Calculation of Stresses in Strained Semiconductor Layers

1994 ◽  
Vol 338 ◽  
Author(s):  
K. Nakajima
Keyword(s):  
Stress Distribution ◽  
Calculation Method ◽  
Thin Layers ◽  
Balance Method ◽  
Misfit Dislocations ◽  
Improved Method ◽  
Strained Layers ◽  
Stress Calculation ◽  
The Third

ABSTRACTA stress calculation method is proposed by improving the force and moment balance method to calculate the stress in semiconductor layers. The following three points are improved. The first point is that the vertically precise stress distribution in multilayers can be calculated by using imaginary thin layers. The second point is that the stress can be calculated on the basis of threedimensional deformation. The third point is that the stress can be calculated in strained layers with interfacial misfit dislocations. The stress distribution in strained semiconductor layers such as InGaAs/GaAs multilayers, InGaAs/graded lnGaAs/GaAs layers and GaAs/Si structures is calculated using this improved method.

Very Thick Coherently Strained GexSi1−x Layers Grown in a Narrow Temperature Window

1991 ◽  
Vol 220 ◽  
Author(s):  
C. H. Chern ◽  
K. L. Wang ◽  
G. Bai ◽  
M. -A. Nicolet
Keyword(s):  
Growth Temperature ◽  
Strain Relaxation ◽  
Gas Pressure ◽  
High Density ◽  
Misfit Dislocations ◽  
High Quality ◽  
Strained Layers ◽  
Temperature Window ◽  
Residual Gas

ABSTRACTStrain relaxation of GexSi1−x layers is studied as a function of growth temperature. Extremely thick coherently strained layers whose thicknesses exceed more than fifty times of the critical thicknesses predicted by Matthews and Blakeslee's model were successfully grown by MBE. There exits a narrow temperature window from 310 °C to 350 °C for growing this kind of high quality thick strained layers. Below this temperature window, the layers are poor in quality as indicated from RHEED patterns. Above this window, the strain of the layers relaxes very fast accompanied with a high density of misfit dislocations as the growth temperature increases. Moreover, for samples grown in this temperature window, the strain relaxation shows a dependence of the residual gas pressure, which has never been reported before.

Stress Relaxation in Uniquely Oriented SiGe/Si Epitaxial Layers

1999 ◽  
Vol 594 ◽  
Author(s):  
M. E. Ware ◽  
R. J. Nemanich
Keyword(s):  
Stress Relaxation ◽  
Surface Morphology ◽  
Strain Relaxation ◽  
Epitaxial Layers ◽  
Misfit Dislocations ◽  
Strained Layers ◽  
Force Microscopy ◽  
Si Substrates ◽  
Atomic Force ◽  
Deposited Films

AbstractThis study explores stress relaxation of epitaxial SiGe layers grown on Si substrates with unique orientations. The crystallographic orientations of the Si substrates used were off-axis from the (001) plane towards the (111) plane by angles, θ = 0, 10, and 22 degrees. We have grown 100nm thick Si(1−x) Ge(x) epitaxial layers with x=0.3 on the Si substrates to examine the relaxation process. The as-deposited films are metastable to the formation of strain relaxing misfit dislocations, and thermal annealing is used to obtain highly relaxed films for comparison. Raman spectroscopy has been used to measure the strain relaxation, and atomic force microscopy has been used to explore the development of surface morphology. The Raman scattering indicated that the strain in the as-deposited films is dependent on the substrate orientation with strained layers grown on Si with 0 and 22 degree orientations while highly relaxed films were grown on the 10 degree substrate. The surface morphology also differed for the substrate orientations. The 10 degree surface is relatively smooth with hut shaped structures oriented at predicted angles relative to the step edges.

