bluuebunny/crossref_metadata_2025_split huggingface dataset:
Persistent photocurrent effects in GaN/AlGaN multiquantum wells
Authors: Bonfiglio A. , Traetta G. , Lomascolo M. , Passaseo A. , Cingolani R. 
Published: April 2011

ABSTRACTPhotoCurrent (PC) experiments on GaN/AlGaN multiple quantum wells, both spectrally and temporally resolved, have shown that a photopersistence effect exists in our samples even at room temperature. A peak in the rise and decay times of PC vs. time appears in correspondence of wavelengths typical of Yellow-Band features while this is not seen in PL. This fact seems to indicate that YB defects give rise here to carrier trapping rather than recombination. Furthermore, the observed persistence times seem to be peculiar of MultiQuantum Wells and this possibly calls into play the role of built-in fields in the defects dynamics.
Stress Effects in p-Type AlGaN/GaN Heterostructures
Authors: Sutandi Agustinus , Ruden P. Paul , Brennan Kevin F. 
Published: April 2011

ABSTRACTThe physics of bulk wurtzite-structure III-nitride materials and of III-nitride heterostructures includes many phenomena that can be modulated by the application of stress. In particular, p- type material is expected to display a rich variety of piezo-resistive and piezo-optic effects that originate from the stress-induced modulation of lattice polarization charges, of valence band energies, and of bulk, surface, and interface defect states in the band gap. Here we focus on the expected effects of in-plane uniaxial on p-channel AlGaN/GaN heterostructures grown along the hexagonal axis on sapphire substrates. The valence band structure in the channel region is calculated self-consistently in the framework of a six-band Rashba-Sheka-Pikus (RSP) Hamiltonian. Stress-effects are included (in linear elastic theory) through deformation potentials and through the modulation of interfacial polarization charges associated with the piezoelectric nature of the constituent materials.
Characterization of Inversion Domains in GaN by Electric Force Microscopy in Conjunction with Transmission Electron Microscopy and Wet Chemical Etching
Authors: Yun F. , Visconti P. , Jones K. M. , Baski A. A. , Morkoç H. , Passaseo A. , Piscopiello E. , Catalano M. , Cingolani R. 
Published: April 2011

ABSTRACTInversion domains (IDs) in III-nitride semiconductors degrade the performance of such devices, and so their identification and elimination is critical.An inversion domain on a Ga- polarity samples appears as an N-polarity domain, which has a polarization reversed with respect to the rest of the surface and therefore has a different surface potential. Surface-contact-potential electric force microscopy (SCP-EFM) is an extension of atomic force microscopy (AFM) that allows imaging of the surface electrostatic potential. Previously, we established the particular mode of operation necessary to identify inversion domains on III-nitrides using a control sample. We have now studied inversion domains in GaN films grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). The existence of inversion domains was also verified by transmission electron microscopy (TEM) using multiple dark field imaging. In MOCVD grown GaN, we found predominant Ga-polarity with very low density of IDs, while in the MBE GaN, a mix polarity feature was identified.
Surface Evaluation of 6H-SiC after Doping by Diffusion
Authors: Gao Ying , Soloviev S. I. , Sudarshan T. S. 
Published: April 2011

ABSTRACTDoping by diffusion of aluminum into 6H-SiC has been carried out in the temperature range of 1800-2100°C. Aluminum carbide (Al4C3) is thought to be one of the best candidates for a p-type diffusion source material. A thin layer graphite mask was developed to protect the wafer surface from deteriorating by sublimation/epigrowth during high temperature diffusion. High-resolution optical microscope (HROM) and atomic force microscopy (AFM) were employed to evaluate the surface morphology of the diffused samples. The protective mask significantly decreased the surface roughness. In addition, secondary ion mass spectroscopy (SIMS) was used to identify the influence of the thin graphite mask on the diffusion properties in SiC. There were no significant differences in doping profiles in the samples with and without the graphite mask.
The Influence of Contact Composition, Pretreatment, and Annealing Gas on the Ohmic Behavior of Ti/Al-Based Ohmic Contacts to n-Al0.4Ga0.6N
Authors: Schweitz K. O. , Pribicko T. G. , Mohney S. E. , Isaacs-Smith T. F. , Williams J. , Pophristic M. , Gotthold D. , Birkhahn R. , Ferguson I. 
Published: April 2011

