bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of oxygen-free nanosized InN by pulse discharge
Authors: Yang Wei-Dong , Cheah K.W. , Wang Pei-Nan , Li Fu-Ming 
Published: April 2011

AbstractOxygen-free nanosized InN was synthesized by pulse discharge. NH3/N2 mixture and bulk indium were used as nitrogen source and discharge cathode, respectively. Optical emission spectra show that N2 and NH3 were highly dissociated in the discharge and oxygen could be eliminated effectively. A comparison was made among samples produced in the discharge of N2, NH3 and N2/NH3, respectively. The XPS was used to determine the composition of the synthesized materials. Only In-N was produced when N2/NH3 was used as the discharge gas, whereas indium oxide was found in the case using N2 or NH3 as the discharge gas. The size of the produced InN was between 5 and 200 nm. A broad band with a blue shift of 150 nm from that of bulk InN was detected in the photoluminescence of the produced nanosized InN.
Micro-Raman Scattering From Hexagonal GaN, AlN, and AlxGa1-xN Grown on (111) Oriented Silicon: Stress Mapping of Cracks
Authors: Ramkumar C. , Prokofyeva T. , Seon M. , Holtz M. , Choi K. , Yun J. , Nikishin S. A. , Temkin H. 
Published: April 2011

AbstractWe report post-growth micro-Raman stress mapping of cracks in GaN, AlN, and AlxGa1-xN grown on (111) oriented silicon. Cracks with an average spacing of ~ 100 m are observed. These cracks are categorized into two types. The first type of crack propagates through the epilayer, and several microns deep into the substrate and is observed in all the samples investigated. The second type cracks epilayer only and is observed only in GaN. The micro-Raman stress mapping of the first type of crack shows that the epilayers are under biaxial tensile (< 0) stress and the silicon substrate is under compressive (> 0) stress far away from the cracks. The stress in the epilayers as well the substrate is found to relax from the equilibrium (far away from the cracks) value of –0.5 GPa (AlN), -0.16 GPa (GaN), -0.6 GPa (AlxGa1-xN) and 0.36 GPa (Si) as the crack position is approached. Partial relaxation is observed to occur over a range of 10 m m. At the crack position, the epilayers and the substrate are relaxed to nearly zero stress values. The stress mapping of the second type of crack reveals that the substrate is completely relaxed (stress is close o zero) far away from the cracks. At the crack position the GaN epilayer is partially relaxed from –0.2 GPa to –0.08 GPa, while the silicon substrate is seen to be under tensile stress of –0.39 GPa. The stress map of epilayers is well described by the distributed force model for both types of cracks. Furthermore, the calculated stress profiles of cracked and uncracked substrate using the above mentioned model are in excellent agreement with the experimental data.
400-nm Band AlGaInN-Based High Power Laser Diodes
Authors: Asano Takeharu , Takeya Motonobu , Tojyo Tsuyoshi , Ikeda Shinro , Mizuno Takashi , Ansai Shinichi , Goto Shu , Kijima Satoru , Hino Tomonori , Uchida Shiro , Ikeda Masao 
Published: April 2011

AbstractHigh-power AlGaInN-based laser diodes (LDs) operating with high reliability in the 400-nm band have been successfully fabricated using a high-productivity process. Epitaxial lateral overgrowth (ELO) over a 10-m m region was employed to obtain a broad growth area with low dislocation density, and the thickness of the ELO-GaN layer was limited to approximately 5 m in order to minimize wafer bending. These techniques allow for the easy and reproducible alignment of the laser stripe on the region of low dislocation density. The insertion of a GaInN interlayer between the active layer and the AlGaN electron blocking layer was effective for reducing the strain between these two layers, resulting in homogeneous luminescence from the active layer and lower operating current. A mean time to failure of 15000 h under 30-mW continuous-wave operation at 60°C was realized as a direct result of the lower operating current. Productivity was remarkably improved by performing epitaxial growth on a 3-inch substrate. Highly uniform laser wafers were successfully fabricated by achieving minimal temperature variation (1000 ±7°C) over the 3-inch substrate. The resultant laser structures varied in thickness by only ±5%, and the photoluminescence wavelength was consistent within ±2.5 nm over the entire 3-inch substrate. The average threshold current of 550 LDs selected from a fourth wafer was 32.7 mA, with small standard deviation of 3.2 mA.
AlGaN/GaN based MOSHFETs with Different Gate Dielectrics and Treatments
Authors: Mistele D. , Rotter T. , Bougriouaa Z. , Moermanna I. , Röver K.S. , Seyboth M. , Schwegler V. , Stemmer J. , Fedler F. , Klausing H. , Semchinova O.K. , Aderhold J. , Graul J. 
Published: April 2011

