CBED Investigations of Mesoscopic Semiconductor Structures

1999 ◽  
Vol 5 (S2) ◽  
pp. 208-209
Author(s):  
H. Lakner ◽  
F. Schulze-Kraasch ◽  
C. Mendorf ◽  
G. Brockt
Keyword(s):  
High Speed ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Local Strain ◽  
Tetragonal Distortion ◽  
Strained Layers ◽  
Spatially Resolved ◽  
Relaxation Effects ◽  
Convergent Beam ◽  
Induced Defects

Ternary and quaternary heterostructures from III-V-semiconductors get more and more importance in the fabrication of high-speed/high frequency devices in telecommunication systems. One of the key parameters for the performance of such devices is the crystalline quality and especially the amount of tetragonal distortion in strained layers on a nanometer scale. Strain can cause problems for the growth of such layers like relaxation induced defects, especially for the case of a high value of lattice mismatch. However, strain and the associated influence on the band structure can be used consciously for the design of tailor-made heterostructures (band gap engineering). Therefore, the spatially resolved investigation of local crystal properties (tetragonal distortion or strain and strain relaxation) is a key tool for the characterization of strained layers.Convergent beam electron diffraction (CBED) patterns and convergent beam imaging (CBIM) can be used to evaluate informations on the local crystalline structure. E.g. the position of the High Order Laue Zone (HOLZ) lines in the CBED patterns is sensitive to the local strain and therefore can be used to determine strain and relaxation effects in heterostructures quantitatively. But in practice the applicability of CBED is often limited by a lack of ultimate spatial resolution and/or of sensitivity.

The Roles of Stress, Geometry and Orientation on Misfit Dislocations Kinetics and Energetics in Epitaxial Strained Layers.

1991 ◽  
Vol 239 ◽  
Author(s):  
R. Hull ◽  
J. C. Bean ◽  
F. Ross ◽  
D. Bahnck ◽  
L. J. Pencolas
Keyword(s):  
Misfit Dislocation ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Misfit Dislocations ◽  
Slip Systems ◽  
Strained Layers ◽  
Burgers Vector ◽  
Partial Dislocations ◽  
Strain Stress ◽  
Kinetics Of

ABSTRACTThe geometries, microstructures, energetics and kinetics of misfit dislocations as functions of surface orientation and the magnitude of strain/stress are investigated experimentally and theoretically. Examples are drawn from (100), (110) and (111) surfaces and from the GexSi1–x/Si and InxGa1–x/GaAs systems. It is shown that the misfit dislocation geometries and microstructures at lattice mismatch stresses < - 1GPa may in general be predicted by operation of the minimum magnitude Burgers vector slipping on the widest spaced planes. At stresses of the order several GPa, however, new dislocation systems may become operative with either modified Burgers vectors or slip systems. Dissociation of totál misfit dislocations into partial dislocations is found to play a crucial role in strain relaxation, on surfaces other than (100) under compressive stress.

Elastic Strain Relaxation in Si1-xGex Layers Epitaxially Grown on Si Substrates

1998 ◽  
Vol 05 (01) ◽  
pp. 133-138 ◽  
Author(s):  
I. Berbezier ◽  
B. Gallas ◽  
J. Derrien
Keyword(s):  
Elastic Constants ◽  
Elastic Strain ◽  
Lattice Mismatch ◽  
Strain Relaxation ◽  
Experimental Conditions ◽  
Si Substrates ◽  
Critical Lattice ◽  
Convergent Beam ◽  
Plane View