Numerical calculation of crack width in prestressed concrete beams with bond-slip effect

2019 ◽  
Vol 15 (2) ◽  
pp. 523-536
Author(s):  
Jinliang Liu ◽  
Yanmin Jia ◽  
Guanhua Zhang ◽  
Jiawei Wang
Keyword(s):  
Numerical Calculation ◽  
Numerical Model ◽  
Prestressed Concrete ◽  
Calculation Method ◽  
Crack Width ◽  
Calculation Model ◽  
Content Type ◽  
Bond Slip ◽  
Stress Calculation ◽  
Bonding Performance

Purpose The calculation of the crack width is necessary for the design of prestressed concrete (PC) members. The purpose of this paper is to develop a numerical model based on the bond-slip theory to calculate the crack width in PC beams. Design/methodology/approach Stress calculation method for common reinforcement after beam crack has occurred depends on the difference in the bonding performance between prestressed reinforcement and common reinforcement. A numerical calculation model for determining the crack width in PC beams is developed based on the bond-slip theory, and verified using experimental data. The calculation values obtained by the proposed numerical model and code formulas are compared, and the applicability of the numerical model is evaluated. Findings The theoretical analysis and experimental results verified that the crack width of PC members calculated based on the bond-slip theory in this study is reasonable. Furthermore, the stress calculation method for the common reinforcement is verified. Compared with the model calculation results obtained in this study, the results obtained from code formulas are more conservative. Originality/value The numerical calculation model for crack width proposed in this study can be used by engineers as a reference for calculating the crack width in PC beams to ensure the durability of the PC member.

Performance Evaluation of Japanese Nuclear Power Plant Based on Open Data and Information (3)

2010 ◽  
Author(s):  
Tadahisa Nagata ◽  
Ken-ichiro Sugiyama
Keyword(s):  
Renewal Process ◽  
Calculation Method ◽  
Nuclear Power ◽  
Power Plants ◽  
Failure Modes ◽  
Continuous Data ◽  
Weibull Analysis ◽  
Improved Method ◽  
Early Failure ◽  
Restoration Process

The excessive maintenance of the nuclear power plants (NPPs) may cause the early (infant) failure in Japan. An easy analysis; the Weibull analysis was applied to the evaluation of the failure mode. The Weibull analysis needs the hazard data. The maintenance information of the equipment which caused plant shutdown was required for the hazard calculation. However, maintenance information of the equipment was not open. Therefore, all equipment was assumed to be maintained during every shutdown. This assumption was based on renewal process. However, a repair after unplanned shutdown of NPP is generally a restoration of only failed function without system overhaul. The system must be considered to age continuously. The system was not renewed. The operation data must be regarded as one continuous data before and after unplanned shutdown. An improvement of the Weibull analysis was required for NPPs. The model of the Weibull analysis was investigated. The competitive model in which shutdown caused by other than focused equipment/cause may be supposed to be continuous data could not be applied for a comprehensive analysis. Furthermore, the calculation method of the Weibull analysis was investigated. The calculation method of the hazard was viewed. A denominator of the hazard is the number of data which is cut for every continuous data by renewal process. However, multiple considerations of operation periods before unplanned shutdowns might cause underestimation of the failure rate in case of restoration process. Therefore, a dominator of the hazard was not supposed to be the number of data but the number of survived equipments (plants) at each time according to the definition of the hazard. This improved method is for the restoration process. The performance of Japanese NPPs was evaluated by improved method. The failure modes of Japanese NPPs were early failure modes. Moreover, performances of U.S. NPPs was tried to be evaluated by improved method. Operation data was collected from “NRC Power Reactor Status Reports”. However, many “maintenance outage”s which are the shutdowns of unknown origin were found. Therefore, DOE information was supplemented to investigate the “maintenance outage”. Failure modes of U.S. NPPs were the early failure modes, and failure rates were larger than Japanese NPPs.

Stress Calculation of a Spherical Tank on Settled Ground Based on FEM

2013 ◽  
Vol 331 ◽  
pp. 110-113
Author(s):  
Hong Li Gao ◽  
Wei Jun Li ◽  
Zhi Hai Li
Keyword(s):  
Stress Distribution ◽  
Maximum Stress ◽  
Differential Settlement ◽  
Foundation Settlement ◽  
Stress Calculation ◽  
Spherical Tank

In this paper, a model of a LGP spherical tank supported by 8 equator tangent-type supporting on settled ground was built.The stress on the shell,on the pillars and on the connection of pillars with shell were calculated,the stress distribution on shell,pillars and the connection of pillars with shell were obtained, the influence of foundation settlement to the stress of shell and pillars were studied. The results showed that the differential settlement produced a less affect on the shell,but a greater impact on the pillars. The maximum stress arose at the connection between pillars and shell ,there is a big stress area in the connectors area.

