The effect of initial growth interface on the grain structure in HPMC-Si ingot

2017 ◽  
Author(s):  
Giri Wahyu Alam ◽  
Etienne Pihan ◽  
Benoit Marie ◽  
Nathalie Mangelinck-Noel
Keyword(s):  
Grain Structure ◽  
Initial Growth ◽  
Growth Interface

scholarly journals Thermal Analysis of AlGaN/GaN HEMTs Considering Anisotropic And Inhomogeneous Thermal Conductivity

2021 ◽  
Author(s):  
Yao Li ◽  
Zixuan Zheng ◽  
Qun Li ◽  
Hongbin Pu
Keyword(s):  
Thermal Conductivity ◽  
Temperature Rise ◽  
Power Dissipation ◽  
Thermal Characteristics ◽  
Maximum Temperature ◽  
Base Temperature ◽  
Initial Growth ◽  
Boltzmann Transport ◽  
Growth Interface ◽  
Anisotropic Thermal Conductivity

Abstract To examine the differences of thermal characteristics introduced by material thermal conductivity, anisotropic polycrystalline diamond (PCD) and GaN are analyzed based on the accurate model of grain sizes in the directions of parallel and vertical to the interface and an approximate solution of the phonon Boltzmann transport equation. Due to the space-variant grain structures of PCD, the inhomogeneous-anisotropic local thermal conductivity, homogeneous-anisotropic thermal conductivity averaged over the whole layer and the typical values of inhomogeneous-isotropic thermal conductivity are compared with/without anisotropic GaN thermal conductivity. The results show that the considerations of inhomogeneous-anisotropic PCD thermal conductivity and anisotropic GaN thermal conductivity are necessary for the accurate prediction of temperature rise in the GaN HEMT devices, and when ignoring both, the maximum temperature rise is undervalued by over 16 K for thermal boundary resistance (TBR) of 6.5 to 60 m2K/GW at power dissipation of 10 W/mm. Then the dependences of channel temperature on several parameters are discussed and the relations of thermal resistance with power dissipation are extracted at different base temperature. Compared with GaN, SiC and Si substrates, PCD is the most effective heat spreading layer though limited by the grain size at initial growth interface.

Mosaic Crystal Tilts and Their Relationship to Dislocation Structure, Surface Roughness and Growth Conditions in Relaxed SiGe Layers

1998 ◽  
Vol 533 ◽  
Author(s):  
D. J. Wallis ◽  
D. J. Robbins ◽  
A. J. Pidduck ◽  
G. M. Williams ◽  
A. Churchill ◽  
...  
Keyword(s):  
Surface Roughness ◽  
High Performance ◽  
Surface Defects ◽  
Growth Conditions ◽  
Buffer Layers ◽  
Great Promise ◽  
Threading Dislocation ◽  
Initial Growth ◽  
Growth Interface ◽  
Mosaic Crystal

AbstractIn recent years the growth of virtual substrates using graded SiGe buffer layers has shown great promise for the development of high performance devices. Whilst significant progress has been made in the control of growth conditions to produce low threading dislocation densities of the order suitable for commercial exploitation, several technological problems still have to be overcome. An example of such problems are cosmetic surface defects such as pits and the cross hatched surface roughness associated with mosaic crystal tilts. The work described here utilises a variety of techniques, including X-ray diffraction reciprocal space maps, TEM, AFM and SIMS to provide a comparison between several SiGe virtual substrates grown using low pressure-CVD at high (≈800°C) and low (≈6000°C) temperatures, and at different grade rates (5–50% Ge μm−1). The growth conditions are seen to have a strong effect on the crystal tilts present in the layers with the low temperature layers showing a much larger spread of mosaic tilts. The origin of these tilts is seen to occur during the early stages of the relaxation process irrespective of growth temperature and at similar Ge fractions for all samples. TEM imaging close to the initial growth interface shows that dislocation pileups occur in this region and also suggest that the pileups have a characteristic spacing of 1–2μm. A similar characteristic length scale is also observed in the surface roughness by AFM, the form of which is seen to depend upon the growth conditions.

Microgravity and Hypergravity Observations of Equiaxed Solidification of Al-Cu Alloys Using In Situ X-Radiography Recorded in Real-Time on Board a Parabolic Flight

2014 ◽  
Vol 790-791 ◽  
pp. 52-58 ◽  
Author(s):  
Andrew G. Murphy ◽  
J. Li ◽  
Olle Janson ◽  
Antonio Verga ◽  
David J. Browne
Keyword(s):  
Real Time ◽  
Parabolic Flight ◽  
Grain Structure ◽  
Initial Growth ◽  
Subsequent Growth ◽  
Cu Alloy ◽  
Cu Alloys ◽  
Equiaxed Solidification ◽  
Gradient Furnace

