The growth of strained, continuous Si1-xGex epitaxial alloy layers on Si can, under certain conditions, result in the occurrence of marked, small-scale layer thickness fluctuations in the form of crystallographically-aligned, interlocking ripple arrays. In the present work, combined transmission electron microscope (TEM) and atomic force microscope studies are employed to reveal the detailed nature of these surface ripples. TEM contrast studies demonstrate that well-defined, oscillatory strain variations accompany these ripple structures, the presence of which is shown to be associated with partial elastic strain-relief and lowering of the energy of die strained-layer system.

Microstructural evolution in systems containing strained islands (coherent, incoherent or both) is investigated. The growth rate of an individual island coarsening in an ensemble of strained islands is obtained by including elastic effects on surface diffusion of adatoms to and the equilibrium solubility of strained islands. For strained islands growing on a quasi-rigid substrate, coherent islands grow more slowly than incoherent islands of the same radius. Consequently, the island growth rate accelerates at the coherent to incoherent transition. The model agrees with recent experimental observations in Ge/Si(100) heteroepitaxy.

The characteristics of epitaxial growth in large lattice mismatch TiN/Si and TiN/GaAs systems are analyzed. The epitaxial growth in these large mismatch systems is modelled in terms of various energy contributions to the epilayer. The new mode of growth, defined as domain epitaxial growth in these high mismatch systems is maintained by the formation of misfit dislocations at repeated intervals. The epitaxial relationship within the domain consists of n interplanar distances of the overlayer film closely matching with m interplanar distances of the substrate, where m and n are integers. The interfacial energy is found to be a very important term in determining the orientation relationships. The results of the model calculations are compared with the experimental observations.

The initial stage of film formation process was studied by 2 dimensional (2D) Monte-Carlo (MC) simulation and 3D molecular dynamics (MD) simulation. The atomistic interaction was simple pair-wise Lcnnard-Joncs potential for the 2D MC study and embedded atom potential (EAM potential) for the 3D MD simulation. The 2D MC study has revealed the dependence of film growth mode on the potential parameters that correspond to atomic size and binding energy. More realistic MD simulation has been performed using EAM potential for the three kinds of systems, Ni/Cu(111), Ag/Cu(111) and Au/Ni(111). The relaxed atomic structures of such systems showed the difference of atomic combination; coherent interface was obtained for Ni/Cu(111) system, incoherent interface with specific rotational relationships for Ag/Cu(111) andAu/Ni(111).

Dislocation accumulation in patterned gallium-arsenide film, which is deposited on silicon substrate and cooled down from the deposition to room temperature, is numerically simulated under a continuum mechanics approximation. A new approach to suppression of dislocation accumulation is proposed where selective growth of the film and partial doping of impurities into it are combined. The results show the possibility to keep the surface region of the film almost dislocation free.

We have performed high resolution x-ray diffraction measurements of the strain field in UHV deposited Ag(111) films on a 7×7 reconstructed Si(111) surfaces shows a faulted epitaxial layer with a 0.4% out-of-plane strain, and a -1% in-plane strain. The strain field anisotropy is similar to that observed on epitaxial YSi2-x on Si(111), and is an unexpected result for the present system, due to the lack of a lattice match between the silver and silicon unit cells. The out-of-plane diffraction peaks have an angular distribution of 1.23°, full width at half maximum (FWHM), as determined from rocking curve measurements.

In this paper we investigate the defect morphology and misfit strain in InAs films grown on (100) InP substrates using two-step metal organic chemical vapor deposition (MOCVD). High quality InAs films were obtained despite the 3.2% lattice-mismatch between the InAs film and the InP substrate. Cross-sectional and plan-view transmission electron microscopy has been used to characterize the ∼3μm thick InAs films. Almost all the lattice mismatch is accomodated by an orthogonal array of pure edge Lomer dislocations which are favored over the 60° type since they are more efficient in relieving misfit strain. In addition to misfit dislocations, threading dislocations were observed propagating through the film. Most of the threading dislocations were 60° type dislocations along the < 211 > and < 110 > directions on inclined {111} planes. The threading dislocations originate from island coalescence during film growth. High resolution electron microscopy shows the epitaxial relationship between the film and the substrate and reveals an abrupt and sharp interface with periodic dislocation cores.