A rapid stress calculation method for short flexspline harmonic drive

2019 ◽  
Vol 36 (6) ◽  
pp. 1852-1867 ◽  
Author(s):  
Shuang Wang ◽  
Gedong Jiang ◽  
Xuesong Mei ◽  
Chuang Zou ◽  
Xian Zhang ◽  
...  
Keyword(s):  
Finite Element ◽  
Calculation Method ◽  
Circumferential Stress ◽  
Element Model ◽  
Analytical Relationship ◽  
Analysis Method ◽  
Content Type ◽  
Stress Calculation ◽  
Mechanics Analysis ◽  
Rapid Calculation

Purpose Because of the compact structure, short flexspline (FS) harmonic drive (HD) is increasingly used. The stress calculation of FS is very important in design and optimization of HD system. This paper aims to study the stress calculation methods for short FS, based on mechanics analysis and finite element method (FEM). Design/methodology/approach A rapid stress calculation method, based on mechanics analysis, is proposed for the short FS of HD. To verify the stress calculation precision of short FS, a complete finite element model of HD is established. The results of stress and deformation of short FS in different lengths are solved by FEM. Findings Through the rapid calculation method, the analytical relationship between circumferential stress and length of cylinder was obtained. And the circumferential stress has proportional relation with the reciprocal of squared length. The FEM results verified that the rapid stress calculation method could obtain accurate results. Research limitations/implications The rapid mechanics analysis method is practiced to evaluate the strength of FS at the design stage of HD. And the complete model of HD could contribute to improving the accuracy of FEM results. Originality/value The rapid calculation method is developed based on mechanics analysis method of cylinder and equivalent additional bending moment model, through which the analytical relationship between circumferential stress and length of cylinder was obtained. The complete three-dimensional finite element model of HD takes the stiffness of bearing into consideration, which can be used in the numerical simulation in the future work to improve the accuracy.

Investigation of Semiconductor Heterostructures by White Beam Synchrotron X-Ray Topography in Grazing Bragg-Laue and Conventional Bragg Geometries

1991 ◽  
Vol 35 (A) ◽  
pp. 247-253
Author(s):  
G.-D. Yao ◽  
J. Wu ◽  
T. Fanning ◽  
M. Dudley
Keyword(s):  
Penetration Depth ◽  
Grazing Incidence ◽  
Semiconductor Heterostructures ◽  
Misfit Dislocations ◽  
Strained Layers ◽  
X Ray ◽  
Main Reflection ◽  
White Beam ◽  
Topographic Imaging

AbstractWhite beam synchrotron X-ray topography has been applied both to the characterization of two semiconductor heterostructures, GaAs/Si and InxGa1-xAs/GaAs strained layers, and a substrate to be used for growing semiconductor epilayers, Cd1-xZnxTe. In the case of the heterostructures, misfit dislocations were observed using depth sensitive X-ray topographic imaging in grazing incidence Bragg-Laue geometries. The X-ray penetration depth, which can be varied from several hundreds of angstroms to hundreds of micrometers by rotating about the main reflection vector, which in this specific case was (355), is governed by kinernatical theory. This is justified by comparing dislocation contrast and visibility with the extent of the calculated effective misorientalion field in comparison to the effective X-ray penetration depth. For the case of Cd1-xZnxTe, twin configurations are observed, and their analysis is presented.