During solidification of metallic alloys, thermosolutal natural convection plays a significant role in grain nucleation, subsequent growth and morphology, as well as the formation of casting defects. In this work, an Al-5wt%Ti-1wt%B inoculated Al-20wt%Cu alloy was solidified, near-isothermally, using a Bridgman-type gradient furnace, while being monitored in real-time via in-situ X-radiography as part of a parabolic flight microgravity campaign. Each parabola consisted of a transition through 24 seconds of hypergravity (1.8 g), followed by 22 seconds of microgravity, and a then a further 24 seconds of hypergravity. Solidification was controlled such that nucleation occurred coincident with the onset of microgravity. This allowed for the effects of microgravity on equiaxed nucleation and initial growth, followed by continuing solidification in hypergravity, to be observed, as well as the effect on the semi-coherent grain structure when transitioning between the two.

scholarly journals Investigation of the Grain Boundary Character and Dislocation Density of Different Types of High Performance Multicrystalline Silicon

Crystals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 341 ◽  
Author(s):  
Gaute Stokkan ◽  
Adolphus Song ◽  
Birgit Ryningen
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Performance ◽  
Coincidence Site Lattice ◽  
Grain Structure ◽  
Multicrystalline Silicon ◽  
Initial Growth ◽  
Cluster Density ◽  
Dislocation Cluster

Wafers from three heights and two different lateral positions (corner and centre) of four industrial multicrystalline silicon ingots were analysed with respect to their grain structure and dislocation density. Three of the ingots were non-seeded and one ingot was seeded. It was found that there is a strong correlation between the ratio of the densities of (coincidence site lattice) CSL grain boundaries and high angle grain boundaries in the bottom of a block and the dislocation cluster density higher in the block. In general, the seeded blocks, both the corner and centre block, have a lower dislocation cluster density than in the non-seeded blocks, which displayed a large variation. The density of the random angle boundaries in the corner blocks of the non-seeded ingots was similar to the density in the seeded ingots, while the density in the centre blocks was lower. However, the density of CSL boundaries was higher in all the non-seeded than in the seeded ingots. It appears that both of these grain boundary densities influence the presence of dislocation clusters, and we propose they act as dislocation sinks and sources, respectively. The ability to generate small grain size material without seeding appears to be correlated to the morphology of the coating, which is generally rougher in the corner positions than in the middle. Furthermore, the density of twins and CSL boundaries depends on the growth mode during initial growth and thus on the degree of supercooling. Controlling both these properties is important in order to be able to successfully produce uniform quality high-performance multicrystalline silicon by the advantageous non-seeding method.

SEM analysis of DC magnetron sputtered beryllium films

1988 ◽  
Vol 46 ◽  
pp. 960-961
Author(s):  
E. F. Lindsey ◽  
C. W. Price ◽  
E. L. Pierce ◽  
E. J. Hsieh
Keyword(s):  
Fine Structure ◽  
Electron Emission ◽  
Secondary Electron ◽  
Low Voltage ◽  
Ion Beam ◽  
Secondary Electron Emission ◽  
Sem Analysis ◽  
Fused Silica ◽  
Grain Structure ◽  
Silica Substrate

Columnar structures produced by DC magnetron sputtering can be altered by using RF biased sputtering or by exposing the film to nitrogen pulses during sputtering, and these techniques are being evaluated to refine the grain structure in sputtered beryllium films deposited on fused silica substrates. Beryllium is brittle, and fractures in sputtered beryllium films tend to be intergranular; therefore, a convenient technique to analyze grain structure in these films is to fracture the coated specimens and examine them in an SEM. However, fine structure in sputtered deposits is difficult to image in an SEM, and both the low density and the low secondary electron emission coefficient of beryllium seriously compound this problem. Secondary electron emission can be improved by coating beryllium with Au or Au-Pd, and coating also was required to overcome severe charging of the fused silica substrate even at low voltage. The coating structure can obliterate much of the fine structure in beryllium films, but reasonable results were obtained by using the high-resolution capability of an Hitachi S-800 SEM and either ion-beam coating with Au-Pd or carbon coating by thermal evaporation.

Defects in β-SiC thin films grown on α-SiC substrates

1988 ◽  
Vol 46 ◽  
pp. 568-569
Author(s):  
Karren L. More
Keyword(s):  
Thin Films ◽  
Semiconductor Device ◽  
Lattice Mismatch ◽  
Chemical Vapor ◽  
Substrate Material ◽  
Growth Interface ◽  
Si Substrates ◽  
Thermal Expansion Coefficients ◽  
Device Applications ◽  
Expansion Coefficients

Beta-SiC is an ideal candidate material for use in semiconductor device applications. Currently, monocrystalline β-SiC thin films are epitaxially grown on {100} Si substrates by chemical vapor deposition (CVD). These films, however, contain a high density of defects such as stacking faults, microtwins, and antiphase boundaries (APBs) as a result of the 20% lattice mismatch across the growth interface and an 8% difference in thermal expansion coefficients between Si and SiC. An ideal substrate material for the growth of β-SiC is α-SiC. Unfortunately, high purity, bulk α-SiC single crystals are very difficult to grow. The major source of SiC suitable for use as a substrate material is the random growth of {0001} 6H α-SiC crystals in an Acheson furnace used to make SiC grit for abrasive applications. To prepare clean, atomically smooth surfaces, the substrates are oxidized at 1473 K in flowing 02 for 1.5 h which removes ∽50 nm of the as-grown surface. The natural {0001} surface can terminate as either a Si (0001) layer or as a C (0001) layer.

