Effects of buffer layer thickness and film compositional grading on strain relaxation kinetics in InAs/GaAs(111)A heteroepitaxy (original) (raw)
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Surface Science, 2003
A systematic theoretical analysis is presented of the combined effects of substrate compliance and film compositional grading on the relaxation of strain due to lattice mismatch in layer-by-layer semiconductor heteroepitaxy. The analysis is based on a combination of continuum elasticity theory and a novel atomistic simulation approach for modeling structural and compositional relaxation in layer-by-layer heteroepitaxial systems. Results are presented for InAs epitaxy on GaAs(1 1 1)A compliant substrates with some marginal film compositional grading that consists of one monolayer of In 0:50 Ga 0:50 As grown on the substrate surface prior to InAs growth. A parametric study is carried out over a wide range of substrate thicknesses. Interfacial stability with respect to misfit dislocation formation, the dependence on substrate thickness of a thermodynamic critical film thickness, and the completion of the coherent-to-semicoherent interfacial transition are examined in detail. In addition, the structural characteristics and compositional distribution of the corresponding semicoherent interfaces, the associated strain fields, as well as the film surface morphological characteristics are analyzed. Most importantly, the role of segregation at defects of a semicoherent interface in the thermodynamics of layer-by-layer heteroepitaxial growth is demonstrated. Our study shows that systematic combination of the mechanical behavior of thin compliant substrates with grading of the epitaxial film composition provides a very promising engineering strategy for strain relaxation in heteroepitaxy.
Theoretical Investigations for Strain Relaxation and Growth Mode of InAs Thin layers on GaAs(111)A
Condensed Matter
The growth mode of InAs/GaAs(111)A is systematically investigated using our macroscopic theory with the aid of empirical potential calculations that determine parameter values used in the macroscopic theory. Here, stacking-fault tetrahedron (SFT) found in InAs/GaAs(111)A and misfit dislocation (MD) formations are employed as strain relaxation mechanisms. The calculated results reveal that the MD formation occurs at the layer thickness h about 7 monolayers (MLs). Moreover, we found that the SFT forming at h about 4 MLs makes surface atoms move upward to reduce the strain energy to promote the two dimensional (2D) growth. Therefore, the SFT in addition to the MD plays an important role in strain relaxation in InAs thin layers on GaAs(111)A. The macroscopic free energy calculations for the growth mode imply that the InAs growth on the GaAs(111)A proceeds along the lower energy path from the 2D-coherent (h ≤ 4 MLs) to the 2D-MD (h ≥ 7 MLs) via the 2D-SFT (4 MLs ≤ h ≤ 7 MLs). Consequently, the 2D growth on the InAs/GaAs(111)A results from strain relaxation due to the formation of the SFT near the surface and the subsequent MD formation at the interface.
Growth and characterization of InAs epitaxial layer on GaAs(111)B
Physical Review B, 2004
The behavior of InAs deposition on GaAs͑111͒B substrates and the corresponding routes toward strain relaxation have been investigated. InAs growth was for depositions ranging from 2 monolayers to 30 monolayers. Over this deposition range, different routes for strain relaxation caused by the lattice mismatch were observed. The strain relaxed through ragged step edge formation and GaIn intermixing for low InAs deposition and through the formation of step bunching and dislocations for thicker depositions.
Computational Materials Science, 2002
A systematic study is presented of interfacial stability and strain relaxation through misfit dislocation formation in III-V semiconductor layer-by-layer heteroepitaxy. A multiscale modeling strategy is developed that links continuum elasticity theory with atomistic structural relaxation and Monte Carlo simulations using a valence force field description of interatomic interactions. Results are presented for the energetics of the transition from a coherent to a semicoherent film/substrate interface consisting of a misfit dislocation network, the semicoherent interface structures, the associated strain fields, and the film surface morphological characteristics for InAs epitaxy on GaAs(1 1 1)A. The capability of continuum elasticity theory to provide a satisfactory description of the atomistic simulation results is discussed. In addition, using thin compliant substrates and grading the composition of the deposited film are demonstrated to have beneficial effects on film strain relaxation. Furthermore, the dynamics of strain relaxation is analyzed based on a phenomenological mean-field theoretical framework. Our theoretical results are in very good agreement with our experimental measurements on InAs/GaAs(1 1 1)A samples for films grown by molecular beam epitaxy on thick and thin GaAs buffer layers.