Comparison of high resolution x-ray diffraction and transmission electron microscopy measurements of Si-based heterostructures demonstrates that diffraction is much more sensitive to strain relaxation than previously reported. This study used as-grown and annealed Si1-x Gex structures grown on (001) Si by UHV/CVD. (004), (113), and (115) rocking curves were employed. Using the TEM measurements as a quantitative guide, relaxation was observed in rocking curves when the misfit dislocation line density was as low as 1 μ-1. Also, interference fringes strongly depend on the presence of interfacial defects. At higher dislocation densities, the diffraction peak from the epitaxial layer broadens considerably but does not shift to a position that represents complete relaxation. Broadening of the substrate diffraction peak also occurs, which is due to dislocations that loop into the substrate.

Convergent beam electron diffraction (CBED) was applied to the local measurement of lattice parameter across a strained interface with small mismatch. GaAs layers grown at low temperature with excess As (with 0.15% misfit) on a GaAs substrate were chosen for these studies. Tetragonal distortion was detected in the layer up to 0.5μm from the interface. With an increase of the layer thickness lowering of the symmetry of these CBED patterns was observed. This lowering of symmetry is most probably due to saturation of As solubility and the strain build into these layer.

A cross-sectional TEM study of the defect structure in CdTe buffer layers grown on 2°-off (001) GaAs substrates by MOVPE is presented. The nature and distribution of defects in the buffer layers are shown to be highly anisotropic. Images obtained with the beam direction parallel to [110] show that high densities of stacking faults are present on one of the two equivalent (111} planes, whereas those obtained with the beam direction parallel to [110] show subgrain boundaries perpendicular to the interface. HREM images of the interfacial region along these two directions show a pronounced difference in the character of the misfit dislocations with b = a/2 <110>. Those with line directions parallel to [110] are all edge (90°) dislocations whilst the orthogonal set are an intimate mixture of edge and mixed character (60°) dislocations. This anisotropy is attributed to the combined effects of substrate off-cut and the formation of high aspect ratio island nuclei, giving differences in misfit accommodation.

To date, primarily only idealized equilibrium models for the growth mode and strain relaxation of elastically strained overlayers have been proposed. Here we present a general continuum model for lattice-mismatched epitaxy. As molecular beam epitaxy is inherently a nonequilibrium growth process, surface diffusion kinetics is incorporated in the model. Additionally, a new strain relaxation mechanism in a dislocation-free film is considered. Experimental support for our view is obtained from measurements made by reflection high energy electron diffraction, scanning tunneling microscopy, and transmission electron microscopy on the growth of InGaAs on GaAs(100). These results demonstrate the strong effects which strain, surface diffusion kinetics, and surface energy have on growth mode. From analytical and numerical analysis in 1 + 1 dimensions, the interrelationship of such physical factors is revealed. Our improved understanding enables control over the growth behavior of strained-layer superlattices and heterostructures.

We have observed significant increases in the misorientation of Ge films on Si (001) grown by ion-assisted molecular beam epitaxy. The misorientation between the Ge films and Si substrates was found to be a function of the ion-to-atom flux ratio and growth temperature. The parametric dependence of the misorientation on the growth conditions suggests that defects generated by low energy ion bombardment are responsible for the observed increase in misorientation. The amplification of misorientation produced by concurrent low energy ion bombardment during epitaxial growth was attributed to an increase in the fraction of misfit strain accommodated by threading dislocations.

The accommodation of misfit stresses during heteroepitaxial growth of Ge0.85Si0.15 on Si(110) from In solution is studied by transmission electron microscopy. The regular misfit dislocation network forms at the interface and can be explained by glide of dislocations in a secondary a/2<110>{311} glide system. The occurrence of this secondary glide system is analyzed in terms of a mechanical equilibrium analysis that includes a frictional force due to a static Peierls barrier.