High-resolution EM study of submicrometer-grained Al-Mg solid solution alloys

1995 ◽  
Vol 53 ◽  
pp. 524-525
Author(s):  
Z. Horita ◽  
D. J. Smith ◽  
M. Furukawa ◽  
M. Nemoto ◽  
R. Z. Valiev ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
High Resolution ◽  
Grain Boundaries ◽  
Energy State ◽  
High Energy ◽  
Grain Structure ◽  
Boundary Structure ◽  
Solid Solution Alloy ◽  
Average Grain Size

It is possible to produce metallic materials with submicrometer-grained (SMG) structures by imposing an intense plastic strain under quasi-hydrostatic pressure. Studies using conventional transmission electron microscopy (CTEM) showed that many grain boundaries in the SMG structures appeared diffuse in nature with poorly defined transition zones between individual grains. The implication of the CTEM observations is that the grain boundaries of the SMG structures are in a high energy state, having non-equilibrium character. It is anticipated that high-resolution electron microscopy (HREM) will serve to reveal a precise nature of the grain boundary structure in SMG materials. A recent study on nanocrystalline Ni and Ni3Al showed lattice distortion and dilatations in the vicinity of the grain boundaries. In this study, HREM observations are undertaken to examine the atomic structure of grain boundaries in an SMG Al-based Al-Mg alloy.An Al-3%Mg solid solution alloy was subjected to torsion straining to produce an equiaxed grain structure with an average grain size of ~0.09 μm.

High-resolution scanning electron microscopy of thin-film magnetic media of magnetic recording disk

1992 ◽  
Vol 50 (2) ◽  
pp. 1334-1335
Author(s):  
K. Ogura ◽  
H. Nishioka ◽  
N. Ikeo ◽  
T. Kanazawa ◽  
J. Teshima
Keyword(s):  
Thin Film ◽  
Fine Structure ◽  
High Resolution ◽  
Magnetic Recording ◽  
High Performance ◽  
Magnetic Hysteresis ◽  
Grain Structure ◽  
Magnetic Media ◽  
Cross Sectional ◽  
Resolution Observation

Structural appraisal of thin film magnetic media is very important because their magnetic characters such as magnetic hysteresis and recording behaviors are drastically altered by the grain structure of the film. However, in general, the surface of thin film magnetic media of magnetic recording disk which is process completed is protected by several-nm thick sputtered carbon. Therefore, high-resolution observation of a cross-sectional plane of a disk is strongly required to see the fine structure of the thin film magnetic media. Additionally, observation of the top protection film is also very important in this field.Recently, several different process-completed magnetic disks were examined with a UHR-SEM, the JEOL JSM 890, which consisted of a field emission gun and a high-performance immerse lens. The disks were cut into approximately 10-mm squares, the bottom of these pieces were carved into more than half of the total thickness of the disks, and they were bent. There were many cracks on the bent disks. When these disks were observed with the UHR-SEM, it was very difficult to observe the fine structure of thin film magnetic media which appeared on the cracks, because of a very heavy contamination on the observing area.

Microstructure Development in a High Current Density NbTi Superconducting Composite

1985 ◽  
Vol 43 ◽  
pp. 186-189
Author(s):  
P. J. Lee ◽  
D. C. Larbalestier
Keyword(s):  
Current Density ◽  
High Current Density ◽  
Cold Drawing ◽  
Heat Treatments ◽  
Grain Structure ◽  
Fine Grain ◽  
Boundary Film ◽  
Quantitative Basis ◽  
Cold Worked ◽  
Very High

Several features of the metallurgy of superconducting composites of Nb-Ti in a Cu matrix are of interest. The cold drawing strains are generally of order 8-10, producing a very fine grain structure of diameter 30-50 nm. Heat treatments of as little as 3 hours at 300 C (∼ 0.27 TM) produce a thin (1-3 nm) Ti-rich grain boundary film, the precipitate later growing out at triple points to 50-100 nm dia. Further plastic deformation of these larger a-Ti precipitates by strains of 3-4 produces an elongated ribbon morphology (of order 3 x 50 nm in transverse section) and it is the thickness and separation of these precipitates which are believed to control the superconducting properties. The present paper describes initial attempts to put our understanding of the metallurgy of these heavily cold-worked composites on a quantitative basis. The composite studied was fabricated in our own laboratory, using six intermediate heat treatments. This process enabled very high critical current density (Jc) values to be obtained. Samples were cut from the composite at many processing stages and a report of the structure of a number of these samples is made here.

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