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J.e. Ayers - One of the best experts on this subject based on the ideXlab platform.
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progression of strain relaxation in linearly graded gaas1 ypy gaas 001 epitaxial layers approximated by a finite number of sublayers
International Journal of High Speed Electronics and Systems, 2017Co-Authors: Tedi Kujofsa, J.e. AyersAbstract:We have investigated the residual in-plane strain and width of the surface Misfit Dislocation free zone in linearly-graded GaAs1-yPy metamorphic buffer layers as approximated by a finite number of ...
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equilibrium lattice relaxation and Misfit Dislocations in step graded in x ga 1 x as gaas 001 and in x al 1 x as gaas 001 metamorphic buffer layers
Journal of Electronic Materials, 2016Co-Authors: Tedi Kujofsa, J.e. AyersAbstract:The inclusion of metamorphic buffer layers (MBLs) in the design of lattice-mismatched semiconductor heterostructures is important in enhancing reliability and performance of optoelectronic and electronic devices through proper control of threading Dislocations; threading Dislocation can be reduced by allowing the distribution of the Misfit Dislocations throughout the MBL, rather than concentrating them at the interface where substrate defects and tangling can pin Dislocations or otherwise reduce their mobility. Compositionally graded layers have been particularly used for this purpose and in this work we considered heterostructures involving a step-graded InxGa1−xAs or InxAl1−xAs epitaxial layer on a GaAs (001) substrate. For each structure type, we present minimum energy calculations including (i) the surface and (ii) average in-plane strain and (iii) the Misfit Dislocation density profile with various grading coefficients (thickness and indium composition variation). In both types of structures, the average in-plane strain and Misfit Dislocation density profile scale with the average grading coefficient, but InxAl1−xAs structures with a greater average elastic stiffness constants exhibit slightly higher average compressive in-plane strain (absolute valued) which is associated with higher Misfit Dislocation densities. However, the rate of change in the normalized relaxation percentage per unit thickness of each step with respect to the lattice mismatch of the step is lower in the InxAl1−xAs material system. The difference of the in-plane strain is small (<3%), however, so that these material systems are virtually interchangeable in terms of their mechanical behavior (<5.1% change in elastic constants).
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lattice relaxation and Misfit Dislocations in nonlinearly graded inxga1 xas gaas 001 and gaas1 ypy gaas 001 metamorphic buffer layers
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2014Co-Authors: Tedi Kujofsa, J.e. AyersAbstract:Recent results have shown that nonlinearly graded buffer layers may be beneficial for the reduction of threading Dislocation densities in metamorphic semiconductor devices. In this work, the authors have studied the equilibrium strain relaxation and Misfit Dislocation densities in nonlinearly graded heterostructures with logarithmic grading, and compare the cases of InxGa1−xAs/GaAs and GaAs1−yPy/GaAs buffer layers. The authors show that differences in the elastic stiffness constants give rise to significantly different behavior in these two commonly used buffer layer systems. Moreover, the width of the dislocated region, the average Misfit Dislocation density, and surface in-plane strain may be related to the nonlinearity coefficient of the grading profile.
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Misfit Dislocation density and strain relaxation in graded semiconductor heterostructures with arbitrary composition profiles
Journal of Applied Physics, 2009Co-Authors: B Bertoli, J.e. Ayers, E Suarez, F C JainAbstract:We present a computational approach for the determination of the equilibrium Misfit Dislocation density and strain in a semiconductor heterostructure with an arbitrary compositional profile. We demonstrate that there is good agreement between our computed results and known analytical solutions for heterostructures containing a single linearly graded layer or a single uniform composition layer. We have calculated the Dislocation density and strain profiles in Si1−xGex/Si(001), InxGa1−xAs/GaAs(001), and ZnSySe1−y/GaAs(001) heterostructures, each containing a uniform composition layer (uniform layer) on a linearly graded buffer layer (graded layer). The density of Misfit Dislocations in the graded layer is inversely proportional to its grading coefficient and is unchanged by the presence of the uniform layer, but the dislocated thickness increases with the uniform layer thickness. If the uniform layer is sufficiently thick, Misfit Dislocations will exist throughout the graded layer, but additional Misfit dis...
