Defect-free coalescence of Si layers which grow laterally over partially oxidized Si substrates is achieved in liquid phase epitaxy from indium solution. An adequate design of the oxide pattern on (111) substrates ascertains that the growth fronts of the Si layers merge gradually on the SiO2 and avoids the formation of inclusions or crystallographic defects. Electron Microscopy in diffraction contrast and convergent beam electron diffraction reveal that the epitaxial Si layers bend towards the substrate as they grow laterally over the SiO2 film. The layers straighten out again as they merge and form a perfect seam of coalescence.

The effects of nitrogen doping as a terminator in an anodically oxidized film of tantalum have been investigated.

In the oxide film of nitrogen-free tantalum, the electric leakage current abruptly increased with the applied voltage. It is well-known as the Poole-Frenkel effect [1] [2]. After annealing at 623K in a hydrogen atmosphere, the leakage current increased.

On the other hand, in the oxidized films of nitrogen-doped tantalum the leakage current increased in proportion to the applied voltage, but it was very small as compared with the nitrogen-free oxide. Moreover the leakage current decreased after annealing. The decrement strongly depended on the amount of doped nitrogen.

We introduce a model to calculate the static equilibrium configuration between two monolayers of large, planar organic molecules bonded by van der Waals (vdW) forces. The Model significantly simplifies analysis by replacing the conventional atom-atom potential summation with a single ellipsoidal potential centered in the molecular plane. Our results indicate that recent observations of crystalline “quasi-epitaxial” growth of these planar molecular films in ultrahigh vacuum results from the relatively large intralayer elasticity as compared to the small interlayer stress. Good agreement between calculated and observed structures is achieved using no adjustable parameters. The Model is used to predict molecular structures which are likely to form quasi-epitaxial layers. Quasi-epitaxy is a general feature of large planar molecules of similar shape and size in adlayers and substrates where there is comparatively weak vdW bonding between layers.

A review of surface and interface stresses relevant to thin film growth is presented. It is shown that surface stress effects that are generally ignored in the analysis of epitaxy can have an influence on the critical thickness for epitaxy, especially at larger Misfits. A discussion of intrinsic stress generation from surface stress is also presented.

High resolution X-ray diffraction space mapping has been used to follow the change in the distribution of residual strain and localised relaxation in low mismatched epitaxial layers. Using this new technique, we have obtained a series of diffraction space maps of partially relaxed epitaxial layers of In.1Ga.9As on GaAs. The layers have different thicknesses and hence different degrees of strain relaxation. The diffuse scatter close to the Bragg peaks provides information about the imperfect and distorted regions in the structure and this has allowed us to examine the extent and distribution of residual strain close to the dislocations. We have followed the evolution of local relaxation, which is confined initially to regions around isolated dislocations, through to the case of overlapping dislocation strain fields, leading to a more homogeneous strain field distribution and microscopic and macroscopic tilting of the layers.

Utilizing Marker layer experiments and Z-contrast imaging, we have observed the formation of surface cusps during SixGe1−x alloy growth. The formation of cusps can be understood in terms of stress-driven surface diffusion, and we consider the large stress build-up at the cusp tip as a potential source for the nucleation of misfit dislocations.

Theoretical and experimental studies have suggested that surface roughness may significantly enhance the nucleation of misfit dislocations in a strained heteroepitaxial film, especially in view of a stress-induced roughening instability which tends to form cusp-like stress singularities along the film surface. In this paper, the process of dislocation nucleation is perceived as a single dislocation emerging from a gradually sharpening surface groove. An analysis similar to the Rice-Thomson model for dislocation nucleation from a crack tip is carried out to determine the nucleation condition in terms of the depth and curvature of the surface groove. Specific applications are made to Si1−xGex alloy films on Si (100) substrates.

The appearance of misfit dislocations at the interface between a strained layer and its substrate induces a nonuniform chemical potential along the surface of the layer. Under the assumption that the resulting chemical potential gradient will drive coherent mass rearrangement by surface diffusion, a model of evolution of surface shape is considered which leads to estimates of the surface roughness induced by this mechanism.

The defect structure of GaAsP layer grown by Atomic Layer Molecular Beam Epitaxy on (001) GaAs substrate has been studied by Transmission Electron Microscopy. The phosphorous content and the epilayer thickness have been changed below 25% and 1μm respectively. Three kinds of defect structure have been found: a) α-δ fringes at the interface for coherent epilayer, b) Misfit dislocation for thin epilayers and c) Multiple cracks normal to the interface and parallel to one <110> direction for thick epilayers.

We report ab initio calculations for Sb and Ag adsorption on Ag (111): evidence is found for substitutional adsorption and surface segregation of Sb, and for the formation of a disordered surface Sb-Ag alloy. The average diffusion barrier for Ag is enhanced on Sb-covered Ag (111), which favors the formation of a high density of small-sized islands: this is suggested to be the cause of the surfactant action of Sb on Ag reported recently.

We present atomistic calculations for the system In on Cu (100), using the atom-embedding model of Finnis and Sinclair. It was found that the energy banier for Cu adatoms to jump off a descending step is higher than the adatom migration energy, i.e. descending steps form an additional barrier for diffusion. The presence of In atoms at or in step edges or island edges drastically reduces the energy barrier for interlayer diffusion of Cu adatoms. Therefore, we predict that In atoms may be used as surfactants to improve the homoepitaxial growth of Cu on Cu (100), especially in the temperature range between 150 and 200 K.

