In-Situ Measurements of Islanding and Strain Relaxation of Ge/Si(111)

1996 ◽  
Vol 441 ◽  
Author(s):  
P. W. Deelman ◽  
L. J. Schowalter ◽  
T. Thundat
Keyword(s):  
Initial Rate ◽  
Strain Relaxation ◽  
Misfit Strain ◽  
High Energy ◽  
Lattice Parameter ◽  
Dislocation Nucleation ◽  
Island Growth ◽  
Aspect Ratios ◽  
Surface Lattice ◽  
Increasing Temperature

AbstractWe have measured strain relaxation and islanding in Ge films grown by molecular beam epitaxy on Si(111) at substrate temperatures between 450°C and 700°C in real time with reflection high energy electron diffraction (RHEED). At 450°C, we observe an oscillation of the surface lattice parameter for the first three bilayers (BL), followed by a sharp 2D–3D growth mode transition, when transmission diffraction features appear in RHEED. The surface lattice parameter then begins to relax at an initial rate of about 0.5%/BL. The mechanisms of island growth and strain relaxation change with growth temperature. At 500°C the surface lattice parameter begins to relax after only 1BL; at 550°C relaxation begins immediately. However, 3D spots do not appear until after 3.5BL at either temperature. The initial rate of strain relaxation decreases with increasing temperature until, at 700°C (when 3D spots never appear), it is only 0.04%/BL. This behavior may be explained by a temperature-dependent roughness length scale, as well as by differences in dislocation nucleation at low and high temperatures. At low temperature, atomic force microscope images show the development of small (1000Å), faceted islands with aspect ratios (height/width) on the order of 0.07. The formation of well-defined facets is inhibited at higher temperatures. At 700°C, islands grow very large (lμm) from the outset, with aspect ratios less than 0.015. These islands cannot thicken much, because dislocations can glide in easily at their edges. The islands grow laterally quickly, and the strain in the “new” islands is not substantially less than that in the “old.” At 700°C, 28% of the Ge/Si misfit strain may be relieved by diffusion.

Temperature-Dependent Strain Relaxation and Islanding of Ge/Si(111)

1995 ◽  
Vol 417 ◽  
Author(s):  
P. W. Deelman ◽  
L. J. Schowalter ◽  
T. Thundat
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Rutherford Backscattering Spectrometry ◽  
Strain Relaxation ◽  
Areal Density ◽  
High Energy ◽  
Lattice Parameter ◽  
The Body ◽  
Small Islands ◽  
Island Growth

AbstractIn order to understand Ge island nucleation and evolution, we have studied strain relaxation and clustering of Ge grown on Si(111) by molecular beam epitaxy (MBE) with in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Our goal is to tailor the size and density of the nanocrystals by controlling thermodynamics and kinetics. At low temperature (∼ 450°C), we observe a sharp 2D–3D growth mode transition after 2.5ML ±0.1ML (we define a thickness of 1ML to be one-third the length of the body diagonal of the Ge conventional unit cell), when transmission diffraction features appear in RHEED and the surface lattice constant begins to relax. The mechanisms of island growth and strain relaxation change with growth temperature. At ∼ 700°C, transmission diffraction spots never appear in RHEED for Ge/Si(111) and strain relaxation occurs gradually. After 37ML of growth, the apparent in-plane lattice parameter increases only 1.5% over that of the Si substrate. This behavior is explained by the different manner in which islands initially nucleate and grow in the two temperature regimes. At low temperature, small islands nucleate and grow on a relatively rough wetting layer (which itself provides preferential sites for dislocation introduction). The areal density of the small islands is relatively high. At high temperature, a small number of islands grow very large from the outset. A general model indicates how, at low temperature. The relative difficulty of overcoming the barrier to dislocation formation actually results in an apparent larger degree of strain relief than at high temperature.