ABSTRACTAs the group III nitride semiconductor technology matures, an increasing number of devices are being fabricated with high Al fraction AlGaN. In this study, ohmic behavior is achieved using Ti/Al/Pt/Au contacts to n-Al0.4Ga0.6N, which is the highest Al fraction for which ohmic contact formation has been reported. The effect of contact composition, pretreatment, and annealing conditions is studied by 30 s isochronal annealing experiments between 500°C and 1000°C. A specific contact resistance ρC of (5±3) × 10−5 ωcm2 is obtained using Ti(26 nm)/Al(74 nm)/Pt(50 nm)/Au(50 nm) contacts to n-Al0.4Ga0.6N annealed in N2 at 800°C; however, this value is shown to be artificially high because the metal sheet resistance RM is 4 ω/⊏ causing an artifact in the data analysis. All contacts with ρC < 10−3 ωcm2 exhibit a local minimum in ρC after annealing at 800°C. The observed increase in ρC upon annealing at 850°C and 900°C, however, is not an artifact originating from a change in RM. The top Au layer is found to play an active role in forming ohmic contacts with low ρC, since omitting the Au layer yields an increase in ρC of two orders of magnitude after annealing at 800°C. Furthermore, leaving out the Au layer requires an annealing temperature of 700°C to result in linear I-V curves for currents up to 100 µA, as opposed to 500°C when the Au layer is present. The role of Au is further studied in Ti(26 nm)/Al(74 nm)/Ni(50 nm)/Au(50 nm) contacts, where Rutherford backscattering spectroscopy reveals Ga in the metal layer and/or Au buried deeper than the original semiconductor-metal interface, and x-ray diffraction indicates the formation of new phases to happen concurrently with a decrease in ρC of three orders of magnitude.
Structural and Electrical Characterisation of Nickel Silicides Contacts on Silicon Carbide
Authors: Via F. La , Roccaforte F. , Raineri V. , Musumeci P. , Calcagno L. 
Published: April 2011

ABSTRACTThe interfacial reaction and phase formation as a function of the annealing temperature (600÷1000°C) and times were investigated on nickel thin films evaporated on n type 6H-SiC (0001) substrate. The study was carried out employing a combination of Rutherford Backscattering Spectrometry, X-Ray Diffraction, Transmission Electron Microscopy and sheet resistance measurements. Also several TLM structures and Schottky diodes were fabricated with the same processes and a correlation has been found between the annealing process and the electrical measurements. The only nickel silicide phase that has been observed between 600 and 950 °C was the Ni2Si. The carbon of the consumed silicon carbide layer has been dissolved in the silicide film, during the reaction, forming carbon precipitates. The Ni2Si/SiC Schottky diodes show an almost ideal characteristics (n=1.07) and a barrier height of about 1.3 eV. From the electrical characterisation a non uniform Schottky barrier height seems to be formed.
Optical Characterization of Mg- and Si-Implanted GaN
Authors: Fellows James A. , Yeo Yung Kee , Hengehold Robert L. , Krasnobaev Leonid 
Published: April 2011

ABSTRACTThe optical and electrical properties of Mg- and Si-implanted GaN were investigated using photoluminescence, cathodoluminescence, and Hall-effect measurements. Implantation of Mg, Si, Mg+Si, Mg+O, Mg+C, and Mg+P was made into undoped semi-insulating MBE-grown GaN at energies from 125 to 260 keV at room temperature and 800 oC with doses of 1x1014 to 5x1015 cm−2. The samples were capped with AlN and annealed at temperatures ranging from 1100 to 1300 oC for 9 s to 20 min. The dominant luminescence peak in all Mg-implanted and annealed GaN is a broad green luminescence (GL) band at 2.36 eV, which may be related to a deep donor-deep acceptor complex transition resulting from the Mg implant, residual implant damage, and/or native defects. The relative intensities of this GL band and secondary peaks from 2.75-3.28 eV vary as a function of implantation temperature, ion dose, species, and anneal temperature. All Mg single and dual implantation resulted in extremely resistive GaN layers, except Mg+Si, which resulted in weakly n-type GaN. However, the Si-implanted GaN produced an electrical activation efficiency as high as 73% after annealing at 1200 oC for 5 min.
Low Temperature Epitaxial Growth of ZnO Layer on Sapphire by Plasma-Assisted Epitaxy
Authors: Yamauchi Satoshi , Hariu Takashi 
Published: April 2011

