Deformation Behavior of Strained Layer Heterostructures

1995 ◽  
Vol 399 ◽  
Author(s):  
A. Fischer ◽  
H. KüHNE
Keyword(s):  
Strain Relaxation ◽  
Equilibrium Theory ◽  
Surface Relaxation ◽  
Image Method ◽  
Surface Boundary ◽  
Misfit Dislocations ◽  
Strained Layer ◽  
Elastic Interactions ◽  
Relaxation Effects ◽  
Surface Boundary Conditions

ABSTRACTWe present a new Volterra dislocation approach in equilibrium theory for strain relaxation in heteroepi-taxial semiconductor structures, one which includes surface relaxation effects and elastic interactions between straight misfit dislocations. The free-surface boundary conditions are satisfied by placing an image dislocation outside the crystal in such a manner that its stress field cancels that of the real interface misfit dislocation at the surface. The effect of the Airy stress function that removes the fictitious shear and normal stresses at the surface are discussed. This image method provides an equilibrium theory which correctly predicts critical strained layer thicknesses and completely describes the elastic and plastic strain relief as well as the phenomenon of work hardening in lattice mismatched epilayers.

Strain Relaxation Mechanisms in Lattice Mismatched Epitaxy

1990 ◽  
Vol 198 ◽  
Author(s):  
R. Hull ◽  
J.C. Bean ◽  
J.M. Bonar ◽  
L. Peticolas
Keyword(s):  
Strain Relaxation ◽  
Epitaxial Layers ◽  
Misfit Dislocations ◽  
Strained Layer ◽  
Device Structures ◽  
Lattice Mismatched Epitaxy

ABSTRACTThe relaxation of strained epitaxial layers by the introduction of misfit dislocations is reviewed. Current theoretical and experimental understanding of the nucleation, propagation and interaction of misfit dislocations are summarized. The ramifications for applicability of strained layer epitaxy to practical device structures are discussed.

STRAIN RELAXATION IN SEMICONDUCTOR HETEROSTRUCTURES

1995 ◽  
Vol 09 (11n12) ◽  
pp. 655-664
Author(s):  
A. FISCHER ◽  
H. KÜHNE
Keyword(s):  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Elastic Interaction ◽  
Equilibrium Theory ◽  
Semiconductor Heterostructures ◽  
Misfit Dislocations ◽  
Strain Relief ◽  
New Approach ◽  
Semiconductor Structures ◽  
Theoretical Predictions

A brief review is presented for our new approach in equilibrium theory for strain relaxation in metastable heteroepitaxial semiconductor structures, one which includes the elastic interaction between straight misfit dislocations and the lattice mismatch accommodation by tetragonal distortion of the cubic lattice cells. This approach provides an equilibrium theory which correctly predicts critical strained layer thicknesses and completely describes the strain relief via plastic flow and the phenomenon of work hardening in lattice mismatched epilayers. Experimentally observed values of critical layer thickness and strain relief are discussed and compared with our theoretical predictions.

A comparative study on the stress image and adaptive parameter-modified methods for implementing free surface boundary conditions in elastic wave numerical modeling

Geophysics ◽  
2021 ◽  
Vol 86 (6) ◽  
pp. T451-T467
Author(s):  
Jing-Bo Chen ◽  
Jian Cao ◽  
Zheng Li
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Elastic Wave ◽  
Image Method ◽  
Shear Stresses ◽  
Surface Boundary ◽  
Modified Method ◽  
Adaptive Parameter ◽  
Surface Boundary Conditions ◽  
Physical Foundation

The stress image method is a simple and effective approach for implementing the free surface boundary conditions in elastic wave numerical modeling. This method assumes that the normal and shear stresses perpendicular to the free surface are antisymmetric with respect to the free surface. In this way, the values of the normal and shear stresses above the free surface can be updated. However, the stress image method is based on an intuitive viewpoint and lacks a physical foundation. The adaptive parameter-modified method is a recently proposed approach for implementing the free surface boundary conditions. Through adaptive modifications of the density and elastic parameters at the free surface, the implementation of the free surface boundary conditions is achieved. Based on the adaptive parameter-modified method, a new interpretation of the stress image method is used. We determine that the stress image method is equivalent to the adaptive parameter-modified method in terms of the staggered-grid finite-difference scheme for the elastic wave equation in displacement form. This result provides a physical foundation and explanation of the stress image method. Therefore, we can further develop the stress image method from a physical viewpoint. Numerical examples are also developed to perform the theoretical analysis.