Temperature-Dependent Strain Relaxation and Islanding of Ge/Si(111)

1995 ◽  
Vol 399 ◽  
Author(s):  
P.W. Deelman ◽  
L.J. Schowalter ◽  
T. Thundat
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Rutherford Backscattering Spectrometry ◽  
Strain Relaxation ◽  
Areal Density ◽  
High Energy ◽  
Lattice Parameter ◽  
The Body ◽  
Small Islands ◽  
Island Growth

ABSTRACTIn order to understand Ge island nucleation and evolution, we have studied strain relaxation and clustering of Ge grown on Si(111) by molecular beam epitaxy (MBE) with in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Our goal is to tailor the size and density of the nanocrystals by controlling thermodynamics and kinetics. At low temperature (∼ 450°C), we observe a sharp 2D-3D growth mode transition after 2.5ML ±0.1ML (we define a thickness of 1ML to be one-third the length of the body diagonal of the Ge conventional unit cell), when transmission diffraction features appear in RHEED and the surface lattice constant begins to relax. The mechanisms of island growth and strain relaxation change with growth temperature. At ∼ 700°C, transmission diffraction spots never appear in RHEED for Ge/Si(111) and strain relaxation occurs gradually. After 37ML of growth, the apparent in-plane lattice parameter increases only 1.5% over that of the Si substrate. This behavior is explained by the different manner in which islands initially nucleate and grow in the two temperature regimes. At low temperature, small islands nucleate and grow on a relatively rough wetting layer (which itself provides preferential sites for dislocation introduction). The areal density of the small islands is relatively high. At high temperature, a small number of islands grow very large from the outset. A general model indicates how, at low temperature, the relative difficulty of overcoming the barrier to dislocation formation actually results in an apparent larger degree of strain relief than at high temperature.

Some Computer Simulations of Semiconductor Thin Film Growth and Strain Relaxation in a Unified Atomistic and Kinetic Model

1995 ◽  
Vol 408 ◽  
Author(s):  
A. Madhukar ◽  
W. Yu ◽  
R. Viswanathan ◽  
P. Chen
Keyword(s):  
Kinetic Model ◽  
Defect Formation ◽  
Kinetic Monte Carlo ◽  
Strain Relaxation ◽  
High Energy ◽  
Fixed Number ◽  
Dislocation Nucleation ◽  
Relative Significance ◽  
Stepped Surfaces ◽  
Kinetic Processes

AbstractAn overview is provided of an evolving atomistic and kinetic model of semiconductor growth that unifies the main features of strain relaxation in low and high lattice misfit heteroepitaxy. The model reveals a kinetic pathway for dislocation formation during growth with little or no energy cost at low misfits, thus providing a way out of the longstanding dilemma of too high dislocation nucleation energies predicted by classical theories of the equilibrium behaviour of a fixed number of particles at low misfits. The essential kinetic processes underlying the model are identified on the basis of comparison of the predictions of kinetic Monte-Carlo simulations of growth with real-time or in-situ data obtained in such experiments as reflection high-energy electron diffraction (RHEED) and scanning probe microscopy (SPM). Relative significance of these atomistic kinetic processes is shown to naturally lead to strain relaxation via defect initiation at low misfits while maintaining smooth surface morphology or at high misfits change to 3-dimensional morphology while initially maintaining coherence. The potential role of steps in providing sources for defect formation is examined through molecular dynamics simulations of Ge overlayers on Si (001) stepped surfaces.

Detection of Misfit Strain Relaxation in MBE Grown Si1-xGex Films by Dynamic Monitoring of Rheed Diffraction Features

1992 ◽  
Vol 263 ◽  
Author(s):  
J.W. Maes ◽  
O.F.Z. Schannen ◽  
J. Trommel ◽  
K. Werner ◽  
S. Radelaar ◽  
...  
Keyword(s):  
Detection Limit ◽  
Lattice Constant ◽  
Strain Relaxation ◽  
Ccd Camera ◽  
Misfit Strain ◽  
High Energy ◽  
Dynamic Monitoring ◽  
Rheed Pattern ◽  
High Energy Electron ◽  
Substrate Temperatures