We present the results of a study of Pt/Pt (111) epitaxial thin-film growth with Molecular-dynamics simulation and static-energy calculation. Interatomic forces are modeled with Corrected-Effective-Medium theory. Atomic details of deposition, such as dissipation of the kinetic energy of an impinging gas atom, adatom motion on and approaching descending step edges, effects of the geometry of a step edge on the interlayer transport of adatoms, etc., have been intensively investigated. We have observed a novel mechanism for adatom incorporation into descending-step edges which involves a concerted motion of the adatom and edge atoms. Our study supports the “island size and shape” model which has been proposed to explain the reentrant layer-by-layer growth mode seen experimentally in Pt/Pt (111) homoepitaxy.

We have examined macroscopic island (Macro-island) formation in Stranski-Krastanov (SK) growth of Ge on Si (001) surfaces at various growth temperatures in molecular beam epitaxy (MBE). The nucleation mode of Macro-island formation was observed to be predominantly heterogeneous at medium growth temperatures less than 450°C, but homogeneous at high temperatures. In the heterogeneous Mode, Macro-island formation is mediated by particular V-shaped defects running preferentially along the <110> direction, which form as a result of coalescence of the well-faceted islands.

Activation energies for the migrations of H, F, and Cl on the diamond C(110) surface are calculated by quantum chemical methods using hydrocarbon cluster Models. The calculations include extensive basis sets with Many-body effects at the level of single and double excitations from Hartree-Fock and Complete-Active-Space wavefunctions. The calculated activation barriers for the (1,2) and (1,3) Migrations indicate that such migrations are too slow to compete with gas-surface reactions during chemical-vapor deposition of diamond. However, the (1,4) migrations of both H and Cl are calculated to be sufficiently fast to compete with gas-surface reactions under typical diamond growth conditions.

An empirical TersofF-type interatomic potential has been developed for describing Si-H interactions. The potential gives a reasonable fit to bond lengths, angles and energetics of silicon hydride molecules and hydrogen-terminated silicon surfaces. The frequencies of most vibrational modes are within 15% of the experimental and ab initio theory values. The potential is computationally efficient and suitable for molecular dynamics investigations of various processing treatments of hydrogen-terminated silicon surfaces.

Within a valence force field framework, we calculate the critical thickness of a film lattice mismatched to the substrate on which it is epitaxially deposited. A capping layer lattice matched to the substrate is known to enhance the critical thickness. We calculate the efficiency of the capping layer and study how the capping layer thickness modifies this efficiency. We also demonstrate how using a capping layer which is no more lattice matched to the substrate may improve the effect of the capping layer. Extension to strain compensation in multilayer systems is provided. In the case of uncapped systems, or systems with a thick capping layer lattice matched to the substrate, the results we have obtained using a microscopic description are compared to recent results, obtained using continuous classical elasticity.

As a model for Stranski-Krastanow island formation in strained heteroepitaxial layers, this paper investigates the surface-diffusion controlled morphological evolution of a two dimensional semi-infinite solid loaded in the lateral direction. Numerical Methods are developed to simulate the surface diffusion process, and examples are presented to demonstrate three distinct evolution patterns which are characterized by two critical wavelengths. The results show that, according to the wavelength, a slightly wavy surface can evolve into a cusped, a smoothly undulating, or a flat configuration. The diffusion wavelength and cusp-formation time compare favorably with recent experimental observations.

Computer simulations were used to study nucleation and development of misfit dislocations in coherent films on lattice mismatched substrates. Nucleation of a misfit dislocation was characterized as insertion of vacancies in the top layer of the film, whereas further development of the misfit dislocation was accompanied by the movement of a half dislocation loop towards the interface (1). The energetics of nucleation phenomenon was studied in the presence or absence of surfactants (a Monolayer of different atoms on top of the thin film) and also under different compressive stresses. An Au/Ni film substrate system and Au films with Ni or Ag as surfactants were used for calculations. In absence of a surfactant or when the surfactant atom lattice constant was larger (Ag) than the film atoms (Au), the energy of vacancy insertion (EVI) decreased with increase in compressive strains. When the surfactant atom was smaller (Ni), EVI increased with increase in compressive strains. This should inhibit insertion of vacancies into the film and thus formation of defects such as misfit dislocations.

We present ab initio studies of oxygen adsorption on Al (111) using a density-functional local-orbital method. Our results indicate that, for very low oxygen exposures, the oxygen atoms are incorporated in the first Al (111) layer. For exposures corresponding to approximately a monolayer of oxygen, an ordered oxygen overlayer with the O atoms sitting on the 3-fold sites was seen. These results are consistent with EXAFS experiments. We have also studied clean Al surfaces and have analyzed their surface relaxations.

A rate equation model based on the master equation is developed for the study of MBE doping kinetics. The Model includes elementary surface processes such as adsorption, evaporation and migration of atoms. The Model is applied to the study of the surface segregation phenomenon during the In doping of Si. The doping studies were performed for the following growth conditions: T in the range 500 — 750°C; a growth rate of 1 μm/hr.; and a flux ratio, JIn/JSi equal to 2.0 × 10-4. The predicted sticking coefficient of In versus obtained shows excellent agreement with experiments. The sticking coefficient decreases with T due to surface segregation aided evaporation of In at higher temperature. The results of dopant depth profile also show excellent qualitative agreement with experiments. The surface segregation of In occurs due to a strong repulsive interaction between In and the host lattice. The results of this study show that there is a dopant depleted zone (DDZ) where the In concentration is lower than both the bulk and the top surface layer. The observed DDZ matches with that observed in experiments.