Luis A. Zepeda-Ruiz

Theoretical study of the energetics, strain fields, and semicoherent interface structures in layer-by-layer semiconductor heteroepitaxy

A theoretical analysis based on continuum elasticity theory and atomistic simulations is presented of the interfacial stability with respect to misfit dislocation formation, the strain fields, and the film surface morphology during layer-by-layer semiconductor heteroepitaxy. The strain in the coherently strained films, the energetics of the transition from a coherent to a semicoherent interface consisting of misfit dislocation arrays or networks, the structure of the corresponding semicoherent interfaces, the strain fields associated with different equilibrium states of strain, and the morphological characteristics of the film surfaces are calculated for InAs/GaAs(110) and InAs/GaAs(111)A. The thickness of the epitaxial film is used as the dynamical variable in the analysis. Critical film thicknesses for transition from one equilibrium state of strain to another are computed. The analysis is presented for the more general case of heteroepitaxy on a finite-thickness compliant substrate, while the common ca...

Semicoherent interface formation and structure in InAs/GaAs(111)A heteroepitaxy

Abstract A theoretical analysis based on atomistic simulations is presented of both the semicoherent interface structure, which is formed to relax the strain due to lattice mismatch during InAs/GaAs(111)A heteroepitaxy, and the energetics of interface formation. The semicoherent interface consists of a network of intersecting misfit dislocations, which includes both perfect 90° dislocations along 〈112〉 directions and Shockley partials along 〈110〉 directions that bound faulted interfacial regions. This interface structure becomes stable for film thicknesses greater than four monolayers. Our simulation predictions of the interface structure and the critical film thickness for full strain relief are in excellent agreement with recent experimental data.

Kinetics of strain relaxation through misfit dislocation formation in the growth of epitaxial films on compliant substrates

A phenomenological mean-field theory is presented for the kinetics of strain relaxation due to misfit dislocation generation in the strained-layer growth of epitaxial semiconductor films on thin compliant substrates. The theory provides a generalized dislocation kinetic framework by coupling the mechanics of an epitaxial film on a compliant substrate with a well-known description of plastic deformation dynamics in semiconductor crystals. The theoretical results reproduce successfully recent experimental data for strain relaxation in the InAs/GaAs(110) heteroepitaxial system.

Surface morphology in InAs/GaAs(111)A heteroepitaxy: Experimental measurements and computer simulations

The surface morphology of InAs films grown on GaAs(111)A has been studied by scanning tunneling microscopy. The vertical surface displacement on the InAs films has been found to depend on the underlying GaAs buffer layer thickness: specifically, thin GaAs layers are observed to behave mechanically similar to compliant substrates. Atomistic simulations within a valence force field model have been used to compare quantitatively how the InAs surface morphology depends on film thickness and the underlying GaAs layer thickness. The experimental and theoretical results are in excellent agreement over a range of film thicknesses where the misfit dislocation network at the semicoherent InAs/GaAs interface is fully developed.

Kinetics of strain relaxation through misfit dislocation formation in InAs/GaAs(111)A heteroepitaxy

The kinetics of strain relaxation through misfit dislocation formation is investigated in InAs/GaAs(111)A layer-by-layer heteroepitaxy. Experimental measurements are presented of strain relaxation as a function of InAs film thickness for epitaxial film growth on thin and thick GaAs buffer layers. The experimental measurements are described successfully through a phenomenological mean-field theoretical analysis. The analysis reveals that the mechanical behavior of our heteroepitaxial system with a thin buffer layer is similar to that of a system with a thin compliant substrate that is practically unconstrained at its base.

Mechanical behavior of thin buffer layers in InAs/GaAs(111)A heteroepitaxy

The mechanical behavior of thin buffer layers for InAs/GaAs(111)A heteroepitaxy has been investigated by x-ray diffraction (XRD). XRD θ–2θ spectra are presented for the (220) reflection for two monolayers (MLs) of InAs deposited on GaAs buffer layers of both 20 ML and 150 nm (≅ 460 ML) in thickness. For the thicker buffer layer, the XRD spectrum exhibits a single, symmetric peak at a reflected angle corresponding to the bulk GaAs lattice parameter, while for the thinner one it exhibits asymmetry around the GaAs substrate reflection with the spectrum tailing to lower angle. This indicates that the thin buffer layer possesses a distribution of interlayer distances in the [220] direction that are larger than that of the GaAs substrate. The XRD data agree very well with theoretical calculations in which the thin GaAs buffer layer is modeled as unconstrained at its base. Our results provide direct evidence that thin GaAs buffer layers behave mechanically similarly to compliant substrates.

Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the st...

Effects of buffer layer thickness and film compositional grading on strain relaxation kinetics in InAs/GaAs(111)A heteroepitaxy

Abstract The effects on the strain relaxation kinetics of a thin buffer layers mechanical response and of the epitaxial film compositional grading are investigated in the epitaxial growth of InAs on GaAs(111)A. Two heteroepitaxial systems are analyzed, consisting of thin and thick GaAs buffer layers grown on GaAs(111)A epi-ready substrates. In both cases, one monolayer of In0.50Ga0.50As is grown initially on the buffer layer followed by growth of several monolayers of InAs. In both systems, strain relaxation in the grown film is measured as a function of film thickness. The experimental measurements are described successfully by a phenomenological mean-field theoretical analysis. Our results support that the mechanical response of a thin buffer layer is similar to that of a thin compliant substrate that is unconstrained at its base. Furthermore, our results indicate that the mechanical behavior of a thin buffer layer can be used in conjunction with film compositional grading toward strain relaxation engineering in semiconductor heteroepitaxy.

Interfacial stability and structure in InAs/GaAs(111)A heteroepitaxy: Effects of buffer layer thickness and film compositional grading

Interfacial stability and the morphology of the epitaxial film surface have been studied in InAs/GaAs(111)A heteroepitaxy based on atomistic simulations and scanning tunneling microscopy. Effects of buffer layer thickness were examined by analyzing two heteroepitaxial systems consisting of thin and thick GaAs buffer layers. In both cases, one monolayer of In0.50Ga0.50As is grown initially on the buffer layer prior to InAs growth. Our results indicate that film compositional grading and the resulting segregation of In atoms at defects in the semicoherent interface can be used effectively in conjunction with the mechanical compliance of thin buffer layers to delay the completion of the coherent-to-semicoherent interfacial transition.