ABSTRACTReflection high energy electron diffraction (RHEED) has been used to detect strain relaxation in SiGe during growth on <001>- oriented Si for various layer compositions and substrate temperatures. The RHEED-technique permits the dynamic monitoring of the in-plane lattice constant of the growing layer by measuring the distance between diffraction features. The actual RHEED pattern is recorded by a CCD camera and subsequently processed in real time by a computer. This way, the layer relaxation can be followed conveniently; a detection limit for a variation in the lattice constant of Δa/a=5.10−4 has been obtained.

scholarly journals A Study of Recrystallization and Phase Transitions in Intermetallic Titanium Aluminides by In Situ High-Energy X-Ray Diffraction

2007 ◽  
Vol 539-543 ◽  
pp. 1519-1524 ◽  
Author(s):  
Klaus Dieter Liss ◽  
A. Bartels ◽  
Helmut Clemens ◽  
S. Bystrzanowski ◽  
A. Stark ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Titanium Aluminides ◽  
Strain Relaxation ◽  
High Energy ◽  
Internal Stresses ◽  
X Ray Diffraction ◽  
X Ray ◽  
In Situ Heating ◽  
Increasing Temperature

High-energy synchrotron X-ray diffraction is a novel and powerful tool for bulk studies of materials. In this study, it is applied for the investigation of an intermetallic γ-TiAl based alloy. Not only the diffraction angles, but also the morphology of reflections on the Debye-Scherrer rings are evaluated in order to approach lattice parameters and grain sizes as well as crystallographic relationships. An in-situ heating cycle from room temperature to 1362 °C has been conducted starting from massively transformed γ-TiAl which exhibits high internal stresses. With increasing temperature the occurrence of strain relaxation, chemical and phase separation, domain orientations, phase transitions, recrystallization processes, and subsequent grain growth can be observed. The data obtained by high-energy synchrotron X-ray diffraction, extremely rich in information, are interpreted step by step.

Growth of Si on Ge(001)2×l by gas-source molecular beam epitaxy

1993 ◽  
Vol 51 ◽  
pp. 806-807
Author(s):  
H.Z. Xiao ◽  
R. Tsu ◽  
I.M. Robertson ◽  
H.K. Birnbaum ◽  
J.E. Greene
Keyword(s):  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Strain Relaxation ◽  
Misfit Strain ◽  
High Energy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Gas Source ◽  
High Quality Result ◽  
Strained Layer Superlattices

The growth of SiGe strained-layer superlattices (SLS) has been received considerable attention due to the electronic and optoelectronic properties of these layers. In addition, these structures offer tantalizing possibilities for "band gap engineering" through the use of strain and chemically ordered alloys. The remaining barriers to grow the SiGe SLS structures with high quality result from the generation of large densities of defects, such as dislocations, twins, stacking faults, etc., at the heterointerfaces arising from the misfit strain relaxation. Other problems associated with the growth of the SiGe SLS structures are segregation and low incorporation of the dopants and inter-diffusion of Si and Ge. In the present study, the inter-mixing of Si and Ge and the generation of the defects in Si epilayers grown on Ge(001)2×1 at 550 °C by gas-source molecular beam epitaxy (MBE) from Si2H6 were studied using transmission electron microscopy (TEM), in-situ reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM) and electron energy-loss spectroscopy (EELS).

Observations on the Mechanics of Strained Epitaxial Island Growth

1995 ◽  
Vol 399 ◽  
Author(s):  
L. B. Freund ◽  
H. T. Johnson ◽  
R. V. Kukta
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Free Energy ◽  
Aspect Ratio ◽  
Misfit Dislocation ◽  
Strain Distribution ◽  
Strain Relaxation ◽  
Lattice Parameter ◽  
Island Growth ◽  
Numerical Finite Element

ABSTRACTAn epitaxial material island which has a lattice parameter differing by a small amount for that of its substrate is considered within the framework of continuum mechanics. The strain distribution in the island is determined for a range of aspect ratio, taking into account the compliance of the substrate. It is demonstrated that the total free energy of a strained island is minimum for some value of aspect ratio, and that this value depends on the volume of the island. To consider strain relaxation, the nucleation of a dislocation at the edge of a strained island is examined and the equilibrium aspect ratio of a dislocated island is computed. In particular, it is shown that an island can reduce its free energy by reducing its aspect ratio and, simultaneously, forming an interface misfit dislocation. The simulations are based on the numerical finite element method.