A. E. Romanov - One of the best experts on this subject based on the ideXlab platform.
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Misfit stresses and their relaxation by Misfit Dislocation loops in core shell nanoparticles with truncated spherical cores
European Journal of Mechanics A-solids, 2020Co-Authors: Mikhail Yu Gutkin, A L Kolesnikova, Dmitry S Mikheev, A. E. RomanovAbstract:Abstract For the first time, we suggest a theoretical model, which describes the Misfit stress relaxation in spherical core-shell nanoparticles with axisymmetric truncated spherical cores through the formation of circular prismatic loops of Misfit Dislocations at the core-shell interface. The special case of a semispherical core with base in the equatorial plane of the nanoparticle is considered and analyzed in detail. It is shown that the formation of Misfit Dislocation is energetically favorable when the Misfit strain reaches its critical value, which depends on the system parameters. When forming, the Misfit Dislocation occupies in most cases its optimal position at the distance about of 1/4 of the core radius from the core base. Nanoparticles with cores of radius about of 3/4 of the shell radius are the less stable to generation of Misfit Dislocation loops.
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Misfit Dislocation loops in hollow core shell nanoparticles
Scripta Materialia, 2014Co-Authors: Yu M Gutkin, A. E. Romanov, A L Kolesnikova, S A Krasnitckii, A G ShalkovskiiAbstract:A theoretical model is suggested to determine the critical conditions for generation of circular prismatic Misfit Dislocation loops in hollow core–shell nanoparticles. Based on a strict solution of the linear elasticity boundary-value problem for a circular prismatic Dislocation loop in a free-surface shell, we examine the loop formation energy in the nanoparticle and show a potential opportunity to fabricate hollow, coherently bonded, i.e. Dislocation-free, core–shell nanoparticles by using thin-wall shells with inner-to-outer radii ratio >0.8 as supporting cores.
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Misfit Dislocation loops in composite core shell nanoparticles
Physics of the Solid State, 2014Co-Authors: A. E. Romanov, A L Kolesnikova, Yu M Gutkin, S A KrasnitskyAbstract:The critical conditions have been calculated for the generation of circular prismatic loops of Misfit Dislocations at the interfaces in spherically symmetric composite core-shell nanoparticles. It has been shown that the formation of these loops becomes energetically favorable if the Misfit parameter exceeds a critical value, which is determined by the geometry of the system. The most preferred position of the Dislocation loop is in the equatorial plane of the nanoparticle. For a given radius of the nanoparticle, there is a minimum value of the critical Misfit parameter below which the generation of a Misfit Dislocation is energetically unfavorable for any ratio of the core and shell radii. For a Misfit parameter exceeding the minimum critical value, there are two critical values of the reduced radius of the particle core in the interval between which the generation of a Dislocation loop is energetically favorable. This interval increases with increasing Misfit parameter for a fixed particle size and decreases with decreasing particle size for a fixed Misfit parameter.
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stress relaxation and critical thickness for Misfit Dislocation formation in 101 0 and 3031 ingan gan heteroepitaxy
Applied Physics Letters, 2012Co-Authors: Po Shan Hsu, Shuji Nakamura, Steven P Denbaars, A. E. Romanov, Erin C Young, Matthew T Hardy, James S SpeckAbstract:Cathodoluminescence imaging was used to study the onset of plastic relaxation and critical thickness for Misfit Dislocation (MD) formation by basal plane (BP) or nonbasal plane (NBP) slip in In0.09Ga0.91N/GaN heterostructures grown on nonpolar (101¯0) and semipolar (3031¯) substrates. Layers grown on both orientations were shown to stress relax initially via generation of NBP MDs as a result of prismatic slip on inclined m-planes. Analysis of the resolved shear stress on the two slip planes (i.e., basal and an inclined m-plane) reveals a crossover at which the resolved shear stress on the m-planes becomes larger than that on the BP.
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Misfit Dislocation formation via pre existing threading Dislocation glide in 112 2 semipolar heteroepitaxy
Applied Physics Letters, 2011Co-Authors: Po Shan Hsu, Shuji Nakamura, Steven P Denbaars, A. E. Romanov, Erin C Young, Kenji Fujito, James S SpeckAbstract:Cathodoluminescence (CL) was used to study the onset of mechanical stress relaxation in low indium composition semipolar (112¯2) InxGa1−xN lattice-mismatched layers grown on bulk GaN substrates. Monochromatic CL of short interfacial Misfit Dislocation (MD) segments showed a single threading Dislocation (TD) associated with each MD segment—demonstrating that the initial stage of MD formation in semipolar III-nitride heterostructures proceeded by the bending and glide of pre-existing TDs on the (0001) slip plane. The state of coherency as determined by panchromatic CL is also compared to that determined by x-ray diffraction analysis based on crystallographic epilayer tilt and Matthew-Blakeslee’s critical thickness calculations.