Additional Stress Distribution in DJM Pile Composite Foundation and Simplified Calculation Method

2012 ◽  
Vol 594-597 ◽  
pp. 274-279
Author(s):  
Fang Ding He ◽  
Guang Jun Guo ◽  
Jian Qing Wu
Keyword(s):  
Stress Distribution ◽  
Calculation Method ◽  
Influential Factors ◽  
Composite Foundation ◽  
Good Effect ◽  
Additional Stress ◽  
Soft Foundation ◽  
Simplified Calculation ◽  
Simplified Calculation Method

Although DJM-Pile have a good effect on strengthening soft foundation,theories about additional stress are too complex or too simply to be used in project well.By adopting FEM software with considering of friction between soil and pile,simulate the additional stress in composite foundation because of DJM pile construction and compare with results gotten in Bossinesq method.The comparison shows that the distribution of additional stress is very similar.So considering several major influential factors,the paper updates the Bossinesq method and brings forward a simplified calculation method.

Rapid calculation of the pressures and clearances in rough, rolling-sliding elastohydrodynamically lubricated contacts. Part 1: Low-amplitude, sinusoidal roughness

2007 ◽  
Vol 221 (5) ◽  
pp. 535-549 ◽  
Author(s):  
C J Hooke ◽  
K Y Li ◽  
G Morales-Espejel
Keyword(s):  
Surface Roughness ◽  
Rough Surface ◽  
Perturbation Analysis ◽  
Curve Fitting ◽  
Calculation Method ◽  
The Third ◽  
Lubricated Contacts ◽  
Rapid Calculation ◽  
Low Amplitude ◽  
Rough Rolling

Surface roughness in elastohydrodynamically lubricated (EHL) contacts may have a significant effect on component life and there is a need to be able to assess its effects quickly. This article describes a rapid calculation method, which provides accurate results where the amplitude of the roughness is relatively low and which gives good indications of the likely behaviour for higher amplitudes. In the first part, the effect of low-amplitude, sinusoidal roughness is examined, and it is shown that the behaviour can, for any wavelength and roughness orientation, be characterized by three complex quantities. Calculation of two of these is straightforward; the third requires curve fitting to the results obtained using a perturbation analysis. Details of the process are given. The second part of the article discusses how these results can be used to predict the behaviour of any rough surface under rolling-sliding EHL conditions.

Threading Dislocation Density Reduction in GaN/Sapphire Heterostructures.

1999 ◽  
Vol 595 ◽  
Author(s):  
A. Kvit ◽  
A. K. Sharma ◽  
J. Narayan
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
High Density ◽  
Thin Layers ◽  
Interfacial Region ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Plan View ◽  
Partial Dislocations

AbstractLarge lattice mismatch between GaN and α-Al2O3 (15%) leads to the possibility of high threading dislocation densities in the nitride layers grown on sapphire. This investigation focused on defect reduction in GaN epitaxial thin layer was investigated as a function of processing variables. The microstructure changes from threading dislocations normal to the basal plane to stacking faults in the basal plane. The plan-view TEM and the corresponding selected-area diffraction patterns show that the film is single crystal and is aligned with a fixed epitaxial orientation to the substrate. The epitaxial relationship was found to be (0001)GaN∥(0001)Sap and [01-10]GaN∥[-12-10]Sap. This is equivalent to a 30° rotation in the basal (0001) plane. The film is found to contain a high density of stacking faults with average spacing 15 nm terminated by partial dislocations. The density of partial dislocations was estimated from plan-view TEM image to be 7×109 cm−2. The cross-section image of GaN film shows the density of stacking faults is highest in the vicinity of the interface and decreases markedly near the top of the layer. Inverted domain boundaries, which are almost perpendicular to the film surface, are also visible. The concentration of threading dislocation is relatively low (∼;2×108 cm−2), compared to misfit dislocations. The average distance between misfit dislocations was found to be 22 Å. Contrast modulations due to the strain near misfit dislocations are seen in high-resolution cross-sectional TCM micrograph of GaN/α-Al2O3 interface. This interface is sharp and does not contain any transitional layer. The interfacial region has a high density of Shockley and Frank partial dislocations. Mechanism of accommodation of tensile, sequence and tilt disorder through partial dislocation generation is discussed. In order to achieve low concentration of threading dislocations we need to establish favorable conditions for some stacking disorder in thin layers above the film-substrate interface region.

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