ABSTRACTZnO layer was epitaxially grown with a high growth rate around 800nm/hour on C-sapphire at relatively low temperature 400°C by plasma-assisted epitaxy in oxygen plasma which was excited by radio- frequency power at 13.56MHz. Photoluminescence spectra, which were dominated by strong donor-bound exciton emissions and free-exciton emissions at 10K, indicated deep levels native-defects were well prevented in the layers grown by the optimized growth condition including the power to discharge oxygen gas. Initial layers grown at very low temperature increased the probability of ZnO-crystal nucleation, compared with the direct growth on the sapphire, and were very effective in decreasing surface roughness and then improving the crystal quality of the successively grown ZnO layers. The full-width at half-maximum of donor-bound exciton emission was dependent on the initial layer growth condition and the narrowest value of the FWHM was obtained as 1.7meV on PAE-layers deposited at 400°C on the initial layer grown at 150°C.
Characterization of p-type 4H-SiC epitaxial layer grown on (11-20) substrate
Authors: Kojima Kazutoishi , Ohno Toshiyuki , Kushibe Mituhiro , Masahara Koh , Ishida Yuuki , Takahashi Tetuo , Suzuki Takaya , Tanaka Tomoyuki , Yoshida Sadafumi , Arai Kazuo 
Published: April 2011

ABSTRACTGrowth and characterization of p-type 4H-SiC epitaxial layers grown on (11-20) substrates are reported. P-type 4H-SiC epilayers with smooth surface morphology have been grown on (11-20) substrates by low-pressure, hot-wall type CVD with SiH4–C3H8–H2–TMA system. The doping concentration can be controlled in the range from about 1×1016cm−3 to 1×1019cm−3. Anisotropy of the crystalline quality is observed by x-ray diffraction measurement. P-type epilayers, in which near band-gap emissions are dominated and D-A pair peak is not observed, are obtained. Hole mobility of (11-20) epilayers is smaller than that of (0001) epilayers probably due to the lack of crystalline quality compared to (0001) epilayers. The results of both low-temperature photoluminescence and the temperature dependence of Hall effect measurements indicate that the boron concentration as undoped impurity in (11-20) epilayer is lower than that of (0001) epilayer. This may be caused by the smaller incorporation efficiency of boron into (11-20) epilayer than that of (0001) epilayer.
Investigation of Mechanical Stresses in Underlying Silicon due to Lead-Tin Solder Bumps via Synchrotron X-Ray Topography and Finite Element Analysis
Authors: Kanatharana J. , Pérez-Camacho J.J. , Buckley T. , McNally P.J. , Tuomi T. , Danilewsky A.N. , O'Hare M. , Lowney D. , Chen W. 
Published: April 2011

ABSTRACTSolder based flip-chip packaging has prompted interest in many integrated circuit (IC)packaging applications due to its many advantages in terms of cost, package size, electricalperformance, input/output density, etc. The ball grid array (BGA) is one of the most commonflip-chip packaging techniques used for microprocessor applications. However, mechanicalstresses induced by the flip-chip process can impact adversely on the reliability of production.White beam synchrotron x-ray topography (SXRT), a non-destructive technique, has beenemployed to investigate the spatial extent of strain fields imposed on the underlying siliconsubstrate for Intelν®Pentiumν®III microprocessors due to the lead-tin solder bump process for BGApackaging. Large area and section back-reflection SXRT images were taken before and after asimulation of the reflow process at 350°C in atmosphere. The presence of induced strain fields inthe Si substrate due to the overlying bump structures has been observed via the extinction contrasteffect in these x-ray topographs. In addition, orientational contrast effects have also been foundafter the reflow process due to the severe stresses in the underlying silicon beneath the lead bumps.The estimated magnitudes of stress, ∣σ∣, imposed on the underlying silicon were calculated to be100 MPa. The spatial strains in the underlying silicon were relieved dramatically after the leadbumps were removed from the wafer, which confirms that the bumps are indeed a major source ofstrain in the underlying Si. Finite element analysis (FEA) has also been performed in 2-D planestrain mode. The magnitudes and spatial distribution of the stresses after the reflow process are ingood agreement with the SXRT results.
Dislocation Pattern Formation – Simulations of Annealing in Two Dimensions
Authors: Argaman Nathan , Levy Ohad , Makov Guy 
Published: April 2011

