sapphire Substrate Grown by MOCVD
Authors: Egawa T. , Ishikawa H. , Jimbo T. , Umeno M. 
Published: April 2011

ABSTRACTWe report an optical degradation of an InGaN/AIGaN double-heterostructure light-emitting diode (LED) on a sapphire substrate grown by metalorganic chemical vapor deposition. The InGaN/AIGaN LED exhibited an optical output power of 0.17 mW, external quantum efficiency of 0.2 %, and the peak emitting spectrum at 437 nm with full width at half-maximum of 63 nm under 30 mA dc operation at 300 K. The InGaN/AIGaN LED showed the optical degradation under high injected current density. Electroluminescence, electron-beam induced current and cathodoluminescence observations show that the degraded InGaN/AIGaN LED exhibits formation and propagation of dark spots and a crescent-shaped dark patch, which act as nonradiative recombination centers. The values of degradation rate under injected current density of 0.1 kA/cm2 were determined to be 1.1 × 10-3, 1.9 × 10-3 and 3.9 × 10-3 h-1 at ambient temperatures of 30, 50 and 80°C, respectively. The activation energy of degradation was also determined to be 0.23 eV.
Spontaneous and Stimulated Recombination in the Nitrides
Authors: Hangleiter A. , Scholz F. , Härle V. , Im J. S. , Frankowsky G. 
Published: April 2011

ABSTRACTBoth spontaneous and stimulated emission processes are essential ingredients for constructing a laser from the nitrides. Based on our picosecond time-resolved photoluminescence studies we show that spontaneous radiative recombination is strongly influenced by excitonic effects, both in bulk GaN and in quantum wells. Particularly in quantum wells, localization of excitons plays an important role. We have studied the optical gain spectra in GaInN/GaN and GaN/AlGaN double heterostructures and quantum wells, grown by LP-MOVPE, using the stripe excitation method. Both room temperature and low temperature measurements were performed. Based on our results, we discuss the physical mechanism of optical gain in the nitrides as well as consequences for laser operation. We show that localization or, equivalently, the formation of quantum dot like structures, governs the optical gain mechanism in the nitrides.
Gain Spectra and Stimulated Emission in Epitaxial (In,Al) GaN Thin Films
Authors: Wiesmann D. , Brener I. , Pfeiffer L. N. , Khan M. A. , Sun C. J. , Chang C. S. , Fang W. , Chuang S. L. 
Published: April 2011

ABSTRACTWe measured the emission of (In,Al) GaN films under high intensity optical pumping both in the direction parallel and perpendicular to the film growth. In the edge emission geometry we determine the gain magnitude from the variable stripe length (VSL) method. We use the spontaneous emission collected perpendicular to the layer plane to calculate the spectral dependence of the gain. Theoretical calculations are in good agreement with those experimentally determined gain spectra. We also show that the observalion of a stimulated emission peak perpendicular to the film is predominantly due to scattering of the in-plane stimulated emission but without ruling out contributions from microstructures in the films.
Optical Quenching of Photoconductivity in GaN Photo-conductors
Authors: Huang Z.C. , Mott D.B. , Shu P.K. , Zhang R. , Chen J.C. , Wickenden D.K. 
Published: April 2011

ABSTRACTWe report the first observation of optical quenching of photoconductivity in GaN photoconductors at room temperature. Three prominent quenching bands were found at Ev+1.44, 1.58 and 2.20 eV, respectively. These levels are related to the three hole traps in GaN materials based on a hole trap model to interpret the quenching mechanism. The responsivity was reduced about 12% with an additional He-Ne laser shining on the detector.
An Optical Waveguide Formed by Aluminum Nitride thin film on Sapphire
Authors: Tang Xiao , Yuan Yifang , Wongchotigul K. , Spencer Michael G. 
Published: April 2011

ABSTRACTWe have investigated an optical waveguide formed by aluminum nitride (AlN) thin film on sapphire. A good quality AlN thin film on sapphire substrate was prepared by metal organic chemical vapor deposition (MOCVD) in this laboratory. A rutile prism coupler was employed to display the waveguide modes (N-lines) with wavelengths of 632.8, 532.1, 514.5 and 488.0 nm. The refractive index and thickness of the waveguide material is obtained by prism-coupler measurement. The dispersion curve of the AlN film is given and the dispersion equation is derived. The attenuation in the waveguide is evaluated by scattering loss measurements using a fiber probe. The attenuation coefficient alpha (α) is 1.5- 2.1 cm−1 depending on the sample and the different modes of waveguide. The accuracy of the measurement is discussed.
In-Plane Optical Anisotropies of AlxGa1-xN films in their Regions of Transparency
Authors: Rossow U. , Edwards N. V. , Bremser M. D. , Kern R. S. , Liu H. , Davis R. F. , Aspnes D. E. 
Published: April 2011

ABSTRACTGaN, AlxGa1–xN, and AlN layers exhibit interference oscillations and bandgap-related features in their reflectance-difference (-anisotropy) (RD/RA) spectra. We concentrate on the interpretation of interference-related data, providing a general expression for these optical anisotropics and discussing mechanisms that originate in the layers themselves. These include anisotropic strain in the plane of the layer, a tilt of the c axis with respect to the surface normal, and non-normal-incidence illumination. We estimate the magnitudes of these contributions, and show that they are consistent with those observed. In principle these contributions can be separated by their different azimuthal dependences. The complex pattern of the data for AlxGa1–xN and AlN indicate that contributions from several layers are present.
In-situ Real Time Spectroscopic Ellipsometry Applied to the Surface Monitoring of Semiconductors
Authors: Boher P. , Stehle J. L. 
Published: April 2011

AbstractA new kind of Real Time Spectroscopie Ellipsometer (RTSE) system is presented in detail. A multichannel analyser with photointensifier allows one to get spectroscopie measurements over the 0.25–0.85μm wavelength range with resolution λ/Δλ better than 500 and a good signal to noise ratio even for samples with poor reflectance. Precision and reproducibility of the system are around 0.3 and 0.1% for the two ellipsometric parameters. The measurement speed can be increased up to 15 spectra/s but must be adapted accurately to the process under control. An example of the heating process of a GaAs substrate measured in-situ by RTSE is presented and the temperature and native oxide thickness are deduced.