Minsheng Huang - One of the best experts on this subject based on the ideXlab platform.
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quantitative study on interactions between interfacial Misfit Dislocation networks and matrix Dislocations in ni based single crystal superalloys
Acta Mechanica Solida Sinica, 2017Co-Authors: Jun Xiong, Yaxin Zhu, Minsheng HuangAbstract:Abstract The interactions between the moving Dislocation within matrix channel and the interfacial Misfit Dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic modeling, with special focus on the factors influencing the critical bowing stress of moving Dislocations in the matrix channel. The results show that the moving matrix Dislocation type and its position with respect to the interfacial Misfit Dislocation segments have considerable influences on the interactions. If the moving matrix Dislocation is pure screw, it reacts with the interfacial Misfit Dislocation segments toward Dislocation linear energy reduction, which decreases the critical bowing stress of screw Dislocation due to Dislocation linear energy release during the Dislocation reactions. If the moving matrix Dislocation is of 60 ○ -mixed type, it is obstructed by the interaction between the mixed matrix Dislocations and the Misfit interfacial Dislocation segments. As a result, the critical bowing stress increases significantly because extra interactive energy needs to be overcome. These two different effects on the critical bowing stress become increasingly significant when the moving matrix Dislocation is very close to the interfacial Misfit Dislocation segments. In addition, the matrix channel width also has a significant influence on the critical bowing stress, i.e. the narrower the matrix channel is, the higher the critical bowing stress is. The classical Orowan formula is modified to predict these effects on the critical bowing stress of moving matrix Dislocation, which is in good agreement with the computational results.
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Atomistic modeling of the interaction between matrix Dislocation and interfacial Misfit Dislocation networks in Ni-based single crystal superalloy
Computational Materials Science, 2013Co-Authors: Zhenhuan Li, Minsheng HuangAbstract:Abstract To reveal the intrinsic strengthening mechanism in Ni-based single crystal superalloy, the interaction between matrix Dislocations and interfacial Misfit Dislocation networks was modeled in this contribution via molecular dynamics (MD) method. Our results show that the role of interfacial Dislocation networks is very complex. On the one hand, the interfacial Dislocation networks can act as Dislocation sinks to absorb/accommodate the matrix Dislocations. During the accommodation process of matrix Dislocation by the networks, both the interfacial Lomer–Cottrell locks and a[1 0 0] Dislocation junctions are formed, which stabilize and strengthen the interfacial Dislocation networks. On the other hand, the interfacial Dislocation networks can provide Dislocation pins to prevent the matrix Dislocations from cutting into the γ′ precipitate. These matrix Dislocation segments pinned at the phase interface can serve as Frank–Read sources with their length being about half of the Dislocation network spacing, providing an explanation for the effect of Dislocation network spacing on the creep strength of the Ni-based single crystal superalloy.
R Hull - One of the best experts on this subject based on the ideXlab platform.
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effect of the surface upon Misfit Dislocation velocities during the growth and annealing of sige si 001 heterostructures
Journal of Applied Physics, 1998Co-Authors: Eric A Stach, R Hull, R M Tromp, M C Reuter, M Copel, F K Legoues, J C BeanAbstract:We have measured the velocity of Misfit Dislocation threading segments in real time during ultrahigh vacuum (UHV) chemical vapor deposition heteroepitaxial growth of thin SiGe epilayers on Si (001) using ultrahigh vacuum transmission electron microscopy. We observe no measurable difference in Dislocation velocities during growth and during post-growth annealing of samples with an atomically clean surface, in contrast to previous observations in the InGaAs/GaAs (001) system. However, Dislocations are seen to move approximately three times slower during growth and post-growth UHV annealing than during annealing of samples which have a native oxide present on the surface. We have used post-growth depositions of arsenic and oxygen to investigate the effect of surface condition on Dislocation velocities, and discuss possible causes for the increase in Dislocation velocities in the presence of a native oxide. These systematic studies suggest a hitherto unappreciated interaction between moving Dislocations and t...