ABSTRACTA two-dimensional discrete dislocation dynamics code was developed and used to simulate dislocation patterning. For the present study of annealing, both glide and some climb were allowed in the simulations. In these circumstances patterning takes place even in the absence of external stresses and of dislocation sources. A triangular underlying lattice was assumed, with the three slip systems equally populated initially. Well-defined dislocation walls and cells are observed to form from random initial conditions. The structure coarsens with time, i.e. the typical size of the cells increases as annealing takes place (the smaller cells shrink and disappear from the structure). In the spirit of a bottom-up multiscale approach, it is suggested that a new simulation methodology should be developed, in which the discrete moving objects will be dislocation wall segments rather than individual dislocations.
The Interaction of a Circular Dislocation Pile-up with a Short Rigid Fiber: a 3-D Dislocation Dynamics Simulation
Authors: Khraishi Tariq A. , Zbib Hussein M. 
Published: April 2011

ABSTRACTThis paper presents a dislocation dynamics simulation of the interaction of a circular dislocation pile-up with a short rigid fiber, say as in metal-matrix composites. The pile-up is composed of glide dislocation loops surrounding the fiber. This problem is treated here as a boundary value problem within the context of dislocation dynamics. The proper boundary condition to be enforced is that of no or zero elastic displacements at the fiber's surface. Such a condition is satisfied by a distribution of rectangular dislocation loops, acting as sources of elastic displacements, meshing the fiber's surface. Such treatment is similar to crack modeling using distributed dislocations and falls under the category of “generalized image stress analysis.” The unknown in this problem is the Burgers vectors of the surface loops. Once those are found, the Peach-Koehler force acting on the circular dislocation loops, and emulating the fiber's presence, can be determined and the dynamical arrangement of the circular pile-up evolves naturally from traditional dislocation dynamics analysis.
Teaching Undergraduate and Graduate Students Results From Recent Research As Part of a Class
Authors: Martínez-Miranda L. J. , Kidder J. , Lloyd I. , Briber R. J. , Wilson O. , Al-Sheikly M. , Salamanca-Riba L. G. 
Published: April 2011

ABSTRACTWe have integrated recent research results in the curriculum of the University of Maryland, while leaving the basics intact. This allows us to teach the fundamental laws and to show the students how these help us to answer questions that are of importance today. This can be done as part of a laboratory and as part of a class. In the laboratory classes, we emphasize what is measured (the main topic), then measure samples recently done in the literature. If available, we measure two samples and have a discussion on what are the differences. These are then related to the manner the samples have been grown. In the classes, we show the basic equation or relation, and introduce how it can answer a question that is pertinent to today's research.
The Genesis Space Probe as a Platform for Materials Education
Authors: Hays Charles C. 
Published: April 2011

ABSTRACTNASA's Genesis mission provides an interesting opportunity for educational outreach in a wide variety of materials related disciplines. This mission is one the Discovery planetary exploration series, and its purpose is to return to earth quantitative data regarding the composition of the Sun's solar wind. In doing so, the mission requires a number of materials technology platforms that provide examples of how fundamental questions in science might be answered. Specifically, the Genesis mission provides an educational pathway showing how experiment design and the process of materials selection are combined to realize evidence that will increase our understanding of the cosmological transition from solar nebula to planetary bodies.
The RET Program in the Center for Materials for Information Technology at the University of Alabama
Authors: Nikles David E. , Warren Garry W. 
Published: April 2011