We have investigated the elastic strain relaxation in Si 1-x Ge x layers grown by the molecular beam epitaxy (MBE) technique and in situ controlled with RHEED. Up to ≈0.8% critical lattice mismatch (about 20% Ge) uniform strained and flat layers were grown both on (111) and on (001) Si substrates. Calculations of the elastic constants evidenced a tetragonal distortion about 50% higher on (001) than on (111) in the same experimental conditions. At higher misfits (and/or thicknesses) a growth instability was evidenced only on (001) Si substrates. Si 1-x Ge x layers there displayed a surface layer undulation. On the contrary, Si 1-x Ge x layers grown on (111) Si substrates remained smooth throughout the growth up to the plastic relaxation of the layers. To determine stress fields in the Si 1-x Ge x layers, a high spatial resolution convergent beam electron diffraction (CBED) experiment was performed with a field effect analytical microscope. The CBED technique was applied to two typical cases: totally strained layer and undulated dislocation-free layer. In the latter case, CBED patterns recorded on nanometer scale areas of an undulation crest (cross-section sample) showed a gradual elastic relaxation mainly directed along the growth axis (z). Moreover a triclinic distortion of the unit cell was pointed out. These results were confirmed on a plane view sample. In conclusion, our results show that the driving force for the undulation is not the in-plane elastic relaxation since CBED experiments proved an important elastic relaxation of the (001) Si 1-x Ge x layers along the z axis. This was in agreement with the calculations of the elastic constants. We think that this could be at the origin of the undulation.

TEM study of phosphorus-implanted pseudomorphic Si0.88Ge0.12 on Si(100)

1995 ◽  
Vol 53 ◽  
pp. 468-469
Author(s):  
N. David Theodore ◽  
Donald Y.C Lie ◽  
J. H. Song ◽  
Peter Crozier
Keyword(s):  
Integrated Circuits ◽  
Heterojunction Bipolar Transistors ◽  
Integrated Circuit ◽  
High Speed ◽  
Room Temperature ◽  
Strain Relaxation ◽  
Bipolar Transistors ◽  
Sige Hbt ◽  
Integrated Circuit Manufacturing ◽  
Microstructural Behavior

SiGe is being extensively investigated for use in heterojunction bipolar-transistors (HBT) and high-speed integrated circuits. The material offers adjustable bandgaps, improved carrier mobilities over Si homostructures, and compatibility with Si-based integrated-circuit manufacturing. SiGe HBT performance can be improved by increasing the base-doping or by widening the base link-region by ion implantation. A problem that arises however is that implantation can enhance strain-relaxation of SiGe/Si.Furthermore, once misfit or threading dislocations result, the defects can give rise to recombination-generation in depletion regions of semiconductor devices. It is of relevance therefore to study the damage and anneal behavior of implanted SiGe layers. The present study investigates the microstructural behavior of phosphorus implanted pseudomorphic metastable Si0.88Ge0.12 films on silicon, exposed to various anneals.Metastable pseudomorphic Si0.88Ge0.12 films were grown ~265 nm thick on a silicon wafer by molecular-beam epitaxy. Pieces of this wafer were then implanted at room temperature with 100 keV phosphorus ions to a dose of 1.5×1015 cm-2.

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

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.

On velocity gradient dynamics and turbulent structure

2015 ◽  
Vol 780 ◽  
pp. 60-98 ◽  
Author(s):  
J. M. Lawson ◽  
J. R. Dawson
Keyword(s):  
Velocity Gradient ◽  
Local Strain ◽  
Turbulent Structure ◽  
Stochastic Estimation ◽  
Spatially Resolved ◽  
Gradient Dynamics ◽  
Layer Structures ◽  
Non Local ◽  
Conditional Averaging

The statistics of the velocity gradient tensor $\unicode[STIX]{x1D63C}=\boldsymbol{{\rm\nabla}}\boldsymbol{u}$, which embody the fine scales of turbulence, are influenced by turbulent ‘structure’. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by $\unicode[STIX]{x1D63C}$. Structures are studied through the footprints they leave in conditional averages of the $Q=-\text{Tr}(\unicode[STIX]{x1D63C}^{2})/2$ field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the $Q$ field conditioned upon $\unicode[STIX]{x1D63C}$ and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191–225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the $Q$ field, which is used to validate the stochastic estimation and provide insights towards the model’s refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other.

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