AbstractAlGaN/GaN based hetero field effect transistors (HFETs) were capped with different dielectrics, characterized, and tested for DC performance. As dielectrics we use SiO2 and photoelectrochemical (PEC) grown AlxGa2-xO3. Combination of this two dielectrics show best performance with respect to gate leakage current and controllability of the drain current ID. TheMOSHEFTs work also at positive gate voltages in accumulation, which is also demonstrated in a broad transconductance peak. The PEC oxidation shows low density of interface states Dit and the insulating properties depend strongly on the PEC conditions. Pre-treatments before the SiO2 deposition result in varying threshold voltages |Vth| and it seems that (NH4)Sx pre-treatment leaves the surface in best conditions. Comparison of Ti/Al and Ti/Al/Ti/Au as source/drain contacts for AlGaN/GaN HFETs are done and the annealing behavior of Ti/Al/Ti/Au is displayed resulting in contact resistance as low as RC = 2 &mm after annealing at 850°C in N2.
Electrical Properties of n-GaN/p-SiC and n-AlGaN/p-SiC Heterojunction Diodes
Authors: Luo B. , Kim J. , Mehandru R. , Ren F. , Lee K. P. , Pearton S.J. , Polyakov A.Y. , Smirnov N.B. , Govorkov A.V. , Kozhukhova E.A. , Osinsky A.V. , Norris P.E. 
Published: April 2011

AbstractProperties of n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions prepared by HVPE on 4H SiC substrates were studied by means of C-V, C/G-T, C-f, I-V and DLTS. It is shown, in agrrement with earlier publications, that the GaN/p-SiC HJ is staggered type II with ΔEc=-0.4 eV andΔEv=0.6 eV. Whenchanging GaN for AlGaN with Al mole fraction of x=0.25-0.3 the band alignment becomes normal type I with ΔEc=0.2 eV andΔEv=0.6 eV. I-V characteristics of both heterojunctions bear evidence of strong tunneling via defect states, particularly centers with activation energy of 1.25 eV for GaN/4H SiC HJ. The tunneling was found to be more pronounced in the AlGaN/SiC HJs even though these HJs showed no evidence of formation of dark line defects at the interface, in contrast to GaN/SiC. DLTS measurements on both types of HJs revealed the presence of broad bands whose behavior is indicative of these bands being related to continuous states in the gap, most likely near the nitride/carbide interface.
Crystalline and Electrical Properties of AlInN/GaN and AlN/GaN superlattices on GaN Grown by Metalorganic Vapor Phase Epitaxy
Authors: Yamaguchi Shigeo , Iwamura Yasuo , Kosaki Masayoshi , Watanabe Yasuhiro , Mochizuki Shingo , Nakamura Tetsuya , Yukawa Yohei , Nitta Shugo , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

AbstractWe have studied the crystalline and electrical properties of AlInN/GaN superlattices (SLs) and strained AlN/GaN SLs on GaN grown by metalorganic vapor phase epitaxy. A (0001) sapphire substrate was used. The SLs were grown using N2 carrier gas. X-ray analysis showed the eighth order satellite peak in AlInN/GaN SLs. Hall measurement showed an electron mobility of 946 cm2/Vs at highest (a sheet carrier density of 2.9x1012 cm-2) for AlInN/GaN 5SLs on GaN at 295K, and showed a value of 11432 cm2/Vs (1.99x1012cm-2) at 170K, and a value of 2610 cm2/Vs (3.38x1012cm-2) at 295K for AlN/GaN 10SLs on GaN.
Erbium-Doped Barium Titanate Thin Film Waveguides For Integrated Optical Amplifiers
Authors: Teren Andrew R. , Kim Seong-Soo , Ho Seng-Tiong , Wessels Bruce W. 
Published: April 2011