ABSTRACTThe Center for Materials for Information Technology has a mission of outreach to middle school students. For the past two years our Center has run a summer research experiences for teachers (RET) program. A primary emphasis of the Center's educational outreach activities involves collaboration with a very innovative 6th to 8th grade Integrated Science (IS) curriculum based in the Center for Communication and Educational Technology at the University of Alabama. Each summer three teachers from the IS program spent ten weeks working in the Center to develop demonstrations or activities for use in their classrooms. The emphasis was on demonstrations of magnetism and magnetic materials. In addition to these activities, the teachers have also assisted in the development of Computer Aided Instructional (CAI) software for use in their science classrooms. Both the activities and the software developed this summer will be made available to all of the teachers and students participating in the IS curriculum, approximately 1400 teachers and 170,000 students.
Ways That Engineers Can Get Involved In Recruiting Future Materials Scientists and Engineers
Authors: Gleixner Stacy H. 
Published: April 2011

ABSTRACTFor materials science and engineering departments across the country, recruitment of students is a critical concern. To increase enrollment, students' interest in materials science needs to be sparked early, preferably before they begin college. However, many entering college students have never heard of the major and/or are unsure of what a career in materials science would be like. There are many excellent resources that have been developed to target this problem directly including comprehensive career resources on the web, videos describing careers in materials engineering, and teaching materials developed for middle and high school teachers.
Materials Science and Engineering at Boise State University: Responding to an Industrial Need
Authors: Moll Amy J. , Knowlton William B. , Bunnell David E. , Burkett Susan L. 
Published: April 2011

ABSTRACTThe College of Engineering at Boise State University (BSU) is a new program in only its fifth year of existence. Bachelor's degrees in Civil Engineering (CE), Electrical and Computer Engineering (ECE) and Mechanical Engineering (ME) are offered with M.S. Degrees in each discipline added this year. The industrial advisory board for the College of Engineering at BSU strongly recommended enhancement of the Materials Science and Engineering (MS&E) offerings at BSU. In response to local industry's desire for an increased level of coursework and research in MS&E, BSU has created a minor in MS&E at both the undergraduate and graduate level.The MS&E program is designed to meet the following objectives: provide for local industry's need for engineers with a MS&E competency, add depth of understanding of MS&E for undergraduate and graduate students in ECE, ME and CE, prepare undergraduate students for graduate school in MS&E, improve the professional skills of the students especially in the areas of materials processing and materials selection, provide applied coursework for Chemistry, Physics, and Geophysics students, and offer coursework in a format that is convenient for students currently working in local industry.
Web Modules Linking Mechanics and Materials Science
Authors: Roylance David , Jenkins C. H. , Khanna S. K. 
Published: April 2011

ABSTRACTIn 1996, the MIT subject 3.11 Mechanics of Materials in the Department of Materials Science and Engineering began using an experimental new textbook approach, written with a strongly increased emphasis on the materials aspects of the subject. It also included several topics such as finite element methods, fracture mechanics, and statistics that are not included in most traditional Mechanics of Materials texts. These nontraditional aspects were designed to fit the curriculum in Materials Science and Engineering, although admittedly Mechanics instructors in other departments and schools might not find all of them suitable for their own subjects. Further, a number of topics may be of interest in educational curricula and industrial practice outside traditional Mechanics subjects.One approach to increasing the flexibility and adaptability of this materials-oriented text is to make discrete and coherent portions of it available as stand-alone, web-available modules. Instructors could then pick and choose among topics, and assemble a subject offering in whatever way they choose. It would also be possible for instructors of specialty engineering subjects, for instance bridge or aircraft design, to add modules on mechanics of materials aimed at their own needs.A series of such modules are now being developed under a National Science Foundation Course, Curriculum and Laboratory Improvement (CCLI) grant aimed at strengthening the links in the engineering curriculum between materials and mechanics. Each module is intended to be capable of standing alone, so that it will usually be unnecessary to work through other modules in order to use any particular one. This approach will be outlined and demonstrated, both as an approach to the specific topic of a mechanics-materials linkage, and as a possibility for more general implementation in distance learning.