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equilibrium and metastable strained layer semiconductor heterostructures
Current Opinion in Solid State & Materials Science, 1996Co-Authors: R Hull, Eric A StachAbstract:Abstract Recent progress has been made in the understanding of strain accommodation and relief in lattice-mismatched semiconductor heterostructures. Specific recent advances include the following: improved understanding and modeling of competing strain relaxation mechanisms; quantification of Misfit Dislocation nucleation processes; improved modeling of critical epilayer thickness for Misfit Dislocation introduction; improved understanding of Misfit Dislocation nucleation mechanisms; new experimental techniques for in-situ observation of strain relaxation; new techniques for reduction of strain-relieving Dislocations; and new calculations of Dislocation electronic structure.
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observations of new Misfit Dislocation configurations and slip systems at ultrahigh stresses in the al gaas inxga1 xas gaas 100 system
Applied Physics Letters, 1992Co-Authors: J M Bonar, R Hull, J Walker, R J MalikAbstract:We have observed new Misfit Dislocation configurations and slip systems in (Al)GaAs/InxGa1−xAs/GaAs(100) heterostructures for x≥0.4. Dislocations are observed running along 〈001〉 directions in the interface, which are inconsistent with conventional glide of Misfit Dislocations on {111} planes in the zincblende lattice. Diffraction contrast analysis in a transmission electron microscope (TEM) shows that these Dislocations are of the edge type with b=a/2〈011〉, inclined at 45° to the interface. In situ TEM heating experiments reveal Dislocation propagation velocities ∼tens of μm s−1 at 600 °C, suggesting that they are moving by glide, rather than climb. The only slip planes consistent with these observations are {101} planes inclined to the interface. This represents a new relaxation mechanism in highly strained semiconductor heterostructures.
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dependence of Misfit Dislocation velocities upon growth technique and oxygen content in strained gexsi1 x si 100 heterostructures
Applied Physics Letters, 1991Co-Authors: R Hull, J C Bean, D B Noble, J L Hoyt, J F GibbonsAbstract:Misfit Dislocation velocities in strained GexSi1−x/Si(100) heterostructures are compared for layers grown by molecular beam epitaxy and limited reaction processing. We demonstrate that velocities are substantially lower in structures with oxygen concentrations ∼1020 cm−3 compared to layers with oxygen concentrations ∼1018 cm−3. For layers with the lower oxygen concentration, the sample growth technique does not appear to be a significant factor affecting Misfit Dislocation velocity.
Edward Yi Chang - One of the best experts on this subject based on the ideXlab platform.
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Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial Misfit Dislocation GaSb film by metalorganic chemical vapor deposition
Materials Research Express, 2017Co-Authors: Hoang Huynh, Huy Binh, Tuan Anh Nguyen, Quang Ho Luc, Edward Yi ChangAbstract:High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading Dislocation density of around 7.1 × 106 cm−2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial Misfit Dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.
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impact of interfacial Misfit Dislocation growth mode on highly lattice mismatched inxga1 xsb epilayer grown on gaas substrate by metalorganic chemical vapor deposition
Applied Physics Letters, 2016Co-Authors: Sa Hoang Huynh, Minh Thien Huu Ha, Huy Binh Do, Hung Wei Yu, Edward Yi ChangAbstract:Highly lattice-mismatch (over 8%) ternary InxGa1-xSb alloy directly grown on GaAs substrates was demonstrated by metalorganic chemical vapor deposition (MOCVD). The influence of growth parameters, such as growth temperature, indium vapor composition, and V/III ratio, on the film properties was investigated, and it was found that the growth temperature has the strongest effect on the surface morphology and the crystal quality of the InxGa1-xSb epilayer. An optimized growth temperature of ∼590 °C and a V/III ratio of 2.5 were used for the growth of the InxGa1-xSb epilayer on GaAs that displays a lower surface roughness. High-resolution transmission electron microscopy micrographs exhibit that InxGa1-xSb epilayer growth on GaAs was governed by the interfacial Misfit Dislocation growth mode. Furthermore, the variation of the intermixing layer thickness at the InxGa1-xSb/GaAs heterointerface was observed. These results provide an information of growing highly lattice-mismatched epitaxial material systems by MO...
