Raman and X-ray diffraction study of relaxation in Si–Si1–xGex strained-layer superlattices

1989 ◽  
Vol 67 (4) ◽  
pp. 351-357 ◽  
Author(s):  
D. J. Lockwood ◽  
J.-M. Baribeau ◽  
P. Y. Timbrell
Keyword(s):  
Sharp Decrease ◽  
Growth Direction ◽  
Longitudinal Optical ◽  
Acoustic Mode ◽  
Progressive Relaxation ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
Raman Scattering Spectroscopy ◽  
X Ray

We report a study of the relaxation of Si–Si1–xGex strained single layers and superlattices by Raman scattering spectroscopy, double crystal X-ray diffraction, and transmission and scanning electron microscopy. Samples of various dimensions and compositions were produced by molecular beam epitaxy at a growth temperature of 500 ± 30 °C. The thermal stability of the various specimens was investigated by annealing experiments at temperatures between 600 and 900 °C. Considerable deterioration of the crystal quality and progressive relaxation were observed in some of the samples. Relaxation occurred through formation of misfit dislocations at the first Si–Si1–xGex interface and these caused threading dislocations to form within the epilayer. The degradation of the superlattice interfaces on annealing is correlated with a sharp decrease in the acoustic mode Raman intensities. Strain values perpendicular to the growth direction as a function of annealing temperature are obtained from a kinematical simulation of the X-ray rocking curves. These results are compared with the frequency shifts of the longitudinal optical phonons in the Raman spectra. The results obtained for the critical layer thicknesses versus x are consistent with the excess stress model of Tsao and co-workers.

Strain Shift Coefficients for Phonons in Si-Ge Heterostructures

1991 ◽  
Vol 239 ◽  
Author(s):  
J.-M. Baribeau ◽  
D. J. Lockwood
Keyword(s):  
Molecular Beam ◽  
Composition Dependence ◽  
Vibration Mode ◽  
Phonon Frequency ◽  
Longitudinal Optical ◽  
Stress Factor ◽  
Double Crystal ◽  
Raman Scattering Spectroscopy ◽  
X Ray ◽  
Shift Coefficient

ABSTRACTStrain shift coefficient measurements for longitudinal optical phonons in molecular beam epitaxy grown metastable pseudomorphic Si1−xGex layers on (100) Si (0 < x < 0.35) and Ge (0.80 < x < 1) are reported. Strain in partially relaxed annealed specimens was obtained by double-crystal x-ray diffractometry and the corresponding strain phonon shift was measured by Raman scattering spectroscopy. For epilayers grown on Si it was found that the epilayer Si-Si phonon frequency varies linearly with strain. The magnitude of the strain shift coefficient b however showed a small composition dependence varying from b ≈ -700 cm-1 at x = 0 to b ≈ -950 cm-1 at x = 0.35, corresponding to a stress factor τ = 0.40 + 0.57x: + 0.13x2 cm-1/kbar. For the Ge-Ge vibration mode in epilayers grown on Ge, b decreased from ∼-425 cm-1 at x = 1 to ∼-500 cm-1 at x = 0.8, corresponding to a stress factor τ ≈ 0.52 – 0.14x - 0.08x2 cm-1/kbar.

Structural properties of molecular beam epitaxy grown Ni/Pt superlattices

1997 ◽  
Vol 12 (1) ◽  
pp. 161-174 ◽  
Author(s):  
W. Staiger ◽  
A. Michel ◽  
V. Pierron-Bohnes ◽  
N. Hermann ◽  
M. C. Cadeville
Keyword(s):  
Molecular Beam ◽  
Growth Direction ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Plan View ◽  
X Ray ◽  
Transmission Electron ◽  
Superlattice Peak ◽  
Diffraction Peaks ◽  
Diffraction Patterns

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.

Double Crystal X-Ray Diffraction Measurement of a Triclinicly Distorted and Tilted AlxGa1-xAs Unit Cell Produced by Growth on Offcut GaAs Substrates

1989 ◽  
Vol 159 ◽  
Author(s):  
A. Leiberich ◽  
J. Levkoff
Keyword(s):  
Strain Relaxation ◽  
Growth Direction ◽  
Unit Cell ◽  
Diffraction Measurement ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
X Ray ◽  
Additional Cell ◽  
Additional Strain ◽  
Film Substrate

ABSTRACTCorrections are required for double crystal X-ray diffraction characterization of epitaxial AlxGa1-xAs layers grown on offcut GaAs (100) substrates. Double crystal X-ray diffraction measurements show that the cubic film unit cell defined by Vegard's law is triclinicly distorted and tilted with respect to the substrate unit cell. The distortion and tilt angles oppose each other defining a crystal geometry where the substrate and film <100= axes remain approximately coplanar with the surface normal. This film/substrate crystal geometry leads to formulation of a model describing heteroepitaxy on offcut (100) substrates. When film atoms are bonded to an offcut substrate, the already tetragonaly distorted film unit cell is subjected to additional cell distortions. The magnitude of this additional strain depends on where the film atoms are positioned on a substrate terrace. The first few layers of film atoms establish swain grades across individual substrate terraces. Constrained by the geometry of this interface region and driven by strain relaxation in the net growth direction, subsequent heteroepitaxy forms the measured film/substrate crystal geometry.