“Barrierless” Misfit Dislocation Nucleation in SiGe/Si Strained Layer Epitaxy

1992 ◽  
Vol 263 ◽  
Author(s):  
D.D. Perovic ◽  
D.C. Houghton
Keyword(s):  
Activation Energy ◽  
Misfit Dislocation ◽  
Strain Relaxation ◽  
Dislocation Nucleation ◽  
Theoretical Treatment ◽  
Misfit Dislocations ◽  
Plan View ◽  
Strained Layer ◽  
Wide Range ◽  
Peierls Barrier

ABSTRACTThe study of the critical thickness/strain phenomenon inherent in metastable, layered heterostructures has led to the development of several models which describe elastic strain relaxation. Hitherto, the nucleation of misfit dislocations required for coherency breakdown is the least well understood aspect of strain relaxation, due to the paucity of experimental data. Moreover, existing theoretical calculations predict relatively large activation energy barriers (>10 eV) for misfit dislocation nucleation in relatively low misfit (<2%) systems. In this work it will be shown that the nucleation of misfit dislocations can occur spontaneously demonstrating a vanishingly small activation energy barrier. Specifically, experimental studies of a wide range of GexSi1−x/Si (x< 0.5) hetero-structures, grown by MBE and CVD techniques, have provided quantitative data from bulk specimens on the observed misfit dislocation nucleation rate and activation energy using large-area diagnostic techniques (eg. chemical etching/Nomarski microscopy). In parallel, the strained layer microstructure was studied in detail using crosssectional and plan-view electron microscopy in order to identify a new dislocation nucleation mechanism, the ‘double half-loop’ source. From the combined macroscopic and microscopic analyses, a theoretical treatment has been developed based on nucleation stress and energy criteria which predicts a “barrierless” nucleation process exists even at low misfits (< 1%). Accordingly, the observed misfit dislocation nucleation event has been found both experimentally and theoretically to be rate-controlled solely by Peierls barrier dependent, glide-activated processes with activation energies of ∼2 eV.

scholarly journals Study of Strain Relaxation in InAs/GaAs Strained-layer Superlattices by Raman Spectroscopy and Electron Microscopy

2000 ◽  
Vol 53 (5) ◽  
pp. 697
Author(s):  
A. K. Gutakovsky ◽  
S. M. Pintus ◽  
A. I . Toropov ◽  
N. T. Moshegov ◽  
V. A. Haisler ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Raman Spectroscopy ◽  
Elastic Strain ◽  
Strain Relaxation ◽  
Misfit Dislocations ◽  
Strained Layer ◽  
Transmission Electron ◽  
Dimensional Network ◽  
Order Of Magnitude ◽  
Strained Layer Superlattices

InAs/GaAs strained-layer superlattices (SLS) grown on a GaAs(100) substrate were studied by both Raman spectroscopy (RS) and transmission electron microscopy (TEM). It was shown that the interfaces inside the superlattice are coherent, but the superlattice–substrate interface contain an orthogonal two-dimensional network of 60° misfit dislocations. Using these experimental data values of elastic strain in individual layers and the average values of the residual elastic strain in SLS were determined. The latter are approximately one order of magnitude higher than theoretically predicted data, which suggests that the relaxation of elastic strains was not fully complete. Subsequent annealing of these structures led to the generation of more misfit dislocations, consistent with further relaxation of elastic strain.

In situ TEM measurements of the electrical properties of interface dislocations

1992 ◽  
Vol 50 (2) ◽  
pp. 1338-1339
Author(s):  
F. M. Ross ◽  
R. Hull ◽  
D. Bahnck ◽  
J. C. Bean ◽  
L. J. Peticolas ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Electronic Device ◽  
In Situ Tem ◽  
Device Performance ◽  
Misfit Dislocations ◽  
Electrical Characteristics ◽  
Strained Layer ◽  
Transmission Electron ◽  
Interfacial Dislocations

We describe an investigation of the electrical properties of interfacial dislocations in strained layer heterostructures. We have been measuring both the structural and electrical characteristics of strained layer p-n junction diodes simultaneously in a transmission electron microscope, enabling us to correlate changes in the electrical characteristics of a device with the formation of dislocations.The presence of dislocations within an electronic device is known to degrade the device performance. This degradation is of increasing significance in the design and processing of novel strained layer devices which may require layer thicknesses above the critical thickness (hc), where it is energetically favourable for the layers to relax by the formation of misfit dislocations at the strained interfaces. In order to quantify how device performance is affected when relaxation occurs we have therefore been investigating the electrical properties of dislocations at the p-n junction in Si/GeSi diodes.

The limits of strain and lattice parameter measurements by CBED

1989 ◽  
Vol 47 ◽  
pp. 518-519
Author(s):  
Hamish L. Fraser
Keyword(s):  
Electron Beam ◽  
Mirror Symmetry ◽  
Local Symmetry ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Surface Relaxation ◽  
Strained Layer ◽  
Axis Parallel ◽  
Local Lattice ◽  
Strained Layer Superlattice

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.

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