Strains and Relaxations Near metal Alumlnide/Semiconductor Interfaces

1991 ◽  
Vol 226 ◽  
Author(s):  
W.W. Gerberich ◽  
J.E. Angelo ◽  
R.R. Keller ◽  
A.M. Wowchak ◽  
P.I. Cohen
Keyword(s):  
Strain Distribution ◽  
Strain Relaxation ◽  
High Energy ◽  
Lattice Parameter ◽  
Layer Growth ◽  
Layer By Layer ◽  
Material Interfaces ◽  
Kinetic Measurements ◽  
Film Substrate ◽  
The Impact

AbstractMechanisms and phenomena of strain relaxation at bi-material interfaces have been studied for over half a century. The details, however, and limiting kinetics, thermodynamics and mechanics are still being sorted out - particularly for large misfit systems. Three techniques are required to accurately portray strain distributions during and after epitaxial growth: RHEED, TEM and SACP. Reflection high energy electron diffraction (RHEED) is used to measure the lattice parameter during growth. Both transmission electron microscopy (TEM) and selected area electron channeling pattern (SACP) analysis are necessary to identify the defects and the strain distribution. These techniques have been applied to NiAl and FeAl grown by MBE on GaAs with a thin AlAs buffer layer. It is shown that both island and layer by layer growth can occur with the corresponding defects being remarkably similar in character. From a combined Moiré, HREM and computer simulation, the dislocation character is assessed. Both <100> dislocations from half-loops or island edges may occur providing only partial relaxation of the film-substrate systems. The impact of the remaining elastic strain distribution on kinetic measurements of dislocation velocities is discussed.

Effects of Substrate Misorientation Direction on Strain Relaxation at InGaAs/GaAs(001) Interfaces

1995 ◽  
Vol 379 ◽  
Author(s):  
R.S. Goldman ◽  
H.H. Wieder ◽  
K.L. Kavanagh
Keyword(s):  
Activation Energy ◽  
Strain Relaxation ◽  
Misfit Strain ◽  
Dislocation Nucleation ◽  
Experimental Results ◽  
Step Edge ◽  
Shear Stresses ◽  
Slip Systems ◽  
Dislocation Glide ◽  
Local Roughness

ABSTRACTWe have investigated the effects of substrate misorientation direction on strain relaxation at InGaAs/GaAs(001) interfaces. Calculations of the shear stresses due to the misfit strain, resolved on the glide plane in the glide direction, suggest that the dislocation glide force and the activation energy for dislocation nucleation are essentially identical for the α and β slip systems. However, experimental results indicate that asymmetries in strain relaxation are sensitive to A-type misorientation and/or step-edge densities. Thus, a dislocation nucleation source or glide velocities sensitive to step densities or local roughness may explain these results.

scholarly journals Ubiquitous organic molecule-based free-standing nanowires with ultra-high aspect ratios

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Koshi Kamiya ◽  
Kazuto Kayama ◽  
Masaki Nobuoka ◽  
Shugo Sakaguchi ◽  
Tsuneaki Sakurai ◽  
...  
Keyword(s):  
Critical Dimension ◽  
High Energy ◽  
Free Standing ◽  
Dry Process ◽  
3D Space ◽  
Aspect Ratios ◽  
Structural Functions ◽  
Planar Structures ◽  
Organic Nanostructures ◽  
Straight Trajectory

AbstractThe critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems.

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