1,720,965 research outputs found
Micro-Raman for Local Strain Evaluation of GaN LEDs and Si Chips Assembled on Cu Substrates
Get PDFIntegrated circuits are created by interfacing different materials, semiconductors, and metals, which are appropriately deposited or grown on substrates and layers soldered together. Therefore, the characteristics of starting materials and process temperatures are of great importance, as they can induce residual strains in the final assembly. Identifying and quantifying strain becomes strategically important in optimizing processes to enhance the performance, duration, and reliability of final devices. This work analyzes the thermomechanical local strain of semiconductor materials used to realize LED modules for lighting applications. Gallium Nitride active layers grown on sapphire substrates and Si chips are assembled by soldering with eutectic AuSn on copper substrates and investigated by Raman spectroscopy in a temperature range of -50 to 180 °C. From the Raman mapping of many different samples, it is concluded that one of the leading causes of strain in the GaN layer can be attributed to the differences in the thermal expansion coefficient among the various materials and, above all, among the chip, interconnection material, and substrate. These differences are responsible for forces that slightly bend the chip, causing strain in the GaN layer, which is most compressed in the central region of the chip and slightly stretched in the outer areas
Thermomechanical local stress in assembled GaN LEDs investigated by Raman optical spectroscopy
No full textIntegrated circuits constitute a complex mosaic, where materials with different characteristics, grown or deposited in different ways and at different temperatures, are linked together in various geometries. It is well known that during and after processing of these devices, mechanical stresses develop in the layers. These stresses may be due to thermal steps, intrinsic stresses, which are inherent in the formation process of the film, or due to the geometry of the material. For example, high stresses are present in the substrate at film edges. The presence of local residual stress has an important effect on the electrical properties of electronic devices, in particular on the reliability and the lifetime of the semiconductor components. The present work focuses on the optical investigation of the thermomechanical stress of semiconductor materials used to realize new LED modules for front lighting application. Blue LEDs, based on gallium nitride (GaN) on sapphire, are bonded to a silicon carrier using gold silicon. Afterwards the sapphire is removed. The GaN on silicon devices are soldered by eutectic AuSn soldered on copper substrates, with different thicknesses. In the solder process different AuSn solder layer are achieved by varying the bond force. Raman spectroscopy is used to investigate the influence of the assembly process and assembly material on the local stress in the semiconductor. By that the physical, mechanical and chemical properties of the interconnect material can be analyzed. A model is developed to simulate the thermomechanical stress in the GaN LED assemblies. The Raman results validate the computational model. The phenomena are evaluated at room temperature, at -50°C and at 180°C
SEM Images of Arrays of III-V Nanowires with Labelled Data
No full text<p>The Dataset is a .zip folder.</p><p>The Dataset contains 240 .tiff images in black and white, each paired by file name to a .json file containing labeling information. </p><p>Each image consists of an array of 66 nanowire structures. Some images contain parasitic crystals and defective wires. Wires growing from seed surfaces parallel to and misaligned with the array walls are present.</p><p>The .json label files were created and can be processed with LabelMe (<a href="https://github.com/wkentaro/labelme">https://github.com/wkentaro/labelme</a>). The explanation for the labels can be found in the associated open-access paper currently submitted for publication.</p><p>The Licensor, IBM Corp.</p>
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Heterointerface control in III-V nanowires monolithically integrated on silicon
Get PDFIntegration of photonic integrated circuits (PICs) serving as interconnects on the silicon electronic platform is gaining momentum as computational requirements increase. Due to material compatibility, silicon-based photonic components remain the main choice for industrial integration. However, research focused on integrating III-V semiconductor-based photonic components has made great progress in tackling the problem of lattice mismatch, which has hindered the use of this material on silicon platforms so far.
A promising monolithic method for the integration of III-V components in CMOS wafers is template assisted selective epitaxy (TASE), which employs a silicon oxide (SiO2) template to guide the metal-organic chemical vapor deposition (MOCVD) of III-V devices from a silicon seed defined in the device layer of a silicon on insulator (SOI) wafer. TASE enables high defect control but is still affected by a multifaceted growth front, which limits its compositional control and efficient integration of quantum confinement structures.
This work focuses on the monolithic growth of III-V nanowires from silicon, and, in particular, on the control of the morphology of the growth front and the sharpness of heterointerfaces as enablers for the creation of superlattices embedded in the nanowires. Stabilisation of a growth front consisting of a single {111}B facet was achieved on two SOI wafers with (001) and (110) device layer crystallographic orientations by exploiting the growth of InP with high precursor V / III ratios. With an overall growth yield of 92.55 % calculated on a sample of 15840 growth sites on two (110) chips, the method has proven to be very reliable even under laboratory conditions.
This method enabled the fabrication of InGaAs and InAs quantum wells in a InP matrix. Compositionally sharp heterointerfaces and perfect alignment of concentration profiles of the V and III group elements in the sub-10 nm layers were achieved by employing hold steps in the MOCVD recipe. The growth regime was estimated to be "layer-by-layer", with a very early stabilisation of a single {111}B facet as the growth front, as single crystals resulting from the merging of crystals grown from three nucleation sites were observed with the methodology used in this study. These merged crystals had a crystalline quality fully comparable to that of crystals grown from a single seed.
The growth rate homogeneity and highly predictable heterointerface positioning achieved in this work are expected to aid in the monolithic integration of photonic devices on the wafer scale. The integration of quantum well structures demonstrated in this thesis into the intrinsic region of p - i - n photodiodes and their in-depth electrooptical characterisation are the natural next step in proving an improvement in the performance of TASE-based photodetectors. Such an improvement, in conjunction with recent progress on TASE based modulators and microdisk lasers, will enable a fully TASE-fabricated PIC
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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