Growth temperature dependence of strain relaxation during InGaAs/GaAs(001) heteroepitaxy
Journal of Crystal Growth, 2011
Growth temperature dependence of strain relaxation during In 0.12 Ga 0.88 As/GaAs(0 0 1) molecular beam epitaxy was studied by in situ X-ray reciprocal space mapping. Evolution of the residual strain and crystal quality for the InGaAs film was obtained as a function of film thickness at growth temperatures of 420, 445 and 477 1C. In the early stages of strain relaxation, it was found that evolution of the residual strain and crystal quality was dependent on the growth temperature. In order to discuss this observation quantitatively, the strain relaxation model was proposed based on the Dodson-Tsao kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. Additionally, rate coefficients reflecting dislocation motions during strain relaxation were obtained as a function of growth temperature and strain relaxation was discussed in terms of the thermally active dislocation motion.
Strain Relaxation in GaSb/GaAs(111)A Heteroepitaxy Using Thin InAs Interlayers
ACS Omega, 2018
We have systematically studied the strain relaxation processes in GaSb heteroepitaxy on GaAs(111)A using thin InAs interlayers. The growth with 1 ML-and 2 ML-InAs leads to formation of an InAsSb-like layer, which induces tensile strain in GaSb films, whereas the GaSb films grown with thicker InAs layers (≥3 ML) are under compressive strain. As the InAs thickness is increased above 5 ML, the insertion of the InAs layer becomes less effective in the strain relaxation, leaving residual strain in GaSb films. This leads to the elastic deformation of the GaSb lattice, giving rise to the increase in the peak width of X-ray rocking curves.
Strain relaxation in graded composition In[sub x]Ga[sub 1−x]As/GaAs buffer layers
Journal of Applied Physics, 1999
A model to compute the strain relaxation rate in In x Ga 1Ϫx As/GaAs single layers has been tested on several compositionally graded buffer layers. The existence of a critical elastic energy has been assumed as a criterion for the generation of new misfit dislocations. The surface strain accuracy results are within 2.5ϫ10 Ϫ4 . The influence of different grading laws and growth conditions on residual strain, threading dislocation density, misfit dislocation confinement, and surface morphology has been studied. The probability of dislocation interaction and work hardening has been shown to strongly influence the mobility and the generation rate of the dislocations. Optimization of the growth conditions removes residual strain asymmetries and smoothes the surface roughness.
Strain Relaxation in Compositionally Graded InGaAs/GaAs Heterostructures
Epilayer strain relaxation in the InGaAs/GaAs system occurs via two mechanisms, plastic deformation and/or surface roughening. Under conditions of two-dimensional growth, we find that compositionally graded InGaAs/GaAs (001) multi-layer buffer structures will plastically deform with < 110 > misfit dislocations approaching 100 % strain relaxation. At higher growth temperatures, large-amplitude roughening is observed preferentially along the [110] direction, and the strain relaxation becomes asymmetric in the < 110 > directions. In single epilayers, the symmetry of the strain relaxation is dependent on the magnitude of the substrate offcut angle. In all cases, the epilayers develop a tilt about an in-plane axis in proportion to and opposite in direction to the substrate offcut. With roughening, there is also a change in the orientation of the tilt axis such that only the dislocations with [ll O] line directions develop a preferred tilt component. These results illustrate the importance of surface steps and morphologies to strain relaxation and perhaps offer clues to the identification of the dislocation formation mechanisms at these interfaces.
Strain relaxation in InAs heteroepitaxy on lattice-mismatched substrates
Scientific Reports, 2020
Strain relaxation processes in InAs heteroepitaxy have been studied. While InAs grows in a layer-by-layer mode on lattice-mismatched substrates of GaAs(111)A, Si(111), and GaSb(111)A, the strain relaxation process strongly depends on the lattice mismatch. The density of threading defects in the InAs film increases with lattice mismatch. We found that the peak width in x-ray diffraction is insensitive to the defect density, but critically depends on the residual lattice strain in InAs films.
Residual strain measurements in InGaAs metamorphic buffer layers on GaAs
European Physical Journal B, 2007
This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes, respectively). By relating the GaAs-like longitudinal optical phonon frequency ωLO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ωLO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends on the thickness t of the buffer layer following a ~t-1/2 power law, that can be explained by an energy-balance model.