We have studied die evolution of the lattice parameter of epitaxial Fe(001) on MgO(001) vs. thickness between 1 and 200 monolayers using Grazing Incidence X-ray Scattering. We show that an interaction exists between the islanded film and the substrate, which allows the film to be incommensurate, even when the islands are too small to allow full dislocations to exist. For the conditions studied, the Fe lattice parameter increases toward the MgO lattice parameter with increasing thickness in the 1–10 monolayer coverage regime, and then relaxes back toward the bulk Fe lattice parameter at greater thicknesses. We employ a model for the interaction between film islands and the substrate which explains large changes in the lattice parameter of the Fe in the 1–10 monolayer thickness range. Relaxation at larger thicknesses is described by continuum elasticity theory.

Impurity induced layer disordering (JILD) has been demonstrated as an extremely powerful technique for the fabrication of optoelectronic devices within the AlGaAs alloy system. The success of this technique in this material system is due in large part to the similarity of the lattice parameters between the two binary constituents in this system, AlAs and GaAs. There are many alloy systems in which it would be highly desirable to exploit the fabrication technique of JILD, but within which the binary alloy constituents are not so well matched in lattice parameter. Perhaps the most extensively explored of such systems are the AlGaInP alloy system lattice matched to a GaAs substrate and the InGaAsP alloy system lattice matched to an InP substrate.

The defect structure in a GaP/GaAs/GaP heterostructure deposited on a (001) GaAs substrate with a GaAs buffer layer has been characterized by cross sectional TEM. The buffer layer presents dislocations and (α-δ)-fringe contrast parallel to (001) interface plane. HREM study reveals uniformly distributed amorphous capsules in the first GaP/GaAs buffer layer interface. The dominant defects are microtwins which are propagated into the overall heterostructure. Microtwin density is different in the GaP and GaAs layers.The different stress signs may explain the density difference.

Heteroepitaxial growth of indium arsenide films on indium phosphide substrates is being actively pursued since the electronic properties of these films make them promising materials for optoelectronic and other high speed devices. The various structural aspects of the film that affect their electronic properties are structural defects like dislocations, film-substrate interface roughness and chemical inhomogeneities. In InAs films, electrons accumulate at the film-air interface, making surface morphology an important factor that decides the electronic properties. The InAs films used in this study were grown on InP substrates by metal organic vapor deposition, at different temperatures. A higher growth temperature not only resulted in poor surface morphology of the film, but also created a rough film-substrate interface. However, at all deposition temperatures, the film-substrate interfaces are sharp. At lower growth temperature, the interfaces were flat. Films grown at lower temperatures had good surface morphology and a flat and shaip heterointerface.

Epitaxial solid solutions Au1-x Nix (100) have been obtained at room temperature on Au(100) substrates by the MBE technique. The layers are 10 nm-thick and the composition x has been varied up to 0.37. A large strain (2–3%) has been measured by X-ray diffraction. The lattice parameters have been measured in two perpendicular directions, perpendicular and parallel to the surface. In the latest case, the grazing-incidence technique has been used. Because this technique is very sensitive to the surface, the strain results may be re-interpreted if, the upperlOO nm are enriched in Au.

The structure and intrinsic stresses of sputter-deposited thin films are studied via a two-dimensional molecular dynamics (MD) model. Two body potentials are used to represent the interaction between film atoms, substrate atoms, ions and argon molecules. First, a nearly perfect substrate having zero stress is constructed using constant temperature and constant pressure algorithms. Then the film is deposited with and without in-situ argon ion bombardment and with and without an argon background gas; a source of impurities. The adatom energy is varied in order to investigate its influence on the film structure. During the simulation the film is allowed to expand and contract depending on the intrinsic stresses. The models demonstrate, for the first time, that the transition from large tensile to large compressive stresses in sputter deposited thin films is caused by the incorporation of tightly packed argon impurity atoms, achieved only at sufficiently high levels of argon ion bombardment and nickel adatom energies.

We discuss the static and quasi-static problems appearing in the theory of morphological instability of interfaces. The approach has allowed to predict the corrugations in He4 films and to explain the dislocation-free Stranski-Krastanow pattern of epitaxial growth of thin solid films with the critical film thickness H = σμ/τ2 (σ is a surface energy, μ- the shear modulus, and τ - the mismatch stress). In this paper we discuss possible morphological patterns of corrugations and their changes which appear in result of the stress driven “rearrangement” destabilization of originally flat interfaces.