AbstractThe factors affecting optical gain were studied for Er-doped BaTiO3 thin film waveguides. Er-doped BaTiO3 with dopant concentrations of 0.3 – 9 at.% was deposited by metal-organic chemical vapor deposition. The luminescence efficiency was maximized by optimizing the growth temperatureand erbium concentration as well as by post-deposition annealing. Stimulated emission was studied using the pump-probe technique over the spectral range of 1,520-1,550 nm. A maximum differential gain of 3 dB/cm wasmeasured at 1,540 nm in an 8 mm long, 8 μm wide ridge waveguide.
Analysis of Nucleation of Dislocation Loops from Stressed Surfaces Based on the Peierls-Nabarro Dislocation Model
Authors: Xu Guanshui 
Published: April 2011

ABSTRACTNucleation of dislocation loops from stressed crystal surfaces is analyzed based on a variational boundary integral method in the Peierls-Nabarro framework. The stress dependent activation energies required to activate dislocation loops from their stable to unstable saddle point configurations are determined. Compared to previous analyses of this problem based on continuum elastic dislocation theory, the presented analysis provides more definitive solutions because it eliminates the uncertain core cutoff parameter by allowing for the existence of an extended dislocation core as the embryonic dislocation evolves. Moreover, the shape of the dislocation loop is solved by the variational principle instead of assumed to be semicircular as in previous analyses based on continuum elastic dislocation theory. It is noteworthy that the presented methodology can be readily used to study effects of surface inhomogeneities such as cracks and steps on dislocation nucleation.
Thermal Stability of Self-Supported Metallic Multilayered Thin Films
Authors: Misra A. , Kung H. , Hoagland R.G. 
Published: April 2011

ABSTRACTThe morphological stability and strength retention following elevated temperature exposure or thermal cycling will be crucial in exploiting the extremely high strengths of nanolayered materials in advanced engineering applications. The effects of elevated temperature (≤800°C) vacuum annealing on the morphological stability and mechanical properties of sputter deposited Cu-Nb multilayers with 75 nm bilayer period are reported here. Even after 800°C/ 1 hour anneal, the continuity of the layered structure is maintained and the bilayer periods are unchanged. The in-plane grain sizes in both Cu and Nb coarsened but were anchored at grooved boundaries preventing further growth. For a constant bilayer period, the effect of increasing the in-plane grain size on the multilayer hardness is found to be insignificant. After annealing, the layers are observed to be offset by shear along a vertical plane at the triple point junctions that have equilibrium groove angles aligned in a zig-zag pattern. A new mechanism is proposed for the evolution of this “anchored” structure that is resistant to further morphological instability.
A New Type of Dislocation Mechanism in Ultrathin Copper Films
Authors: Balk T. John , Dehm Gerhard , Arzt Eduard 
Published: April 2011

ABSTRACTIn this study of thin film plasticity, the relationship between thermomechanical behavior and dislocation motion has been investigated in copper constrained by a silicon substrate. The stress-temperature behavior as determined from wafer curvature experiments has been directly compared to deformation microstructures observed during in situ thermal cycling of plan-view specimens in the transmission electron microscope. The flow stress of copper films with thicknesses ranging from 100 nm to 400 nm was found to be constant, indicating that strengthening mechanisms may be saturated in this thickness regime. Moreover, unexpected dislocation glide on a plane parallel to the film surface, which should experience no resolved shear stress, provides potential evidence for the occurrence of constrained diffusional creep in a 270 nm film.
Bulge Test Characterization of Static Softening and Dynamic Instabilities in Foils of an Al-Based Alloy
Authors: Cieslar Miroslav , Karimi Ayatollah , Martin Jean-Luc 
Published: April 2011

ABSTRACTEffects of recovery and recrystallization on subsequent stress – strain behavior were studied in foils of non-age hardenable Al based alloy. A bulge testing device for mechanical testing of thin free standing films and foils, enabling the detection of large strains, was employed. The bulge tester was used at RT both for the predeformation of the foil in the biaxial mode and also for the study of softening after subsequent one-step annealing. Three stages of strength drop as a function of the annealing temperature were observed between RT and 590°C. The contribution of different annealing processes to the softening was established using transmission electron microscopy. It was found that below 200°C only redistribution of dislocations inside dislocation cells and refinement of the cell structure occurred. Between 200°C and 380°C the formation of a subgrain structure was observed. The softening process is terminated as partial recrystallization takes place at higher annealing temperatures. Dynamic interaction of solutes with dislocations was revealed during prestraining as well as poststraining of foils. This effect resulted in the appearance of a negative strain rate sensitivity and dynamic instabilities after appropriate prestraining and annealing conditions. The above results show that bulge testing of Al foils allows to study the successive annealing stages by measuring the most important macroscopic parameters of plastic deformation (yield stress, work hardening rate, ductility, strain rate sensitivity, etc.). These stages could be related to the microstructure evolution.
Gold/Niobium Thin Film Metallizations for GaAs Devices and Circuits
Authors: Esser Robert , Christou Aris 
Published: April 2011