Index of Refraction Anisotropy in InGaAs/InP Heterostructures Measured by Ellipsometry

1989 ◽  
Vol 160 ◽  
Author(s):  
Brian R. Bennett ◽  
Jesús A. Del Alamo
Keyword(s):  
Optical Properties ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Index Of Refraction ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
X Ray ◽  
Asymmetric Pattern ◽  
Optical Effects

AbstractWe applied ellipsometry to characterize layers of InxGa1-xAs grown by molecular beam epitaxy on (001) InP. Samples with mismatched layers exhibit significant anisotropy in the index of refraction. We explain these observations by the presence of misfit dislocations which form in an asymmetric pattern. This results in asymmetric strain and, via piezo-optical effects, an anisotropy in the optical properties. This effect makes ellipsometry a more sensitive technique than double-crystal x-ray diffraction for detecting misfit dislocations in these heterostructures.

Thermal Strain Study of Almost Lattice-Matched Epitaxial InuGa1-uAs1-vP1-v Films on InP(100) Substrates

1989 ◽  
Vol 160 ◽  
Author(s):  
G. Bai ◽  
M-A. Nicolet ◽  
S.-J. Kim ◽  
R.G. Sobers ◽  
J.W. Lee ◽  
...  
Keyword(s):  
Room Temperature ◽  
Epitaxial Film ◽  
Lattice Mismatch ◽  
Thermal Strain ◽  
Growth Direction ◽  
Epitaxial Films ◽  
Double Crystal ◽  
X Ray ◽  
Lattice Matched ◽  
Coherent Interfaces

AbstractSingle layers of ~ 0.5µm thick InuGa1-uAs1-vPv (0.52 < u < 0.63 and 0.03 < v < 0.16) were grown epitaxially on InP(100) substrates by liquid phase epitaxy at ~ 630°C. The compositions of the films were chosen to yield a constant banndgap of ~ 0.8 eV (λ = 1.55 µm) at room temperature. The lattice mismatch at room temperature between the epitaxial film and the substrate varies from - 4 × 10-3 to + 4 × 10-3. The strain in the films was characterized in air by x-ray double crystal diffractometry with a controllable heating stage from 23°C to ~ 700°C. All the samples have an almost coherent interfaces from 23°C to about ~ 330°C with the lattice mismatch accomodated mainly by the tetragonal distortion of the epitaxial films. In this temperature range, the x-ray strain in the growth direction increases linearly with temperature at a rate of (2.0 ± 0.4) × 10-6/°C and the strain state of the films is reversible. Once the samples are heated above ~ 300°C, a significant irreversible deterioration of the epitaxial films sets in.

Double-Crystal x-Ray Diffraction Study on Ta/Al Multilayers

1992 ◽  
Vol 9 (11) ◽  
pp. 605-608
Author(s):  
Xiu Lisong ◽  
Yuan Xiangyang ◽  
Wu Ziqin ◽  
Jiang Shusheng ◽  
Hu An ◽  
...  
Keyword(s):  
Diffraction Study ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
X Ray

Study of various types of diamonds by measurements of double crystal x‐ray diffraction and positron annihilation

1995 ◽  
Vol 78 (3) ◽  
pp. 1510-1513 ◽  
Author(s):  
S. Fujii ◽  
Y. Nishibayashi ◽  
S. Shikata ◽  
A. Uedono ◽  
S. Tanigawa
Keyword(s):  
Positron Annihilation ◽  
X Ray Diffraction ◽  
Double Crystal ◽  
X Ray

Crystallinity of YBa2Cu3O7−x single crystals grown by the pulling method

1996 ◽  
Vol 11 (4) ◽  
pp. 804-812 ◽  
Author(s):  
Y. Namikawa ◽  
M. Egami ◽  
S. Koyama ◽  
Y. Shiohara ◽  
H. Kutami
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Growth Direction ◽  
Annealed Sample ◽  
Seed Crystal ◽  
X Ray Diffraction ◽  
Rocking Curve ◽  
X Ray ◽  
Crystal Seed ◽  
Better Than

Large YBa2Cu3O7−x (Y123) single crystals (larger than 13 mm cubed) have been grown along the c-axis reproducibly by the modified pulling method. The crystallinity of Y123 single crystal was investigated by x-ray diffraction and x-ray topography. Crystals grown from an MgO single crystal seed had some low angle subgrain boundaries which tilted 0.1–0.8° from each other. These grain boundaries originated from the seed crystal, and the subgrains were extended along the growth direction from the seed crystal. Y123 single crystals with no marked subgrains in the whole area were obtained by using Y123 single subgrain crystal seeds. FWHM of the x-ray rocking curve for the crystal so produced was about 0.14°, which was much better than the spectrum consisting of several separated peaks obtained from the previous crystals. Tc onset of the annealed sample was about 93.6 K, and the transition width was about 0.9 K. The low angle subgrain boundaries did not seem to be effective pinning centers for the magnetic flux.

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