ABSTRACTA refractory metallization of Au/Nb is proposed for use in first level metallization of GaAs devices. The diffusion and reaction kinetics are explored using sheet resistance measurements, along with X-ray diffraction and Auger electron spectroscopy depth profiling. The interdiffusion coefficients are reported. Diodes are fabricated using Nb/Au metallization and characterized
The Effects of Copper on the Interfacial Failure of Gold Films
Authors: Moody N. R. , Adams D. P. , Cordill M. J. , Yang N. , Bahr D. F. 
Published: April 2011

ABSTRACTNanoindentation test techniques were combined with deposition of highly stressed overlayers to study the interfacial fracture susceptibility of gold-on-copper and gold-2w/o-copper alloy films. The gold-on-copper film blistered readily following deposition of stressed tungsten overlayers. Additional stress from nanoindentation was required to trigger delamination and blister formation in the gold-copper alloy film. Fracture energies were then determined using mechanics-based models. The results show that the gold-copper alloy exhibited higher fracture energies than the gold-on-copper films. This increase scaled with film strength suggesting that the higher measured fracture energies in the gold-copper alloy film were due to solid solution hardening.
Interfacial Adhesion of Cu to Self-Assembled Monolayers on SiO2
Authors: Cui G. , Lane M. , Vijayamohanan K. , Ramanath G. 
Published: April 2011

ABSTRACTAs the critical feature size in microelectronic devices continues to decrease below 100 nm, new barrier materials of > 5 nm thickness are required. Recently we have shown that self-assembled monolayers (SAMs) are attractive candidates that inhibit Cu diffusion into SiO2. For SAMs to be used as barriers in real applications, however, they must also promote adhesion at the Cu/dielectric interfaces. Here, we report preliminary quantitative measurements of interfacial adhesion energy and chemical binding energy of Cu/SiO2 interfaces treated with nitrogen-terminated SAMs. Amine-containing SAMs show a ~10% higher adhesion energy with Cu, while interfaces with Cu-pyridine bonds actually show degraded adhesion, when compared with that of the reference Cu/SiN interface. However, X-ray photoelectron spectroscopy (XPS) measurements show that Cu-pyridine and Cu-amine interactions have a factor-of-four higher binding energy than that of Cu-N bonds at Cu/SiN interfaces. The lack of correlation between adhesion and chemical binding energies is most likely due to incomplete coverage of SAMs.
Effects of Film Thickness on the Yielding Behavior of Polycrystalline Gold Films
Authors: Espinosa H.D. , Prorok B.C. 
Published: April 2011

ABSTRACTA Membrane Deflection Experiment was used to test the mechanical response of freestanding thin film gold specimens. We present stress-strain curves obtained on films 0.3, 0.5 and 1.0 μm thick. Elastic modulus was consistently measured in the range of 53-55 GPa. Several size effects on the mecha nical properties were observed including yield stress variations with membrane width and film thickness. It was observed that thickness plays a key role in deformation behavior with a major transition in the material inelastic response occurring between a thickness of 0.5 and 1.0 μm. The size effects here reported are the first of their kind in the sense that the measurements were performed under a macroscopically homogeneous axial deformation, i.e., in the absence of macroscopic deformation gradients.
Simulation of Mechanisms in Strained Silicon Germanium Epitaxy
Authors: Wagner Richard J. , Gulari Erdogan 
Published: April 2011

AbstractGrowth of strained semiconductors can lead to self-assembly of interesting structures such as quantum dots. Simulation of this growth requires an accurate and efficient model for the interactions of lattice mismatched materials. We present a potential for calculating the bond energies in a diamond-like crystal of silicon and germanium. With this potential we predict the strain profiles in an embedded quantum dot and discuss the mechanisms of island formation.
Stress Generation and Relaxation during Film Heteroepitaxy on a Compliant Substrate with a Viscoelastic Glass Interlayer
Authors: Feng Zhaohua , Lovell Edward G. , Engelstad Roxann L. , Moran Peter D. , Kuech Thomas F. 
Published: April 2011

AbstractLattice mismatch strain between films and substrates causes stresses in each and degrades the film quality. Compliant substrates can decrease the stresses and dislocation density in the film. A particular type of compliant substrate, which consists of a thin template, a handle wafer and a glass interlayer, is discussed here. Three-dimensional axisymmetric finite element models were developed to simulate the film-substrate structure and analyze stress generation and relaxation. The materials of film and template were considered as elastic but the glass interlayer was viscoelastic at the film growth temperature. Factors affecting stress generation and relaxation are reported.
Shape Transitions of Self-Assembled Ge Islands on Si (001)
Authors: Rastelli Armando , Kummer Matthias , von Känel Hans 
Published: April 2011

AbstractCoherently strained Ge islands were grown at a substrate temperature of 550°C by magnetron sputter epitaxy on Si (001) and studied by scanning tunnelling microscopy (STM). The shape changes induced by exposure to a Si-flux at 450°C were investigated as a function of the Sicoverage. During Si-capping, multifaceted domes were found to flatten and to transform into {105}-faceted pyramids and subsequently into stepped mounds through intermediate shapes. The observed sequence of morphological changes is induced by Si-Ge intermixing and is shown to be the inverse of that occurring during Ge or Si1-xGex growth on Si (001). The results are interpreted with a model in which the stable shape of an island mainly depends on its volume and composition.
Compositionally Modulated Structures Studied by in Situ Scanning Tunneling Microscopy
Authors: Pearson Chris A. , Dorin Catalina , Millunchick Joanna Mirecki , Chen Yunqing , Orr Brad G. 
Published: April 2011

AbstractTwo different short period superlattice (SPS) structures with nominally equivalent lattice mismatch, InAs/AlAs and InAs/GaAs are examined using in situ scanning tunneling microscopy (STM). Depending upon the growth conditions, the composition of the InAs/AlAs SPS structure can be either homogeneous or modulated in the lateral direction. Distinct periodic structures are clearly visible in images of the modulated SPS while no periodicity is observed in the homogeneous SPS. For a 30 period SPS consisting of 2 monolayers of AlAs and 2 monolayers of InAs we observe structures 20 nm in size with an average spacing of ∼25 nm in orthogonal directions, which is approximately the same length scale as the composition modulation. Despite the nominally equivalent lattice mismatch, the InAs/GaAs SPS structures are quite different. Some degree of modulation is always observed in these structures. Homogeneous structures are not observed. For the modulated SPS structures, scanning tunneling spectroscopy can be used to characterize the chemical profile.
Computer Simulation on the Relations between the Porosity and the Microwave Properties in Dielectric Ceramics
Authors: Park Jae-Hwan , Park Jae-Gwan , Kim Yoonho 
Published: April 2011

AbstractEffects of porosity on the microwave properties in dielectric ceramics were studied by the electromagnetic simulation. Scattering matrix S21 obtained from the network analyzer was compared to the S21 obtained from the simulation. From electric field distribution, the dominant resonant TE01 mode could be easily determined. The effects of the porosity inside the dielectrics on the microwave properties were investigated. Quality factor decreased with the porosity and the pore size.
Determination of Surface Space Charge Density on Semiconductor from Displacement Current-Voltage Curve using a Scanning Vibrating Probe
Authors: Majima Yutaka , Masuda Tomohiko , Uehara Setsuri , Okuda Atsushi , Iwamoto Mitsumasa 
Published: April 2011

AbstractA determination method of the local surface space charge density in thin films on semiconductor surfaces is described. In this method, the displacement current and the tunneling current flow periodically in accordance with the perpendicular vibration of the probe of the scanning tunneling microscopy (STM). The external circuit current is separated into the mean displacement current and the mean tunneling current by using the two-phase lock-in amplifier. The displacement current-probe voltage curve of a p-type silicon with a native oxide layer was measured in a vacuum (>3×10−9 torr). The displacement current-voltage curve has been analyzed taking into account surface space charge. The theoretical displacement current-voltage curve has been fitted to the measurement in order to obtain both the local surface space charge density and the surface potential difference of thin films, and the theory is in good agreement with the measurement in both voltage regions where the majority carriers are accumulated and depleted. We also demonstrate a simple determination method of both the surface space charge density and the surface potential difference of thin films from flat-band conditions in the displacement current-voltage curve.